Total knee replacement (TKR) is one of the most commonly performed orthopedic procedures worldwide, offering substantial relief from pain and disability caused by end-stage osteoarthritis of the knee. With the growing aging population and increased demand for mobility and independence, the number of TKRs performed annually has surged significantly, particularly in low- and middle-income countries [1]. Despite advances in surgical techniques, prosthetic designs, and perioperative care, a significant proportion of patients report suboptimal functional outcomes, including reduced range of motion, persistent weakness, and prolonged recovery times [2].

Among various factors influencing postoperative recovery, preoperative functional status has garnered considerable attention. One specific component of this functional status—quadriceps muscle strength—has emerged as a critical determinant of postoperative mobility and quality of life [3]. The quadriceps play a pivotal role in knee joint stabilization, gait efficiency, stair climbing, and transitioning from sitting to standing. Following TKR, patients often experience marked quadriceps weakness, attributed to both surgical trauma and arthrogenic muscle inhibition, which may persist for months or even years postoperatively [4].

Previous investigations have suggested that patients with better preoperative quadriceps strength demonstrate faster gait normalization, improved functional scores, and enhanced satisfaction following TKR [5]. However, the predictive value of preoperative muscle strength on recovery metrics has not been uniformly established, with some studies yielding inconclusive or conflicting results due to variations in patient populations, measurement tools, rehabilitation protocols, and outcome definitions [6].

Given the growing emphasis on patient-centered outcomes and individualized perioperative care, there is a pressing need to refine our understanding of modifiable predictors of recovery. Identifying patients at risk of delayed recovery can aid in stratifying prehabilitation strategies, optimizing rehabilitation timelines, and improving postoperative counseling. Moreover, establishing objective, quantifiable predictors such as isometric quadriceps strength may contribute to a more precise functional prognosis after TKR.

This study aims to assess the correlation between preoperative quadriceps strength and postoperative recovery in patients undergoing primary total knee replacement.

Study Design and Setting

This prospective observational study was conducted in the Department of Orthopedics at Government Medical College, Kothagudem and Hospital over a 12-month period, from June 2024 to May 2025. The study aimed to evaluate the correlation between preoperative quadriceps strength and postoperative recovery in patients undergoing primary unilateral total knee replacement (TKR) for osteoarthritis.

Participants

A total of 120 patients scheduled for primary TKR were recruited. Inclusion criteria included: age between 50 and 80 years, diagnosis of primary knee osteoarthritis (Kellgren-Lawrence grade III or IV), and ability to participate in quadriceps strength assessment. Exclusion criteria were: history of neuromuscular disorders, prior major knee surgery, revision TKR, systemic inflammatory arthritis, or inability to provide informed consent.

All participants gave written informed consent. The study was approved by the Institutional Ethics Committee.

Data Collection Procedures

Preoperative Assessment: Quadriceps strength was measured one week before surgery using an isometric dynamometer (Biodex System 3, USA). Each patient performed three maximal voluntary contractions of the dominant quadriceps with 30-second rest intervals. The highest peak torque value (in kilograms) was recorded and used for analysis.

Baseline demographic data (age, sex, BMI, comorbidities) and functional scores [Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Society Score (KSS)] were recorded preoperatively.

Surgical Procedure and Postoperative Care: All surgeries were performed by a single experienced surgeon using a standardized medial parapatellar approach with cemented posterior-stabilized prostheses. Postoperative care and physiotherapy protocols were uniform across all patients, including early mobilization, pain control, and supervised rehabilitation beginning on postoperative day 1.

Postoperative Outcome Assessment: Recovery was evaluated at 3 months postoperatively using:

• KSS functional component
• WOMAC function subscale
• Timed Up and Go (TUG) test
• Range of motion (ROM) of the operated knee

The composite recovery score was derived by z-scoring and averaging these four parameters.

Statistical Analysis

Data were entered and analyzed using IBM SPSS Statistics Version 26. Descriptive statistics were calculated for baseline characteristics. Pearson correlation coefficient was used to evaluate the relationship between preoperative quadriceps strength and composite recovery score. Patients were also stratified into tertiles based on quadriceps strength to compare recovery outcomes across groups using one-way ANOVA. A p-value < 0.05 was considered statistically significant. Confidence intervals were reported where applicable.

