gms | German Medical Science

Objectives: Evaluating the effect of dislocation type on pelvic development in adults with development dysplasia of hip (DDH).

Methods: Preoperative pelvic radiographs were examined in 57 patients with DDH who underwent total hip arthroplasty (THA) between January 2011 and December 2013 retrospectively. The patients, who represented 114 hips, had a mean age of 37.2 years (range, 18-73 years). Degree of dysplasia was determined according to the Crowe classification system. Both sides of the pelvis were separated into three areas by horizontal lines drawn over the iliac wings from the ischium inferior, from the acetabular teardrops and from the inferior sacroiliac joints. The area containing the iliac wing was labeled as “area 1”, the acetabulum as “area 2” and the ischium as “area 3”. The height of each area was calculated as a proportion of the whole hemipelvis height of the same side. The heights and ratios for each area for healthy hips and for contralateral hips with DDH were compared.

Results and Conclusion: Of 114 hips, 51 had Crowe type IV dysplasia, 11 had type III, eight had type II, 10 had type I, and 34 were healthy. When the area heights in Crowe type II, III, and IV hips were compared, we found that in dysplastic hips, the values for the iliac wing (area 1) were significantly low, those for the acetabulum (area 2) were significantly high, and those for the ischium (area 3) were significantly low. In comparison with the healthy contralateral hips, the acetabular teardrop was a mean 10.56 mm more distal in Crowe type IV hips, eight mm more distal in Crowe type III hips, and five mm more distal in Crowe type II hips.

In the majority of studies of DDH, the acetabular teardrops and the ischial tuberosities have been used as fixed pelvic reference points in preoperative planning. However, our findings indicate that those reference points are not appropriate for determining proper placement of acetabular components in patients with DDH. In preoperative planning, surgeons should pay attention especially to the mean 11-mm distal displacement of the teardrops in Crowe type IV hips. To achieve a functional hip joint with correct soft-tissue balance in DDH, surgeons performing THA should take into consideration our findings regarding the use of reference points for calculating leg-length discrepancy and the appropriate placement of acetabular components.