Meniscus degeneration contributes to knee arthritis progression, but the cellular and molecular mechanisms of meniscus aging remain poorly understood. We aimed to characterize age-related changes in the rat meniscus using single-cell RNA sequencing (scRNA-seq) and identify key pathogenic cell populations and pathways.

Meniscal tissues from young (12 weeks) and aged (24 months) rats were processed for histology, flow cytometry, and scRNA-seq. Bioinformatics tools, including Seurat, Monocle 2, and CellChat, were used to analyze cellular composition, pseudotime trajectories, and intercellular communication. Senescence-related features and signaling pathways were evaluated.

Knee joint of aged rats exhibited higher Osteoarthritis Research Society International (OARSI) scores and synovial inflammation. scRNA-seq revealed three major chondrocyte subpopulations: Sox9 + stable chondrocytes, Fndc1 + fibrochondrocytes, and Atf3 + senescent chondrocytes. Aging caused a significant increase in Atf3 + senescent chondrocytes, characterized by the expression of senescence markers (Cdkn1a/Cdkn2a) and activation of inflammatory pathways such as tumor necrosis factor (TNF) and nuclear factor-κB (NF-κB). These cells were predominantly located at the endpoint of differentiation trajectories. CellChat analysis identified the ANGPTL4-SDC4 axis as a key signaling pathway mediated by Atf3 + cells. Immunostaining confirmed elevated Angiopoietin-Like Protein 4 (ANGPTL4) expression in aged menisci.

We identified Atf3 + senescent chondrocytes as a key pathogenic population in the aging meniscus, driving degeneration via the ANGPTL4 pathway. Targeting Atf3 + cells or ANGPTL4 signaling may offer new therapeutic strategies for age-related meniscus degeneration and arthritis.

Evaluations of 3D joint space measurements between study groups have traditionally relied on surface regional divisions, which attenuate the impact of shape on joint measurements. Advancements in morphometric analyses have enabled evaluation of population-based shape variations as they relate to disease progression and deformity. Specifically, correspondence model-based shape analyses offer co-registered landmarks that address shape variability in joint structures and can be utilized for comparison of joint space measurements. This study proposes a method using correspondence models to perform group-wise statistical analyses in static or quasi-static positions during movement, offering a more comprehensive assessment of joint space variability. The primary objective was to verify and validate the measurement methods of a developed open-source toolbox. Testing was performed with surface meshes of varying edge length (0.5-, 1-, and 2-mm) and with different expected joint space distances (1- and 4-mm). Validation testing of accuracy revealed <1% error for 0.5- and 1-mm mesh edge lengths for 4 mm joint space, sensitivity testing demonstrated best results for 0.5 mm edge length, and repeatable/reliable measurements yielded low coefficient of variation and high intraclass correlation coefficient. These findings support the use of correspondence model-based approaches for robust and accurate analysis of joint measurements related to anatomical features. This method addresses limitations in traditional techniques by incorporating shape variability, providing a practical tool for assessing joint-level disease and deformity. Future work will focus on evaluating the application of this approach in diverse clinical scenarios, including highly deformed joint structures.

To the best of our knowledge, no prior studies have identified any risk factors for subchondral insufficiency fractures of the medial tibial condyle. This study aimed to explain relationships between subchondral insufficiency fractures of the medial tibial condyle and the meniscus status, lower extremity alignment, or osteoporosis.

This retrospective study included 325 consecutive patients whose chief complaint is knee joint pain and who had visited one institution between April 2016 and March 2021, of which 70 patients (8 men and 62 women) who had suspected subchondral insufficiency fractures of the medial tibial condyle had undergone magnetic resonance imaging and radiographic examination. These patients were divided into two groups based on the results of their magnetic resonance imaging: the insufficiency fracture group included 46 patients who had subchondral insufficiency fractures of the medial tibial condyle and the nonfracture group included 24 patients without fractures. The meniscus injury and medial meniscus extrusion (MME) were evaluated by using magnetic resonance imaging. The Kellgren-Lawrence grade, the femorotibial angle, and the percent mechanical axis (%MA) were evaluated with the use of knee radiographs. T-scores were also measured by using dual-energy X-ray absorptiometry with a bone densitometer.

MME were significantly larger and the %MA was significantly smaller in the insufficiency fracture group than that in the nonfracture group. The prevalence of medial meniscus injuries and pathological MME were higher in the insufficiency fracture group than those in the nonfracture group. The prevalence of varus knee and osteoporosis did not vary remarkably different between the two groups.

The patients who had insufficiency fractures of the medial tibial condyle tended to have medial meniscus extrusion.

Anterior cruciate ligament (ACL) injury often leads to posttraumatic osteoarthritis (PTOA), despite ACL reconstruction (ACLR). Medial meniscal extrusion (MME) is implicated in PTOA progression but remains understudied after ACL injury and ACLR.

It was hypothesized that MME would increase longitudinally after ACL injury and ACLR, with greater changes in the ipsilateral knee compared with the contralateral knee, leading to cartilage degeneration. The study aimed to assess MME 3 years after ACLR and its relationship with magnetic resonance imaging (MRI) T1ρ and T2 as cartilage degeneration markers.

Cohort study; Level of evidence, 2.

MME and relative percentage of extrusion (RPE) were measured on 3 coronal slices of 3-dimensional fast spin-echo images and the mean values were used. T1ρ and T2 sequences were obtained and cartilage compositional measurements were performed using in-house developed software with MATLAB. Mixed models were used to assess the longitudinal changes and linear regression was used to assess the relationships between RPE and T1ρ and T2 values.

A total of 54 participants with unilateral ACL injuries underwent preoperative bilateral knee MRI. A total of 36 participants completed MR scans at 6 months and 3 years after ACLR. MME and RPE measurements demonstrated high reliability (ICC > 0.88 and > 0.91, respectively). The predicted values of MME and RPE from the mixed models showed that the ipsilateral side had significantly greater MME and RPE than the contralateral side at all 3 time points (P = .023 for MME; P = .013 for RPE at baseline; and P < .001 at 6 months and P < .001 at 3 years for both MME and RPE). The rate of change of MME and RPE on the ipsilateral side was significantly greater than that on the contralateral side (P < .001). Postoperative RPE was associated with T1ρ and T2 values in the posterior medial femoral condyle.

MME and RPE obtained pre- and postoperatively after ACLR on the ipsilateral side were significantly greater than those on the contralateral side, and the longitudinal increases on the ipsilateral side were greater than those on the contralateral side. Postoperative RPE was significantly associated with cartilage degeneration in the posterior medial femoral condyle.

The current literature evaluating meniscectomy outcomes often mixes various tear patterns, failing to elucidate the impact of specific tear types on procedure results. Flap tears, which are prone to causing mechanical symptoms, require targeted research. This study aims to examine Lysholm scores following a meniscectomy for medial meniscus flap tears, to determine if extensive resections lead to poorer one-year outcomes, and to assess their impact on postoperative bone marrow lesion (BML) risk and medial meniscus extrusion (MME) width.

Patients undergoing arthroscopic meniscectomy for medial meniscal flap tears were classified into three groups: minimum resection, single leaf resection, and subtotal resection. Lysholm scores and medial joint space (MJS) width on Rosenberg view radiographs were measured preoperatively and one year postoperatively. BMLs and MMEs were assessed via MRI preoperatively and at 1, 3, 6, and 12 months postoperatively.