Table 1: Demographic Characteristics (n = 120)

Table 2: Quadriceps Strength Tertiles and Recovery

Table 3: Functional Outcomes – Preoperative vs 3 Months Postoperative

Table 4: Tertile-wise Comparison of Recovery Metrics at 3 Months

The findings from this study demonstrate a statistically significant positive correlation between preoperative quadriceps strength and postoperative recovery outcomes following total knee replacement (TKR). The Pearson correlation coefficient between quadriceps strength and the composite recovery score was r = 0.61 (p < 0.001, 95% CI: 0.49 – 0.72), indicating a moderate to strong relationship.

Patients were stratified into three tertiles based on preoperative strength levels. As seen in Table 2, individuals in the High Strength group (>28 kg) had a mean recovery z-score of 0.39, while those in the Low Strength group (<22 kg) had a mean score of -0.42, reflecting a notable gradient in recovery outcomes aligned with muscle strength.

Functional recovery at 3 months post-surgery improved significantly across all parameters. According to Table 3, the mean KSS functional score increased from 52.8 ± 11.3 to 75.9 ± 8.7, and the WOMAC function score improved from 48.2 ± 10.1 to 67.3 ± 9.2. The Timed Up and Go (TUG) performance also shortened from 13.2 ± 2.6 seconds to 10.4 ± 2.1 seconds, while knee ROM improved from 92.5° to 116.8°.

Table 5 further emphasizes that patients in the High Strength group achieved significantly better functional scores (KSS: 82.3 ± 5.5), lower TUG times (9.5 ± 1.8 seconds), and greater ROM (123.2° ± 6.1) compared to those in the Low Strength group (KSS: 69.4 ± 6.9, TUG: 11.2 ± 1.9 seconds, ROM: 109.3° ± 7.1), with all differences reaching statistical significance (p < 0.001 or 0.002).

These results highlight the potential value of preoperative quadriceps assessment and targeted strengthening in predicting and improving postoperative functional recovery.

Total knee replacement (TKR) is widely performed to alleviate pain and improve mobility in patients with end-stage knee osteoarthritis, yet significant variability persists in postoperative recovery trajectories. This study investigated whether preoperative quadriceps strength serves as a reliable predictor of functional recovery at 3 months following TKR.

The moderate-to-strong positive correlation (r = 0.61, p < 0.001) observed in our study underscores the importance of muscle strength as a modifiable predictor of outcome. Mizner et al. [7] previously found that quadriceps strength explained 35% of the variance in stair-climbing time and 31% in walking speed at 3 months, reinforcing our findings. In our tertile-based subgroup analysis, patients with strength >28 kg had a mean KSS functional score of 82.3, while those with <22 kg scored 69.4 — a pattern echoed in the work of Petterson et al. [8], who reported a 23% greater improvement in Knee Society Scores among stronger patients.

Stevens-Lapsley et al. [9] found that patients with better preoperative quadriceps strength demonstrated significantly faster improvements in stair-climbing time and gait speed, with differences evident within the first 2 weeks postoperatively. Similarly, Gstoettner et al. [10] showed that preoperative quadriceps strength predicted short-term outcomes, including hospital discharge readiness and 6-week walking endurance.

Although our findings are consistent with these, not all literature supports a strong predictive role. For example, Bade et al. [11] reported only a weak association between baseline strength and long-term functional outcomes at 12 months, highlighting the confounding influence of post-op rehabilitation adherence, pain tolerance, and psychosocial variables.

The current study suggests that evaluating quadriceps strength before surgery can help stratify patients by expected recovery and guide prehabilitation interventions. In this regard, Skoffer and Dalgas [12] demonstrated that 4 weeks of preoperative neuromuscular exercise significantly improved early functional recovery in TKR patients, suggesting that such strategies may enhance the predictive power of strength by making it actionable.

This study has limitations. Being single-centered, it limits generalizability. Though strength was objectively assessed, we did not evaluate muscular endurance or patient-reported pain levels, which may also impact recovery. Rehabilitation compliance was not uniformly monitored.

This prospective observational study revealed a significant positive correlation between preoperative quadriceps strength and postoperative recovery outcomes following total knee replacement. Patients with higher quadriceps strength exhibited superior functional scores, faster mobility restoration, and improved range of motion within three months postoperatively. Stratified analyses further confirmed that recovery outcomes were progressively better across increasing strength tertiles, with statistically significant differences observed in Knee Society Scores, WOMAC function scores, TUG tests, and ROM. These findings emphasize the role of quadriceps strength as a measurable and modifiable predictor of functional recovery. Integrating quadriceps strength assessment into preoperative protocols and initiating targeted prehabilitation could optimize postoperative outcomes. Future multi-center randomized trials are needed to validate these findings and develop evidence-based prehabilitation programs for patients undergoing total knee replacement.

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