Abstract
Introduction: The Optiplug® bio-absorbable cement restrictor, marketed by Biomet inc., is manufactured from ‘PolyActive’ – a polymer of poly(ethylene glycol) and butylene terephthalate. Biodegradation is thought to be by a combination of hydrolysis and oxidation.
The potential benefit – eliminating the need for restrictor removal at future revision surgery – led to Optiplug becoming our cement restrictor of choice over the last 5 years.
Anecdotally we have seen marked osteolysis around the distal cement mantle in a number of follow up radiographs in these patients. To date we have not seen an associated peri-prosthetic fracture.
We undertook a retrospective, radiographic study to determine incidence, severity and progression of this osteolysis over the first 5 years of follow up.
Method: 100 patients for whom 5 year follow up had been undertaken were identified from the departmental database. Patients with loose prostheses and or infection were excluded as were those who had undergone revision surgery.
Radiographs from the immediate post operative period, twelve months and five years follow up visits were identified and reviewed.
Osteolysis was quantified by calculating the ratio of maximum medullary diameter to the overall cortical diameter of the bone. Comparison was made over time and, where radiographs allowed, to the immediately adjacent femur.
Results: 87% of radiographs showed greater than 10% thinning of the cortex at 1 year cf. immediate post op. 5 cases showed greater than 33% thinning. These changes do not appear to progress or regress significantly between 1 and 5 years.
Discussion: While marked osteolytic changes appear to be uncommon, some degree of cortical thinning was almost universal in this series. The zone immediately distal to the cement mantle is commonly involved in peri-prosthetic fractures. Any weakening in this area is undesirable.
Correspondence should be addressed to: British Hip Society, 35–43 Lincoln’s Inn Fields, London, WC2A 3PE, England. Email: c.wilson@boa.ac.uk
