Screw Angulation and Insertion Sequence Increase Interfragmentary Compression When Using Plates for Midfoot Arthrodesis: Foam-Surrogate and Cadaveric Validation.
BACKGROUND: Achieving interfragmentary compression and stability is critical for successful bone healing in fracture fixation and arthrodesis procedures. Modern orthopaedic plating systems incorporating variable-angle screw designs offer greater versatility; however, the impact of screw trajectory on interfragmentary compression and contact area has not been adequately explored. We questioned if the resultant forces applied by screw orientation would follow the basic principles of vector geometry. METHODS: Interfragmentary compression and contact area were quantified in foam bone surrogate osteotomy models using plates allowing maximum screw angulation of either 15 or 30 degrees, with screws inserted at various angles. Cadaveric second-tarsometatarsal (TMT) arthrodesis constructs were subsequently used to validate the mechanical findings from surrogate testing. RESULTS: Compression and contact area increased from 0 degrees to 15 degrees to 30 degrees in surrogate models (overall analysis of variance P < .001). Angling screws in the second bone fragment after securing the plate to the first fragment produced the largest compression gains. In cadaveric second-TMT constructs, 30-degree divergence increased compression (~15-fold; 49.4 ± 35.1 N vs 3.4 ± 3.8 N; P < .001) and contact area (~4-fold; 47.8 ± 28.9 mm² vs 12.8 ± 7.3 mm²; P < .001) compared with 0-degree divergence. CONCLUSION: With plate fixation, screw divergence from the arthrodesis/fracture line improved interfragmentary compression and contact area, particularly when divergent screws were inserted into the second bone fragment after the plate was secured to the first fragment. As hypothesized, the findings followed basic vector geometry. CLINICAL RELEVANCE: Surgeons can optimize plate fixation quality and enhance stability in midfoot arthrodesis (and other procedures) by strategically angling locking screws in the second bone fragment after securing the plate to the first fragment. These biomechanical insights offer practical guidance for achieving superior interfragmentary compression and potentially reducing the risk of nonunion in clinical practice.
