- See:
Acetabular Component Menu:
- Acetabular Component:
-
press fit components
- note whether acetabular component is hemispheric or non-hemispheric;
- non hemispheric components (ie over sized components or components with a peripheral flare) may be more appropriate for protrusio or for situations where
acetabulum will be medialized where as hemisperic components may be more appropriate for shallow or osteoporotic acetabuli;
-
acetabular liner / femoral head size:
- as pointed out by
M. Jasty et al (JBJS 1997), the thickness of the polyethylene component is especially important in metal backed press fit components;
- w/ smaller acetabular components consider using a 26 mm rather than a 28 mm head;
- in the report by RL Url MD et al, the authors performed a bench top study to evaluate the consquences of mixing different modular THR components;
- the authors noted that the combination of a skirted neck, smaller femoral head, and a posterior lipped liner can have the effect of
of causing impingement of the neck on the raised liner (which can cause the femoral head to lever out of socket);
- references:
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Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: a new concept.
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Wear of Polyethylene Acetabular Components in THA. An Analysis of 128 Components Retrieved at Autopsy or Revision Operations
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over-sizing the acetabular component:
- Technical Considerations in Component Insertion:
-
acetabular reaming:
-
acetabular component position:
- component is inserted in same direction of reaming;
- component insertion;
- w/ proper acetabular alignment, impact acetabular cup into place;
- listen for change in pitch as component seats down;
- probe screw holes and if gap is present then impact further;
- ref:
Impact biomechanics and pelvic deformation during insertion of press-fit acetabular cups.
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screw placement:
- anterior & inferior osteophytes;
- if the acetabulum is retroverted then anterior wall itself will project beyond edges of cup if it is set in anteversion;
- reflected head of the rectus may be attached to osteophyte;
- anterio-inferior wall osteophytes must be removed w/ osteotome, cutting along the edge of the cup;
- failure to heed this may cause posterior dislocation in flexion and internal rotation;
-
polyethylene insertion:
-
hiwall acetabular liner:
- as noted by
Cobb et al 1996, the presence of a high wall liner can reduce the incidence of dislocation in primary THR from about 3.8% to 2.2%
- the beneficial effect is probably higher w/ revision surgery;
- paradoxically, the high wall liner may actually increase the incidence of anterior dislocation (due to impingement between
femoral neck and the elevated lip of the liner);
- liners may also contribute to increased
polyethylene wear;
-
latealized acetabular liner:
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Offset acetabular components introduce torsion on the implant and may increase the risk of fixation failure.
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Iliopsoas impingement on the acetabular component: radiologic and computed tomography findings of a rare hip prosthesis complication in eight cases.
Load transfer and fixation mode of press-fit acetabular sockets.
