RADIOGRAPHIC APPEARANCE OF THE EQUINE STIFLE FROM BIRTH TO 6 MONTHS

Lateromedial radiographs of 74 stifles from foals with no stifle swelling or lameness were evaluated to determine the range of normal variation. Foals ranged in age from 0 to 25 weeks with approximately one half of the foals being younger than 11 weeks of age. Nine breeds were represented, with Standardbred and Quarter horse being the most common. Femoral trochlear ridges and patellas were graded on a scale of 1–4 from regular and well defined (1) to very irregular (4). Femoral and tibial condyles were evaluated for irregularity. Twelve stifles were evaluated at necropsy. Irregular to very irregular patellas and trochlear ridges were found in foals up to 20 weeks of age. In foals younger than 11 weeks of age, 77% of bone borders were irregular or very irregular, whereas only 23% of bone borders from foals 11–25 weeks of age had irregular borders. A grade of very irregular was found in 33% of bone borders of foals younger than 11 weeks old, whereas only 1.25% of bone borders of older foals were graded very irregular. Asymmetry in the bone borders between left and right stifle was evident in 36% of the studies, but did not vary by more than one grade. Femoral and tibial condyles were nearly all regular and well defined regardless of age. These findings suggest that obvious irregularities of the femoral or tibial condyles in foals should be interpreted as pathologic. Patellas and trochlear ridges were ranked smooth in 3% of foals younger than 11 weeks of age and in 55% of bone borders of foals 11–25 weeks of age. Obvious irregularities of the patellas or femoral trochlear ridges may be well within normal limits in foals younger than 5 months. Consistent and diagnostic radiographic studies can be obtained safely in most standing foals with little or no sedation.