Stifle radiography in Thoroughbreds from 6 to 18 months of age

Abstract

SummaryThe radiographic appearance of the stifle of young horse changes during the first 18 months of life but is not well described in Thoroughbreds. Our objective was to describe the radiographic appearance of the Thoroughbred stifle from 5 to 18 months of age and determine whether limiting exercise impacts the prevalence of radiographic abnormalities (RA). Bilateral stifle radiographs were obtained at a mean of 161 days of age in 141 subjects (set 1) and 347 days (set 2), and in 114 available subjects at 534 days (set 3), and graded for RA of the trochlear ridges (TR) and medial femoral condyle (MFC). The impact of exercise limits on RA was determined from a subgroup of subjects with set 1 RA that had 30–90 days limited exercise. Stifle RA were present in 50 subjects (35%) at set 1: 39 TR and 11 MFC. At set 2, 24 subjects (15.6%) had RA: 13 TR and 11 MFC. Set 1 RA had resolved in 36 (72%) subjects, persisted in 11 (22%) and changed location in 3. Ten of 91 (11%) subjects developed new RA at set 2. Twenty‐seven subjects were unavailable for set 3 imaging, 6 with LTR RA at set 2. At set 3, 12/114 (11%) subjects had RA: 5 TR and 7 MFC. Set 2 RA resolved in 9 (50%) subjects, persisted in 8 (44%), and changed location in one. Three of 96 subjects developed new RA at set 3. Radiographic abnormality prevalence at set 3 was not different after limiting exercise. It was concluded that RA in the TR and MFC are common in 6‐month‐old Thoroughbreds and often resolve by 18 months. Radiographic abnormalities that develop later (~12 months of age) are less likely to resolve.