Fifty patients (mean age 60 ± 13 years) underwent meniscectomy: minimum resection in 21 (42%), single leaf in 23 (46%), and subtotal in 6 (12%). The Lysholm scores improved significantly, from 65.5 ± 17.6 to 93.4 ± 16.5 (n = 50) at 12 months in patients overall (p < 0.001), while MJS width decreased from 3.9 ± 0.7 mm to 3.5 ± 0.8 mm (p < 0.001). There were no significant differences in Lysholm scores or MJS widths among the three resection patterns. The occurrence rate of BMLs in the medial femoral condyle and tibial plateau increased post-surgery, peaking at 1 month, but then improved to near-baseline by 12 months. The occurrence rate of BMLs was higher in the single leaf and subtotal meniscectomy groups post-surgery, but declined across all groups by 12 months. Among the three groups with different resection patterns, MME width at 12 months was 2.7 ± 1.8 mm in the subtotal resection group, which was significantly larger than in the other groups.

Arthroscopic partial meniscectomy for flap tears yielded favorable 12-month outcomes. Larger resections were associated with greater BML incidence and greater MME width.

This study aims to develop a hierarchical classification method to automatically assess the severity of knee osteoarthritis (KOA).

This retrospective study recruited 4074 patients. Clinical diagnostic indicators and clinical diagnostic processes were applied to develop a hierarchical classification method that involved four sub-task classifications. These four sub-task classifications were the classification of Kellgren-Lawrence (KL) grade 0-2 and KL grade 3-4, KL grade 3 and KL grade 4, KL grade 0 and KL grade 1-2, and KL grade 1 and KL grade 2, respectively. To extract the features of clinical diagnostic indicators, four U-Net models were first used to segment the total joint space (TJS), the lateral joint space (LJS), the medial joint space (MJS), and osteophytes, respectively. Based on the segmentation result of TJS, the region of knee subchondral bone was generated. Then, geometric features were extracted based on segmentation results of the LJS, MJS, TJS, and osteophytes, while radiomic features were extracted from the knee subchondral bone. Finally, the geometric features, radiomic features, and combination of geometric features and radiomic features were used to construct the geometric model, radiomic model, and combined model in KL grading, respectively. A strict decision strategy was used to evaluate the performance of the hierarchical classification method in all X-ray images of testing cohort.

The U-Net models achieved relatively satisfying performances in the segmentation of the TJS, the LJS, the MJS, and the osteophytes with the dice similarity coefficient of 0.88, 0.86, 0.88, and 0.64 respectively. The combined models achieved the best performance in KL grading. The accuracy of combined models was 98.50%, 81.65%, 82.07%, and 74.10% in the classification of KL grade 0-2 and KL grade 3-4, KL grade 3 and KL grade 4, KL grade 0 and KL grade 1-2, and KL grade 1 and KL grade 2, respectively. For all X-ray images of the testing cohort, the accuracy of the hierarchical classification method was 65.98%.

The hierarchical classification method developed in the current study is a feasible approach to assess the severity of KOA.

Magnetic resonance imaging (MRI) is the imaging of choice for meniscal extrusion (ME). However, they may underappreciate the load-dependent changes of the meniscus. There is growing evidence that weight-bearing ultrasound (WB US) is more suitable, particularly in revealing occult extrusion. We therefore perform a systematic review and meta-analysis on the validity and reliability of US in diagnosing extrusion. Furthermore, we explored whether it detects differences in extrusion between loaded and unloaded positions and those with pathological (osteoarthritis and meniscal injury) and healthy knees.

The Cochrane Controlled Register of Trials, PubMed, Medline, and Embase were used to perform a systematic review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Data pertaining to intra- and interrater reliability of US in measuring meniscal extrusion (ME), its correlation with magnetic resonance imaging (MRI), and head-to-head comparison of potential factors to influence ME were included [loading versus unloading position; osteoarthritis (OA) or pathological menisci (PM) versus healthy knees; mild versus moderate-severe knee OA]. Pooled data were analyzed by random or fixed-effects models.

A total of 31 studies were included. Intraclass correlation coefficients (ICC) for intra- and interrater reliability were minimum 0.94 and 0.91, respectively. The correlation between US and MRI was (r = 0.76). US detected ME to be greater in the loaded position in all knees (healthy, p < 0.00001; OA, p < 0.00001; PM, p = 0.02). In all positions, US detected greater extrusion in OA (p < 0.0003) and PM knees (p = 0.006) compared with healthy controls. Furthermore, US revealed greater extrusion in moderate-severe OA knees (p < 0.00001).

This systematic review suggests ultrasonography can play an important role in the measurement of meniscal extrusion, with results comparable to that of MRI. However, to what extent it can differentiate between physiological and pathological extrusion requires further investigation, with an absolute cutoff value yet to be determined. Nevertheless, it is an appropriate investigation to track the progression of disease in those with meniscal pathologies or osteoarthritis. Furthermore, it is a feasible investigation to evaluate the meniscal function following surgery.

IV, Systematic review of level III-IV evidence.

Osteoarthritis (OA) is marked by the progressive degradation of joint cartilage and subchondral bone. The precise molecular mechanisms driving meniscus deterioration in OA, especially at the single-cell level, remain poorly understood.

We analyzed two datasets from the GEO database, GSE220243 and GSE98918, focusing on meniscus tissue sequencing data from OA and non-OA patients. The standard Seurat procedure was employed to process single-cell data and identify differentially expressed genes (DEGs). Immune cell infiltration was assessed using the Microenvironment Cell Populations (MCP) counter and CIBERSORT algorithms. For the microarray data, DEGs were identified with the limma package, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed using ClusterProfiler. The overlapping DEGs from both datasets were imported into Cytoscape to generate protein-protein interaction (PPI) networks and identify hub genes. Transcription factor (TF) and miRNA interaction networks were analyzed using NetworkAnalyst, and gene-related predictive drugs were enriched through the DSigDB platform.

After quality control, 34,763 cells from the OA patients and 34,145 cells from the healthy controls were analyzed. UMAP identified and SingleR annotated 14 cell clusters. The 10 largest cell clusters were selected for further analysis. The OA group exhibited a notable increase in macrophages and a reduction in cytotoxic lymphocytes and endothelial cells in the meniscus. In GSE98918, 220 DEGs were identified, and the MCODE plug-in in Cytoscape pinpointed a key module containing 12 candidate genes. The MCC methodfiltered the top 20 DEGs in each GSE220243 cluster. Overlapping DEGs from GSE220243 and GSE98918 identified COL1A1, COL3A1, COL5A2, COL6A3, LOX, and VEGFA as significantly decreased in OA, with COL3A1, COL5A2, LOX, and VEGFA upregulated in meniscal chondrocytes. The interaction network highlighted 3 key miRNAs and 13 shared TFs. Ten gene-related predictive drug molecules were identified.

This research highlights crucial genes in the OA meniscus and uncovers their differing regulatory patterns between chondrocytes and non-chondrocytes. These findings enhance our understanding of the molecular mechanisms driving OA pathogenesis and aid in identifying potential drug targets.

To evaluate the postoperative meniscal extrusion between all-inside suture (AIS) and trans-capsular suture (TCS) repair techniques.

Thirteen patients (mean age, 19.4 years) underwent AIS repairs using only sutures (AIS group) for radial tears in the middle segment of the lateral meniscus (RTMLM), and seven patients (mean age, 20.3 years) underwent inside-out repairs among TCS (TCS group). For all cases, lateral (LE), anterior (AE) and posterior (PE) meniscal extrusions of the lateral meniscus were measured during preoperative and 3-, 12- and 24-week postoperative MRIs. Then, the change of each extrusion from preoperative to each postoperative period was calculated as ∆LE, ∆AE and ∆PE.

