The Influence of Acetabular Morphologic Variations on the Cup Position in Total Hip Arthroplasty for Crowe type III Dysplastic Hip
Abstract Background: We aimed to (1) evaluate the acetabular morphologic variations of Crowe III hips; (2) study the influence of different morphologies on the cup position in total hip arthroplasty.Methods: From November 2008 to February 2019, we retrospectively evaluated 101 patients (110 hips) with Crowe III developmental dysplasia of the hip. We classified Crowe III hips into two subtypes, the IIIA when the acetabular roof was extensively deficient and the junction between the false and the true acetabulum was indistinct, and the IIIB when there is a significant crest between the false and the true acetabulum. Based on the radiographs, we measured the morphological characteristic of the acetabulum and the postoperative cup position.Results: The false acetabulum of IIIB hips had larger Tonnis angle and smaller center-edge angle than the IIIA hips. The width of true acetabular roof in the IIIB hips was thicker than the IIIA group. Fifty-one (100%) IIIA hips and 48 (81.4%) IIIB hips were reconstructed using high hip center while 11 (18.6%) IIIB hips were reconstructed anatomically. The mean vertical distance of center of rotation in the IIIA group was 33.5±4.5 mm while it was 31.2±6.3 mm in the IIIB group (p=0.040). The vertical distance of the hip center was positively correlated with the height of dislocation in the IIIA group (r=0.493, p<0.001). According to the four-zone system, in the IIIA group, 5 hips were located in the inferomedial zone, 23 hips in the superomedial zone, 22 hips in the superolateral zone and 1 hip in the inferolateral zone. In the IIIB group, the corresponding numbers were respectively 15, 17, 1 and 5. Compared with the IIIA group, there were more IIIB hips located in the inferomedial zone (p=0.008) and less in the superolateral zone (p=0.033).Conclusions: There are distinct morphologic subtypes based on the relationship between the false and the true acetabulum. More bone stock located in the superior wall of the true acetabulum can bring more possibilities for anatomical reconstruction, and lower the height of center of rotation when using high hip center.