Use of single photon emission computed tomography (SPECT) to study the distribution of 90Y in patients with Baker's cysts and persistent synovitis of the knee.

The presence of a Baker's cyst may diminish the therapeutic effect of intra-articular 90Y treatment to the knee joint. SPECT (single photon emission computed tomography) was used in 10 patients with Baker's cysts, treated with intra-articular 90Y for persistent synovitis of the knee, to measure the amount of radioisotope within the cyst. Comparison was made with the arthrographic appearances. The likelihood or extent of uptake into Baker's cysts of 90Y injected into the synovial cavity of the knee was not predictable from arthrograms. Deposition of 90Y in cysts was variable, ranging from little or no measurable uptake to a substantial proportion of the administered activity (40% in one case out of 10). It did not appear to relate to clinical response. The low mean uptake (6.3%) in cysts of nine out of 10 patients was probably insignificant in view of the large uncertainty in the prediction of synovial radiation dose.