Potential of polymethylmethacrylate cement-augmented helical proximal femoral nail antirotation blades to improve implant stability--a biomechanical investigation in human cadaveric femoral heads.

BACKGROUND: Cement augmentation may improve fixation stability and reduce cut-out rate in the treatment of intertrochanteric hip fractures. The aim of this study was to compare the number of cycles to failure of polymethylmethacrylate (PMMA)-augmented helical blades with nonaugmented ones in human cadaveric femoral heads. METHODS: Six pairs of cadaveric femoral heads were instrumented with a perforated proximal femoral nail antirotation blade. Within each pair, one blade was augmented using 3 mL of PMMA. All specimens underwent cyclic axial loading under physiologic conditions.Starting at 1,000 N, the load was monotonically increased by 0.1 N/cycle until construct failure occurred. To monitor the migration of the blade, anteroposterior radiographs were taken at 250 cycle increments. Nonparametric test statistics were done to calculate correlations and identify differences between study groups. RESULTS: Inducing failure required a significantly higher number of cycles in the augmented group (p = 0.028). Bone mineral density was significantly related with the number of cycles to failure in nonaugmented specimens (p 0.001, R2 = 0.97), but not in the augmented group (p = 0.91, R2 = 0.34). CONCLUSION: Implant augmentation with small amounts of PMMA enhances the cut-out resistance in proximal femoral fractures. Especially in osteoporotic bone, the procedure may improve patient care.

Cardiovascular changes after PMMA vertebroplasty in sheep: the effect of bone marrow removal using pulsed jet-lavage.

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.

The effect of pulsed jet lavage in vertebroplasty on injection forces of PMMA bone cement: an animal study.

Percutaneous vertebroplasty, comprising of the injection of polymethylmethacrylate (PMMA) into vertebral bodies, is an efficient procedure to stabilize osteoporotic compression fractures as well as other weakening lesions. Besides fat embolism, cement leakage is considered to be one of the major and most severe complications during percutaneous vertebroplasty. The viscosity of the PMMA during injection plays a key role in this context. It was shown in vitro that the best way to lower the risk of cement leakage is to inject the cement at higher viscosity, which is requires high injection forces. Injection forces can be reduced by applying a newly developed lavage technique as it was shown in vitro using human cadaver vertebrae. The purpose of this study was to prove the in vitro results in an in vivo model. The investigation was incorporated in an animal study that was performed to evaluate the cardiovascular reaction on cement augmentation using the lavage technique. Injection forces were measured with instrumentation for 1 cc syringes, additionally acquiring plunger displacement. Averaged injection forces measured, ranged from 12 to 130 N and from 28 to 140 N for the lavage group and the control group, respectively. Normalized injection forces (by viscosity and injection speed) showed a trend to be lower for the lavage group in comparison to the control group (P = 0.073). In conclusion, the clinical relevance on the investigated lavage technique concerning lowering injection forces was only shown by trend in the performed animal study. However, it might well be that the effect is more pronounced for osteoporotic vertebral bodies.

Temperature evaluation during PMMA screw augmentation in osteoporotic bone--an in vitro study about the risk of thermal necrosis in human femoral heads.

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.