For cup implantation in dysplastic acetabulum, the vertical height of the cup center (V-HCC) should be carefully and precisely controlled in order to achieve sufficient host bone-cup coverage (BCC), but excessively superior placement of the cup should be avoided. Using computer software, pelvis models were separately reconstructed in 51 patients (61 hips) with severe osteoarthritis secondary to Crowe type I-III hips. Acetabular height and doom thickness were measured on the mid-acetabular coronal cross section. V-HCC was defined as the vertical distance from the cup center to the interteardrop line (ITL). In the cup implantation simulation, the cup was placed at the initial preset position, with a V-HCC of 15 mm, and moved proximally by 3-mm increments. At each level, the BCC was automatically calculated by computer. There were no significant between-group differences in maximum thickness of the acetabular doom; however peak bone stock values were obtained at heights of 41.63 mm ± 5.14 mm (Crowe type I), 47.58 mm ± 4.10 mm (Crowe type II), and 55.78 mm ± 3.64 mm (Crowe type III) above the ITL. At 15 mm of HCC, BCC was 79%±7% (Crowe type I), 74%±9% (Crowe type II), and 61%±6% (Crowe type III). In order to achieve 80% of the BCC, the evaluation distance was 1.33 ± 1.62 mm (95% CI 0.67–2.01), 3.32 ± 2.94 mm (95% CI 1.94–4.69), and 9.68 ± 3.91 mm (95% CI 7.60–11.77) for Crowe type I, II, and III hips, respectively. Acetabular bone stock for cup placement correlates with the degree of hip dysplasia in patients. During acetabular reconstruction in Crowe type I, II, or III hips, slightly superior placements, <25 mm from the ITL, retained sufficient bone coverage.
The Best Bone of Acetabulum for Cup Component Placement in Total Hip Arthroplasty in Patients with Crowe Type I-III Dysplastic Hips: a Computer Simulation Study