Der umgedrehte Plattenfixateur zur osteosynthetischen Stabilisierung bei erschwerter Frakturheilung am proximalen Femur

When is the stability of a fracture fixation limited by osteoporotic bone?

This article is concerned with the search for threshold values for bone quality beyond which the risk of fixation failure increased. For trochanteric fractures we recognized a BMD lower than 250mg/cm(3) as an additional risk for cut out. For medial femoral neck fractures since joint replacement surgery is available and produces excellent functional results, we see no indication for further differentiation or analysis of bone quality in relation to fracture fixation. In the area of osteoporotic vertebral body fractures, there are many experimental studies that try to identify BMD limits of screw fixation in the cancellous bone on the basis of QCT analysis. However, these values have not yet been introduced for application in clinical practice. In case of indication for surgical fixation, we favor minimally invasive, bisegmental, fourfold dorsal instrumentation with screw-augmentation for a T-value less than -2.0 SD (DXA analysis, total hip or total lumbar spine). For proximal humerus fractures, BMD value of 95mg/cm(3) could be seen as a threshold value below which the risk of failure rises markedly. In relation to osteoporotic distal radius fractures, based on our clinical experience and scientific analyses there are virtually no restrictions as far as bone quality is concerned on the application of palmar locking implants in the surgical management of distal radius fractures. Optimization of preoperative diagnostics might help to revise the treatment algorithm to take bone density into account, thus reducing the risk of failure and, at the same time, acquiring additional data for future reference.

Sliding of the load carrier in third-generation intramedullary nails for proximal femur fractures: an in vitro mechanical comparison study

Dynamic osteosynthesis of proximal femur fractures facilitates compression at the fracture site through distal glide of the femoral head load carrier in the intramedullary nail. Modern implants are currently designed according to diverse gliding principles. The aim of this study was to compare the sliding mechanisms of different types of nails. As in other similar mechanical studies the load patterns occurring around the femoral head load carrier and the intramedullary nail under full load were simulated for three different types of intramedullary nail - PFNA, Targon PFT and Trigen Intertan. The load necessary to trigger distal displacement of the femoral head implant in the nail was determined. The lengths of the load carriers were varied. For the three lengths of load carrier, mechanical testing showed that the Targon PFT started to slide at a significantly lower load compared to the other two implants. Comparison of the PFNA and Trigen Intertan in terms of load to dynamization for 77 mm carriers revealed a significantly lower load for the PFNA. Slide efficacy for the PFNA and the Trigen Intertan was found to improve as the length of the blade/screw was shortened. The dynamization properties of the Targon PFT with its cylindrical sliding mechanism, similar to the DHS, were far better compared to the PFNA and the Trigen Intertan that have more complex sliding actions. Since theoretical considerations indicate that a less efficient gliding action leads to a higher complication rate, implants of the next generation should be optimized in this regard.

Failure after osteosynthesis of trochanteric fractures. Where is the limit of osteoporosis?

SUMMARY

The aim of this study is to identify osteoporosis values, beyond which there is a high risk of osteosynthesis failure. Bone mineral density (BMD) of 30 cadaveric femora with a pertrochanteric fracture osteotomy was correlated to the risk of cut out after osteosynthesis on a biomechanical testing approach. For a BMD less than 250 mg/cm(3), there is a high risk of fixation failure after surgical treatment of pertrochanteric fractures. This value can be regarded as a reference value for future experimental and clinical studies.

INTRODUCTION

Despite continuous modification of intramedullary load carriers for the surgical stabilization of trochanteric fractures, cut out remains the most frequent complication. The aim of this experimental study was to identify threshold osteoporosis values, beyond which there is a high risk of osteosynthesis failure.

METHODS

Bone mineral density (BMD) of 30 cadaveric femora was recorded for the femoral head by QCT measurement. Subsequently, a standardized osteotomy mimicking an unstable trochanteric type fracture was stabilized by intramedullary nailing. The constructs were loaded axially at a force of 2,100 N up to 20,000 cycles. Cut out at the femoral head was documented by radiograph. Statistical evaluation of the cohort group was performed by calculation of relative risk in relation to the BMD values.

RESULTS

In total, there were six cases of cut out after 10,000 cycles. The incidence of cut out for BMD less than 250 mg/cm(3) was 0.55 (5 of 9) and for BMD greater than 250 mg/cm(3), it was 0.05 (1 of 21). Therefore, the relative risk of cut out for BMD <250 mg/cm(3) is 11× greater than for a BMD >250 mg/cm(3). After 20,000 cycles, an additional test caused one cut out (relative risk of cut out for a BMD <250 mg/cm(3) 5.8).

