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TECHNICAL PAPERS

Correlation of Patellar Tracking Pattern With Trochlear and Retropatellar Surface Topographies

[+] Author and Article Information
A. M. Ahmed, N. A. Duncan

Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada

J Biomech Eng 122(6), 652-660 (Jul 24, 2000) (9 pages) doi:10.1115/1.1322036 History: Received May 18, 1999; Revised July 24, 2000
Copyright © 2000 by ASME
Topics: Particle spin , Tension , Knee
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References

Figures

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Femoral and patellar reference systems: (A) Definition of femoral bone-stub axis as the line joining the centers of two transverse sections, one located at 8–10 cm and the other at 19–22 cm from the joint line. (B) XF−YF−ZF system fixed to the femur: YF axis collinear with the femoral shaft; XF axis parallel to the plane touching posterior aspects of both condyles. (C) XP−YP−ZP system fixed to the patella. The location of the origin Op is defined using the parallelogram enclosing the patella and YP axis is defined parallel to the tangent 1–1. (D) Relative locations and orientations of the two systems. The XP−YP−ZP system is parallel to the XF−YF−ZF system but rotated by the angle η about the XF axis. (E) Patellar translations of the origin Op. (F) Patellar extension and spin rotations. (G) Patellar tilt rotation.
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(A) Definition of the topographic index for patellar medial translation with knee extension, M, as the medial location of the patellofemoral contact point on the trochlear curve at a knee angle of 30 deg (point BF) relative to the contact point at a knee angle of 100 deg (point AF) minus the medial location of the contact point on the patellar ridge at a knee angle of 30 deg (point BP) relative to the contact point at a knee angle of 100 deg (point AP). (B) Definition of the topographic index for patellar abduction spin with knee extension, S, as the medial inclination of the tangent at the patellofemoral contact point on the developed trochlear curve at a knee angle of 30 deg (point BF) relative to that at the contact point at a knee angle of 100 deg (point AF) minus the medial inclination of the tangent at the contact point on the developed patellar ridge at a knee angle of 30 deg (point BP) relative to the contact point at a knee angle of 100 deg (point AP). Note: For clarity, the curvatures of the trochlear curve and the patellar ridge have been exaggerated.
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(A) Definition of the local coordinate system (X−Y−Z) at points AF and BF, with the Z axis made normal to the projection of the trochlear curve in the YF−ZF plane. (B) Definition of the local coordinate system (X−Y−Z) at the points AF and BF, with the X axis made parallel to the XF axis at the point AF, but rotated about the Z axis by the amount of the measured abduction spin at the point BF. (C) Definition of the topographic index for patellar medial tilt, T, as the medial inclination of the lateral flank of the trochlear surface at a knee angle of 30 deg (at point BF) relative to that at a knee angle of 100 deg (at the point AF) minus the medial inclination of the lateral facet on the retropatellar surface at a knee angle of 30 deg (at point BP) relative to that at a knee angle of 100 deg (at point AP).
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Correlation of the measured patellar displacements in the knee extension range 100 to 30 deg with their corresponding topographic indices. (A) Medial translation (Δx) versus M. (B) Abduction spin (Δψ) versus S. (C) Medial tilt (Δθ) versus T. (D) Effect of variations in the tension distribution among the quadriceps muscle components on the correlation between patellar abduction spin (Δψ) and the corresponding index S.
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(A) Transverse profile of the trochlear surface across four different points on the trochlear curve of a typical specimen. Two of the points are the patellofemoral contact points at knee angles 100 deg (point AF) and 30 deg (point BF) and the other two are estimated contact points at knee angles of 70 and 50 deg. (B) Transverse profile of the retropatellar surface across four different points on the patellar ridge of the same specimen as in (A). The characteristics of the locations of the points are identical to those for the trochlear surface. (C) The transverse profile of the retropatellar surface across the point AP of a specimen with a particularly convex medial facet.

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