The humerus is a long bone of the upper limb, which extends from the shoulder to the elbow.
The proximal aspect of the humerus articulates with the glenoid fossa of the scapula, forming the glenohumeral joint. Distally, at the elbow joint, the humerus articulates with the head of the radius and trochlear notch of the ulna.
In this article, we shall look at the anatomy of the humerus - its bony landmarks and clinical correlations.
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Proximal Landmarks
The proximal humerus is marked by a head, anatomical neck, surgical neck, greater and lesser tuberosity and intertubercular sulcus.
The upper end of the humerus consists of the head. This faces medially, upwards and backwards and is separated from the greater and lesser tuberosities by the anatomical neck.
The greater tuberosity is located laterally on the humerus and has anterior and posterior surfaces. It serves as an attachment site for three of the rotator cuff muscles – supraspinatus, infraspinatus and teres minor - they attach to superior, middle and inferior facets (respectively) on the greater tuberosity.
The lesser tuberosity is much smaller, and more medially located on the bone. It only has an anterior surface. It provides attachment for the last rotator cuff muscle - the subscapularis.
Separating the two tuberosities is a deep groove, known as the intertubercular sulcus. The tendon of the long head of the biceps brachii emerges from the shoulder joint and runs through this groove.
The edges of the intertubercular sulcus are known as lips. Pectoralis major, teres major and latissimus dorsi insert on the lips of the intertubercular sulcus. This can be remembered with the mnemonic “a lady between two majors”, with latissimus dorsi attaching between teres major on the medial lip and pectoralis major laterally.
The surgical neck extends from just distal to the tuberosities to the shaft of the humerus. The axillary nerve and circumflex humeral vessels lie against the bone here.
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Clinical Relevance: Surgical Neck Fracture
The surgical neck of the humerus is a frequent site of fracture – usually by a direct blow to the area, or falling on an outstretched hand.
The key neurovascular structures at risk here are the axillary nerve and posterior circumflex artery.
Axillary nerve damage will result in paralysis to the deltoid and teres minor muscles. The patient will have difficulty performing abduction of the affected limb. The nerve also innervates the skin over the lower deltoid (regimental badge area), and therefore sensation in this region may be impaired.
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Shaft
The shaft of the humerus is the site of attachment for various muscles. Cross section views reveal it to be circular proximally and flattened distally.
On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.
The radial (or spiral) groove is a shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery lie in this groove. The following muscles attach to the humerus along its shaft:
- Anteriorly - coracobrachialis, deltoid, brachialis, brachioradialis.
- Posteriorly - medial and lateral heads of the triceps (the spiral groove demarcates their respective origins).
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Clinical Relevance: Mid-Shaft Fracture
A mid-shaft fracture of the humerus risk damage to the radial nerve and profunda brachii artery (as they are tightly bound in the radial groove).
The radial nerve innervates the extensors of the wrist. In the event of damage to this nerve (either direct or as a consequence of swelling), the extensors will be paralysed. This results in unopposed flexion of the wrist, known as ‘wrist drop’.
There can also be some sensory loss over the dorsal (posterior) surface of the hand, and the proximal ends of the lateral 3 and a half fingers dorsally.
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Distal Region
The lateral and medial borders of the distal humerus form medial and lateral supraepicondylar ridges. The lateral supraepicondylar ridge is more roughened, providing the site of common origin of the forearm extensor muscles.
Immediately distal to the supraepicondylar ridges are extracapsular projections of bone, the lateral and medial epicondyles. Both can be palpated at the elbow. The medial is the larger of the two and extends more distally. The ulnar nerve passes in a groove on the posterior aspect of the medial epicondyle where it is palpable.
Distally, the trochlea is located medially, and extends onto the posterior aspect of the bone. Lateral to the trochlea is the capitulum, which articulates with the radius.
Also located on the distal portion of the humerus are three depressions, known as the coronoid, radial and olecranon fossae. They accommodate the forearm bones during flexion or extension at the elbow.
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Articulations
The proximal region of the humerus articulates with the glenoid fossa of the scapula to form the glenohumeral joint (shoulder joint).
Distally, at the elbow joint, the capitulum of the humerus articulates with the head of the radius and the trochlea of the humerus articulates with the trochlear notch of the ulna.
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Clinical Relevance: Supracondylar Fracture
A supracondylar fracture is a fracture of the distal humerus just above the elbow joint. The fracture is typically transverse or oblique, and the most common mechanism of injury is falling on an outstretched hand. It is more common in children than adults.
In this type of injury, the brachial artery can be damaged; either directly, or via swelling following the trauma. The resulting ischaemia can cause Volkmann’s ischaemic contracture – uncontrolled flexion of the hand - as flexor muscles become fibrotic and short.
