Assistant
Definition
By Gregory R. Waryasz, MD
The humerus of the musculoskeletal system is characterized by being the largest and longest bone in the upper extremity.
It is part of the upper limb. The humerus is part of the glenohumeral and elbow joints. The humerus articulates in the elbow with the ulna and the radius. It consists of bone and cartilage tissue once mature.
Its unique structural features include its being composed of a head, shaft, and distal component. The proximal humerus is retroverted 18 to 40 degrees in relation to the epicondyles. The average adult has a humeral head radius of curvature of between 22 and 25mm and articulates with the glenoid of the scapula.
The anatomic neck of the humerus is a groove that circumscribes the head and separates it from the greater and lesser tuberosities. The glenohumeral joint capsule attaches here.
The surgical neck of the humerus is a narrow portion of the humerus just distal to the head and tubercles.
The greater tuberosity is a lateral prominence where the supraspinatus, infraspinatus, and teres minor or the rotator cuff attach to the humerus.
The lesser tuberosity is anteriorly located and is the site where the subscapularis muscle attaches.
The groove in between the greater and lesser tuberosities is known as the intertubercular or bicipital groove. The long head of the biceps tendon courses through this groove.
The shaft or body of the humerus has a deltoid tuberosity and a radial groove. The deltoid tuberosity is located laterally and serves as the deltoid muscle insertion. The radial groove is an oblique structure located posteriorly. The radial groove is where the radial nerve passes along with the deep artery of the arm.
The humeral shaft widens as it becomes more distal into the supracondylar ridges (medial and lateral). Distal to the supracondylar ridges are the medial and lateral epicondyles. The medial and lateral epicondyles are the sites for muscular attachments.
The distal humerus is made up of a trochlea, capitellum, olecranon fossa, coronoid fossa, and radial fossa. The capitellum articulates with the radial head. It is located laterally. The trochlea is a pulley-like structure that articulates with the ulna. The coronoid fossa allows the coronoid process of the ulna to rest during flexion of the elbow. The olecranon fossa is located posteriorly and accommodates the ulna’s olecranon process during full extension. The radial fossa is a shallow structure where the radial head sits during flexion of the forearm.
The muscles that attach to the humerus are the latissimus dorsi, pectoralis major, deltoid, teres major, subscapularis, supraspinatus, infraspinatus, teres minor, brachialis, coracobrachialis, triceps brachii, anconeus, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and supinator muscles.
The blood supply is from the anterolateral branch of the anterior humeral circumflex artery, it passes lateral to the long head of the biceps to form the arcuate artery. As the arcuate artery, the bone is penetrated to perfuse the entire epiphysis of the humeral head. The posterior circumflex artery helps to supply a small posteroinferior area of the humeral head. The shaft of the humerus is supplied by the perforating branches of the brachial artery leading to the main nutrient artery that enters the medial humerus distal to the midshaft.
The humerus has one primary and seven secondary ossification centers. The body is the primary ossification center that appears at 8 weeks of fetal gestation. The head appears at 1 year. The greater tuberosity appears at 3 years. The lesser tuberosity appears at 5 years. The body, head, greater tuberosity, and lesser tuberosity blend at age 6 and unite at age 20. The capitellum appears at 2 years. The medial epicondyle appears at 5 years. The trochlea appears at 9 years. The lateral epicondyle appears at 13 years. The capitellum, medial epicondyle, trochlea, and lateral epicondyle blend and unity with the body of the humerus between 16 and 18 years of age. The humerus as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in embryo.
The function of the humerus is to allow movement of both the shoulder and the elbow. The humerus articulates with the glenoid of the scapula and with both the radius and ulna to make the elbow joint.
Common diseases of the humerus include arthritis, fracture, dislocation, tumor, osteomyelitis, osteoporosis, Hegemann’s disease, and Panner disease.
Arthritis can occur at either the glenohumeral or elbow joint. Common arthritis types that can occur at these locations include osteoarthritis and rheumatoid arthritis.
Fracture of the humerus can occur with trauma. Fractures are described as being either of the humeral head, shaft, or supracondylar regions.
Dislocation or subluxation of the glenohumeral joint can occur with trauma. Dislocation of the elbow can occur with trauma.
Osteomyelitis is an infection of the bone usually due to bacteria.
Osteoporosis is a condition of decreased bone mineral density.
Tumors can either be primary or from metastasis. A few primary tumors that can occur in bone include leukemia, lymphoma, neuroblastoma, osteoblastoma, osteosarcoma, osteoid osteoma, enchondroma, and Ewing’s Sarcoma.
Hegemann’s disease is a condition of osteonecrosis of the humeral trochlea.
Panner disease is a form of osteonecrosis of the capitellum.
Osteochondritis dissecans can occur in the elbow leading to bone fragments.
Commonly used diagnostic procedures include clinical history, physical exam, x-ray, MRI, bone scan, and CT scan.
It is usually treated with internal or external surgical fixation or non-operative approaches for fractures. Dislocations are usually treated non-operatively with a sling, however can require surgery in some instances. Tumors can be treated with surgery, chemotherapy, and radiation. Arthritis is treated initially with physical therapy, NSAIDs, and steroid injections. A shoulder replacement or elbow replacement can help improve pain from glenohumeral or elbow joint arthritis. Osteomyelitis is treated both surgically and with antibiotics. Osteonecrosis conditions such as Panner’s and Hegemann’s disease are generally treated non-operatively.
References
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Wheeless’ Textbook of Orthopaedics: Fractures of the Humerus (http://www.wheelessonline.com/ortho/fractures_of_the_humerus)