Comparison of tibial plateau angle between clinically normal Greyhounds and Labrador Retrievers with and without rupture of the cranial cruciate ligament

Objective - To compare tibial plateau angle (TPA) between Greyhounds without damage to the cranial cruciate ligaments and Labrador Retrievers with and without damage to the cranial cruciate ligaments. Design - Clinical study. Animals - 87 client-owned dogs and 15 research colony Greyhounds. Procedure - Standing position, horizontal-beam radiography was performed on Greyhounds and unaffected Labrador Retrievers to determine standing TPA. Lateral radiography of the stifle joint was performed on all dogs to determine traditional TPA. Age and body weight were recorded for unaffected and affected Labrador Retrievers. Results - Greyhounds had mean standing TPA of 1.56° and mean traditional TPA of 22.50°. Unaffected Labrador Retrievers had mean standing TPA of 3.52° and traditional TPA of 27.97°. Affected Labrador Retrievers had mean traditional TPA of 25.55°. No significant difference was found in mean standing TPA between Greyhounds and unaffected Labrador Retrievers. Standing TPAs in Greyhounds and unaffected Labrador Retrievers were not significantly different from a plane drawn parallel to the ground. Significant differences in traditional TPAs were detected among all 3 groups. Conclusions and Clinical Relevance - Greyhounds had mean traditional TPA of 22.50°; similar angles should be considered normal for dogs. Although affected Labrador Retrievers had mean traditional TPA that was significantly greater than that of Greyhounds, the steepest TPA was found in unaffected Labrador Retrievers. Because Greyhounds and unaffected Labrador Retrievers had similar standing TPAs, we conclude that although TPA may be associated with damage to the cruciate ligaments, many dogs with a steep TPA do not develop cruciate ligament disease.