A histological study of retrieved Cambridge acetabular components.
A new uncemented acetabular component, the Cambridge cup, has been designed to mimic the anatomy and physiology of subchondral bone in order to minimise stress shielding and enhance long-term component stability. Cambridge cups were implanted in a cohort of 50 women who presented with displaced sub-capital fracture of the femoral neck. The cups were manufactured with an hydroxyapatite (HA) coating. Twenty six cups were implanted after removal of the HA. Twelve Cambridge cups were retrieved post-mortem between two and 84 months after implantation. Histological and histomorphometric testing was undertaken to analyse the residual HA coating thickness, bone apposition to the implant surface and particulate wear debris in the surrounding tissues. The HA-coated implants showed significantly greater bone apposition to the implant surface with significantly less fibrous tissue formation than the uncoated implants. Where HA resorption occurred, bone and bone marrow was seen adjacent to the implant. Excessive wear of the ultra high molecular weight polyethylene liner was not seen. The HA-coated components demonstrated good initial bone implant bonding and the flexible carbon polymer appeared to maintain stability following HA resorption. The uncoated implants showed little or no bony apposition but had a fibrous membrane apposed to the implant surface. This may be explained by a combination of micro-motion at the bone implant interface and having a component surface finish that was poorly suited to osseous attachment. Hydroxyapatite coated acetabular components can provide reliable osseous attachment. Subsequent HA resorption need not compromise medium-term osseous fixation to an appropriate implant surface.
Orthopaedic Research Unit, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK. rb10003@cam.ac.uk
Roger A
RA
Brooks
Richard E
RE
Field
Eric
E
Jones
Asheesh
A
Sood
Neil
N
Rushton
D000077:Acetabulum; D017886:Durapatite; D005260:Female; D005265:Femoral Neck Fractures / Q000601:surgery*; D006621:Hip Joint / Q000473:pathology; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design
D017886:Durapatite