Anterior locking plate reduces trochanteric fracture migrations during hip extension.

BACKGROUND: Greater trochanter fractures or osteotomies fixed with lateral plates still present high rates of complications. Unblocked greater trochanter anterior movement during hip extension might be a possible cause of failure. This study aimed to determine, under stair climbing conditions, the biomechanical behaviour of a greater trochanter fragment and the impact of an anterior locking plate on its migration. METHODS: Eighteen femurs paired from nine fresh frozen cadaveric specimens were tested on a quasi-dynamic stair climbing cycling test bench. Left and right sides with greater trochanter fractures were randomly fixed either with an antero-lateral locking plate or with a lateral locking plate. Migrations, defined as the remaining movements of the unloaded greater trochanter fragment, were measured for all 18 femurs. FINDINGS: During hip extension, multi-directional greater trochanter fragment movements occurred and showed a back-and-forth anterior rotation. The lateral locking plate failed due to greater trochanter fragment rotation around the superior axis and anterior translation. The antero-lateral locking plate significantly reduced greater trochanter anterior migration (-0.9 mm ± 1.6) compared to the lateral locking plate (9.6 mm ± 9.5). INTERPRETATION: Hip extension provides a plausible explanation for the high rate of post-operative failures of greater trochanter fixations. An antero-lateral locking plate represents an efficient surgical alternative counteracting the multi-directional greater trochanter movements occurring during hip extension.

Biomechanical analysis of trochanteric fracture fixations using a Y-shaped locking plate.

OBJECTIVES: Clinical evidence suggests that the use of Y-shaped locking plates with anterior and lateral locking screws provide improved primary fixation stability over the use of straight locking plates in the treatment of greater trochanter (GT) fractures. However, it remains unclear how the use of cable cerclages, in replacement or addition to the locking screws, would impact the primary fixation stability. METHODS: Nine surgical fixations were tested on a dynamic test bench through 27 sawbones experiments. These fixations on the GT and bone shaft (BS) included locking screws alone, cable cerclages alone, or 7 combinations of both. Migrations, defined as the remaining movements of the unloaded GT fragment, were measured for all 9 fixations submitted to dynamic stair climbing cycling after an experimental plan. RESULTS: Under dynamic stair climbing conditions: (1) Y-shaped locking plates fixed by locking screws alone (vs cable cerclages alone) significantly reduced GT migrations, (2) adding cable cerclages to screws provided no significant reduction of migrations, and (3) cable cerclages alone can be used on the BS but is not recommended on the GT. CONCLUSIONS: Y-shaped locking plates with anterior and lateral locking screws improved primary stability of GT fractures over fixation with cable cerclages. Cable cerclages provided acceptable primary stability when screw fixations were unachievable but on the BS only.

The effects of femoral neck cut, cable tension, and muscles forces on the greater trochanter fixation.

Greater trochanter (GT) stabilization techniques following a fracture or an osteotomy are still showing high levels of postoperative complications. Understanding the effect of femoral neck cut placement, cable tension and muscles forces on GT fragment displacements could help surgeons optimize their techniques. A 3D finite element model has been developed to evaluate, through a statistical experimental design, the impact of the above variables on the GT fragment gap and sliding displacements. Muscles forces were simulating typical daily activities. Stresses were also investigated. The femoral neck cut placement had the most significant effect on the fragment displacement. Lowering it by 5 mm increased the gap and sliding fragment displacements by 288 and 128 %, respectively. Excessive cable tightening provided no significant reduction in fragment displacement. Muscle activities increased the gap and the sliding displacements for all muscle configurations. The maximum total displacement of 0.41 mm was present with a 10 mm femoral neck cut, a cable tension of 178 N, and stair climbing. Caution must be used not to over tighten the cables as the potential damage caused by the increased stress is more significant than any reduction in fragment displacement. Furthermore, preservation of the contact area is important for GT stabilization.

Biomechanical study of anterior spinal instrumentation configurations.

The biomechanical impact of the surgical instrumentation configuration for spine surgery is hard to evaluate by the surgeons in pre-operative situation. This study was performed to evaluate different configurations of the anterior instrumentation of the spine, with simulated post-operative conditions, to recommend configurations to the surgeons. Four biomechanical parameters of the anterior instrumentation with simulated post-operative conditions have been studied. They were the screw diameter (5.5-7.5 mm) and its angle (0 degrees - 22.5 degrees), the bone grip of the screw (mono-bi cortical) and the amount of instrumented levels (5-8). Eight configurations were tested using an experimental plan with instrumented synthetic spinal models. A follower load was applied and the models were loaded in flexion, torsion and lateral bending. At 5 Nm, average final stiffness was greater in flexion (0.92 Nm/degrees) than in lateral bending (0.56 Nm/degrees) and than in torsion (0.26 Nm/degrees). The screw angle was the parameter influencing the most the final stiffness and the coupling behaviors. It has a significant effect (p < or = 0.05) on increasing the final stiffness for a 22.5 degrees screw angle in flexion and for a coronal screw angle (0 degrees) in lateral bending. The bi-cortical bone grip of the screw significantly increased the initial stiffness in flexion and lateral bending. Mathematical models representing the behavior of an instrumented spinal model have been used to identify optimal instrumentation configurations. A variation of the angle of the screw from 22.5 degrees to 0 degrees gave a global final stiffness diminution of 13% and a global coupling diminution of 40%. The screw angle was the most important parameter affecting the stiffness and the coupling of the instrumented spine with simulated post-operative conditions. Information about the effect of four different biomechanical parameters will be helpful in preoperative situations to guide surgeons in their clinical choices.