Effect of head size and rotation on taper corrosion in a hip simulator

Aims This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads. Methods In all, six 28 mm and six 36 mm titanium stem-cobalt chrome head pairs with polyethylene sockets were tested in a novel instrumented hip simulator. Samples were tested using simulated gait data with incremental increasing loads to determine corrosion onset load and electrochemical activity. Half of each head size group were then cycled with simulated gait and the other half with gait compression only. Damage was measured by area and maximum linear wear depth. Results Overall, 36 mm heads had lower corrosion onset load (p = 0.009) and change in open circuit potential (OCP) during simulated gait with (p = 0.006) and without joint movement (p = 0.004). Discontinuing gait’s joint movement decreased corrosion currents (p = 0.042); however, wear testing showed no significant effect of joint movement on taper damage. In addition, 36 mm heads had greater corrosion area (p = 0.050), but no significant difference was found for maximum linear wear depth (p = 0.155). Conclusion Larger heads are more susceptible to taper corrosion; however, not due to frictional torque as hypothesized. An alternative hypothesis of taper flexural rigidity differential is proposed. Further studies are necessary to investigate the clinical significance and underlying mechanism of this finding

T-Lymphocytes Enable Osteoblast Maturation via IL-17F during the Early Phase of Fracture Repair

While it is well known that the presence of lymphocytes and cytokines are important for fracture healing, the exact role of the various cytokines expressed by cells of the immune system on osteoblast biology remains unclear. To study the role of inflammatory cytokines in fracture repair, we studied tibial bone healing in wild-type and Rag1−/− mice. Histological analysis, µCT stereology, biomechanical testing, calcein staining and quantitative RNA gene expression studies were performed on healing tibial fractures. These data provide support for Rag1−/− mice as a model of impaired fracture healing compared to wild-type. Moreover, the pro-inflammatory cytokine, IL-17F, was found to be a key mediator in the cellular response of the immune system in osteogenesis. In vitro studies showed that IL-17F alone stimulated osteoblast maturation. We propose a model in which the Th17 subset of T-lymphocytes produces IL-17F to stimulate bone healing. This is a pivotal link in advancing our current understanding of the molecular and cellular basis of fracture healing, which in turn may aid in optimizing fracture management and in the treatment of impaired bone healing

The Effect of Sustained Compression on Oxygen Metabolic Transport in the Intervertebral Disc Decreases with Degenerative Changes

Intervertebral disc metabolic transport is essential to the functional spine and provides the cells with the nutrients necessary to tissue maintenance. Disc degenerative changes alter the tissue mechanics, but interactions between mechanical loading and disc transport are still an open issue. A poromechanical finite element model of the human disc was coupled with oxygen and lactate transport models. Deformations and fluid flow were linked to transport predictions by including strain-dependent diffusion and advection. The two solute transport models were also coupled to account for cell metabolism. With this approach, the relevance of metabolic and mechano-transport couplings were assessed in the healthy disc under loading-recovery daily compression. Disc height, cell density and material degenerative changes were parametrically simulated to study their influence on the calculated solute concentrations. The effects of load frequency and amplitude were also studied in the healthy disc by considering short periods of cyclic compression. Results indicate that external loads influence the oxygen and lactate regional distributions within the disc when large volume changes modify diffusion distances and diffusivities, especially when healthy disc properties are simulated. Advection was negligible under both sustained and cyclic compression. Simulating degeneration, mechanical changes inhibited the mechanical effect on transport while disc height, fluid content, nucleus pressure and overall cell density reductions affected significantly transport predictions. For the healthy disc, nutrient concentration patterns depended mostly on the time of sustained compression and recovery. The relevant effect of cell density on the metabolic transport indicates the disturbance of cell number as a possible onset for disc degeneration via alteration of the metabolic balance. Results also suggest that healthy disc properties have a positive effect of loading on metabolic transport. Such relation, relevant to the maintenance of the tissue functional composition, would therefore link disc function with disc nutrition

Image registration demonstrates the growth plate has a variable affect on vertebral strain

