Plantar flexor deficits following Achilles tendon rupture: a novel small animal dynamometer and detailed instructions

Abstract

Plantar flexor functional deficits measured using joint dynamometry are associated with poor outcomes in patients following Achilles tendon rupture. In this study, we developed a small animal dynamometer to quantify functional deficits in a rat Achilles tendon rupture model. Like our reported plantar flexor deficits in patients recovering from Achilles tendon ruptures, we found in our small animal model functional deficits across the ankle range of motion, resulting in an average 34% less positive work being done compared to the uninjured contralateral limb. These functional deficits are similar to 38% less plantar flexor work done by patients who were treated non-surgically in our prior research. Further, these deficits were greater in plantar flexion than dorsiflexion, which agree with clinical complaints of limited function during tasks like jumping and hiking. These findings highlight the impact of muscle-tendon loading during early tendon healing on long-term plantar flexor function and serve as compelling evidence that our Sprague Dawley rat model of an Achilles tendon rupture recapitulates the human disease. We provide thorough documentation for other groups to build their own dynamometers, which can be modified to meet unique experimental criteria. SIGNIFIGANCEPreclinical models are critical tools for translating knowledge discovery to clinical decision making. We developed a low-cost and flexible joint dynamometer that quantifies joint function in small animals. Here, we used a rat model to test the implications of Achilles tendon ruptures not surgically repaired on plantar flexor function. We found that Achilles tendon ruptures in a rodent model closely resemble the functional deficits our group has observed in patients.