Article ID: JJPTF_2024_04
Muscle dysfunction remains semipermanent after Achilles tendon rupture. The main factors contributing to this are reduced force transmission function due to tendon scar healing and reduced muscle tension associated with tendon elongation. The relationship between these issues and the mechanobiological mechanisms of the tendon healing process remains unclear, preventing the establishment of physiotherapy strategies. This study aimed to elucidate the effects of reducing the tensile load on tendons after Achilles tendon rupture and suture on tendon lengthening, strength recovery, and collagen maturation. We used a mouse model in which mechanical stress on the tendon was controlled by joint immobilization and muscle paralysis. Muscle contraction-maintained mice showed that the tendon length ratio and the maximum failure force returned to the same level as on the non-operative side at 4 weeks after surgery. Contrastingly, muscle paralysis mice indicated that the tendon strength remained inferior, and the length was elongated compared to the non-operated side. On the other hand, collagen maturation and stress were still limited, even though muscle contraction was maintained under ankle immobilization. Our result suggested that unloading the tendon early after Achilles tendon rupture surgery, particularly restriction of muscle contraction, leads to structural changes in the tendon and contributes to permanent muscle weakness. This study reveals negative aspects of tendon unloading and the necessity of muscle contraction in early rehabilitation after Achilles tendon rupture and suture.
