Associations Between Patient Characteristics and Cartilage T1ρ Relaxation Times Vary Over Time Following Patellar Dislocation

The characteristics of patients that promote progressive cartilage degradation following patellar dislocations are not well understood. The study hypothesis is that associations relating cartilage degradation to low BMI, high activity and youth in the early months following patellar dislocation are not exhibited for contralateral knees or a longer time from injury. Quantitative MRI-based evaluation of injured and contralateral knees occurred within 5 months of a unilateral patellar dislocation (baseline evaluation, 36 subjects) and beyond 5 months (follow-up evaluation, 20 subjects). Linear regressions correlated T1ρ relaxation times for regions of patellofemoral and tibiofemoral cartilage against body mass index, age, and activity level. Long relaxation times indicate cartilage degradation. Baseline T1ρ relaxation times were significantly inversely correlated with body mass index throughout patellofemoral cartilage for injured knees (p < 0.001 to 0.03). Similar relationships were identified for all regions of patellar cartilage for contralateral knees (p = 0.011 to 0.015). Injured and contralateral T1ρ relaxation times were also correlated with activity level (positive correlation) and age (inverse correlation) for various regions of cartilage (p < 0.001 to 0.047). The only significant correlations for the follow-up groups related increasing body mass index to long cartilage T1ρ relaxation times for the contralateral medial trochlear groove, femoral condyles, and lateral tibial plateau (p = 0.008 to 0.026). The attributes of a dislocation that determine characteristics influencing cartilage are common to both knees but dissipate over time. A systemic, transient inflammatory response to injury could explain the short-term similarities between injured and contralateral knees following dislocation.