Characterizing the biomechanical behavior of the vertebrae is important in understanding the impact of structural and material changes on spinal growth and fracture risk. The growth plate is critical for the normal development of the skeleton, with abnormalities leading to uneven maturation. Little is known about how growth plates affect the stress and strain experienced by the surrounding bone. Concentrated strain within the growth plate may influence mechanical cell signaling during development, lead to increased fracture risk at this site and may influence average bone strain measures. It is hypothesized that the growth plates and adjacent bony areas will take up a large amount of the strain within rat-tail vertebrae under axial compressive loading, leading to increased average bone strain measures. The sixth caudal vertebrae of 8 rnu/rnu rats were muCT scanned in both loaded (20-32 N axial compression) and unloaded configurations. Image registration was used to calculate strain in the bone due to the applied load by finding a spatial mapping between the two scans. In seven of the eight rats, the majority of the strain measured within their vertebrae was concentrated in the growth plates. Five of the specimens had growth plates that demonstrated rigid behavior in contrast to compliant growth plate behavior seen in the other three rats. The presence of a compliant growth plate led to higher average (-0.03 vs. -0.01) and maximum (-0.13 vs. -0.02) strains. The strain within the growth plate is important to consider when interpreting apparent tissue level biomechanical data commonly reported in the literature as this study suggests strains are not uniformly distributed with high concentrations in and around the growth plate. This strain distribution may provide insight into the mechanical signals that cells experience during the formation of new bone, with the higher strains near the growth plate signaling cells to lay down more bone, while also leading to increased risk of fracture in this region

Avaliação do tratamento cirúrgico nos pacientes com metástase vertebral secundária ao carcinoma de mama Evaluación del tratamiento quirúrgico en pacientes con metástasis vertebrales secundarias a carcinoma de mama Evaluation of surgical treatment of patients with vertebral metastasis secondary to breast carcinoma

OBJETIVO: Avaliar os resultados cirúrgicos dos pacientes com metástase vertebral secundária ao carcinoma de mama. MÉTODOS: Vinte e duas pacientes operadas com doença metastática vertebral secundária ao carcinoma de mama foram avaliadas no pré-operatório, pós-operatório imediato e depois de 1 mês e 6 meses do procedimento cirúrgico, usando a escala numérica da dor e o índice de incapacidade de Oswestry (ODI). RESULTADOS: As medidas para dor produziram valor de p de 0,0001 para a diferença entre o pré-operatório e o pós-operatório imediato, 0,0005 entre o pós-operatório imediato e 1 mês de pós-operatório, e 0,0908 entre 1 mês de pós-operatório e 6 meses de pós-operatório, portanto, encontram-se evidências de diferenças entre o pré-operatório e o pós-operatório imediato, assim como entre o pós-operatório imediato e após o 1º mês, mas não há tal evidência entre o 1º e o 6º mês de pós-operatório. Quanto ao ODI, a diferença foi significativa em todos os períodos. CONCLUSÃO: A cirurgia melhora a dor e diminui a incapacidade dos pacientes com doença metastática secundária ao carcinoma de mama.<br>OBJETIVO: Evaluar los resultados quirúrgicos de los pacientes con metástasis vertebrales secundarias a carcinoma de mama. MÉTODOS: Veintidós pacientes operados con enfermedad metastásica espinal secundaria a carcinoma de mama fueron evaluadas antes de la cirugía, inmediatamente después de la operación y después de 1 mes y 6 meses de la cirugía, mediante la escala numérica del dolor y el índice de discapacidad de Oswestry. RESULTADOS: Las medidas para el dolor produjeron un valor de "p" de 0,0001 para la diferencia entre el pre y postoperatorio, 0,0005 entre el postoperatorio inmediato y un mes después de la operación, y 0,0908 entre 1 mes después de la cirugía y el postoperatorio de 6 meses, por lo tanto, son la evidencia de las diferencias entre el pre y postoperatorio, así como entre el postoperatorio inmediato y después de un mes, pero no hay evidencia de tales diferencias entre 1 y 6 meses después de la operación. En cuanto al ODI, la diferencia fue significativa en todas las épocas. CONCLUSIÓN: El procedimiento mejora el dolor y reduce la discapacidad en pacientes con enfermedad metastásica secundaria a carcinoma de mama.<br>OBJECTIVE: To evaluate the surgical outcomes of patients with spinal metastasis secondary to breast carcinoma. METHODS: Twenty-two patients operated spinal metastatic disease secondary to breast carcinoma were assessed preoperatively, immediately postoperatively and after 1 and 6 months of surgery, using the numerical scale of pain and Oswestry Disability Index (ODI). RESULTS: The measures for pain produced a p-value of 0.0001 for the difference between the preoperative and postoperative, 0.0005 between the immediate postoperative period and 1 month postoperatively, and 0.0908 between 1 month and six months postoperatively, therefore, there is evidence of differences between the preoperative and postoperative periods, as well as between the immediate postoperative and after the 1st month, but there is no such evidence between 1st and 6th month postoperatively. As for the ODI, the difference was significant in all periods. CONCLUSION: The procedure improves pain and reduces disability in patients with metastatic disease secondary to breast cancer