Etiology of total knee arthroplasty failure and functional outcome of revision knee arthroplasty

Abstract

BACKGROUND

Total knee arthroplasty (TKA) is a widely used treatment for advanced knee osteoarthritis; however, the incidence of failures requiring revision surgery is increasing. Identifying the causes of TKA failure and assessing the outcomes of revision procedures are essential for improving patient care. We hypothesized that infection and aseptic loosening are the primary causes of TKA failure and that revision TKA (rTKA) significantly enhances functional outcomes.

AIM

To examine the primary causes of TKA failure and evaluate the functional outcomes following rTKA.

METHODS

This descriptive study was conducted at the Department of Orthopedic Surgery, Civil Hospital, Bahawalpur, from April to September 2024. A total of 118 patients undergoing rTKA for failed primary TKA were included. Data on demographics, causes of failure, and surgical details were collected. Functional outcomes were evaluated using the Knee Society Score and Visual Analog Scale before and six months after surgery. Statistical analysis was performed using SPSS version 25.0, with statistical significance set at P < 0.05.

RESULTS

The leading causes of TKA failure were infection (45.8%), aseptic loosening (44.1%), and periprosthetic fractures (10.2%). The rTKA significantly improved knee function, with the mean Knee Society Score increasing from 39.43 ± 6.18 to 78.91 ± 6.17 (P < 0.001). Pain levels decreased substantially, with the mean Visual Analog Scale scores reducing from 7.99 ± 1.37 to 1.42 ± 1.17 (P < 0.001). No significant differences in outcomes were observed between single-stage and two-stage revision procedures.

CONCLUSION

Infection and aseptic loosening are the predominant causes of TKA failure. The rTKA effectively enhances knee function and alleviates pain, offering significant benefits to patients.

Key Words: Total knee arthroplasty; Revision surgery; Knee Society Score; Visual Analog Scale; Functional outcomes; Infection; Aseptic loosening

Core Tip: Total knee arthroplasty failures, primarily due to infection and aseptic loosening, present significant clinical challenges. This study demonstrates that revision total knee arthroplasty significantly enhances knee function and pain relief, as shown by substantial improvements in Knee Society Score and Visual Analog Scale scores. These findings underscore the effectiveness of revision procedures in addressing complications and optimizing patient outcomes, providing valuable insights for clinicians to improve surgical strategies and postoperative care.

INTRODUCTION

Total knee arthroplasty (TKA) is a highly effective surgical intervention for managing severe knee arthritis and joint dysfunction, significantly enhancing mobility and quality of life for millions of patients worldwide. Despite its established success, TKA failures remain a significant challenge, necessitating revision surgery to address complications such as implant loosening, infection, and instability[1,2]. Revision TKA (rTKA) is inherently more complex than primary TKA, involving technical difficulties such as bone loss, soft tissue compromise, and infection management[3]. While functional outcomes following rTKA are generally positive, they often fall short of those achieved with primary TKA[4]. With the increasing demand for TKA and a corresponding rise in revision procedures, understanding the causes of TKA failure and optimizing revision strategies are critical for improving patient outcomes[5]. TKA failures are broadly categorized as septic or aseptic. Periprosthetic joint infection (PJI) is a leading cause of early failure, accounting for up to 50% of revisions and contributing to poor surgical outcomes[1,6]. Aseptic failures, including implant loosening, instability, polyethylene wear, and malalignment, typically manifest years after the initial procedure and dominate late failures[3,7]. The risk and timing of TKA failure are influenced by surgical and implant-related factors, as well as patient-specific characteristics such as age, obesity, and comorbidities[8].

