Estimating the osteolysis-free life of a total hip prosthesis depending on the linear wear rate and head size.

We present a model to estimate the osteolysis-free life of total hip arthroplasty, depending on linear wear rate and femoral head size. An estimate of the radiologic osteolysis threshold was calculated, which was based on volumetric wear. The osteolysis-free life of the cup was estimated from the quotient of the osteolysis threshold and volumetric wear rate, which was calculated from the linear wear rate. The impact of the direction of linear wear was determined by sensitivity analysis. From our review, we calculated a weighted mean polyethylene volume of approximately 670 mm3 as osteolysis threshold. Osteolysis-free life of less than 20 years was estimated for linear wear rates of 50 µm/year for head sizes of 32 mm or more, or for linear wear rates of 100 µm/year for any head size. For head sizes of 36 and 40 mm with a linear wear rate of 50 µm/year, the osteolysis-free period is estimated to be only 14.10 and 11.42 years, respectively. Sensitivity analysis showed reasonably robust results. With the aim of osteolysis-free life of more than 20 years, our study presents a viable model to determine maximum possible head size for articulations. Osteolysis-free period for 36 and 40 mm head sizes are far too low for conventional polyethylenes. As the threshold wear volume for highly crosslinked polyethylene is, as of yet, unknown, more research is warranted before our model can be generalized to XLPE.

Fibrous cartilage of human menisci is less shock-absorbing and energy-dissipating than hyaline cartilage.

PURPOSE: To test meniscal mechanical properties such as the dynamic modulus of elasticity E* and the loss angle δ at two loading frequencies ω at different locations of the menisci and compare it to E* and δ of hyaline cartilage in indentation mode with spherical indenters. METHODS: On nine pairs of human menisci, the dynamic E*-modulus and loss angle δ (as a measure of the energy dissipation) were determined. The measurements were performed at two different strain rates (slow sinusoidal and fast single impact) to show the strain rate dependence of the material. The measurements were compared to previous similar measurements with the same equipment on human hyaline cartilage. RESULTS: The resultant E* at fast indentation (median 1.16 MPa) was significantly higher, and the loss angle was significantly lower (median 10.2°) compared to slow-loading mode's E* and δ (median 0.18 MPa and 16.9°, respectively). Further, significant differences for different locations are shown. On the medial meniscus, the anterior horn shows the highest resultant dynamic modulus. CONCLUSION: In dynamic measurements with a spherical indenter, the menisci are much softer and less energy-dissipating than hyaline cartilage. Further, the menisci are stiffer and less energy-dissipating in the middle, intermediate part compared to the meniscal base. In compression, the energy dissipation of meniscus cartilage plays a minor role compared to hyaline cartilage. At high impacts, energy dissipation is less than on low impacts, similar to cartilage.

Work stressors and resources in a Swiss orthopedic clinic and their relationship with employees' health and the patient orientation of employees.

QUESTIONS UNDER STUDY: At present, the health service system is under pressure to reduce costs. This situation is associated with risks for the health of the employees themselves, as well as for the quality of treatment and care. The aim of the study was to investigate stressors and resources which are present in the interactions of employees with patients at an orthopaedic clinic of a Swiss cantonal hospital and to analyse their relationship to the health of employees and their patient orientation. METHODS: A questionnaire was administered to 162 employees of different occupational groups at the clinic (including physicians, nurses and secretaries). In order to investigate the relationships between working conditions, employee health and the patient orientation of employees, correlations were calculated and regression analyses were conducted. RESULTS: The results of the study demonstrate that working conditions in the interaction with patients indeed predict health problems, as well as quality of health services provided. Especially stressors in the form of barriers to patient-oriented work are significant predictors of emotional exhaustion, aversion to patients, physical complaints and a (lower) patient orientation of employees. CONCLUSIONS: The results of the investigation of the clinic in question led to the formation of health circles, including the participation of different occupational groups, and to the introduction of measures for reducing stressors in the interaction with patients.