Anatomy, Shoulder and Upper Limb, Subscapularis Muscle


Article Author:
Kenneth Aguirre


Article Editor:
John Kiel


Editors In Chief:
Amie Kim
Todd May
Matthew Varacallo


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Abbey Smiley
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
2/10/2019 1:00:31 AM

Introduction

 The subscapularis muscle is a triangle shaped muscle originating at subscapular fossa and inserting at the lesser tubercle of the humerus. The muscle is named for its orientation under the scapula: sub (under) scapula (wing bone). The subscapularis is 1 of the 4 muscles which compose the rotator cuff apparatus. The other 3 are supraspinatus, infraspinatus, and teres minor. The subscapularis muscle’s primary function is internal rotation but can also aid in adducting the humerus. The subscapularis nerve innervates the muscle. The subscapular artery provides blood supply, and lymph drainage flows into the axillary nodes. This muscle and tendon are less likely to tear than other rotator cuff muscles. When there is an insult to the muscle or tendon, loss of function produces weakness in internal rotation. Non-operative management is the treatment of choice for partial tears and tendinopathies. Surgical intervention may be required (1) if conservative management fails, (2) depending on the activity level or profession of the individual, for example, athletes, and (3) in the case of full-thickness tears.[1][2][3]

Structure and Function

The subscapularis is the largest, strongest muscle of the rotator cuff. The rotator cuff muscles are important in shoulder movement and help maintain glenohumeral joint stability. The subscapularis muscle lies at the anterior surface of the scapula. It originates at the subscapular fossa, specifically the medial and lower two-thirds of the groove on the lateral border. The muscles transitions to a tendon which inserts on the lesser tubercle of the humerus in front of the joint capsule. Some fibers extend to the greater tubercle and bicipital groove. An outpouching of the glenohumeral joint lies between the subscapularis muscle and anterior surface of the scapula functioning as a bursa. The remainder of the rotator cuff muscles (supraspinatus, infraspinatus, and teres minor), insert into the greater tubercle. When the subscapularis muscle contracts it will internally or medially rotate the humerus. This is the only rotator cuff muscle that has this function. In certain positions, subscapularis has some adduction and extension function. This function also helps prevent anterior displacement of the humerus.

Embryology

There are 3 primary germ layers, which are made up of endoderm, ectoderm, and mesoderm during embryogenesis. The mesoderm forms muscles that make up the rotator cuff to include subscapularis.

Blood Supply and Lymphatics

Blood supply is composed of the subscapular artery, which is a branch of the axillary artery. Lymph drains into the axillary lymph nodes.

Nerves

The subscapular nerve which originates from branches of the posterior cord of the brachial plexus (C5 to C7) and trifurcates into the upper, middle, and lower subscapular nerves. The upper and lower subscapular nerves innervate the subscapularis muscle. The upper subscapular nerve innervates the cranial half of the muscle, while the lower subscapular nerve bifurcates into 2 branches with the cranial branch innervating the caudal half of the muscle. The inferior branch of the lower subscapular nerve provides innervation to the teres major and the middle scapular nerve, also known as thoracodorsal nerve, innervates the latissimus dorsi muscle.

Muscles

The large and powerful triangular muscle originates at the subscapular fossa and inserts into the lesser tubercle of the humerus. The muscle works to internally and adducts the humerus. The bicep tendon lies underneath the subscapularis tendon in the bicipital groove.

Physiologic Variants

Has no physiologic variants.

Surgical Considerations

Partial tears are treated non-operatively. Surgical evaluation occurs when there is a full-thickness tear, depending on the activity level or profession of the individual, and patients who fail conservative management. Surgery is performed either by arthroscopy or open technique. Biceps pathology frequently co-occurs and may require tenotomy or tenodesis.[4][5][6][7]

Clinical Significance

Causes of shoulder pain due to subscapularis etiology may include tendonitis, tendinopathy, and tears. Tendonitis of the subscapularis is usually due when it comes in contact with the coracoid process from overuse in throwing or overhead athletes. Tendinopathy occurs when the symptoms become more chronic, and remodeling of the tendon begins to occur. Rotator cuff tears tend to occur with chronic degenerative tears from over-head use or acutely in athletes with overhead motion. The incidence of subscapularis tears is less than that of other rotator cuff tendons. When tears do occur its due to an anterior shoulder dislocation, fall on the outstretched arm during abduction, iatrogenic following anterior shoulder surgery, lesser tubercle avulsion, or associated with rotator cuff tear.

History and Physical

Although any patient can injure their subscapularis tendon, they most commonly occur in young males. In acute injuries, the patient will likely report a history of forced external rotation. The patient will primarily complain of pain in front of the shoulder. A focused physical exam will include inspection, palpation, the range of motion, strength and special tests. On physical exam, there may be weakness or pain with internal rotation weakness at 0 degrees and increase passive external rotation. The patient may be tender on the tendinous insertion of the upper arm along the lesser tubercle. The provider should perform a full examination of the shoulder as the patient may have injuries to other rotator cuff muscles or the biceps.

