An in vitro study comparing the use of suture anchors and drill hole fixation for flexor digitorum longus transfer to the navicular.

BACKGROUND: The surgical management of posterior tibial tendon dysfunction often includes transfer of the flexor digitorum longus (FDL) tendon through a tunnel in the navicular. Fixation often is obtained by sewing the tendon back onto itself. The purpose of this study was to compare this standard method of fixation with suture anchor fixation, a technique that may be associated with less surgical morbidity, because it requires the harvesting of less tendon length.

METHODS: FDL tendon transfer to the navicular was done in 13 fresh-frozen cadaver specimens. In six feet comprising the standard group, the FDL tendon was transected distal to the master knot of Henry, placed through a drill hole into the navicular, and sutured back onto itself. In seven feet the FDL tendon was transected proximal to the master knot of Henry, placed into a drill hole into the navicular, and fixed with a suture anchor. Load was applied to the proximal FDL muscle and tendon using a materials testing system (MTS) machine and peak load to failure was measured.

RESULTS: The mean load to failure was 142.48 N +/- 38.06 N for the standard group and 142.12 N +/- 59.26 N for the suture anchor group (p = 0.305 for the Student-t test and p = 0.945 for the Mann-Whitney test).

CONCLUSION: Transfer of the FDL tendon to the navicular using suture anchor fixation requires less tendon length yet provides similar fixation strength as compared to sewing the tendon back onto itself. However, suture anchors are considerably more expensive than sutures.

CLINICAL IMPLICATIONS: Suture anchors allow comparable fixation of FDL tendon transfer into a navicular without the need to disrupt the master knot of Henry. This technique may be associated with less morbidity including a shorter incision, decreased risk of medial plantar nerve injury, and decreased loss of lesser toe plantarflexion strength secondary to maintenance of the normal interconnections between the flexor hallucis longus (FHL) and FDL tendons.