Summary

Based on one-year serial quantitative MRI assessment, the soleus muscle volume did not fully recovery and fatty degeneration in the soleus muscle progressed in the first postoperative year. On the other hand, FHL showed early muscle volume recovery, and it suggested that FHL compensates for decreased ankle plantarflexion strength.

Abstract

Background

Recovery of calf muscle function is one of the important factors that influence the clinical outcome of Achilles tendon repair. A number of studies reported the calf muscle atrophy is a common long-term problem after surgery, however, there is still lack of data concerning early postoperative morphological changes in calf muscle following Achilles tendon repair. The aim of this study was to investigate changes over time in the calf muscle volume and fatty degeneration during one year after Achilles tendon repair with use of quantitative MRI measurements.

Methods

A prospective one-year serial MRI study was carried out with 20 patients who underwent tendon repair surgery for unilateral acute Achilles tendon rupture. MRI assessment was performed at 1, 3, 6, and 12 months after surgery. The healthy contralateral leg was also scanned at 12 months after surgery as control. The muscle volume was measured for medial and lateral gastrocnemius (MG/LG), soleus (SOL), and flexor hallucis longus (FHL). The fatty degeneration was measured for MG, LG, and SOL. Relative volume or fatty degeneration changes in the affected leg compared to the healthy contralateral leg were calculated as percentage ((injured/healthy control)x100 (%)) to assess structural changes over time. One-way repeated measures analysis of variance with the Bonferroni post hoc analysis was performed to compare the change in each value over time.

Results

Muscle volumes of MG, LG, SOL, and FHL were 93.1%, 91.9%, 85.7%, and 96.9% at 12 months after surgery, respectively. MG, LG, and FHL muscle volumes improved over time and recovered to almost equal to the healthy side at 12 months after surgery (p=0.062, 0.224, and 1.000, respectively). SOL muscle volume was significantly lower than the healthy side at all time points (p<0.001), with poor recovery over time. Fatty degeneration of MG, LG, and SOL were 118.2%, 113.9% and 121.1% at 12 months after surgery, respectively. MG and LG fatty degeneration did not change significantly (p=0.289 and 0.553, respectively), but there was a statistically significant increase in fatty degeneration of SOL over time (p<0.001).

Conclusion

Among the triceps surae muscle, SOL muscle was most negatively affected by surgery as for muscle volume and fatty degeneration. Contrary to other calf flexors, the SOL muscle volume decreases with time for 6 months and recovered only 85% of healthy control at 1 year after surgery. These early postoperative findings were similar to previous studies of long-term follow-up and may affect the clinical outcome of Achilles tendon repair. Postoperative management to recover soleus muscle function at early phase after surgery before return-to-sporting activities should be considered.