Background

In assessing articular cartilage lesion grade in knee osteoarthritis patients, conventional MR imaging has been used as gold standard diagnosing tool. However, conventional MR imaging has limitations in accurately evaluating cartilage lesions because it is difficult to distinguish the boundary between the subchondral bone and the calcified cartilage, and the boundary between the superficial layer of cartilage and the synovial fluid or infrapatellar fat pad. Clinically, conventional MR imaging is often different from the intra-operative status, especially for trochlea lesions. The trochlear cartilage lesion is an important factor in determining the knee arthroplasty options (unicompartmental or total knee arthroplasty). In several studies, CT arthrography compared conventional MR image, but few studies focused on trochlea. The purpose of this study was to compare knee CT arthrography and conventional MR imaging with intra-operative status to find out which tests evaluate trochlea cartilage lesions better.

Method

We evaluated 24 patients (31 knees) who had both CT arthrography and MR imaging among patients who underwent total knee arthroplasty (TKA) or unilateral knee arthroplasty (UKA) in our institution. The femoral articular cartilage was divided into 14 areas (medial 6, lateral 6, and trochlea 2 areas), and each area was evaluated by CT arthrography, MR imaging, and intra-operative status using ICRS grading system. In addition, in 5 cases of the patients who underwent TKR, the resected osteocartilage was evaluated by histological analysis in 14 areas and compared with CT arthrography and conventional MR imaing.

Result
The total sensitivity was 87.6% for CT arthrography and 79.2% for MR imaging, and the sensitivity of CT arthrography was high in all areas except 2 areas of lateral femoral condyle. The total specificity was 93.5% for CT arthrography and 90.9% for MR imaging. In particular, the specificity of the trochlear area was 96.8% for CT arthrography and 83.9% for MR imaging.

Conclusion

CT arthrography has higher sensitivity and specificity when evaluating femoral articular cartilage than MR imaging. Especially in trochlear lesions, CT arthrography has a high sensitivity and specificity, which is useful for determining knee arthroplasty options.