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• Results of a randomized controlled trial with five-­year radiostereometric analysis of Vitamin E-­infused highly crosslinked versus moderately crosslinked polyethylene in reverse hybrid total hip arthroplasty

Peder S. Thoen^1,2,4, Lars Nordsletten^1,4, Are H. Pripp³, Stephan M. Röhrl¹

1. Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway

2. Department of Surgery, Vestfold Hospital Trust, Tønsberg, Norway

3. Oslo Centre of Biostatistics and Epidemiology, Oslo University Hospital, Oslo, Norway

4. Institute of Clinical Medicine, University of Oslo, Oslo, Norway

Introduction: The beginning of the 21st century has seen the arrival of Vitamin E-infused highly cross-linked polyethylene (VEPE), which has the potential to further improve the wear properties of moderately and highly crosslinked polyethylenes (ModXLPE and HXLPE) used in total hip arthroplasty (THA). There are few studies analysing the outcomes of Vitamin E-infused components in cemented arthroplasty, though early acetabular component migration has been reported. The goal of this study was to measure five-­year polyethylene wear and acetabular component stability of a cemented VEPE acetabular component compared with a ModXLPE cemented acetabular component.

Material and method: In a prospective randomized controlled trial, we assessed polyethylene wear and acetabular component stability (primary outcome) with radiostereometric analysis in 68 patients with reverse hybrid THA at five years follow-­up. Patients were randomized to either a VEPE or a ModXLPE cemented acetabular component.

Results: Mean polyethylene wear in the proximal direction was 0.17 mm (SD 0.15) for the VEPE group and 0.20 mm (SD 0.09) for the ModXLPE group (p = 0.005) at five years. Annual proximal wear rates were 0.03 mm/year (VEPE) and 0.04 mm/year (ModXLPE). Total 3D wear was 0.21 mm (SD 0.26) and 0.23 mm (SD 0.10) for the VEPE and ModXLPE groups, respectively (p = 0.009). Total 3D cup translation was 0.72 mm (SD 0.70) (VEPE) and 0.50 mm (SD 0.44) (ModXLPE) (p = 0.409).

Interpretation and conclusion: Both VEPE and ModXLPE cemented components showed low annual wear rates at five years. There was less polyethylene wear in the VEPE group than in the ModXLPE group. Component stability was similar in the two groups and remained constant up to five years. Whether these results will equate to a lower long-term revision rate is still unknown.

30

• Vitamin-E doped polyethylene show superior wear pattern compared with conventional polyethylene in cemented cups. A randomized 5-year RSA study.

Halldor Bergvinsson, Vasilieos Zampelis, Martin Sundberg, Jon Tjörnstrand and Gunnar Flivik.

Department of Orthopedics, Skåne University Hospital, Clinical Sciences, Lund University, Lund, Sweden.

Introduction: The manufacturing process of highly cross-linked polyethylene (HXLPE) can produce free radicals that can contribute to wear. To improve the oxidative stability of the HXLPE, vitamin-E was introduced in the manufacturing process. There have been several studies published on vitamin-E in uncemented THA but only a handful for cemented cups.

The purpose of this study was to compare the initial creep and following wear pattern of cemented vitamin-E doped polyethylene (VEPE) and conventional ultra-high molecular weight polyethylene (UHMWPE) cups, using radiostereometry (RSA) over a 5-year period. 

Material and method: 48 patients with primary osteoarthritis, scheduled for a cemented THA were randomized 1:1 to either a VEPE (E1®) or UHMWPE (Arcom®) cup. The patients were followed-up for 5 years with repeated RSA examinations (postoperatively, then at 3, 12, 24, and 60 months), as well as a hip-specific outcome questionnaire (HOOS).

Results: During the first 3 months both groups showed expected polyethylene creep of 0.07 mm (95% CI, ±0.04) mm for the UHMWPE and 0.06 mm (95% CI, ±0.07) mm for the VEPE cups. Between 3 months and 5 years there was steady linear wear of the UHMWPE cup with total y-translation of 0.46mm (95% CI, ±0.11) mm, corresponding to 0.08 mm/year. The VEPE showed total y-translation of 0.09 (95% CI, ±0.07) mm at 5-years, annual wear 0.01 mm/year. There was no difference in cup migration or clinical outcome between the groups and no cups were revised.

Interpretation and conclusion: Vitamin-E doped HXLPE shows good results and very little wear when compared with UHMWPE in cemented cups up to 5 years. There was no difference in cup migration or patient self-reported outcome.

Keywords: Radiostereometry, RSA, cemented, THA, wear, VEPE, UHMWPE. 

