Individuals with a history of anterior cruciate ligament reconstruction (ACLR) have a higher risk of developing accelerated knee osteoarthritis compared to individuals without a history of knee injury. It is necessary to establish reliable tools (i.e. ultrasound assessment) that assess knee joint health, determine how early these tools can identify poor knee joint health changes in high-risk populations, and examine which modifiable risk factors (i.e. mechanical knee joint loading) contribute to accelerated poor knee joint health development. The purposes of this dissertation were to: 1) establish the intra-rater and test-retest reliability of two ultrasound assessment techniques (resting cartilage and cartilage response to loading assessments) of femoral articular cartilage structure and deformation, 2) assess resting femoral articular cartilage structural differences between the involved limb and contralateral limb and changes over time from 4- to 6-months post-ACLR, and 3) determine the ability of cumulative knee joint loading (gait knee biomechanics and volume of loading) at 4-months post-ACLR to predict resting medial femoral articular cartilage structure at 6-months post-ACLR. In the first observational study, femoral articular cartilage structure and deformation were evaluated via the resting cartilage and cartilage response to loading ultrasound assessment techniques in 30 participants without a history of knee injury. In 2 identical testing sessions, the resting cartilage and post-loading cartilage images were capture after 30 minutes of rest and 3,000 steps of walking, respectively. A total of 20 participants post-ACLR completed the resting cartilage ultrasound assessment in their involved and contralateral limb at 4- and 6-months post-ACLR for the second longitudinal study. At 4-months post-ACLR, knee gait biomechanics (knee extension moment, knee abduction moment, and vertical ground reaction force) were assessed with motion capture and force plates, and volume of activity (steps/day) were assessed with a hip worn accelerometer over 7 days. All ultrasound images were processed using a semi-automated processing technique to divide the total cartilage cross-sectional area into medial, intercondylar, and lateral compartments normalized to compartment length for cartilage thickness (mm). Resting cartilage ultrasound assessment demonstrated excellent test-retest and intra-rater reliability (ICC2,k= 0.97-0.99). Cartilage response to loading ultrasound assessment demonstrated poor test-retest reliability (ICC2,k=-0.36-0.46), but good to excellent intra-rater reliability (ICC2,k=0.84-0.94). Individuals 4- to 6-months post-ACLR did not demonstrate any significant limb main effects (p range=0.50-0.92), time main effects (p range=0.22-0.72), or interactions (p range=0.24-0.49) for resting medial, intercondylar, or lateral femoral articular cartilage compartmental thickness. Lesser knee extension moment (unstandardized β=2.82, p=0.02) and greater steps per day (unstandardized β=0.00, p=0.04) at 4-months post-ACLR predict greater medial femoral articular cartilage compartmental thickness at 6-months post-ACLR (R2= 0.39, p=0.03). The resting cartilage ultrasound assessment is a reliable technique between multiple processing and testing sessions, but the cartilage response to loading ultrasound assessment is not reliable between testing sessions. Femoral articular cartilage structural differences between limbs or change over time may not be present before 6 months post-ACLR. Individuals with poor biomechanics who take more steps per day demonstrate articular cartilage structural changes indicative of articular cartilage swelling within 6-months post-ACLR. Cumulative mechanical knee joint loading is a multifactorial risk factor of knee joint health during the early phases of recovery after ACLR.
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