Article Outline
To the Editor:
I read with interest the “Current Concepts” article on the diagnosis and treatment of the snapping scapula in the November 2009 issue.1 I am glad to see more articles that address all aspects on scapular function and dysfunction. I thank the authors for their interest and their efforts to improve understanding and treatment of the various scapular problems. The review of the literature and the suggestions about pathophysiology and treatment are extensive but incomplete. I would suggest that several points need expansion and clarification to make the article maximally useful to the readers.
1.The authors are correct to state that most cases of snapping scapula are disorders of movement. However, the article does not address critical aspects of anatomy and physiology that explain the basis of normal movement or point to the abnormal movements. In the discussion on anatomy, the statement regarding stability is incomplete. The scapula is attached to the axial skeleton through the clavicle and its sternoclavicular and acromioclavicular joints, with each structure playing key roles in guiding and limiting scapular motion.2 In the discussion on musculature, no mention is made of the important roles the upper trapezius and lower trapezius, working as separate muscles in force couples, play in the normal motion of the scapula with arm motion. These muscles provide the largest contribution to the smooth motion.3, 4
2.In the discussion on pathophysiology, there is no mention of normal scapular motion. Several studies have shown the normal 3-dimensional motions that occur in scapulohumeral rhythm (SHR).5, 6 No mention is made of the important motion of anterior/posterior tilting, which is probably the key motion to prevent excessive snapping. There is also no mention of normal progression of the instant center of rotation (ICR) of scapular motion in SHR in arm elevation. The ICR is located at the base of the scapular spine on the medial border with the arm at the side and then moves progressively along the spine to end up at the acromioclavicular joint with maximal arm elevation.7 Non-bony causes of snapping scapula, which make up the large majority of the cases, occur when there is a failure of posterior tilting and a failure of progression of the ICR along the spine as the arm elevates. The anteriorly tilted scapula compresses the medial border against the ribs, and the scapula pivots around its medial border rather than sliding laterally. We have documented these findings with motion monitor evaluations in our laboratory. This combination creates the extra pressure that causes the bursitis.
3.In the discussion regarding patient presentation, although the case is made that this is a movement disorder, there is no discussion of how to perform the evaluation of the movement disorder. There is no mention of evaluation of the scapular resting position or dynamic motion on arm elevation;8 evaluation of the other anatomic factors that may contribute to altered motion, such as tight scalene muscles, tight pectoralis minor or major muscles, or upper trapezius hypertrophy, that create anterior tilting; or factors such as serratus anterior and lower trapezius weakness that decrease the rotation of the scapula and its ICR. In addition, there is no mention of scapular corrective maneuvers, especially the scapular assistance test, which can decrease the snapping by increasing the posterior tilt.
4.Nonoperative treatment centers around correcting the physiologic and biomechanical alterations that create the altered kinematics. A general “one size fits all” approach will not address the varied factors. The approach should be guided by identification of the inflexibilities and muscle imbalances shown on the examination. In general, stretching of the inflexible structures, followed by strengthening of the weakened structures, followed by reorganization of the coupled activation patterns, will re-create the kinematics. Care should be taken not to emphasize motions or exercises such as shoulder shrugs that activate the levator scapulae or upper trapezius. The pectoralis minor is frequently found to be very tight, and it should be addressed early, because it plays a major role in creating the anterior tilt.9 Exercises for lower trapezius activation are also key to normalizing the desired posterior tilt and ICR movement.10 Exercises that allow scapular protraction increase anterior tilt and should be de-emphasized in the early rehabilitation.
5.Operative treatment is very rarely indicated or necessary if good evaluation and rehabilitation are provided. However, if it is required, the treatment should not make the pathophysiology worse. Several key points are not presented in the article. If the problem is of bony origin (bone spur, osteochondroma), then bony resection is indicated. Minimal bone should be removed, because larger bone resection does not allow normal reattachment of the muscles. If the amount of bone suggested in the article is removed, reattachment of the muscles is difficult at best and will result in a posture of superior positioning of the scapula, with return of the symptoms or decrease in function due to the superior translation. If no bony problem is present, no bone should be removed. Only excision of the bursa should be performed because this is the cause of the symptoms. In either case, muscular reattachment must be done through drill holes, to restore the muscle's capability to act on the scapula. Poor functional results can be expected if the muscles are only repaired to themselves, because they will not have secure attachments to exert force on the scapula.
6.The diagrams illustrating the open surgical procedure are misleading and possibly inaccurate. Figure 6B is especially misleading. The deltoid does not attach along the medial scapular border or the medial half of the spine, as depicted. The “trapezius” likewise does not attach in the manner described. The lower trapezius arcs across the medial spine from inferior/medial to superior/lateral, whereas the middle and upper trapezius muscles run more superior to the spine. In Figs 6E, 6F, and 6G, removal of 1.5 to 2 cm of bone does not allow “a more natural articulation … when the muscles are reattached.” This amount of bony resection will require some compromise of either anatomy or mechanics. Attempted reattachment of the levator scapulae and upper rhomboids either will fail, as the muscles detach because of excessive tension from stretch of the repair, or will result in permanent superior scapular translation if the repair heals. Either case will result in altered scapular kinematics, with return of the snapping or other consequences for SHR, rather than “normal articulation.”
Much more information regarding scapular mechanics in shoulder injury needs to be presented to improve our understanding of how to evaluate and treat altered scapular motions as part of the entire shoulder problem. I would hope that the information presented in these early stages of our understanding will be accurate enough and clinically applicable so that all readers will be able to use it to further their treatment skills.
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References
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- Kibler WB, Sciascia AD, Uhl TL, Tambay N, Cunningham T. Electromyographic analysis of specific exercises for scapular control in early phases of shoulder rehabilitation. Am J Sports Med. 2008;36:1789–1798