31

• Polyethylene wear in total hip arthroplasty; comparing Oxinium and CoCr femoral heads using radiostereometry with 10 years follow-up.

Håkon Greve Johannessen¹, Thomas Kadar², Geir Hallan^1,3,4, Anne Marie Fenstad³, Kristin Haugan⁵, Paul Johan Høl^1,6, Mona Badawy⁴, Terje Stokke⁷, Benedikt Jonsson⁹, Kari Indrekvam^1,4, Arild Aamodt⁸, Ove Furnes^1,3,

¹Department of Clinical Medicine, Faculty of Medicine, University of Bergen, Bergen,    Norway. ²Department of Physical Medicine and Rehabilitation, Haukeland University Hospital, Bergen, Norway. ³The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway. ⁴Coastal Hospital in Hagavik, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway. ⁵Department of Orthopaedic Surgery, St. Olavs Hospital, Trondheim, Norway. ⁶Department of Orthopaedic Surgery, Biomatlab, Haukeland University Hospital, Bergen, Norway. ⁷Department of radiology, Haukeland University Hospital, Bergen, Norway. ⁸Department of Orthopaedic Surgery, Lovisenberg Diakonal Hospital, Oslo, Norway. ⁹Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway.

Introduction: This study was done, in part, to investigate the polyethylene (PE) wear resulting from femoral heads made of oxidized zirconium (OxiniumÔ) in total hip arthroplasty. Oxinium was introduced as a material aiming to reduce the amount of PE wear and therefore the risk of aseptic loosening. We wanted to measure the difference in PE wear in hips with Oxinium heads to cobalt-chromium (CoCr) heads in a randomized clinical trial using radiostereometric analysis (RSA).

Material and method: From 2004 to 2007, 120 patients with a mean age of 70 years were included and randomized into four groups. An additional group that received a cemented Charnley/Ogee prosthesis was also included, but is not a part of this sub study. All patients received a cemented Spectron EF stem with a 28 mm femoral head and a cemented Reflection All-Poly cup. The head-cup couplings were either Oxinium or CoCr as head material against conventional or highly crosslinked PE in the acetabular cup. The patients were followed with repeated RSA examinations over ten years. The Harris Hip Score was used for clinical outcome assessment.

Results: Forty-two patients had adequate RSA measurements at ten years follow-up. We found no statistical significant difference in PE wear in hips with Oxinium heads or CoCr heads, neither with conventional (1.64 mm (SD 0.66 mm) vs. 1.58 mm (SD 0.49) (p=1.0)) nor highly-crosslinked (0.21 mm (SD 0.12 mm) vs. 0.28 mm (SD 0.12 mm) (p=0.66)) PE cups. There was also no statistical difference in HHS between the groups (p=0.679).

Interpretation and conclusion: After 10 years Oxinium heads did not give statistically significant reduction of PE wear compared with CoCr heads. Considering the additional cost, widespread use of Oxinium could be questioned, and potential benefits other than PE wear should be studied.

32

• Low wear of thin second-generation highly cross-linked polyethylene liners with large articulations at ten years

David Campbell^1,2; John Field¹; Stuart Callary^2,3. ¹Centre for Orthopaedic and Trauma Research, The University of Adelaide, Adelaide, South Australia. ²Wakefield Orthopaedic Clinic, Calvary Wakefield Hospital, Adelaide, SA. ³Department of Orthopaedics and Trauma, Royal Adelaide Hospital, Adelaide, South Australia

Introduction: The reduced in vivo wear properties of highly cross linked polyethylene (XLPE) in total hip arthroplasty (THA) has led to an increased use of larger articulations which have been shown to reduce the incidence of early dislocation. To date, there are no long term reports of the wear of second generation XLPE liners against larger articulations. The aim of this study was to measure the early bedding-in and the ten year wear rate of a second generation XLPE liner in combination with articulations of 36mm and 40mm and compared our findings with previous clinical and in vitro studies of the same material.

Materials and Methods: All patients received either a 36 or 40mm articulation at the time of primary THA (1). Using radiostereometric analysis (RSA) the femoral head penetration was measured for 13 patients at 6 months, 1, 2, 5 and 10 years. The annual wear rate was compared to our previous cohort of 17 patients who received a 32mm articulation (2).

Results: The median proximal bedding-in observed within the first postoperative year, was 0.016 mm (range -0.157 to 0.138). The median proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 10 years were all less than 0.01 mm/year. There was no significant difference in the bedding-in or wear of the current study of larger articulations when compared to our previous study of 32mm articulations.

Interpretation and conclusion: The in vivo wear rate of these larger articulations was very low at 10 years and similar to the 32mm articulations. This low level of wear remains encouraging for the future clinical performance of this material.