Functional outcomes after rTKA vary widely. While most patients experience significant pain relief and improved mobility, these benefits are often limited by preoperative complications, surgical complexity, and patient-specific factors[9]. Implant survival rates following rTKA range from 70% to 85% at 10 years, with re-revision commonly required for cases involving infection or aseptic loosening[10]. Despite advancements in implant design and surgical techniques, managing complex cases with significant bone loss or soft tissue deficiencies remains challenging[1]. Recent improvements in rTKA outcomes are attributable to advanced surgical techniques and enhanced implant designs. The use of constrained prostheses, metal augments, and bone grafts has shown promise in restoring joint stability and improving functional outcomes in cases with severe bone loss[7]. However, these interventions carry risks, including reinfection and reduced range of motion, which continue to pose significant obstacles to optimal outcomes[3]. To enhance care for patients undergoing rTKA, a comprehensive understanding of the causes of TKA failure and the factors influencing functional outcomes is essential. This study aims to identify the primary reasons for TKA failure, evaluate the effectiveness of revision strategies, and provide insights to guide clinical decision-making, refine surgical techniques, and improve patient outcomes. These findings will support the development of targeted interventions to minimize complications, extend implant longevity, and enhance quality of life for patients following rTKA.

MATERIALS AND METHODS

Study design and setting

This study was conducted to investigate the etiology of failure and evaluate the functional outcomes of rTKA. The study was carried out at the Department of Orthopedic Surgery, Civil Hospital, Bahawalpur, over a six-month period from April to September 2024.

Sample size and sampling technique

The sample size was determined based on a reported PJI rate of 45.45% from Wahab et al[11], using a 95% confidence level and a 9% margin of error, resulting in a required sample of 118 patients. A non-probability consecutive sampling technique was employed to recruit participants. All eligible patients presenting consecutively for rTKA at the Department of Orthopedic Surgery, Civil Hospital, Bahawalpur, during the study period were approached for enrollment. Recruitment continued sequentially until the target sample size was achieved, ensuring that every patient meeting the inclusion criteria and providing informed consent was included without random selection.

Inclusion and exclusion criteria

Patients eligible for inclusion were those undergoing rTKA for failed primary TKA, aged 18 years or older, of any gender, and who provided written informed consent. Patients were excluded if they had incomplete medical records, were lost to follow-up within six months post-revision, or were undergoing revision for reasons unrelated to TKA failure, such as trauma.

Ethical considerations

The study received approval from the Institutional Ethical Review Committee. Written informed consent was obtained from all participants, and strict measures were implemented to ensure confidentiality and anonymity throughout the study.

Data collection

Data were collected using a structured proforma that recorded demographic details [age, gender, body mass index (BMI)], causes of TKA failure (PJI, aseptic loosening, implant wear and tear), surgical details (time since primary TKA, type of revision surgery), and functional outcomes. Functional outcomes were assessed using the Knee Society Score (KSS), pain levels measured via the Visual Analog Scale (VAS), and mobility metrics, including walking distance and range of motion.

Follow-up and outcome assessment

Patients were followed up at six months post-rTKA during clinical visits, where KSS, VAS pain levels, and mobility improvements were evaluated.

Statistical analysis

Data analysis was performed using SPSS version 25.0. Continuous variables, such as age, BMI, KSS, and VAS, were reported as means ± SD, while categorical variables, including etiology, gender, and surgery type, were presented as frequencies and percentages. Paired t-tests were used to compare pre- and post-rTKA functional outcomes. χ² tests assessed associations between categorical variables, such as etiology and gender or surgery type and functional improvement. To explore the influence of patient characteristics, independent samples t-tests compared age, BMI, and time since primary TKA between groups with and without mobility improvement. Although comorbidities and socioeconomic status were not collected in this study, these factors should be considered as potential covariates in future research to adjust for their impact on functional outcomes. A P-value < 0.05 was considered statistically significant.

RESULTS

Participant characteristics

The study included 118 patients with a mean age of 61.01 ± 7.08 years and a mean BMI of 28.07 ± 3.91 kg/m². The average time since primary TKA was 7.62 ± 4.31 years.

Functional outcomes

The rTKA significantly improved functional outcomes. The mean KSS increased from 39.43 ± 6.18 pre-rTKA to 78.91 ± 6.17 post-rTKA (P < 0.001), indicating substantial improvement in knee function. The mean VAS pain score decreased from 7.99 ± 1.37 pre-rTKA to 1.42 ± 1.17 post-rTKA (P < 0.001), demonstrating significant pain relief (Table 1).