There was no significant difference between the AIS and TCS groups in the preoperative extrusions. As for postoperative extrusions, only ∆LEs in the AIS group was significantly smaller than those in the TCS group at all postoperative periods (-1.5 ± 1.7 vs. 0.9 ± 0.7 mm at 3-week, -0.9 ± 0.9 vs. 0.4 ± 0.9 mm at 12-week and -0.3 ± 1.0 vs. 0.6 ± 1.1 mm at 24-week postoperation). In ∆AEs and ∆PEs, at all three postoperative periods, there were no significant differences.

Postoperative LE, AE and PE on MRIs after AIS and TCS repairs for RTMLM were investigated. Significantly smaller lateral extrusion was observed within 24 weeks after AIS repairs of RTMLM compared to TCS repairs, which could lead to stabilization of the repair site and prevent degenerative changes.

Case-control study, retrospective comparative study, Level Ⅲ.

Some patients who undergo anterior cruciate ligament (ACL) reconstruction experience abnormal mechanical stress in the meniscus. Medial meniscal extrusion (MME) is reflected in the pathological condition of the meniscus, which expands owing to repetitive mechanical stress. Thus, the effect of the reconstructed ACL on increasing MME under weight-bearing conditions remains unclear. This study investigated the effect of ACL reconstruction on meniscal extrusion under non-weight-bearing and weight-bearing conditions.

Seventeen patients who underwent unilateral ACL reconstruction (ACL group) and 20 age-matched healthy volunteers (control group) were enrolled. Ultrasonography was performed in the supine, standing, and walking positions in preoperative and postoperative ACL patients. MME during walking was evaluated based on the dynamic behavior of extrusion, and kinetic and kinematic data were synchronously obtained. Moreover, the ACL group underwent magnetic resonance imaging (MRI) evaluation at two points: preoperatively and 12 months postoperatively, and the ultrasound findings were compared.

MME in the supine position measured using both ultrasonography and MRI was not significantly different preoperatively and postoperatively in the ACL group. However, postoperative MME and dynamic behavior of extrusion under standing and walking conditions were significantly higher than those in the preoperative state (dynamic behavior: 0.9 ± 0.4 mm preoperatively, 1.2 ± 0.4 mm postoperatively). Moreover, the deficits in knee extension during walking persisted postoperatively and were significantly higher than those in the control group.

MME in patients with ACL reconstruction including meniscus repair was different under mechanical stress compared to the non-weight bearing condition.

To study the medial meniscus extrusion (MME) in subjects with and without medial meniscal tears on magnetic resonance imaging (MRI), supine ultrasound (US), and weight-bearing US.

Forty-seven cases (mean age 43.7 years) with medial meniscus tears and 53 healthy controls (mean age 36.6 years) were assessed. Two experienced sonographers performed the US evaluations, and a fellowship-trained musculoskeletal radiologist assessed the menisci on MRI. Independent and paired T-tests and ICC were used for statistical analyses.

On supine US, the mean MME was 3.9 mm for the cases and 2.3 mm for the controls (p < 0.001). On weight-bearing US, the values were 4.2 and 2.8 mm (p < 0.001), and on MRI 3.0 and 2.0 mm (p < 0.001), respectively. The mean difference between supine and weight-bearing US extrusion was 0.38 mm for the cases and 0.49 mm for the controls (p = 0.291). Correlation between supine US and MRI MME measurements was good (ICC = 0.660, CIs [0.533-0.758]).

MME can be assessed using US with good correlation to MRI. US-observed extrusion was significantly increased in supine and standing positions for medial meniscus tears. The mean difference between examination positions was reduced with medial meniscus tears although this result was statistically insignificant.

There is only limited literature available evaluating the preferable treatment for active mid-age or elderly patients presenting with a degenerative medial meniscus root tear (d-MMRT) with medial meniscal extrusion (MME) and early-phase radiographic osteoarthritis (OA), failing to provide solid evidence. The aim of this study was to evaluate early outcomes of medial unicompartimental arthroplasty (mUKA) in active patients presenting a d-MMRT with meniscal extrusion and mild radiographic OA of the knee. To prove this claim we hypothesized that (1) patients with a d-MMRT with initial grade 1-3 KL OA of the medial compartment of the knee present the same pre-operative symptoms as patients with an end-stage grade 4 K-L OA, and that (2) those patients with d-MMRT and low-grade OA achieve the same early clinical and functional outcomes when treated with mUKA compared to patients with end-stage medial OA.

We reviewed the prospectively collected data of 185 patients undergoing robotic-assisted image-based mUKA from January 2021 to July 2022 at a single Institution. We identified two different cohorts of non-consecutive patients: a group of 24 patients undergoing mUKA surgery following d-MMRT combined with K-L grades 1-3 OA (group 1), and a group of 161 patients who underwent mUKA but presenting with an end-stage bone-on-bone K-L grade 4 OA (group 2). Preoperative and postoperative clinical assessments at one-year follow-up included the Oxford Knee Score (OKS), 5-level EQ-5D version (EQ-5D-5L score), and a standard weight-bearing X-ray protocol. The paired t-test was used to compare clinical outcomes and radiologic values of the two cohorts and in-between the two cohorts. Statistical significance was set at p < 0.05.

The mean follow-up for group 1 was 16.4 ± 2.5 months, and the mean age at the time of operation was 63 ± 8.6 years with a mean time from diagnosis to intervention of 53 ± 47.5 days. Preoperative impairment was greater in group 1 compared to group 2, but with no significant difference. Postoperatively, both groups showed excellent mean outcomes at 1-year follow-up, with no significant difference. The mean preoperative HKA, mPTA, and LDFA were 176.3 ± 3.1, 88.1 ± 2.3, and 86.6 ± 1.7 respectively. The mean postoperative HKA, coronal femoral component angle, and coronal tibial component angle were 179.1 ± 2.6, 87.2 ± 2.3, and 87.2 ± 3.3. No difference was found between preoperative age, BMI, between the two cohorts.

Favorable early clinical outcomes were obtained after mUKA in active mid-age and elderly patients presenting with degenerative medial meniscus root tear and mild isolated medial OA. Patients with mild no bone-on-bone OA but with degenerative medial meniscus root tear and medial meniscal extrusion presented the same or worse pre-operative symptoms as patients with end-stage medial OA and benefit the same from mUKA.

Medial meniscal extrusion (MME) has been associated with knee osteoarthritis (OA). However, there is no standardized method to measure MME.

The purpose of this study was to investigate the relationship between MME and outcome measures related to knee OA and discuss different magnetic resonance imaging (MRI) methods of measuring MME. It was hypothesized that MME would be associated with outcome measures of OA and that the distance extruded over the tibial plateau would be the most common MRI method to measure MME.

Systematic review; Level of evidence, 3.

The MEDLINE, Embase, Cochrane Library, Scopus, Web of Science Core Collection, Global Index Medicus, and ClinicalTrials.gov databases were systematically searched. The inclusion criteria were studies that (1) measured MME on nonoperated knees using MRI; (2) evaluated knee OA with at least 1 knee OA grading scale, outcome measure, or direct characterization of cartilage or bone; (3) statistically evaluated the association between MME and knee OA outcome measure; (4) were randomized controlled trials, nonrandomized controlled trials, cohort studies, or case series; and (5) reported original results.

