Osteotomy of the patella in the patellofemoral pain syndrome. The significance of increased intraosseous pressure during sustained knee flexion.

In 40 patients with patellofemoral pain, intra-osseous pressure measurements were recorded under anaesthesia with the knee first in extension and then in flexion prior to performing a longitudinal osteotomy of the patella. There was a statistically significant increase of pressure in painful knees compared with normal knees (29 mm Hg. vs 15 mm Hg.), and a marked increase when compared during sustained flexion (97 mm Hg. vs 60 mm Hg.). However wide variability of individual results made the diagnostic value of a single pressure measurement unreliable. A clinical test, based on reproduction of the characteristic pain by sustained knee flexion, proved to be reliable in predicting a good response to operation. The effect of the operation was encouraging, with significant relief of pain as measured by a visual analogue scale.