In this pilot study, we assessed the relationship between three-dimensional patellar kinematics and patellofemoral cartilage morphology in 10 individuals with varus or valgus alignment and early knee osteoarthritis (OA). We used a novel, validated, non-invasive magnetic resonance imaging (MRI)-based technique to assess three-dimensional patellar kinematics and a validated quantitative MRI (qMRI) technique to assess cartilage morphology at the patellofemoral joint. Varus and valgus alignment was assessed from a standing anteriorposterior radiograph.

Differences in three-dimensional patellar kinematics between the varus and valgus groups were assessed using a random effects model. We found that the varus group displayed constant medial tilt, constant external spin and decreasing anterior translation with increasing tibiofemoral flexion. We found that the valgus group displayed increasing medial tilt, constant internal spin, a greater proximal position and a constant anterior position with increasing tibiofemoral flexion. N o difference was seen in lateral translation between the varus and valgus groups and the patella was centred in the trochlear groove.

Medial and lateral compartment cartilage morphology was compared to varus and valgus alignment using a two-way analysis of variance (ANOVA). No difference was found between the varus and valgus groups. A power analysis revealed that 30 subjects are required in each group to detect a significant difference.

The relationship between three-dimensional patellar kinematics and the ratio of medial to lateral compartment cartilage morphology was assessed using a regression model. We found that the rate of medial tilt increased with decreasing ratio of medial to lateral compartment bone/cartilage interface area. Results suggested a relationship between lateral patellar translation and proportion of medial to lateral cartilage normalized volume, mean thickness and percentage cartilage coverage. This finding was greatly influenced by two data points and therefore this result is not conclusive.

Cartilage degeneration at the patellofemoral joint cannot be completely explained by the presence of varus or valgus malalignment. Other local biomechanical factors, such as kinematics, are likely involved. A better understanding of the relationship between three- dimensional patellar kinematics and cartilage degeneration allows for the development of improved treatment strategies to arrest the onset and progression of patellofemoral OA.