Aims

Radiostereometric analysis (RSA) studies of vitamin E-doped, highly crosslinked polyethylene (VEPE) liners show low head penetration rates in cementless acetabular components. There is, however, currently no data on cemented VEPE acetabular components in total hip arthroplasty (THA). The aim of this study was to evaluate the safety of a new cemented VEPE component, compared with a conventional polyethylene (PE) component regarding migration, head penetration, and clinical results.

Introduction: Uncemented total hip arthroplasty (THA) is gaining in popularity. Modern stem designs function well also in the long term perspective. However, on the acetabular side, results have been more discouraging, with excessive wear and focal osteolysis being two major problems, which, though often asymptomatic, are common reasons for revision. The quality of the polyethylene liner, geometry and locking mechanism are often discussed as possible causes.

Since 1990, an uncemented titanium screw-in cup with the same outer design, but with two different types of polyethylene liners, has been used at our department. The aim of this study is to detect any differences between the two types of liners in terms of wear behaviour, focal osteolysis and revisions. We present results after a minimum 10 years of follow-up.

Patients and Methods: All patients undergoing a primary uncemented THA at our institution since 1990, who received a Romanus screw-in cup with a hydroxyapatite and porous coated titanium alloy shell were included in the study. Between 1990 and 1994 a cylindrical Hexlocliner with a snap-fit locking mechanism was used (125 patients, 160 hips) and a hemispherical Ringloc-liner was used between 1995 and 1997 (94 patients, 114 hips). All liners articulated with a 28 mm Cobolt-Chrome head on a uncemented Bi-Metric femoral stem. Ein-Bild-Roentgen-Analyse (EBRA) was used to measure the linear wear rate at the 5 and 10 year postoperative follow-up. Osteolysis was assessed on plain radiographs and verified with computed tomography.

Results: Nine patients were lost to follow-up. There were 17 dislocations (8 Hexloc, 9 Ringloc), of which 5 required revision due to dislocation (2 Hexloc, 3 Ringloc). No sign of aseptic loosening in any of the cups or stems was seen. The 10-year survival rate, with revision for excessive wear and/or osteolysis as endpoint, was 88% for the Hexloc group and 98% for the Ringloc group. Patients undergoing cup revision were significantly younger (p=0.029). The mean linear wear rate was 0.21 mm/year in the Hexloc group and 0.10 mm/year in the Ringloc group (p=0.01). After 10 years, the frequency of osteolysis was significantly higher in the Hexloc group (p< 0.001). Risk factors increasing the risk for revison was age below 53 years at surgery, Charnley class A and a Body Mass Index (BMI) below 25.

Discussion: As has been shown in other studies, the Hexloc liner performed poorly with a high percentage of focal osteolysis, a high wear rate and a low 10-year survival. The Ringloc liner performed better in all these aspects. Possible explanations for this could be the better quality of the polyethylene and the hemispherical geometry of the Ringloc-liner. A more rigid attachment to the shell and thereby less fluid pressure changes may also minimize bone resorption.

Background: The standard fixation of femoral stems used for patients with femoral neck fractures is bone cement. Bone cement has side effects related to co-morbidity. The purpose of this study is to evaluate fixation, bone remodelling and clinical results with a new uncemented, fully hydroxyapatite-coated tapered femoral stem (Fracture Stem^®) designed for press-fit insertion in patients with femoral neck fractures.

Methods: Forty patients (25 women, 15 men) at a mean 82 (70–92) years of age with an acute displaced femoral neck fracture were included in the study. The patients were operated with the new stem and received a total hip arthroplasty. Tantalum markers were placed in the proximal femur during surgery. We have so far followed the patients for 1 year postoperatively with radiostereometric measurements, dual-energy x-ray absorptiometry and clinical evaluation including Harris hip score, pain numerical rating scale and health related quality of life.

Results: The stem showed good fixation. Subsidence and stem rotation for all stems but five were close to zero. Maximum total point motion increased above precision error at the 6 weeks follow-up but did not increase significantly after that. All stems with significant migration were stable after 3 months. We have had no per–or postoperative fracture. One stem has had to be revised because of a deep infection. Median bone loss after 6 months was significant (p=0.018 to 0.028) in all zones but Gruen zone 4. Bone loss was greatest in Gruen zone 1, 2, 6 and 7 with 29%, 22%, 18% and 32% loss respectively. Median Harris hip score decreased significantly (p=0.003) from 89 before fracture to 75 and 78 at the 6 weeks and 6 months follow-up. Pain numerical rating scale and Health related quality of life decreased until the 6 week visit but returned to prefracture value at 6 months.

Conclusions: According to these early 1-year results, Fracture Stem^® shows good fixation and fast ingrowth in osteoporotic bone. Periprosthetic bone loss due to stress-shielding was significant in all zones but zone 4. Clinically the stem behaved as expected. According to our results, we propose a randomized cinical trial in a larger patient population as the next step to evaluate this femoral stem.