There also can be damage to the anterior interosseous nerve (branch of the median nerve), ulnar nerve or radial nerve. The anterior interosseous nerve can be tested by asking the patient to make an ‘okay’ sign, testing for weakness of flexor pollicis longus.
The Gartland classification is used for these fractures:
- Type 1 is minimally displaced
- Type 2 is displaced with but with an intact posterior cortex
- Type 3 is completely off-ended.
Type 1 can usually be managed conservatively with an above elbow cast whereas types 2 and 3 typically require surgical fixation with crossed, bi-cortical k-wires.
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Your deltoid muscles cover the top of your shoulder. They help you lift your arm to front, side and back. Deltoid muscle pain can affect swimmers, pitchers or anyone who performs repetitive overhead arm movements.
Your deltoid muscles are in your shoulder, which is the ball-and-socket joint that connects your arm to the trunk of your body. Deltoid muscles help you move your arms in different directions. They also protect and stabilize your shoulder joint.
Like most other muscles in your body, the deltoids are skeletal muscles. Tendons attach them to bones. Skeletal muscles are voluntary muscles, meaning you choose to move them. Skeletal muscles are different than smooth, or involuntary, muscles (such as your heart) that work without you having to think about it.
Your deltoid muscles work alongside your other shoulder muscles, such as the rotator cuff muscles, to help you perform a variety of movements. Deltoid muscle functions include:
- Arm abduction, which means raising your arm out to the side of your body.
- Compensation for lost arm strength if you have an injury, such as a rotator cuff tear.
- Flexion (moving your arm forward, toward an overhead position) and extension (moving your arm backward, behind your body).
- Stabilization of your shoulder joint to prevent dislocations as you lift your arm or while you carry weight with your arms at your side.
Your deltoid muscles crown your shoulder, covering the front, side and back of the joint. They’re superficial, which means they’re close to the surface of your skin. The deltoid looks like an upside-down triangle. Tendons connect each of the three side to bones.
The base of the deltoids connects to the upper part of your scapula (shoulder blade) and the side of your clavicle (collarbone). The point of the deltoids attaches to the side of your humerus (the arm bone between your shoulder and elbow).
How are the deltoid muscles structured?
The deltoid muscles have three parts, or heads:
- Anterior deltoids: The front delts that help move your arm forward. They connect to your clavicle. You use your front delts if you reach for an object on a shelf.
- Lateral deltoids: Side delts that help move your arm out to the side, as well as up and down. They connect to your acromion, a bony nob on your shoulder blade. You use your side delts if you do jumping jacks.
- Posterior deltoids: Rear delts that help move your arm backward. They connect to the flat surface of your shoulder blade. You use your rear delts if you pitch a baseball.
What are the deltoid muscles made of?
Like other muscles in your body, deltoid muscles in your shoulder contain elastic fibers. These fibers make the muscles flexible, so they can perform lots of movements. Skeletal muscles are red and white, making them appear striated (striped or streaked).
Conditions that may affect your deltoid muscles include:
- Adhesive capsulitis: This condition occurs when the capsule around your shoulder joint gets thick and stiff. It can cause shoulder pain, muscle spasms and stiffness. Another name for adhesive capsulitis is frozen shoulder.
- Axillary nerve palsy: The axillary nerve supplies sensation to the deltoid muscle. Compression of or damage to the nerve can happen during surgery or due to a traumatic injury or overuse of a crutch. These issues can lead to shoulder weakness or numbness, especially around your deltoid muscle.
- Bursitis: Shoulder bursitis is inflammation of the bursa (tiny, fluid-filled sacs) in your shoulders. The inflammation can make it hard to move your shoulder joint. It may also cause muscle irritation.
- Deltoid fibrosis: Repeated shoulder muscle injections can lead to fibrosis. This condition causes the muscle to stop repairing itself. You may experience deltoid muscle pain or loss of muscle strength and mobility.
- Rotator cuff tears: Sometimes severe rotator cuff tears damage or dislocate the deltoid muscle.
- Shoulder impingement syndrome: Your shoulder muscles or tendons rub against bones. This friction, called shoulder impingement syndrome, leads to joint pain and inflammation.
- Shoulder separation: A separated shoulder happens when the ligaments tear between the collarbone and the shoulder blade. In severe cases, surgery may be necessary.
- Strains and overuse injuries: A shoulder strain is the result of overstretched muscle fibers. Strains can happen suddenly, or they might develop slowly over time due to repetitive overhead arm movements.
- Tendonitis: Shoulder tendonitis occurs when the tendons in your shoulder get inflamed. Tendonitis can cause delt pain or make it difficult for you to use your shoulder muscles or move the joint.
How common are deltoid muscle injuries?
