Associations of patient characteristics, rate of torque development, voluntary activation of quadriceps with quadriceps strength, and knee function before anterior cruciate ligament reconstruction

Good preoperative knee function（KF) and quadriceps strength（QS）relate to good prognoses after anterior cruciate ligament reconstruction (ACLR). This study aimed to investigate the associations between patient characteristics, rate of torque development (RTD), voluntary activation (VA) of the quadriceps against preoperative KF and QS. A cross-sectional study was conducted. Forty patients with a primary, unilateral ACL injury who had finished their preoperative rehabilitation and were waiting for an ACLR were included. KF was evaluated using the International Knee Documentation Committee (IKDC) score. All quadriceps-related outcomes were measured with the knee flexion at 45°. QS was measured by maximal voluntary isometric contractions (MVIC). RTD was divided into the early (RTD_0-50) and the late phase (RTD_100-200), respectively. Quadriceps VA was measured using the superimposed burst technique. Our results showed that patients with poor preoperative KF (IKDC score<60.9, N=8) had more deficits in RTD_0-50 (P=0.025), higher body mass index (BMI, P=0.043), and more meniscus injuries (P=0.001) than those with good knee function (N=32). Patients with asymmetrical QS (N=22) showed lower BMI (P=0.020) and shorter time from injury (P=0.027) than those with symmetrical QS(N=18). Additionally, a higher pre-injury Tegner score combined with greater RTD100-200 contributed to greater QS on the injured limb (R²=0.357, P=0.001). To conclude, BMI, time from injury, concomitant meniscus injury, pre-injury physical activity level, and quadriceps RTD are related to QS and KF in patients before ACLR.