T1ρ mapping of articular cartilage grafts after autologous osteochondral transplantation for osteochondral lesions of the talus: A longitudinal evaluation.

BACKGROUND: Clinical results of autologous osteochondral transplantation (AOT) for treatment of osteochondral lesions of the talus have been mixed. T1ρ imaging can be used to noninvasively detect early cartilage degeneration. PURPOSE OR HYPOTHESIS: To quantitatively assess, by means of T1ρ imaging, changes over time in the biochemical health of grafted cartilage after AOT for osteochondral lesions of the talus. STUDY TYPE: Retrosepctive case series. POPULATION: The study group comprised nine patients who underwent AOT for an osteochondral lesion of the talus and in whom T1ρ mapping was performed 1 and 2 years postoperatively. FIELD STRENGTH/SEQUENCE: 3 Tesla. T1ρ-weighted turbo field echo. ASSESSMENT: The mean T1ρ value of full-thickness cartilage at the repair site and that of full-thickness cartilage elsewhere in the same image (far-field cartilage) were determined. Clinical assessment was based on the American Orthopaedic Foot & Ankle Society (AOFAS) scale. Correlation between the T1ρ ratios (grafted-to-far-field cartilage T1ρ values) and clinical outcomes was examined. STATISTICAL TESTS: Mixed effects model. Pearson correlation analysis. RESULTS: At 1 year, a significant difference existed between the mean T1ρ value of the grafted cartilage (57.0 ± 7.7 ms) and that of the far-field cartilage (41.8 ± 4.6 ms) (P < 0.001). At 2 years, the mean T1ρ value of the grafted cartilage (49.1 ± 6.4 ms) was significantly lower than that at 1 year (P = 0.011). Moderate negative correlation was found between the 1-year T1ρ ratio and 1-year AOFAS score (r = -0.60) and between the 2-year T1ρ ratio and 2-year AOFAS score (r = -0.50). DATA CONCLUSION: Our observation of substantial restoration of the proteoglycan content of the grafted cartilage approximately 2 years after AOT for osteochondral lesions of the talus indicates that the content changes gradually and that the cartilage reparation process is slower than previously believed. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 3 J. MAGN. RESON. IMAGING 2018;48:398-403.