Angle-specific analysis of knee strength deficits after ACL reconstruction with patellar and hamstring tendon autografts

After anterior cruciate ligament reconstruction (ACLR) there are differences in the neuromuscular deficits observed in patients with bone-patellar tendon-bone (BPTB) and with hamstring tendon (HT) autografts. Differences in knee extensor and flexor strength are commonly reported, but analyses have largely focused on peak torque metrics despite the requirement to generate torque through range when returning to sport. The aim of this study was to investigate the angle-specific strength and strength asymmetry differences between BPTB and HT around the time of return to play after ACLR. A total of 357 male field sport athletes with either a BPTB (n=297) or an HT (n=60) autograft underwent concentric knee flexor and extensor isokinetic strength testing nine months post-ACLR. Angle-specific torques were compared between grafts and limbs using 1D Statistical Parametric Mapping and discrete-point variables. Inter-limb extensor torque asymmetry was greater in BTPB than HT at knee angles of >30° (p=0.001, peak d=5.53), with flexor torque asymmetry lower in BPTB than HT at flexion angles of >25° (p=0.001, peak d=2.68). Angle of maximum asymmetry and angle of operated limb peak torque differed in knee extension for BPTB (p<0.001, d=0.32) but not HT, whereas knee flexion angle of maximum asymmetry and operated limb peak torque differed in both BTPB (p<0.001, d=0.75) and HT (p