[Experience with the Aesculap Parhofer-Mönch type cementless hip prosthesis (preliminary report)].
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In 1987 we made a review of all total hip prostheses inserted at Hopital Henri Mondor in 1974-1975-1976. These were of the metal-polyethylene Charnley-Muller or Lagrange-Letournel type (430 prostheses inserted in 349 patients). 178 hips were reexamined and 177 were lost to follow up. 61 patients had died. Overall, good results were found in 65% of patients reviewed - 12.5% had been reoperated upon. Although the newer models of prostheses are full of promise, none has stood the test of 10 years of use.
The pattern of operation injuries of the arterial vessels which may occur during hip surgery is illustrated by this summary of our own cases. Injuries of the femoral vessels seem to be preventable if the Hohmann-retractor is carefully placed on the anterior margin of the acetabular rim under digital control. Furthermore drilling damage of the iliac vessel appears to be avoidable. However, the replacement manoeuvre of the artificial acetabulum can be associated with massive bleeding despite greatest care. Under these circumstances immediate surgical intervention through an inguinal retroperitoneal approach is mandatory.
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The aim of this study was the evaluation of the release of bone-resorbing cytokines in peripheral blood mononuclear cells (PBMC) of patients with aseptic loosening of Co-Cr hip prostheses. TNF-alpha, IL-6, and GM-CSF were measured in both unstimulated and PHA-stimulated PBMC, and in PBMC cultured in the presence of chromium and cobalt extracts. Blood samples from healthy donors were used as controls. Serum samples of both patients and healthy donors were tested to determine the concentration of metal ions. The proportion of lymphocyte, monocyte and lympocyte subpopulation in cultured PBMC did not differ in patients and the control group. In unstimulated PBMC the release of TNF was significantly higher in patients than in the control group, while IL-6 was significantly decreased and no change was observed for GM-CSF. When the PBMC were challenged with chromium extract, all the 'index of cytokine release' resulted higher in patients than in the control group; cobalt extract increased both the TNF and GM-CSF index, but not the index of IL-6 release. Metal concentrations in serum from patients were significantly increased and correlated with the TNF release in PBMC stimulated with both metal extract. Our results suggest that a CoCr-implant releases a large amount of metal ions which could mediate the priming or the renewal of a cell-mediated hypersensitivity reaction. The prevalence of circulating lymphocytes responsible for the delayed hypersensitivity, namely Thl, would justify both the significant increase of TNF and the significant decrease of IL6 in unstimulated PBMC of patients, as well as the significant increase of the 'index of cytokine release' after the challenge with metal ions.
Experiments have shown that stress shielding resulting from implantation of a prosthesis is related to the stiffness of the implant. Stiffness depends on the Young's modulus of the material used and the design of the implant. Most published studies have not attempted to define the relative importance of these two components. We have studied the influence of the elastic modulus only in an experiment using implants of a uniform design. Strain gauges were attached to the calcar in five femurs, three of which also had gauges placed on their medial, lateral and anterior aspects. Surface strain was measured in the intact femur and after implantation of cemented prostheses of the same design but manufactured with or without a collar in stainless steel or titanium alloy. The highest level of calcar strain was recorded with the titanium alloy prosthesis, and the presence of a collar appeared to increase the stress transfer of bone. This effect on stiffness was statistically significant, but was limited to the proximal part of the upper femur. It was not significant in the sub-trochanteric area, due to individual variations in bone geometry and cortical thickness. These results indicate that stress shielding can be directly related to the Young's modulus of the material used, independent of the design of the prosthesis.
In the course of replacing more than 500 total hip prostheses over a period of five years the authors have developed a new set of instruments for the removal of the defective prosthesis and cement and for improved anchorage of the new prosthetic cup. The set comprises: 1. A set of special chisels and an axially guided drill for removal of the old cement from the femur. These instruments greatly simplify the latter procedure. 2. A new type of prosthetic cup with a weight-bearing collar. This cup is used for cases in which the amount or structure of the acetabular bone is such that it will not support a conventional cup. 3. A new type of drill with a flexible drive and easily exchangeable drill bits for cutting anchorage holes in otherwise inaccessible parts of the acetabular bone.
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