A Model of Stress and Strain in the Interosseous Ligament of the Forearm Based on Fiber Network Theory

[+] Author and Article Information
H. James Pfaeffle

Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PApfaeffle@pitt.edu

Kenneth J. Fischer

Department of Mechanical Engineering, University of Kansas, Lawrence, KS 66045-7609fischer@ku.edu

Arun Srinivasa

Department of Mechanical Engineering, Texas A&M University, College Station, TXarun-r-srinivasa@tamu.edu

Theodore Manson

Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, MDtmanson1@jhmi.edu

Savio L-Y. Woo

Department of Bioengineering, University of Pittsburgh, Pittsburgh, PAslyw@pitt.edu

Matthew Tomaino

Department of Orthopaedics, University of Rochester, Rochester, NYmatthew_tomaino@urmc.rochester.edu

J Biomech Eng 128(5), 725-732 (Apr 28, 2006) (8 pages) doi:10.1115/1.2241730 History: Received April 11, 2005; Revised April 28, 2006

Fiber network theory was developed to describe cloth, a thin material with strength in the fiber directions. The interosseous ligament (IOL) of the forearm is a broad, thin ligament with highly aligned fibers. The objectives of this study were to develop a model of the stress and strain distributions in the IOL, based on fiber network theory, to compare the strains from the model with the experimentally measured strains, and to evaluate the force distribution across the ligament fibers from the model. The geometries of the radius, ulna, and IOL were reconstructed from CT scans. Position and orientation of IOL insertion sites and force in the IOL were measured during a forearm compression experiment in pronation, neutral rotation, and supination. An optical image-based technique was used to directly measure strain in two regions of the IOL in neutral rotation. For the network model, the IOL was represented as a parametric ruled three-dimensional surface, with rulings along local fiber directions. Fiber strains were calculated from the deformation field, and fiber stresses were calculated from the strains using average IOL tensile properties from a previous study. The in situ strain in the IOL was assumed uniform and was calculated so that the net force predicted by the network model in neutral rotation matched the experimental result. The net force in the IOL was comparable to experimental results in supination and pronation. The model predicted higher stress and strain in fibers near the elbow in neutral rotation, and higher stresses in fibers near the wrist in supination. Strains in neutral forearm rotation followed the same trends as those measured experimentally. In this study, a model of stress and strain in the IOL utilizing fiber network theory was successfully implemented. The model illustrates variations in the stress and strain distribution in the IOL. This model can be used to show surgeons how different fibers are taut in different forearm rotation positions—this information is important for understanding the biomechanical role of the IOL and for planning an IOL reconstruction.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

IOL from dissection demonstrating visualization of local fiber direction. The radius is below and the elbow to the left in this picture.

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Figure 2

Sample digital image obtained for strain analysis. The image shows the IOL between the ulna (left) and radius (right) in the Neutral rotation, Unloaded configuration (NU) with the optical markers on the ligament. The markers are placed near the insertion sites, among the proximal and distal fibers of the ligament. The physical scale reference markers are shown just above the ligament.

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Figure 3

Ruled surface for IOL geometry defined from CT reconstruction. Left: CT reconstruction. Right: Ruled surface. In each image, the ulna is at the top, the radius is below, and proximal is to the left. The coordinate system shown is for the ulnar registration block.

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Figure 4

Ruled surface for IOL geometry defined from CT reconstruction of Specimen 1 (right forearm) along with corresponding dissection picture shown in neutral rotation and pronation. The IOL inserts on the interosseous ridge of the radius and ulna. The IOL folds sharply at its insertion site on the ulna as the radius moves into pronation (similar also seen in supination).

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Figure 5

Plots of fiber strain and stress (MPa) magnitudes predicted by the network model for the two specimens. The X axis is the parametric location on insertion site measured by normalized length along the insertion from distal (closer to the wrist, s=0) to proximal (closer to the elbow, s=1).

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Figure 6

Results for force (left) and strain (right) in neutral rotation, pronation, and supination displayed in 3D on computer model using Tecplot (Specimen 1 only, right forearm). In all images, the radius is at the top, the ulna is below and the elbow is to the right.



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