Orthopedics

Editor’s note:

As knowledge of the performance and outcomes of hip arthroplasty with metal-on-metal bearings increases, the guest commentaries below and here revisit the many issues surrounding this type of arthroplasty. We hope these opinion pieces will provide important information to help readers arrive at their own answers to the many outstanding questions regarding these treatments.

We still lack an ideal solution for the younger patient with hip arthritis who tends to be a more active individual demanding more of their artificial implant.

Fares Haddad

Harry Benjamin-Laing

Polyethylene wear is a major concern as younger patients often attempt to maintain/regain their pre-operative level of activity. Hip resurfacing has long been recognized as an attractive concept particularly in patients who are likely to need revision hip replacements in their lifetime. Due to improvements in materials, design, and manufacturing techniques, metal-on-metal (MoM) hip resurfacing arthroplasty gained popularity in the last decade with perceived advantages of bone conservation and relative ease of revision to a conventional total hip replacement (THR) if it fails.

Hip resurfacing preserves proximal femoral bone stock, retains proprioception, optimizes stress transfer to the proximal femur and, because of the large diameter of articulation, offers inherent stability and optimal range of movement. This leads to a lower risk of dislocation. Intra-operatively the absence of femoral canal reaming in hip resurfacing theoretically reduces the risks of fat embolism to the lung.

Evolving concerns

Although modern hip resurfacing has recognized early complications, such as femoral neck fractures and avascular necrosis of the head, the early and medium term results were encouraging. The technique attracted a great deal of media attention and was rapidly taken up.

MoM hip resurfacing was initially used as an option in very active people with advanced hip disease who would otherwise receive and are likely to outlive a conventional primary THR. Initial success led to a widening of the indications and to the use of resurfacing cups with standard femoral stems and metal heads.

However, over the past few years concerns have been raised in relation to reports of catastrophic soft tissue reactions resulting in implant failure and associated complications. One implant has recently been withdrawn and hip arthroplasty registries suggest worrying trends for others.

Consider merits of resurfacing

We must be careful not to “throw out the baby with the bathwater.” The concerning data in relation to stemmed/modular large-head MoM hips (>36 mm) is likely to be related to the taper junction/trunnion and to be a different failure mode than for resurfacing. Resurfacing failures seem instead to relate to poor technique including component malposition, use in unsuitable patients whose anatomy dictated malposition/edge bearing, and the wide introduction of some unsatisfactory implants with sufficient in vivo evaluation. The evidence from the literature is clear that all medical devices depend on appropriate surgical technique and patient selection. It appears that these simple rules affect the success of MoM hips more than other hip types.

Hip resurfacing remains a viable successful operation in younger males with appropriate anatomy. Examples of cases associated with increased failure rates include cup inclination angles greater than 55°, use of the procedure in women and in those with small head sizes. Resurfacing has some additional risk factors because of the retained head and neck. Thus, clinical results currently best support the use of a resurfacing implant with a long track record, positioned with a cup inclination angle of 45° or less and version angle of 20° or less, to treat a man aged less than 65 years suffering from osteoarthritis with a well-covered acetabulum and cam-shaped hips. In this cohort, there may well still be advantages to resurfacing.

Hip function studied

We undertook a prospective randomized study of cementless THR with a 32-mm metal-on-polyethylene bearing versus MoM hip resurfacing in young adults under the age of 55 years. Eighty patients were enrolled between 1999 and 2002. All the patients have been followed clinically and radiographically up to a minimum follow-up of 8 years and a mean of 10.1 years. In this cohort, there have been no failures in the MoM articulation group and there has only been one dislocation in the total hip group. A higher proportion of hip resurfacing patients were running and involved in sport and heavy manual work after 5 years, 8 years and 10 years. The University College Hospital functional hip score showed significantly higher function in hip resurfacing patients compared with hip replacement patients; this was maintained at 1 year, 5 years and 8 to 10 years. We continue to use hip resurfacing in such patients.

Appropriate use

Our knowledge of MoM bearings and their behavior is evolving rapidly. There are currently major question marks over large-head MoM THR. However, current data suggest that an appropriate surgical technique for hip resurfacing in an appropriately selected cohort of patients using appropriate implants is associated with a low incidence of adverse soft tissue reactions and good functional outcomes.

Recent controversy regarding the recall of the ASR (DePuy Orthopaedics) resurfacing prosthesis and in relation to trunnion related failures of large head MoM prostheses have generated a great deal of uncertainty. Nevertheless, devices that preserve bone stock, facilitate later revision and potentially allow better functional recovery are attractive. MoM hip resurfacing remains a good option in well-selected patients with appropriate anatomy under the care of experienced and skilled surgeons.

References:

• Amstutz HC, Grigoris P, Dorey FJ. Evolution and future of surface replacement of the hip. J Orthop Sci. 1998; 3:169-186.
• Australian Orthopaedic Association National Joint Replacement Registry. Annual Report. Adelaide, Australia: AOA; 2010.
• Daniel J, Pynsent PB, McMinn, DJ. Metal on metal resurfacing of the hip in patients under the age of 55 with osteoarthritis. J Bone Joint Surg Br. 2004;86:177-184.
• De Haan R, Pattyn C, Gill HS, et al. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br. 2008;90(10):1291-1297.
• Grigoris P, Roberts P, Panousis K, Bosch H. The evolution of hip resurfacing arthroplasty. Orthop Clin North Am. 2005;36(2):125-134, vii.
• Haddad FS, Bull J. Hip resurfacing has superior sustained functional outcomes when compared to total hip arthroplasty. Proceedings of the 75th Annual American Academy of Orthopaedic Surgeons Meeting. p. 428. San Francisco. 2008.
• National Institute for Health and Clinical Excellence guidelines. Hip disease - metal on metal hip resurfacing (TA44). June 2002.

• Fares Haddad, MCh(Orth), FRCS, can be reached at +44 20 7908 2251; email: fares.haddad@ucl.ac.uk.
• Harry Benjamin-Laing, BSc(Hons), MBChB(Hons), MRCSEd, can be reached at +44 20 3447 9413; email: h.benjamin-laing@docotors.org.uk.
• Haddad and Benjamin-Laing are at the Department of Trauma & Orthopaedic Surgery, University College Hospital, 235 Euston Road, London, NW1 2BU United Kingdom.
• Disclosures: Haddad is a paid consultant to Corin, Smith & Nephew and Stryker. Benjamin-Laing has no relevant financial disclosures.