Introduction

The objective of this study was to determine if a synthetic bone substitute would provide results similar to bone from osteoporotic femoral heads during in vitro testing with orthopaedic implants. If the synthetic material could produce results similar to those of the osteoporotic bone, it could reduce or eliminate the need for testing of implants on bone.

We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm. 3. ) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests. The bovine cancellous blocks were only subjected to static pull-out testing. We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations. In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs. In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration. Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations. In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading

We have treated 14 patients (15 fractures) with nonunion of an intra-articular fracture of the body of the calcaneum. The mean follow-up was six years (2 to 8.5). A total of 14 fractures (93%) had initially been treated operatively with 12 (86%) having non-anatomical reductions. Four feet (27%) had concomitant osteomyelitis. Of the nonunions, 14 (93%) went on to eventual union after an average of two reconstructive procedures. All underwent bone grafting of the nonunion. The eventual outcome was a subtalar arthrodesis in ten (67%) cases, a triple arthrodesis in four (27%) and a nonunion in one (6%). Three patients had a wound dehiscence; all required a local rotation flap. The mean American Orthopaedic Foot and Ankle Society score at latest follow-up was 69, and the mean Visual analogue scale was 3. Of those who were initially employed, 82% (9 of 11) eventually returned to work. We present an algorithm for the treatment of calcaneal nonunion, and conclude that despite a relatively high rate of complication, this complex surgery has a high union rate and a good functional outcome.