Research Article: No adverse effects of submelt-annealed highly crosslinked polyethylene in cemented cups

Date Published: April 24, 2012

Publisher: Informa Healthcare

Author(s): Stephan M Röhrl, Bo Nivbrant, Kjell G Nilsson.


Highly crosslinked polyethylene (PE) is in standard use worldwide. Differences in the crosslinking procedure may affect the clinical performance. Experimenatal data from retrieved cups have shown free radicals and excessive wear of annealed highly crosslinked PE. We have previously reported low wear and good clinical performance after 6 years with this implant, and now report on the 10-year results.

In 8 patients, we measured wear of annealed highly crosslinked PE prospectively with radiostereometry after 10 years. Activity was assessed by UCLA activity score and a specifically designed activity score. Conventional radiographs were evaluated for osteolysis and clinical outcome by the Harris hip score (HHS).

The mean (95% CI) proximal head penetration for highly crosslinked PE after 10 years was 0.07 (–0.015 to 0.153) mm, and the 3D wear was 0.2 (0.026 to 0.36) mm. Without creep, proximal head penetration was 0.02 (–0.026 to 0.066) mm and for 3D penetration was 0.016 (–0.47 to 0.08) mm. This represents an annual proximal wear of less than 2 µm. All cups were clinically and radiographically stable but showed a tendency of increased rotation after 5 years.

Wear for annealed highly crosslinked PE is extremely low up to 10 years. Free radicals do not affect mechanical performance or lead to clinically adverse effects. Creep stops after the first 6 months after implantation. Highly crosslinked PE is a true competitor of hard-on-hard bearings.

Partial Text

In 2000, 10 hips in 10 patients were operated consecutively with annealed highly crosslinked polyethylene cups. The patients had a mean age of 61 (49–79) years. We refer to Röhrl et al. (2005, 2007) for further information regarding the surgical technique and information about the patients.

Since the introduction of highly crosslinked PE, there has been an ongoing discussion about whether the free radicals that are scarcely trapped in the annealed PE would lead to degeneration and cause inferior performance of the PE. Excessive wear of annealed HXLPE has been detected in various retrieval studies (Kurz et al. 2006b, Wannomae et al. 2006, Currier et al. 2007). In accordance with earlier clinical studies reporting on PE full of free radicals (Oonshii et al.1998), we found hardly any wear in the cemented cups with annealed highly crosslinked PE at 10 years. The clinical outcome was excellent.