Abstract
[Purpose] This study aimed to investigate the effects of a preoperative exercise intervention program on physical function in patients with knee osteoarthritis (KOA) scheduled for total knee arthroplasty (TKA). [Participants and Methods] Twenty-four patients with KOA scheduled for TKA participated in a preoperative exercise program focusing on non-operated limbs. Physical function was evaluated pre- and post-intervention, including knee extension strength (KES), hip abduction strength (HAS), knee range of motion (ROM), pain during activity and at rest (NRS), and performance measures (CS-30, 40 mFWT). Changes were analyzed for statistical significance, and 95% confidence intervals were compared with previously reported MDC95 values. [Results] Activity-related pain, KES, HAS, knee ROM, and CS-30, and 40 mFWT showed statistically significant changes post-intervention. Changes in activity-related NRS and CS-30 levels exceeded the MDC95. [Conclusion] Knee joint function and physical performance of patients with KOA scheduled for TKA significantly changed after eight weeks of preoperative exercise program. Changes exceeding the MDC95 in activity-related pain and CS-30 suggest that our exercise program may have enhanced preoperative physical function.
Key words: Knee osteoarthritis, Total knee arthroplasty, Exercise therapy
INTRODUCTION
Knee osteoarthritis (KOA) is prevalent among older adults1) and significantly impairs activities of daily living (ADL) and quality of life (QOL) because of pain, limited range of motion (ROM), and muscle weakness2). Total knee arthroplasty (TKA) is a common surgical intervention for KOA that improves pain and ADL3). However, some patients remain suboptimally satisfied after TKA4, 5), and these outcomes have been reported to be associated with preoperative physical function6). During the waiting period before TKA, functional decline may progress due to pain and reduced activity7).
Exercise intervention has been proposed to enhance preoperative physical function and facilitate recovery after TKA, and previous studies have reported beneficial effects on early postoperative recovery and treatment satisfaction8, 9). However, most preoperative exercise programs have focused on the operated limb, and their effectiveness may be limited, because improvements achieved preoperatively may not be fully maintained after surgery due to substantial postoperative impairments in ROM and knee extensor strength (KES)10, 11).
Alnahdi et al. reported that the temporary functional decline of the operated limb after TKA increased the load on the non-operated limb12). Furthermore, Zeni and Snyder-Mackler demonstrated that the KES of the non-operated limb was significantly correlated with walking speed and ADL ability at six months postoperatively13). In addition, Hamada et al. reported that non-operated knee extensor strength was a significant predictor of ambulatory ability at one year after TKA14). These findings suggest that improving non-operated limb function may support postoperative functional recovery. However, previous studies on preoperative exercise interventions have primarily focused on the operated limb and have not clearly addressed interventions targeting the non-operated limb or reported detailed changes in physical performance in patients with KOA8, 9).
Contrastingly, this study clearly specified a preoperative exercise intervention incorporating exercises targeting the non-operated limb, with exercises performed on both lower limbs. Preoperative changes in knee joint function and physical performance were comprehensively recorded. Therefore, this study aimed to statistically evaluate preoperative changes in knee joint function and physical performance of the non-operated limb following a preoperative exercise program in patients scheduled for TKA. We hypothesized that the preoperative exercise program would improve knee extensor strength and physical performance outcomes of the non-operated limb.
PARTICIPANTS AND METHODS
This single-center, single-arm pre-post study was conducted between April 1, 2022, and December 31, 2023. A total of 24 patients with primary knee osteoarthritis who met the eligibility criteria and provided written informed consent were enrolled in this study. All participants were scheduled to undergo unilateral total knee arthroplasty at our orthopedic department. The inclusion criteria were independent or cane-assisted ambulation. Patients with comorbidities that could interfere with participation (cardiovascular disease, cerebrovascular disease, and dementia) were excluded. If the participant experienced pain exacerbation or trauma during the intervention, continuation was determined by a physician.
