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Researchers find two failure mechanisms related to ARMD

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Finnish researchers found critical differences in failure mechanisms related to adverse reaction to metal debris, according to presented at the EFORT Congress.

They found that pseudotumors are formed by a lymphocyte-dominated immune response whereas intracapsular reactions are related to a macrophage-dominated foreign body reaction.

“Our results are a good representation of adverse reaction to metal debris [ARMD],” Aleksi Reito, MD, of the Coxa Hospital for Joint Replacement in Tampere, Finland, said. “There are two different failure mechanisms, and based on our results, we could in our further studies divide the possible adverse reactions and have some type of basis to classify the failed hips or those hips which have been revised. [We could] study those unrevised cases with abnormal findings and how they develop during follow-up,” Reito said.

After the ASR Hip System recall (DePuy), Reito and colleagues at Coxa Hospital established a screening protocol to identify patients with adverse soft tissue reactions. They used the Norwich classification system to prospectively classify the MRI findings. They used the Imperial classification system to retrospectively reclassify all hips that were revised until May 2012.

After taking samples for histological analysis, the researchers performed semiquantitative analysis on the amount of synovial fibrin (none, focal, moderate or extensive), macrophages and perivascular lymphocytes (absent, mild, moderate or high). Because the researchers introduced the aseptic lymphocytic vasculitis associated lesions (ALVAL) score 9 months after the protocol began, ALVAL scores were not available for all samples.

There were 92 revised hips in 92 patients with full clinical data available for the study; 64 patients had ALVAL scores. Preoperatively, the researchers diagnosed pseudotumors in 61 patients.

Results showed a positive correlation between the amount and presence (absence or mild vs. moderate to high of perivascular lymphocytes (PVLs) and the severity of MRI findings. Twenty percent of patients with no pseudotumor seen on MRI had moderate-to-high PVL levels, whereas all patients classified as Imperial 3 had moderate-to-high PVL levels.

The researchers found a negative but weak link between macrophage infiltration and MRI findings. Total ALVAL score and severity of MRI finding were associated.

Reito and colleagues saw no significant differences in histological findings or in ALVAL-subscores between T1-weighted core signals in patients with pseudotumors. ALVAL scores were higher in patients with hyperintense T1-weighted core signal.

T2-weighted images were different. “High metal ion levels can be seen and MRI shows hyperintense pseudotumour core signal intensity in T2-weighted images,” Reito said. “In these cases, the histology is more macrophage-dominated whereas the other entity is the one with the aggressive histology with a lot of lymphocytes and necrosis. In these cases, the MRI findings are different. They have isointense or variable pseudotumour core signal intensity in the T2-weighted MRI images.”

References:

Reito A. Paper #13-5523. Presented at: EFORT Congress. June 5-8, 2013; Istanbul.

Disclosures: Reito has no relevant financial disclosures.