Abstract
In Musgrave Park Hospital, Belfast, younger patients requiring THR were treated by custom-made titanium alloy femoral prosthesis. The identifit hips, which were used initially, were intraoperatively customised by preparing a silicon mould of the endosteal cavity and immediate computer assisted fabrication. The Xpress hips used measurements from preoperative marker x-rays allowing creation of templates and subsequent computer analysis to mill a stem prior to surgery.
7 identifit and 51 Xpress primary uncemented custom THRs were inserted in 50 patients between May 92 and June 96. The average age for the indentifit cases was 47 years (range 24–72) and the Xpress cases 39 years (range 23–51). The Xpress cases were followed up to an average of 47 months (range 12–74 months) and identifit cases to an average of 59 months (range 14–77 months). The indications for arthroplasty were osteoarthrosis in 15 hips, CDH in 14, dysplasia in 11, AVN in 4, rheumatoid arthritis in 3 and other diagnosis in 11. Clinical assessments were made using the Oxford score and the Modified Harris Hip score. The postoperative radiographs were evaluated for subsidence of the prosthesis; and adaptive osseous changes like osteolysis, hypertrophic cortical remodelling, sclerotic radiolucent line formation around the prosthesis and formation of a bone pedestal below the tip of the prosthesis.
The average post-op Oxford hip score for those patients not revised was 32.5 /60 (range 12–51).
16 of the 51 Xpress hips underwent revision and 2 were awaiting revision, which is a failure rate of 35.3%. Of the identifit hips 1 out of the 7 was revised (14.3%). Overall 32.8% was the rate of failure. The average duration from primary operation to revision was 47 months for Xpress hips and 90 months for the identifit hips. Of the Xpress hips, revision was done for acetabular component in 1, femoral component in 4, both components in 1, acetabular liner + femoral head in 1 and acetabular liner + femoral component in 9. The 1 revision in the identifit hip was for recurrent dislocation.
The reasons for revision in the Xpress hips were dislocation in 2 cases, loose femoral component in 13 cases and infection in 1.
Average subsidence of the femoral component was 6mm (range 0–25.9) and this did not have significant correlation with predicting outcome. Pedestal formation (intramedullary formation of bone beneath the tip of the femoral stem) was seen in 87%, sclerotic rediolucent lines were seen in 64%, osteolysis was found in 31% and hypertrophic cortical remodelling was seen in 31%. These also did not reach significance in predicting outcome.
Thus even though the idea of an uncemented custom THR is attractive, especially in the younger age group, the failure rate was found to be unacceptably high. On the basis of these data we have discontinued the use of this custom made non-porous uncemented femoral prosthesis.
The abstracts were prepared by Mr Ray Moran. Correspondence should be addressed to him at the Irish Orthopaedic Association, Secretariat, c/o Cappagh Orthopaedic Hospital, Finglas, Dublin
