Technical Briefs

Multiplane Loading of the Extensor Mechanism Alters the Patellar Ligament Force/Quadriceps Force Ratio

[+] Author and Article Information
Christopher M. Powers1

Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90036powers@usc.edu

Yu-Jen Chen, Irving S. Scher

Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90036

Thay Q. Lee

Orthopaedic Biomechanics Laboratory VA Long Beach Healthcare System, Long Beach, CA Departments of Orthopaedic Surgery, University of California, Irvine, CA 92697


Corresponding author.

J Biomech Eng 132(2), 024503 (Jan 29, 2010) (5 pages) doi:10.1115/1.4000852 History: Received March 25, 2008; Revised October 02, 2009; Posted December 17, 2009; Published January 29, 2010; Online January 29, 2010

Since the direction of the quadriceps force and location of the patellofemoral contact point likely differ between axial and multiplane loadings, the force and moment balance solutions for a multiplane loading condition may not yield the same patella ligament force/quadriceps force ratio (FPL/FQ ratio) when compared with an axial loading condition. The purpose of this study was to compare the effects of an axial loading condition and an anatomical, multiplane loading condition on the FPL/FQ ratio at various knee flexion angles. Ten cadaver knees were used in this investigation. Each was mounted on a custom jig that was fixed to an Instron frame. Quadriceps muscle loads were applied with same resultant force magnitudes under two force directions, as follows: (1) axial loading (central quadriceps tendon loading parallel to the femoral axis), and (2) an anatomically based, multiplane loading condition (individual vasti loaded, taking into consideration physiologic muscle fiber orientation). Patellar ligament tension was measured using a buckle transducer. The patellar ligament force/quadriceps force ratio (FPL/FQ ratio) was calculated for both loading conditions at 0 deg, 20 deg, 40 deg, and 60 deg of knee flexion. Across the range of knee motion evaluated, the FPL/FQ ratio for the axial loading condition was significantly greater than the FPL/FQ ratio for the multiplane loading condition. Our results suggest that loading orientation affects the transfer of forces from the quadriceps tendon to the patellar ligament.

Copyright © 2010 by American Society of Mechanical Engineers
Topics: Force , Muscle , Knee , Mechanisms , Tendons
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Figure 1

Frontal view of the experimental setup

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Figure 2

Two-dimensional representations of the quadriceps loading for the (a) multiplane and (b) axial loading conditions. The line of pull of each component of the quadriceps was adjusted so that the force application of the respective musculature represented the primary fiber direction and orientation. Black force vectors represent the resultant forces and the gray force vectors represent individually loaded vasti.

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Figure 3

Comparison of the average FPL/FQ ratios between loading conditions across all knee flexion angles tested. Error bars equal 1 SE. Solid and dashed lines correspond to the least-squares, best-fit lines for the multiplane (R2=0.96) and axial (R2=0.98) loading data.

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Figure 4

Average FPL/FQ ratios from the current study (○=multiplane loading and △=axial loading) compared with results from Huberti (9,14) (×), van Eijden (10) (●), Buff (8) (◼), and, Yamaguchi and Zajac (1) (▲)

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Figure 5

Free-body diagram of the patella. The resultant patellofemoral joint reaction force (PFJRF) acts at the effective contact point. MPL and MQ are the moment arms of the resultant patellar ligament and quadriceps forces about the patellofemoral point of contact. For slow motions, a quasi-static moment balance yields the following relationship: FPL⋅MPL=FQ⋅MQ

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Figure 6

The direction of resultant quadriceps force can influence the FPL/FQ ratio. Multiplane quadriceps loading produced a more posteriorly directed resultant force (FQ2) when compared with axial loading (FQ1); this direction change decreases the quadriceps force moment arm (MQ1>MQ2).

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Figure 7

Changes in patella kinematics can influence the FPL/FQ ratio. The multiplane loading condition results in increased patella extension (i.e., decreased flexion) when compared with the axial loading condition. With greater patella extension, the patellofemoral contact point moves superiorly on the patella, thereby decreasing the moment arm of FQ while simultaneously increasing the moment arm of FPL. Such a shift in moment arms would decrease the FPL/FQ ratio.




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