Unexpected long femur in adults with acetabular dysplasia.

Femoral length symmetry is assumed when assessing a patient with a dysplastic acetabulum. An unexpected long femur has been observed in some adults with acetabular dysplasia. We undertook a retrospective observation study of 18 adults with unilateral and 11 adults with bilateral acetabular dysplasia. Femoral lengths were assessed using CT measurements. The ipsilateral femur was found to be 5-10 mm longer in 66% (12 patients) with unilateral dysplastic acetabulae. Femoral lengths varied greatly in the presence of bilateral dysplastic acetabulae. In the presence of a acetabular dysplasia, asymmetry of femoral lengths is common and unpredictable. Femoral and total limb length assessment (with CT) is advised preoperatively. This will alert the surgeon and patient to the possible risk of post operative ipsilateral limb lengthening.