Factors predicting quadriceps femoris muscle atrophy during the first 12 weeks following anterior cruciate ligament reconstruction

Abstract Background Factors predicting quadriceps femoris muscle (QF) atrophy during the early period after arthroscopic ACL reconstruction have not been extensively studied. It is also yet to be confirmed whether muscle atrophy is a key determinant of postoperative QF weakness. Methods Mean changes in QF volume, MVIC torque and isometric endurance time were analysed in 25 patients prior to and at 4 and 12 weeks after surgery. A multivariable regression model of change in QF volume was made from preoperative QF volume deficit, MVIC torque and isometric endurance time combined with postoperative changes in knee extension ROM and mid-patellar girth. The contribution of QF atrophy to MVIC torque change was evaluated with univariate regression and MVIC torque to volume ratio at postoperative week 12 only. Results QF volume and MVIC torque were reduced throughout the recovery period, whereas endurance time was decreased only at postoperative week 4. The model of QF volume change was significant ( P < 0.01) only at postoperative week 4, explaining 57% of its variation, where endurance time had a negative and knee extension ROM deficit a positive weight. Change in QF volume explained ( P < 0.05) 46% of the MVIC torque variation at postoperative week 12. Also, a significant change ( P < 0.05) in QF MVIC torque to volume ratio was observed at postoperative week 12. Conclusions Good prediction of QF atrophy in the first postoperative month can be made from studied variables, with isometric endurance and knee extension ROM deficit being the most significant contributors. The atrophy explained the larger part of QF muscle weakness, whereas factors contributing to the remaining portion need further research.