Khalifa AA, Moustafa M, Lemma S, Fayez M, Abdelaal AM, Fadle AA. Coronal plane alignment of the knee phenotypes and ankle joint coronal plane alignment patterns in Egyptian population. World J Orthop 2026; 17(1): 111824 [DOI: 10.5312/wjo.v17.i1.111824]
Corresponding Author of This Article
Ahmed A Khalifa, MD, Assistant Professor, FRCS, Department of Orthopaedics, Qena Faculty of Medicine and University Hospital, South Valley University, Kilo 6 Qena-Safaga Highway, Qena 83523, Egypt. ahmed_adel0391@med.svu.edu.eg
Research Domain of This Article
Orthopedics
Article-Type of This Article
Retrospective Study
Open-Access Policy of This Article
This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Ahmed A Khalifa, Department of Orthopaedics, Qena Faculty of Medicine and University Hospital, South Valley University, Qena 83523, Egypt
Mohamed Moustafa, Mostafa Fayez, Ahmed M Abdelaal, Amr A Fadle, Department of Orthopedic Surgery and Traumatology, Assiut University Hospital, Assiut 71515, Egypt
Shikuria Lemma, Department of Orthopaedics, Black Lion Specialized Hospital, Addis Ababa 1165, Ethiopia
Author contributions: Khalifa AA carried out the study conception and design; Khalifa AA, Fayez M, Lemma S, and Moustafa M performed data acquisition, assessment, literature search, and prepared the images and tables; Fadle AA and Lemma S performed the measurements; Khalifa AA carried out the statistical analysis; Khalifa AA, Abdelaal MA, and Fadle AA drafted the manuscript; Abdelaal AM and Khalifa AA did the critical revision. All authors read, discussed, and approved the final manuscript.
Institutional review board statement: This study was approved by Institutional Review Board of Faculty of Medicine in Assiut University, No. 04-2024-300470.
Informed consent statement: This study was conducted retrospectively using anonymized radiographic data. No patient-identifiable information was collected or reported, and no direct patient contact occurred. Therefore, the requirement for informed consent was waived.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
Data sharing statement: All the data are included within the manuscript; however, the raw data could be provided and shared upon a written request sent to the corresponding author.
Open Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Ahmed A Khalifa, MD, Assistant Professor, FRCS, Department of Orthopaedics, Qena Faculty of Medicine and University Hospital, South Valley University, Kilo 6 Qena-Safaga Highway, Qena 83523, Egypt. ahmed_adel0391@med.svu.edu.eg
Received: July 10, 2025 Revised: August 24, 2025 Accepted: November 13, 2025 Published online: January 18, 2026 Processing time: 183 Days and 12.6 Hours
Abstract
BACKGROUND
In an era leaning toward a personalized alignment of total knee arthroplasty, coronal plane alignment of the knee (CPAK) phenotypes for each population are studied; furthermore, other possible variables affecting the alignment, such as ankle joint alignment, should be considered.
AIM
To determine CPAK distribution in the North African (Egyptian) population with knee osteoarthritis and to assess ankle joint line orientation (AJLO) adaptations across different CPAK types.
METHODS
A cross-sectional study was conducted on patients with primary knee osteoarthritis and normal ankle joints. Radiographic parameters included the mechanical lateral distal femoral angle, medial proximal tibial angle, and the derived calculations of joint line obliquity (JLO) and arithmetic hip-knee-ankle angle (aHKA). The tibial plafond horizontal angle (TPHA) was used for AJLO assessment, where 0° is neutral (type N), < 0° is varus (type A), and > 0° is valgus (type B). The nine CPAK types were further divided into 27 subtypes after incorporating the three AJLO types.
RESULTS
A total of 527 patients (1054 knees) were included for CPAK classification, and 435 patients (870 knees and ankles) for AJLO assessment. The mean age was 57.2 ± 7.8 years, with 79.5% females. Most knees (76.4%) demonstrated varus alignment (mean aHKA was -5.51° ± 4.84°) and apex distal JLO (55.3%) (mean JLO was 176.43° ± 4.53°). CPAK types I (44.3%), IV (28.6%), and II (10%) were the most common. Regarding AJLO, 70.2% of ankles exhibited varus orientation (mean TPHA was -5.21° ± 6.45°). The most frequent combined subtypes were CPAK type I-A (33.7%), IV-A (21.5%), and I-N (6.9%). A significant positive correlation was found between the TPHA and aHKA (r = 0.40, P < 0.001).
