Background: Transfer of the flexor hallucis longus (FHL) tendon aims to restore function and relieve pain in chronic Achilles tendon (AT) disease. The goal of the present study was to investigate the clinical and radiographic outcomes of FHL transfer to the AT and to compare the transtendinous technique to the transosseous technique. We hypothesized that the type of technique would have a notable impact on outcome.
Methods: Forty patients (42 ankles) were retrospectively reviewed and divided into group 1 (transtendinous technique, 22 patients/24 ankles) and group 2 (transosseous technique, 18 patients/18 ankles). Outcome parameters included the American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot score, Victorian Institute of Sports Assessment-Achilles (VISA-A) score, Foot Function Index (FFI), and Short Form-36 (SF-36) scores. Magnetic resonance imaging of the lower leg was performed preoperatively to assess muscle quality and fatty infiltration. Postoperatively, isokinetic plantar flexion strength was assessed using a Con-Trex dynamometer.
Results: In group 1 (follow-up, 73 months; age, 52 years), the AOFAS score improved from 66 points to 89 points (P < .001) with average values for the VISA-A of 76 points, FFI-D pain 15%, and FFI-D function 22%. In group 2 (follow-up, 35 months; age, 56 years), the AOFAS score increased from 59 points to 85 points (P < .001) with mean values for the VISA-A 76 points, FFI-D pain 25%, and FFI-D function 24%. At follow-up, the average SF-36 score in group 1 was 66% and in group 2 was 77%. Isokinetic testing at 30 deg/s in group 1 revealed notable weakness in the operated ankle averaging 54.7 N·m (75% of normal), and in group 2 the average was 58.2 N·m (77% of normal). No statistically significant differences were found between the groups.
Conclusion: The hypothesis was disproved. Both techniques for FHL transfer to AT, intratendinous and transosseous, provided good to excellent clinical and functional outcome in the treatment of irreparable AT disease.
Level of evidence: Level III, retrospective comparative series.
Keywords: Achilles tendon tear; chronic Achilles tendon disease; flexor hallucis longus transfer.