Objectives
Anterior cruciate ligament reconstruction (ACLR) using semitendinosus (ST) autograft results in donor muscle atrophy and uncertain tendon regeneration. The effects of harvesting these muscles on muscle moment arm and torque generating capacity have not been well described. This study aimed to determine between-limb differences (ACLR vs uninjured contralateral) in muscle moment arm and torque generating capacity across a full range of hip and knee motions.
Methods
A secondary analysis of magnetic resonance imaging was undertaken from 8 individuals with unilateral history of ST autograft ACLR with complete ST tendon regeneration. All hamstring muscles and ST tendons were manually segmented. Muscle length (cm), peak cross-sectional area (CSA) (cm2), and volume (cm3) were measured in ACLR and uninjured contralateral limbs. OpenSim was used to simulate and evaluate the mechanical consequences of changes in normalised moment arm (m) and torque generating capacity (N.m) between ACLR and uninjured contralateral limbs.
Results
Compared to uninjured contralateral limbs, regenerated ST tendon re-insertion varied proximal (+) (mean = 0.66cm, maximum = 3.44cm, minimum = -2.17cm, range = 5.61cm) and posterior (+) (mean = 0.38cm maximum = 0.71cm, minimum = 0.02cm, range = 0.69cm) locations relative to native anatomical position. Compared to uninjured contralateral limbs, change in ST tendon insertion point in ACLR limbs resulted in 2.5% loss in peak moment arm and a 3.4% loss in peak torque generating capacity. Accounting for changes to both max isometric force and ST moment, the ST had a 14.79% loss in peak torque generating capacity.
Conclusion
There are significant deficits in ST muscle morphology and insertion points following STÂ autograft ACLR. The ST atrophy and insertion point migration following ACLR may affect force transmission and distribution