All-Inside Endoscopic Zone 1 Flexor Hallucis Longus Transfer: A Cadaveric Feasibility Study

Endoscopic flexor hallucis longus (FHL) tendon transfer addresses chronic Achilles tendon ruptures. Traditional percutaneous plantar incisions gain FHL length but risk neurovascular injury. This study evaluated the feasibility of an all-inside endoscopic FHL zone 1 tenotomy and transfer technique, which avoids plantar incisions by using zone 1 of the FHL tendon. We hypothesized that this technique would (1) provide sufficient tendon length, (2) avoid neurovascular damage, and (3) securely anchor the FHL tendon without tunnel blowout.

Ten cadaveric all-inside endoscopic zone 1 FHL tendon transfers were performed without fluoroscopic guidance. Specimens were independently assessed post hoc by 2 board-certified orthopaedic foot and ankle surgeons. Tendon length, anchor placement, tunnel integrity, and neurovascular bundle preservation were analyzed.

No neurovascular injuries or calcaneal tunnel blowouts occurred. Mean FHL tendon length for tunnel fixation was 17.5 (3.7) mm; 2 specimens had FiberLoop suture visible above the biotenodesis screw.

Our study supports the feasibility, reproducibility and preliminary safety of an all-inside FHL zone 1 tenotomy and endoscopic transfer. These cadaveric findings support further clinical investigation of this technique for Achilles rupture repair.

This cadaveric study provides anatomical evidence that an all-inside endoscopic zone 1 FHL tendon transfer can be performed without neurovascular injury or tunnel blowout, offering preliminary support for future clinical investigation of this technique as a minimally invasive approach to Achilles tendon repair.