Are Hook Plates Advantageous Compared to Antiglide Plates for Vertical Shear Malleolar Fractures?
This study was designed to evaluate the biomechanical properties of a hook plate (HP) vs an antiglide (AG) plate for supination-adduction (SAD)–ankle fractures. Identical polyurethane tibial models were obtained and vertical fractures were created. The fractures were stabilized with 1 of the following: one-third tubular plate in an AG fashion with 2 screws proximal to the fracture; an AG plate with an additional screw perpendicular to the vertical shear fragment (MAG), or an HP.
Ten models were randomly assigned to each of the 3 groups. The constructs were tested in offset-axial loading and were evaluated for construct stiffness and load-to-failure. The MAG construct yielded better stiffness compared with the AG plate (P < .05) and the HP (P < .05). The plate stiffness of the HP construct compared with the AG was not significant (P = .350). In regards to load-to-failure, the difference between MAG and AG was 638 N, and MAG and HP was 530 N (both P < .05). The HP had a load-to-failure that was, on average, 108 N more than the AG but was not significant (P = .063). A one-third tubular plate in the MAG fashion provided a stable, strong construct for fixation of vertical shear medial malleolus fractures.
Our study investigated loading only in the offset-axial direction, a difference when compared to the Dumigan and colleagues8 and Toolan and colleagues9 studies. The offest transverse loading previously investigated would most likely represent an external rotation moment. While fixation in vivo could experience an external rotation moment, the specific fracture pattern of interest fails in offset-axial loading. In the original discription of the SAD fracture, Lauge-Hanson7 stated that the talus causes the vertically oriented medial malleolar fracture in the extreme of ankle supination with an adduction moment. Considering this, we investigated failure with a force in the direction that causes this type of fracture.
There are some additional limitations. This study demonstrated superiority of a one-third tubular plate with 2 screws proximally and 1 lag screw. While this was shown in the laboratory under pure offset-axial loading conditions, this may not reproduce daily forces experienced by the constructs. Additionally, this study examined load-to-failure of the constructs and did not investigate cyclic loading that a construct would experience in vivo. Because the testing is not recognizably consistent with day-to-day stresses of these constructs in vivo, this confounds the clinical application of our study.
The stiffness required for clinical healing is undetermined and, therefore, all 3 types of fixation could be adequate clinically. Patients are typically instructed to adhere to weight-bearing limitations on the affected extremity, and casts or splints are applied postoperatively for extended periods of time. Clinical studies would have significant benefit in the evaluation of fixation of vertical shear medial malleolar fractures.
Conclusion
AG plating technique with lag-screw placement is biomechanically superior to the other 2 constructs investigated. The clinical applications of these results are not known, and clinical trials are suggested to determine the best type of fixation for SAD-type medial malleolar fractures.
