The following has been accepted as gospel, mostly because it seems to make sense: A forward head posture (FHP) - usually associated with an increase in the thoracic kyphosis angle, forward shoulder posture, and therefore, a scapula forced to protract, tilt anterior and rotate downward - is a possible cause of increased compression in the subacromial space, causing a subacromial impingement syndrome (SIS). Associated with abnormal posture is an imbalance of the associated muscles. With this forward-head type of posture, resulting in a depressed acromion process as the patient elevates his or her arm, the supraspinatus tendon and/or the subdeltoid bursa become impinged against the anterior portion of the acromion process.
Studies supporting this theory are limited and equivocal. However, a recent study1 evaluated the posture of 60 asymptomatic subjects and 60 subjects with SIS, to determine if there was a relationship between FHP and the associated postural abnormalities, and to determine the relationship between this type of posture and glenohumeral joint range of movement. It was evident that just because there was an FHP, the rest of the postural deviations were not necessarily associated with it. Other studies have agreed with these findings, in that no relationship was found to exist between FHP, FSP, and the curve of the thoracic kyphosis.2-3
The assumption that deviations from what is considered an ideal posture will result in abnormal joint stress and an imbalance of surrounding musculature has not been confirmed in vivo.1 It appears asymmetry is normal in the human structure. For example, there are large variations in the osseous anatomy of the clavicle, acromion and humerus, and ideal symmetrical posture with balanced muscles may not be possible. So-called postural deviations may be considered normal deviations and normal shoulder girdle development for that individual. Even though posture may appear abnormal, an individual may be flexible and capable of large ranges of motion.1
Many studies express the idea of abnormal scapular positioning resulting in tendinitis or compressive tendinopathy due to acromial pressure on the cuff tendons. If this were true, most of the tendinosis found in shoulders would be found on the bursal (acromial) side of the tendon, which is not the case. Most of the time, the articular (non-acromial) side of the tendon is the major site of degeneration.
It appears at this point that the postural causation of SIS remains in doubt. The authors of this study admitted they did not investigate whether scapular rotation and anterior tilt were postural patterns associated with SIS. When an individual elevates his or her arm, the scapula should be in a posterior-tilted position; if the scapula tilts anterior, it will shift up and over, causing impingement. Kibler4 proved the abnormality of an anteriorly tilted scapula with the use of the scapular retraction test.
For example, if a patient has a weak supraspinatus, found on testing it at 90 degrees of abduction in the scapular plane, and the practitioner then holds down the scapula in a retracted position, thereby maintaining the posterior tilt of the scapula, and at the same time retests the supraspinatus, this muscle may test strong. Increased rotator cuff strength may mean the cuff muscle is dysfacilitated due to scapular anterior tilting, and the cuff muscles are actually strong. This test repositions the scapula in retraction, thereby decreasing glenoid antetilting, and reducing mechanical impingement and pain.
It appears poor shoulder posture does not automatically incriminate the posture as a cause. Much too often, we assume an ideal postural position should be stressed, when in reality it may be impossible to perform, and often totally unrelated to the causation of the pain.
References
- Lewis JS, Green A, Wright C. Subacromial impingement syndrome: the role of posture and muscle imbalance. J Shoulder Elbow Surg 2005;14(4):385-392.
- Raine S, Twomey LT. Head and shoulder posture variations in 160 asymptomatic women and men. Arch Phys Med Rehab 1997;78:1215-1223.
- Greenfield B, Catlin PA, Coats PW, et al. Posture in patients with shoulder overuse injuries and healthy individuals. J Orthop Sports Phys Ther 1995;21:287-295.
- Burkhart SS, Morgan CD, Kibler WB. Shoulder injuries in overhead athletes. Clin Sports Med 2000;19(1):125-158.
Warren Hammer, MS, DC, DABCO
Norwalk, Connecticut
softissu@optonline.net
www.warrenhammer.com
