The anatomy and clinical applications of flexor hallucis longus tendon transfer in treatment of chronic Achilles tendinopathy

Abstract

Objective To evaluate the effectiveness of flexor hallucis longus tendon transfer in treatment of chronic Achilles tendinopathy using different technique. Methods Sixty-four embalmed feet of 32 cadavers were analyzed and classified anatomically with respect to the individual cross links in the Henry's knot. These three techniques were then combined to determine the total potential tendon graft length obtainable using single incision, double incision and minimally invasive incision. From January, 2012 to June, 2015, 10 patients (10 feet) with chronic Achilles tendinopathy were treated with double incision technique. The score was 63.04 ±7.75 according to American Orthopedic Foot and Ankle Society (AOFAS) ankle and hindfoot score system. Results Only two different configurations were found. Type 1, a tendinous slip branched from the FHLT to the FDLT was 96.9% (62 of 64 feet) . Type 2, a slip branched from the FHLT to the FDLT and another slip from the FDLT to FHLT was 3.1% (2 of 64) . The average length of the FHLT graft available from a single incision measured (5.08±1.09) cm, double incision technique measured (6.72 ± 1.02) cm, and minimally invasive incision measured (17.49 ± 1.80) cm. The difference between the lengths obtained from these three techniques was statistically significant. Ten patients were followed-up 12-36 months (mean, 13.7 months) . At 12 months after operation, the AOFAS ankle and hindfoot score was 93.28 ± 3.72, showing significant difference when compared with that before operation. The results were excellent in 6 cases, good in 3 cases, and fair in 1 case with an excellent and good rate of 90%. No sural nerve injury, posterior tibial nerve injury, medial plantar nerve injury, and lateral plantar nerve injury occurred. Conclusion In over 96% of the feet, a proximal to distal connection from the FHLT to the FDLT was found, which might contribute to the residual function of the lesser toes after FDLT transfer. The distal stump of the FHLT tendon should be sutured onto the FDLT tendon under tension to enable a co-activation of the great toe, preserved hallux plantar flexion. Chronic Achilles tendinopathy reconstruction with flexor hallucis longus tendon harvested using double incision technique offers a desirable outcome in operative recovery, tendon fixation, preserved hallux plantar flexion and less complications. Key words: Flexor hallucis longus; Flexor digitorum longus; Achilles tendon disorders; Tendon transfer