Impacts of malalignment in medial compartment knee osteoarthritis on the patellofemoral joint: A quantitative analysis during staircase motion.

Abstract

The progression of medial compartment knee osteoarthritis (MCKOA) tends to be accompanied by degeneration of the patellofemoral joint (PFJ). However, the underlying biomechanical mechanisms have not been investigated. This study aims to quantitatively analyse the six-degrees-of-freedom (6-DOF) motion and contact patterns of the PFJ during staircase motion and explore the relationship between lower limb alignment and PFJ kinematics. Thirty-two patients with unilateral MCKOA and intact contralateral extremities were enrolled. All patients performed continuous staircase motion under the surveillance of a dual fluoroscopic imaging system (DFIS) to investigate the PFJ 6-DOF, contact pattern and hip-knee-ankle angle (HKA) of their MCKOA knee and contralateral native knee. During staircase motion, MCKOA side patella presented greater flexion and varus degrees and more posterior, distal and medial translations (P < 0.05). Besides, the contact centre on the medial patellar facet shifted more medially, whereas the lateral contact centre shifted more proximally (P < 0.05). The HKA angle of the MCKOA knees was significantly greater than that of the native knees (P < 0.05). A larger HKA angle was associated with greater patellar flexion (r = 0.37, P < 0.05) and lower patellar anterior translation (r = -0.45, P < 0.05). Our study revealed significant alterations in PFJ kinematics and contact patterns in MCKOA knees during motion, characterized by increased patellar flexion, varus rotation and certain altered translations. These changes were associated with the HKA angle, underscoring the importance of addressing malalignment in the MCKOA knee and providing valuable insights for restoring PFJ function and preserving joint health.