Achilles Tendon Surgical Repair Partially Restores Early Plantar Flexor Structure and Function in a Rat Model

Achilles tendon ruptures significantly impair long-term patient function, with two-thirds of patients experiencing persistent functional deficits. Although nonsurgical treatment has gained popularity due to its perceived lower risk of complications, the specific effects of this approach on tendon healing, muscle function, and overall performance remain poorly understood. Directly comparing surgical and nonsurgical treatment options in a clinical population is challenging given the diverse nature of the patient population. Preclinical models are essential to isolate the mechanisms underlying these treatments, enabling a detailed examination of the structural and functional outcomes that are difficult to assess in human studies. Here, we surgically induced Achilles tendon ruptures in 20 adult male Sprague Dawley rats and repaired the rupture in half of these animals. Then, functional outcomes were assessed by measuring plantar flexor torque across the ankle's range of motion using a custom-developed small animal dynamometer, and structural changes were evaluated through measurements of Achilles tendon elongation and plantar flexor muscle mass. We found that surgical treatment led to 11%-35% increased functional plantar flexor torque outcomes compared to nonsurgical treatment. Additionally, plantar flexor muscle mass decreased by 21% in nonsurgically treated animals compared to only 12% in the surgically treated group. Our results suggest that surgically repairing a tendon rupture restores plantar flexor function more effectively than nonsurgical treatment; however, persistent functional deficits in both groups indicate that enhanced rehabilitation strategies are necessary for full functional restoration.