LIN, F., G. WANG, J. L. KOH, R. W. HENDRIX, and L.-Q. ZHANG. In vivo and Noninvasive Three-Dimensional Patellar Tracking Induced by Individual Heads of Quadriceps. Med. Sci. Sports Exerc., Vol. 36, No. 1, pp. 93-101, 2004.
Purpose: Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components.
Methods: Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements.
Results: Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella.
Conclusions: The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.
Patellofemoral pain (PFP) syndrome is one of the most commonly observed physical abnormalities involving the knee in sports medicine clinics. Although PFP is a fairly broad definition of a set of symptoms involving pain around the patella, its etiology is still not very clear and its clinical treatment is often not satisfactory (12,9). PFP is considered to be associated with patellar malalignment and abnormal patellar tracking. In clinics, patellar alignment and subluxation are generally evaluated by physical examination and measurement of the Q angle and tightness of parapatella soft tissues. Patellar alignment and tracking has been evaluated with radiographic x-ray imaging, computed tomography, and magnetic resonance imaging at different knee flexion angles (6,9,26,18), which, however, does not provide quantitative information on the actions of individual quadriceps components on the patella.
Appropriate patellar tracking is dependent on balanced actions of the different quadriceps components. Reduced action of the medial stabilizers, especially the vastus medialis oblique (VMO), is thought to be an important factor in patellofemoral malalignment and abnormal patellar tracking (3,14,15,24). Therefore, it is important to understand patellar movement induced by different quadriceps components. However, although patellar tracking has been investigated in several cadaver-based studies (28,8,19,3), there has been a lack of information on patellar tracking induced by individual quadriceps components, especially under in vivo and noninvasive conditions.
The purpose of this study was to investigate six degrees-of-freedom (DOF) patellar tracking induced by individual quadriceps components in vivo and noninvasively. It was hypothesized that VMO, vastus medialis longus (VML), and vastus lateralis (VL) pull and rotate and pull the patella differently in three-dimensional space. Quantitative evaluation of the roles of individual quadriceps components in patellar tracking will help us better understand the knee extensor mechanism, gain insight into the mechanisms underlying patellofemoral disorder, and evaluate pathological changes accurately. Relevant six-DOF patellar tracking during voluntary knee flexion and extension has been reported recently (17).