The position of the acetabular component affects the result of total hip arthroplasty(THA) in terms of postoperative dislocation, impingement, wear etc.

However, as it is much difficult to place the component in the appropriate position for the cases of severe acetabular deformity, we used a Computed tomography(CT)-based navigation for THA in such cases. Therefore, the purpose of this study was to estimate the accuracy of a CT-based navigation in terms of acetabular component positioning in THA for severe acetabular deformities.

13 patients (1 man, 12 women), 14 hips underwent THA using a posterolateral approach with a CT-based navigation. The diagnoses were severe developmental dysplasia (Crowe group III, IV) in 6, ankylosis in 3, destructive arthritis after infection in 2, Charcot joint, and arthrodesed hip. And, we evaluated the differences of component position from the center of the anterior pelvic plane(APP), anteversion angle, and inclination angle relative to APP between the intraoperative data from the navigation system and the data from postoperative CT. Considering the intra-observer error, the measurement was done three times respectively and the mean value was accepted. We also estimated the difference between the component size planned and that implanted.

The mean difference between intraoperative records and actual postoperative results of the component position shows 3.3 mm(range: 0–7.0, SD: 2.2) for the horizontal position, 3.2 mm(range: 0–9.7, SD: 4.5) for the vertical position, 4.4 mm(range: 2.0–7.7, SD: 1.6) for the antero-posterior position from the center of the APP, 1.3 degrees(range: 0–3.0, SD: 0.9) for the inclination and 2.9 degrees(range: 0.3–8.3, SD: 2.2) for the anteversion respectively. All components were placed in the safe zone by Lewinnek. The component size was predicted in 10/14(71.4%) hips. There were no complications related to the use of the navigation.

This study showed the accuracy of cup positioning using a CT-based navigation in THA for the cases of severe acetabular deformity. We concluded that this system was a useful tool for surgeon to identify orientation, implant acetabular component at the precise position and angle, and to reduce the incidence of some complications especially for patients with these severe acetabular deformities.

Objective: The treatment of osteonecrosis of the femoral head (ONFH) in young active patients remains a challenge. The purpose of this study was to determine and compare the clinical and radiographic results of the two different hip resurfacing systems, hemi-resurfacing and metal-on-metal total-resurfacing, in patients with ONFH.

Materials and Methods: We retrospectively reviewed 20 patients with 30 hips with ONFH who underwent hemi-resurfacing or total-resurfacing between November 2002 and February 2006. We mainly performed hemi-resurfacing for early stage ONFH, and total-resurfacing for advanced stage. Fifteen hips in 11 patients had a hemi-resurfacing component (Conserve, Wright Medical Co) with the mean age at operation of 50 years and the average follow-up of 5.5 years. Fifteen hips in 10 patients had a metal-on-metal total-resurfacing component (Birmingham hip resurfacing, Smith & Nephew Co.) with the mean age at operation of 40 years and the average follow-up of 5 years. Clinical and radiographic reviews were performed.

Results: The average postoperative JOA hip scores were 86 points in hemi-resurfacing, 96 points in total-resurfacing. The difference of pain score was a main factor to explain the difference of total JOA hip score in the two groups. Both implants were radiographically stable, but radiolucent lines around the metaphyseal stem were more frequent in total-resurfacing. In hemi-resurfacing patients, ten of 15 hips had groin pain or groin discomfort, three hips were revised to total hip arthroplasties (THA) because of femoral neck fracture, acetabular pro-trusio, and osteoarthritic change, respectively. On the other hand, in total-resurfacing patients, there were no revision and no groin pain.

Discussion: In the prosthetic treatment of young active patients with ONFH, it is theoretically desirable to choose an implant with conservative design in anticipation of the future revision surgery. Hemi-resurfacing hip arthroplasty is the most conservative implant for the treatment of ONFH. However, the results of hemi-resurfacing in this study have been very disappointing due to high revision rates and insufficient pain relief despite of the good implant stability. On the other hand, the pain relief and implant survivorship after total-resurfacing were superior to the results of hemi-resurfacing, although the usages of the total-resurfacing were for more advanced cases. These results suggested that total-resurfacing was a more valuable treatment option for active patients with ONFH than hemi-resurfacing