Bone scan in the patellofemoral pain syndrome.

Eighty patients who complained of retropatellar pain underwent evaluation by bone scintigraphy, intraosseous pressure determination, radiography, arthroscopy and physical diagnostic tests. The bone scans showed that 48% of the painful knees had an increased uptake compared with 9% for the normal joints. A highly significant correlation was evident between an increased uptake and established chondromalacia. For the diagnosis of a high pressure patella, radiography was only 7% sensitive (6/88), compared with 44% (39/88) for bone scintigraphy and 78% for the clinical "sustained flexion" test. The positive predictive value of a bone scan for detecting a high pressure patella was 0.72 (39/54). The best predictor was a positive sustained flexion test with a predictive value of 0.85 (69/81).