Mechanical integrity of a flexor hallucis longus tendon transfer using an all-inside endoscopic approach

Flexor hallucis longus (FHL) tendon transfer is a common and effective procedure used to treat chronic Achilles tendon rupture. Minimally invasive techniques have risen in popularity in response to wound-healing problems associated with open techniques. In addition, surgical approaches with a percutaneous plantar incision to harvest the FHL tendon at zone 2 have reported potential for damage to neurovascular structures. Previously, we reported the development of a novel all-inside endoscopic FHL zone 1 tenotomy and transfer approach that exhibited no insult to the neurovascular structures. The aim of this study was to evaluate the biomechanical integrity of the FHL tendon construct. An all-inside endoscopic FHL tendon transfer was performed on 10 cadaveric specimens without fluoroscopic guidance. The FHL tendon construct was isolated and attached to a uniaxial hydraulic loading platform where specimens were viscoelastically conditioned and loaded until failure. Eight specimens successfully completed testing and were evaluated. Mean failure strength of the FHL tendon construct was 222.08(74.83) N. This failure strength was not influenced by whether the tendon was medial or lateral to the screw (222.08(57.63) N, 222.08(98.71) N, respectively; p > 0.99). The ultimate failure strength of our FHL tendon transfer construct met or exceeded that of other literature reported FHL transfer techniques (172(40) N), including both anchor (189(26) N) and suture (110(46) N) fixation. Our novel all-inside endoscopic FHL zone 1 tenotomy and transfer approach exhibits lower propensity for neurovascular damage and equivalent or greater construct strength versus existing FHL tendon transfer techniques, making it a viable surgical approach.