Poor predictive value of broad-range PCR for the detection of arthroplasty infection in 92 cases.

BACKGROUND: The diagnosis of prosthetic infection remains a challenge, as no test is 100% sensitive and 100% specific. Recent advances in molecular biology have enabled the detection of infection in culture negative cases. PATIENTS AND METHODS: We evaluated the effectiveness of polymerase chain reaction (PCR) in detecting infection in failed joint replacements prospectively in 91 consecutive patients (92 prosthetic joints) undergoing revision total hip or knee arthroplasty. Synovial fluid was collected intraoperatively and examined by broad-range PCR assay for detection of bacterial DNA. The clinical diagnosis of infection was based on the results of blood tests, preoperative joint aspiration, culture and histology of multiple intraoperative tissue samples, as well as the surgeon's assessment. 12 joints (13%) were infected, but the PCR was positive in 32 cases. The sensitivity of the technique was 92%, the specificity 74%, the accuracy 76%, the positive predictive value 34%, and the negative predictive value was 98%. INTERPRETATION: The PCR technique cannot be recommended for the routine detection of prosthetic infection. The large number of false positive results may represent sample contamination, or bacterial presence related to low-virulence organisms, low bacterial load, or a strong host immune response.

Howse II cemented titanium metal-backed acetabular cups: poor 10-year results in 107 hips.

We report a retrospective clinical and radiographic review of 107 consecutive primary total hip replacements, using the cemented Howse II prosthesis. The review concentrates on the long-term performance of the acetabular cup, which was designed with a cylindrical titanium metal backing and a polyethylene liner. In all the hips in the series, this cup was used with a modular titanium straight femoral stem and a 32-mm diameter titanium head. At a mean follow-up of 9.8 (7-11) years, 28 hips had already been revised and 10 others were recognized as clinical or radiographic failures. The indication for revision in 26 of the hips was aseptic loosening and the mean time to revision was 7.2 (3.7-10.9) years This metal-backed cup has only 42% survival at 10 years, which seems to be related to certain of its design features. These include an inadequate thickness of polyethylene sterilized by gamma irradiation in air, a lack of mechanical bonding between the liner and its metal shell, and the high wear rate from the use of a 32-mm titanium femoral head.

Mid-term results and migration behaviour of a ti-alloy cemented stem.

Between 1991 and 1994, 147 patients (154 hips) underwent a primary cemented total hip replacement using the Ultima ti-alloy, collarless, double-tapered stem and a UHMWPE cup. The average age at operation was 66.4 years. Ninety-one patients (97 hips) were available for review with an average follow-up of 76 months. The Harris hip score had improved from pre-operative average of 43.1 (12.5-65.0) to the latest score of 88.9 (67.5-100). There were 11 revisions in total, eight of which were for aseptic stem loosening. The results of Kaplan-Meier survival analysis, based on stem revision for aseptic loosening as an end-point, was 92% at 8 years. Early stem migration analysis at 2 years was possible in 114 cases using digitised radiographs analysed by the EBRA method. Sixty-three stems had not migrated and 35 migrated less than 2 mm with only one of these ending in failure. Sixteen stems showed early migration of more than 2 mm and five of these failed. Early stem migration is predictive of stem failure. Osteolytic lesions occurred in 12 femurs and four of these stems failed.