Aim: To see the efficacy of white cell scan in the diagnosis of prosthetic joint infections.

Materials and methods: A retrospective study was done from Jan 2001 to Dec 2003 on patients with suspected joint infections after prosthetic joint surgery that had white cell scans. 109 patients were identified. We excluded 13 patients due to lack of proper documentation. The case notes for clinical details, laboratory investigations, radiological investigations were reviewed for this purpose. All the patients who did not have intervention were followed for a year for signs of infection.

Results: After exclusion, of 13 patients, 96 patients were taken into the study. Of these, 44 were males and 52 were females. The age range was from 53 years to 91 years with an average of 76 years. We identified 30 total hip replacements, 61 total knee replacements, 3 shoulder replacements and 2 hemi-arthroplasties. 77 of these were cemented and 19 uncemented. The scan was done on an average of 23 months, with a range of 4 months to 16 years after the surgery. The chief complaint was persistant pain at rest and walking in all patients.11 patients had swelling, 7 had redness. None of the patients had discharge. White cells were raised in 6, ESR was raised in 28, and CRP was raised in 15 patients. Antibiotics were started on clinical grounds in 10 patients of which 4 patients showed no response. Plain X-Rays suggested infection in 5 patients. White cell scan suggested infection in 26 patients. Irrespective of scan report, 28 patients were operated for symptoms. There was surgical evidence of infection in 11 patients and 17 had aseptic loosening. Of the 11 surgically confirmed cases of infection, white cell scan showed infection only in 7 patients.

Infection +ve Infection –ve

Positive White Cell Scan 7 19

Negative White Cell Scan 5 65

The specificity of the WCS is 0.77 and sensitivity is 0.58. The positive predictive value is 0.36, and negative predictive value is 0.92.

Conclusion: White cell scan has a good predictive value for exclusion of prosthetic joint infections it has high false positive rate. However caution must be excised in interpreting the negative scans. Persistent symptoms should not be ignored. We recognise that the limitation of our study is our small sample size.