Abstract
Introduction: Osteolysis is a recognised complication in both cemented and cementless arthroplasty. This may be caused by macrophage mediated reaction to small particulate polyethylene debris. The effective joint space describes the area where polyethylene particles may travel, such as through holes in the cup, to cause a local osteolytic process.
Methods: Twenty four cases of osteolysis (in twenty three patients) requiring revision were identified from patients on whom we had performed the primary arthroplasty. These cases were compared to an overall group of 560 primary hip arthroplasty cases performed during the same time and with the same implants.
Results: The 24 index cases were revised for osteolysis. This represents 4.3% of the total group in this series of implants. Secondary loosening of the acetabular component was present in 7/24 with 13/24 cups being well fixed at the time of revision. All the cups with secondary loosening had evidence of bone ingrowth & had been undermined by the osteolytic process. In 4 cases, either a pelvic fracture or pelvic dissociation had occurred through an osteolytic lesion. In 21 cases femoral stems were revised, but none of these were loose, and none had significant osteolysis around the stems.
The average time from primary procedure to revision was 72 months. The osteolytic group was younger than the overall group at the time of index surgery (53 years vs 63 years, p< 0.0001). There were 16 females and 7 males (p = 0.06). The osteolytic group were also less likely to have an initial diagnosis of primary osteoarthritis than the control group (p=0.05). Other diagnoses in the osteolytic group included dysplasia, previous trauma and inflammatory arthropathy.
Acetabular liner thickness was assessed for all patients. The osteolytic group had a significantly higher proportion of cases with polyethylene thickness of less than 7mm (p < 0.005), and less than 6mm (p < 0.0001). There was no difference in the mean height and weight of the two groups.
Conclusion: Osteolysis is multifactorial and facilitated by screw holes in the acetabular shell that increase the “effective joint space.” Younger females with small ace-tabular components and thin polyethylene are most at risk. Alternate bearing surfaces or acetabular components without holes may alleviate this problem. These cases represent our experience with osteolytic lesions within the acetabulum requiring revision. There were no cases of cup loosening in our overall group other than the 7/24 that had been undermined by the osteolytic process. Revision to ceramic on ceramic bearing implants is our preferred method of treating this problem.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