Our exercise program included static self-stretching of muscles around the knee joint (quadriceps and hamstrings), therapeutic ultrasound applied to the hamstrings (intensity: 1.4 W/cm2, duty cycle: 100%, duration: 4 min), lower limb strengthening exercises using resistance machines, closed kinetic chain strengthening exercises such as squats, and aerobic exercises on a stationary bicycle (Supplementary Table 1). Strengthening exercises were prescribed according to the participants’ 15 repetition maximum (15RM), corresponding to approximately 60–70% of the estimated 1RM, as previously reported15). The 15RM was determined separately for each limb. Each exercise was performed for two sets of 10–15 repetitions, with a 1-min rest between sets. Exercise intensity and progression were adjusted under the supervision of a physical therapist to ensure that pain levels remained <3 on the Numerical Rating Scale (NRS) (Supplementary Table 1). The preoperative exercise program was implemented before TKA, and all evaluations were conducted preoperatively. The intervention frequency was set at twice weekly, with each session lasting 40 min, for eight weeks (16 sessions in total). Participants who attended <12 sessions (<80% of the total sessions) were considered as dropouts.
Outcome measures included the NRS for pain at rest and during activity, passive knee ROM, knee extension strength (KES), hip abduction strength (HAS), the 30-s chair stand test (CS-30), and 40 m fast-paced walk test (40 mFWT). Pain was assessed according to the method described by Alghadir et al16). The ROM was measured using a goniometer (OG Wellness Co., Ltd., Okayama, Japan) according to Miner et al17). Muscle strength was assessed using a handheld dynamometer (Mobi MT-100; Sakai Medical Co., Ltd., Tokyo, Japan) following established protocols18). Participants were seated at the edge of a treatment bed with their arms crossed in front of the chest. The hip and knee joints were positioned at 90° flexion. A stabilization belt was applied to the anterior surface of the distal lower leg and fixed to the bed frame. The lever arm length was defined as the distance from the medial knee joint space to the center of the belt attachment point. Knee extension torque was calculated by multiplying the measured force by the lever arm length. Hip abductor strength was measured in the supine position. A stabilization belt was applied around both lateral femoral epicondyles. The lever arm length was defined as the distance from the greater trochanter to the center of the belt attachment point. Hip abduction torque was calculated by multiplying the measured force by the lever arm length. All torque values were normalized to body mass. CS-30 and 40 mFWT were conducted according to the OARSI recommendations19). Each muscle strength and performance test were performed twice, and the maximum value was used for the analysis.
All statistical analyses were performed using SPSS version 29 (IBM Corp., Armonk, NY, USA). Paired t-tests were used to compare pre- and post-intervention outcomes, with significance set at p<0.05. To address the potential instability of estimates owing to the small sample size, the 95% confidence interval (CI) of the mean differences was estimated using a bootstrap resampling procedure (10,000 iterations, bias-corrected, and accelerated method). Furthermore, the 95% CI was compared with the minimal detectable change (MDC95) values reported previously16, 20,21,22,23). In the referenced study, SEM values were reported for both an iPhone application and a plastic goniometer. Therefore, we calculated MDC95 using the SEM values obtained from the plastic goniometer, consistent with our ROM measurement procedure22). Sample size estimation was conducted with G*Power (version 3.1.9.4, Heinrich-Heine-Universität, Düsseldorf, Germany), assuming α=0.05, power (1−β)=0.80, and a medium effect size (d=0.6). This effect size was determined based on previous meta-analyses reporting standardized effect sizes of approximately 0.4–0.6 for pain and physical function outcomes following exercise therapy in individuals with knee osteoarthritis24). The required sample size was calculated to be 24 participants.
This study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained from the International University of Health and Welfare Ethics Committee (21-NR-036), and the trial was registered with the University Hospital Medical Information Network (000050472).
RESULTS
All participants attended at least 13 of the 16 preoperative exercise sessions (attendance rate ≥80%). No adverse events, such as worsening pain or falls, were reported during the intervention period.
The baseline characteristics of the study participants are presented in Table 1. The changes in each outcome measure before and after the exercise program are summarized in Table 2.
Table 1. Demographic data (n=24).
| Age (years) | 74.1 ± 7.6 |
| Height (cm) | 155.1 ± 9.4 |
| Weight (kg) | 61.0 ± 12.6 |
| BMI (kg/m²) | 25.2 ± 3.7 |
| Sex (male) | 7 |
| K–L grade (operated side, grades: n) | Ⅱ: 1, Ⅲ: 12, Ⅳ: 11 |
| K–L grade (non-operated side, grades: n) | 0: 1, Ⅰ: 2, Ⅱ: 4, Ⅲ: 11, Ⅳ: 6 |
| FTA (operated side, degree) | 183.8 ± 4.2 |
| FTA (non-operated side, degree) | 180.7 ± 4.2 |
Mean ± standard deviation. The operated side was defined as the knee scheduled for total knee arthroplasty. BMI: body mass index; K–L grade: Kellgren–Lawrence grading system; FTA: femoro-tibial angle.
