SLR - December 2018 - Parth J. Bhakta

Biomechanical Evaluation of Two Methods of Fixation of a Flexor Hallucis Longus Tendon Graft

Reference: Benca E., Willegger M., Wenzel F., Hirtler F., Zandieh S., Windhager R., Schuh R. Biomechanical Evaluation of Two Methods of Fixation of a Flexor Hallucis Longus Tendon Graft. Bone Joint J, 2018 Sept; 100-B: 1175–81.

Scientific Literature Review

Reviewed By: Parth J. Bhakta, DPM
Residency Program: Hunt Regional Medical Center, Greenville, TX

Podiatric Relevance: Achilles tendon pathology of any nature diminishes the strength of the tendon itself, whether it is an Achilles tendon rupture, tendinopathy or even postsurgical. To help reinforce the strength of the Achilles tendon, a graft is often used in conjunction with other procedures. The use of the Flexor Hallucis Longus tendon as an autograft is considered by many to be the gold standard for strengthening any Achilles tendon injury when an allograft is not warranted. The traditional technique requires multiple incisions and the use of a transosseous tendon-to-tendon fixation through the calcaneus. Although this technique is widely used for its increased patient satisfaction and restoration of biomechanics, there are many complications that arise, of which damage to the branches of the plantar nerves is the greatest. A newer single-incision technique using a shorter FHL tendon graft was developed that utilizes a tendon-to-bone fixation with a tenodesis screw into the calcaneus. Although minimally invasive, this technique may be at a biomechanical disadvantage when compared to the tendon-to-tendon fixation. The purpose of the study was to compare the biomechanical strength of each technique.

Methods: Twenty-one cadaveric legs were randomly assigned to either a tendon-to-tendon suture group (12) or a tendon-to-bone screw group (nine). Tenodesis was achieved with a 2-0 Arthrex fiber wire for the suture group and an Arthrex Bio-Tenodesis screw for the screw group. The specimens were then fixed in a servo hydraulic load frame positioned to simulate early heel rise. All FHL tendons were loaded axially with 1,000 cycles at a tensile force of 60N, followed by a quasistatic ultimate load test at a rate of 0.1mm/s until failure.

Results: Four of 12 (33 percent) and four of nine (44 percent) specimens failed during cycling loading in the suture and screw groups, respectively. The ultimate load was calculated as the maximum load achieved in the ultimate load test or the maximum load withstood by the construct during cyclic loading. It was 110.1 N in the suture group and 133.6 N in the screw group. The mean ultimate load in the two groups was not statistically significantly different.

Conclusions: The results showed no reduction in stability under cyclical loading when the Bio-Tenodesis Screw System was used in the attachment of the FHL tendon to the calcaneus compared with the conventional suture technique. The less invasive screw fixation method did not show to have a biomechanical disadvantage. Limitations existed for the statistical analysis primarily from the small sample size and the high age of the donors. This study demonstrates that the minimally invasive tenodesis screw for Achilles injuries has biomechanically comparable results to tendon-to-tendon fixation, while avoiding potential trauma to the plantar nerves.

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