Table 1 Comparison of pre- and post-revision functional outcomes, mean ± SD.

Variable	Pre-revision	Post-revision	N	P value
KSS	39.43 ± 6.18	78.91 ± 6.17	118	< 0.001
Pain VAS	7.99 ± 1.37	1.42 ± 1.17	118	< 0.001

KSS: Knee Society Score; VAS: Visual Analog Scale.

Etiology of TKA failure by gender

Among males (n = 65), PJI was the most common cause of TKA failure (33, 50.8%), followed by aseptic loosening (27, 41.5%) and implant wear and tear (5, 7.7%). Among females (n = 53), aseptic loosening was the most frequent cause (25, 47.2%), followed by PJI (21, 39.6%) and implant wear and tear (7, 13.2%). Overall, PJI accounted for 54 (45.8%) cases, aseptic loosening for 52 (44.1%), and implant wear and tear for 12 (10.2%). The association between gender and etiology was not statistically significant (P = 0.391) (Table 2).

Table 2 Association between gender and etiology of total knee arthroplasty failure, n (%).

Gender	Infection	Aseptic loosening	Implant wear and tear	Total	P value
Male	33 (50.8)	27 (41.5)	5 (7.7)	65	0.391
Female	21 (39.6)	25 (47.2)	7 (13.2)	53
Total	54 (45.8)	52 (44.1)	12 (10.2)	118

Mobility improvement by revision surgery type

Of patients undergoing single-stage rTKA (n = 62), 32 (51.6%) showed mobility improvement, while 30 (48.4%) did not. For two-stage rTKA (n = 56), 26 (46.4%) demonstrated mobility improvement, and 30 (53.6%) did not. Overall, 58 (49.2%) patients showed mobility improvement, and 60 (50.8%) did not. The association between surgery type and mobility improvement was not statistically significant (P = 0.574) (Table 3).

Table 3 Association between type of revision surgery and mobility improvement, n (%).

Type of revision	Improved	Not improved	Total	P value
Single-stage	32 (51.6)	30 (48.4)	62	0.574
Two-stage	26 (46.4)	30 (53.6)	56
Total	58 (49.2)	60 (50.8)	118

Factors associated with mobility improvement

An independent samples t-test compared age, BMI, and time since primary TKA between patients with and without mobility improvement. The mean age was 60.09 ± 7.01 years in the improved group and 61.90 ± 7.09 years in the not-improved group (P = 0.165). Mean BMI was 27.96 ± 3.76 kg/m² in the improved group and 28.19 ± 4.08 kg/m² in the not-improved group (P = 0.753). Time since primary TKA was 7.52 ± 4.40 years in the improved group and 7.72 ± 4.26 years in the not-improved group (P = 0.803). These factors were not significantly associated with mobility improvement (Table 4).

Table 4 Comparison of age, body mass index, and time since primary total knee arthroplasty between mobility improvement groups.

Variable	Mobility improved (n = 58)	Mobility not improved (n = 60)	P value
Age (years)	60.09 ± 7.01	61.90 ± 7.09	0.165
BMI (kg/m2)	27.96 ± 3.76	28.19 ± 4.08	0.753
Time since primary TKA (years)	7.52 ± 4.40	7.72 ± 4.26	0.803

BMI: Body mass index; TKA: Total knee arthroplasty.

