Initially, the scapular diskinesis was defined as “a nonspecific response to shoulder dysfunction”, as there is no clear association between diskinesis and any specific shoulder pathology diagnosis (1).
In 2013, in the Second International Scapular Summit, celebrated in Kentucky (USA), it was agreed that scapular dyskinesis is not an injury or diagnosis, but a condition present in between 67% and 100% of shoulder pathology, and can be defined as the alteration of posture and/or normal movement of the scapula (2).
Some studies have related scapular dyskinesis to an inhibition mechanism induced by pain, due to the redistribution of intra and inter-muscular force that is produced as a response to compensation and protection (3).
However, the relationship between dyskinesis and pain is not clear. Tate and McClure (4) showed that the presence of dyskinesis is not related to pain, which has also been supported by other authors. In contrast, a recent meta-analysis that included 419 athletes concluded that those with scapular dyskinesis have a risk 43% higher to suffer shoulder pain, compared to the athletes without dyskinesis (5). In the same way, dyskinesis presence has also been identified as a potential risk factor to shoulder injury. It was shown in a study of 120 rugby players ( with I evidence level) that those players who presented asymptomatic scapular dyskinesis during the pre-season showed a higher incidence of shoulder injury during the season (6).
The hypothesis of the change in muscle activation patterns seems to be stronger everyday, as shown in a recent study with competitive swimmers, in which scapular dyskinesis prevalence is higher as the training season goes on; that supports the relationship with muscle fatigue because of an excessive solicitation (7).
Specifically, there have been identified changes in different muscle group activity, such as serratus anterior (8), the three parts of trapezius (9,10,11), minor pectoralis (12), the subescapular (2) and the glenohumeral external rotators (13).
The presence of scapular dyskinesis can lead to the break of the kinetic chain, as the scapula plays a crucial role in the transference of force from the inferior limbs and trunk to the most distant link in the chain, the hand (14). Dr. Kibler´s team has shown that supraspinatus strength deficit can be related to a lack of a stable base in the origin of the kinetic chain (15)
Later on, a study from University of Pennsylvania, identified dyskinesis as a direct cause mechanism of histological changes in supraspinatus and biceps tendon, diminishing their mechanical, structural and compositional properties (16).
So, if it is either a cause or an effect, the relationship between scapular dyskinesis and shoulder pathology is widely proven. Furthermore, a study of over 1.030 patients with shoulder pathology identified a good prognostic sign of a change in pain level or ROM when scapular movement is manually assisted (17).
The findings provided by all these researchers support the need to assess systematically scapular movement, as well as the implementation of programs specifically directed to restore normal kinematics, in the context of shoulder pathology.
REFERENCES:
1. “Scapular dyskinesis and its relation to shoulder pain” KIBLER WB, MCMULLEN J. J Am Acad.Orthop Surg.2003 Mar-Apr;11(2):142-51
2. “Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the scapular summit´” KIBLER WB, LUDEWIG PM, MCCLURE PW, MICHENER LA, BAK K, SCIASCIA AD. Br J Sports Med 2013;47:877-88
3. “Rehabilitation of scapular dyskinesis: from the office worker to the elite overhead athlete” COOLS AM, STRUYF F, DE MEY K, MAENHOUT A, CASTELEIN B, CAGNIE B. Br J Sports Med 2014;48:692–69
4. “A clinical method for identifying scapular dyskinesis: part 2 – validity”. TATE AR; MCCLURE P, KAREHA S, IRWIN D, BARBE MF. J Ath Train 2009 Mar-Apr;44(2):165-73
5. “Scapular dyskinesis increases the risk of future shoulder pain by 43% in asymptomatic athletes: a systematic review and meta-analysis”. HICKEY D, SOLVIG V, CAVALHERI V, HARROLD M, MCKENNA L. Br J Sports Med. 2017 Jul 22.
6. “Does scapular dyskinesis affect to rugby players during a game season?” KAWASAKI T, YAMAKAWA J, KAKETA T, KOBAYASHI H, KANEKO K. J Shoulder Elbow Surg. 2012 Jun;21(6):709-14
7. “Scapular dyskinesis among competitive swimmers” MAOR MB, RONIN T, KALICHMAN L. J Body Mov Ther. 2017 Jul;21(3):633-636.
8. “Specific kinematics and associated muscle activation in individuals with scapular dyskinesis” HUANG T, OU H, HUANG C, LIN J. J Shoulder Elbow Surg 2015, Feb 19;1-8.
9. “Visual scapular dyskinesis: kinematics and muscle activity alterations in patients with subacromial impingement syndrome” LOPES AD, TIMMONS MK, GROVER M, CICONELLI RM, MICHENER LA. Arch Phys Med Rehabil. 2015 Feb;96(2):298-306
10. “Effect of trapezius muscle strength on three-dimensional scapular kinematics” TURGUT E, DUZGUN I, BALTACI G. J Phys Ther. Sci. 2016; 28: 1864–1867
11. “A comparison of change in 3D scapular kinematics with maximal contractions and force production with scapular muscle tests between asymptomatic overhead athletes with and without scapular dyskinesis” SEITZ AL, McCLELLAND RI, JONES WJ, JEAN RA, KARDOUNI JR. Int J Sports Phys Ther 2015 (10:3)309
12. “The effect of long versus short pectoralis minor resting length on scapular kinematics in healthy individuals” BORSTAD JD, LUDEWIG PM. J Orthop Sports Phys Ther 2005 Apr, 35(4):227-38
13. “Strength and muscle activity of shoulder external rotation of subjects with and without scapular dyskinesis” DAISUKE UGA, RIE NAKAZAWA, MASAAKI SAKAMOTO. J Phys Ther Sci. 2016; 28: 1100–1105
14. “Rehabilitation of scapular dyskinesis: from the office worker to the elite overhead athlete” COOLS AM, STRUYF F, DE MEY K, MAENHOUT A, CASTELEIN B, CAGNIE B. Br J Sports Med 2014;48:692–69
15. “Evaluation of apparent and absolute supraspinatus strength in patients with shoulder injury using the scapular retraction test” KIBLER WB, SCIACIA A, DOME D. Am J Sports Med 2006 Oct;34(10):1643-7.
16. “Scapular dyskinesis is detrimental to shoulder tendon properties and joint mechanics in a rat model”. REUTHER KE, THOMAS SJ, TUCKER JJ, YANNASCOLI SM, CARO AC, et als. J Orthop Res. 2014 November; 32(11): 1436–1443
17. “Psychological factors are associated with the outcome of physiotherapy for people with shoulder pain: a multicentre longitudinal cohort study” CHESTER R, JEROSCH-HEROLD C, LEWIS J, SHEPSTONE L. Br J Sports Med. 2018 Feb;52(4):269-275.