Abstract
The incidence of comminuted proximal femur fractures is increasing, due to the growing proportion of elderly people in the general population. Severely depleted cancellous bone in the femoral head and neck prevent stable proximal purchase, mandatory for intertrochanteric and subtrochanteric fractures. Osteoporotic bones are associated with high implant failure rates, evidenced by cutout and upward screw penetration of the hip joint.
A new method for femoral head fixation is described. The peg consists of a distal end that can expand in diameter from 7.8mm to 10.5mm by using pressurized saline, allowing good abutment into the femoral head. The peg may be connected to a side plate or an intramedullary device for inter or subtrochanteric fractures.
Materials and Methods: Ten femoral heads were retrieved from patients who underwent hip hemiarthroplasty due to subcapital fracture. The heads were covered with a transparent epoxy resin until full solidification was obtained. An 8mm drill-hole was used to drill from the distal femoral neck along the femoral head axis, not penetrating the subchondral bone and cartilage. Afterwards, 1.4mm drill was used to penetrate the cartilage and subchondral bone of the femoral head for insertion of a pressure gage. Intraosseous pressure measurements were then recorded. The peri-prosthetic bone density was evaluated by Dual Energy X-ray Absorptiometry (DEXA) and Microradiography Computer Analysis in two stages: 1) with the peg unexpanded, and 2) with the peg expanded. In addition, Instron 8871 tested axial load, pullout and rotatory strengths of the peg.
Results: Increased periprosthetic bone density following peg expansion was demonstrated on DEXA and microradiography with no increase in the intraosseous pressure. The friction coefficient of the bone implant interface, calculated by axial load measurements, was less than the coefficient of steel to steel. Pullout and rotatory strengths were as good as those reported for the Dynamic Hip Screw (DHS).
Conclusions: Bone stock preservation due to compression of the depleted cancellous bone (rather than removed bone by drilling) may improve the mechanical properties of the periprosthetic bone and the stability of the fixation. Due to the strong abutment of the peg, hardware failure, mainly bone cutout can be reduced. Due to its lower friction coefficient, the hip peg will begin to slide following axial load through the plate or the intramedullary device, rather than penetrating the femoral head.
Preliminary positive results indicate that this new method may be suitable for inter or subtrochanteric femoral fracture fixation.
The abstracts were prepared by Orah Naor. Correspondence should be addressed to him at the Israel Orthopaedic Association, PO Box 7845, Haifa 31074, Israel.