There are multiple special tests which can be used to examine the subscapularis. The "Gerber" or lift-off test is performed by having the patient internally rotate their shoulder and place the dorsum of their hand against their lower back. A positive test is noted when the patient is unable to move the hand away from lower back with or without resistance or when they experience pain. If the patient is unable to get their hand behind their back, the abdominal compression or belly-press test may be employed. This test is performed by having the patient internally rotate their arm to their abdomen, with their elbow bent to 90 degrees, and the hand, wrist, and elbow forming a straight line and then pressing against the abdomen. A positive test is noted when the elbow falls posteriorly, with pain or weakness with the maneuver, or with the inability to compress without flexing the wrist. The bear hug test is performed by having the patient place their hand on the opposite shoulder. The examiner tries to externally rotate the arm while the patient tries to maintain their hand on the shoulder. A positive test occurs when the patient cannot hold against the external force applied by the examiner. The Napoleon test is performed similarly to the abdominal compression test. A positive result occurs when the patient can press only by flexing the wrist to 90 degrees and an intermediate result, suggesting partial function of the subscapularis muscle, occurs when the wrist is flexed between 30 and 60 degrees. One study found the bear hug test to be the most sensitive for subscapularis tears (60%), followed by the belly-press (40%), Napoleon (25%) and lift off test (17.6%).

Imaging

Shoulder radiographs are typically first the first-line imaging modality for undifferentiated shoulder pain. In the case of a subscapularis injury, they are likely to be normal however an avulsion injury may produce a bony abnormality. In general, MRI is considered the best imaging modality to evaluate for rotator cuff injuries, including the subscapularis muscle. A tear of the subscapularis tendon can range from mild degenerative changes to a full thickness tear of the tendon. The MRI can also evaluate the muscle belly as well. Diagnostic ultrasound is a cheap and easy modality to evaluate the subscapularis tendon in the hands of a skilled sonographer. Although it provides less detail than an MRI, it can help with diagnosis and management.

Treatment

Subscapularis tendonitis and tendinopathy are managed conservatively. Generally, this includes rest and activity modification, including discontinuation of offending activities, analgesia including acetaminophen and NSAIDs, ice and physical therapy. In most patients, this will resolve their symptoms. In refractory cases, corticosteroid injections are indicated.

Tears of the subscapularis tendon are often underdiagnosed and require a high index of suspicion by the clinician. Elderly patients with partial tear can be managed non-operatively with NSAIDs and physical therapy for 6 to 12 weeks. The short-term intra-articular injection can be effective for relieving pain and improving function. If no improvement with conservative management then the patient should be referred to orthopedic for surgical evaluation. Full thickness tears, athletes and younger individuals with a tear should also have a surgical evaluation. Surgery is performed either arthroscopically or in an open technique. Biceps pathology frequently co-occurs and may require tenotomy or tenodesis.


  • Image 8597 Not availableImage 8597 Not available
    Image courtesy S Bhimji MD
Attributed To: Image courtesy S Bhimji MD

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Anatomy, Shoulder and Upper Limb, Subscapularis Muscle - Questions

Take a quiz of the questions on this article.

Take Quiz
A 34-year-old male carpenter presents complaining of worsening left shoulder pain. On palpation, he is tender at the anterior aspect of the shoulder and has pain with active and passive internal rotation. A three-view shoulder x-ray shows no bony abnormality. Which muscle is most likely affected?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which rotator cuff muscle provides internal rotation of the shoulder?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
The lesser tubercle of the humerus receives the tendon of the:



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 40-year-old was in a motor vehicle accident. The patient was not wearing a seatbelt during the accident and banged his shoulder on the steering wheel. The patient was placed in a sling in the field. Shoulder x-rays show an avulsion fracture of the lesser tubercle. Which rotator cuff muscle will be affected?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Anatomy, Shoulder and Upper Limb, Subscapularis Muscle - References

References

Eovaldi BJ,Varacallo M, Anatomy, Shoulder and Upper Limb, Shoulder Muscles 2018 Jan;     [PubMed]
Kadi R,Milants A,Shahabpour M, Shoulder Anatomy and Normal Variants. Journal of the Belgian Society of Radiology. 2017 Dec 16;     [PubMed]
Bakhsh W,Nicandri G, Anatomy and Physical Examination of the Shoulder. Sports medicine and arthroscopy review. 2018 Sep;     [PubMed]
Juneja P,Hubbard JB, Anatomy, Shoulder and Upper Limb, Arm Teres Minor Muscle 2018 Jan;     [PubMed]
Javed O,Ashmyan R, Anatomy, Shoulder and Upper Limb, Muscles 2018 Jan;     [PubMed]
Rathi S,Taylor NF,Green RA, The upper and lower segments of subscapularis muscle have different roles in glenohumeral joint functioning. Journal of biomechanics. 2017 Oct 3;     [PubMed]
Dischler JD,Baumer TG,Finkelstein E,Siegal DS,Bey MJ, Association Between Years of Competition and Shoulder Function in Collegiate Swimmers. Sports health. 2018 Mar/Apr;     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Sports Medicine. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Sports Medicine, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Sports Medicine, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Sports Medicine. When it is time for the Sports Medicine board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Sports Medicine.