A biomechanical study comparing a raft of 3.5 mm cortical screws with 6.5 mm cancellous screws in depressed tibial plateau fractures

Patil, Sunit and Mahon, Andrew and Green, Sarah and McMurtry, Ian and Port, Andrew (2006) A biomechanical study comparing a raft of 3.5 mm cortical screws with 6.5 mm cancellous screws in depressed tibial plateau fractures. Knee, 13 (3). pp. 231-235. ISSN 0968-0160

Abstract

There has been a recent trend towards using a raft of : mail diameter 3.5 mm cortical screws for supporting depressed tibial plateau fractures (Schatzker type III). Our aim was to compare the biomechanical properties of a raft of 3.5 mm cortical screws with that of 6.5 mm cancellous screws in a synthetic bone model. Ten rigid polyu ethane foam (sawbone) blocks, with a density simulating osteoporotic bone and ten blocks with a density simulating normal density bone were obtained. A Schatzker type III fracture was created in each block. The fracture fragments were then elevated and supported using two 6.5 mm cancellous screws in ten blocks and four 3.5 mm cortical screws in the remaining. The fractures were loaded using a Lloyd testing: machine. The mean force needed to produce a depression of 5 turn was 700.8N with the four-screw construct and 512.4N with the two-screw construct in the osteoporotic model. This difference was highly statistically significant (p = 0.009). The mean force required to produce the same depression was 1878.2N with the two-screw construct and 1938.2N with the four-screw construct in the non-osteoporotic model. Though the difference was not statistically significant (p = 0.42), an increased fragmentation of the synthetic bone fragments was noticed with the two-screw c instruct but not with the four-screw construct. A raft of four 3.5mm cortical screws is biomechanically stronger than two 6.5mm cancellous screws in resisting axial compression in osteoporotic bone. (C) 2006 Elsevier B.V. All rights reserved.