Table 2. Physical function data before and after intervention (n=24).
| Baseline | Post-intervention | 95% CI | |
| NRS (rest, points) | 0.9 ± 1.7 | 1.5 ± 2.6 | [−0.3 to 0.6] |
| NRS (activity, points) | 6.3 ± 2.4 | 3.8 ± 2.4** | [−4.3 to −2.0] |
| Knee flexion ROM (degrees) | 117.5 ± 11.6 | 121.5 ± 13.6* | [1.7 to 6.3] |
| Knee extension ROM (degrees) | −8.1 ± 6.4 | −5.6 ± 5.4* | [1.3 to 3.8] |
| Knee extension strength (operated side, N*m/kg) | 0.97 ± 0.32 | 1.10 ± 0.31* | [0.06 to 0.20] |
| Knee extension strength (non-operated side, N*m/kg) | 0.97 ± 0.32 | 1.06 ± 0.27* | [0.05 to 0.21] |
| Hip abduction strength (operated side, N*m/kg) | 0.67 ± 0.24 | 0.76 ± 0.22* | [0.02 to 0.14] |
| Hip abduction strength (non-operated side, N*m/kg) | 0.68 ± 0.23 | 0.79 ± 0.23* | [0.05 to 0.18] |
| CS-30 (repetitions) | 11.5 ± 2.4 | 15.1 ± 3.9** | [2.5 to 5.0] |
| 40mFWT (m/s) | 0.78 ± 0.16 | 0.87 ± 0.19* | [0.04 to 0.15] |
Mean ± standard deviation. *p<0.05, **p<0.001.
NRS (rest, points) refers to pain intensity assessed while the participant is at rest.
NRS (activity, points) refers to pain intensity during active movement of the knee joint.
NRS: numerical rating scale; ROM: range of motion; CS-30: 30 seconds chair-stand test; 40mFWT: 40 m fast-paced walk test.
Excluding the NRS score at rest, all outcome measures showed significant changes following the preoperative exercise program (Table 2). For pain assessment, NRS during activity decreased after the intervention (95% CI; −4.3 to −2.0 points). For knee ROM, flexion (95% CI; 1.9 to 6.0°) and extension angles (95% CI; 1.3 to 4.0°) significantly changed after pre-rehabilitation. For muscle strength, KES significantly increased in the operated (95% CI; 0.06 to 0.20 N·m/kg) and non-operated limbs (95% CI; 0.05 to 0.21 N·m/kg). Similarly, HAS increased in the operated (95% CI; 0.02 to 0.14 N·m/kg) and non-operated limbs (95% CI; 0.05 to 0.18 N·m/kg). For physical performance, CS-30 (95% CI; 2.5 to 5.0 repetitions) and 40 mFWT (95% CI; 0.04 to 0.15 m/s) significantly increased after the program.
DISCUSSION
This study evaluated the physical function of patients with KOA scheduled for TKA before and after a preoperative exercise program. To interpret changes in each outcome, we assessed statistical significance and calculated the 95% CI using the bootstrap method and compared the results with the MDC95 values reported in previous studies (Table 3)16, 20,21,22,23). The MDC95 provides an objective criterion for determining whether observed changes exceed random variation or measurement error25). In this study, the use of MDC95 was useful for identifying changes that exceeded measurement error. In addition, the bootstrap method allows robust estimation without assuming normality of the population distribution26), thereby enabling more accurate estimation of changes in the non-operated limb resulting from the exercise intervention.
