Measuring hip joint looseness to diagnose dog hip dysplasia

Abstract

ObjectiveTo propose a direct measure of subluxation of the femoral head (S) in the assessment of hip joint laxity and evaluate it for clinical use.Study DesignMethod comparison study.AnimalsDogs (n = 51).MethodsDogs were sedated or anesthetized for a dorsolateral subluxation (DLS) examination. Two sets of radiographs were acquired, 1 each by a different technologist. A calibrated measuring bar was included on the image at the height of the hip to assess magnification. TheDLSwas calculated for each hip and different persons unaware of these details measured the “S”‐value. One person measured theS‐value 3 times over 3 days. Box plots were used to determine a cut‐off for the empiric (8 mm) and corrected (4 mm)S‐value.ResultsOf 51 dogs, 33 were dysplastic based on aDLSscore <55%. Magnification and body weight were strongly correlated (r = 0.4922,P= .0006). Both empiric and correctedSmeasurements showed good agreement with theDLSscore (κ = 0.688 and κ = 0.681, respectively). The correctedSmeasurement produced more false negatives.Bland–Altman analysis showed interobserver and technician variance acceptable for clinical use (limits of agreement < ±3 mm). Intraobserver repeatability was acceptable for the right hip (95% of differences were ≤1.3 mm and 100% ≤ 1.9) but not for the left hip.ConclusionUsing a cut‐off value of 5 mm, the empiricalSmeasurement can be used to exclude hip dysplasia in young dogs of various body proportions.