A total of 19 studies were included, of which 14 reported MME as the distance extruded over the tibial plateau, 7 reported MME as the volume extruded over the tibial plateau, and 1 reported MME as the percentage of the tibial plateau covered by the meniscus. All studies reported that MME was significantly associated with at least 1 OA outcome measure-including increased Kellgren-Lawrence grade, osteophytes, cartilage damage, varus alignment, knee pain, bone marrow lesions, and progression to arthroplasty. Eight studies found that MME was associated with worse OA outcomes over time (range, 2-10 years).

All 19 reviewed studies reported that MME was associated with at least 1 knee OA outcome measure reflective of worsening arthritis, suggesting a strong association between OA and MME. Future research is needed to investigate this relationship and standardize the methods of measuring MME.

The meniscal position within the knee is critical to maintain normal knee function. The joint capsule might dynamically coordinate the medial meniscus (MM) by transmitting a semimembranosus action. However, their interrelationships in vivo are unclear. We aimed to determine relationships among the MM, joint capsule, and semimembranosus during passive tibial external-internal and isometric tibial internal rotation at the medial and posteromedial knees of 10 healthy individuals in vivo using ultrasound. We analyzed images of the MM and joint capsule locations at the medial and posteromedial knee and the velocity waveform similarity of each structure during rotational tasks. Both isometric internal rotation with semimembranosus action and passive tibial external rotation displaced the MM inward at the medial knee. The MM and joint capsule during these MM displacements coordinately moved with more than moderate cross-correlation coefficients (passive external and isometric internal rotations, ≥ 0.54 and ≥ 0.90, respectively). The movements of the MM and joint capsule to the semimembranosus during isometric internal rotation also coordinated with moderate cross-correlation coefficients (≥ 0.62). Therefore, the joint capsule might dynamically coordinate the MM by transmitting semimembranosus action. Whether increased tibial internal rotation or semimembranosus shortening causes MM extrusion awaits further investigation.

The correlation of cartilage thickness measured by three-dimensional (3D) magnetic resonance imaging (MRI) and the medial meniscal coverage ratio (MMCR), which presented pathology of the medial meniscus extrusion (MME) in 3D MRI, has not yet been elucidated. The study's purpose was to retrospectively verify whether the average cartilage thickness calculated by the automatic MRI 3D analysis system for each subregion was correlated with MMCR.

A total of 60 patients underwent medial meniscus repair or high tibial osteotomy to treat their medial knee osteoarthritis. Cartilage thickness and MMCR were automatically calculated using 3D MRI software. The MMCR was defined as the ratio of the area covered by the meniscus within the medial tibial cartilage area to the total medial tibial cartilage area. The association between MMCR and the average cartilage thickness at 15 subregions in the medial femoral condyle (MFC) and medial tibial plateau (MTP) was evaluated using Spearman's rank correlation coefficient.

Kellgren-Lawrence grade exhibited a negative correlation with MMCR and a positive correlation with MME width. Cartilage thickness in the MTP had a moderately positive correlation with MMCR at four subregions and a weakly positive correlation at another subregion. Cartilage thickness in the MFC showed a moderately positive correlation with MMCR at five subregions and a weakly positive correlation at one subregion.

Cartilage thickness calculated by automatic MRI 3D analysis system had a positive correlation with MMCR for all subregions of the anterior and middle subregions in the MFC and for five regions of nine subregions of the anterior and middle subregions in the MTP.

Level II, cross-sectional study (diagnosis).

Meniscus pathologies (damage, extrusion) and synovitis are associated with knee osteoarthritis (KOA); however, whether synovitis mediates the relationship between meniscus pathologies and KOA radiographic progression remains unclear. We conducted an observational study in the Osteoarthritis Initiative (OAI) cohort, with a 48-month follow-up. Meniscus pathology and synovitis were measured by MRI osteoarthritis knee score (MOAKS) at baseline and 24 months, and a comprehensive synovitis score was calculated using effusion and Hoffa synovitis scores. The knee osteoarthritis radiographic progression was considered that Kellgren-Lawrence (KL) grade and joint space narrowing (JSN) grade at 48 months were increased compared to those at baseline. This study included a total of 589 participants, with KL grades mainly being KL1 (26.5%), KL2 (34.1%), and KL3 (30.2%) at baseline, while JSN grades were mostly 0 at baseline. A logistic regression model was used to analyze the relationship between meniscus pathology, synovitis, and KOA progression. Mediation analysis was used to evaluate the mediation effect of synovitis. The average age of the participants was 61 years old, 62% of which were female. The medial meniscus extrusion was longitudinally correlated with the progression of KL (odds ratio [OR]: 2.271, 95% confidence interval [CI]: 1.412-3.694) and medial JSN (OR: 3.211, 95% CI: 2.040-5.054). Additionally, the longitudinal correlation between medial meniscus damage and progression of KOA (OR: 1.853, 95% CI: 1.177-2.941) and medial JSN (OR: 1.655, 95% CI: 1.053-2.602) was significant. Synovitis was found to mediate the relationship between medial meniscus extrusion and KL and medial JSN progression at baseline (β: 0.029, 95% CI: 0.010-0.053; β: 0.022, 95% CI: 0.005-0.046) and beyond 24 months (β: 0.039, 95% CI: 0.016-0.068; β: 0.047, 95% CI: 0.020-0.078). However, we did not find evidence of synovitis mediating the relationship between meniscal damage and KOA progression. Synovitis mediates the relationship between medial meniscus extrusion (rather than meniscus damage) and KOA progression.

To investigate the up-to-date clinical outcomes of tissue-engineered meniscus implants for meniscus defects.

A search was performed by 3 independent reviewers on PubMed, MEDLINE, EMBASE, and Cochrane from 2016 to June 18, 2023, with the term "meniscus" with all the following terms: "scaffolds," "constructs," "implant," and "tissue engineering." Inclusion criteria included "Clinical trials" and "English language articles" that involved isolated meniscus tissue engineering strategies for meniscus injuries. Only Level I to IV clinical studies were considered. The modified Coleman Methodology score was used for quality analysis of included clinical trials. The Methodological Index for Non-Randomized Studies was employed for analysis of the risk of study bias and methodological quality.

The search identified 2,280 articles, and finally 19 original clinical trials meeting the inclusion criteria were included. Three types of tissue-engineered meniscus implants (CMI-Menaflex, Actifit, and NUsurface) have been clinically evaluated for meniscus reconstruction. Lack of standardized outcome measures and imaging protocols limits comparison between studies.

Tissue-engineered meniscus implants can provide short-term knee symptom and function improvements, but no implants have been shown to propose significant long-term benefits for meniscus defects.

Level IV, systematic review of Level I to IV studies.

We reported that the full-length width of medial tibial osteophytes comprising cartilage and bone parts correlates with medial meniscus extrusion (MME) in early-stage knee osteoarthritis (OA). However, no data exist on the prevalence of MME and its relationship with osteophytes in the elderly population. 1191 elderly individuals (females 57%; 72.9 years old on average) in the Bunkyo Health Study underwent standing plain radiograph and proton density-weighted MRI on knee joints. MRI-detected OA changes were evaluated according to the Whole-Organ Magnetic Resonance Imaging Score. A new method of assessing the cartilage and bone parts of osteophytes was developed using pseudo-coloring images of proton density-weighted fat-suppressed MRI. Most subjects showed Kellgren-Lawrence grade 1 or 2 radiographic medial knee OA (88.1%), MME (98.7%, 3.90 ± 2.01 mm), and medial tibial osteophytes (99.3%, 3.27 ± 1.50 mm). Regarding OA changes, MME was closely associated with the full-length width of medial tibial osteophytes (β = 1.114; 95% CI 1.069-1.159; p < 0.001) in line with osteophyte width (intraclass correlation coefficient, 0.804; 95% CI 0.783-0.823). Our data revealed that MME and medial tibial osteophytes are observed in the elderly and demonstrate that the degree of MME is consistent with the full-length width of medial tibial osteophytes, suggesting that osteophytes might be implicated in MME.

