Evaluation of Adaptive Bone Remodeling after Total Hip Arthroplasty Using Finite Element Analysis

We compared equivalent stress and strain energy density (SED) to bone mineral density (BMD) in the femur after total hip arthroplasty (THA) using subject-specific finite element analysis (FEA). Equivalent stress and BMD were maintained in the distal femur after THA, whereas both decreased in the proximal femur. A significant correlation was observed between the rates of changes in BMD and equivalent stress before and after THA. Therefore, FEA can predict adaptive bone remodeling after mechanical loading changes. Additionally, we evaluated the effects of two different types of stem geometries (Zweymüller-type stem and fit-and-fill-type stem) on load distribution and BMD using the same method. Equivalent stress and BMD in the medial side of the proximal femur were significantly lower with the Zweymüller-type stem than with the fit-and-fill-type stem. Therefore, FEA can assess the effects of stem geometry on bone remodeling after THA. Moreover, we evaluated the effects of bone geometry on load distribution and BMD after THA. Equivalent stress in the medial side of the proximal femur was significantly lower in the stovepipe model implanted with large tapered wedge-type stems than in the champagne flute and intermediate models, and there was a significant loss of BMD in the stovepipe model. Therefore, a large tapered wedge-type stem and stovepipe femur may be associated with significant proximal BMD loss

The Effectof Insert of WC Powder on the Surface Hardening of Non Magnetic Foundry Materials

Non magnetic foundry materials such as the austenitic stainless cast steel had not been used for abrasion resistant materials, because their hardnesses were very low. Usually, ceramics, cermets and cemented carbides are used for the abrasion resistant materials even though they are expensive compared with foundry materials. In this study, WC powder were inserted by using the austenitic stainless cast steel (JIS SCS13A) and the austenitic cast iron (JIS FCA-NiCr202) for producing surface hardened non magnetic materials. The melting temperature (pouring temperature) is lower in the austenitic cast iron than in the austenitic stainless cast steel while the fluidity of the melts is superior in the austenitic cast iron. For the WC powder inserted specimens, the hardness, the abrasion resistance and the magnetic property were examined. As a result, it was found that the hardness in the region of inserted WC powder was much higher than that of base metals of the cast steel and the cast iron, and that the magnetic permeability did not change by the inserting. Especially, a lot of WC powder was found to dissolve into the base metal in the cast steel than in the cast iron. In the case of the cast steel, Fe3W3C compound phase having high hardness of HV800 was formed in the region of inserted WC powder. The hardness in the region of inserted WC powder was higher in the cast steel than in the cast iron, because the cast steel contained a lot of chromium compared with the cast iron

The Effectof Insert of WC Powder on the Surface Hardening of Non Magnetic Foundry Materials

Non magnetic foundry materials such as the austenitic stainless cast steel had not been used for abrasion resistant materials, because their hardnesses were very low. Usually, ceramics, cermets and cemented carbides are used for the abrasion resistant materials even though they are expensive compared with foundry materials. In this study, WC powder were inserted by using the austenitic stainless cast steel (JIS SCS13A) and the austenitic cast iron (JIS FCA-NiCr202) for producing surface hardened non magnetic materials. The melting temperature (pouring temperature) is lower in the austenitic cast iron than in the austenitic stainless cast steel while the fluidity of the melts is superior in the austenitic cast iron. For the WC powder inserted specimens, the hardness, the abrasion resistance and the magnetic property were examined. As a result, it was found that the hardness in the region of inserted WC powder was much higher than that of base metals of the cast steel and the cast iron, and that the magnetic permeability did not change by the inserting. Especially, a lot of WC powder was found to dissolve into the base metal in the cast steel than in the cast iron. In the case of the cast steel, Fe3W3C compound phase having high hardness of HV800 was formed in the region of inserted WC powder. The hardness in the region of inserted WC powder was higher in the cast steel than in the cast iron, because the cast steel contained a lot of chromium compared with the cast iron

Influence of Pelvic Tilt on Polyethylene Wear after Total Hip Arthroplasty

We aimed to evaluate the effects of pelvic tilt on polyethylene wear after total hip arthroplasty (THA). A total of 105 joints treated with primary THA were included; conventional polyethylene (CPE) liners were used in 43 hips and highly cross-linked polyethylene (HXLPE) liners were used in the remaining 62 hips. The pelvis was tilted 6° posteriorly in the standing position as compared to the supine position, which resulted in significant increases of 1.7° and 2.8° in cup inclination in the CPE and HXLPE groups, respectively. Moreover, the change in pelvic tilt resulted in significant increases of 3.6° and 4.9° in cup anteversion in the CPE and HXLPE groups, respectively. For the CPE group, multiple regression analysis showed a significant association between the angle of pelvic tilt (PTA) and cup inclination and the polyethylene wear ratio. The adjusted R2 of the regression model was larger for measures obtained in the standing position as compared to the supine position. For the HXLPE group, there was no significant relationship between radiographic parameters and polyethylene wear. Close observation of polyethylene wear is recommended for patients with severe posterior pelvic tilt who have undergone THA with conventional polyethylene

Ten-year survival rate after rotational acetabular osteotomy in adulthood hip dysplasia

Abstract Background Rotational acetabular osteotomy (RAO) is an effective joint-preserving surgical treatment for adulthood hip dysplasia (AHD). Despite sufficient correction of acetabular dysplasia, some patients still experience osteoarthritis (OA) progression and require total hip arthroplasty (THA). The purposes of the current study were to investigate the survival rate and the risk factors for OA progression or THA requirement after RAO and to explore whether acetabular overcorrection relates to OA progression. Methods Fifty-six patients (65 hips, mean age: 36.5 ± 11.7 years) with AHD who underwent RAO and were followed up for >10 years (mean: 15.0 ± 3.2 years) were enrolled in this study. A Kaplan-Meier survival analysis was performed to assess the non-OA progression rate and THA-free survival rate of RAO during the 10-year follow-up. To analyze the risk factors for OA progression and THA requirement, the Cox proportional hazards regression analysis was performed. Results No OA progression was found in 76.7% of the patients, and THA was not required in 92.3% during the 10-year follow-up. By multivariate regression analysis, older age at the time of surgery was a risk factor for both OA progression (hazard ratio [HR] = 1.047, 95% confidence interval [CI] = 1.005–1.091) and THA requirement (HR = 1.293, 95% CI = 1.041–1.606). Conclusion RAO is an effective surgical procedure for symptomatic patients with AHD that prevents OA progression and protects the hips from undergoing THA. However, older patients have a higher risk for both OA progression and THA requirement

Late-Onset Screw Migration into Iliac Vessels 21 years after Hip Arthrodesis

Iatrogenic injuries to the vascular system are a rare but serious complication of hip surgery. We report a case of an 83-year-old man who presented with intrapelvic migration of a screw into the space between the external iliac artery and vein 21 years after hip arthrodesis. The patient was treated with laparotomy, and the damaged artery was excised and sutured. This is the first case of a late vascular complication secondary to screw migration after hip arthrodesis