CONCLUSION
In this North African cohort, varus knee alignment with apex distal JLO and varus AJLO predominated. CPAK types I, IV, and II were the most common types, while subtypes I-A, IV-A, and I-N were commonly occurring after incorporating AJLO types; furthermore, the AJLO was significantly correlated to aHKA.
Core Tip: We consider the current study one of the few studies that have investigated the coronal plane alignment of the knee in a North African population; furthermore, adding subtypes based on the ankle joint line orientation was not previously proposed. After evaluating 527 patients (1054 knees), we found that most knees demonstrated varus alignment (76.4%) and an apex distal joint line obliquity (55.3%). Understanding the coronal plane alignment of the knee classification in our knee osteoarthritis population will help surgeons who are willing to adopt a more personalized total knee arthroplasty alignment approach; furthermore, the added subtypes based on the ankle joint line orientation should be considered during preoperative planning.
Citation: Khalifa AA, Moustafa M, Lemma S, Fayez M, Abdelaal AM, Fadle AA. Coronal plane alignment of the knee phenotypes and ankle joint coronal plane alignment patterns in Egyptian population. World J Orthop 2026; 17(1): 111824
For several years, aiming at neutral mechanical alignment (MA) after total knee arthroplasty (TKA) was the aim for most surgeons by obtaining perpendicular tibial and femoral cuts to their respective mechanical axes with proper soft tissue balancing; however, patients’ dissatisfaction after surgery even with a well-aligned knee and prosthetic components was attributed to placing the knee in a non-physiological position without considering the possibility of constitutional alignment, which properly affected the mechanics and kinematics[1-3].
To compensate for such non-physiological alignment accomplished with MA philosophy, various attempts have been made to understand natural knee alignment by incorporating various parameters to categorize and classify the knees into different phenotypes, most commonly the coronal plane alignment of the knee (CPAK) classification and functional knee phenotypes[4,5].
As differences in the lower limb alignment attributed to regional, racial, and ethnic characteristics had been reported in previous studies[6-8]; knee phenotypes per CPAK classification were applied to various populations[9], which further eased the replacement of the classic MA by alternative alignment techniques, including and not limited to kinematic, inverse kinematic, restricted kinematic alignment, and functional (patient-specific) alignment philosophies aiming nearly to one aim, which is restoring the pre-disease patient’s own alignment[2,10,11].
The lower limb is considered as one mechanical unit, where changes at one joint (spine, hip, knee, ankle, and foot) might force the other joints to realign and adapt[12-14]. A clear example that has garnered attention in the past few years is the spinopelvic relationship and its impact on acetabular cup positioning during total hip arthroplasty[15]. A similar relationship has been shown between the knee and ankle joints, where correcting knee deformity after TKA might lead to a weight-bearing line (WBL) shift (from medial to lateral after correcting knee varus deformity and vice versa for the valgus knee deformity); this shift will affect the location of tibiotalar contact surface area with subsequent change in the intraarticular ankle loading pressure aggravating ankle pain or even enhance ankle osteoarthritis (OA) progression, which might be a reason for patients dissatisfaction after TKA[16-23]. Assessing the preoperative ankle joint alignment and anticipating its change and adaptation after TKA could be an essential step during preoperative planning and patient counseling; furthermore, some authors mathematically calculated the ankle joint realignment after correcting the deformity at the knee joint level[24-27].
Therefore, evaluating the knee phenotype differences among various populations is paramount; furthermore, understanding the ankle joint’s adaptation to each phenotype is crucial, allowing surgeons to properly plan and provide more personalized knee arthroplasty alignment options[9,17,20]. To the best of our knowledge, reports on knee phenotyping according to the CPAK classification in the North African population are scarce[28]; furthermore, we are unaware of previous studies documenting the ankle joint line orientation (AJLO) changes in each CPAK type.
The study’s primary objective was to determine the constitutional alignment subtypes in a North African (Egyptian) population by applying the CPAK classification system. The secondary objectives were as follows: First, to propose CPAK subtypes after evaluating and incorporating the AJLO in the coronal plane for each CPAK type. Second, to compare our population’s knee phenotypes per CPAK classification with results reported from other populations.
