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Revision of Articular Bearing Complications
Revision of Metal-on-Metal Bearing Surfaces in Hip Arthroplasty
CASE STUDY
A 60-year-old woman, who had left primary metal-on-metal hip resurfacing 3.5 years earlier for severe osteoarthritis, presented with increasing left hip pain, clicking, and swelling over the preceding several months. Her postoperative course had been uncomplicated, and she had excellent pain relief for more than 3 years. She denied fevers, shakes, or chills. On physical examination, she was found to have a normal gait and equal leg lengths. She was neurovascularly intact but had a painful range of motion of her hip and audible squeaking.
Chromium and cobalt metal ion levels were elevated to 65 and 53 ppb, respectively. Results for the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and white blood cell (WBC) count were within normal limits. Plain radiographs showed a left total hip resurfacing in an unchanged position with no evidence of loosening. Computed tomography revealed a 1.6 × 1.4 cm lytic lesion in the supraacetabular region of the left ilium, which was consistent with a pseudotumor ( Figs. 73A.1 and 73A.2 ).
The patient subsequently underwent resurfacing revision with conversion to a ceramic-on-polyethylene total hip arthroplasty ( Figs. 73A.3 to 73A.11 ) using a posterior Kocher-Langenbeck approach. On opening the hip capsule, 50 to 60 mL of grayish fluid was released. An extensive pseudocapsule with the grayish staining of metallosis was observed in the posterior and anteroinferior aspects of the hip joint. This was carefully debulked to maintain as much viable tissue as possible while completely excising the damaged tissue. A femoral neck osteotomy was made around the stem of the size 42 femoral resurfacing component. Next, the well-fixed, well-positioned, 48-mm resurfacing cup was removed, and a 52-mm, press-fit trabecular metal acetabular shell with a polyethylene liner was placed. The femoral resurfacing component was converted to a standard single-taper, proximally fixed femoral component with a modular ceramic head.
Histologic analysis of the tissue sampled intraoperatively revealed dense fibrous tissue with reactive changes, chronic inflammation, and particulate-laden macrophages consistent with an adverse reaction to metal debris. The patient was allowed to bear weight as tolerated and had an uncomplicated postoperative course. At the 3-month follow-up evaluation, she had a slight Trendelenburg gait, no instability, and a good range of motion.
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Chapter Synopsis
In this chapter, we focus on the complications associated with the use of metal-on-metal (MoM) bearing surfaces in hip arthroplasty, the workup of symptomatic and asymptomatic individuals with these prostheses, and techniques used in revision or conversion that are specific to MoM bearings.
Important Points
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Although popular media have focused on the adverse effects of metal ions, most revisions performed on MoM prostheses are not for adverse reactions to metal debris (ARMD) but rather for mechanical problems such as aseptic loosening and fractures.
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Common causes of failure should be excluded before testing for ARMD, but physicians should remain alert to the possibility of these tissue reactions due to the high degree of associated morbidity.
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ARMD should be considered in any symptomatic patient presenting with unexplained pain or mechanical symptoms.
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The use of a clinical evaluation algorithm, early revision, larger revision femoral heads, and patient education can reduce the rate of complications and repeat revisions.
Clinical/Surgical Pearls
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Advanced imaging to look for fluid collection seems a more useful tool than obtaining ion levels at this time.
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In revision for ARMD, the bearing surface should be revised to a non-MoM bearing to prevent recurrence of ARMD or continued symptoms.
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If infection cannot be ruled out preoperatively, a two-staged revision should be planned with intraoperative tissue sampling to help distinguish between infection and ARMD. Only after infection is ruled out should a single-stage revision for ARMD be considered.
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In revision for pseudotumors, especially those infiltrating periprosthetic vessels and nerves, a multidisciplinary team, including a vascular or plastic surgeon, may need to be assembled to remove the entire lesion.
Clinical/Surgical Pitfalls
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In cases of ARMD, especially pseudotumors, the surgical site should be thoroughly cleared of all metal debris and nonviable tissue to prevent recurrence of pseudotumors or other ARMD. Débridement of the surgical site of metal debris should be done with care to preserve as much muscle and soft tissue as possible to maintain hip stability and avoid dislocation.
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Metal ion testing should not be used alone when deciding to proceed to surgery or to exclude the diagnosis of ARMD. There is no metal ion threshold level above which revision is indicated, and ARMD may occur in the absence of elevated metal ion levels.
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Revision of both components leads to better outcomes and fewer complications than a single-sided revision. If the viability of either component is in question, both components should be revised.
Introduction
The first metal-on-metal total hip arthroplasty (MoMTHA) was performed in 1937 by Philip Wiles. He used stainless steel components affixed to bone with bolts and screws. Use of modern MoM hip prostheses began in the late 1950s with the McKee-Farrar prostheses. After loosening led to early failure of stainless steel and press-fit models, McKee eventually used a cobalt–chromium–molybdenum alloy for the acetabular component combined with a modified Thompson femoral stem; both were fixed with acrylic cement. Ring and others followed this concept, but poor early and midterm survival due to loosening led to the abandonment of MoM in favor of Charnley’s metal-on-polyethylene, low-friction arthroplasty.
