There are definite reasons why patients use this particular plane of arm elevation and these same reasons are being quoted for using the scapular plane in shoulder functional testing and rehabilitation. Some of the reasons stated are: that the mechanical axis of the humerus approximates the mechanical axis of the scapula.1 This optimally aligns the deltoid and supraspinatus for elevation of the arm,2 thereby avoiding subacromial impingement during arm abduction. When the arm is raised straight ahead (sagittal plane) or coronally, the shoulder capsule is stressed from the obligatory humeral rotation. In the scapular plane the inferior part of the capsule is lax, since no appreciable humeral rotation is required.
From a rehabilitation3,4 point of view, exercising in the scapular plane puts less stress on the shoulder capsule. When the shoulder is brought back to the coronal plane the anterior capsular structures are tensioned, which may complicate soft tissue healing. Since the rotator cuff muscles originate off the scapular, the position of the humerus in the scapular plane increases the length-tension of the deltoid and cuff muscles, helping to facilitate optimal muscle force.5 Exercising the infraspinatus and teres minor may create greater external rotatory force and less compressive force, because the scapular attachment of the infraspinatus and teres minor is more posterior than normal in the glenohumeral joint in this plane.3 Studies on the effect of the scapular plane on the large internal rotators, such as the pectorals and latissimus dorsi, did not show increased strength output.3
Dr. Warren6 performs passive motion testing in this plane since it is the position of maximum motion. In testing for anterior or posterior instability, with the patient supine at the edge of the table, he coronally abducts the shoulder about 80o,forward flexes the shoulder to the scapular plane, and tests with the arm in neutral rotation. Since this position allows maximum shoulder motion we have a more accurate assessment of the capsuloligamentous issue.
- Poppen NK, Walker PS. Normal and abnormal motion of the shoulder. J Bone Joint Surg Am. 1976; 58: 195-201.
- Johnston TB. Movements of the shoulder joint -- plea for use of "plane of the scapula" as a plane of reference for movements occurring in at humeroscapula joint. Br J Surg. 1937; 25: 252.
- Greenfield B. Special considerations in shoulder exercises: plane of the scapula. In: Andrews JR, Wilk KE. The Athlete's Shoulder. New York: Churchill Livingstone; 1994: 513-522.
- Dines DM, Levinson M. The conservative management of the unstable shoulder including rehabilitation. Clin S Med 1995; 14: 797-816.
- Lucas D. Biomechanics of the shoulder joint. Arch Surg 1973; 107: 425.
- Warren RF. Personal communication, 3/95.
Warren Hammer, MS, DC, DABCO
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