Abstract
Retrospective analysis of 25 consecutive metal on metal proximal femoral replacements performed at our unit between 1965 and 1979.
Methods. Patients were: clinically evaluated using the Modified Harris Hip and Enneking Scoring Systems and radiologically using the ISOLOS scoring system.
The concentration of Cr, Co, Ti, Al, V, Mo & Ni in whole blood and urine was also measured by High-Resolution Inductively Coupled Mass Spectrometry and compared with controls and patients with other implants.
Retrieved prostheses (in situ for in excess of 25 years) were analysed for roughness and wear using a Mitutoya form tracer and an electron microscope.
Results. Thirteen patients have since died; nine from metastatic disease and four from other causes. Of the remainder, eleven (44%) are still alive, five still retaining metal on metal articulations and one has been lost to follow up. They have been in situ for an average of 32 years. The average modified Harris Hip score is 76 (53–93) and the average Enneking Score is 74 (63–90).
In the retrieved prostheses the contact zones were found to be smoother (Ra 0.05?m), have fewer and smaller carbides together with evidence of ‘self-healing’ when compared to the original surface (Ra 0.32?m).
Blood & urine levels of Co & Cr were significantly elevated. Co levels were exceptionally elevated in loose prostheses but levels quickly fell following revision.
Conclusion. We have shown the potential longevity of metal on metal arthroplasty. The wear seen in retrieved specimens is low and we might expect to improve the fixation by reducing the torque with apical bearing and encouraging extra-cortical bone bridging with hydroxy-apatite coated collars. Elevated serum and urine Co levels may well predict a loose prosthesis and may be useful as a screening tool.
The abstracts were prepared by Mr Roger Tillman. Correspondence should be addressed to BOOS at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PN
