Stability of Locking and Non-Locking Plates in an Osteoporotic Calcaneal Fracture Model

Abstract

The aim of this biomechanical cadaver study of calcaneal fractures was to investigate whether a locking calcaneal plate provides more stiffness in osteoporotic bone compared to a non-locking plate. Sixteen fresh frozen bone mineral density (BMD)-matched cadaver feet were tested in a four-part model of a Sanders Type IIB calcaneal fracture. The fractures were fixed either with a non-locking AO (Sanders) plate or an interlocking AO plate (Synthes, Paoli, PA) to the lateral calcaneal wall with six screws. Specimens were subjected to cyclic loading which was increased stepwise to full body weight. Displacement of the posterior facet fragment was measured with an optical tracking system in the sagittal and transverse planes. No statistically significant differences were observed between the non-locking and the locking plates with respect to number of cycles to failure or 1-mm displacement of the posterior facet. The initial stiffness was significantly higher for non-locking plates. In osteoporotic bone, the greater stiffness of the screw-locking-plate construct was offset by the smaller diameter of the screw threads and the lower friction between the plate and bone when a locking plate was used. In clinical practice, the plate should first be compressed to osteoporotic bone with cancellous screws and at least two screws should be placed in the anterior process and in the tuberosity of the calcaneus.