DISCUSSION

The findings of this study corroborate the findings regarding the etiology of TKA failure and outcomes after rTKA as reported in the extant research and thus offer valuable insight into the management of these difficult cases. Our study shows that the most common causes of TKA failure reported in the present study, which include infection, aseptic loosening, and periprosthetic fracture, are congruent with those reported by Wahab et al[11] and Postler et al[12]. Infection was reported as the leading cause of rTKA in 45.45% of cases by Wahab et al[11], followed closely by aseptic loosening (42.42%), whereas Postler et al[12] reported infection as the primary cause in 36.1% of the revisions. These studies underscore the importance of infection prevention and management strategies to decrease revision rates. Similar to Qazi et al[13], the present study also shows that rTKA results in substantial functional improvement. Postoperatively, the American Hospital for Special Surgery Knee Score increased markedly from a preoperative score of 59.44 to 73.17 at three months and to 78.91 at six months. In a similar fashion, this study showed that rTKA gave considerable improvement in KSS and pain relief, together with significant improvement in overall knee function, which amounted to a very satisfying result.

The observed improvements in KSS (mean increase of 39.48 points) and VAS (mean decrease of 6.57 points) are not only statistically significant but also exceed the minimal clinically important differences (MCID) reported in the literature, confirming their clinical relevance. For the KSS, the MCID in rTKA is approximately 6.3 points for the function score and 6.6 points for the knee score[14-16], far surpassed by our results, indicating meaningful enhancements in knee function and patient mobility. Similarly, for VAS pain on a 0-10 scale (equivalent to 0-100 mm), the MCID for improving pain in TKA patients is around 2.26 points[17-19], which our substantial reduction well exceeds. In clinical practice, these improvements translate to profound impacts on patients’ quality of life, including reduced chronic pain, decreased reliance on pain medications, improved ability to perform daily activities, and enhanced social participation and overall well-being[20,21]. Furthermore, such marked improvements in KSS and VAS scores likely contribute to greater independence in activities of daily living, reduced healthcare utilization, and overall psychosocial benefits, as patients experience less disability and higher satisfaction with their mobility[22]. However, as a single-center study with potential selection bias from non-probability sampling, these findings may have limited generalizability, highlighting the need for multicenter studies to validate and broaden their applicability. The non-probability consecutive sampling method, while practical for recruiting patients in a timely manner at a single site, may introduce selection bias by potentially favoring more severe or accessible cases, such as those referred to a tertiary center[21,22]. This could lead to an overestimation of infection rates or underrepresentation of milder etiologies seen in community settings, thereby affecting the external validity of the results.

Roman et al’s findings further this narrative that rTKA results are multifactorial[14]. Infection and aseptic loosening were the most common causes of failure; however, factors related to the patient, such as age, comorbidities, and quality of the primary procedure, heavily impacted the revision outcome. Individualized patient assessment and optimization remain important prior to and after rTKA. In our analysis, while age, BMI, and time since primary TKA were examined as potential influencers of mobility improvement and found to have no significant association, other individual differences, such as comorbidities (e.g., diabetes, cardiovascular disease) and socioeconomic status (e.g., access to rehabilitation), were not captured. These unmeasured variables could confound the assessment of revision surgery effectiveness, as they may influence recovery rates, adherence to postoperative care, and overall functional outcomes. Future studies should incorporate these as covariates in multivariate models to provide a more comprehensive evaluation.

Although the association between gender and etiology of TKA failure was not statistically significant (P = 0.391), observed trends warrant discussion. Males exhibited a higher proportion of infection-related failures (50.8% vs 39.6% in females), while females had slightly more aseptic loosening (47.2% vs 41.5%) and implant wear (13.2% vs 7.7%). These differences may stem from biological factors, such as variations in bone density, joint anatomy, or immune responses; for instance, women often present with greater varus alignment in cases of aseptic loosening, potentially contributing to higher mechanical stress on implants[23]. Social and behavioral factors could also play a role, including differences in activity levels, obesity rates (higher in women, which may exacerbate wear), or delays in seeking care among women, leading to advanced disease at the time of primary TKA and subsequent failure modes[24,25]. Further research is needed to elucidate these gender-specific influences and tailor preventive strategies accordingly.

