CATASTROPHIC FAILURE OF METAL HEADS IN REVISION TOTAL HIP ARTHROPLASTY DONE FOR CERAMIC FRACTURES.

Abstract

Introduction: The tribiological properties of bearing surfaces are one of the main topics in discussion in the orthopaedic research. Hard-on-hard bearings are one of the ways to reduce wear rates. Modern hard-on-hard bearing low wear rates depend on the correct pairing of bearing surfaces and strict manufacturing tolerances in surface roughness, clearance, and roundness.

There have been some concerns in using ceramic bearings, particularly regarding the fracture rate and their subsequent management. Hence, we present here 2 similar cases that highlight the catastrophic failure of metal head when used subsequently to treat the complication of ceramic fractures in Total Hip Arthroplasty (THA).

Case Details: Two patients underwent primary THA at different centres with ceramic-on-ceramic bearing. After an initial asymptomatic period of 2 years, ceramic fracture occurred in both the cases, which were subsequently replaced by metal-on-polyethylene bearings by the primary surgeons. One year after the revision of bearings, both the patients developed severe pain and discomfort, which on further investigation revealed massive metallosis, wear of the metal head and aseptic loosening of the acetabular components with cavitation in acetabulum.

Both the patients underwent revision THA under the senior author at our tertiary centre-Wrightington Hospital. Intraoperatively near total erosion of the metal head was noted with more than one litre of black, dense material collection in and around the hip joint revealing extensive metallosis. The acetabular cup was grossly loose and significant loss of bone stock was noted due to metallosis.

Single stage revision surgery was performed with impaction bone grafting for deficient acetabulum and cemented components were used. At one-year follow-up none of the cases have shown any further wear or complications.

Conclusion: One of the main objectives of successful THA is to improve implant longevity. To achieve this understanding the mechanisms of wear between the interacting surfaces is extremely important. The use of ceramic head is good, but there is always a risk of fracture. We do not recommend using metal heads in cases with prior ceramic fractures, as the wear of metal is most likely to occur as it is an ongoing process due to the residual ceramic debris. Hence in these difficult scenarios we recommend usage of ceramic-on-polyethylene as a safe option to prevent catastrophic erosion of metal head and improve implant longevity.