Yan Bourgeois

Improving greater trochanteric reattachment with a novel cable plate system.

Cable-grip systems are commonly used for greater trochanteric reattachment because they have provided the best fixation performance to date, even though they have a rather high complication rate. A novel reattachment system is proposed with the aim of improving fixation stability. It consists of a Y-shaped fixation plate combined with locking screws and superelastic cables to reduce cable loosening and limit greater trochanter movement. The novel system is compared with a commercially available reattachment system in terms of greater trochanter movement and cable tensions under different greater trochanteric abductor application angles. A factorial design of experiments was used including four independent variables: plate system, cable type, abductor application angle, and femur model. The test procedure included 50 cycles of simultaneous application of an abductor force on the greater trochanter and a hip force on the femoral head. The novel plate reduces the movements of a greater trochanter fragment within a single loading cycle up to 26%. Permanent degradation of the fixation (accumulated movement based on 50-cycle testing) is reduced up to 46%. The use of superelastic cables reduces tension loosening up to 24%. However this last improvement did not result in a significant reduction of the grater trochanter movement. The novel plate and cables present advantages over the commercially available greater trochanter reattachment system. The plate reduces movements generated by the hip abductor. The superelastic cables reduce cable loosening during cycling. Both of these positive effects could decrease the risks related to grater trochanter non-union.

Testing System for the Comparative Evaluation of Greater Trochanter Re‐attachment Devices

The scope of this study was to propose and validate a specialized test bench that applies biaxial forces on an orthopedic model of Greater Trochanter (GT) re-attachment with integrated cable tension measurement. Stability of the GT fragment is evaluated using a custom triplanar video movement-analysis system with the first camera’s field of view (FOV) corresponding to the GT osteotomy plane and the second and third camera’s FOVs corresponding to the median plane of the femur in frontal and posterior views, respectively. A typical experimentation and its critical analysis conclude the paper.

Effect of force tightening on cable tension and displacement in greater trochanter reattachment

The purpose of this study was to evaluate cable tension during installation, and during loading similar to walking in a cable grip type greater trochanter (GT), reattachment system. A 4th generation Sawbones composite femur with osteotomised GT was reattached with four Cable-Ready® systems (Zimmer, Warsaw, IN). Cables were tightened at 3 different target installation forces (178, 356 and 534 N) and retightened once as recommended by the manufacturer. Cables tension was continuously monitored using in-situ load cells. To simulate walking, a custom frame was used to apply quasi static load on the head of a femoral stem implant (2340 N) and abductor pull (667 N) on the GT. GT displacement (gap and sliding) relative to the femur was measured using a 3D camera system. During installation, a drop in cable tension was observed when tightening subsequent cables: an average 40+12.2% and 11±5.9% tension loss was measured in the first and second cable. Therefore, retightening the cables, as recommended by the manufacturer, is important. During simulated walking, the second cable additionally lost up to 12.2+3.6% of tension. No difference was observed between the GT-femur gaps measured with cables tightened at different installation forces (p=0.32). The GT sliding however was significantly greater (0.9±0.3 mm) when target installation force was set to only 178 N compared to 356 N (0.2±0.1 mm); p<0.001. There were no significant changes when initial tightening force was increased to 534 N (0.3±0.1 mm); p=0.11. In conclusion, the cable tightening force should be as close as possible to that recommended by the manufacturer, because reducing it compromises the stability of the GT fragment, whereas increasing it does not improve this stability, but could lead to cable breakage.

Finite element model of a greater trochanteric reattachment system

Detachment of greater trochanter (GT) is generally associated with hip arthroplasty complications and needs for repositioning and fixation. A new GT reattachment system (Y3) was proposed to reduce GT displacements in anterior-posterior direction to decrease non-union issues. The goal of this study is to develop and validate a FEM of the Y3 GTR system. FEM validation suggests a good concordance between numerical and experimental GT displacements. Sensitivity study show that the transition between proximal and distal branches of Y3 design is the most influent part on all GT displacements. The anterior branch affects more anterior-posterior displacements and rotation while the posterior branch affects more proximal displacements and rotation. This study provides an improved understanding of the influence of Y3 geometry on GT displacements.