A Comparison of Talar Surface Area Occupied by 2- Versus 3-Screw Fixation for Ankle Arthrodesis.

Background. Ankle arthrodesis is a procedure utilized in the treatment of end-stage ankle arthritis. Internal fixation with screws is traditionally relied on to achieve union. Although the use of screw fixation alone has produced satisfactory outcomes, nonunion rates can range from 9% to as high as 35%. Adding an additional screw to the traditional 2-screw fixation construct may improve the likelihood of union by adding strength and stiffness; however, this addition may counteract the theoretical fusion enhancement benefit by reducing the joint surface area (SA) available for fusion. Methods. A cadaver study was performed to compare the amount of SA lost from a standard 2-screw (group 1) versus the 3-screw ankle fusion construct (group 2). A total of 10 fresh cadaveric below-knee specimens were used. Cannulated 7.0-mm partially threaded screws were placed across the ankle joint. Each talus was examined to precisely determine joint SA loss following each procedure. Results. The mean total talus SA in group 1 was 1833.71 mm2 compared with 2125.76 mm2 in group 2. The mean SA lost by the 2-screw construct was 5.91%, versus 9.51% in the 3-screw construct group. The talus SA loss percentage difference between groups reached statistical significance (P = .0220). Conclusion. The addition of a third 7.0-mm screw to a 2-screw ankle fusion construct raised the percentage of joint surface lost from 5.91% to 9.5%. Clinical Relevance. Surgeons may consider using extra-articular plates with 1 or 2 intra-articular screws instead of the traditional 3-screw construct if there is an elevated concern for nonunion. Levels of Evidence: Level IV: Cadaveric case series.