Dynamic stabilization of glenohumeral joint

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Original Editor - Khloud Shreif Top Contributors - Khloud Shreif

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Introduction

The stability of shoulder joint like any other joints in body depend on static and dynamic stabilizer ,static stabilizers of shoulder are joint labrum and capsuloligaments component. .Dynamic stabilizers we mean muscles for example (supraspinatus, infraspinatus, subscapularis ,teres minor) plus periscapular muscles[1], which are very important for homogeneous shoulder movement to avoid some of shoulder problems for example: shoulder impingement .Dynamic stability of shoulder divided into; glenohumeral stability/local and scapulothoracic contribution stability/global.

Glenohumeral joint stability

Deltoid and glenohumeral stabilization

figure 1 line of action of three parts of deltoid follows line of pull of middle deltoid the resultant (Fd) resolved into a very large translatory component (Fx) and a small rotatory component (Fy).[2]

Deltoid has a significant role as a stabilizer and generally accepted as a prime mover for glenohumeral abduction along with supraspinatus.

From the figure that show the line of action of deltoid with arm at side , the parallel force component (fx)directed superior is larger of three other component so that , the majority of deltoid contraction causes humeral head translate superior and a small applied perpendicular force is directed to rotate humerus . That we need an inferior pull force to offset the (fx) component of middle deltoid for active arm elevation as gravity force can't balance this force.[3]

Rotator cuff and glenohumeral stabilization

Rotator cuff not only abduct the shoulder it play a role as a stabilizer muscles[4]

From figure 2 we can see all three muscles (teres minor,subscapularis,infraspinatus) in relation to their anatomical position and their muscle fiber direction from origin to insertion, tend to have similar inferior line of pull[2] and with the summation of three forces of rotator cuff they nearly offset superior translation of humeral head created by deltoid. The wide range of motion of the shoulder is allowed by the variety of rotational moments of the cuff muscles[5]. Teres minor ,Infraspinatus as they are external rotators they contribute in abduction of arm by external rotation that participate clearing greater tubercle underneath the acromion.
figure 2

Supraspinatus and glenohumeral stabilization

Regarding to supraspinatus location more superior than the three other rotator cuff it has a line of pull superior that can't offset deltoid force.

Even though it still an effective stabilizer due to it's larger moment arm ,it's capable to elevate glenohumeral joint near normal.[2]

From illustrated above we can consider deltoid and rotator cuff as one of a force couple of glenohumeral joint.

Imbalance of one or more of these muscle consider a contribution cause to shoulder problems (impingement , bursitis , instability )

Scapulothoracic contribution

Trapezius and serratus anterior

Conclusion

figure 3
For smooth synchronous movement of shoulder we need deltoid and rotator cuff muscles to work in proper timing and adequate forces to offset each other.As deltoid act to stabilize humeral head against glenoid cavity with small participation to abduct the arm, there are(subscapularis, teres minor, infraspinatus) their force of pull balance deltoid action along with supraspinatus that participate mainly in arm abduction.

Deficit in one of these forces for example;insufficient activation of rotator cuff /deltoid over activation participate to narrowing coracoacomial space (figure 3) that compress tendons in this space[6]

Physical therapy intervention

Imbalance of local or global dynamic stabilizers or both result in improper movement of shoulder girdle, scapular dyskinesia, shoulder impingement.

Scapular and shoulder mobilization for pain relieve if present or for restricted direction of movement.

Inhibition techniques for over activated muscles eg; deltoid, upper trapezius.

Strength for weak or inhibited muscles like serratus anterior, rotator cuff muscles.

Muscles re-education to be activated in proper time is important to restore balance.

for more exercise this page below:

What kind of exercises can be used /select exercises for rotator cuff strengthening

For shoulder impingement(sub acromian impingement)

[7]

Related topics:

anatomy and biomechanics/biomechanics of shoulder movement/static structure and mechanoreceptors

shoulder musculature

  • Stability and instability of the glenohumeral joint: the role of shoulder muscles[8]

References

  1. Curl LA, Warren RF. Glenohumeral joint stability: selective cutting studies on the static capsular restraints. Clinical Orthopaedics and Related Research®. 1996 Sep 1;330:54-65.
  2. 2.0 2.1 2.2 Levangie PK, Norkin CC. Joint Structure and Function; A Comprehensive Analysis. 5th. Philadelphia: Fadavis Company. 2012.
  3. Levangie PK, Norkin CC. Joint Structure and Function; A Comprehensive Analysis. 5th. Philadelphia: Fadavis Company. 2012.
  4. Escamilla RF, Yamashiro K, Paulos L, Andrews JR. Shoulder muscle activity and function in common shoulder rehabilitation exercises. Sports medicine. 2009 Aug 1;39(8):663-85.
  5. Longo UG, Berton A, Papapietro N, Maffulli N, Denaro V. Biomechanics of the rotator cuff: European perspective. InRotator Cuff Tear 2012 (Vol. 57, pp. 10-17). Karger Publishers.
  6. <article> Joseph B. Myers, Ji-Hye Hwang, Maria R. Pasquale, J. Troy Blackburn and Scott M. Lephart. Rotator cuff coactivation ratios in participants with subacromial impingement syndrome.  Journal of Science and Medicine in Sport, Volume 12, Issue 6, November 2009, Pages 603-608 </article>
  7. Physiotutors. Subacromial Pain Syndrome (SAPS) | Late Phase Eccentric Rehab. Available from: https://www.youtube.com/watch?v=mC_gYttfbBw [last accessed 14/2/2020]
  8. Labriola JE, Lee TQ, Debski RE, McMahon PJ. Stability and instability of the glenohumeral joint: the role of shoulder muscles. Journal of shoulder and elbow surgery. 2005 Jan 1;14(1):S32-8.