Stability of Locking Plate and Compression Screws for Lapidus Arthrodesis: A Biomechanical Comparison of Plate Position

Lapidus (first tarsometatarsal joint) arthrodesis is an established and widely used procedure for the management of moderate to severe hallux valgus, especially in cases involving hypermobility of the first tarsometatarsal joint. Multiple fixation methods are available, and several previous investigations have studied the relative strengths of these methods, including dorsomedial and plantar plating comparisons. However, these studies compared plates of varying designs and mechanical properties and used varying modes of compression and interfragmentary screw techniques. The present study mechanically investigated the resulting motion, stiffness, and strength of identical locking plate constructs fixed at various anatomic positions around the first tarsometatarsal joint. In a bench-top study, fourth-generation composite bones were divided into 3 fixation groups, each having identical interfragmentary screw applications, and randomized to 1 of 3 plate positions: dorsal, medial, or plantar. The plates applied in each case were identical locking plates, precontoured to fit the anatomy. Each construct was experimentally tested using a cantilever bending approach. The outcomes obtained were stiffness, yield force, displacement at yield, ultimate force, and displacement at ultimate force. The plantar plate position showed superior initial stiffness and force to ultimate failure. The plantar and medial plate positions exhibited superior force to yield. The medial plate position was superior regarding displacement tolerated before the yield point and catastrophic failure. The dorsal plate position was not superior for any outcome measured. Plantar and medial plating each offered biomechanical benefits. Clinical studies using similarly matched constructs are required to show whether these findings translate into improved clinical outcomes.