On "resting position variables ..." Borstad. Phys Ther. 2006;86(4):549-557.

To the Editor:

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 impairment (3) 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 Sahrman (7) 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 [greater than or equal to] .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.

Christopher Kevin Wong, PT, PhD, OCS 

Director, Physical Therapy Programs

Department of Physical Therapy

Touro College

New York, NY 10010

[e-mail]

References

(1)Ludewig PM, Cook TM, Nawoczenski DA. Three-dimensional scapular orientation and muscle activity at selected positions of humeral elevation. J Orthop Sports Phys Ther. 1996;24:57-65.

(2) Lukasiewicz AC, McClure P, Michener L, et al. Comparison of 3D scapular position and orientation between subjects with and without shoulder impingement. J Orthop Sports Phys Ther. 1999;29:574-586.

(3) Greenfield B, Catlin P, Coats P, et al. Posture in patients with shoulder overuse injuries and healthy individuals. J Orthop Sports Phys Ther. 1995;21:287-295.

(4) Gosling JA, Harris PF, Whitmore I, Willan PLT. Human Anatomy. 4th ed. Edinburgh, Scotland: Mosby; 2002.

(5) Jenkins DB. Hollinshead's Functional Anatomy of the Limbs and Back. 7th ed. Philadelphia, Pa: WB Saunders Co; 1998.

(6) Porterfield JA, DeRosa C. Mechanical Shoulder Disorders: Perspectives in Functional Anatomy. Philadelphia, Pa: WB Saunders Co; 2004.

(7) Sahrman S. Diagnosis and Treatment of Movement Impairment Syndromes. St Louis, Mo: Mosby; 2002.

(8) Kendall FP, McCreary EK, Provance PG. Muscles: Testing and Function. 4th ed. Baltimore, Md: Williams & Wilkins; 1993.

(9) Wang SS, Trudelle-Jackson EJ, Tossey LL, et al. Effectiveness of two physical therapy treatments for increasing length in the pectoralis minor. J Orthop Sports Phys Ther. 2006;36: A11.

(10) Wong CK, Coleman D, diPersia V, et al. The effects of pectoralis minor mobilization and stretching on shoulder posture and lower trapezius strength. J Orthop Sports Phys Ther. 2006;36:A33.

[DOI: 10.2522/ptj.2006.86.10.1442]

Author Response:

Dr Wong questions the use of the sternocostal junction of the fourth rib as a landmark for the pectoralis minor muscle. This is a valid concern that I will address with some clarification of how the landmark was selected. I selected the fourth sternocostal junction landmark for several reasons--to accurately represent the pectoralis minor muscle's origin, (1,2) to be in line with the muscle's line of action, (1,2) and to be practical for in vivo data collection. I also considered another landmark, the junction between the fourth rib and its cartilage, which is likely closer to the muscle's true insertion, but it was not consistently located during palpation, especially on female cadavers due to subcutaneous breast tissue overlying the junction. Therefore, because women were to be used for the in vivo study, moving to the sternocostal junction became the best alternative. Importantly, the use of this landmark was supported by the validation analysis with cadavers: landmarks were first palpated and digitized on a cadaver; the skin and fascia were incised to allow visualization of the actual insertion of the pectoralis minor muscle; and the actual muscle insertions were digitized to serve as the gold standard measurement. All cadavers showed muscle digitations on the fourth sternal cartilage, very near the proposed landmark. Visualizing the actual insertions of the muscle verified that the landmarks very closely represented the underlying pectoralis minor muscle. I am confident that the process used in selecting and verifying the pectoralis minor muscle landmarks for validating the measurement technique was sound.

Dr Wong also asserts that it was the pectoralis major muscle being measured, not the pectoralis minor muscle. The problem with this assertion is that it fails to consider both anatomical landmarks used in the measurement. By palpating the fourth sternocostal junction and the coracoid process, the vector that is calculated represents the length of the pectoralis minor muscle, but more importantly it is oriented with the longitudinal direction of the muscle fibers. This is critical because the hypothesis of the study was that a change in muscle length will change the number of sarcomeres in series and subsequently the mechanical properties of the muscle. It is the mechanical change, primarily increased passive tension, that ultimately affects posture or movement. Dr Wong asserts that the vector represents the length and line of action of the pectoralis major muscle. However, a vector representing the pectoralis major muscle would require palpation of the bicipital ridge of the humerus and perhaps a different landmark (or landmarks) on the sternum in order to be parallel with the longitudinal fibers. The result of a pectoralis major muscle measurement would be a more horizontal vector than the pectoralis minor muscle vector, as the bicipital ridge is lateral and distal to the coracoid process. In fact, the distance between the coracoid process and the bicipital ridge of the humerus is considerably greater than the distance between the sternocostal junction and the medial end of the fourth rib (assuming this is a more suitable point to represent the pectoralis minor muscle). This greater distance between the coracoid process and the bicipital ridge creates a large source of error when interpreting this measurement to represent the pectoralis major muscle. By failing to consider the proximal landmark of the 2 muscles in question, the argument put forth in Dr Wong's letter is misleading.

