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Background: Vertebral compression fractures are the most common osteoporotic fractures. Since the introduction of vertebroplasty and screw augmentation, the management of osteoporotic fractures has changed significantly., Aims: The biomechanical characteristics of the risk of adjacent fractures and novel treatment modalities for osteoporotic vertebral fractures, including pure cement augmentation by vertebroplasty, and cement augmentation of screws for posterior instrumentation, are explored., Materials and Methods: Eighteen human osteoporotic lumbar spines (L1-5) adjacent to vertebral bodies after vertebroplasty were tested in a servo-hydraulic machine. As augmentation compounds we used standard cement and a modified low-strength cement. Different anchoring pedicle screws were tested with and without cement augmentation in another cohort of human specimens with a simple pull-out test and a fatigue test that better reflects physiological conditions., Results: Cement augmentation in the osteoporotic spine leads to greater biomechanical stability. However, change in vertebral stiffness resulted in alterations with the risk of adjacent fractures. By using a less firm cement compound, the risk of adjacent fractures is significantly reduced. Both screw augmentation techniques resulted in a significant increase in the withdrawal force compared with the group without cement. Augmentation using perforated screws showed the highest stability in the fatigue test., Discussion and Conclusion: The augmentation of cement leads to a significant change in the biomechanical properties. Differences in the stability of adjacent vertebral bodies increase the risk of adjacent fractures, which could be mitigated by a modified cement compound with reduced strength. Screws that were specifically designed for cement application displayed greatest stability in the fatigue test.

Contact between high-frequency cauterising instruments and metal endoprostheses can cause visible flashovers. The resulting local heating might partially transform the microstructure of the prostheses. In the present case a flashover to the in situ titanium hip endoprosthesis during the revision of a fractured ceramic head decreased the fatigue strength of the prosthesis and ultimately caused its failure. During revision surgery it is essential to prevent contact between in situ metal components and high-frequency cauterising instruments.

In order to allow speedy mobilization after vertebral body replacement, high primary stability as well as prevention of implant dislocation are required. It is unclear whether differences between common vertebral body replacement systems exist and whether spreadable implants improve primary stability. Migration characteristics of 3 different vertebral body replacement systems were determined using human lumbar spine specimens. Primary stability was assessed by loading specimens successively in 5 conditions: native, after dorsal spondylodesis, after laminectomy and after vertebral body replacement. Migration was shown to depend on cage design and spike shape. Dorsal spondylodesis in combination with vertebral body replacement reduced flexion/extension movement effectively independent of cage design. Stabilization potential in lateral bending was limited. None of the cages limited movement under torsional loading effectively. The possibility to spread the cage had a positive effect on stabilization.

Periacetabular surface deformation of the pelvis and micromotion between implant and bone were measured in three cementless acetabular components. Pelvic deformation was greater in cementless implants than in cemented ones-independent of the stiffness of the implant. The results of micromotion measurements confirmed the function of certain of anchorage concepts, but they also illustrated the limitations of such measurements in single locations.