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Abstract: Background: Helically shaped cephalic implants have proven their benefit to provide an improved stabilization of unstable hip fractures. However, cut out ratios up to 3.6% still occur. This in vitro study evaluated the biomechanical performance of a novel cement augmentation technique of the Proximal Femoral Nail Antirotation in surrogate femora. Methods: Four study groups were formed out of 24 polyurethane foam specimens with low density. Proximal Femoral Nail Antirotation blades were implanted, either non-augmented, or augmented using 3ml of injectable Polymethylmethacrylate bone-cement. The influence of implant mal-positioning was investigated by placing the blade either centered in the femoral head or off-centric in an anteroposterior direction. All specimens underwent cyclic loading under physiological conditions. Starting at 1000N, the load was monotonically increased by 0.1N/cycle until construct failure. Movement of the head was identified by means of optical motion tracking. Non-parametric test statistics were carried out on the cycles to failure, to compare between study groups. Findings: Compared to control samples; augmented samples showed a significantly increased number of cycles to failure (P =0.012). In the groups with centric position of the Proximal Femoral Nail Antirotation blade, cement augmentation led to an increase in loading cycles of 225%. In the groups with off-centric positioning of the blade, this difference was even more accentuated (933%). Interpretation: Cement augmentation of the Proximal Femoral Nail Antirotation blade with small amounts of bone-cement for treatment of osteoporotic hip fractures clearly enhances fixation stability and carries high potential for clinical application. [Copyright &y& Elsevier]

Abstract: The tension band principle as applied to transverse olecranon fractures fixed by tension band wiring is based on the premise that distraction forces on the outer cortex of the ulna during elbow flexion are converted to compression forces on the articular surface of the olecranon at the fracture site. In view of some clinical outcomes, where hardware failure and secondary dislocations occur, the question arises if the dynamic compression theory is correct. Compressive forces during active flexion and extension after tension band wiring of a transverse osteotomy of the olecranon were measured in 6 fresh frozen human cadaveric models using a pressure-sensor in the osteotomy gap. We could collect 30 measurements during active flexion and 30 during active extension. Active flexion did not cause any compressive forces in the osteotomy gap. Extension with the humerus in an upright position and the elbow actively extended causes some compression (0.37–0.51MPa) at the articular surface comparing with active flexion (0.2MPa) due to gravity forces. Posterior, there was no significant pressure difference observed (0.41–0.45 versus 0.36–0.32MPa) between active flexion and extension. The tension band wiring principle only exists during active extension in a range of 30–120° of flexion of the elbow. Postoperative exercise programs should be modified in order to prevent loss of compression at the fracture site of transverse olecranon fractures, treated with tension band wiring when the elbow is mobilised. [Copyright &y& Elsevier]

BACKGROUND: Tibiotalocalcaneal arthrodesis with a retrograde nail is an established procedure. Many patients considered for this arthrodesis have poor bone stock, which may make it difficult to obtain construct stability. This study was undertaken to determine whether stability could be enhanced by the cement augmentation of the calcaneal locking screws. METHODS: A cannulated and perforated screw, and a technique for cement augmentation via this screw, were developed. Eight pairs of human cadaver bones were instrumented with a retrograde intramedullary device (Expert Hindfoot Arthrodesis Nail, Synthes AG, Solothurn, Switzerland). Within each pair, one specimen was randomized to have the nail interlocked in the calcaneus with two conventional screws; while the other specimen was similarly instrumented with the use of two cement-augmented screws. The bone mineral density was determined. In quasi-static tests, the neutral zone and the range of motion of the constructs were determined. Subsequently the specimens were tested in dorsiflexion/plantar flexion until failure occurred. The neutral zone and the range of motion of the constructs were determined every 200 cycles. FINDINGS: Augmentation resulted in significantly greater stiffness and a significantly smaller range of motion in the quasi-static dorsiflexion/plantar flexion test, and in a significantly smaller neutral zone in all quasi-static tests. With cyclic loading, the number of cycles to failure was significantly larger in the augmented group. In both groups, bone mineral density was significantly correlated with the number of cycles to failure. Two augmented screws broke. INTERPRETATION: Cement augmentation confers significant mechanical benefit in hindfoot arthrodesis and therefore can be used as a salvage procedure. Further development should be performed to validate the concept. [ABSTRACT FROM AUTHOR]