Research Methods and Progress of Patellofemoral Joint Kinematics: A Review

Abstract

Patellofemoral pain syndrome has a high morbidity, and its pathology is closely associated with patellofemoral joint kinematics. A series of in vivo and in vitro studies have been conducted to explore patellofemoral kinematics, and the findings are relevant to the diagnosis, classification, and management of patellofemoral diseases and even the whole knee joint. However, no definite conclusion on normal patellofemoral kinematics has been established. In this study, the measurement methodologies of patellofemoral kinematics (including data collection methods, loading conditions, and coordinate system) as well as their advantages and limitations were reviewed. Motion characteristics of the patella were analyzed. During knee flexion, the patellar flexion angle lagged by 30-40% compared to the tibiofemoral joint flexion. The patella tilts, rotates, and shifts medially in the initial stage of knee flexion and subsequently tilts, rotates, and shifts laterally. The finite patellar helical axis fluctuates near the femoral transepicondylar axis or posterior condylar axis. Moreover, factors affecting kinematics, such as morphology of the trochlear groove, soft tissue balance, and tibiofemoral motion, were analyzed. At the initial period of flexion, soft tissues play a vital role in adjusting patellar tracking, and during further flexion, the status of the patella is determined by the morphology of the trochlear groove and patellar facet. Our findings could increase our understanding of patellofemoral kinematics and can help to guide the operation plan for patients with patellofemoral pain syndrome.

Figure 1

The overview schematic of this review. In this review, different measurement methodologies were reviewed, which often related to the description of patellar tracking. Then, the patellofemoral kinematics of previous studies was summarized and analyzed. The factors influencing the patellofemoral kinematics are also discussed.

Figure 2

Six DOFs of patellar tracking (right knee). As the knee flexes and extends, six DOFs are involved in patellar kinematics. These are (a) flexion, (b) tilt, (c) rotation, (d) medial-lateral shift, (e) anterior-posterior translation, and (f) proximal-distal translation. Of the six DOFs, the first four indices, which are detailed in the most correlational studies, are closely related to clinical applications. In terms of DOF classification, the first three DOFs belong to the rotation parameters expressed as angles, and the last three belong to the translation parameters expressed as distance.

Figure 3

The change tendency of average patellar flexion angle with knee flexion. Considering the evident difference in sample sizes among studies, we calculated the weighted average of the patellar tracking based on the number of subjects (blue curve), as well as the unweighted average of the patellar tracking (red curve). Studies with knee flexion above 90° are included.

Figure 4

The change tendency of average patellar tilt angle with knee flexion. Blue curve is the weighted average of the patellar tracking (based on the number of subjects); red curve is the unweighted average. Studies with knee flexion above 90° are included.

Figure 5

The change tendency of average patellar rotation angle with knee flexion. Blue curve is the weighted average of the patellar tracking (based on the number of subjects); red curve is the unweighted average. Studies with knee flexion above 90° are included.

Figure 6

The change tendency of average patellar shift angle with knee flexion. Blue curve is the weighted average of the patellar tracking (based on the number of subjects); red curve is the unweighted average. Studies with knee flexion above 90° are included.

Figure 7

The change of patellar flexion angles with knee flexion in 12 studies. Twelve curves of different colors indicate the patellar flexion angles over knee flexion angle in 12 studies. All of the patellar flexion angles increased at a similar rate (60%–70%) with knee flexion angle.

Figure 8

The change patellar tilt angle with knee flexion in 10 studies. Ten curves of different colors indicate the patellar tilt angles over knee flexion angle in 10 studies. Eight curves contain kinematic information from 0° to 90° of knee flexion; curves of Merican and Amis [15], Wilson et al. [38], Stephen et al. [43], and Cheung et al. [44] decreased by 1°–3° and then increased by 1°–15.5°; while curves of Nha et al. [31], Yao et al. [32], Amis et al. [39], and Philippot et al. [–42] increased from the full knee extension. Curves of Nha et al. [31] and Cheung et al. [44] tend to decrease after knee flexion exceeds 90°.

Figure 9

The change of patellar rotation angle with knee flexion in 10 studies. Ten curves of different colors indicate the patellar tilt angles over knee flexion angle in 10 studies. Within 30° of knee flexion, all curves are confined to the range from −1° to 2°. After knee flexion exceeds 80°, curves of Nha et al. [31], Cheung et al. [44], and Philippot et al. [–42] increased to greater than 2°, while curves of Merican and Amis [15] and Wilson et al. [38] decreased to −2°.

Figure 10

The change patellar shift angle with knee flexion in 11 studies. Eleven curves of different colors indicate the patellar shifts over knee flexion angle in 11 studies. Curves of Merican and Amis [15], Suzuki et al. [30], Nha et al. [31], Amis et al. [39], Philippot et al. [–42], and Cheung et al. [44] decrease first and then increase, while curves of Wilson et al. [38] increases first and then decreases.

Figure 11

Patellofemoral arm and moment of force during flexion or extension. Patellofemoral arm of force is defined as the distance from the resultant force of the quadriceps to FHA. Patellofemoral moment of force is defined as the product of the arm of force and the resultant force of quadriceps. F: resultant force of quadriceps, FHA: patellar finite helical axis, L: arm of resultant force of quadriceps, and M: moment of resultant force of quadriceps (F × L).