The value of a new ultrasound stress test in assessment and treatment of clinically detected hip instability.

Fifty patients with clinical suspicion of hip dislocation were investigated prospectively with a dynamic ultrasound stress test. A posterior force was applied to hips in flexion and any movement between the femoral head and the acetabulum was measured. The results of this test showed that posterior movement ranged from 0 to 13.0 mm. Hips that were clinically normal had a mean movement of 1.4 mm, hips with minor clinical instability had a mean movement of 0.6 mm, hips with moderate instability had a mean movement of 4.5 mm, and those with major instability had a mean movement of 5.1 mm. This was statistically significant to a 1% confidence interval. We propose two groups of ultrasound-detected movement: group A less than 5.0 mm representing physiologic laxity, and group B greater than or equal to 5.0 mm being pathological and requiring treatment.