As manufacturers and surgeons strive for advances in the use and longevity of hip replacements, designs of implants may change. It is inherent upon us as surgeons, who have the interests of our patients as primary concern, to monitor the results of our interventions and report them.
The paper by Donell et al is important for several reasons. They identify a prosthesis that they have found to fail early warranting further scrutiny, the paper adds further data to the emerging understanding of patients who have a reaction to ions produced by their metal-on-metal articulation, and it highlights the benefits of comprehensive data collection and surveillance of patients.
The authors report a cohort of 652 hips in young patients (mean age 57 years) with a standard range of pre-operative hip pathology undergoing a hybrid metal-on-metal total hip arthroplasty using an uncemented acetabular component and a cemented cobalt-chromium polished stem. The cohort has high data capture and low loss-to-follow-up. They report on a cohort that is realistic and recognisable to many institutions in terms of grade of operating surgeon, number of surgeons, range of approaches used, cement grade, component positioning and early post-operative complications. At a mean five-year follow-up they report a 14% rate of revision. Half of these hips were revised for pain, and the majority of these patients had normal radiographs. Revisions for infection and dislocation were within expected limits.1
Of the hips that were revised, 76% had an acetabular inclination measured between 30° and 50°, thus demonstrating that factors other than implant malpositioning might be contributory. The authors attribute the early failure to localised necrosis following massive metallosis of unknown cause. Peri-prosthetic necrosis and fluid under pressure can be the result of a tissue reaction to localized high volume of metal ions, or as a result of a type IV hypersensitivity reaction.
The authors report nerve involvement in a pseudotumour, resulting in a sciatic nerve palsy that did not improve after revision. Case reports are emerging of this phenomenon, also those involving the femoral nerve. The results of grafting the nerve in this situation are unknown.2 The continued reporting of the outcome of nerve injury under these circumstances is important.
The majority of patients with a metal-on-metal articulation have a well performing implant, and the impulse to ‘throw the baby out with the bath water’ should perhaps be avoided. However, adverse reactions in patients with specific implants and bearings are important for selection of well-performing implants. The risk of developing adverse soft tissue reactions to metal-on-metal implants may be multi-factorial3 and related to patient factors, surgical positioning of the implant and specific implant tribology. In the context of the Medical Device Alert of Metal-on-metal hip replacements issued by the MHRA on 22nd April 20104 and Advice to surgeons from the British Hip Society and the British Orthopaedic Association regarding the withdrawal of the DePuy ASR and XL metal-on-metal bearings 25th October 2010,5 this paper highlights the importance of surveillance of patients with a metal-on-metal hip articulation. Donell et al draw attention to pain as one of the first clinical features of a failing metal-on-metal hip and (after exclusion of infection, fracture, referred pain, loosening and soft tissue impingement) MARS MRI or ultrasound examination and measurement of blood cobalt and chromium ions are indicated. Pain may be related to fluid under pressure in the soft tissues. Revision surgery should be performed early to prevent progressive and extensive soft tissue damage, which is associated with poor outcomes after revision.6
The biological patient factors associated with early failure of metal-on-metal hips are incompletely understood. Donell et al suggest that a subtype of patients may have an idiosyncratic immune response to ions generated by their hip articulation. This raises the possibility of genetic or environmental factors contributing to the patients’ biological reaction to metal ions. This perhaps furthers the case for localised patient surveillance of all arthroplasty patients; registries may not pick up adverse reactions in patients in a geographical area where there is a higher than expected failure rate of an implant or bearing.
The management of patients with a painful metal-on-metal hip arthroplasty requires a multi-disciplinary approach; specialist hip surgeons, radiologists and pathologists are necessary to perform the appropriate investigations and management of the patient. Donell et al formed an investigating committee of expert personnel at the request of the Research and Ethics Committees. The quality of interpretation of radiological and pathological specimens is clinician dependent, as is the results of revision surgery. These patients may be optimally managed in regional centres of expertise. Retrieved implants should be sent for analysis to institutions with special interest in such work if meaningful data is to be gleaned from large numbers of specimens.
The paper of Donell et al contains useful implant-specific data, and adds to the body of knowledge on metal-on-metal hip arthroplasty. The clinical significance of reporting adverse early outcomes of an implant is far higher than that of early good results. Surveillance of our patients and the outcome of our interventions are important for our future patients and our profession.
1. Atrey A, Leslie I, Carvell J, et al. Standardised consent forms on the website of the British Orthopaedic Association. J Bone Joint Surg [Br] 2008;90-B:422-3.
3. Glyn-Jones S, Pandit H, Kwon YM, et al. Risk factors for inflammatory pseudotumour formation following hip resurfacing. J Bone Joint Surg [Br] 2009;91-B:1566-74.
4. Medicines and Healthcare products Regulatory Agency. Medical Device Alert Ref MDA/2010/033 22nd April 2010. www.mhra.gov.uk/Publications/Safetywarnings/MedicalDeviceAlerts/CON079157
5. BOA. Withdrawal of the DePuy ASR Resurfacing and XL metal on metal bearings – Information for and Advice to Surgeons from the British Hip Society and the British Orthopaedic Association 25th October 2010. www.boa.ac.uk/en/news/whats-new/#item_307686.
6. Grammatopoulos G, Pandit H, Kwon YM, et al. Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg [Br] 2009;91-B: 1019-24.
Biant LC, Consultant Trauma and Orthopaedic Surgeon
The Royal Infirmary of Edinburgh, Edinburgh, United Kingdom