The Anatomy of the Humerus

The Largest Bone in the Upper Arm

In This Article

The humerus is the largest bone in the entire upper extremity. The top of the humerus joins with an area called the glenoid fossa on the scapula or shoulder blade. The bottom of the humerus touches the top of the radius and ulna which joins the upper arm with the lower arm.

The meeting of these bones allows for the wide range of motion which is possible at the shoulder joint, along with movement at the elbow.

Anatomy

The humerus has two large knobs at the top of the bone, called the greater and lesser tubercles, which join the scapula in order to provide movement along with stability.

The rhythm between the scapula and the humerus is a very important one for adequate shoulder function.

Another important landmark is the anatomical neck, a slightly more narrow area just below the tubercles but above the shaft, which is the long part of the bone. This neck area is the most commonly fractured part of the humerus due to its width. Unfortunately, fracture at this point in the humerus can be damaging to children and adolescents, as this is also the location of the epiphyseal plate or growth plate.

The shoulder joint, comprised in part by the humerus bone, is considered a ball-and-socket joint. This type of joint is the most versatile in the body, allowing for all degrees of motion. The corresponding anatomy must allow for this movement, which also makes this joint quite vulnerable to injury when improper movements and forces are present.

As mentioned the growth plate is an integral yet sensitive part of the humerus. Birth defects, infection, and/or trauma can act on this growth plate to disrupt the growth process. This can lead to shortening or other deformities of the humerus. In situations such as these, medical intervention can assist with bone lengthening techniques to achieve a more normalized and functional appearance of the bone.

Function

The head of the humerus makes up a portion of the ball-and-socket shoulder joint. This area also serves as the insertion point for muscles which make up the shoulder girdle. This includes the long head of the biceps tendon, along with supraspinatus, infraspinatus, teres minor, and subscapularis which are known as the rotator cuff muscles.

The humerus works in conjunction with these muscles to raise forward and lower (also called flexion and extension) the upper arm, raise laterally and lower (also called abduction and adduction) the upper arm, move the arm in small and large circular motions (also called circumduction), and rotate inward or outward (also called internal rotation and external rotation).

Many ligaments are also present in this area not only to assist with securing the musculature but also to provide motion to the shoulder joint.

There is also a large network of nerves which lies across the front portion of the humerus, called the brachial plexus.

This provides sensation and motion not only to every muscle in the arm but also portions of the neck and spinal cord.

Associated Conditions

Tendonitis or Bursitis

This is a common condition in which the tendons surrounding the humerus or the humerus itself becomes inflamed and irritated. This can be age-related or due to overuse such as in a job with repetitive motions or sports which require frequent forceful movement of the arm.

Frozen Shoulder

Frozen shoulder is the condition resulting from the shoulder capsule thickening, causing painful movement and significant stiffness. While this is a connective tissue dysfunction, it occurs directly over the head of the humerus which can cause degeneration and misalignment to the humerus if not treated accordingly.

Osteoarthritis

As with most large joints, the head of the humerus is susceptible to osteoarthritis. This condition typically occurs with age and results from the wearing down of the cartilage at the end of a bone. This can cause significant pain from any and all joint motion.

Each of these conditions can be treated conservatively (meaning without surgery) by a physical or occupational therapist, or by a doctor. Treatment by a doctor may include surgery or their own conservative methods which typically includes injections for pain and inflammation.

Rehabilitation

As with most fractures, treatment of humeral neck fractures follows a protocol to maximize function. Though similar, there are different protocols to follow to treat fractures of the shaft or distal end of the humerus.

Open and Closed Reduction

Open reduction with internal fixation will occur in instances where doctors need to fixate the bone fragments using rods, screws, plates, or other hardware. Closed reduction is also completed by a doctor in a simple procedure where no surgical incisions need to be made. Each of these procedures is typically followed by placement of a cast or sling to protect the arm and prevent re-injury while the patient slowly resumes some daily activities.

Rehabilitation protocols will differ based on the type of fracture, however, passive range of motion (where a therapist completes stretching exercises for the patient) is recommended 24 to 48 hours after surgery to prevent loss of motion. The patient is able to complete light exercises with therapist supervision around four weeks after surgery. More intensive strengthening exercises begin around three months after surgery.

Therapy programs provided by an occupational or physical therapist will vary depending on each individual’s demonstrated deficits. These programs typically include splinting in cases of overuse, as well as exercises to improve coordination, strengthening, and range of motion of the upper arm and shoulder joint.

The purpose is also for the education on equipment use to compensate for some loss of function during the healing process and for the practice of daily activities which may be more difficult to do since the injury and/or surgery.

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