Posterior Malleolar Fracture Fixation: Posterior Plating vs a Modified Anterior-to-Posterior 4-Screw Construct in a Cadaveric Biomechanical Model.

BACKGROUND

There continues to be controversy regarding the optimal fixation strategy of large posterior malleolar fractures while treating trimalleolar ankle fractures. This study compared the biomechanical stability in a cadaveric model of a modified anterior-posterior (AP) 4-screw construct vs posterior plate fixation of Mason 2A posterior malleolar fractures.

METHODS

Twenty fresh frozen human cadaveric below-knee specimens were prepared with an oblique osteotomy of the posterior malleolus, resection of medial and lateral ankle ligaments, and posterior dislocation of the tibiotalar joint to produce unstable Mason 2A posterior malleolar fractures. Specimens were fixed with either a modified AP 4-screw construct or with a 5-hole one-third tubular plate with 4 cortical screws. The specimens were axially loaded in neutral ankle position for 50 000 cycles to simulate protected weightbearing, then loaded to failure in 20 degrees of plantarflexion. Fracture displacement and load to failure were recorded.

RESULTS

Two specimens from the plate group had early failure with displacement at the fracture site >2 mm; otherwise, there was no difference in displacement between the 2 constructs after axial cyclic loading (screws, 1.32 ± 0.26 mm vs plate, 1.26 ± 0.48 mm, P = .82). Additionally, there was no difference in the load to failure (screws, 3856 ± 617 N vs plate, 3939 ± 569 N, P = .81). Maximum load to failure was statistically equivocal between the 2 constructs (screws, 4867 ± 718 N vs plate, 4862 ± 1020 N, P = .99).

CONCLUSION

For the fixation of large, unstable Mason 2A posterior malleolar fractures involving roughly 50% of the articular surface, our modified AP 4-screw construct may offer similar biomechanical stability while avoiding prone positioning and additional posterior surgical exposures associated with posterior plating.

CLINICAL RELEVANCE: This cadaveric study demonstrates that a modified anterior-posterior 4-screw construct provides biomechanical stability equivalent to posterior plating for large posterior malleolar fractures.