Elsevier

Journal of Biomechanics

Volume 33, Issue 12, December 2000, Pages 1711-1715
Journal of Biomechanics

Technical note
The position of the rotation center of the glenohumeral joint

https://doi.org/10.1016/S0021-9290(00)00141-XGet rights and content

Abstract

To validate the assumption that the center of rotation in the glenohumeral (GH) joint can be described based on the geometry of the joint, two methods for calculation of the GH rotation center were compared. These are a kinematic estimation based on the calculation of instantaneous helical axes, and a geometric estimation based on a spherical fit through the surface of the glenoid. Four fresh cadaver arms were fixed at the scapula and fitted with electromagnetic sensors. Each arm was moved in different directions while at the same time the orientation of the humerus was recorded. Subsequently, each specimen was dissected and its glenoid and humeral head surfaces were digitized. Results indicate no differences between the methods. It is concluded that the method to estimate the GH center of rotation as the center of a sphere through the glenoid surface, with the radius of the humeral head, appears to be valid.

Introduction

Musculoskeletal models of the upper extremity have defined the glenohumeral (GH) joint as a single rotation point (Hogfors et al., 1987; Helm et al., 1992), the position of which was based on the assumption that the rotation center equals the center of the humeral head. The position of this ‘geometric’ rotation center was specified as the center of a sphere fitted through the glenoid surface with a radius based on the size of the humeral head (Helm et al., 1989). Based on the same assumption, Meskers et al. (1998) described regression equations to the define this position relative to the anatomical landmarks on the scapula.

The position of the kinematic rotation center has, however, scarcely been measured. Poppen and Walker (1976) and Jackson et al. (1977) reported on the position of the rotation center relative to the humeral head during abduction. Their method was, however, based on a two-dimensional estimation.

The question remains whether the assumption that the geometric rotation center is also the kinematic rotation center is valid and whether this geometric rotation center can be described as the center of a sphere fitted through the glenoid surface.

To estimate the rotation center of the GH joint, an in vitro study has been performed which comprised both the estimation of the kinematic center of the intact glenohumeral joint and the geometric center of the joint, based on the shapes of both the humeral head and the glenoid. It was hypothesized that both methods would lead to identical results.

Section snippets

Method

Four fresh specimens were obtained with the approval of the Mayo Clinic internal review board. The specimens weighed between 62 and 98 kg and ranged in stature from 1.63 to 1.91 m. (Table 1). The specimens did not show visible degenerative changes in the shoulder. After anthropometric measurements, each upper extremity was disarticulated from the thorax by severing the extremity at the sternoclavicular joint and at the thoracic gliding plane. This left the arm fully intact.

A magnetic position and

Results

The measurement errors for the anatomical landmarks were typically less than 0.4 mm. The standard deviation for TS indicates differences in size between the four scapulae (Table 2).

The estimation of the kinematic rotation center was based on IHA estimations for three different movements. A typical example for these data is given in Fig. 2. Individual IHA values showed surprisingly little scatter, especially for endo-exorotation. The mean error varied from 8 mm (#1_r) to 16.5 mm (#4_r).

The rotation

Discussion

It has long since been assumed that the normal glenohumeral joint acts as a ball-and-socket joint with a fixed rotation center (Fick, 1911). Based on the assumption that kinematic behavior follows from the joint geometry, previous studies have quantified the position of the ‘geometric’ rotation center on the basis of the geometry of glenoid and humerus, relative to anatomical landmarks (Helm et al., 1989). Recently, Meskers et al. (1998) described regression equations to define this position.

Acknowledgements

This work was partially supported by a NATO Science Fellowship awarded by the Netherlands Organization for Scientific Research and NIH Grants HD07447 and AR41171.

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