After THA, Metal Ion Measurement and MRI Recommended to Evaluate Suspected Head–Neck Taper Corrosion
Key findings
- Among patients who had head–neck taper corrosion associated with metal-on-polyethylene THA, high rates of early complications and re-revisions were observed after revision surgery
- The most common complication was dislocation, despite the use of large femoral head sizes during revision
- Risk factors for early complications after revision were intraoperative tissue damage and one or more solid lesion(s) with abductor deficiency
- The revision surgery approach used in this study was associated with significant decreases in both median serum levels of cobalt and the average cobalt–chromium ratio
- Patients suspected of having head–neck taper corrosion should have serum levels of metal ions measured and undergo metal artifact reduction sequence MRI to confirm adverse local tissue reactions
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Total hip arthroplasty often makes use of metal-on-polyethylene implants where there is head–neck modularity of the femoral component. This allows greater intraoperative flexibility for the surgeon, but the additional interface is susceptible to fretting and corrosion, particularly when the implant has a titanium femoral stem and a cobalt–chromium femoral head. The degradation may lead to elevated levels of metal ions, or adverse local tissue reactions (pseudotumors), which are emerging as important factors in the failure of these implants.
Orthopedic Surgeon Young-Min Kwon, MD, PhD, of Massachusetts General Hospital's Center for Hip & Knee Replacement, and colleagues recently reviewed data from a large, homogenous cohort of patients who underwent metal-on-polyethylene THA. In The Journal of Arthroplasty, they confirmed high rates of complications and re-revision and suggest approaches to managing such patients.
Many patients undergoing revision surgery for head–neck taper corrosion are concerned about high systemic levels of metal ions, the authors note. Their findings were reassuring. The revision surgery approach they used was associated with significant decreases in both median serum levels of cobalt and the average cobalt–chromium ratio.
The researchers reviewed 40 consecutive revision surgeries, all performed by the same surgeon, after metal-on-polyethylene THA (39 patients, 53% female, average age 68). At the time of index surgery, all patients had received implants that had cobalt–chromium femoral heads on titanium alloy femoral stems, with a single site of modularity at the head-neck taper junction.
All patients developed symptomatic local tissue reactions that were confirmed on metal artifact reduction sequence MRI. They were also documented to have elevated serum levels of cobalt and chromium ions. The average time between the index surgery and revision was 59 months (range, 14–182 months). The revision strategy was to retain well-fixed femoral and acetabular components, exchange the polyethylene liner, and implant a new ceramic femoral head with a titanium adaptor sleeve.
At the time of revision surgery, 11 hips (27%) had grade 2 tissue damage and 29 hips (73%) had grade 3 damage. In all 40 hips, black metal debris was visible that indicated corrosion of the head-neck taper junction. All patients required debridement of varying degrees of necrotic periarticular soft tissue, muscle and bone.
The researchers retrieved 22 femoral heads and observed high fretting or corrosion damage (Goldberg score ≥3) in 82% of them. There was no significant correlation between the grade of degradation and the serum cobalt or chromium ion level.
During the post-revision follow-up period (average length 15 months), 10 patients (25%) developed complications, of whom four (10%) required re-revision. The most common complication was dislocation (n=6), including two cases of recurrent dislocation that required re-revision. This was true, the authors note, even though the surgeon always used the largest femoral head size that was compatible with the acetabular component already in place.
One patient developed an acute periprosthetic joint infection that required re-revision, and two others developed superficial wound infections. One patient had pseudotumor recurrence with chronic pain nine months after revision that required re-revision and additional debridement.
On regression analysis, risk factors for post-revision complications were intraoperative tissue damage and one or more solid lesions associated with abductor deficiency.
The authors emphasize the importance of a systematic approach to management of patients who are suspected of having head–neck taper corrosion. The evaluation should include serum metal ion level measurement and metal artifact reduction sequence MRI, because early diagnosis is necessary to allow revision surgery before substantial tissue necrosis occurs.
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