Comparison of migration behavior between single and dual lag screw implants for intertrochanteric fracture fixation

Abstract

BackgroundLag screw cut-out failure following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. This study tested if resistance to cut-out failure can be improved by using a dual lag screw implant in place of a single lag screw implant. Migration behavior and cut-out resistance of a single and a dual lag screw implant were comparatively evaluated in surrogate specimens using an established laboratory model of hip screw cut-out failure.MethodsFive dual lag screw implants (Endovis, Citieffe) and five single lag screw implants (DHS, Synthes) were tested in the Hip Implant Performance Simulator (HIPS) of the Legacy Biomechanics Laboratory. This model simulated osteoporotic bone, an unstable fracture, and biaxial rocking motion representative of hip loading during normal gait. All constructs were loaded up to 20,000 cycles of 1.45 kN peak magnitude under biaxial rocking motion. The migration kinematics was continuously monitored with 6-degrees of freedom motion tracking system and the number of cycles to implant cut-out was recorded.ResultsThe dual lag screw implant exhibited significantly less migration and sustained more loading cycles in comparison to the DHS single lag screw. All DHS constructs failed before 20,000 cycles, on average at 6,638 ± 2,837 cycles either by cut-out or permanent screw bending. At failure, DHS constructs exhibited 10.8 ± 2.3° varus collapse and 15.5 ± 9.5° rotation around the lag screw axis. Four out of five dual screws constructs sustained 20,000 loading cycles. One dual screw specimens sustained cut-out by medial migration of the distal screw after 10,054 cycles. At test end, varus collapse and neck rotation in dual screws implants advanced to 3.7 ± 1.7° and 1.6 ± 1.0°, respectively.ConclusionThe single and double lag screw implants demonstrated a significantly different migration resistance in surrogate specimens under gait loading simulation with the HIPS model. In this model, the double screw construct provided significantly greater resistance against varus collapse and neck rotation in comparison to a standard DHS lag screw implant.

Rotationally Stable Screw-Anchor Versus Sliding Hip Screw Plate Systems in Stable Trochanteric Femur Fractures

“…3,4 Particularly, varus collapse and cutout of the lag screw pose daunting problems to the surgeon and remain amongst the main causes of treatment failure. 5,6 Inherently unstable fracture patterns in mainly osteoporotic bone in conjunction with the quality of the reduction and screw positioning in the femoral headneck fragment predispose to many complications, including implant cutout. 1,5,7 In general, cranial screw migration tends to result in cutout, whereas migration in the axial position leads to cut-through.…”

Hip screw migration testing: First results for hip screws and helical blades utilizing a new oscillating test method

“…The most common failure cause is varus collapse and cutting-out of the lag screw within the femoral head. [2][3][4] Cut-out of sliding hip screws accounts for 84% of all fixation failures. 1 The cutout rate for intramedullary (IM) nails has been reported to be as high as 8.3%.…”

Locked minimally invasive plating versus fourth generation nailing in the treatment of AO/OTA 31A2.2 fractures: A biomechanical comparison of PCCP® and Intertan nail®

“…Regarding the narrow configuration of screws, the IT can be considered as a single lag screw implant. Dual lag screw implants exhibited significantly less migration in comparison to single lag screw implants [42]. We found no difference in cut-out rates in this biomechanical study between the implants.…”