Summary

Preoperative rehabilitation resulted in significant improvements in quadriceps peak torque and knee flexion excursion prior to reconstructive surgery. Importantly, preoperative knee function predicted post operative outcomes associated with successful recovery following an ACLR.

Abstract

Introduction

Quadriceps weakness and gait impairments develop rapidly after anterior cruciate ligament (ACL) injury. Left unresolved, these impairments have significant detrimental effects on outcomes after ACL reconstruction (ACLR). There is considerable debate on whether this ‘prehab’ period results in better postoperative recovery of quadriceps strength (peak torque) and resolution of gait impairments. To date, there have been few studies that quantify the effects of preoperative rehabilitation, and it’s influences on postoperative strength and biomechanical outcomes. The primary purpose of this study was to evaluate if preoperative rehabilitation improves postoperative outcomes by: (1) assessing if quadriceps strength and knee flexion excursion improve with preoperative rehabilitation and (2) identifying if quadriceps strength and knee flexion excursion at the time of surgery were predictive of their respective recovery at a 4 month follow up.

Methods

Fifty-one participants (21F, age: 21.0 ± 5.6 yrs, injury to baseline: 22.2 ± 16.6 days, graft type: 48 patellar tendon, 3 hamstring tendon) were evaluated at three time points: baseline (T0), post-preoperative rehabilitation (T1), and 4 months post-ACLR (T2). Isometric quadriceps strength was assessed using an isokinetic dynamometer with the knee positioned at 90° of flexion. Peak torque was recorded as the highest value across four trials and normalized to body mass. Participants then performed a 3D instrumented gait analysis while walking at a self-selected speed (T0: 0.91± 0.29 m/s T1: 1.15 ±0.25 m/s T2:1.21 ± 0.23 m/s). Knee flexion excursion was extracted during the stance phase using a custom computer code. One-sided paired t-tests were performed to determine if quadriceps peak torque and knee flexion excursion increased from T0 to T1. Simple linear regression models were fit to evaluate the relationship between peak torque and knee flexion excursion at T1 with their respective values at T2.

Results

From T0 to T1, average quadriceps peak torque increased by 0.6 Nm/kg (T0: 2.08 ± 0.67 Nm/Kg, T1: 2.68± 0.77 Nm/Kg, p<.001) and average knee flexion excursion increased by 3.3° (T0: 11.65 ± 4.63°, T1: 14.91 ± 4.14°, p <.001) during gait. Quadriceps peak torque at T1 significantly predicted quadriceps peak torque at T2 (r=0.55, F(1,46) =19.85, p <.001). Knee flexion excursion at T1 also significantly predicted knee flexion excursion at T2 (r= 0.51, F(1,46) =16.55, p <.001).

Discussion

We found that a 4-week preoperative rehabilitation program resulted in significant improvements in quadriceps strength and knee flexion excursion at the time of surgery. Additionally, the outcomes of this preoperative rehabilitation program (T1) predicted quadriceps strength and knee flexion excursion at a 4 month follow up (T2). Successful recovery of quadriceps strength has been associated to higher return to sport rates and lower re-injury risk, and increased knee flexion excursion has been linked to improved knee joint loading. Collectively, the findings of this study reinforce the importance of preoperative rehabilitation to optimize recovery after ACLR.