Does 99mTc-MDP bone scintigraphy add to the investigation of patients with symptomatic unicompartmental knee replacement?

The purpose of this study was to determine whether nuclear medicine ^99mTc-Methyl diphosphonate bone scintigraphy ( ^99mTc-MDP bone scintigraphy) added information over plain radiographs loosening infection in symptomatic unicompartmental knee replacements (UKRs).

A cohort of 39 patients who presented with knee pain following UKR was retrospectively reviewed. All had undergone nuclear medicine bone scans for possible loosening or infection of the prosthesis. The findings of the bone scintigraphy were compared to subsequent operative findings during diagnostic arthroscopic investigation or revision surgery for those patients who had undergone these procedures.

Of the 39 patients with painful knees following UKR, surgical findings confirmed that 11 had either loose (n = 9) or infected (n = 2) implants. Logistic regression analysis demonstrated no statistically significant combination of features on nuclear medicine or radiographs associated with failure of the prosthesis due to infection or loosening (p > 0.05).

Classification of a satisfactory position of the UKR on plain radiography exhibited a high negative predictive value (96% for infections, and 80% for loosening). However, plain radiograph was not sensitive for loosening (50%) or infection (37%) of the UKR with very low positive predictive values (9.1% for infection and 27.3% for loosening).

This study provides no evidence to support the routine use of ^99mTc-MDP bone scintigraphy in the clinical decision-making for patients with a painful UKR.

Level of evidence: level 4.