Summary

Jones fractures should be fixed with hardware parallel to the cuboid and collinear with the intramedullary cortex, to maximize compression and pull-out strength and minimize irritation of adjacent soft tissue during screw placement—mitigating but not avoiding injury to the PB and PF.

Abstract

Introduction

Jones fractures (JF) are among the most common fractures in the foot, mainly occurring in athletes. To facilitate return to sport and good functional outcomes, management with intramedullary screw fixation is recommended. Optimal screw dimension and location vary in literature, but it is clear that adequate fracture compression, maximizing pull-out strength, and minimizing irritation to surrounding structures are important. Potential compromise of the plantar fascia (PF) and peroneal tendon (PB) remains controversial. Characterizing optimal fixation of JF therefore requires better understanding of the anatomy of the metatarsal and its surrounding structures. The aim of this study was to improve guidelines regarding optimal insertion trajectory and screw parameters of JF by more accurately defining the anatomy of the fifth metatarsal bone.

Methods

Following IRB approval, 21 cadaveric fifth metatarsal bones were harvested. To facilitate registration, three reference screws (1mm diameter) were placed and secured on each bone with 2 screws distally and 1 screw proximally. All bones were CT scanned to create 3D reconstructions using modeling software (Rhinoceros, v5.0). The outer cortex, intramedullary canal and articular cortex of each bone were identified.
Using a digitizer (MircoScribe, G2LX), the PB and PF insertions, together with the reference screws were mapped on its corresponding bone in the modeling software. Based on the length of the bone, the shape and diameter at the narrowest point of the intramedullary canal, an optimal screw was modulated for each bone. Next, the JF zone was determined for each bone. Screw and thread length were calculated in this position, and the impact of screw placement on the insertion sites of both the PB and PF was recorded.

Results

The mean length of the bones was 74 ± 3.6mm, with the narrowest diameter of the intramedullary canal being 4.3 ± 0.7 mm. Ideal screw position was identified as parallel to the cuboid and coaxial with the intramedullary cortex, partially sacrificing the PB and PF insertions in 62% (13/21) and 33% (7/21), respectively; with an average of 1.6 ± 0.8 mm of the PB and 1.3 ± 0.8 mm of the PF insertion. The ideal screw length was 48 ± 5.8 mm, with a minimal thread length of 28 ± 6.8 mm and a minimal diameter of 4.5 mm. The screw length - total bone length ratio was 0.64 (range .050-0.72).

Discussion

To maximize compression and pull-out strength and minimize irritation of adjacent soft tissue during screw placement, JF should be fixed with hardware parallel to the cuboid and collinear with the intramedullary cortex—mitigating but not avoiding injury to the PB and PF. Average optimal length of the screw should be 64% of the length of the bone, with a minimum 4.5 mm diameter and 50% thread length. Given variability in anatomy, screw choice should be tailored to the individual.

Significance

JF not only represents a common foot injuries, it also comprises one of the more controversial surgical techniques in foot care today. Improving understanding of the implications of screw insertion will be paramount to maximizing functional outcomes.