Meniscus extrusion is crucial for the diagnosis and treatment of meniscal injury, but the literature on this topic has not yet been systematized. The purpose of this systematic review was to compare diagnostic methods and summarize the data of medial and lateral meniscal extrusion in knees with and without osteoarticular pathology.

This systematic review was conducted according to the PRISMA 2020 statement. Searches were conducted on PubMed, EMBASE and Cochrane databases to identify studies that measured meniscal extrusion using magnetic resonance imaging (MRI) or ultrasound (US). Meniscal extrusion data was summarized as weighted mean for medial and lateral meniscus, and stratified according to the method of measurement (MRI or US) and presence of knee osteoarticular pathology.

A total of 26 studies were included in this review. Weighted mean values of meniscal extrusion were always higher for the medial than the lateral meniscus, regardless of the method of measurement. The medial meniscus extrusion was always higher in knees with osteoarticular pathology than those without. For the lateral meniscus extrusion, the mean values were higher in those knees without osteoarticular pathology. When classifying pathological meniscal extrusion with pre-defined cut-off values, the higher the cut-off used, the lower the percentage of knees classified as pathological meniscal extrusion.

The medial meniscus presents on mean higher extrusion and extrusion is higher in knees with osteoarticular pathology. Based on summary data, the most suitable cut-offs for pathological meniscal extrusion for both MRI and US seem to fall within >2 and >3 mm.

Although it is established that structural damage of the meniscus is linked to knee osteoarthritis (OA) progression, the predisposition to future development of OA because of geometric meniscal shapes is plausible and unexplored. This study aims to identify common variations in meniscal shape and determine their relationships to tissue morphology, OA onset, and longitudinal changes in cartilage thickness.

A total of 4,790 participants from the Osteoarthritis Initiative data set were studied. A statistical shape model was developed for the meniscus, and shape scores were evaluated between a control group and an OA incidence group. Shape features were then associated with cartilage thickness changes over 8 years to localize the relationship between meniscus shape and cartilage degeneration.

Seven shape features between the medial and lateral menisci were identified to be different between knees that remain normal and those that develop OA. These include length-width ratios, horn lengths, root attachment angles, and concavity. These "at-risk" shapes were linked to unique cartilage thickness changes that suggest a relationship between meniscus geometry and decreased tibial coverage and rotational imbalances. Additionally, strong associations were found between meniscal shape and demographic subpopulations, future tibial extrusion, and meniscal and ligamentous tears.

This automatic method expanded upon known meniscus characteristics that are associated with the onset of OA and discovered novel shape features that have yet to be investigated in the context of OA risk.

Meniscal extrusion has become increasingly utilized when evaluating meniscus root abnormalities. However, no consensus definition or approach exists on how to measure extrusion.

The purpose of this study was to evaluate the extent of heterogeneity in meniscal extrusion measurement techniques and reported extrusion values in knees with posterior medial meniscus root tears (PMMRTs). We hypothesized that meniscal extrusion measurement techniques would vary considerably throughout reported studies, with resultant wide-ranging published extrusion values.

Systematic review; Level of evidence, 4.

A systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. The inclusion criteria consisted of all clinical and cadaveric studies reporting on meniscal extrusion after PMMRTs, excluding studies lacking data in full extension, those presenting only semiquantitative analyses, articles reporting only differences in meniscal extrusion, and review articles.

A total of 45 studies were included. Imaging modality types included magnetic resonance imaging (89%), 3-dimensional reconstruction with computed tomography (7%), linear displacement transducers (2%), and a combination of magnetic resonance imaging and ultrasound (2%). The 3 most commonly used landmarks to acquire coronal images for meniscal extrusion measurements were the medial collateral ligament (38%), the midpoint of the anterior-posterior length of the medial meniscus (23%), and the middle of the medial femoral condyle (19%). The pooled mean extrusion values according to the measurement location were 3.5 ± 0.7 mm, 3.9 ± 0.8 mm, and 4.5 ± 2.1 mm, respectively, with no significant differences noted between the modality types (P = .23). The pooled mean meniscal extrusion from all included studies was 3.2 ± 2.0 mm.

Substantial variation exists in measurement techniques for meniscal extrusion, particularly as it relates to the coronal cross-sectional reference location. Further studies should aim to provide clear descriptions of the measurement method and have uniform measurement methodology to allow comparisons and pooling between studies.

Whether the medial meniscus morphology and movement occur under upright loading conditions in early knee osteoarthritis (OA) or medial meniscus posterior root tear (MMPRT) remains unknown. This study aimed to evaluate the medial and anteroposterior extrusion of the medial meniscus under unloaded and upright-loaded conditions in patients with early knee OA.

Twelve patients with early knee OA and 18 healthy adult volunteers participated in this study. Magnetic resonance imaging using special equipment was performed with the participants in the unloaded and upright-loaded conditions. Medial, anterior, and posterior extrusions of the medial meniscus against the tibial edge were evaluated and compared between the early knee OA and healthy adult control groups. Additionally, 12 patients in the early knee OA group were divided into 2 subgroups based on whether MMPRT was observed, and the extrusion of the medial meniscus was compared.

The amount of medial extrusion of the medial meniscus in both the unloaded and upright-loaded conditions was significantly greater in the early knee OA group than in the control group (unloaded: 2.6 ± 1.0 mm vs 0.7 ± 0.5 mm; upright-loaded: 3.7 ± 0.9 mm vs 1.8 ± 0.8 mm). Similarly, the anterior and posterior extrusion of the medial meniscus in the upright-loaded condition was significantly larger in the early knee OA group (anterior: 4.6 ± 1.0 mm vs 3.7 ± 1.1 mm; posterior: -3.4 ± 1.1 mm vs -4.6 ± 1.6 mm). However, no difference was observed in meniscal extrusion between unloaded and upright-loaded conditions. The posterior extrusion of the medial meniscus in the upright-loaded condition was significantly greater in MMPRT cases than in non-MMPRT cases in the early knee OA group (MMPRT: -2.7 ± 1.1 mm; non-MMPRT -4.1 ± 1.5 mm).

In early knee OA, significantly large meniscal extrusions of the medial meniscus in both unloaded and upright-loaded conditions were found compared with healthy adults. Among patients with early knee OA, those with MMPRT showed a large posterior extrusion of the medial meniscus in the upright-loaded condition compared with those without MMPRT.

Level IV.

Medial meniscal extrusion (MME) is a structural abnormality that leads to early knee osteoarthritis; however, its formation remains debated. For anatomical consideration of the mechanism underlying MME formation, we examined the capsular attachment on the posteromedial tibia and its layered association with the semimembranosus. Fourteen knees of eight body donors were analyzed in this study; six knees were grouped for macroscopic analysis, whereas four knees each were grouped for histological and phosphotungstic acid-enhanced micro-computed tomography analyses. The capsular attachment varied in width according to location and was not distant from the articular cartilage and posterior root. A portion of the posteromedial joint capsule formed the semimembranosus tendinous sheath. The dense fibrous membrane superficial to the semimembranosus, which was continuous from its tendinous sheath, existed as one of the layers of the joint capsule. The aforementioned findings were confirmed in all specimens. Based on the capsular attachment and its layered association with the semimembranosus, the conventional posteromedial knee ligaments may be only a part of the joint capsule divided into two layers by the semimembranosus. If the coordinated action of the joint capsule and semimembranosus partially contributes to the medial meniscus stability, such a structural problem may affect MME formation.

