Objectives: To compare lag-screw sliding characteristics and fixation stability of two cephalomedullary nails (CMN) with different lag-screw designs (solid and telescopic), we conducted a biomechanical study and an analysis of clinical results.
Methods: Six pairs of cadaver femurs with simulated intertrochanteric fractures were randomly assigned to one of two CMN fixations. Femur constructs were statically then cyclically loaded on an MTS machine. Lag-screw sliding and inferior and lateral femoral head displacements were measured, following which failure strength of the construct was determined. Forty-five patients with intertrochanteric fractures treated with these CMN were identified. Medical records and radiographs were reviewed and analyzed using Fisher's exact test and Student's t test to determine lag-screw sliding.
Results: No difference was seen with cycling in inferior femoral head displacement between the two screw designs. The solid screw had an average inferior head displacement of 1.75 mm compared with 1.59 mm for the telescoping screw (p = 0.772). The solid lag screws slid an average of 2.79 mm lateral from the nail, whereas the telescoping screws slid an average of 0.27 mm (p = 0.003). In our clinical review, the average lateral sliding of the telescoping screw was 0.5 mm and of the solid screw was 3.7 mm (p < 0.001). Despite differences in lateral sliding, there were no reoperations for prominent or painful hardware in either group.
Conclusions: Both designs are acceptable devices for stabilization of intertrochanteric fractures. Clinical and biomechanical data demonstrate greater lateral sliding in the solid lag-screw group, making for greater potential for lateral-sided hip pain in CMNs with solid lag screws as opposed to telescoping lag screws.