Abstract
Following anterior cruciate ligament reconstruction (ACLR) using a semitendinosus (ST) autograft measures such as length, cross-sectional area, and volume may not fully describe the effects of tendon harvest on muscle morphology as these discrete measures cannot characterize three-dimensional muscle shape. This study aimed to determine between-limb ST shape similarity and regional morphology in individuals with a unilateral history of ACLR using a ST graft, and healthy controls.
A secondary analysis of magnetic resonance imaging was undertaken from 18 individuals with unilateral history of ST ACLR and 18 healthy controls. ST muscles were manually segmented, and shape similarity were assessed between limbs and groups using Jaccard index (0-1) and Hausdorff distance (mm). ST length (cm), peak cross-sectional area (CSA) (cm2), and volume (cm3) was compared between surgically reconstructed and uninjured contralateral limbs, and between the left and right limbs of control participants with no history of injury. Cohen's d was reported as a measure of effect size.
Compared to healthy controls, the ACLR group had significantly (p<0.001, d= −2.33) lower bilateral ST shape similarity. Furthermore, the deviation in muscle shape was significantly (p<0.001, d= 2.12) greater in the ACLR group. Within the ACLR group, maximum Hausdorff distance indicated ST from the ACLR limb deviated (23.1±8.68 mm) from the shape of the healthy contralateral ST, this was observed particularly within the distal region of the muscle. Compared to the uninjured contralateral limb and healthy controls, deficits in peak cross-sectional area and volume in ACLR group were largest in proximal (p<0.001, d= −2.52 to −1.28) and middle (p<0.001, d= −1.81 to −1.04) regions.
Findings highlight morphological features in distal ST not identified by traditional discrete morphology measures. ST shape was most different in the distal region of the muscle, despite deficits in CSA and volume being most pronounced in proximal and middle regions. ST shape following ACLR may affect force transmission and distribution within the hamstrings and contribute to persistent deficits in knee flexor and internal rotator strength.
