Gait Mechanics and T1ρ MRI of Tibiofemoral Cartilage 6 Months Post ACL Reconstruction

Purpose Aberrant walking biomechanics following anterior cruciate ligament reconstruction (ACLR) are hypothesized to associate with deleterious changes in knee cartilage. T1ρ magnetic resonance imaging (MRI) is sensitive to decreased proteoglycan density of cartilage. Our purpose was to determine associations between T1ρ MRI inter-limb ratios (ILR) and walking biomechanics 6-months post-ACLR. Methods Walking biomechanics (peak vertical ground reaction force [vGRF], vGRF loading rate [vGRF-LR], knee extension moment [KEM], knee abduction moment [KAM]) were extracted from the first 50% of stance phase in 29 individuals with unilateral ACLR. T1ρ MRI ILR (ACLR limb/uninjured limb) were calculated for regions of interest in both medial and lateral femoral (MFC and LFC) and tibial (MTC & LTC) condyles. Separate, stepwise linear regressions were used to determine associations between biomechanical outcomes and T1ρ MRI ILR after accounting for walking speed and meniscal/chondral injury (P≤0.05). Results Lesser peak vGRF in the ACLR limb associated with greater T1ρ MRI ILR for the LFC (Posterior ΔR2=0.14 P=0.05; Central ΔR2=0.15, P=0.05) and MFC (Central ΔR2=0.24, P=0.01). Lesser peak vGRF-LR in the ACLR limb (ΔR2=0.21, P=0.02) and the uninjured limb (ΔR2=0.27, P=0.01) associated with greater T1ρ MRI ILR for the Anterior LFC. Lesser KAM for the injured limb associated with greater T1ρ MRI ILR for the Anterior LFC (ΔR2=0.16, P=0.04) as well as the Posterior MTC (ΔR2=0.13, P=0.04). Conclusion Associations between outcomes related to lesser mechanical loading during walking and greater T1ρ MRI ILR were found 6-months post-ACLR. While preliminary, our results suggest under-loading of the ACLR limb at 6 months post-ACLR may be associated with lesser proteoglycan density in the ACLR limb compared to the uninjured limb. Corresponding Author: Steven Pfeiffer, MS, University of North Carolina at Chapel Hill, CB# 8700, 209 Fetzer Hall, Chapel Hill, NC 27599. Phone: 919-962-7187. Fax: 919-962-0489. Email: stevenpf@email.unc.edu Research reported in this original manuscript was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (1R03AR066840-01A1), North Carolina Translational and Clinical Sciences (TRaCS) Institute, and National Athletic Trainers Association Research and Education Foundation (#14NewInv001). The results of the current study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Conflicts of Interest. No conflicts of interests are reported. The results of the present study do not constitute endorsement by the American College of Sports Medicine. Accepted for publication October 2018. © 2018 American College of Sports Medicine

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