In the study by Brown et al[15], temporal trends in the etiology of TKA failure are studied, showing greater responsibility of infection for early revisions, while greater responsibility of aseptic loosening for late failures. Our findings support this observation, as we find that infection continues to be the leading cause of both early and late failures, requiring focused preventive measures throughout the perioperative period. Additionally, Hecker et al[16] showed that although routine outcome monitoring and patient satisfaction improved after rTKA, these functional outcomes are dependent on rTKA type and etiology. We found in this present study that there is no statistically significant difference in functional outcome between one- and two-stage revision, but functional outcome is influenced by the cause of failure.

The six-month follow-up in our study captures short-term improvements effectively but may not fully reflect long-term functional durability or late-onset complications, emphasizing the importance of extended follow-up periods in future research to better assess sustained outcomes. An important finding of the current study was that functional outcomes vary according to etiology. Weis et al[17] found better long-term results for aseptic loosening and instability compared to infection and arthrofibrosis. This is consistent with the current results, where mobility improvement and total functional scores varied in response to the etiology of failure. Weis et al[17] also emphasize the role of patient characteristics, including BMI and comorbidities, in the surgical and postoperative approaches that are required.

Compared to general data, the large number of infection-related revisions noted by Postler et al[12] and Sardar et al[18] in specialized centers shows how complicated the cases are that these advanced hospitals handle. The implications of these findings for resource allocation are considerable; infection-related revisions are more costly and have lower success rates. Finally, based on work presented in[19], clinical outcomes were shown to be more favorable when revisions were done on implants with longer survival times (> 5 years) over early revisions (< 5 years). This finding, combined with the observations of Lee et al[20]. The improvements in implants and surgical techniques have minimized mechanical failure as a cause of TKA revisions, indicating that septic complications now represent a significant burden, necessitating ongoing innovation and vigilance in TKA practice.

Future directions

Future research should focus on multicenter studies with diverse patient populations to enhance the generalizability of findings. Long-term follow-up studies, extending beyond six months, are needed to evaluate the durability of functional improvements and the incidence of late complications after rTKA. Additionally, investigating the role of patient-specific factors, such as comorbidities, BMI, and socioeconomic determinants, could provide insights into optimizing preoperative and postoperative care. Exploring advanced infection prevention strategies, including novel antimicrobial coatings and perioperative protocols, may reduce the burden of infection-related TKA failures. Finally, comparative studies evaluating the cost-effectiveness of single-stage vs two-stage revision surgeries could inform resource allocation in tertiary care settings.

Limitations

This study has several limitations that warrant consideration. First, the study was conducted at a single tertiary care center, which may limit the generalizability of the findings to other settings, such as community hospitals or regions with different patient demographics. Second, the six-month follow-up period may not fully capture long-term functional outcomes or complications following rTKA. Third, the way patients were chosen for the study might lead to bias, which could affect how well the study represents all the reasons for TKA failure. This sampling approach, reliant on the sequential enrollment of presenting patients, could bias the sample toward more complex cases typical of a referral center, impacting the distribution of the etiologies and outcomes observed. Finally, patient-specific factors, such as comorbidities and socioeconomic status, were not comprehensively analyzed, which could influence functional outcomes and revision success rates. Although we included BMI in our analysis and found it didn't significantly affect mobility improvement, not having information on other health issues (like chronic diseases) and socioeconomic factors (like education and income) makes it hard to account for these factors, which might lead us to underestimate their impact on how well revision surgery works.

CONCLUSION

This study confirms that infection, aseptic loosening, and periprosthetic fractures are the predominant causes of TKA failure. The rTKA greatly improves knee function and reduces pain, shown by significant increases in the KSS from 39.43 to 78.91 and the VAS from 7.99 to 1.42. These findings underscore the efficacy of revised TKA in restoring functionality, despite the complexities of managing failed TKA. Tailored surgical strategies and robust infection prevention measures are critical to optimizing outcomes and reducing revision rates.

ACKNOWLEDGEMENTS

We extend our sincere gratitude to the patients who participated in this study for their willingness and cooperation, without which this research would not have been possible. We also thank the medical and administrative staff at the Department of Orthopedic Surgery, Civil Hospital, Bahawalpur, for their invaluable support in facilitating data collection and patient follow-up.