Tuesday, April 29, 2008

Estimating the Elbow Carrying Angle With an Electrogoniometer: Acquisition of Data and Reliability of Measurements

A scientific paper on the lifting capacity of the elbow ...

"The carrying angle of the elbow is defined as the angle formed by the long axis of the arm and the long axis of the forearm in the frontal plane.1 The carrying angle value and its pathologic variations are important in the management of elbow fractures2,3 and in the diagnosis of diseases of the lateral and medial epicondyles.4

Based on the theory of general rigid body motion, in 1976, Morrey and Chao1 computed the carrying angle by isolating the 3-dimensional rotation occurring at the elbow joint in 2 cadaveric specimens. They obtained 10° in full extension of the elbow and observed a linear decrease of the carrying angle with flexion. Since then, several authors have measured the carrying angle in vitro using mechanical instrumentations, hinged boards, or goniometers rigidly attached to the humerus5; kinematics or geometrical computations6; or radiographs,7 thus obtaining results not always in agreement with those reported by Morrey and Chao.1 The main reasons for this are differences in the definition of the angle and variations in the measuring instruments.

Few investigators have studied the carrying angle in vivo. Paraskevas et al8 measured the carrying angle in full extension in 600 adults using a special goniometer and compared these values to measures obtained radiographically. Yilmaz et al9 adopted a universal standard goniometer to estimate the full extension carrying angle in healthy volunteers.

Van Roy et al10 adopted a protractor goniometer and an electromagnetic tracking device to estimate the carrying angle in full extension and also during flexion of the elbow joint. They noted the carrying angle is an important anatomic feature when restoration of the elbow’s function is required. In clinical practice, the carrying angle generally is assessed in full extension by radiographs or by a standard goniometer to evaluate reduction of distal humerus or radial head fractures.11,12

This study examined a noninvasive method for evaluating the carrying angle in vivo in full extension by using a digitizer suitable for orthopedic applications to acquire easily identifiable anatomical landmarks on the arm and forearm. An experimental analysis of reliability was performed by comparing repeated acquisition by the same operator and also by 2 different operators with varying levels of expertise. The major advantage of this method, other than its simple derivation, is the possibility of being adapted to a commercial digitizer and easily being used in computer technologies for assisted medical treatment during practical clinical application by providing a graphic display and qualification of anatomic and functional features of the joint.
Materials and Methods

This study received approval from the local ethics committee, and written informed consent was obtained from all participants. The right and left arms in 37 adults (17 men and 20 women) were measured. Patient age ranged from 41 to 81 years (mean age, 60.5±12.1 years). In 2 adults, only right arms were measured, obtaining a total of 72 measurements. All participants were healthy and had no symptoms or signs of relevant pathologies affecting the shoulder, elbow, and wrist joints."    (Continued via Ortho Supersite)    [Ergonomics Resources]

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