MATERIALS AND METHODS
Study design
After obtaining ethical committee approval (No. 04-2024-300470) and following the ethical considerations outlined in the Helsinki Declarations, we conducted a retrospective study at a North African (Egyptian) arthroplasty unit, adhering to the STROBE guidelines[29].
Research participants, inclusion, and exclusion criteria
Between January 2021 and December 2024, we reviewed the radiographic records of skeletally mature patients diagnosed with primary knee OA who were scheduled for, or had undergone, either TKA or unicompartmental knee arthroplasty for inclusion. Furthermore, they should have proper long-leg, standing anteroposterior [hip to knee to ankle (HKA)] radiographs; their adequacy was determined per the Paley and Pfeil criteria[30]. We excluded patients diagnosed with other knee conditions rather than primary OA, those with extraarticular deformities, windswept deformities, patients who had hip surgeries (including hip arthroplasty or around hip fracture fixation); furthermore, regarding the ankle joint radiographs, ankles that showed arthritic changes (Kellgren-Lawrence grade ≥ 2), previous fracture fixation, or fusion were excluded from the analysis.
Radiographic assessment and classification
Radiographic parameters were measured by one of the authors; the assessment was performed per MacDessi et al[5,31] and Griffiths-Jones et al[32] description. The mechanical lateral distal femoral angle (mLDFA) and the medial proximal tibial angle (MPTA) were measured first (Figure 1A). Then, the arithmetic HKA (aHKA) was calculated as MPTA-mLDFA, where a negative value indicated varus alignment and a positive value indicated valgus alignment. The joint line obliquity (JLO) was calculated as MPTA + mLDFA, where values < 180° indicate apex distal obliquity, values > 180° indicate apex proximal obliquity, and 180° indicate parallel joint line. The CPAK classification was determined by three aHKA subgroups (neutral alignment if aHKA is between +2° and -2°, varus alignment if aHKA < -2°, and valgus alignment if aHKA > +2°) against three JLO subgroups (neutral JLO is between 177° and 183°, “apex distal” if JLO is < 177°, and “apex proximal” if JLO is > 183°, leading eventually to nine knee phenotypes) (Figure 1B)[5,31,32].
Figure 1 Radiological assessment and classification details.
A: Long-leg, standing anteroposterior (hip to knee to ankle radiograph showing how mechanical lateral distal femoral angle, medial proximal tibial angle, and tibial plafond horizontal angle were measured; B: Schematic representation of the coronal plane alignment of the knee classification following MacDessi et al[5] description; C: Ankle joint line orientation directions and types. mLDFA: Mechanical lateral distal femoral angle; MPTA: Medial proximal tibial angle; TPHA: Tibial plateau horizontal angle; aHKA: Arithmetic hip, knee, and ankle; AJLO: Ankle joint line orientation.
The AJLO was assessed using the tibial plafond horizontal angle (TPHA), which is the angle between the horizontal plane (ground level) and the tibial plafond tangential line[16,25]. The AJLO was presented in three groups: Neutral (TPHA = 0°, type N) if the tibial plafond tangent was parallel to the horizontal axis, while varus (TPHA < 0°, type A) or valgus (TPHA > 0°, type B) AJLO were considered if the tibial plafond tangent had a medial upward slope (i.e., apex proximal) or a medial downward slope (i.e., apex distal), respectively (Figure 1A and C)[25]. Finally, we combined the three AJLO types with the nine CPAK types, resulting in 27 subtypes of combined CPAK knee phenotypes and AJLO types.
Final inclusion and inter-observer reproducibility
A total of 678 patient records were evaluated; 527 patients (1054 knees) were eligible for inclusion to assess CPAK classification, while 435 patients (including 870 knees and ankles) were eligible for AJLO assessment. A different author measured a random sample of 100 radiographs to ensure consistency, and the interobserver intraclass correlation coefficient (ICC) was evaluated.
Statistical analysis
Statistical analysis was carried out using the Statistics Kingdom online platform (https://www.statskingdom.com/index.html). First, the data normal distribution was evaluated using the Shapiro-Wilk test. Data was presented as mean ± SD and 95% confidence intervals (CIs) to reflect the precision of the estimate, while n (%) were used as appropriate. The ICC was used to evaluate interobserver agreement regarding the mLDFA and MPTA angle measurements. A two-way random effect model for absolute agreement was employed to calculate the ICC with a 95%CI. A scatter plot was created to illustrate the distribution of alignments within the evaluated population and the addition of cutoff values for alignment ranges, as defined by MacDessi et al[5]. Pearson correlation coefficients were calculated to determine the strength and direction of the linear relationships between TPHA and both aHKA and JLO. Furthermore, a post hoc power analysis was conducted for this correlation testing using G*Power software (version 3.1.9.7) based on the observed effect sizes (r) and the sample size (n). The significance level of P < 0.05 was considered statistically significant.
