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Letters and Responses |
It was with acute interest that I read John Borstad's recent article. Although the link between postural alignment deviations and musculoskeletal impairment has been suggested, it is indeed critical to support this link with objective evidence.
The author has attempted to highlight this link by demonstrating an association between postural alignment of the scapula and a structural alteration in pectoralis minor muscle length. Connections between pectoralis minor muscle length and pathomechanical alterations in scapular kinematics,1 between pain and impairment and alterations in scapular kinematics,2 and even directly between postural alignment and impairment3 have been suggested previously.
The author reported the methods for validating the palpation points that were used to infer the pectoralis minor muscle length. Anatomical landmarks were palpated and marked on cadavers. The length of the pectoralis minor muscle was measured as the distance between the 2 landmarks: the coracoid process of the scapula and the sternum at the level of the 4th sternocostal junction. Unfortunately, the sternal landmark more closely describes the origin of the sternal portion of the pectoralis major than the pectoralis minor muscle, which originates on the 2nd–5th ribs lateral to the costocartilaginous junction.4–6 Erroneously choosing anatomical landmarks that closely resemble those of the pectoralis major muscle invalidates on its face the direct measure used in this study for the pectoralis minor muscle length and the "Pectoralis Minor Index" (Pectoralis Minor Index=pectoralis minor length/height).
The primary result reported by the author was that the distance from the sternal notch to the coracoid process was most correlated with the Pectoralis Minor Index (r=.48). However, the horizontal line running from the sternal notch to the coracoid process is approximately parallel to the clavicular portion of the pectoralis major muscle fibers. In contrast, the pectoralis minor muscle fibers run more vertically down from the coracoid process to the costocartilaginous junction of the 2nd–5th ribs.4–6 Because the landmarks chosen to measure pectoralis minor length actually describe the pectoralis major, the correlation between the 2 measures is understandable.
The study reported poor correlation between the author's proposed Pectoralis Minor Index and the supine measures for the forward scapular position associated with pectoralis minor muscle shortness described by Sahrman7 and Kendall et al.8 This finding is not surprising because the proposed Pectoralis Minor Index is more closely related to the pectoralis major muscle.
The use of an anatomical landmark closely related to the pectoralis major muscle instead of the pectoralis minor muscle renders the results of the Borstad study inconclusive and misleading. Supine measurments of scapular position taken from the posterolateral angle of the acromion to the supporting table have shown good reliability (r
.80) in 2 recent studies.9,10 Supine measures of scapular position may be of value clinically when assessing pectoralis minor muscle length, although more research is needed to establish their validity.
The author proposed a "Scapula Index" (distance from the sternal notch to the coracoid process divided by the distance from the posterolateral acromion to the thoracic spine) as a potential measure of scapular position. It appears that the most appropriate conclusion for this study is that the distance from the sternal notch to the coracoid process is correlated with the length of the pectoralis major muscle and scapular position.
Director, Physical Therapy Programs
Department of Physical Therapy
Touro College
New York, NY 10010
ckwong{at}touro.edu
References
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