Hip
The debate of which bearing to use in a total hip arthroplasty continues.
A recent paper in The Bone & Joint Journal by Garcia-Rey et al1 added further weight to the argument that metallic heads on highly cross-linked polyethylene maybe the answer. This group reported on a randomised study comparing highly cross-linked polyethylene (HXLPE) with ultra-high molecular weight polyethylene (UHMWPE). The mean penetration of the femoral head at 6 weeks was 0.08 mm for the HXLPE and 0.16 mm for the UHMWPE group. The mean yearly linear penetration was 64.8% lower in the HXLPE group compared with the UHMWPE group and the results at 10 years showed a mean linear femoral head penetration in the HXLPE group that was 61% less. There was one possible, significant confounding factor in that a stainless steel head was used in the UHMWPE group and a cobalt chrome head was used in the HXLPE group. However, the authors argued that these materials have practically the same hardness, roughness and wettability and therefore behave the same tribologically. Although the clinical and radiological results in this study are encouraging there are still some concerns regarding the hosts’ response to the wear-debris from HXLPE.2 A bearing which generates less ‘biologically-active’ debris such as ceramic on ceramic may be a more attractive option. ...
Delta ceramic with its smaller grain size, smaller asperities and being highly wettable has many positive characteristics when considering it as a bearing in total hip arthroplasty. Some authors have even considered using it in a revision setting. Jack et al3 reported 165 revisions in situations when there was a well fixed femoral stem. In an isolated acetabular revision the authors revised the femoral heads to a ceramic head with a titanium sleeve over the used trunnion of the retained stem. The revised socket also had a ceramic liner creating a ceramic on ceramic bearing. Of the 165 revisions there were 65 Delta ceramic bearings and 100 Alumina. There were no reports of squeaking but there were 2 fractures of the alumina femoral heads. There were no fractures in the Delta ceramic group. At 8.3 years the survival with any cause of failure as an endpoint was 96.6% for the acetabular component and 94% for the femoral component. We still need more long term data on ceramic-on-ceramic bearings particularly in the younger, more active patient group. Whether we should be using it in the revision setting is up for debate but this courageous study has great results at mid-term follow up.
In hip preservation surgery a number of authors have suggested that femoro-acetabular impingement results from a combination of cam and pincer pathology. Masjedi et al4 have given more weight to the argument that cams occur in isolation and attempts to trim the acetabular rim in this group may result in edge loading and subsequent accelerated wear. This study highlights the importance of getting good imaging of the hip before making a diagnosis. In a patient with clinical impingement a standing AP Pelvis gives a good ‘functional’ view of the acetabulum to help determine whether there is either a retroverted socket or a true pincer. In addition a Dunn lateral view gives a good profile view of the head neck junction. If there is any doubt a dynamic hip arthrogram performed in theatre by the surgeon involved in the patients’ care and an MRI arthrogram including sagittal oblique slices through the hip can be helpful.
Mr Chris Gooding, Locum Consultant Orthopaedic Surgeon, Addenbrooke's Hospital, Cambridge
May 2013
References
1. García-Rey E, García-Cimbrelo E Cruz-Pardos A. New polyethylenes in total hip replacement: A ten- to 12-year follow-up study. Bone Joint J 2013;95-B:326-332.
2. Illgen RL 2nd, Forsythe TM, Pike JW, Laurent MP, Blanchard CR. Highly crosslinked vs conventional polyethylene particles--an in vitro comparison of biologic activities. J Arthroplasty 2008;23:721–731.
3. Jack CM, Molloy DO, Walter WL, Zicat BA, Walter WK. The use of ceramic-on-ceramic bearings in isolated revision of the acetabular component. Bone Joint J 2013;95-B:333-338.
4. Masjedi M, Nightingale CL, Azimi DY, Cobb JP. The three-dimensional relationship between acetabular rim morphology and the severity of femoral cam lesions. Bone Joint J 2013;95-B:314-19.