RESULTS
Participants’ characteristics
The 527 participants (1054 knees) included in the CPAK classification assessment had a mean age of 57.21 ± 7.78 (40 to 81) years, with 419 (79.5%) being females and 108 (20.5%) being males. The 435 patients (870 knees and ankles) included in the subsequent AJLO assessment had a mean age of 56.6 ± 8.5 (40 to 81) years, with 343 (78.9%) being females and 92 (21.1%) being males (Table 1).
Table 1 Demographic characteristics and angle measurements of the included participants.
The radiographic measurements’ interobserver reliability showed excellent agreement as follows: For the mLDFA assessment, the ICC was 0.994 (95%CI: 0.990-0.997). For the MPTA assessment, the ICC was 0.984 (95%CI: 0.975-0.990). For the TPHA assessment, the ICC was 0.919 (95%CI: 0.863-0.953).
Radiological measurements, knee and ankle alignment
Knee: For 1054 knees, the mean MPTA was 85.46° ± 3.5°, and the mean mLDFA was 90.97° ± 3.12°. The mean aHKA was -5.51° ± 4.84°, indicating predominant knee varus alignment. The mean JLO was 176.43° ± 4.53°, indicating an overall apex distal knee JLO. The most common limb alignment types were varus (types I, IV, VII; 76.38%), neutral (types II, V, VIII; 19.35%), and valgus (types III, VI, IX; 4.27%). In contrast, the common JLO was an apex distal in 55.31% of the knees, neutral in 38.80%, and apex proximal in only 5.88%.
Ankle: For the 870 knees and ankles included in the AJLO analysis, the mean aHKA was -5.30° ± 4.84°, indicating an overall varus alignment, and a mean JLO of 176.34° ± 4.71°, indicating an overall apex distal knee JLO. The overall mean of TPHA was -5.21° ± 6.45°, indicating an overall apex proximal orientation (varus AJLO, type A). Furthermore, 180 (20.7%) ankles were neutral (type N), 611 (70.2%) were in varus alignment (type A), having a mean TPHA of -8.25° ± 4.63°, and 79 (9.1%) were in valgus alignment (type B), having a mean TPHA of 6.62° ± 4.47°.
CPAK types
For the 527 participants (1054 knees), the most common three CPAK types were type I (n = 467, 44.3%), type IV (n = 301, 28.6%), and type II (n = 105, 10%) (Table 2 and Figure 2).
Figure 2 Scatterplot of knee joint line orientation against arithmetic hip, knee, and ankle (aHKA) showing distribution by percentage of the nine coronal plane alignment of the knee phenotypes.
aHKA: Arithmetic hip, knee, and ankle; mLDFA: Mechanical lateral distal femoral angle; MPTA: Medial proximal tibial angle.
Table 2 Coronal plane alignment of the knee classification of the included participants, n = 527 participants, 1054 knees, n (%).
Combining the CPAK types with the AJLO types for the 435 participants (870 knees and ankles) showed that the most common three subtypes were type I-A: 293 (33.7%), type IV-A: 187 (21.5%), and type I-N: 60 (6.9%) (Table 3 and Figure 3).
Figure 3 A bar chart showing the distribution of coronal plane alignment of the knee subtypes (ankle joint line orientation types against each coronal plane alignment of the knee type).
CPAK: Coronal plane alignment of the knee; AJLO: Ankle joint line orientation; TPHA: Tibial plateau horizontal angle.
Table 3 Coronal plane alignment of the knee and ankle joint line orientation combined subtypes, n = 435 participants, 870 knees and ankles, n (%).
There was a statistically significant positive correlation between TPHA and aHKA (r = 0.40, P < 0.001), with a statistical power for this analysis of > 99.9% (which confirms that our study was highly powered to detect this significant relationship) indicating that as the knee alignment becomes more valgus (positive aHKA values), the AJLO also tends to tilt in the valgus direction (Figure 4A). Conversely, the correlation between TPHA and JLO was weak and not statistically significant (r = 0.03, P = 0.425), with a statistical power for this analysis of 58%, suggesting no meaningful linear association between AJLO and knee JLO and confirms that this was a real insignificant difference (absence of a clinically meaningful linear relationship) rather than due to underpowered analysis (Figure 4B).
