[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › Infraspinatus tendon [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # Infraspinatus tendon The infraspinatus tendon crosses the back of the shoulder to the [humerus](https://durgical.com/en/anatomy/humerus/); it turns the arm outward and holds the ball back in the socket. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=infraspinatus_tendon&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The rotator cuff tendon at the back of the shoulder; large cuff tears often extend into it, weakening outward rotation. ## What it does Turns the arm outward and holds the ball back in the socket. ## Key points - A lag on the external rotation lag sign means the tendon is torn, not just painful; resisted lateral rotation with the arm at the side loads it - Large posterosuperior tears spread back from the [supraspinatus](https://durgical.com/en/anatomy/supraspinatus/) into this tendon; weakness of lateral rotation signals that the tear has reached it - Wasting of the infraspinous fossa with an intact tendon suggests suprascapular nerve compression at the spinoglenoid notch, often by a paralabral cyst ## Key facts **Attaches** [Infraspinatus](https://durgical.com/en/anatomy/infraspinatus/) to the middle facet of the greater tubercle, between the supraspinatus and [teres minor](https://durgical.com/en/anatomy/teres-minor/) tendons **Function** Main lateral rotator; holds the humeral head back in the glenoid; tested by resisted lateral rotation with the arm at the side **Tight in** Medial rotation with horizontal adduction ## Relations **Course** From the infraspinous fossa it runs laterally across the back of the shoulder joint, behind the humeral head, to the greater tubercle **Superficial** Posterior deltoid and the back of the subacromial–subdeltoid bursa; the posterior edge of the acromion above **Deep** Posterior [shoulder capsule](https://durgical.com/en/anatomy/shoulder-joint-capsule/), which it reinforces, and the back of the humeral head **Above** [Supraspinatus tendon](https://durgical.com/en/anatomy/supraspinatus-tendon/), with interlacing fibres near the insertion **Below** [Teres minor tendon](https://durgical.com/en/anatomy/teres-minor-tendon/), often hard to separate from it **Medial** Spinoglenoid notch at the lateral edge of the scapular [spine](https://durgical.com/en/anatomy/region/spine/), where the [suprascapular nerve](https://durgical.com/en/anatomy/suprascapular-nerve/) and vessels curve round under the [spinoglenoid ligament](https://durgical.com/en/anatomy/inferior-transverse-scapular-ligament/) to reach the muscle ## How to find it Seated, with the arm flexed forward and brought across the [chest](https://durgical.com/en/anatomy/region/chest/), the tendon is drawn out from under the acromion and is felt just below the posterolateral corner of the acromion. Resisted lateral rotation tightens it under the posterior deltoid. ## Examination - Resisted lateral rotation with the elbow at the side and bent to 90°: weakness points to a tear or a suprascapular nerve palsy; pain alone suggests tendinopathy - External rotation lag sign: the examiner turns the forearm outward almost fully and lets go; if it drifts back inward, the posterosuperior cuff is torn ## On imaging MRI and ultrasound show whether a superior cuff tear extends back into it. On sagittal MRI, wasting and fatty change of the muscle (Goutallier grading) help predict whether a tear can be repaired. Muscle wasting with an intact tendon points to a nerve cause. ## Common problems - Rotator cuff tear, partial or full, from wear with age or from a fall; the most common cause of shoulder weakness. - Tendinopathy and impingement: pain lifting the arm and at night. - Calcific tendinitis: calcium deposits that cause sudden severe pain. ## How it is diagnosed Weakness and pain on cuff tests (for example the empty-can test). Ultrasound or MRI shows the tear size and muscle quality. ## Treatment - Physical therapy, pain medicines and sometimes injections, especially for partial and age-related tears. - Arthroscopic rotator cuff repair with suture anchors for many full-thickness tears, especially recent ones in active people. - Reverse shoulder replacement for large, irreparable tears with arthritis. ## Clinical notes - Suprascapular nerve compression at the spinoglenoid notch, often by a ganglion linked to a labral tear, weakens the infraspinatus alone; seen in overhead athletes such as volleyball players - With the [subscapularis](https://durgical.com/en/anatomy/subscapularis/) in front it forms the transverse force couple that centres the humeral head; losing both sides of the couple lets the head ride up - The interval between it (suprascapular nerve) and the teres minor ([axillary nerve](https://durgical.com/en/anatomy/axillary-nerve/)) is the internervous plane of the posterior approach to the shoulder joint ## Anatomical variants - Its muscle may be fused with the teres minor ## Test yourself Think of the answer, then tap the question to see it. ## Where does the infraspinatus tendon insert, and what is its main action? On the middle facet of the greater tubercle; it is the main lateral rotator and holds the humeral head back in the glenoid. ## What does a positive external rotation lag sign mean for the infraspinatus tendon? The tendon is torn, not just painful: the forearm drifts back inward after being released in near-full lateral rotation. ## What does infraspinatus wasting with an intact infraspinatus tendon suggest? Suprascapular nerve compression at the spinoglenoid notch, often by a paralabral cyst. ## What internervous plane lies beside the infraspinatus tendon in the posterior shoulder approach? Between the infraspinatus (suprascapular nerve) and the teres minor (axillary nerve). [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/infraspinatus-tendon/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** tendo musculi infraspinati TA2 2458 **Official Spanish (DeCS)** Tendón del músculo infraespinoso **English (TA2)** Infraspinatus tendon ## Related - [Supraspinatus tendon](https://durgical.com/en/anatomy/supraspinatus-tendon/) - [Infraspinatus](https://durgical.com/en/anatomy/infraspinatus/) - [Humerus](https://durgical.com/en/anatomy/humerus/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Infraspinatus Muscle](https://www.ncbi.nlm.nih.gov/books/NBK513255/); [Anatomy, Rotator Cuff](https://www.ncbi.nlm.nih.gov/books/NBK441844/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/infraspinatus-tendon/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/infraspinatus-tendon/