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MRI Comparison of Periprosthetic Structures Around Zirconium Knee Prostheses and Cobalt Chrome Prostheses

¹ Department of Diagnostic Radiology, Yale University School of Medicine, 333 Cedar St., PO Box 20804, New Haven, CT 06520-8042.
² Department of Medical Imaging, Mt. Sinai Hospital and the University Health Network, Toronto, ON, Canada.
³ Department of Orthopedics and Rehabilitation, Yale University School of Medicine, New Haven, CT.

OBJECTIVE. The purpose of our study was to compare reviewer confidence and interobserver agreement in the evaluation of MR images of periprosthetic structures around zirconium total knee prostheses and cobalt chrome prostheses.

MATERIALS AND METHODS. Three board-certified radiologists blinded to prosthesis type used identical MRI protocols to independently evaluate 21 total knee prostheses: 14 zirconium prostheses and seven cobalt chrome prostheses. The radiologists evaluated the following eight parameters: integrity of the medial and lateral collateral ligaments, the quadriceps and the patellar tendons, presence of a joint effusion, and for evidence of periprosthetic osseous signal abnormality around each of the three components. The reviewers gave their degree of confidence in evaluating each of the findings on a five-point scale, 0 being no confidence and 4 being high confidence in the finding. The degree of confidence was used as the vehicle for comparing the two groups of patients.

RESULTS. The confidence ratings for all MRI variables were significantly higher for the zirconium group than for the cobalt chrome group. The confidence ratings varied less for the zirconium group than for the cobalt chrome group with an SD of 0.45 versus 0.95, respectively. There was greater interobserver agreement in the zirconium group (coefficient of interobserver agreement, 0.82 vs 0.35). The reviewers had the highest degree of confidence when examining for joint effusion in both groups (3.9 for the zirconium group; 3.7 for the cobalt chrome group). The greatest discrepancies between the two groups were in evaluation of periprosthetic osseous signal changes with the greatest difference being between the femoral component of each group with an average confidence rating of 3.3 for the zirconium group and 0.8 for the cobalt chrome group.

CONCLUSION. Reviewers had significantly more confidence, less variability, and greater interobserver agreement in MRI evaluation of periprosthetic structures around zirconium knee prostheses than those around cobalt chrome knee prostheses.

Keywords: arthroplasty • MRI • knee • knee prosthesis

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