Biomechanical Comparison of Zone 1 5th Metatarsal Base Fracture Fixation

Abstract

Category: Basic Sciences/Biologics; Midfoot/Forefoot Introduction/Purpose: Zone 1 5th metatarsal base fractures are more common than zone 2 or 3 fractures, but significant debate still exists as to their optimum management, particularly for large fragments. The objective of this study was to compare the biomechanical strength of two headless compression screws versus a hook plate for fixation of large zone 1 5th metatarsal fractures. We hypothesized that hook plates would be biomechanically superior. Methods: Ten matched pairs of fresh-frozen 5th metatarsal cadaveric specimens were used. Large zone 1 avulsion fractures were simulated. Specimens were randomly assigned to fixation with two 2.5-mm headless compression screws or an anatomic 5th metatarsal hook plate. Specimens were mounted on a test frame and cyclically loaded through the plantar fascia, peroneus brevis tendon, and metatarsal base. Each specimen underwent 100 cycles at 50% physiological load (12 N on bone, 70 N on plantar fascia, 17.5 N on peroneus brevis), 100 cycles at 75% load (18 N on bone, 105 N on fascia, 26.25 N on peroneus brevis), and 100 cycles at 100% load (24 N on bone, 140 N on fascia, 35 N on peroneus brevis). Maximum cycles and maximum force were recorded. Results: The hook plate group had significantly higher cycles to completion of loading or failure compared with the screw group (270.7 +- 66.0 [range 100-300] cycles versus 178.6 +- 95.7 [range 24-300] cycles, respectively; P=0.011). Seven of 10 hook plate specimens and 2 of 10 screw specimens were intact at the maximum 300 cycles. Mean maximum force on the plantar fascia did not differ between the plate and screw groups (133.0 +- 22.1 [range 70-140]) N versus 119.0 +- 4.5 (range 70-140) N, respectively; P=0.098). Nine of 10 plate specimens and 5 of 10 screw specimens were intact at maximum force of 140 N. Conclusion: To our knowledge, this is the first biomechanical study comparing fixation constructs for 5th metatarsal avulsion fractures while loading the plantar fascia, which is the primary deforming force in vivo. These data suggest an anatomic hook plate is biomechanically superior to headless compression screw fixation of large zone 1 5th metatarsal avulsion fractures, which may prove pertinent in the setting of morbid obesity, fracture comminution, and/or fracture nonunion. Limitations include the relatively small sample size and the use of cadaveric bone which imperfectly mimics living tissue.