Humerus Bone Disorders

Humerus Bone:  An overview

The long bone that connects the shoulder to the elbow is called humerus.  From the elbow, it connects to the ulna which subsequently connects to the wrist from the radial bone.  The glenoid fossa of the scapula connects the humerus at the shoulder joint.  Numerous muscles and ligaments are attached to the humerus causing multiple raised surfaces on the bone surface.

Anatomy of the Humerus Bone

Proximal Region:  A round and thin neck and couple of tubercles account for the upper portion of the humerus.  The greater tubercle is situated sideways and consists of both anterior and posterior face.  The rotator cuff muscles namely the supraspinatus, infraspinatus and teres minor connect to the greater tubercle.  On the other hand, the lesser tubercle is situated in the middle and only has an anterior face.  Only one rotator cuff muscle called subscapularis muscle connects to the lesser tubercle.  Both the tubercles are separated by a deep groove called intertubercular sulcus and the groove edges are called lips.  Three muscles connect to the lips namely the pectoralis major, teres major, and the latissimus dorsi.

Shaft:  The deltoid tuberosity and the radial groove accommodate the humerus shaft.  The deltoid tuberosity is present in sideways with a rough structure where the deltoid muscles attach themselves.  The radial groove is placed parallel to the deltoid tuberosity and extends diagonally along the posterior surface.  Numerous muscles attach to the humerus shaft namely the coracobrachialis, deltoid muscles, brachialis, brachioradialis, as well as the lateral and medial heads of the triceps.

Distal region:  The distal humerus is the elbow joint.  Two epicondyles, capitulum process, trochlea process, radial fossa, coronoid fossa, and the olecranon fossa are all present in the lower portion.  The trochlea process is situated in the middle and extends onto the posterior portion.  The capitulum is beside the trochlea and joins with the radius bone.  Radial fossa, coronoid fossa, and olecranon fossa are the depressions on the forearm when the arm is being moved.

Humerus bone innervation:  Three important nerves namely the axillary nerve, radial nerve, and the ulnar nerve connect the humerus.  The axillary nerve connects at the proximal side of the bone.  Dislocation of the shoulder leads to axillary nerve damage and results in loss of regular shoulder contour.  The radial nerve connects from behind the bone in the spiral groove.  Fracture at this point may damage the radial nerve.  The distal region of the bone contains the ulnar nerve.  The tingling sensation caused when the elbow gets hit is due to the presence of the ulnar nerve.  Since this nerve is situated in front of the medial epicondyle, there are higher chances of it getting damaged during an elbow injury.

Blood Supply to the humerus bone:  Anterolateral branch of the anterior humeral circumflex artery provides the blood supply to the humerus bone.  The anterolateral branch passes beside the biceps forming arcuate artery and entering the head of the humerus in the intertubercular groove.  This artery then branches out into multiple tuberosities.

Functions of the Humerus Bone

The humerus bone assists in several movements with respect to the shoulder and the elbow joint.  It is also responsible for attaching several muscles and ligaments that aid with shoulder and elbow movements.  Adduction and extension of the shoulder joint are accomplished with the use of deltoid muscle which is inserted on the deltoid tuberosity.  Adduction and internal rotation of the humerus are accomplished with the help of pectoralis major, teres major, and the latissimus dorsi.  Any physical activity involving the arm such as lifting objects is accomplished with the help of humerus bone.  The humerus bone not only helps with movement and support to the muscles but also acts as an anchor to the three main nerve roots namely the axillary nerve, radial nerve, and the ulnar nerve.

Fractures associated with the humerus bone

The fracture can occur to the humerus bone at three main locations and these include:

• Proximal humerus fracture: This type of humerus fracture occurs at the top portion of the humerus bone which joins the shoulder.
• Midshaft: A mid-shaft fracture occurs when the humerus bone is fractured in the middle between the shoulder and the elbow joint.
• Distal humerus fracture: A fracture occurring near the elbow joint is considered a distal humerus fracture.  This is a more complex fracture and may involve other corresponding bones.

Symptoms and causes of humerus fracture

Falling down is considered the biggest cause of humerus fracture.  Since the bone is connected to two important joints, there is a high possibility that the joints may become dislocated even with a limited amount of pressure.  Pain accompanied by swelling and discoloration at the site of fracture is some of the common symptoms.  Since three main nerve roots pass through this bone, damage to the bone may also affect the nerves.  This can lead to loss of blood supply as well as a tingling sensation in the hand.  Fractures occurring at the tip of the proximal and distal region can lead to shortening of the bone, which needs correction with the help of surgery.  A nondisplaced humerus fracture generally only requires rest to heal.  Supportive brace and immobilization are two key factors for fast healing of the bone fracture.

