The scapula has an integral role in the overhead throwing motion. It must rotate during cocking and acceleration to clear the acromion to prevent impingement on the rotator cuff. The phases of throwing are seen in Illustration A.
Kibler describes 5 important roles of the scapula during throwing: 1. provide a stable glenohumeral articulation; 2. retraction and protraction; 3. elevation of the acromion; 4. serve as a base for muscular attachment; 5. to be a link in the kinetic chain.
Burkart et al. created the acronym "SICK" scapula (Scapular malposition, Inferior medial border prominence, Coracoid pain and malposition, and dysKinesis of scapular movement) to describe common signs and symptoms in the disabled throwing shoulder. This is felt to be an overuse muscular fatigue syndrome and is a recognized cause of shoulder pain in the throwing athlete.
1. & 2. The scapula maximally retracts during late cocking and protracts during acceleration and ball release (through activity of the serratus anterior muscle, which is innervated by the long thoracic nerve).
4. The scapula is dynamic and normal motion is needed to generate maximal force transfer.
5. The scapula keeps the humeral head centered thereby increasing concavity-compression and therefore stability.
Kibler WB. The role of the scapula in athletic shoulder function. Am J Sports Med. 1998 Mar-Apr;26(2):325-37. Review
PMID:9548131 (Link to Abstract)
Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology Part III: The SICK scapula, scapular dyskinesis, the kinetic chain, and rehabilitation. Arthroscopy. 2003 Jul-Aug;19(6):641-61. Review.
PMID:12861203 (Link to Abstract)