The issue of considering both landmarks and the orientation of the vector between them is important with reference to another point made in Dr Wong's letter. Dr Wong states that the correlation of the sternal notch-to-coracoid process distance with the pectoralis minor muscle measurement is understandable because the sternal notch-to-coracoid process distance measurement is "approximately parallel to the clavicular portion of the pectoralis major muscle fibers." Had one landmark been the bicipital ridge and the other landmark been near the sternoclavicular joint to capture the clavicular portion of pectoralis major muscle, perhaps this argument would have some merit. However, by using the appropriate pectoralis minor muscle landmarks, there is no question that the resulting vector is much more vertically oriented than one intended to represent the pectoralis major muscle, particularly the clavicular portion. I stand by my interpretation of this finding that it is the difficulty in capturing 3-dimensional segment orientations with linear measures that results in correlations among static posture variables that may not be intuitive.

It appears from Dr Wong's comments that he questions the preciseness of the pectoralis minor muscle measure. As discussed in my response earlier, the sternocostal junction landmark may be considered a compromise for the actual muscle insertion, and readers will have to determine for themselves whether my response adequately answers the issues raised in Dr Wong's letter. However, the latter part of the letter reveals that perhaps it is the measurement technique itself that is in question. Dr Wong's letter refers to research, including his own, that measures pectoralis minor muscle tightness using a supine measurement technique? The fundamental problem is that the supine measure has not been demonstrated to be valid for measuring pectoralis minor muscle length. The findings of my analysis indicate that the supine measure is not appropriate for measuring pectoralis minor muscle length because it is poorly correlated with a valid measure of the pectoralis minor muscle. There are several logical reasons for this: the treatment table affects the pectoralis minor muscle by influencing scapular position, it is not a normalized measurement, and the effect of gravity on the system is altered.

It is perfectly reasonable to conduct research using the best possible methods at your disposal. If the most valid measurement requires instrumentation that is unavailable, then exploring a research question using another technique may be acceptable. The supine measure of pectoralis minor muscle tightness in a within-subject design, such as that used by Dr Wong, appears to be such an example. However, everyone should be cautious about discrediting another researcher's work when trying to justify their own. My kinematic and static posture analyses, as described in the current report and previously, (4) remain the only ones to use a validated measure for the length of the pectoralis minor muscle. The concurrent validity (5) of the measure was established by using the actual muscle insertions in the gold standard measure, following the anatomical orientation of the muscle fibers, and choosing appropriate anatomical landmarks that represent the true muscle of interest. This validation of the pectoralis minor muscle measurement prior to in vivo analysis reflects a rigorous and thorough scientific process, allowing readers to make their own critical deductions regarding published studies.

John D Borstad, PT, PhD

Physical Therapy Division

Ohio State University 

516 Atwell Hall

453 W Tenth Ave

Columbus, OH 43210-1234 (USA)

[e-mail]

References

(1) Pick TP, Howden R, eds. Gray's Anatomy. New York, NY: Bounty Books; 1977.

(2) Moore KL. Clinically Oriented Anatomy. Baltimore, Md: Williams & Wilkins; 1985.

(3) Wong CK, Coleman D, diPersia V, et al. The effects of pectoralis minor mobilization and stretching on shoulder posture and lower trapezius strength [abstract]. J Orthop Sports Phys Ther. 2006;36:A33.

(4) Borstad JD, Ludewig PM. The effect of long versus short pectoralis minor resting length on scapular kinematics in healthy individuals. J Orthop Sports Phys Ther. 2005;35:227-238.

(5) Portney LG, Watkins ME Foundations of Clinical Research: Applications to Practice. Upper Saddle River, NJ: Prentice Hall; 2000.

[DOI: 10.2522/ptj.2006.86.10.1443]