Abstract presented at the
First Conference of the International Shoulder Group
26 and 27 August 1996
Delft University of Technology,
The Netherlands

Orientation of axes in the elbow and forearm for biomechanical modelling

DirkJan Veeger1, Bing Yu2, Kay-Nan An2

1Institute for Fundamental and Clinical Human Movement Sciences, VU Amsterdam

2Orthopaedic Biomechanics Laboratory, Mayo Clinic, Rochester MN

Introduction:

To extend a three-dimensional (3-D) model of the shoulder [1], a cadaver study was performed in which quantitative information on the 3-D orientations of rotation axes in the elbow and forearm was collected.

Method:

Five upper extremities were harvested from four fresh specimen at the level of the scapula (four right, one left). Subsequently, the extremities were fastened onto a measuring table such that the scapula was fixed and the arm was fully free to move. Following fixation of 3-D electromagnetic sensors (Isotrack, Polhemus) on scapula, humerus, ulna and radius, the positions of local anatomical landmarks were digitized with an extra sensor, mounted with a stylus. Subsequently, each arm was moved through a selection of standard directions (elbow flexion-extension, forearm pro-supination and glenohumeral movements), during which the position of each sensor was recorded. A typical movement consisted of two cycles in which a joint was moved through its full range of motion. The sampling period was 15 sec. (Fs=10Hz).

For each condition the Instantaneous Helical Axes (IHA) were calculated [2]. For each specimen, axes were subsequently expressed relative to a local co-ordinate system with its origin in the Epicondylus Medialis (EM) and its X-axis in the direction of the Epicondylus Lateralis (EL), and the Ulnar Styloid (US) in the X-Y plane. Each arm was mathematically rotated around the elbow axis such that both the long axes of the humerus and ulna lie within the X-Y plane. In this position, the elbow flexion angle is zero. The rotation to this theoretical anatomical position was performed on all landmarks on the humerus: the Acromion (AC), EL and EM.

Results and discussion:

The kinematic flexion-extension axes deviate from the axes through EM and EL (Table 1). The data for AC and the estimated center of the humeral head indicate that the orientations of the humerus relative to the ulna was relatively constant over the five specimen. The pro-supination axis crosses the flexion-extension axis at 3.3 ± 0.8 mm and an angle of 88.9 ± 5.1°. This axis runs through the radial head and lies close to the anatomical landmarks EL (13.1±2.2 mm) and US (8.0±4.5 mm). The average distance to the center of the radial head was found to be 3.2±4.0 mm.

The findings of this study indicate that the elbow-forearm complex can be modelled as a two DOF system. The data are in the process of being implemented in a model of the shoulder and arm.
 
 

Table 1:

Mean (n=5) axes for flexion-extension and pro-supination, after rotation around the elbow axis to align the ulna and radius. Sflexion = position vector for flexion-extension, vflexion = unit direction vector for flexion-extension. Hum. Head = center of the humeral head.
Mean (N=5)
X (cm)
(std)
Y (cm)
(std)
Z (cm)
(std)
Hum Head
4.33
1.38
-29.52
1.53
0.00
0.00
Acromion (AC)
3.22
1.53
-34.58
1.73
-0.70
1.82
Lateral Epicondyle (EL)
7.13
0.11
0.00
0.00
0.00
0.00
Ulnar Styloid (US)
8.79
1.84
26.79
0.93
0.00
0.00
Sflexion
3.96
0.99
0.52
0.24
0.44
0.82
Vflexion
-0.9759
0.0173
0.1364
0.0860
-0.0392
0.1635
Spronation
6.97
0.67
7.62
3.25
0.31
0.61
Vpronation
0.1177
0.0511
0.9918
0.0069
0.0078
0.0176

References:

[1] F.C.T. Van der Helm "A finite element musculoskeletal model of the shoulder mechanism". J. Biomech. 27(5); 551-570.,1994

[2] H.J. Woltring, "Definition and Calculus of Attitude Angles and Instantaneous Helical Axes from noisy Position and Attitude data". In: Proc. on the Int. Symp. on 3-D Analysis of human Movement, Montreal, 59-62, 1991.