Metal-on-Metal Hip Replacement: MRI Signal Intensities of Different Body Tissues and Their Relations to Blood Metal
Einat Slonimsky1,2, Tammar Kushnir1,2, Assaf Kadar3,2
1Department of Diagnostic Imaging, Sheba Medical Center, Tel Hashomer, Israel.
Background:
Metal-on-metal total hip prostheses (MoM-THR) have been shown to produce hypersensitivity reactions and fluid collection (pseudotumor) by the hip as well as high blood metal ions levels (BMILs).
Objectives:
To evaluate the magnetic resonance imaging (MRI) signal-to-noise ratio (S/N) in selected body tissues around the hip of patients who underwent MoM hip replacement and to correlate to BMILs.
Methods:
Sixty-one MRI hip examinations in 54 post-MoM-THR patients (18 males, 36 females, mean age 65 years) were retrospectively evaluated independently by two readers. The mean S/N ratio in a region of interest was calculated for periprosthetic pseudotumor collection (PPC), the bladder, fat, and muscle on axial T1w, FSE-T2w, and short tau inversion recovery (STIR) sequences on the same location. BMILs were retrieved from patient files.
Results:
PPC was detected in 32 patients (52%) with an average volume of 82.48 mm3. BMIL did not correlate with the presence of PPCs but positively correlated with the PPC's volume. A trend for positive correlation was found between BMILs and S/N levels of STIR images for muscle and bladder as well as for PPC and cobalt levels. A trend for correlation was also seen between BMIL with PPC's T1 w S/N.
Conclusions:
Alteration of MRI S/N for different hip tissues showed a tendency for correlation with BMILs, possibly suggesting that metal deposition occurs in the PPC as well as in the surrounding tissues and bladder.
Insights
Metal-on-metal hip implants can cause fluid collections and high metal ion levels. MRI signal changes in surrounding tissues and fluid collections may correlate with these metal ion levels, suggesting metal deposition.
Area of Science:
- Orthopedic Surgery
- Radiology
- Biomaterials Science
Background:
- Metal-on-metal total hip replacements (MoM-THR) are associated with hypersensitivity reactions, pseudotumor formation (PPC), and elevated blood metal ion levels (BMILs).
- Understanding the relationship between BMILs and imaging findings is crucial for patient management.
Purpose of the Study:
- To assess the magnetic resonance imaging (MRI) signal-to-noise ratio (S/N) in tissues around MoM hip prostheses.
- To investigate the correlation between MRI S/N and blood metal ion levels (BMILs).
Main Methods:
- Retrospective analysis of 61 MRI hip examinations in 54 MoM-THR patients.
- Calculation of mean S/N ratios in periprosthetic pseudotumor collections (PPC), bladder, fat, and muscle using T1w, FSE-T2w, and STIR sequences.
- Correlation of MRI S/N with retrieved BMILs.
Main Results:
- Pseudotumor collections (PPC) were present in 52% of patients.
- BMILs did not correlate with PPC presence but positively correlated with PPC volume.
- A trend for positive correlation was observed between BMILs and MRI S/N in STIR images of muscle and bladder, and in PPCs (especially with cobalt levels).
Conclusions:
- Altered MRI S/N in hip tissues around MoM-THR shows a tendency to correlate with BMILs.
- Findings suggest potential metal deposition within PPCs and surrounding tissues, including the bladder.
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