Summary

Factors associated with diminished knee extension strength symmetry following ACLR with QT autograft include female sex, older age at the time of surgery, larger tibial tunnel diameter, use of BFR, and higher preoperative VAS pain score.

Abstract

Introduction

Quadriceps tendon (QT) autograft has become a popular graft option for anterior cruciate ligament reconstruction (ACLR) given low retear rates and a favorable morbidity profile. However, diminished postoperative knee extension strength can occur following ACLR with QT autograft. Persistent knee extensor strength deficit following ACLR is concerning as it is associated with graft retear, inferior patient reported outcomes, lower rates of return to sport, altered knee joint kinematics, and increased risk of osteoarthritis. Factors influencing the restoration of knee extensor strength following ACLR with QT autograft remain undefined. The purpose of this study was to identify factors that influence the return of knee extensor strength following ACLR with QT autograft.

Methods

A retrospective review of patients undergoing single bundle primary QT ACLR at a single institution was performed. Patients with electromechanical dynamometer testing (Biodex) and isometric knee extension torques obtained postoperatively were included. Knee extension limb symmetry index (LSI) was obtained by comparing the ratio of peak torque of the operative and nonoperative extremities. Variables were divided into four domains including patient, surgical, rehabilitation, and preoperative patient reported outcome score domains. Univariate associations were analyzed with independent t-test and Pearson correlation coefficient. Variables with p<0.15 from the univariate analysis were included in multivariable associations within each domain using linear regression and stepwise backward elimination model to select variables with p<0.15.

Results

A total of 141 patients (78 male) with a mean age of 22.3 years were included. Mean knee extension LSI of the entire cohort was 0.77 at 5.9 months. There were 34 patients (24%) that had a LSI value of 0.9 or greater. Univariate analysis identified age at surgery (p=0.06), sex (p=0.002), QT graft width (p=0.02), femoral tunnel diameter (p=0.08), tibial tunnel diameter (p=0.01), use of blood flow restriction (BFR) therapy postoperatively, preop VAS pain (p=0.01), preop PROMIS-Physical (p=0.04), and preop IKDC (p=0.03) as associated variables to include in multivariate analysis. Multivariate analysis of the final cohort model demonstrated significant associations between female sex (-0.14, p <0.05), age at the time of surgery (-0.01, p<0.05), tibial tunnel diameter (-0.05, p<0.05), use of blood flow restriction therapy (BFR), (-0.08, p<0.05), and preoperative visual analog scale for pain (-0.02, p<0.05) with knee extensor strength symmetry.

Discussion

Factors associated with diminished knee extension strength symmetry following ACLR with QT autograft include female sex, older age at the time of surgery, larger tibial tunnel diameter, use of BFR, and higher preoperative VAS pain score. These factors should be considered when performing ACLR with QT autograft and developing postoperative rehabilitation strategies. Further investigation of the factors identified is warranted to optimize outcomes following ACLR.