Foot peak pressures are comparable to normal foot after flexor hallucis longus transfer for chronic retracted tendo-achilles tear: A pedobarographic analysis of normal foot versus affected foot

Introduction: Foot pressure changes and morbidity after flexor hallucis longus (FHL) transfer in chronic retracted tendoachilles (TA) tears have not been documented. The primary aim of our study is to analyze the peak pressure changes in various zones of the foot at each successive follow-up in the affected foot versus normal foot. The secondary aim is to determine FHL tendon healing and muscle hypertrophy. Methods: This is a prospective study of 46 patients who underwent FHL augmentation for chronic retracted TA tears (between 2019 and 2022). Included TA tear > 6 weeks duration and retraction > 2.5 cm. Excluded open TA tear, < 6 weeks and retraction < 2.5 cm. Depending on the amount of retraction, FHL augmentation combined with TA repair/VY plasty/turn-down-plasty. Functional outcome was analyzed with AOFAS hallux metatarsophalangeal scale. Pedobarographic analysis was done pre-operatively and at 3, 6, 9 months, 1 year and at the final follow-up. Parameters studied included forefoot peak pressure (FFPP), hindfoot peak pressure (HFPP), great toe peak pressure (GTPP), first Mmeta-tarso phalangeal peak pressure (MTPP), area under the pedobarograph and maximum force. At final follow-up MRI was done to assess FHL healing and hypertrophy. Statistical analysis was done for these parameters using appropriate tests. Results: Study involved 29 male and 17 female patients, mean age 49.5 years (33-65 years) and mean follow-up 26.8 months (14-38.4months). Mean hallux MTP-AOFAS score increased from 46.04 +/- 7.31 preoperatively to 96.17 +/- 3.22 at the final follow-up (P < 0.01). There was gradual improvement noted in FFPP, GTPP, MTPP Peak pressures at subsequent follow-ups, and by the end of 1-year foot pressures were comparable to normal side FFPP (8.02 +/- 3.8 N/cm2 to 31.35 +/- 3 N/cm(2)), GTPP(30.78 +/- 13.01 N/cm(2) to23.17 +/- 7.5 N/cm(2)), MTPP(5.22 +/- 2.64 N/cm(2) to 23.3 +/- 9.6 N/cm2). Initial high HFPP showed decline in subsequent follow-up and restored back to normal HFPP (36.91 +/- 5.7 N/cm(2) to 25.09 +/- 3.7 N/cm(2)). Changes in pressures were statistically significant (< 0.001). Six patients had superficial wound infections healed with antibiotics. 23 patients who underwent a post-operative MRI showed a mean of 27 mm muscle thickness and 7.1 mm tendon thickness with complete incorporation of the FHL. Conclusion: Foot peak pressures though initially deranged, are restored and comparable to normal foot after FHL transfer for chronic retracted TA tear. FHL hypertrophy is observed at the muscle thickness and at the distal tendon and provides adequate strength to repair and restore foot pressures.