The Complexity of Shoulder Impingement

Shoulder impingement is very common among the population and accounts for 36% of shoulder of all shoulder complaints.¹ Impingement of the shoulder is a condition/symptom when a patient experiences discomfort with overhead motion with flexion or abduction due to compression of the rotator cuff tendons between the bony structures of the humeral head and the acromion. If shoulder impingement is not corrected it may lead to to a tear of the rotator cuff due to repetitive compression and friction of the rotor cuff against the boney structure of the shoulder

Tests to Determine if Impingement is Present

What Causes Shoulder Impingement?

• Shoulder Instability
  • Impingement may be present if the rotator cuff, shoulder capsule, and the long head of the biceps have too much mobility. These structures function to compress the humerus within the glenoid labrum and if too much movement is present it may allow excessive upward motion of the humerus into the rotator cuff tendons. ⁵

• Weak long head of the biceps
  • During overhead motion, the long head of the bicep provides superior stability of the humeral head.² In other words, the long head of the biceps prevents upwards motion of the humeral head, and thus prevents impingement.
• Poor posture
  • Poor posture that includes a forward head postion, rounded shoulders, and a protracted scapulae may lead to a decrease in the suprahumeral space. The suprahumeral space is the space that occupies above the humerus. This decrease in spaces leads to compression and irritation of the rotator cuff with overhead motion. ³

• AC Joint Dysfunction
  • The AC Joint may present with pain between 170-180 degrees of abudction. Where as impingment may present at 45-60 deg and 120 degees of abuuction. ⁴
• Weak rotator cuff relative to the deltoid
  • The deltoid is a powerful muscle of the shoulder and if left unopposed by the smaller stabilizing muscles – it can lead to excessive upward movement of the humeral head and can compress the soft tissues under the acromion and cause symptoms of impingement. ⁵

• Inadequate external rotation
  • The humerus must externally rotate in order to allow the greater tubercle of the humerus to clear the coracoacromial arch to prevent impingement of the soft tissues. If you are missing external rotaton of the shoulder you may be more prone to impingment due to poor shoulder biomechanics. ⁵

• Tight Posterior Capsule
  • If the posterior capsule of the shoulder joint is tight it may lead to anterior and superior translation of the humeral head. ⁶
• Anatomical structural variations of the acromion
  • Hook or curved shapes of the acromion may predispose you to pinching the rotator cuff with overhead motion. ^{7,8, 9}
• Inflammation of the soft tissues structures that are within the subacromion space
  • If rotator cuff tendons or subacromion bursa are inflamed it will lead to a decrease in suprahumeral space.
• Shoulder hiking
  • This happens when there is in limited upward rotation of the scapula and the body compensates by shrugging the trap to gain more overhead motion. This leads to an increase superior head translation of the humeral head. ⁵
• Poor scapula-thoracic joint mechanics
  • The scapula must upward rotate, posteriorly tilt and external rotate on the rib cage in order to achieve full overhead range of motion. ^{10, 11}

Conclusion

As you can see the cause of shoulder impingement is not as obvious as other injuries of the body. In order to have a successful and efficient rehab program for your shoulder impingement you need to 1st address what exactly is the shoulder dysfunction causing your pain with overhead movement.

A chiropractor can help pin point the exact cause to ensure you are not spinning your wheels with the wrong rehab protocol. For example, correcting shoulder instability with stretching would make your injury worse rather than better. Any joint laxity dysfunction needs to be addressed with strengthening protocols.

I highly recommend that you book an appointment with a local health care provider, such as a physiotherapist or chiropractor, to help you return optimal shoulder function. Correcting an issue as complex as shoulder impingement needs another set of eyes.

References

1. Juel NG, Natvig B. Shoulder diagnoses in secondary care, a one year cohort. BMC Musculoskelet Disord 2014;15:89
2. .Kumar, VP, Satku, K, and Balasubramaniam, P: The role of the long head of the bicep brachii in the stabilization in the head of the humerus. Clin Orthop 244: 172 – 175. 1989
3. Ludewig, PM, and Cook, TC: Alterations in Shoulder Kinematics and associated muscles activity in people with shoulder impingement. Phys Ther 80(3):276-291, 2000
4. Sigel, K. (2020). Shoulder Assessment . In A. Heck (Ed.), Physiotutors Assessment Book (pp. 215–215).
5. Kisner, Carolyn, and Lynn A. Colby. Therapeutic Exercise: Foundations and Techniques. Philadelphia: F.A. Davis, 2012.
6. Harryman, DT, et al: Translation of the humeral head on the glenoid with passive hlenohumeral motion, J Bone Joint Surge Am 71: 982-989
7. Attchek, DW, et al: Arthroscopic acriomioplasty: technique and results, J Bone Joint Surg Am 72: 1198-1207, 1990
8. Miller, DF Flatow, EL, and Bigliani, LU: biomechanics of the coraacromional arch and the rotator cuff: kinematics and contact of the subacromional space, In Iannotti, JP (ed): The Rotator Cuff: Current Concepts and Complex Porgrams. Rosemont, IL: American Academy of Orthopaedic Surgeons, 1998, p 1.
9. Zuckerman, JD, et al: The Influence of coracoacromional arch anatomy on rotator cuff tears. J shoulder Elbow Srug. 1:1-14, 1992.
10. Finley, MA, and Lee, RY: Effect of Sitting Posture on 3 dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors. Arch Phys Med Rehabil 84(4): 563-568, 2003.
11. McClure PW et al: Direct 3 Dimensional of Scapaular Kinematics During movments in vivi. J of Shoulder Elbow Surg 10(3): 269-277, 2001.