Discussion:
- note whether the acetabular component is same size or 1-2 mm > reamers;
- it is essential to obtain a tight metal to bone fit at the time of surgery, inorder to avoid subsequent loosening;
- the surgeon should not expect that residual metal - bone gaps will fill in w/ bone;
- it has also been demonstrated by Kim YS et al (J. Arthroplasty, 10 [Supplement]: S17, 1995) that underreaming by more than 2 mm leaves
gaps in the prosthesis-bone interval in the polar portion of the acetabulum;
- because of this some surgeons have gone back to line to line reaming with hemispherical components;
- this reduces the likelihood of fracture and maximizes bony contact;
- oversized components with peripheral dome contact risk frx in osteoporotic bone and cannot be expected
to achieve full metal to bone contact over the more central portions of the component;
- in contrast, CJ Della Valle MD et al (CORR No 420, March 2004), the authors reported initial good results with line to line reaming w/ screw fixation
but noted better stability and subsequent results with underreaming by 2 mm;
- these results are supported by the bench top study by Curtis et al (JBJS Br. 1992 May;74(3):372-6.) in which the authors advocate underreaming by 2-3 mm;
- references:
- A quantitative in vitro assessment of fit and screw fixation on the stability of a cementless hemispherical acetabular component.
- Stability of press-fit acetabular cups.
- Mechanical stability of porous-coated acetabular components in total hip arthroplasty.
- The initial stability of uncemented acetabular components. MJ Curtis et al. JBJS. Vol 74-B. 1992. p 372-276.
- references:
- Histological and radiographic assessment of well functioning porous coated acetabular components: A human postmortem retrieval study.
- Areas of contact and extent of gaps with implantation of oversized acetabular components in total hip arthroplasty.
- hazards: acetabular fracture
- note that insertion of oversized acetabular component may result in acetabular frx during insertion;
- this can occur w/ components that are only 2 mm oversized;
- patients w/ osteoporotic bone might not be good candidates for oversized cups;
- fracture may be difficult to detect on routine radiographs;
- references:
- Periprosthetic fractures of the acetabulum during and following total hip arthroplasty. Callaghan JJ: J Bone Joint Surg Am 79:1416-1421, 1997
- Fracture of the acetabulum during insertion of an oversized hemispherical component. J Bone Joint Surg Am 77:111-117, 1995 Kim YS, Callaghan JJ, Ahn PB, et al:
- Acetabular fracture associated with cementless acetabular component insertion: a report of 13 cases.
- Intraoperative Fractures of the Acetabulum During Primary Total Hip Arthroplasty.
