Fracture fixation in osteoporotic bone

Abstract

The incidence of osteoporotic fractures will drastically increase in the future as a result of the worldwide demographic change. New challenges for the health care system include not only the rising number of elderly fracture patients requiring surgical treatment, but also the increasing complexity of the single intervention. Post-op mechanical complications occur due to diminished bone mass rendering fracture stabilization considerably difficult. New treatment strategies are needed to encounter these developments.

Within the scope of this thesis, a 3-step approach for osteoporotic fracture management is evaluated from a biomechanical perspective in 20 individual experimental studies. The approach involves:

1. A novel concept for intra-operative assessment of bone strength as potentially important parameter for surgical decision making. 2. A novel design of bone fixation elements, optimized for enhanced anchorage in diminished bone mass: the helical blade. 3. Application of bone cement at the implant-bone interface for additional reinforcement of the implant purchase.

Performance of a bone-strength measuring device was experimentally investigated at the hip, in spine and at the hind-foot. The device involves insertion of a probe into cancellous bone and measurement of the trabeculae's breakaway torque by turning the probe. Measured values correlated significantly with the mechanical fatigue performance of the bone-implant construct. The device output could be used e.g. for decisions on application of bone cement or on a specific implant.

With regard to implant design, the performance of a helical blade for use in osteoporotic bone was experimentally evaluated. At the proximal femur, at the hind-foot and at the proximal humerus, the blade revealed a statistically significant but rather moderate biomechanical advantage over threated bone screws. It was believed that the improvement may result from cancellous bone compaction while inserting the blade. However, further studies suggested that, contrary to common thinking, compaction does not contribute to enhanced mechanical anchorage of the fixation device.

From these experiences, it was hypothesized that in severely porotic bone, the potential of conventional metallic implants is exploited. The additional strategy of implant augmentation with bone cement was biomechanically investigated in several anatomical key-regions: the proximal femur, the proximal tibia, the hind-foot and the proximal humerus. The experiments revealed a significant potential to enhance fracture fixation in porotic bone, but also suggest that cement augmentation cannot be applied as a routine concept. Potential risk factors associated with cement application, such as generation of heat and pressure, were experimentally judged to draw a comprehensive picture of the concept to increase confidence for clinical use.