Semitendinosus force-joint angle relationship after anterior cruciate ligament reconstruction with semitendinosus...

The semitendinosus (ST) tendon is among the most frequently used autografts for anterior cruciate ligament reconstruction (ACLR). Persistent deficits in knee flexion strength at flexed knee angles after ACLR may be attributable to a shift in the force-joint angle relationship of the ST caused by post-operative shortening of the muscle belly. This study aimed to investigate the ST muscle morphology and its force-joint angle relationship following ACLR using the ST tendon by comparing the operated and contralateral non-operated limbs.

Thirteen young adults who had undergone primary ACLR using the ST tendon participated. Participants performed isometric maximal voluntary knee flexion on the non-operated and operated limb at 90° hip flexion and knee flexion angles of 50° and 90°, during which the ST muscle shear modulus (muscle force index) was assessed using ultrasound shear wave elastography. The ST muscle belly length was assessed by identifying its proximal and distal ends in each limb.

The ST muscle belly was shorter in the operated limb than the non-operated limb. The ST muscle shear modulus at 50° of knee flexion was significantly lower than that at 90° in the non-operated limb, but not in the operated limb. The ST muscle shear modulus at 90° was not significantly different between limbs, whereas at 50°, it was greater in the operated limb than the non-operated limb.

These findings suggest that the ST muscle belly shortening following ACLR with the ST tendon autograft alters the muscle's force-joint angle relationship.