Medial meniscus posterior root tears (MMRTs), defined as tears or avulsions that occur within 1 cm of the tibial attachment of the medial meniscus posterior root, lead to biomechanically detrimental knee conditions by creating a functionally meniscal-deficient status. Given their biomechanical significance, MMRTs have recently been gaining increasing interest. Accordingly, numerous studies have been conducted on the anatomy, biomechanics, clinical features, diagnosis, and treatment of MMRTs, and extensive knowledge has been accumulated. Although a consensus has not yet been reached on several issues, such as surgical indications, surgical techniques, and rehabilitation protocols, this article aimed to comprehensively review the current knowledge on MMRTs and to introduce the author's treatment strategies.

The concept of meniscal extrusion has recently been recognized as a hallmark of meniscus dysfunction. This review examines contemporary literature regarding the pathophysiology, classification, diagnosis, treatment, and future directions for investigation regarding meniscus extrusion.

Meniscus extrusion, defined as >3 mm of radial displacement of the meniscus, leads to altered knee biomechanics and accelerated knee joint degeneration. Meniscus extrusion has been associated with degenerative joint disease, posterior root and radial meniscal tears, and acute trauma. Meniscus centralization and meniscotibial ligament repair have been proposed as techniques to address meniscal extrusion with promising biomechanical, animal model, and early clinical reports. Further studies on the epidemiology of meniscus extrusion and associated long-term nonoperative outcomes will help to elucidate its role in meniscus dysfunction and resultant arthritic development. Understanding and appreciation for the anatomic attachments of the meniscus will help to inform future repair techniques. Long-term reporting on the clinical outcomes of meniscus centralization techniques will yield insights into the clinical significance of meniscus extrusion correction.

Previously, we identified a significant association between meniscal extrusion and short-term incident knee osteoarthritis (KOA). To validate these findings, we evaluated long-term incident KOA in knees with meniscus extrusion, using two different cohorts.

We used data from the PROOF study, which evaluated a high-risk population of overweight women, and a female subcohort of the population-based Rotterdam Study (RS). Meniscal extrusion was defined as ≥ 3 mm on MRI. Outcomes were incident radiographic (KL ≥ 2) or clinical KOA according to the ACR criteria, assessed at 6.6 years (PROOF) and 5.1 years (RS). With generalized estimating equations, we determined the association of knees with and without baseline meniscal extrusion and incident KOA, adjusting for confounders. Furthermore, we computed the population attributable risk percentage (PAR%) of meniscal extrusion.

PROOF: of 421 available knees 23% had baseline meniscal extrusion. Incident radiographic KOA was significantly higher in knees with meniscal extrusion compared to those without (adjusted OR 2.54, 95% CI 1.34, 4.80; p = 0.004; PAR 21%). Incident clinical KOA was also significantly higher (adjusted OR 2.44, 95% CI 1.29, 4.60; p = 0.006; PAR 19%). RS: 46% of 872 available knees had meniscal extrusion. Incident radiographic KOA was significantly higher (adjusted OR 9.86, 95% CI 2.13, 45.67; p = 0.002; PAR 77%). Incident clinical KOA was borderline significantly higher (adjusted OR 2.65, 95% CI 0.96, 7.30; p = 0.06; PAR 44%).

Meniscal extrusion is significantly associated with long-term incident KOA. A high number of incident cases were attributable to extrusion.

To evaluate the sensitivity and specificity for screening and diagnosis of medial meniscal root injury using the distance ratio of medial joint space width between affected and unaffected knees in patients with potential medial meniscal root injury (MMRI) using plain radiographs, the study enrolled 49 patients with suspected MMRI who were then evaluated for MMRI using plain radiographs of both knees in the anteroposterior view and magnetic resonance imaging (MRI) findings. The ratios of peripheral medial joint space width between the affected and unaffected sides were calculated. The cut point value, sensitivity and specificity were calculated according to a receiver operating characteristic (ROC) curve. In the study, 18 and 31 patients were diagnosed with and without MMRI, respectively. The mean peripheral medial joint space width ratios comparing the affected side to the unaffected side in the standing position of the anteroposterior view of both knees in the MMRI and non-MMRI groups were 0.83 ± 0.11 and 1.04 ± 0.16, respectively, which was a significant difference (p-value < 0.001). The cut point value of the peripheral medial joint space width ratio between the affected and unaffected sides for suspected MMRI was 0.985, with sensitivity and specificity of 0.83 and 0.81, respectively, and for diagnosis was 0.78, with sensitivity and specificity of 0.39 and 1.00, respectively. The area under the ROC curve was 0.881. Patients with a possible MMRI had peripheral medial joint space width ratios less than patients with non-MMRI. This test can be used for reliably screening for or diagnosing medial meniscal root injury in primary or secondary care settings.

The purpose of this study was to evaluate the effects of arthroscopic meniscal centralization reinforcement for a medial meniscus (MM) posterior root defect on knee kinematics and meniscal extrusion in the anterior cruciate ligament reconstructed (ACLR) knee. The hypothesis was that the medial meniscus centralization would reduce extrusion and anterior laxity in ACLR knee with a medical meniscal defect.

Fourteen fresh-frozen human cadaveric knees were tested using a six-degrees-of-freedom robotic system under the following loading conditions: (a) an 89.0 N anterior tibial load, (b) 5.0 Nm internal and external rotational torques, (c) a 10.0 Nm valgus and varus loadings, and (d) a combined 7.0 Nm valgus moment and then a 5.0 Nm internal rotation torque as a static simulated pivot shift. The tested knee states included: (1) anatomic single-bundle cruciate ligament reconstruction with intact medial meniscus (MM Intact), (2) anatomic single-bundle cruciate ligament reconstruction with medial meniscus posterior root defect (MM Defect), (3) Anatomic single-bundle cruciate ligament reconstruction with medial meniscus arthroscopic centralization (MM Centralization). Medial meniscus arthroscopic centralization was performed using 1.4 mm anchors with #2 suture. The MM extrusion (MME) was measured using ultrasound under unloaded and varus loading conditions at 0° and 30° of flexion.

Anterior tibial translation (ATT) increased significantly with MM posterior root defect compared to MM intact at all flexion angles. With MM centralization, ATT was not significantly different from the intact meniscus at 15° and 30° of flexion. Meniscus extrusion increased significantly with the root defect compared to intact meniscus and decreased significantly with meniscal centralization compared to the root defect at both flexion angles.

In ACL reconstruction, cases involving irreparable medial meniscal posterior root tears, applying arthroscopic centralization for avoiding the meniscal extrusion should be considered. Clinically, in ACL reconstruction cases with irreparable medial meniscal posterior root tears, applying arthroscopic meniscal centralization for avoiding the meniscal extrusion should be considered. Meniscal centralization decreases the extrusion of the MM and offers improvements in knee laxity.

Conventional radiography remains the most widely available imaging modality in clinical practice in knee osteoarthritis. Recent research has been carried out to develop novel radiographic biomarkers to establish the diagnosis and to monitor the progression of the disease. The growing number of publications on this topic over time highlights the necessity of a renewed review. Herein, we propose a narrative review of a selection of original full-text articles describing human studies on radiographic imaging biomarkers used for the prediction of knee osteoarthritis-related outcomes. To achieve this, a PubMed database search was used. A total of 24 studies were obtained and then classified based on three outcomes: (1) prediction of radiographic knee osteoarthritis incidence, (2) knee osteoarthritis progression and (3) knee arthroplasty risk. Results showed that numerous studies have reported the relevance of joint space narrowing score, Kellgren-Lawrence score and trabecular bone texture features as potential bioimaging markers in the prediction of the three outcomes. Performance results of reviewed prediction models were presented in terms of the area under the receiver operating characteristic curves. However, fair and valid comparisons of the models' performance were not possible due to the lack of a unique definition of each of the three outcomes.