Shoulder muscle conditions are common. One study suggests that 18 to 26% of adults experience shoulder pain at some time in their lives. But problems affecting the deltoid muscles aren’t quite as common as other shoulder conditions, such as rotator cuff injuries.
Who gets deltoid muscle injuries?
Anyone can have problems with their deltoid muscles. But they’re more common in athletes that perform a lot of overhead arm movements, such as:
- Baseball pitchers.
- Swimmers.
- Tennis players.
- Weightlifters.
Your risk for shoulder muscle conditions increases if you:
What are the symptoms of deltoid muscle conditions?
Deltoid muscle conditions may cause:
- Difficulty moving your arm in different directions, especially lifting it overhead.
- Inflammation or swelling.
- Joint stiffness or instability.
- Numbness or tingling.
- Pain at rest or with certain movements.
- Spasms.
- Trouble lifting weight.
- Weakness.
How are deltoid muscle conditions diagnosed?
Your healthcare provider reviews your symptoms and performs a physical exam. They may ask you to lift your arm to the front, side and back, possibly against some resistance. If your deltoid muscles are working properly, your provider should be able to feel the muscle contract when you lift your arm.
If you can’t lift your arm, it doesn’t always mean you have a deltoid muscle injury. Arm muscle weakness can also be the result of:
- Cachexia, or extreme muscle loss due to disease or a poor diet.
- Neuromuscular disorders or myopathies (muscle disorders).
- Side effects from a vaccine.
- Your provider may also recommend imaging exams. You may have an X-ray, MRI, ultrasound or CT scan if they suspect any bone fractures, dislocations or tissue tears in your shoulder. An electromyogram (EMG) studies how well your muscles and nerves are working.
How are deltoid muscle injuries treated?
Most deltoid muscle conditions heal with nonsurgical treatments, including:
- Ice or cold compresses to reduce inflammation.
- Pain relievers or muscle relaxants.
- Physical therapy.
- Shoulder exercises to improve strength and mobility.
- Sling or other supportive garment to immobilize your shoulder.
- Steroid injections to relieve pain and swelling.
- Warm compresses to relax muscles.
Serious deltoid muscle injuries, such as a muscle tear, might require surgery. Your healthcare provider may recommend open surgery or minimally invasive arthroscopic shoulder surgery depending on your injury.
What are the risks of deltoid muscle surgery?
Like any surgery, shoulder surgery carries risks of infection, bleeding, blood clots and scar tissue formation. But it’s also important to note that any shoulder surgery can affect your deltoid muscles. Since these muscles run across most of your shoulder and are near the surface of your skin, surgeons often cut through these muscles when they perform rotator cuff repairs, tendon surgeries or other procedures.
Surgical complications specific to your deltoid muscle can include:
- Axillary nerve damage, which may result in reduced arm mobility.
- Blood vessel damage, which can lead to edema (swelling from fluid buildup) in your shoulder and upper arm.
- Detachment of the deltoid muscle from your clavicle, which requires surgical reattachment.
Take care of your deltoid muscles by:
- Adhering to sport-specific safety guidelines, such as pitch-count limits in baseball.
- Not putting strain on your shoulder muscles if they hurt.
- Resting shoulder muscles after performing a lot of overhead arm movements.
- Stretching and warming up your shoulder muscles before activity.
- Using proper technique when throwing, swimming or performing other activities that require repeated shoulder movements.
Contact your doctor right away if you:
- Can’t move your shoulder or arm.
- Can’t feel your shoulder or arm.
- Have severe, sudden pain in your shoulder or anywhere in your arm.
A note from Cleveland Clinic
Your deltoid muscles play an important role in helping you move your arm in different directions. They also stabilize your shoulder joint and protect it from injuries such as dislocations. People who perform a lot of repeated overhead movements, such as swimmers, pitchers or mechanics, are at risk of injuring their deltoid muscles. Most deltoid muscle injuries heal with nonsurgical treatments.
Last reviewed by a Cleveland Clinic medical professional on 09/24/2021.
References
- Dave HD, Shook M, Varacallo M. Anatomy, Skeletal Muscle. (//www.ncbi.nlm.nih.gov/books/NBK537236/) [Updated 2020 Sep 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Accessed 10/19/2021.
- McCausland C, Sawyer E, Eovaldi BJ, Varacallo M. Anatomy, Shoulder and Upper Limb, Shoulder Muscles. (//www.ncbi.nlm.nih.gov/books/NBK534836/) [Updated 2020 Aug 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Accessed 10/19/2021.
- Elzanie A, Varacallo M. Anatomy, Shoulder and Upper Limb, Deltoid Muscle. (//www.ncbi.nlm.nih.gov/books/NBK537056/) [Updated 2020 Aug 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Accessed 10/19/2021.
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