Background: Constrained acetabular components have been used to
treat hips with recurrent instability following total hip arthroplasty and
hips that demonstrate instability during revision surgery. In such hips, when
a secure cementless acetabular shell is present, the surgeon can cement a
constrained liner into the existing shell. The purpose of this study was to
evaluate the clinical and radiographic outcome of this technique with use of a
tripolar constrained liner that was cemented into a well-fixed cementless
acetabular shell.
Methods: Between 1988 and 2000, constrained liners were cemented
into thirty-one well-fixed cementless acetabular shells at three centers. The
average age of the patients at the time of the index surgery was 72.1 years,
and the indications for the procedure were recurrent hip instability in
sixteen hips and intraoperative instability in fifteen hips. The patients were
evaluated with respect to the clinical outcome and radiographic evidence of
shell loosening and osteolysis.
Results: At an average duration of follow-up of 3.9 years,
twenty-nine liners (94%) were securely fixed in the cementless shells and two
constrained liners had failed. One liner failed because it separated from the
cement, and one failed because of fracture of the capturing mechanism. Both
hips were successfully revised with another cemented tripolar constrained
liner. No acetabular component demonstrated radiographic evidence of
progressive loosening or osteolysis.
Conclusions: A constrained tripolar liner cemented into a secure,
well-positioned cementless acetabular shell provides stability and durability
at short-term follow-up. Careful attention to the preparation of the liner,
the sizing of the component, and the cementing technique are likely to reduce
the failure of this construct, which can be used for difficult cases of total
hip instability.
Level of Evidence: Therapeutic study, Level IV (case
series [no, or historical, control group]). See Instructions to Authors for a
complete description of levels of evidence.