Secondary reconstruction of chronic Achilles tendon rupture: flexor hallucis longus transfer versus plantaris longus augmentation

Chronic Achilles tendon rupture is primarily caused by degenerative processes of multifactorial origin. In addition to secondary repair (SR) with augmentation of the plantaris longus tendon, the transfer of the flexor hallucis longus tendon (FHL) to the calcaneus is a recognised reconstruction procedure. This paper aims to provide a direct comparison based on clinical scores and objectifiable strength measurements. We analysed data for 60 patients (46 males and 14 females) with chronic Achilles tendon rupture, including 34 (mean age 57 years) treated with FHL and 26 (mean age 52 years) with SR between 2016 and 2020 (mean follow-up of 49 months). The follow-up included the American Orthopaedic Foot and Ankle Society Ankle-Hindfoot Scoring System (AOFAS-AH) and Visual Analogue Scale Foot and Ankle (VAS FA), the 12-item Short Form Survey (SF-12) and the objectifiable strength measurement using the dynamometer BIODEX®. Pre-existing gait disorders and permanent pain therapy led to exclusion. The mean AOFAS-AH was 87.8 points (FHL: 85.6, SR: 90.6), the mean VAS FA was 78.1 points (FHL: 73.7, SR: 83.6), the mean PCS was 48.2 points (FHL: 46.3, SR: 50.7) and the mean MCS was 54.1 points (FHL: 55.0, SR: 53.0). The maximum torque for plantar flexion was 56.7 Nm on average (FHL: 51.0, SR: 63.7). A total of seven (11.7%) wound infections requiring revision occurred (FHL: 4 (11.8%), SR: 3 (11.5%)). All measurements did not differ significantly between the groups (p > 0.05). The results of the study prove the equivalence of FHL and SR based on the clinical scores as well as on the strength measurement using BIODEX®. Nevertheless, a higher withdrawal because of morbidity with a tendency for prolonged incapacity to work in the FHL group has to be taken into account. The present work provides the basis for a prospective comparison in future studies.