Effects of prior shelf procedure on subsequent conversion total hip arthroplasty

It is unclear if shelf acetabuloplasty provides adequate bone coverage when conversion total hip arthroplasty (THA) is required in patients with developmental dysplasia of the hip (DDH). We aimed to investigate the short-term results of conversion THA after shelf acetabuloplasty. Forty-six patients requiring conversion THAs after a prior shelf acetabuloplasty were matched to THAs for osteoarthritis secondary to Crowe I DDH in a 1:1 ratio. Surgical factors, clinical scores, cup placement, and bone coverage of the cup were evaluated. The preoperative Japanese Orthopaedic Association (JOA) score and flexion range of motion (ROM) were lesser in the shelf group (JOA: 49.2 ± 22.4 vs. 60.1 ± 14.5, p < 0.01, flexion ROM: 69 ± 22.4 vs. 82.1 ± 17.5, p < 0.01). There were no significant differences in JOA (88.7 ± 8.7 vs. 92.1 ± 8.0,p = 0.053) and flexion ROM (93.5 ± 17.3° vs. 99.5 ± 8.0, p = 0.08) after the index THA.All cups in both groups were placed at the anatomical hip centre. The cup centre edge angle (cup CE) was significantly lower in the shelf group (21.3°vs. 28.4, p = 0.0011), and ratio of cup coverage over the cup was lower in the shelf group (77.0% vs. 86.9%, p < 0.0001). There was no significant difference in the number of cases where acetabular bone grafting was performed (87.0% vs. 80.4%, p = 0.46). The operative time tended to be longer in the shelf group (117 ± 30.3 min vs. 106.6 ± 25.3 min, p = 0.06), and there was no significant difference in intraoperative blood loss (294.3 ± 33.8 vs. 313.3 ± 25.9, p = 0.50). Conversion THA after prior shelf acetabuloplasty provided encouraging short-term results with no major complications. Prior shelf acetabuloplasty did not complicate subsequent THA. Bone coverage of the acetabular component was inadequate in total hip arthroplasty, even with prior shelf acetabuloplasty.