Ultrasonographic evaluation of the anterior recess in the normal hip: a prospective study on 166 asymptomatic children.

PURPOSE

To redefine the ultrasonographic features of the normal hip joint in children and to establish a normal value for the neck-capsule distance (NCD) of its anterior recess.

MATERIALS AND METHODS

332 hips of 166 asymptomatic children were examined sonographically. In a sagittal section plane the maximum distance between the anterior surface of the femoral neck and the anterior limit of the articular capsule (NCD-A) was measured.

RESULTS

The hypoechoic synovial membrane occupying the anterior recess could always be differentiated from the capsule. An additional thin layer of synovial fluid was detected in 12% of probands. The configuration of the capsule varied with different rotation positions of the legs. In small children the mean NCD-A increased from 2.5 mm at 65 cm height to 5 mm at 100 cm height. In larger children the mean NCD-A was 5.5 mm. The mean right-to-left difference was 0.5 mm with a pathological limit of 2 mm.

CONCLUSIONS

The pathological limit of the NCD-A increases from 3.5 to 7.5 mm in relation to the height. Sonographic investigation of the pediatric hip joint must include detailed demonstration of anatomical structures to avoid misinterpretations.