The Influence of Knee Position on Ultrasound Imaging of Femoral Cartilage in Individuals with Anterior Cruciate Ligament Reconstruction.

Background: Articular cartilage is important for knee function and can be imaged using ultrasound. The purpose was to compare femoral cartilage thickness and echo intensity (EI) measured at 90° and 140° of knee flexion and between limbs in a cohort with unilateral anterior cruciate ligament reconstruction (ACLR). We also examined associations between gait biomechanics and cartilage outcomes.

Methods: Twenty-seven individuals with primary unilateral ACLR participated (12 men, 15 women; age = 22.3 ± 3.8 years; time since ACLR = 71.2 ± 47.2 months). Ultrasound was used to obtain femoral cartilage measurements. Gait outcomes included peak KFA (knee flexion angle) and peak external knee flexion moment (KFM). Cartilage outcomes were compared using a 2 () × 2 () repeated measures ANOVA (analysis of variance). Gait and cartilage associations were assessed using linear regression.

Findings: There were no position × limb interactions for any cartilage outcome (all > 0.05). Medial ( = 0.038) and central cartilage ( < 0.001) were thicker, whereas central ( = 0.029) and lateral cartilage EI ( = 0.003) were lower when measured at 90° than those at 140° of knee flexion. Medial cartilage was thicker in the ACLR than that in the contralateral limb ( = 0.016). A larger KFM was associated with thicker medial cartilage (ΔR = 0.146, = 0.021) and central cartilage (ΔR = 0.159, = 0.039) measured at 140° of knee flexion in the ACLR limb but not at 90°.

Interpretation: Findings suggest that imaging position influences cartilage thickness and EI measurements in individuals with ACLR and should be considered in study designs and clinical evaluation. A greater KFM was associated with thicker cartilage within specific portions of the distal femur.