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Anterior Cruciate Ligament Transection and Synovial Fluid Lavage in a Rodent Model to Study Joint Inflammation and Posttraumatic Osteoarthritis
Published on: September 2, 2025
Decrease of knee flexion torque in patients with ACL reconstruction: combined analysis of the architecture and
Yukiko Makihara1, Akie Nishino, Toru Fukubayashi
1Department of Life Sciences, Graduate School of Arts and Science, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan.
Summary
Reduced knee flexion torque after anterior cruciate ligament (ACL) reconstruction is linked to semitendinosus muscle atrophy and shortening. Architectural differences in hamstring muscles also contribute to this weakness, impacting recovery.
Area of Science:
- Orthopedic Surgery
- Biomechanics
- Rehabilitation Medicine
Background:
- Decreased deep knee flexion torque is a reported complication following anterior cruciate ligament (ACL) reconstruction using semitendinosus tendon grafts.
- The underlying causes of this persistent weakness remain debated, with potential contributions from hamstring muscle architectural and functional changes.
Purpose of the Study:
- To investigate the architectural and functional adaptations of hamstring muscles after ACL reconstruction.
- To determine the relationship between semitendinosus muscle changes and reduced knee flexion torque.
Main Methods:
- Cadaveric measurement of hamstring muscle fiber lengths.
- Clinical assessment of knee flexion torque and electromyography (EMG) in ACL-reconstructed patients and matched controls.
- Magnetic resonance imaging (MRI) to evaluate muscle volume, tendon regeneration, and musculotendinous junction position.
Main Results:
- Semitendinosus and gracilis muscles have significantly longer fiber lengths than semimembranosus and biceps femoris.
- Reduced semitendinosus muscle volume and a more distal musculotendinous junction were observed in the reconstructed limb.
- Knee flexion torque and hamstring EMG activity decreased with increasing knee flexion angle, particularly in the reconstructed limb.
Conclusions:
- Atrophy and shortening of the harvested semitendinosus tendon contribute to decreased knee flexion torque post-ACL reconstruction.
- Architectural differences among hamstring muscles may limit compensatory mechanisms, exacerbating weakness.
- Understanding these muscle adaptations is crucial for optimizing rehabilitation strategies after ACL reconstruction.
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