Joint scintigraphy using technetium-99m pyrophosphate in experimental hemarthrosis.

To determine the validity of a method for induction of experimental hemarthrosis in dogs and for the nuclear imaging of hemarthrosis, serial technetium-99m pyrophosphate [( 99mTc]PYP) flow and blood-pool scans were performed monthly in eight dogs who received bi-weekly injections of autologous blood into their femoro-tibial joints (also called stifle joint). In four control dogs, one joint was injected with saline while the other joint received only a sham injection. In addition, two dogs received intra-articular injections of autologous blood into their right stifle joint and saline into their left stifle joint. These dogs were studied with 99mTcO4 joint scintigraphy at monthly intervals. The dogs were periodically taken out of the study and explored surgically. Pathologic examination of synovial tissue was performed. Serial radiographs were also obtained and correlated with the scan and surgical findings. There was a striking abnormal increase in blood-pool activity of [99mTc]PYP in the treated stifle joints, commencing at the first examination after 1 mo of blood injections and continuing for the length of the study. All radiographs showed only minimal joint space widening and some soft-tissue swelling. On pathologic examination, both grossly and microscopically, there was profuse pannus formation, with intense inflammatory infiltrate replacing much of the subsynovial fat. The scintigraphic findings correlated well with these pathologic findings. This study not only validates this method for simulating hemophilic hemarthrosis but also suggests that [99mTc]PYP joint scintigraphy is a simple, and noninvasive method for monitoring the early changes in hemophilic arthropathy and is superior to pertechnetate imaging for this disease process. Instead of the previously recommended delayed bone images, we recommend, in addition, flow studies to assess joint hypervascularity and immediate static images to visualize the synovium and joint capsule.