To determine the predictive value of bone scintigraphy with respect to joint space narrowing (JSN) in patients with knee osteoarthritis (OA), based on quantitative estimates of uptake of a bone-seeking radiopharmaceutical and fluoroscopically standardized knee radiography.
Our study group included 86 obese women, 45-64 years of age, with unilateral knee OA. Uptake of technetium medronate (99mTc-MDP) in late-phase bone scans was measured at baseline in 5 regions of interest (ROI: lateral femur, lateral tibia, medial femur, medial tibia, and patellofemoral joint) and was adjusted for uptake (i.e., expressed as a ratio to uptake) in a ROI in the shaft of the tibia, which served as an internal standard. Each subject underwent a fluoroscopically standardized radiograph of the knees (semiflexed anteroposterior view) at baseline, 16, and 30 months. Magnification-corrected minimum joint space width in the medial tibiofemoral compartment was measured by digital image analysis.
Followup was available for 79 patients (92%) at 16 months and from 73 patients (85%) at 30 months. On average, 99mTc-MDP uptake in each ROI and in the whole knee (average of 4 tibiofemoral ROI) was 170-240% of that in the tibial shaft. Uptake in the medial tibia and in the whole knee was significantly correlated with JSN at 16 and 30 months (r = 0.22-0.30, p < 0.05). However, after controlling for age, body mass index, and radiographic severity of OA, the associations between adjusted uptake and JSN were not significant. The rate of JSN in knees of patients with OA who were in the lower tertile with respect to adjusted 99mTc-MDP uptake in the medial tibia was significantly less rapid than in patients in whom uptake was in the middle and upper tertiles (0.04 mm/yr vs 0.18 mm/yr; p < 0.05). However, after controlling for overall radiographic severity at baseline, the difference in 30-month JSN in knees of patients with OA in the lower versus middle/upper tertiles was not significant.
The predictive utility of bone scintigraphy is confirmed by these data. However, its practical value is considerably diminished, insofar as similarly predictive information may be obtained by routine radiographic examination, without the radiation exposure and cost of scintigraphy.