The first MoM prostheses had dichotomous survivorship, with implants failing early or having excellent survival, often lasting more than 20 years. When Weber revisited the MoM implant in 1996, he found no adverse effects from wear in a series of 110 MoM hip implants. Another study by Jacobsson and colleagues found that the McKee-Farrar prosthesis had long-term survival rates comparable to those of Charnley THAs.
These findings and the appeal of prostheses with better wear characteristics than polyethylene generated renewed interest in MoM bearings. Improved manufacturing and tribologic characteristics in the new generation of MoM implants have helped their resurgence. However, concerns about unexplained pain and early failure as a result of adverse reactions to metal debris (ARMD) again led to declining use, with exceptions for selected populations such as young men with appropriate anatomy in hip resurfacing. Registry data from Australia and the United Kingdom have shown that MoM hip replacements have higher revision rates than conventional bearing surfaces. With increasing numbers of MoM hip bearings being implanted and revised, issues related to the proper workup, diagnosis, and surgical technique have become all the more salient.
Indications for Revision
Malpositioning, Fractures, and Loosening
Controversy about the use of MoM bearings has focused on ARMD leading to early failure, unexplained pain, and pseudotumor formation. Although the popular media have focused on these adverse reactions, most revisions performed in metal-on-metal hip resurfacing (MoMHR) cases are for mechanical issues such as malpositioning, aseptic loosening, and fracture.
The indications for revision in MoMTHAs largely coincide with those for THAs of other bearing surfaces, with the exception of a portion of MoMTHAs that fail due to the effects of ARMD. For MoMHR, the distribution of revisions due to various causes is slightly different from those of traditional THAs or MoMTHAs ( Table 73A.1 ). The primary mode of failure, which is unique to MoMHR, is periprosthetic fracture of the femoral neck. Fractures usually occur early, often in the early postoperative years. Risk factors for femoral neck fracture include smaller femoral sizes, head cysts, excessive or inadequate cement penetration, notching of the femoral neck, osteopenia, and varus placement of the femoral component ( Box 73A.1 ).
Table 73A.1
Causes of Revision in Metal-on-Metal Prosthesis
| Causes of Revision | Combined MoMHR and MoMTHA ∗ | MoMTHA | MoMHR | ||||
|---|---|---|---|---|---|---|---|
| Ebramzadeh et al, 2011 (n=378) |
Browne et al,2010 (n=37) |
Milosev et al, 2006 (n=34) |
Porat et al,2012 (n=65) |
Australian National Joint Registry, 2011 | DeSmet et al, 2011 (n=113) |
Carrothers et al, 2010 (n=182) |
|
| Acetabular loosening | 26.9% | 25% (unsp) | 32.3% | 49.2% (unsp) | 33.4% (unsp) | 27.4% (unsp) | 17.6% |
| Femoral loosening | 18.5% | 23.5% | 10.4% | ||||
| Both components loosened | 11.7% | Both 2.7% | |||||
| Neck fracture | 16.7% | 8% | 35.6% | 5.3% | 29.7% | ||
| Malpositioning | 10.1% | 8% | 2.2% | 47.9% | 1.6% | ||
| Unexplained pain | 6.1% | 5.8% | 5.3% | 3.5% | |||
| Sepsis or infection | 6.1% | 19% | 17.6% | 15% | 8.2% | 3.5% | 9.3% |
| Suspected metal allergy or ARMD | 5.3% | 27% | 26.1% | 7.1% | 5.3% | 8.2% (pain) | |
| Impingement | 5.0% | 5% | |||||
| Dislocation or instability | 5% | 2.9% | 1.5% | 2.7% | .9% | 2.7% | |
| Avascular necrosis | 3.1% | Loosening | 16.5% | ||||
| Osteolysis | 1.3% | Loosening | Loosening | ||||
| Other | 2.6% | 1% (THA fx) | 5.8% (1 cup fx after trauma, 1 metal inlay dissociation from polyethylene liner) | 7.7% | 1.1% | 4.4% (3.5% due to elevated metal ion levels alone) | |
ARMD , Adverse reactions to metal debris; fx , fracture; MoMHR , metal-on-metal hip resurfacing; MoMTHA , metal-on-metal total hip arthroplasty; unsp , unspecified as to whether loosening was from acetabular or femoral component.
∗ Combined MoMHR and MoMTHA studies did not separate causes of revision by type of articular bearing. Blank cells indicate that the study did not report on such causes.
Box 73A.1
Risk Factors for Periprosthetic Femoral Neck Fracture in Metal-on-Metal Hip Replacement
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Smaller femoral sizes
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Head cysts
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Excessive or inadequate cement penetration
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Notching of the femoral neck
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Osteopenia
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Varus alignment of the femoral component
Other complications of MoMHR include loosening of the femoral component, impingement, and avascular necrosis of the femoral head. Loosening of the MoMHR femoral component is often a result of improper sizing during the primary procedure. This can be particularly challenging in smaller femurs. After the acetabular component is placed, it dictates what femoral component sizes can be used. For smaller femoral heads, small deviations from the center of the head while drilling can lead to gaps between the femoral bone and resurfacing component, leading to increased rates of loosening.
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