[Biomechanical investigation of fixed-angle plate osteosynthesis of the proximal humerus]

[Pathological and metabolic bone diseases: Clinical importance for fracture treatment]

Pathological and metabolic bone diseases are common and relevant occurrences in orthopedics and trauma surgery; however, fractures are often treated as being the illness itself and not seen as the symptom of an underlying bone disease. This is why further diagnostics and systemic treatment options are often insufficiently considered in the routine treatment of fractures. This review focuses on osteoporosis, osteopetrosis, hypophosphatasia and Paget's disease of bone.In patients with osteoporotic vertebral or proximal femur fractures, pharmaceutical treatment to prevent subsequent fractures is an integral part of fracture therapy together with surgical treatment. Osteopetrosis is caused by compromised osteoclastic bone resorption; therefore, even in the face of an elevated bone mass, vitamin D3 supplementation is crucial to avoid clinically relevant hypocalcemia. Unspecific symptoms of the musculoskeletal system, especially together with stress fractures, are typically found in patients suffering from hypophosphatasia. In these patients measurement of alkaline phosphatase shows reduced enzyme activity. Elevated levels of alkaline phosphatase are found in Paget's disease of bone where bisphosphonates are still the treatment of choice.

Mono- versus polyaxial locking plates in distal femur fractures: a prospective randomized multicentre clinical trial

PURPOSE

Treatment of complex fractures of the distal femur utilizing monoaxial locking plates (e.g. Less Invasive Stabilisation System, LISS®, Synthes) is considered to be superior to conventional plating systems. Due to the limitation that the thread forces the screw into pre-determined positions, modifications have been made to allow screw positioning within a range of 30° (Non Contact Bridging, NCB®-DF, Zimmer). For the first time, this multicenter prospective randomized clinical trial (RCT) investigates the outcome of LISS® vs. NCB®-DF treatment following complex fractures of the distal femur.

METHODS

Since June 2008, 27 patients with a fracture of the distal femur (AO ASIF 33-A-C and periprosthetic fractures) were enrolled in this study by four university trauma centres in southern Germany. Clinical (e.g. range of motion, Oxford knee score, Tegner score) and radiological (e.g. axis deviation, secondary loss of realignment) follow-ups were conducted one and six weeks, as well as three, six, and 12 months after the operation.

RESULTS

This study comprises data of 27 patients (8 male, 19 female; 15 NCB®-DF, 12 LISS®). Polyaxial osteosynthesis using the NCB® system tended to result in better functional knee scores and a higher range of motion. Interestingly, fracture union tended to be more rapid using the polyaxial plating system.

CONCLUSIONS

We present the analysis of a multicenter prospective RCT to compare the monoaxial LISS® vs. the polyaxial NCB®-DF treatment following complex fractures of the distal femur. NCB®-DF treatment tended to result in better functional and radiological outcomes than LISS® treatment.

LEVEL OF EVIDENCE

Level I.

Auxiliary locking plate improves fracture stability and healing in intertrochanteric fractures fixated by intramedullary nail

BACKGROUND

Intertrochanteric fractures present a significant management challenge due to their low inherent stability. The objective of this study was to determine whether an auxiliary locking plate decreases interfragmentary motions and improves fracture healing in intertrochanteric fractures treated by intramedullary nail.

METHODS

Biomechanical tests and a clinical retrospective study in intertrochanteric to subtrochanteric nonunions were performed. Six synthetic femurs were osteotomized intertrochanterically and fixated with a long gamma nail and an additional locking compression plate. Mechanical tests were conducted that simulated the hip joint force during gait cycle. Following the initial test, the locking compression plate (LCP) was removed from each specimen and the test was repeated. Interfragmentary motions, strains on implants and osteosynthesis stiffness were determined. For the clinical part of the study, 13 intertrochanteric to subtrochanteric nonunions were treated with revisional long gamma nail and additional locking compression plate. Complications and time to union were determined.

FINDINGS

Biomechanically, interfragmentary rotation was 48% smaller (P=0.047) and interfragmentary shear movement was 42% smaller (P=0.007) with locking compression plate. Strains on the nail decreased by 20-27% (P<0.027) and the osteosynthesis stiffness increased by 23% (P=0.005) with locking compression plate. Clinically, fracture healing was achieved in eleven out of 13 patients after 9.0months (range 4 to 22months).

INTERPRETATION

The findings of our study indicate that auxiliary locked plating considerably improves biomechanical performance and results in successful healing of unstable intertrochanteric to subtrochanteric femur fractures.

Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

OBJECTIVE

The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.

METHODS

On nine pairs of randomised formalin fixed humerus specimens, standardised osteotomies and osteosyntheses with nine monoaxial (group A) und nine polyaxial (group B) plate/screw systems were performed. A material testing machine by Instron (M-10 14961-DE) was used for cyclic stress tests and crash tests until defined breakup criteria as endpoints were reached.

RESULTS

After axial cyclic stress 200 times at 90 N, plastic deformation was 1.02 mm in group A and 1.25 mm in group B. After the next cycle using 180 N the additional deformation averaged 0.23 mm in group A and 0.39 mm in group B. The deformation using 450 N was 0.72 mm in group A compared to 0.92 mm in group B. The final full power test resulted in a deformation average of 0.49 mm in group A and 0.63 mm in group B after 2,000 cycles using 450 N. When reaching the breakup criteria the plastic deformation of the NCB plate was 9.04 mm on average. The PHILOS plate was similarly deformed by 9.00 mm. As a result of the crash test, in group A the screws pulled out of the humeral head four times whereas the shaft broke one time and another time the implant was ripped out. The gap was closed four times. In group B, there were three cases of screw cut-through, four shaft fractures/screw avulsions from the shaft and two cases of gap closure.

CONCLUSION

The two systems resist the cyclic duration tests and the increasing force tests in a similar manner. The considerable clinical benefits of the polyaxial system are enhanced by equal biomechanical performance.