Two calcium phosphate cements, one monophasic and the other biphasic, have been used as bone void filler in a sheep model. The cements were injected into a slot defect in the proximal tibia and into a cylindrical defect in the distal femur. In this study, we focused on the resorption pattern of the two cement formulations and the subsequent biologic reaction. Bone remodeling occurred synchronously with the resorption of the implant material in a creeping substitution process. Cracks and pores in the monophasic cement were filled with osseous tissues. The biphasic cement showed faster resorption of the matrix. The more slowly resorbing granules were surrounded by newly grown bone, thus providing an inverse scaffold for cancellous bone regeneration. In highly loaded areas, the long-term support function of the fixation appears to be critical. Because cortical bridging of the defects was seen in only one case, it can be concluded that calcium-phosphate cements are preferentially suitable as cancellous bone substitute materials.

The use of polymethylmethacrylate (PMMA) bone cement to augment hip screws reduces cut-out risk but is associated with an exothermic reaction. This in vitro investigation evaluated the risk of thermal necrosis when augmenting the implant purchase with PMMA. A pilot study analyzed the effects of different PMMA layer thicknesses on temperatures around an implant. The main study used either 3.0 or 6.0 cc PMMA for hip screw augmentation in human femoral heads. The risk of thermal necrosis was estimated according to critical values reported in literature. Highest temperatures were measured inside the PMMA with a significant drop of average maximum temperatures from the center of the PMMA to the PMMA/bone interface. Risk of thermal necrosis exists with PMMA layer thicknesses greater than 5.0 mm. In the main study, we found no risk of thermal necrosis at the PMMA/bone interface or in the surrounding bone, neither with 3.0 nor 6.0 cc PMMA. The results of the two studies were consistent regarding average peak temperatures related to associated cement layer thicknesses. The results of this in vitro study reduce objections concerning the risk of thermal necrosis when augmenting cancellous bone around hip screws with up to 6.0 cc PMMA.

A biomechanical investigation on eight pairs of human cadaver proximal femurs was performed to evaluate the impact of a new augmentation method on the internal fixation of osteoporotic proximal femur fractures. The study focused on enhancing implant purchase to reduce the incidence of implant cut-out in osteoporotic bone. In a left-right comparison, a conventional hip screw fixation (control) was compared to the new cement augmentation method. After bone bed preparation through high pressure irrigation to remove fat, blood, and bone debris, the bones were augmented with low viscosity polymethylmethacrylate (PMMA) cement.Step-wise fatigue testing was performed by cyclically loading the femoral heads in a physiological manner, beginning at 1,500 N and increasing 500 N every 5,000 cycles to 4,000 N, and continuously monitoring head displacement. Failure was defined as >5.0 mm head displacement. The head displacement at 2,000 N was significantly smaller (p ¼ 0.018) for the augmented group as compared to the conventionally treated bones (0.09 AE 0.01 mm vs. 0.90 AE 0.32 mm; mean AE SEM). The displacement rate at the second load step was significantly higher (p ¼ 0.018) for the conventionally treated bones as compared to the augmented ones. All of the nonaugmented specimens failed during testing, where 50% of the augmented specimens did not fail. The promising results of these experiments suggest that this new standardized irrigation/augmentation method enhances the implant anchorage and offers a potential solution to the problem of implant cut-out in osteoporotic metaphyseal bone. ß

Facetectomy causes a nominal increase in ROM and NZ in FE and LB, which are not affected by the addition of a crosslink. Although the effect of facetectomy is greater in AR-and crosslink has a measurable restoring effect-all differences are within a few tenths of a degree under this loading paradigm. Thus, the clinical utility of adding a crosslink may not be justified based on these small biomechanical changes. COM can serve as a complement to ROM and NZ, or even as a surrogate when its 2 components are reported together, as it shows strong agreement with ROM, effectively distinguishes between lax and elastic region behaviors, and provides a measure of flexibility independent of the load range.

Clinically, the displacement of intravertebral fat into the circulation during vertebroplasty is reported to lead to problems in elderly patients and can represent a serious complication, especially when multiple levels have to be treated. An in vitro study has shown the feasibility of removing intravertebral fat by pulsed jet-lavage prior to vertebroplasty, potentially reducing the embolization of bone marrow fat from the vertebral bodies and alleviating the cardiovascular changes elicited by pulmonary fat embolism. In this in vivo study, percutaneous vertebroplasty using polymethylmethacrylate (PMMA) was performed in three lumbar vertebrae of 11 sheep. In six sheep (lavage group), pulsed jet-lavage was performed prior to injection of PMMA compared to the control group of five sheep receiving only PMMA vertebroplasty. Invasive recording of blood pressures was performed continuously until 60 min after the last injection. Cardiac output and arterial blood gas parameters were measured at selected time points. Post mortem, the injected cement volume was measured using CT and lung biopsies were processed for assessment of intravascular fat. Pulsed jet-lavage was feasible in the in vivo setting. In the control group, the injection of PMMA resulted in pulmonary fat embolism and a sudden and significant increase in mean pulmonary arterial pressure. Pulsed jet-lavage prevented any cardiovascular changes and significantly reduced the severity of bone marrow fat embolization. Even though significantly more cement had been injected into the lavaged vertebral bodies, significantly fewer intravascular fat emboli were identified in the lung tissue. Pulsed jet-lavage prevented the cardiovascular complications after PMMA vertebroplasty in sheep and alleviated the severity of pulmonary fat embolism.