Aims

The primary aim of this study was to compare the wear properties of vitamin E-diffused, highly crosslinked polyethylene (VEPE) and one formulation of moderately crosslinked and mechanically annealed ultra-high molecular weight polyethylene (ModXLPE) in patients five years after primary total hip arthroplasty (THA). The secondary aim was to assess the clinical results of patients treated with VEPE by evaluating patient-reported outcome measures (PROMs), radiological evidence of fixation, and the incidence of mechanical failure.

The primary purpose of the current study was to evaluate and compare the wear properties of vitamin E-doped, highly-crosslinked PE (VEPE) and one formulation of moderately cross-linked and mechanically-annealed ultra-high molecular weight PE (ModXLPE) in patients five years after primary THA. We also sought to understand whether polyethylene wear is associated with radiographic evidence of bone resorption or with deterioration in patient-reported outcome measures (PROMs).

A total of 221 patients from four international centers were recruited into a prospective RSA and clinical outcomes study. Seventy percent (76%) of patients received VEPE (vs. ModXLPE) liners, and 36% received ceramic (vs. metal) femoral heads. PROMs and radiographs were collected preoperatively and at one, two, and five years postoperatively. In addition, RSA radiographs were collected to measure PE wear.

We observed similar bedding in through the one-year interval and wear through the two-year interval between the two liner types. However, there was significantly more femoral head penetration in the ModXLPE cohort compared to the VEPE cohort at the five-year follow-up (p<0.001). The only variables independently predictive of increased wear were ModXLPE (vs VEPE) liner type (β=0.22, p=0.010) and metal (vs. ceramic) femoral head type (β=0.21, p=0.013). There was no association between increased wear and radiolucency development (p=0.866) or PROMs. No patients were found to have evidence of osteolysis.

At five-years postoperatively, patients treated with VEPE (vs. ModXLPE) and ceramic (vs. metal) femoral heads demonstrated decreased wear. At the longest follow-up (five years postoperatively), the wear rates for both liner groups were very low and have not led to any osteolysis or implant failures via aseptic loosening.

Osteolysis secondary to ultra-high molecular weight polyethylene (UHMWPE) wear is a leading cause of late-term implant failure via aseptic loosening in patients treated with total hip arthroplasty (THA). Radiation crosslinking of UHMWPE has been shown to decrease wear. However, the resulting polymer (crosslinked-PE) has a high free radical content. Two different methods that have been used to reduce the remaining free radicals are mechanical annealing and chemical stabilization using Vitamin E, a free radical scavenger.

The primary purpose of the current study was to evaluate and compare the wear properties of vitamin E-doped crosslinked-PE (VEPE) and one formulation of mechanically annealed crosslinked-PE using radiostereometric analysis (RSA) in patients five years after primary THA. We also sought to understand the association between polyethylene wear and patient-reported outcome measures (PROMs).

Three-hundred and five patients from six international centers were enrolled. Seventy-six percent were treated with highly-crosslinked (95 kGy) VEPE liners, and the rest received moderately-crosslinked (50 kGy) (ModXL), mechanically annealed liners. Data was collected prospectively at one-, two-, and five-year intervals.

At the 5-year follow-up, proximal femoral head penetration into the VEPE liners (median = 0.05mm (range, −0.03–1.20)) was significantly lower than the penetration into the ModXL liners (median = 0.15mm (range, −0.22–1.04)) (p<0.001). In the VEPE cohort the median proximal penetration did not increase from one- to five-year follow-up (p=0.209). In contrast, there was a significant increase in femoral head penetration for the ModXL group (p<0.001) during that same time. Multivariable regression showed that the only variable predictive of increased wear was ModXL liner type (B=0.12, p<0.001). There were no differences in PROMs between the liner groups, and there was no correlation between polyethylene wear and PROMs for the cohort as a whole.

The current study is the largest analysis of polyethylene wear at five-year follow-up using the RSA technique. We observed similar bedding in through the two-year interval between the two liner types, however, there was significantly more wear in the ModXL cohort at five-years. Currently, the wear rates for both liner groups are below the osteolysis threshold and have not led to any implant failures via aseptic loosening. Continued follow-up will provide a better understanding of the association between wear rate and clinical outcomes.

Aims

It has been suggested that cemented fixation of total hip arthroplasty (THA) is associated with an increased peri-operative mortality compared with cementless THA. Our aim was to investigate this through a nationwide matched cohort study adjusting for age, comorbidity, and socioeconomic background.

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.