Quantitative magnetic resonance imaging (MRI) ultrashort echo time (UTE) T2* is sensitive to cartilage deep tissue matrix changes after anterior cruciate ligament reconstruction (ACLR). This study was performed to determine whether UTE-T2* profile analysis is a useful clinical metric for assessing cartilage matrix degeneration. This work tests the hypotheses that UTE-T2* depthwise rates of change (profile slopes) correlate with clinical outcome metrics of walking mechanics and patient reported outcomes (PRO) in patients 2 years after ACLR.
Thirty-six patients 2 years after ACLR completed knee MRI, gait analysis, and PRO. UTE-T2* maps were generated from MRI images and depthwise UTE-T2* profiles were calculated for weight-bearing cartilage in the medial compartment. UTE-T2* profiles from 14 uninjured subjects provided reference values. UTE-T2* profile characteristics, including several different measures of profile slope, were tested for correlation to kinetic and kinematic measures of gait and also to PRO.
Decreasing UTE-T2* profile slopes in ACLR knees moderately correlated with increasing knee adduction moments (r = 0.41, P < 0.015), greater external tibial rotation (r = 0.44, P = 0.007), and moderately negatively correlated with PRO (r = -0.36, P = 0.032). UTE-T2* profiles from both ACLR and contralateral knees of ACLR subjects differed from that of uninjured controls (P < 0.015).
The results of this study suggest that decreasing UTE-T2* profile slopes reflect cartilage deep tissue collagen matrix disruption in a population at increased risk for knee osteoarthritis (OA). That UTE-T2* profiles were associated with mechanical and patient reported measures of clinical outcomes support further study into a potential mechanistic relationship between these factors and OA development.