SCINTIGRAPHIC AND CLINICAL FINDINGS IN THE STANDARD-BRED METATARSOPHALANGEAL JOINT - 114 CASES (1993-1995)

To correlate scintigraphic and clinical findings of the metatarsophala ngeal joint (MTPJ) in Standardbreds, radiographic findings in horses w ith confirmed MTPJ lameness, and determine if;stress reaction and more advanced bone remodelling occurred in the MTPJ, medical records of 11 4 Standardbreds admitted between September 1993 and April 1995 in whic h bone scintigraphy included standing lateral and plantar views of the metatarsophalangeal joint (MTPJ) were reviewed. Images obtained using a large field of view gamma camera were evaluated visually for locati on, definition and intensity of increased radioisotope uptake (IRU), w hich was graded as mild, moderate, or intense. Clinical history and la meness examination findings were recorded and, in horses with document ed MTPJ lameness, radiographic examination included the 30 degrees (do wn-angled) dorsolateral 45 degrees plantaromedial view thought to be u seful in evaluation of the plantarolateral condyle of the third metata rsal bone (MtIII). The most common abnormality, IRU of the plantarolat eral aspect of MtIII, was seen in 67 horses, and horses were further c lassified according to scintigraphic and clinical findings. In 43 hors es in which lameness was not localised to the MTPJ, mild (32 horses), moderate (10 horses), and intense (one horse) IRU of MtIII was found. In 24 horses with lameness localised to the MTPJ, moderate (18 horses) and intense (6 horses) IRU was found. Of 18 horses with moderate IRU of MtIII, 9 had radiographic evidence of abnormal bony remodelling of MtIII, whereas 5 of 6 horses with intense IRU had radiographic changes . In 12 horses with MTPJ lameness and radiographic evidence of bony re modelling without fracture, radiographic changes consisted of plantaro lateral subchondral radiolucency and sclerosis (7 horses), radiolucenc y and osteochondrosis (one horse), and plantar MtIII sclerosis without radiolucency (4 horses). In 2 horses with moderate IRU and MTPJ lamen ess, radiographic evidence of radiolucency and MtIII fracture was foun d. Of 19 starters with MTPJ lameness and IRU of MtIII, 18 horses raced after diagnosis, but only 13 remained at the same racing class or imp roved. The results of this study suggest the most common scintigraphic abnormality of the MTPJ, IRU of the plantarolateral aspect of MtIII, may precede other stress-related changes, and in some horses is associ ated with a continuum of stress-related subchondral bone remodelling w hich results in lameness and later radiographic changes. Since 24 of 3 5 horses with moderate or intense IRU of MtIII had MTPJ lameness, and 5 of 7 horses with intense IRU of MtIII had lameness and radiographic evidence of abnormal remodelling, it was concluded that horses with ad vanced, scintigraphic findings are more likely to have lameness and ra diographic evidence of subchondral bone damage.