Figure 4 Correlation analysis between tibial plateau horizontal angle, representing the ankle joint line orientation.
A: The arithmetic hip, knee, and ankle; B: The knee joint line orientation. aHKA: Arithmetic hip, knee, and ankle; JLO: Joint line obliquity; TPHA: Tibial plateau horizontal angle.
DISCUSSION
To the best of our knowledge, the current study is among the first studies to use such classification in an Egyptian population as a representative of the North African area, which revealed that an overall varus alignment and an apex distal knee joint line orientation, while the commonly occurring and CPAK types were I, IV, and II. Moreover, we proposed CPAK subtypes after incorporating the AJLO into different knee phenotypes, where we found that a varus-oriented ankle joint (apex proximal) was the most commonly occurring, and the most commonly occurring CPAK subtypes were I-A, IV-A, and I-N. Interestingly, only 8.3% of our population were classified as CPAK type V (the target of MA), raising concerns regarding the MA philosophy’s suitability in our population.
Knee geometry differences based on race-related disparities have been reported in various reports, questioning the need for population-specific implants[8,33]. Furthermore, over the past few years, heated discussions have arisen regarding alternative TKA alignment philosophies, primarily based on the differences between populations in their pre-arthritic knee alignment and the updated knee phenotyping categorization[5,4]. One of the most widely used knee phenotyping categorizations is the CPAK classification, introduced by MacDessi et al[5]; furthermore, its application to different populations and the resultant differences were evaluated in a systematic review by Pagan et al[9].
We compared the CPAK phenotypes we obtained in our population with the results obtained from various populations including Indian[34,35], Australian[5], South African[36], Spanish[37,38], Romanian[39], Turkish[40], Japanese[41,42], Malaysian[43], Emiratis[44], South Korean[44], French[45], Austrian[46], and Chinese[47]. Our results were similar to most other populations’ knee phenotypes, where overall varus alignment, apex distal knee joint line, and CPAK types I and II were commonly occurring (Table 4). On the contrary, Coetzee et al[36] reported that valgus alignment and CPAK type III are commonly found in the South African population. It is worth noting that two of the studies were reported on Middle Eastern populations (Turkish by Şenel et al[40], and Emiratis by Park et al[44]), posing characteristics similar to those of the current study population and yielding comparable results. The differences in our population’s knee phenotypes compared to other populations might be attributed to ethnic and genetic differences, which have been confirmed in previous studies[48,49].
Table 4 Comparison between the current study results and studies published from other populations, n (%).
For many decades, MA was the target for most surgeons performing TKA, which aimed at a fixed target in all patients, ignoring variations in morphological, biomechanical, and pre-arthritis alignment[10,50]. This is a common practice among Egyptian joint arthroplasty surgeons as well[51,52]. Although MA-TKA showed acceptable long-term outcomes and implant survivorship[51,53]. Many patients are still dissatisfied with their TKA[54], which might be attributed to natural knee kinematics alteration[55,56].
MacDessi et al[5] reported that the most commonly occurring knee phenotypes in their healthy and knee OA populations were type II (39.2% healthy vs 32.2% OA), type I (26.4% healthy vs 19.4% OA), and type V (15.4% in the healthy vs 14.6% in the OA population). Interestingly, they reported that type V (the aim of MA) represented approximately 15% of both groups, indicating that most patients with an MA TKA will be aligned outside their natural knee alignment. Although our population showed a slightly different distribution compared to the previous study (type I: 44.3%, type IV: 28.6%, and type II: 10%), we showed similar results regarding the low prevalence of type V, which was only 8.3% of the knees, indicating that MA in our population will also place most of the patients outside their natural knee alignment.
As we are moving toward more personalized TKA alignment, surgeons should consider every possible factor that might affect or disturb the alignment target, which, in the case of TKA, will be considering the biomechanical link between the hip, knee, and ankle, where a change in one joint might affect the mechanics of the other joints[11,17]. In the current study, we considered the AJLO in the coronal plane as a possible modifier of the CPAK types, where most of the patients (70.23%) showed varus (type A) AJLO; furthermore, the commonly occurring CPAK subtype was type IA (33.7%), where the knee showed varus alignment and apex distal joint line while the ankle was in varus (apex proximal) alignment.
