Correlation between Anterior and Posterior Obliquity of the Sliding Lag Screw and Stability in Unstable Intertrochanteric Fractures

Abstract

Purpose: To investigate the characteristics of the sliding pattern of the proximal fragment (head and neck) in unstable intertrochanteric fractures, which were fixed with a dynamic hip screw(DHS) with anterior to posterior or posterior to anterior insertion angle in the axial view. Materials and Methods: AO type A2.1 intertrochanteric fracture was reproduced in 10 proximal femur model (Synbone, Malans, Switzerland). Five fractured models were reduced and fixed using DHS with anterior to posterior insertion angle (group 1) and five models were fixed with posterior to anterior angle (group 2). Load of 500 N (30 cycles) was applied to the fracture fragment-plate complex using Instron 6022. Data on the distance of sliding and the angle of rotation of the proximal fragment were collected and analyzed. Results: No significant difference was noted statistically in the distance of sliding between the two groups (p=0.92). However, the mean angle of rotation was 13.4° and 8.0° in group 1 and 2, respectively and the difference was statistically significant (p=0.012). Anterior cortical fracture of distal fragment was noted in 3 cases of group 1. There was no fracture of the anterior cortex in group 2. Conclusion: In unstable intertrochanteric fracture, the insertion angle of the lag screw in axial view does seem to play a role in the fate of bone-plate complex. Early eccentric contact of both fragments caused rotation of the proximal fragment in all cases and anterior cortical fracture of the distal fragment in 3 cases of group 1.