Table 3. Comparison of physical function outcomes with MDC 95 values from previous studies.
| 95% CI | MDC95 (reference) | |
| NRS (rest, points) | [−0.3 to 0.6] | 1.3 |
| NRS (activity, points) | [−4.3 to −2.0] | 1.3 |
| Knee flexion ROM (degrees) | [1.7 to 6.3] | 9.5 |
| Knee extension ROM (degrees) | [1.3 to 3.8] | 4.5 |
| Knee extension strength (operated side, N*m/kg) | [0.06 to 0.20] | 0.23 |
| Knee extension strength (non-operated side, N*m/kg) | [0.05 to 0.21] | 0.23 |
| Hip abduction strength (operated side, N*m/kg) | [0.02 to 0.14] | 0.29 |
| Hip abduction strength (non-operated side, N*m/kg) | [0.05 to 0.18] | 0.29 |
| CS-30 (repetitions) | [2.5 to 5.0] | 2.4 |
| 40mFWT (m/s) | [0.04 to 0.15] | 0.20 |
MDC95 values were referenced from previous studies as follows: NRS from Alghadir et al., 2018, ROM from Mehta et al., 2017, Knee extension strength from Amano et al., 2023, hip abduction strength from Tevald et al., 2016, CS-30, 40mFWT from Villadsen et al., 201216, 20,21,22,23).
NRS: numerical rating scale; ROM: range of motion; CS-30: 30 seconds chair-stand test; 40mFWT: 40 m fast-paced walk test.
Regarding changes in activity-related pain and physical performance, the 95% CI for NRS during activity and CS-30 exceeded the MDC95 values reported in previous studies (Table 3)16, 23), suggesting that these changes exceeded measurement error. In contrast, although statistically significant changes were observed in knee flexion and extension angles, muscle strength (KES and HAS), and walking performance, their 95% CI values did not exceed the respective MDC95 values (Tables 3)20, 21, 23). Therefore, these changes may fall within the range of measurement error and should be interpreted with caution.
Significant changes were observed in activity-related NRS and KES scores (Table 2). Previous studies have shown that activity-related pain in patients with KOA is associated with reduced dynamic stability of the knee joint due to weakened KES27). Therefore, the observed improvement in KES may have contributed to the reduction in activity-related pain by enhancing dynamic knee stability.
Furthermore, changes in KES and HAS in the non-operated limb are important for supporting postoperative mobility and activities of daily living8), highlighting the potential usefulness of focusing on non-operated limb function in preoperative exercise programs. Although statistically significant changes in non-operated limb muscle strength were observed, these changes did not exceed their respective MDC95 values (Table 3). Therefore, the possibility of measurement error cannot be excluded, and careful interpretation of these findings is warranted.
In contrast, resting pain NRS did not improve, and the 95% CI did not exceed the MDC95. Resting pain in KOA may be influenced by neuropathic mechanisms, including central sensitization28) Since the present program mainly consisted of exercise-based intervention, its effect on resting pain may have been limited.
This study is among the few to examine preoperative exercise strategies in patients scheduled for TKA in Japan. Exercise intensity was prescribed at 15RM (approximately 60–70% of the estimated 1RM) to ensure feasibility and safety and to minimize the risk of adverse events, such as pain exacerbation or falls. This intensity was lower than that used in previous high-intensity protocols (8–10RM)8, 9). This may have contributed to the finding that muscle strength changes did not exceed the MDC95 values. Therefore, progressive overload strategies, such as %1RM-based progression or the repetition-in-reserve (RIR) method, should be considered in future studies to optimize training intensity while ensuring safety29)
This study has several limitations. The single-arm study design and small sample size limit causal inference and generalizability. In addition, therapeutic ultrasound was included as a warm-up procedure, which may have influenced pain-related outcomes30), although the intensity and duration were limited. Furthermore, post-intervention assessment timing was within one week after the intervention and was not strictly standardized, and potential confounders such as analgesic use were not controlled. Multiple outcome measures were also analyzed without adjustment for multiple comparisons, which may increase the risk of false-positive findings. In addition, the true effect size of preoperative exercise interventions in patients awaiting TKA may be smaller than assumed, which may have affected the statistical power of this study. In addition, although this study focused on the effects of a preoperative exercise program, future studies should evaluate postoperative outcomes to examine how this preoperative intervention influences postoperative physical function after TKA.
In conclusion, a comprehensive preoperative exercise program focusing on the non-operated limb was associated with significant changes in physical function outcomes. Changes exceeding measurement error were observed for activity-related pain and CS-30, whereas other outcomes should be interpreted with caution.
Funding
This research received no external funding.
Conflict of interest
The authors declare no conflict of interest.
Supplementary
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