Purpose

Articular cartilage lesions remain a challenge in orthopaedic practice. To improve treatment decision and to allow for a more exact prognosis, there is strong demand for predictive imaging biomarkers. It has been shown that even before morphological changes become evident, biochemical changes of the extracellular matrix might occur.¹ T2 mapping is sensitive to water content and collagen ultrastructure of articular cartilage² and thus bears the potential to assess these changes. The purpose of this study was to assess the predictive value of T2 mapping in patients with untreated focal patellar cartilage lesions regarding defect progression in a mean follow-up of four years.

Subjects and Methods

This study was approved by the local ethics committee and written informed consent was obtained from all patients prior to enrolment. We aimed to recruit thirty patients, who previously underwent an MRI examination for anterior knee pain or suspected patellar cartilage defects at our institution. This baseline MRI examination had to include T2 mapping (CPMG) (resolution = 0.4x0.4x3.0 mm; TR=1200; eight echo times (TE) in the range from 13.8 to 82.8 ms, measurement time 4:09 min) and an axial proton density weighted turbo-spin-echo sequence (resolution = 0.2x0.2x2.0 mm; TR/TE=2400/36 ms, measurement time: 6:11 min). Furthermore, only patients who did not receive any surgical treatment of the respective knee joint in the meantime were included in order to avoid any bias due to surgical intervention. At follow up, patients were examined again using the exact same protocol on the same scanner with the same knee coil. In each patient, the most severe patellar cartilage lesion was graded on the axial PD TSE images of the baseline as well as the follow-up examination according to the ICRS grading system. Furthermore, T2 maps were evaluated based on a region-of-interest (ROI) analysis. To do so, the respective defect extents were defined on the morphological PD TSE images of the follow-up examination. The ROIs were subsequently transferred to the T2 mapping follow-up and baseline exams. In addition, a healthy reference cartilage region was defined and evaluated in each patient in the baseline and follow-up exams as internal reference. Differences in the T2 values according to ICRS grading were evaluated using one-way ANOVA with post hoc Tukey test. The predictive values of the global T2 values at baseline regarding future defect progression in the interval was assessed with a ROC analysis. All statistical evaluations were performed using IBM SPSS 23.0. A p-values smaller 0.05 was considered to be statistically significant.

Results

Thirty patients (mean age, 36.7 ± 11.1 years; 16 males, 14 females) were included in the study. The average follow-up time between the baseline and follow-up examination was 4.0 ± 1.6 years. At baseline, ten patients had no defect, 12 patients had a grade 1 defect and 8 patients had a grade 2 defect based on morphological images. Global T2 values correlated well with the defect grades with an average T2 of 40.3 ms for grade 0, 48.5 ms for grade 1 defects and 55.6 ms for grade 2 defects (p < 0.01). Regarding the morphological ICRS grading, 17 patients remained constant over the follow up period whereas 11 patients showed a defect progression of one or more ICRS grades. Patients who showed defect progression in the interval had significantly higher global T2 values at baseline (57.5 ms) than patients who did not show defect progression (40.6 ms) (p < 0.01). Furthermore, patients who remained constant over the follow-up time regarding the ICRS grading, showed only a minor increase in T2 relaxation times from 40.7 ms at baseline to 43.1 ms at follow-up. The ROC analysis (Figure 2) showed an area under the curve of 0.95, demonstrating that global T2 value may serve as a good predictor for defect progression in low-grade cartilage defects.

Discussion

This study provides evidence regarding the possible potential of T2 mapping as a predictive marker for patellar cartilage degeneration in untreated defects. Furthermore, it confirms previous observations³ that T2 relaxation times correlate well with the ICRS grade of cartilage degeneration. Moreover, it demonstrates that T2 relaxation times in patellar cartilage remain relatively constant over time in patients with stable cartilage conditions.

Acknowledgements

No acknowledgement found.