Treatment for humerus fractures

Proximal humeral fracture:

Majority of proximal humerus fracture can be treated non-surgically when the bone fragments are intact.  Displacement of the bone fragments requires surgical repair of the fracture.  Treatment without surgery involves the application of a sling or shoulder immobilizer for a couple of weeks.  This is followed by physical therapy exercises to improve the shoulder’s range of motion.  A biweekly x-ray is taken of the shoulder to monitor the healing of the proximal fracture.

If the fragments are displaced or scattered, the surgical route is required to treat the fracture.  The fracture fragments require plates and screws to fix the fragments in place.  If the fragments are severely damaged or have joint degradation, shoulder replacement surgery is recommended.  Initially, a standard radiograph series of the affected shoulder is undertaken.  A standard radiograph series consists of an AP view of the glenohumeral joint, scapular-Y, and an axillary view.  Among these x-rays, the axillary view may cause some trouble to the patient and would require an assistant to hold the hand in place.  This x-ray is particularly important to assess if the humeral head or the tuberosities are dislocated.

A CT scan may be ordered if there are any discrepancies in the radiographic series, especially for suspicion of coronal plane fracture of the humeral head.  Fracture and displacement of the tuberosities can be better viewed with the help of a CT scan.  Magnetic resonance imaging or MRI is generally not used for diagnosing proximal humerus fracture.  This imaging is used to determine any soft tissue injury which is usually associated with pre-existing rotator cuff pathology.

Humerus Shaft Fracture:

A humerus shaft fracture occurs in the middle of the humerus bone.  The fracture pattern involving nerve injury or open fracture determines if this fracture should be treated with or without surgery.  A temporary splint is used to treat it non-operatively, which is placed from the shoulder to the forearm.  The splint is placed for around three to four weeks and after examination, the doctor will decide if the splint has to be removed or continued.  Humerus shaft fracture may take weeks to months to heal and requires complete rest.

On the other hand, surgery requires fixation of fragments with the help of plates, screws, and nails.  A sling is placed after the surgery to provide comfort.  Since the fracture takes a few weeks to heal, strengthening exercises are delayed depending on the extent of healing.

Humerus shaft fractures can be classified depending on the location of the fracture, if it is open or closed, as well as the bone condition.  Zuckerman and Koval classification is the most commonly used to identify the fracture.  According to Zuckerman and Koval classification, the proximal fragment would deviate towards abduction and external rotation if the fracture occurred above the insertion of the pectoralis major muscle.  Similarly, if the fracture occurs between the insertion of the pectoralis major and deltoid muscles, the proximal fragment would present adduction.

Distal humerus fracture:

Fracture occurring at the lower part of the humerus bone or the elbow joint is called distal humerus fracture.  This fracture is generally caused due to a high energy impact.  Majority of the distal humerus fractures are treated with the help of surgery.  A distal humerus fracture can occur in such a way that the fractured bone may penetrate the skin and be visible from the outside.  These fractures are generally rare and account for only 2% of all the bone fractures.  Simple elbow x-ray can determine the fracture.  Nonsurgical treatment is recommended only when the bone is not displaced severely.

In the majority of the cases, surgical repair is the most relevant treatment.  Open reduction and internal fixation is the most common surgical treatment for distal humerus fracture.  Depending on the severity of the fracture, the doctor may decide to do any of the following procedures such as ulnar nerve placement, bone grafting, osteotomy, total elbow replacement, which is also called arthroplasty, as well as arthrodesis

Complications

Majority of people would recover after a humerus fracture and retain their normal function and mobility.  There is a small possibility of complications associated with a humerus fracture and these include:

• Nonunion: A nonunion is a condition where the fractured bone fails to heal.  This may occur due to numerous factors.  The underlying cause needs to be ascertained and rectified appropriately.  Tobacco smoking is considered one of the reasons for nonunion.
• Malunion: A malunion of the bone occurs when the fractured bone heals with improper alignment.  Surgery may be required for the realignment of the bone.
• Nerve injury: Injury to the radial nerve is quite common when the humerus bone is fractured.  The radial nerve is responsible for providing sensation to the back of the hand.  Injury to this nerve may cause numbness and tingling sensation.  The nerve would require a few months to recover.
• Stiffness or weakness to the shoulder or elbow joint: Loss of range of motion due to fracture of the distal humerus or the proximal humerus can cause stiffness or weakness in the joints.  A muscle or tendon damage also can cause this problem.  Physical therapy exercises need to be started after the fracture has healed to promote an adequate range of motion.

References
https://www.verywellhealth.com/humerus-fracture-2549285
https://orthoinfo.aaos.org/en/diseases–conditions/distal-humerus-fractures-of-the-elbow/
https://www.hopkinsmedicine.org/health/conditions-and-diseases/humerus-fracture-upper-arm-fracture
https://www.healthline.com/health/humerus-fracture
https://www.ncbi.nlm.nih.gov/books/NBK482281/