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Research Papers

Anatomical Study of the Radius and Center of Curvature of the Distal Femoral Condyle

[+] Author and Article Information
Jürgen Kosel

Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabiajuergen@sun.ac.za jurgen.kosel@kaust.edu.sa

Ioanna Giouroudi

Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland 7602, South Africaioanna@sun.ac.za

Cornie Scheffer

Department of Mechanical and Mechatronic Engineering, Stellenbosch University, Private Bag X1, Matieland 7602, South Africacscheffer@sun.ac.za

Edwin Dillon

Knee Clinic Stellenbosch, Stellenbosch Medi-Clinic, Die Boord, Room G3, Stellenbosch 7600, South Africaedwin@orthoclinic.co.za

Pieter Erasmus

Knee Clinic Stellenbosch, Stellenbosch Medi-Clinic, Die Boord, Room G3, Stellenbosch 7600, South Africaknee@orthoclinic.co.za

J Biomech Eng 132(9), 091002 (Aug 16, 2010) (6 pages) doi:10.1115/1.4002061 History: Received March 05, 2009; Revised June 09, 2010; Posted June 25, 2010; Published August 16, 2010; Online August 16, 2010

In this anatomical study, the anteroposterior curvature of the surface of 16 cadaveric distal femurs was examined in terms of radii and center point. Those two parameters attract high interest due to their significance for total knee arthroplasty. Basically, two different conclusions have been drawn in foregoing studies: (1) The curvature shows a constant radius and (2) the curvature shows a variable radius. The investigations were based on a new method combining three-dimensional laser-scanning and planar geometrical analyses. This method is aimed at providing high accuracy and high local resolution. The high-precision laser scanning enables the exact reproduction of the distal femurs—including their cartilage tissue—as a three-dimensional computer model. The surface curvature was investigated on intersection planes that were oriented perpendicularly to the surgical epicondylar line. Three planes were placed at the central part of each condyle. The intersection of either plane with the femur model was approximated with the help of a b-spline, yielding three b-splines on each condyle. The radii and center points of the circles, approximating the local curvature of the b-splines, were then evaluated. The results from all three b-splines were averaged in order to increase the reliability of the method. The results show the variation in the surface curvatures of the investigated samples of condyles. These variations are expressed in the pattern of the center points and the radii of the curvatures. The standard deviations of the radii for a 90 deg arc on the posterior condyle range from 0.6 mm up to 5.1 mm, with an average of 2.4 mm laterally and 2.2 mm medially. No correlation was found between the curvature of the lateral and medial condyles. Within the range of the investigated 16 samples, the conclusion can be drawn that the condyle surface curvature is not constant and different for all specimens when viewed along the surgical epicondylar axis. For the portion of the condylar surface that articulates with the tibia during knee flexion-extension, the determined center points approximate the location of the centers of rotation. The results suggest that the concept of a fixed flexion-extension axis is not applicable for every specimen.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Axial view of the three-dimensional model of the distal femur showing the posterior condylar axis and the intersection planes P1 to P6. (b) 3D laser scanned model of a distal femur with three intersection curves on each condyle.

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Figure 2

Geometric determination of the center point CPxBi and radius RxBi of a circle that approximates the curvature at the point pxBi

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Figure 3

(a) Intersection curve of a lateral condyle showing the investigated section pxL and the track of the center points CPxL, a square and a star marking the start and end points, respectively. The region of smallest curvature variation (SminL) is highlighted by bold lines. (b) Radius RxL of the condyle surface curvature over the angular position αxL.

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Figure 4

(a) Intersection curve of a medial condyle showing the investigated section pxM and the track of the center points CPxM, a square and a star marking the start and end points, respectively. The region of smallest curvature variation (SminM) is highlighted by bold lines. (b) Radius RxM of the condyle surface curvature over the angular position αxM.

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Figure 5

A circle with a radius of 20 mm approximates flat portions of 12.5 mm in length with an error of only 1 mm

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