Knowing the possible changes occurring at the ankle joint level that accompany various CPAK phenotypes and anticipating the potential ankle joint reorientation after TKA may help in proper surgical planning. Furthermore, ankle joint consideration is paramount, especially in patients complaining of pre-TKA ankle pain or signs of ankle OA[23,24]. Therefore, ignoring or misunderstanding the relationship between the knee and ankle joint could be a source of patient dissatisfaction after TKA[16,19].
Furthermore, the importance of evaluating AJLO during planning for TKA may be related to the fact that some patients may already be complaining of ankle pain before undergoing TKA; this pain may improve or worsen after TKA. Kim et al[12] studied the AJLO changes after TKA or high tibial osteotomy in 40 OA knees with varus deformities; the HKA improved significantly in all patients from a varus of 10.6° ± 5.3° to 1.1° ± 3.4° (P < 0.001). Furthermore, the AJLO showed a significant change to a more valgus position postoperatively, from a varus position of 7.8° ± 4.8 to 0.4° ± 3.8° (P < 0.001). They reported a significant correlation between AJLO changes and HKA correction (r = 0.716; P < 0.001); interestingly, they showed a medial to lateral shift of the WBL after knee deformity correction, they concluded that WBL shift and AJLO might improve concomitant symptoms of medial ankle OA, but might worsen symptoms of lateral ankle OA, which highlights the association between knee deformity correction and ankle joint status and the importance of considering their relationship during preoperative planning.
The direction and amount of AJLO after TKA could be anticipated and predicted, as reported by some authors. Nazlıgü et al[26] assessed the AJLO changes after 204 TKAs at a mean follow-up of 32.5 ± 6.7 months; the HKA at the last follow-up improved significantly to a less varus position (from 13.3° ± 4.8° to 4.4° ± 3°), and the AJLO (measured as TPHA) showed less varus orientation from 9.6° ± 4.8° to 4.5° ± 3.9° at the last follow-up. They found a significant positive correlation between HKA and TPHA (r = 0.682), where a one-degree change in HKA resulted in a 0.483-degree change in TPHA.
The effect of different TKA alignment targets was evaluated by Kim et al[56], who compared AJLO after TKA in two groups (90 TKAs in each): One group had KA, while the other had MA. They then compared both groups with measurements obtained from 120 normal knees. They reported that AJLO in the KA-TKA group was comparable to normal knees, while in the MA-TKA group, the AJLO showed a significant lateral tilt compared to normal knees, indicating that KA-TKA, besides obtaining more personalized knee alignment, did not disturb the normal AJLO.
Gursu et al[20] evaluated 80 TKAs where the HKA improved significantly from a preoperative mean of 16.6° to a postoperative mean of 3.6°; furthermore, the AJLO showed less varus post-TKA (preoperative -7.5° ± 4.7° vs postoperative 0.04° ± 3.8°; P < 0.05). They reported that 24% of their patients experienced increased ankle joint pain after TKA. Although no significant correlation was found between knee deformity correction and ankle pain, they recommended keeping the knee under-corrected (in varus alignment) in long-standing knee varus deformities to avoid developing ankle pain secondary to ankle realignment.
In the current study, we found a moderate but significant positive correlation between the aHKA and the TPHA, indicating that as the knee shifts toward a more valgus alignment, the ankle adapts by reorienting into a more valgus position, and vice versa. A similar correlation was reported in the literature, according to Graef et al[57], who evaluated 99 TKAs performed for OA knees with varus deformities; they found a significant positive correlation between preoperative HKA and AJLO (r = 0.94, P < 0.05), where increased knee varus deformity is associated with increased varus AJLO. However, this correlation was lost postoperatively (r = − 1.3, P = 0.2). Interestingly they described a significant positive correlation between HKA correction degrees and the foot function index (r = 0.91, P < 0.05), where change in HKA aggravates the ankle symptoms, they determined that HKA correction of 14.5° is the cutoff value for postoperative ankle pain increase (area under the curve = 0.88, 95%CI: 0.808-0.958, sensitivity = 0.778, specificity = 0.889) where beyond this cutoff value, the odds ratio (OR) for ankle pain development increased significantly (OR = 15.6; 95%CI: 3.2-77.2, P < 0.05)[21]. A later study by the same authors[58] investigated the ankle joint behavior after TKA for knees with valgus deformities and reached the same conclusion as reported for varus knees: That correcting valgus knee deformity (cutoff value of 16.5°) might aggravate ankle joint pain.
