Nailing versus plating for comminuted fractures of the distal femur: a comparative biomechanical in vitro study of three implants.

PURPOSE: The purpose of our study was to determine the biomechanical properties of three different implants utilized for internal fixation of a supracondylar femur fracture. The retrograde supracondylar nail (SCN), the less invasive stabilization system plate (LISS) and the distal femoral nail (DFN) were tested and their biomechanical properties compared. METHODS: Twenty pairs of fresh-frozen human femura were used. Each femur was osteotomised to simulate a comminuted supracondylar fracture (AO/OTA 33.A3) and then randomized to fracture fixation with either SCN (n=9) or LISS (n=9). Each contralateral femur was stabilized with DFN as a control (n=18). Two femur pairs were spent on pretesting. All femura were subjected to axial (10-500 N) and torsional (0.1-14 Nm) loading. RESULTS: Eighteen matched femur pairs were analyzed. The post-loading median residual values were 49.78, 41.25 and 33.51% of the axial stiffness of the intact femur and 59.04, 62.37 and 46.72% of the torsional stiffness of the intact femur in the SCN, LISS and DFN groups. There were no significant differences between the three implants concerning axial and torsional stiffness. CONCLUSIONS: All implants had sufficient biomechanical stability under physiological torsional and axial loading. All three implants have different mechanisms for distal locking. The SCN nail with the four-screw distal interlocking had the best combined axial and torsional stiffness whereas the LISS plate had the highest torsional stiffness.

Dynamic biomechanical analysis of different olecranon fracture fixation devices--tension band wiring versus two intramedullary nail systems: an in-vitro cadaveric study.

BACKGROUND: The aim of this study was to develop a test-setup with continuous angle alteration to imitate joint motion for the evaluation of 3 different olecranon fracture fixation devices. METHODS: Twenty-one fresh cadaver upper extremities underwent olecranon fracture by the means of transverse osteotomy and received 3 different fixation systems. Group 1: Tension band wiring according to Weber. Group 2: XS-nail with 9 holes, all locked with 2mm threaded K-wires. Group 3: Olecranon Nailing System with 90 mm length, locked with 2.7 mm screws, a variable angle locking hole for the proximal fragment and a proximal locking end cap. The servo-pneumatical test stand worked with a rotational angle-adjusted and a linear force-adjusted engine. The fracture model was dynamically tested under cyclic loading imitating elbow motion. There was a continuous angle alteration between 0 degrees and 100 degrees of flexion with continuous changing pull force between 25 N and 150 N. Two steel pins were placed in the proximal, two in the distal olecranon fragment for video analysis of the motion between the two pairs of pins. Displacement in the fracture gap was determined after 4 and 300 cycles. FINDINGS: After 300 cycles the displacement in the fracture fixation model was significantly higher in the tension-band-wiring-group than in the XS-nail group and the olecranon-nailing-system-group. INTERPRETATION: Other studies evaluating biomechanical properties of olecranon-osteosynthesis with joint-involvement did not change the force-direction dynamically. We introduce a test-setup with continuous angle alteration to imitate joint motion. This is an important step for accurate biomechanical evaluation of the treatment of different fixation methods in olecranon fractures. The tested nailing systems showed a higher stability in comparison to tension band wiring.

[Internal fixation of proximal humerus fractures]. / Osteosynthese von Oberarmkopffrakturen Einfluss des Implantatdesigns auf die biomechanische Stabilität.

BACKGROUND: Intramedullary nails and angle-fixed plates have recently been used in proximal humerus fractures. Rigid implants might be associated with an increased risk of failure in osteoporotic conditions. METHODS: Unstable fractures of the surgical neck were created in 24 pairs of human humeri. The biomechanical properties of four implants were analysed. These were a nail with conventional interlocking (PHN-K), a nail with spiral blade interlocking (PHN-S), the T-plate, and an internal fixator with elastic screw properties (reference). The specimens were subjected to axial loading and torque. Stiffness, plastic deformity, and load to failure were assessed. RESULTS: The PHN-S was stiffer than the internal fixator. The PHN-K and T-plate were stiffer only during torque. Less subsidence was observed for the PHN-S. This implant failed at higher loads than the other implants. CONCLUSIONS: The PHN-S offers biomechanical advantages in unstable fractures of the surgical neck of the humerus. Elastic implant properties, however, are disadvantageous.

[Are angle-fixed implants with elastic properties advantageous for the internal fixation of proximal humerus fractures?]. / Sind winkelstabile Plattensysteme mit elastischen Eigenschaften für die Stabilisierung der Oberarmkopffraktur vorteilhaft? Eine in-vitro biomechanische Untersuchung.

There is a recent interest for the use of angle-fixed plates in the management of proximal humerus fractures. Rigid implants might be associated with an increased risk of cutting-out. In order to analyse the potential beneficial effects of the implant elasticity on fracture fixation, the biomechanical properties of a rigid and an elastic angle-fixed plating system were assessed in an experimental study. An unstable fracture of the surgical neck was created in 8 pairs of human humeri. Specimens were subjected to axial loading and torque. Stiffness, subsidence and load to failure were assessed. The implant with elastic properties was characterized by a lower torsional stiffness and a higher subsidence during axial loading and torque. This implant failed at lower loads than the rigid implant did. Elastic implant properties of angle-fixed plates have shown not to be advantageous for the management of fractures of the proximal humerus.