RESUMEN
BACKGROUND: The biomechanical behavior of Pauwels type III fractures should be taken into consideration when performing internal fixation, since this repair should resist the shear force inherent in the vertical fracture line to the greatest extent possible. Recently, the use of a small fragment plate on the medial face of the femoral neck has been proposed by some authors, with satisfactory initial results. In the current study we analyze the mechanical role a medial plate used as a buttress plate for Pauwels type III femoral neck fractures, comparing the resistance of two fixation configurations using three cannulated screws. METHODS: Pauwels type III fractures were simulated in synthetic bones models and two groups were created, one of those using two parallel screws at the bottom of the femoral neck and the third screw crossing the fracture horizontally (G1), and the other fixed in the same arrangement as G1, but with the addition of a medial side plate at the apex of the fracture (G2). The constructs were subjected to axial loading until catastrophic failure. RESULTS: The addition of a medial plate buttressing the femoral neck increased significantly the resistance to maximum loading (p = 0.003). CONCLUSION: Use of a medial buttress plate results in a mechanically superior construction for Pauwels type III fractures fixed with multiple cannulated screws. LEBEL OF EVIDENCE: Level IV. Biomechanical comparative study.
RESUMEN
PURPOSE: The aim of our study is to compare the mechanical resistance of two screw configurations in fixating type II Pauwels femoral neck fractures. METHODS: Fifteen synthetic models of femur bones in young adults were divided into three equal groups: intact (G1), models with fixation of a 5.0-mm failure zone created in the posterior cortex of the femoral neck using an L-shaped screw arrangement (G2, n = 5), and models with an identical failure zone fixated using an inverted triangle assembly (G3, n = 5). Model strength (axial loading) and rotational deviation of the fragments were load-tested until a 5.0-mm displacement was reached (step 1) and then until failure, here considered as 10.0 mm displacement in G2 and G3 or femoral neck fracture in G1 (step 2). RESULTS: In step 1, the mean resistance in G1 was 1593 N (standard deviation [SD] of 62 N); this value in G2 was 1261 N (SD 49 N) and in G3 was 1074 N (SD 153 N). During step 2, the value for G1 was 2247 N (SD 84 N), for G2 was 1895 N (SD 69 N), and for G3 was 1523 N (SD 280 N). G3 (the inverted triangle assembly) showed a significantly lower maximum load than the group using the L-shaped assembly (G2) and the control group (G1), which was significant using Kruskal-Wallis analysis of variance (p = 0.002). CONCLUSION: Under test conditions in synthetic bone, fixation using a L-shaped screw assembly provides greater mechanical resistance than an inverted triangle assembly.