Medial unicompartmental knee arthroplasty (mUKA) requires full-thickness cartilage in the lateral compartment, but slight damage of the cartilage surface can be ignored. However, as this statement lacks literature support, we investigated whether slight cartilage damages in the weight-bearing area of the lateral femoral condyle would affect the outcome of mUKAs.

Outerbridge grading was performed on the cartilage in the weight-bearing area of the lateral femoral condyle intraoperatively. The patients, grouped as normal or as having lateral condyle cartilage of Outerbridge grade 1-2 (slight cartilage damage), underwent mUKA. Full-length lower extremity radiographs were taken and hip-knee-ankle angles (HKAAs) were measured both preoperatively and postoperatively. Using magnetic resonance imaging, the lateral meniscal extrusion distance was also measured. In addition, the Oxford Knee Score (OKS) was assessed preoperatively and at the last follow-up, in addition to the patient satisfaction assessment.

We enrolled 152 knees of 142 patients proposed for mUKAs. The mean age of participants was 69.5 years (51-89 years) and they were followed up for a mean of 25.4 months (15-44 months). There was no significant difference in preoperative (p = 0.746) and postoperative (p = 0.202) mean OKS between the normal, Outerbridge grade 1 and Outerbridge grade 2 groups. While the normal group had a higher change in OKS than the group with cartilage damage, this difference was not significant (p = 0.910). The UKA corrected the patients' mean HKAA from 171.1° (preoperatively) to 176.1° (postoperatively). From all patients, only four had slight lateral meniscus extrusion with MEDs of ≤ 0.25 mm. With the exception of one patient with a poor outcome in normal group, the rest were satisfied with the outcome of mUKA. No patients had prosthesis-related complications or revision surgery.

Cartilage damage of Outerbridge grade 1 and grade 2 in the weight-bearing area of the lateral femoral condyle will not compromise the short-term outcome of medial mobile-bearing UKA.

Medial meniscal extrusion (MME) is the medial displacement of the meniscus, which extends beyond the tibial margin. Studies have shown an association between MME and knee pain and that surgical treatment can reduce the extent of MME. Here, we describe the beneficial effects of physical therapy as a feasible conservative treatment for MME.

Data of 30 patients with knee osteoarthritis who underwent stretching of the semimembranosus tendon and passive range of motion (ROM) exercises twice a week for 8 weeks were retrospectively analyzed. MME was the measured distance between the medial meniscus and the line connecting the medial borders of the femur and tibia using ultrasound. Ultrasound findings of surrounding tissues, including the deep posterior bundle of the medial collateral ligament (dMCL), were recorded. Additionally, knee extension ROM was measured, and inner knee pain when walking was evaluated using a numerical rating scale.

There were significant improvements between the baseline and 8 weeks for MME in the non-weight-bearing position (3.6 ± 0.3 mm vs. 3.0 ± 0.4 mm), MME in the weight-bearing position (4.3 ± 0.4 mm vs. 3.8 ± 0.5 mm), ROM (-12.3° ± 4.1° vs. -3.1° ± 3.8°), and knee pain (7.0 ± 0.9 vs. 1.1 ± 1.4) (each p < 0.001). In almost all cases in which the knee extension ROM improved, the dMCL was bulging at the baseline; after 8 weeks, the dMCL was flattened, suggesting ligament tension on ultrasound imaging.

Stretching of the semimembranosus tendon and passive ROM exercises may reduce the extent of MME in patients with knee osteoarthritis. The ultrasound findings suggest that improvement in knee extension ROM may have led to the re-acquisition of MCL tension, which may have influenced MME reduction. Therefore, physical therapy may be a feasible conservative treatment for the reduction of MME.

Pathologic meniscal extrusion can compromise meniscal function, leading to increased contact forces in the tibiofemoral compartment and the acceleration of osteoarthritic changes.

Extrusion is typically defined as radial displacement of ≥3 mm outside the tibial border and is best diagnosed via magnetic resonance imaging, although ultrasonography has also demonstrated encouraging diagnostic utility.

Surgical management of meniscal extrusion is based on the underlying etiology, the patient's symptom profile, the preexisting health of the articular surface, and the risk of future chondral injury and osteoarthritis.

Meniscus extrusion in medial meniscus posterior root tears (MMPRT) is a consistent MRI finding and correction of extrusion is a primary objective of the meniscal root repair. The purpose of the study is to evaluate feasibility of correction of extrusion and correlation of various factors affecting the postoperative extrusion correction and outcomes in all degenerative medial meniscus posterior roots (MMPRTs).

A retrospective study of patients who presented with degenerative MMPRTs following trivial incident (Jun 2014 and Aug 2018) and included isolated Laprade type 2 root tear with extrusion in MRI. Patients with ligament injuries, tricompartmental arthritis, malalignment (> 50) and irreparable meniscal tears excluded. All patients underwent arthroscopic trans-tibial tunnel suture pull-out repair. A screening MRI was taken at a 6-month follow-up and functional scores (IKDC and Lysholm's) at final follow-up. The effects of age, gender, duration of symptoms, hip-knee-ankle angle on weight-bearing X-rays, ICRS grading of cartilage status, and MRI data (extrusion distance, tunnel location and healing status of meniscus) on outcomes were analysed.

MMPRT (n = 54) with a mean follow-up of 34.6 months (24-48). Mean functional outcomes improved postoperatively IKDC (43.40 ± 5.16-78.65 ± 5.11, p < 0.001) and Lysholm's (65.27 ± 4.28-83.16 ± 4.83, p < 0.001) scores at final follow-up. 57.4% (31) had good correction of extrusion, 3.7% (2) no correction and 38.8% (21) showed increase in extrusion postoperatively. Of all the factors we explored, age, ICRS (low grade) and knee varus (less 2.5 degree) affected extrusion correction. Patients with healed (41 patients), partially healed (9 patients) and anatomic tunnel placement (46 patients) had better extrusion correction than those with non-healing (4 patients) and non-anatomical tunnel (8 patients).

Patients younger than 50 years, with low grade cartilage damage (ICRS 1, 2), lower KL grade and varus alignment (< 2.50) had good correction of extrusion. Correction of extrusion/progression of extrusion did not influence the clinical outcome at the short-term. The progression of meniscal extrusion is inevitable even after successful repair in elderly and high-risk patients.

Retrospective Case series, level of evidence IV.

Meniscal allograft transplantation (MAT) has proven successful in relieving joint pain and providing functional improvement in patients who have undergone subtotal or total meniscectomy. Bone marrow aspirate concentrate (BMAC) is a biological adjuvant that was shown in the literature to be effective in treating cartilage damage and muscle-tendon tissue problems. The aim of the study is the concomitant use of MAT and BMAC, which are both considered biological treatments and would be beneficial in clinical practice.

