Degenerative changes in sacroiliac joints (SIJ) are reported to cause poor performance in horses. The aim of this study was to document the frequency and nature of changes in SIJ surfaces of Thoroughbred (TB) racehorses and to correlate gross morphology and marginal new bone formation to age, body weight and history of back pain.
SIJ surfaces from 37 deceased TBs retired from the Hong Kong Jockey Club were photographed and measurements taken to facilitate subjective and objective analysis of gross changes. SIJ surfaces were described, and the surface area of the joint surfaces determined from the photographs, using Image J. Area and shape of the joint surfaces were recorded and SIJs were graded and allocated a type according to pre-determined criteria. Changes were compared for horses with and without clinical records of back pain.
Mean age was 6.6 ± 2.3 years; weight 494 ± 35 kg; with no differences between horses with (n = 14) and without (n = 23) a history of back pain. There was no relationship between bodyweight (r = 0.08) or age (r = 0.13) and SIJ surface area. SIJs of the back pain group were affected by obvious gross pathology that showed certain characteristics. There was a relationship between surface area of joint and degree of marginal bone formation (P<0.001). SIJs from the group of TBs with no back pain had fewer and less obvious gross findings.
Clinical evidence of back pain, which may reasonably be expected to have affected the horse's racing performance, was associated with characteristic gross pathology of the SIJ.