The effect of peroneus brevis tendon anatomy on the stability of fractures at the fifth metatarsal base.

BACKGROUND

Nonunion of classic Jones fractures has typically been attributed to the precarious vascular anatomy of the proximal fifth metatarsal. Despite this theory, the operative treatment of these fractures utilizes biomechanical solutions. The purpose of the present study was to evaluate the influence of the peroneus brevis (PB) tendon on the stability of fractures of the proximal fifth metatarsal.

METHODS

We utilized 5 matched pairs (10 specimens) of fresh-frozen cadaveric specimens. We used 2 loading conditions: (1) a simulated fracture distal to the PB insertion (Jones equivalent) and (2) a simulated fracture within the footprint of the PB insertion (avulsion equivalent). Following the creation of the fracture, each lower extremity was statically loaded through the Achilles and PB tendons. Our primary outcome measure was the degree of fracture diastasis with loading of the PB. Anteroposterior images with and without loading were obtained to evaluate fracture separation. We utilized a paired Student t test and the intraclass correlation coefficient (ICC) for all statistical analyses.

RESULTS

The average length of the PB footprint was 15.2 mm. The simulated Jones fractures demonstrated greater fracture widening following loading of the PB tendon compared to the simulated avulsion fractures. The simulated avulsion fractures widened 0.4 mm on loading compared to 1.1 mm of widening in the simulated Jones fractures (P = .02). Intraobserver reliability for all radiographic measurements showed substantial agreement (ICC = 0.91).

CONCLUSION

The PB exerted a deforming force on the proximal fragment of simulated Jones fractures. This deforming force was less pronounced in the simulated avulsion fractures. The principal findings of this study were that proximal fifth metatarsal fractures distal to the PB insertion were significantly more unstable than more proximal fractures.

CLINICAL RELEVANCE: Our findings help support the notion that a mechanical component may contribute to the poor healing potential of Jones fractures secondary to deformation exerted by the PB tendon.