Abstract
Background
The clinical results of total hip arthroplasty (THA) with a cementless prosthesis have been constantly improving due to progress in the area of stem design and surface finish. However, majority of stems are well-fixed with canal filling or diaphyseal fit, and cortical hypertrophy or metaphyseal bone atrophy has been often observed. Cementless Spotorno stem (CLS stem; Zimmer, Warsaw, USA) is a double-tapered rectangular straight stem. The purpose of this study is to investigate the mean 13 years' results of CLS stem and to evaluate the press-fit stability of CLS stem.
Methods
Between 1999 and 2004, we treated 134 patients (142 hips) with CLS stem. Of those patients, 86 females (92 hips) and 13 males (14 hips), in total 99 patients (106 hips) were available at minimum of 11 years after surgery. At the time of follow-up, six females and five males were dead. The follow-up rate was 82% and the mean follow-up period was 13 years (SD; 20, range; 11–16). The mean age at the time of surgery was 65 years (SD; 10, range; 38–86). The mean body mass index was 24 (SD; 1.8, range; 19 to 28). Preoperative diagnoses were osteoarthritis in 92 patients, osteonecrosis in five patients, and rheumatoid arthritis in two patients. Majority of the patients were female because 84 patients of osteoarthritis suffered from hip dysplasia. For cementless acetabular reconstruction, APR cups (Zimmer, Warsaw, USA) were implanted in 10 hips, IOP cups (Zimmer, Warsaw, USA) in 22 hips, and Converge cups (Zimmer, Warsaw, USA) in 74 hips. As the liner of acetabular component, conventional UHMWPE (Sulene: Zimmer, Warsaw, USA) was used in APR cup and highly crosslinked UHMWPE (Durasul: Zimmer, Warsaw, USA) in IOP and Converge cups. The lipped liner was chosen in all cases, and lipped lesion was placed posteriorly. The radiographic stability of the femoral stem was determined by Engh's criteria. The ascertained period of spot welds was noted by Gruen zones on the femoral side. The presence of stress shielding, and subsidence was also evaluated.
Results
A stable stem with bony on-growth was identified in all cases. The mean period of expression of spot welds was 11 months in zone 2, 10 months in zone 3, 9 months in zone 5, and 9 months in zone 6. Stress shielding of more than grade 2 was observed in only 8 hips, which was non-progressive at 1 year after surgery. Subsidence of more than 2mm was not observed in any of the hips. The cortical hypertrophy at the tip of stem was not observed. The postoperative dislocation occurred in six hips (6%) and periprosthetic femoral fracture occurred in two hips (2%). Revised surgery was performed in three hips for a recurrent dislocation and two periprosthetic femoral fracture.
Conclusions
Excellent stability of CLS stem has been maintained without abnormal bone reaction at proximal femur. CLS stem is considered to achieve not only press-fit stability at trochanteric and subtrochanteric level, but bony fixation by osseointegration within 1 year after THA.
