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The Subscapularis: Shrug Off Shoulder Pain


Chiropractor Alexander Jimenez investigates the relevant anatomical and biomechanical considerations related to the subscapularis, plus injury within the subscapularis, how to assess subscapularis function & finally rehabilitation ideas for injured as well as dysfunctional subscapularis muscles.

Introduction

Injuries to the muscle are infrequent causes of shoulder pain in the athlete. Immediate injuries to the muscle- tendon unit can affect the athlete like swimmers and tennis players. Malfunction in the subscapularis in the kind of fatigue and inhibition can lead to biomechanical abnormalities in the glenohumeral joint such as poor lateral stabilization of the shoulder joint in the shoulder that is athletic.

Anatomy


The subscapularis originates the anterior scapular (subscapular fossa) and inserts onto the lesser tuberosity of the humerus. It’s the largest of the rotator cuff muscles and its cross-sectional area is larger than the other three rotator cuff joint (infraspinatus, teres minor, surpraspinatus). Its main roles on the glenohumeral joint are:

1. Depressor of the humeral head;

2. Anterior stabilizer of the humeral head (glides the humeral head posteriorly relative to the glenoid fossa);

3. Internal rotator of the shoulder (together with the highly effective pectoralis major and latissimus dorsi).

The tendon fibres mix with the anterior capsule of the shoulder and therefore fortify the posterior shoulder capsule. The muscle is regarded as less significant as a shoulder internal rotator (as the pectoralis major and latissimus dorsi are powerful internal rotators) also is significantly more important as a dynamic anterior stabilizer of the glenohumeral joint through its activity in preventing anterior shear/glide of the humeral head.

The subscapularis has an intimate relationship with the long head of the biceps via the shoulder “Twist”. This is a complex that functions to stabilize the long head of the biceps tendon in the bicipital groove. The pulley complex consists of the superior glenohumeral ligament, the coracohumeral ligament, along with the ventral attachment of the subscapularis

Tendon, and is located inside the rotator Interval between the anterior edge of the subscapularis tendon of the superior edge and the tendon. Injuries to the subscapularis tendon may compromise the integrity of their bicep’s ‘sling’ (Nakata et al 2011). To keep the knee tendon in place and stabilized, tension from the superior glenohumeral ligament and the help of the very superior insertion stage of the subscapularis from supporting the fascia is demanded (Aria et al 2010). Disruption of this ‘biceps sling’ is a frequent pathology in athletes that require forceful and frequent shoulder rotation such as the position in baseball pitching.

Injuries To Subscapularis

Like all of the rotator cuff muscles subscapularis is susceptible to pressure forces which may damage the muscle-tendon and also muscle unit’s integrity. Although tears to the subscapularis are not as prevalent as tears from the other rotator cuff (particularly supraspinatus), injuries to the subscapularis might prove to be problematic due to its anatomical proximity to the long head of the biceps tendon.

Ruptures of the subscapularis have been reported in the literature (Gerber and Krushell 1991). The mechanism is a pressured hyper-extension rotation force such as falling onto an outstretched arm, on the shoulder or infrequently it might be a result of a shoulder dislocation. These kinds of injuries will lead to severe shoulder pain using a painful weakness in internal rotation, greater range of motion into external rotation (which is then constrained by pain at end of range) along with also a weak/pathological ‘lift-off’ test (see below).




Injuries to the subscapularis tendon can also occur in athletes or occupations that take a great deal of forceful shoulder internal rotation (baseball pitching, tennis, swimming). Overuse of those complicated can create a strain response and fibrosis tissue deposition in the gut, may lead to. Trigger points in the muscle can create that weaken and tighten the muscle.

In these instances, pain is felt as a deep anterior shoulder pain, exacerbated by overhead inner spinning movements (swimming and serving), weakness in the ‘lift-off’ evaluation (see above) and also reduced array of passive external rotation whilst the arm is placed by the side is noted (Thurner et al 2013).

Finally, a neighborhood muscle imbalance shoulder between the subscapularis and the infraspinatus can cause positional faults from the mind of the humerus, whereas the humeral head is not centralized in the glenoid fossa and excessive anterior shear of the humeral head happens that leads to impingement and uncertainty sensations in the shoulder.

Role Of Subscap In Shoulder Stability

Hess et al (2005) found that in a simulated throwing action using shoulder rotation, participants with shoulder pathology had a delayed onset on recruiting of subscapularis compared infraspinatus and supraspinatus. Nevertheless, in regular pain free shoulders that the subscapularis was activated earlier and until the shoulder began to externally rotate, evidence that the subscapularis functions in a mechanism to ‘pre-empt’ movement and also to contract to provide anterior shoulder stability.

It is suggested therefore that shoulder pain patients lose part of their energetic mechanisms that are stabilizing in the shoulder and as a result the humeral head shear and can glide anteriorly and superiorly from the glenohumeral joint, thus leading to anterior shoulder impingements.

Imbalances in force production involving the subscapularis and the externally infraspinatus could create a local issue from the glenohumeral joint. It’s typical for the athletic shoulder to really have a misaligned and tight infraspinatus in connection to the subscapularis. This neighborhood imbalance sets a mechanical issue in the shoulder the infraspinatus pushes forward the humeral head in relation to the glenoid and the inhibited subscapularis can’t counteract this lateral shear effect. Consequently the head shears and impinges the anterior pain and shoulder structures may result.

Conclusion

Research shows that the muscle has an significant role in supplying anterior glenohumeral joint stability. It centres the humeral head into the movements of this arm/shoulder. Dysfunction in this muscle may lead to of the humeral head which might be a precursor to shoulder instabilities and the more shoulder impingements.

It’s important for the clinician to detect dysfunction inside this muscle through a battery of tests and also direct exercises will be required to rehabilitate function for this muscle.

References

1. Aria et al (2010) Functional anatomy of the superior glenohumeral and coracohumeral ligaments and the subscapularis tendon in view of stabilization of the long head of the biceps tendon. Journal of Shoulder and Elbow Surgery. 19(1):58-64

2. Barth et al (2006) The bear-hug test: a new and sensitive test for diagnosing a subscapularis tear. Arthroscopy. 20(10). 1076 -1084.

3. Burkhart SS, Tehrany AM. (2002) Arthroscopic subscapularis tendon repair: Technique and preliminary results.

Arthroscopy ; 17:454-463

4. Gerber C and Krushell RJ (1991) Isolated rupture of the tendon of the subscapularis muscle. The Journal of Bone and Joint Surgery. 73-B(3); pp 389-394.

5. Hess et al (2005). Timing of Rotator Cuff Activation During Shoulder External Rotation in Throwers With and Without Symptoms of Pain. JOSPT. 35(12); pp 812-820.

6. Nakata et al (2011). Biceps pulley: normal anatomy and associated lesions at MR arthrography. Radiographics. 31(3):791-810

7. Scheibel et al (2005) The Belly-Off Sign: A New Clinical Diagnostic Sign for Subscapularis Lesions. Arthroscopy: The

Journal of Arthroscopic and Related Surgery, 21(10): pp 1229-1235

8. Thurner et al (2013) Subscapularis Syndrome: a case report. International Journal of Sports Physical Therapy. 8(6); pp 871-882.

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