Kikuchi et al[58] evaluated the mechanical ankle shift at the ankle joint level in 67 patients who had TKA for knee OA with varus deformities. HKA showed significantly less varus postoperatively (2.6° ± 3.5° vs 15.0° ± 6.1°), and the AJLO realigned to less varus post-TKA (4.7° ± 3.9° vs 10.8° ± 5.7°). They found a significant correlation between HKA and TPHA pre- and postoperatively, with r values of 0.58 and 0.54, respectively (P < 0.001). Additionally, a WBL lateral shift was observed at the ankle joint level[59].
Although the current study has some strengths, it undoubtedly poses several limitations. First, till now, we are not aware of any study evaluating the phenotyping of our population’s normal (non-arthritic) knees; however, owing to the demographic similarities between our population and populations from our area (Middle East and North Africa region), characteristics reported from studies which were performed on normal populations such as the Turkish and Iranian population might apply to our population, where they showed that types I, II and III were the commonly occurring phenotype[7,40]. Furthermore, previous studies have shown that aHKA accurately determines knee constitutional alignment, even in the presence of arthritis or deformity[31,32]. Moreover, Colyn et al[59] proposed a prediction model that can predict the pre-diseased coronal alignment based on some radiological parameters in 80% of the varus knees with an accuracy of ≤ 0.5°. Second, we assumed that the AJLO parallel to the horizontal level to be neutral and measured as 0° without proposing a range of values for neutral alignment, which was attributed to a deficiency of such description in the literature regarding the normal ranges for AJLO in the coronal plane; furthermore, there was a diversity of AJLO measurement and assessment parameters in the literature hindering the adoption of particular study results. Third, we did not include hindfoot assessment, a crucial segment closely related to ankle realignment and involved in its adaptation to knee deformities; as for its evaluation, a specific type of views should be ordered, which was not available for most of the included participants. Fourth, we included participants with normal ankle joints. We consider that including participants with ankle OA might reveal different AJLO parameters, as demonstrated in previous studies. Fifth, there is the unequal sex distribution, where the majority of the study population was female. This was reported as a possible limitation in previous studies, as well[5]. However, this might be attributed to the fact that this is the natural distribution of patients having TKA. Sixth, we reported a moderate correlation between TPHA and aHKA (R2 = 0.16), indicating that 84% of the variance in this correlation may be attributed to other factors, such as ligament laxity, cartilage wear, and other anatomical factors, which we did not investigate. Lastly, due to the study’s descriptive nature, we were unable to build a robust multivariate analysis model adjusted for various confounders to properly delineate the relationships between multiple CPAK and AJLO subtypes; however, future studies with larger cohorts are planned for this purpose.
CONCLUSION
In conclusion, understanding various arthritic knee phenotypes in our population is a step toward modifying our practice from the classic MA concept for TKA alignment to a more personalized alignment approach. Most of our population had a varus knee alignment with an apex distal joint line, and the common CPAK phenotypes were similar to those of other populations. Our assessment of the AJLO showed that varus alignment was the most common occurrence, and it was significantly positively correlated with the aHKA. Considering the ankle joint alignment and its possible reorientation post-TKA is crucial during preoperative planning. Further studies to evaluate the AJLO behavior after various TKA alignment approaches are paramount.
Footnotes
Provenance and peer review: Invited article; Externally peer reviewed.
Peer-review model: Single blind
Specialty type: Orthopedics
Country of origin: Egypt
Peer-review report’s classification
Scientific Quality: Grade B
Novelty: Grade A
Creativity or Innovation: Grade B
Scientific Significance: Grade B
P-Reviewer: Yuan Z, MD, Chief Physician, China S-Editor: Wu S L-Editor: A P-Editor: Zheng XM
Samant V, Desai M. Coronal plane alignment of knee joint (C.P.A.K.) classification in Indian population-study of a new classification system in Indian knees.J Orthop Rep. 2024;3:100277.
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Coetzee K, Charilaou J, Burger M, Jordaan J. Increased prevalence of valgus constitutional alignment subtypes in a South African arthritic population group using the coronal plane alignment of the knee (CPAK) classification.Knee. 2024;49:158-166.
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