The objective of this study was to examine the association between preoperative meniscal extrusion of patients undergoing partial medial meniscectomy with clinical outcomes and progression of osteoarthritis and to determine the extent of meniscal extrusion associated with unsatisfactory clinical outcomes and progression of osteoarthritis. Ninety-five patients who underwent partial medial meniscectomy with a minimum follow-up of 5 years were retrospectively reviewed. Preoperative meniscal extrusion was evaluated with magnetic resonance imaging. Patients were assessed preoperatively and postoperatively with Lysholm and International Knee Documentation Committee (IKDC) subjective scores for clinical outcomes and with IKDC radiographic scale for osteoarthritis. An ANOVA (Analysis of Variance) was used to analyze the variations in meniscal extrusion and the clinical and radiological outcomes. A regression analysis was performed to identify factors that affect preoperative medial meniscus extrusion and that influence results after partial meniscectomy. An optimal cutoff value for meniscal extrusion associated with unsatisfactory clinical outcomes and progression of osteoarthritis was established. Significance was set at p < 0.05. The mean ± SD preoperative and postoperative Lysholm scores were 59.6 ± 15.5 versus 83.8 ± 13.1 (p < 0.001) and the mean preoperative and postoperative IKDC subjective scores were 59.4 ± 16.8 versus 82.0 ± 15.8 (p < 0.001). Meniscal extrusion greater than 2.2 mm (sensitivity, 84%; specificity, 81%) and 2.8 mm (sensitivity, 73%; specificity, 85%) was associated with unsatisfactory (poor/fair) Lysholm and IKDC subjective scores, respectively. The progression of osteoarthritis, characterized as a change of at least one category on the IKDC radiographic scale, occurred when meniscal extrusion was greater than 2.2 mm (sensitivity, 63%; specificity, 75%). Patients with higher body mass index (BMI) had significantly greater meniscal extrusion that patients with normal BMI (p < 0.001). The medial meniscus was more extruded in patients with horizontal and root tears. In conclusion, patients with preoperative meniscal extrusion of 2.2 mm or greater had unsatisfactory clinical outcomes and progression of osteoarthritis after partial medial meniscectomy at a minimum of 5 years follow-up. Higher BMI and horizontal and root tears were associated with greater preoperative meniscal extrusion.

To assess serial change up to 2 years in medial meniscus extrusion (MME) following medial open-wedge high tibial osteotomy (MOWHTO) and to determine whether postoperative changes in MME correlated with clinical outcomes and arthroscopic articular cartilage status.

This study included 26 patients from December 2016 to March 2018 who underwent MOWHTO for primary medial osteoarthritis with varus malalignment. Second-look arthroscopy with plate removal was performed at postoperative 2 years. MME was consecutively measured using coronal magnetic resonance imaging at preoperative and postoperative 3 months, 6 months, 1.5 years, and 2 years. We also assessed which preoperative parameters could reflect the postoperative changes in MME and evaluated whether postoperative clinical outcomes and arthroscopic articular cartilage improvement would be influenced by the MME changes.

Regarding the postoperative serial changes in MME values, significant improvement in MME was noted from postoperative 6 months (P = .003), and thereafter, mean MME was further improved with time until postoperative 2 years (P < .001). Regarding the correlation between preoperative parameters and MME changes, preoperative medial proximal tibial angle (MPTA) showed significant correlations in univariate and multivariate analysis (P = .004 and P = .004, respectively). Meanwhile, changes in MME were not correlated with postoperative clinical outcomes or arthroscopic articular cartilage improvement.

After MOWHTO, MME improved with time and was significantly correlated with preoperative MPTA. However, the changes in MME after MOWHTO did not reflect postoperative clinical and arthroscopic articular cartilage improvement.

IV, case series.

The knowledge regarding meniscus has vastly evolved over the past few decades. The meniscus's intact, injured, and repaired status can affect other joint structures, i.e., ligaments, articular surfaces, and overall biomechanics of the knee joint. Due to available evidence's extensiveness, it is challenging to determine the most influential topics and the emerging trends in concurrent meniscus research. This study aims to identify the top fifty cited papers in meniscus research and concurrent knee issues and analyse their characteristics.

A comprehensive search was conducted on the Thompson Reuters Web of Science database to prepare a list of top fifty cited articles that included original articles and review articles concerning meniscus. The included articles were analysed for the source journal, investigating institution, country of the corresponding author, year of publication, total citations, annual citation rate, and a qualitative review.

The search strategy resulted in 6768 original articles and 453 review articles. The top fifty cited articles were published from 1969 to 2014 and belonged to 14 journal sources. There were 43 original articles and seven review articles. The average citations per article were 417.4 and the average citations per paper per year were 22.6. Besides the meniscus, a general interest in the clinical assessment scores, anterior cruciate ligament, long-term osteoarthritis, and cartilage was observed.

Most of the research concerning meniscus relates to the importance of meniscus preservation, the link between meniscus injuries and concomitant anterior cruciate ligament and chondral injuries, and its role in long-term gonarthrosis. The western countries have contributed the maximum to the top-cited evidence concerning meniscus. The meniscus repair and transplantation techniques have recently gained importance and need further research to qualify for the top-cited evidence.

The long-term chondroprotective effect of meniscal allograft transplant (MAT) and its superiority over meniscectomy have rarely been reported.

MAT would reduce osteoarthritis (OA) progression when compared with the meniscus-deficient knee. Graft extrusion distance would strongly affect the chondroprotective effect of the MAT.

Cohort study; Level of evidence, 3.

A total of 17 knees receiving MAT were followed up as the MAT group. The MAT group was further divided into the nonextrusion subgroup (n = 9) and the extrusion subgroup (n = 8) according to 3-mm extrusion on the magnetic resonance imaging (MRI) coronal section. A further 26 consecutive patients receiving meniscectomy in the same period were followed up as the ME group. The healthy control group consisted of healthy contralateral legs chosen from the MAT and ME groups (n = 27). Joint space width (JSW) narrowing was measured on radiographs. Three-dimensional MRI with a T2 mapping sequence was used to quantitatively analyze cartilage degeneration and meniscal allograft extrusion in 5 directions (0°, 45°, 90°, 135°, and 180°). The cartilage degeneration index (CDI) was calculated according to the size and degree of the chondral lesions on MRI scans. The correlation between the CDI increase and the extrusion distance was analyzed.

The mean follow-up time was 11.3 years (range, 10-14 years). The MAT group had moderate superiority in chondral protection with less JSW narrowing (0.58 ± 0.66 mm) and CDI increase (1132 ± 1589) compared with the ME group (JSW narrowing: 1.26 ± 1.13 mm, P = .025; CDI increase: 2182 ± 1958, P = .079). The JSW narrowing (0.71 ± 0.80 mm; P = .186) and CDI increase (2004 ± 1965; P = .830) of the extrusion subgroup were close to those of the ME group, demonstrating that a 3-mm extrusion led to complete loss of the meniscal chondroprotective effect. The nonextrusion group had significantly less JSW narrowing (0.48 ± 0.48 mm; P = .042) and CDI increase (358 ± 249; P = .011) than the ME group. The JSW narrowing of the healthy control group was 0.22 ± 0.27 mm. The cartilage T2 values of the extrusion subgroup were similar to those of the ME group, with more OA features, whereas the T2 values of the nonextrusion subgroup were closer to those of the healthy control group. The extrusion distance in the 90° direction (P = .002) and the follow-up time (P = .019) significantly affected the CDI increase in the multivariate regression model. The average extrusion distance in the 45°, 90°, and 135° directions better predicted chondroprotection compared with the other individual directions.

MAT had moderate advantages in chondroprotection compared with meniscectomy in the long term. Graft extrusion distance strongly affected the chondroprotective effect of MAT. The chondroprotective effect of the nonextruded meniscal allograft was close to that of the native meniscus, whereas the allografts with an extrusion >3 mm completely lost their function after meniscectomy.