Quantitative Assessment of Calf Muscle Volume, Strength, and Quality After Achilles Tendon Rupture Repair: A 1-Year Prospective Follow-up Study

Background: A number of studies have reported that calf muscle atrophy is a common long-term problem after Achilles tendon repair; however, there is still a lack of data concerning early postoperative morphological changes in the calf muscle after surgery. Purpose: To investigate changes over time in calf muscle volume and fatty degeneration during 1 year after Achilles tendon repair. Study Design: Cohort study; Level of evidence, 2. Methods: A prospective 1-year serial magnetic resonance imaging study was carried out with 20 patients who underwent tendon repair for unilateral acute Achilles tendon rupture. The magnetic resonance imaging assessment in addition to clinical and functional evaluations was performed at 1, 3, 6, and 12 months after surgery. The muscle volume of the medial and lateral gastrocnemius, soleus, and flexor hallucis longus (FHL) and fatty degeneration of the medial and lateral gastrocnemius and soleus were measured for the calf muscles, and the relative volume and fatty degeneration changes in the affected leg compared with the healthy contralateral leg were calculated as a percentage ([injured/healthy control] × 100) to assess structural changes over time. Results: Muscle volumes of the medial gastrocnemius, lateral gastrocnemius, soleus, and FHL were 92.3%, 92.8%, 84.6%, and 95.9% at 12 months after surgery, respectively. Medial and lateral gastrocnemius and FHL muscle volumes improved over time and recovered to almost equal to that of the healthy side at 12 months after surgery. The soleus muscle volume did not recover significantly over time and was statistically significantly smaller than that of the healthy side at 12 months ( P = .029). Fatty degeneration rates of the medial gastrocnemius, lateral gastrocnemius, and soleus were 118.2%, 113.9% and 121.1% at 12 months after surgery, respectively. Fatty degeneration of the medial and lateral gastrocnemius did not change significantly, but there was a statistically significant increase in fatty degeneration of the soleus over time ( P < .001). Conclusion: Within the triceps surae muscle, the soleus was the most negatively affected by injury and repair for both muscle volume and fatty degeneration. Postoperative management to recover the soleus muscle function before a return to sporting activities should be considered in the future.