Patellofemoral contact forces and knee gait mechanics 3 months after ACL reconstruction are associated with cartilage degradation 24 months after surgery

OBJECTIVE

Evaluate patellofemoral cartilage health, as assessed by quantitative magnetic resonance imaging (qMRI) T2 relaxation times, 24-months after ACL reconstruction (ACLR) and determine if they were associated with patellofemoral contact forces and knee mechanics during gait 3 months after surgery.

DESIGN

Thirty individuals completed motion analysis during overground walking at a self-selected speed 3 months after ACLR. An EMG-driven neuromusculoskeletal model was used to determine muscle forces, which were then used in a previously described model to estimate patellofemoral contact forces. Biomechanical variables of interest included peak patellofemoral contact force, peak knee flexion angle and moment, and walking speed. These same participants underwent a sagittal bilateral T2 mapping qMRI scan 24-months after surgery. T2 relaxation times were estimated for both patellar and trochlear cartilage. Paired t-tests were used to compare T2 relaxation times between limbs while Pearson correlations and linear regressions were utilized to assess the association between the biomechanical variables of interest and T2 relaxation times.

RESULTS

Prolonged involved limb trochlear T2 relaxation times (vs uninvolved) were present 24-months after surgery, indicating worse cartilage health. No differences were detected in patellar cartilage. Significant negative associations were present within the involved limb for all the biomechanical variables of interest 3 months after ACLR and trochlear T2 relaxation times at 24-months. No associations were found in patellar cartilage or within the uninvolved limb.

CONCLUSIONS

Altered involved limb trochlear cartilage health is present 24-months after ACLR and may be related to patellofemoral loading and other walking gait mechanics 3 months after surgery.

Studies of periodic seawater spray icing with unilateral NMR

Sea water ice has a complicated pore structure consisting of brine-filled pockets within a solid ice matrix. In this work, an unilateral Nuclear Magnetic Resonance instrument was used to characterize the evolution of sea-ice brine inclusions in two types of ice: stationary seawater ice and seawater spray ice formed by periodic spraying on horizontal and vertical surfaces. The portable unilateral NMR was capable of measuring very low amounts of brine (<10% of the water-filled volume). CPMG experiments were performed to extract the information on brine content and T₂ distribution at temperatures between -6 °C and -16 °C. 1D imaging was used to spatially resolve the ice brine accumulation. The results show that the seawater spray ice growth, brine content (greater for the horizontal orientation than for the vertical one), and T₂ distribution (unimodal for stationary ice and bimodal for spray ice) depend on temperature and surface orientation.