Hypertrophy of the flexor hallucis longus muscle after tendon transfer in patients with chronic Achilles tendon rupture.

Background: Flexor hallucis longus tendon (FHLT) transfer has become a popular method for reconstructing a chronic Achilles tendon rupture (ATR). The purpose of this study was to evaluate the clinical outcomes and possible hypertrophy of the FHL muscle after FHLT transfer in patients with chronic ATR.

Methods: Seven patients with chronic ATR underwent an FHLT transfer to heel through single incision. The patients were clinically evaluated 27 (16-39) months after the surgery. The patient satisfaction was assessed with Achilles Tendon Total Rupture Scale (ATRS). Isokinetic strength was measured from both legs. The FHL muscle hypertrophy was evaluated from MRI of both legs. All subjects also performed a gait analysis with an instrumented walkway system (GAITRite(®)).

Results: The plantar flexion strength was 16.1% (-45, 7-2, 4%) weaker in the operated leg. ATRS scores averaged 70.3. Marked hypertrophy, +52% (9-104%) of the FHL muscle was seen in the operated leg compared to the non-operated leg. The gait analysis did not show any marked pathology in any of the patients.

Conclusions: A mean hypertrophy of 52% of the FHL muscle was found after FHLT transfer for the chronic ATR. This indicates strong adaptation capacity of this muscle after FLHT transfer in situation where the function of the gastro-soleus complex was severely impaired preoperatively. The reconstruction of chronic ATR with FHLT transfer provided a good functional outcome and excellent patient satisfaction.