Patellar tracking disorder is recognized as one of the major causes of the pathophysiological mechanism in patellofemoral pain syndrome. This paper reviewed the results of patellofemoral kinematic analyses and summarized the motion characteristics of six-degrees-of-freedom (6DOF) of patellofemoral joints under different functional activities. Patella has a relatively unified trend in lateral, anterior and posterior translation, tilt and flexion. However, different measurements limit an in-depth comparison between studies. In the future, widely applying magnetic resonance(MRI) or/and dual fluoroscopic imaging system (DFIS), standardizing the establishment of coordinate system or definition and use of morphological parameters, and increasing sample size will contribute to explicating the 6DOF motion characteristics of patellofemroal joints in vivo and improve the clinical evaluation on kinematic function of patellofemroal joints.

Objective To investigate the translation and rotation of healthy elbow joints during active flexion and extension, so as to provide references for the treatment of elbow instability and injuries. Methods Ten healthy subjects with no history of upper extremity trauma were recruited. Dual fluoroscopic imaging system (DFIS) was applied to quantify six-degree-of-freedom (6-DOF) kinematics of humeroulnar and humeroradial joint from full extension to maximum flexion in supination position. Correlation analysis was used to evaluate the relationship between the 6-DOF kinematics of the elbow joint. Results Valgus angle of humeroulnar joint gradually decreased from 15.2°±3.1° to 5.3°±2.3° with the flexion increasing. Valgus angle of humeroradical joint gradually decreased from 19.7°±4.2° to 8.2°±2.4° from full extension to maximum flexion. The valgus angle of humeroulnar and humeroradial joint was linearly related to the flexion angle during flexion and extension. The internal rotation of humeroulnar joint was quadratic nonlinearly related to the flexion angle during motion. The maximum internal rotation of the ulnar was 4.0°±4.9° at 110° flexion, and the maximum external rotation was 5.1°±4.2°. The internal rotation of humeroulnar joint gradually increased from 3.2°±16.0° to 27.2°±18.0°. Conclusions During normal flexion and extension of the elbow, the valgus angle of humeroulnar joint decreased linearly, while the internal and external rotation angle showed a nonlinear change, which first rotated internally and then rotated externally. The valgus angle of humeroradial joint decreased linearly and the internal rotation angle increased linearly. Therefore, humeroulnar joint is not a hinge joint during elbow flexion and extension. There is a kinematic difference between humeroulnar joint and humeroracial joint. For clinical treatment of complex elbow injuries, elbow instability and elbow replacement, different motion characteristics in joints should be considered to improve the outcome after surgery.