CONCLUSIONS

For a BMD less than 250 mg/cm(3), there is a high risk of fixation failure after surgical treatment of pertrochanteric fractures. Although this value is based on an experimental in vitro study design with all its associated limitations, it can be regarded as a reference value for future experimental and clinical studies.

Effects of muscle-equivalent forces on the biomechanical behavior of proximal femur fracture models: a pilot study on artificial bones

Introduction:

There has been extensive analysis of the influence of muscle forces and their effects on the biomechanical behavior of the proximal femur. Nevertheless, these forces have only been taken into account in a handful of biomechanical studies in the field of traumatology. The aim of this study was to analyze the biomechanical behavior of two typical fracture models of the proximal femur based on muscle-equivalent forces.

Method:

Plate osteosynthesis was performed on two groups of artificial femora to stabilize either a trochanteric osteotomy ( n = 5) or a femur shaft osteotomy ( n = 5). After fixation axial loading was applied to the constructs first without muscle-equivalent forces and then with the addition of these forces (abductor groups and vastus lateralis). Displacement at the osteotomy site and the stiffness of the whole construct were measured during loading.

Results:

Comparison of the two loading modes revealed no significant differences for displacement or stiffness for the trochanteric fractures. For the femur shaft fractures, a significant difference was found for displacement ( p = 0.023) and stiffness ( p = 0.003) with or without muscle-equivalent forces.

Conclusion:

The loading protocol for implant testing on femur shaft fractures should include muscle-equivalent forces. For trochanteric fractures, consideration of muscle forces is not entirely necessary since they will have little effect on the results, for example, when comparing implants.

Treatment of ipsilateral concomitant fractures of proximal extra capsular and distal femur

OBJECTIVES

Ipsilateral concomitant fractures of proximal extracapsular and distal femur are rare injuries and pose a great challenge for orthopaedics. In this study, we reviewed and examined the approaches and outcomes of this complex injury.

METHODS

From August 2002 to January 2010, seven patients (six males and one female) with a mean age of 39 years (range, 20-48 years) were involved in the study. They had suffered from ipsilateral concomitant fractures of proximal extracapsular and distal femur, with two cases of unstable intertrochanteric fractures, three cases of subtrochanteric fractures and two cases of extracapsular femoral neck fractures. The distal femoral fractures were categorised based on the Arbeitsgemeinschaft für Osteosynthes (AO) classification: 2, A3; 2, C1; 2, C2 and 1, C3, and the proximal femoral fractures were stabilised via nailing, whilst the distal ones via less-invasive stabilisation system-distal femur (LISS-DF) plating in all six patients. In the one with the 'floating knee' injury, the subtrochanteric fracture was stabilised by reversed LISS-DF, and the distal one, by retrograde nailing. The healing of each femoral fracture was evaluated radiologically and clinically with follow-up. The functional outcomes were assessed through the Friedman and Wyman system.

RESULTS

The mean follow-up interval was 2 years (range, 1.5-3 years). Six femoral fractures healed uneventfully, whilst the one with the 'floating knee' injury developed a delayed union postoperatively due to metal failure in 6 months, and, eventually, a malunion with coxa vara deformity 1.5 years later. The clinical functions at the final follow-up were found to be good in five cases, and fair and poor in one case each.

CONCLUSION

The nailing of a proximal femoral fracture and an LISS-DF fixation of a distal one could be a reliable and effective approach to handle ipsilateral concomitant fractures of a proximal extracapsular and distal femur.

Salvage procedures for trochanteric femoral fractures after internal fixation failure: Biomechanical comparison of a plate fixator and the dynamic condylar screw

The aim of this study was the biomechanical evaluation of the reversed less invasive stabilization system (LISS) internal fixation as a joint-preserving salvage procedure for trochanteric fractures. Five LISS plates and five dynamic condylar screws (DCS) were tested using synthetic femora (Sawbones®) with an osteotomy model similar to a type-A2.3 pertrochanteric fracture. The constructs were subjected to axial loading up to 1000 N for five cycles. Then, the force was continuously increased until fixation failure. For the evaluation of the biomechanical behaviour, the stiffness levels were recorded and the osteotomy gap displacement was mapped three-dimensionally. The average stiffness for the constructs with LISS plates was 412 N/mm (with a standard deviation (SD) of 103N/mm) and 572 N/mm (SD of 116 N/mm) for the DCS constructs ( p = 0.051). Local displacement at the osteotomy gap did not yield any significant differences. The LISS constructs failed at a mean axial compression of 2103 N (SD of 519 N) and the DCS constructs at a mean of 2572 N (SD of 372 N) ( p = 0.14). It is concluded that the LISS plate offers a reliable fixation alternative for salvage procedures.