In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain

Abstract

Background: Patellofemoral pain syndrome is one of the most common knee problems and may be related to abnormal patellar tracking. Our purpose was to compare, in vivo and noninvasively, the patellar tracking patterns in symptomatic patients with patellofemoral pain and those in healthy subjects during squatting. We tested the hypothesis that patients with patellofemoral pain exhibit characteristic patterns of patellar tracking that are different from those of healthy subjects.

Methods: Three-dimensional patellar kinematics were recorded in vivo with use of a custom-molded patellar clamp and an optoelectronic motion capture system in ten healthy subjects and nine subjects with patellofemoral pain. The position of osseous knee landmarks was digitized while subjects stood upright, and then patellofemoral kinematics were recorded during squatting. The tracking technique was validated with use of both in vitro and in vivo methodologies, and the average absolute error was <1.2 degrees and <1.1 mm.

Results: At 90 degrees of knee flexion, the patella showed lateral spin (the distal pole of the patella rotated laterally) in subjects with patellofemoral pain (mean and standard deviation, -10.13 degrees +/- 2.24 degrees) and medial spin in healthy subjects (mean, 4.71 degrees +/- 1.17 degrees) (p < 0.001). At 90 degrees of knee flexion, the patella demonstrated significantly more lateral translation in subjects with patellofemoral pain (mean, 5.05 +/- 3.73 mm) than in healthy subjects (mean, -4.93 +/- 3.93 mm) (p < 0.001).

Conclusions: Kinematic differences between healthy subjects and subjects with patellofemoral pain were demonstrated through a large, dynamic range of knee flexion angles. Increased lateral patellar translation and lateral patellar spin in subjects with patellofemoral pain suggest that the patella is not adequately balanced during functional activities in this group. Prospective studies are needed to identify when patellofemoral pain-related changes begin to occur and to determine the risk for the development of patellofemoral pain in individuals with abnormal kinematics.

Fig. 1

Photographs of the patellar tracking setup. A: Custom clamp after molding. B: Custom clamp with an outline of the underlying patella digitally overlaid. C: Custom clamp affixed to the leg with use of elastic wrap with foam inner layer. D: Custom patellar clamp and the goniometer. Active infrared markers are indicated on both the clamp and the goniometer.

Fig. 2

The positive directions of motion for each degree of freedom. A: Patellar flexion-extension occurred about the transepicondylar line of the femur (X_f-axis). B: Patellar medial-lateral tilt occurred about the longitudinal axis of the patella (Y_p-axis). C: Patellar spin occurred about the anterior-posterior floating axis (Z_p-axis; perpendicular to both the X_f and the Y_p axes). Patellar translation relative to the femur was described along the three axes of the femoral coordinate system. D: Medial-lateral translation along X_f. The asterisks indicate the osseous landmarks that were digitized for reference position definitions. E: Proximal-distal translation along Y_f. F: Anterior-posterior translation along Z_f. The positive directions of motion for the patellofemoral joint are extension (A), lateral tilt (B), medial spin (the distal patellar pole rotates medially about the anterior-posterior axis) (C), lateral shift (D), distal shift (E), and anterior shift (F).

Fig. 3

Patellofemoral extension angle for patients with patellofemoral pain (PFP) and healthy subjects for the first 90° of knee flexion. The error bars indicate the standard deviation.

Fig. 4

Medial spin angle for patients with patellofemoral pain (PFP) and healthy subjects for the first 90° of knee flexion. The error bars indicate the standard deviation. *p < 0.05 and **p < 0.01.

Fig. 5

Lateral tilt angle for patients with patellofemoral pain (PFP) and healthy subjects for the first 90° of knee flexion. The error bars indicate the standard deviation.

Fig. 6

Lateral patellar translation for patients with patellofemoral pain (PFP) and healthy subjects for the first 90° of knee flexion. The error bars indicate the standard deviation. *p < 0.05.