N°266 - August/September 2017
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The Hip: Anatomy and Total Replacements
By Philippe Chiron in category SURGICAL TECHNIQUE
CHU Toulouse - France
What are we replacing?
The joint surfaces:
The cartilage, made of collagen, proteoglycans, calcium, chondrocytes and water, is replaced with chrome, cobalt, zinc, molybdenum, ceramic and polyethylene.
The femoral head, made of vascularised hydroxyapatite, collagen, osteoblasts, osteoclasts, H2O and marrow is replaced with avascular chrome, cobalt, molybdenum, zinc and titanium which is therefore not accessible to antibiotics or biofilm-support media. Although these materials are biocompatible, they are nevertheless susceptible to corrosion and fretting and may leach particles that cannot be lysed by cytokines, or carried by macrophages if they measure between 1 and 10 μ in diameter. The leached particles are responsible for local reactions such as ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) (1) or more simply bone lysis that leads to loosening (2,3) (Fig. 1).
Figure 1: Wear debris is resistant to organic chemistry.
Passive stability components
The hip is an enarthrodial joint with three degrees of freedom and in which, the acetabulum and head diameter help maintain stability. We replace an ogival acetabular socket of varying shape with a rigid spherical cup (4). Destruction of the subchondral bone affects stress distribution (5,6). We...
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