Sternum or Breastbone

Referred to as the ‘breastbone’ or ‘breastplate bone,’ the sternum is the cornerstone bone to which the ribs connect. It forms the hub of the thoracic cage or ribcage, playing a pivotal role in safeguarding the heart, lungs, major veins and arteries. The coinage of ‘sternum’ is attributable to the ancient Greek word ‘στέρνον’ or ‘sternon’ (interpreted as hard, tight, firm, or solid) which refers to the chest.

Location & Size

Sternum lies alongside the median plane of the body in the frontal thoracic cage. It is nearly six inches long, about an inch in width and approximately 1/4th inch thick. Of all the long flattened and large bones of the human skeleton system, the sternum happens to be one. The bone in adult males is considerably longer than females.

Structure of Sternum

The bone has a narrow, plane, an elongated structure and somewhat resembles a necktie. It occupies the central section of the frontal part of the chest or thoracic cavity.

  • The uppermost section is overlaid by the interclavicular ligament running through the arms, the chest and it’s posterior.
  • Just beneath is the jugular notch and this indentation forms the gateway to manubrium.
  • The collarbones (clavicles) are bones lying on either side of the manubrium that serves as a link between the breastbone and the scapula.
  • Also linked to the entire length are the ribs of the ribcage. Of the 12 pairs of ribs:
    • The first seven attach directly to the sternum bone at sternocostal joints through their costal cartilages.
    • 8-12 connects to the vertebrae from the back and do not directly link with the sternum at the front. Hence these pairs are called false ribs. The 8th, 9th, and 10th rib pairs connects with the breastbone indirectly through the upper ribs’ costal cartilages.
    • The last two pairs, (11th and 12th) do not connect to the breastplate bone, directly or indirectly. Therefore, the 11th and 12th rib pairs are collectively called floating ribs.

The sternum is positioned obliquely, converging frontally and concaving at the back to some extent. It starts at the manubrium until meeting the body following which it widens, and then again tapers until the end tip of the xiphoid process.

Parts of the Sternum

Manubrium

The topmost part manubrium is also the broadest of all the three sections. Shaped somewhat like a quadrangle, the manubrium has a tapering form. The suprasternal or the jugular notch of the sternum is right at the center of the manubrium, and the clavicular notches lie on its left and right extremities.

It extends up to the sternum body and connects with the 1st rib pair of the rib cage via the costal cartilage and the shoulder blades (clavicles). Its lower border is ovular with a rough surface and thinly layered with cartilage for connecting with rest of the skeleton. The pericardium of the heart connects with the manubrium at the rear through the sternopericardial ligament.

Body of Sternum

Also called gladiolus, it happens to be the most extensive part. It has a flat surface and projects slightly upwards along with three distinct slanting ridgelines. The ‘pectoralis major’ muscle of the chest is linked to the body on its right and left side.

An opening known as the sternal foramen (or perforated sternum) is sometimes visible at the intersection of the body’s 3rd and 4th divisions. Its backside which is relatively curved also has three sloping striations that are less prominent than the frontal ridges. The transversus thoracis muscle located on the chest’s front wall originate from either side of the gladiolus’s inferior section.

The points where the manubrium connects the body are known as the synarthrotic joint or the sternal angle. The frontward projection of the human sternum is maximized at this point. The 2nd rib pair of the thoracic cage which connects to the breastbone at the sternal angle is a significant marker during medical checkups.

Every facet of the body’s upper part merges with a corresponding facet of the manubrium to form a depression for receiving the 2nd rib’s cartilage. Cartilages of four successive rib pairs (3rd, 4th, 5th, and 6th) are joined with the body at the four consecutive cavities beneath the depression for the 2nd rib. A small depression on the body’s lower surface coincides with its counterpart on the hypnotic process, forming an indentation for receiving the 7th rib’s cartilage.

Xiphoid Process

The lowermost division is called the xiphoid process and is sometimes referred to as ‘metasternum’ or ‘xiphisternum.’ Shaped like a tapering faucet and a small triangle in adults and newborns, it originates as a cartilage gradually turning into a bone. Eventually, the end of the sternum merges with the sternum body.

It is situated just below the sternum body and is practically its fused extension. Occasionally, called the ‘ensiform process,’ (a Latin derivative standing for sword-like), the expression ‘xiphoid’ (process) is a variant of the Greek term xiphoid (meaning sword-like). Its naming is indicative of its narrowing structure that is pointed at the extremity.

It is broadest at its upper end where a sinewy joint known as ‘syndesmosis’ connects it to the mid-sternum. The tapering of the inferior part of chest bone starts from syndesmosis till it becomes a tip at the end. Its profile is however not always identical and sometimes varies.

Deviations from Xiphoid Process

The most commonly observed deviations include:

  • Fissuring & branching off on the right and left at the lower end
  • A hole with a tiny foramen or opening in the middle

However, these anatomical anomalies might be hereditary and do not in any way affect the normal functioning of the xiphoid process. In a newborn, it is cartilaginous, developing from hyaline cartilage, transforming into a bone via the ossification process. Nevertheless, owing to the extreme slowness of the process (of ossification), it becomes entirely bony only when one is 40.

Importance of the Xiphoid Process

Many significant muscles link to the breastplate bone through the xiphoid process. It serves as one of the originating points for the thoracic muscle (diaphragm) that separates the abdominal cavity from the thoracic cavity and lies at the ribcage’s base. It also serves as an entry point for the ‘transverse abdominis’ and ‘rectus abdominis’ muscles that facilitate abdominal expansion and contraction.

During SCA (sudden cardiac arrest), a medical emergency, the bystander or the healthcare professional, first, try to locate it for performing CPR (cardiopulmonary resuscitation). So, it serves as an essential pointer for conducting chest compressions to revive the dying individual or patient. Improperly administered CPR could lead to the breaking of the xiphoid bone which could perforate through the diaphragm to reach the liver, thereby causing mortal hemorrhage.

Growth & Development of Sternum

Following birth, cartilaginous bars connected to costal cartilages on either side of the ribcage begin to merge along the midline causing the development of sternum. Hence it in its formative stage is cartilaginous structurally. Eventually, the appearance of ossification centers takes place at four distinct stages of life, starting from the prenatal to postnatal phase, resulting in six separate regions.

Of the six centers:

  1. One is for manubrium
  2. The next four for the sternum body
  3. The last develops into the xiphoid process.

The emergence and development of the divisions happen during the sixth and seventh months of gestation, in the first year following birth, and finally from the fifth till the eighteenth year.

The appearance happens in a descending order i.e. the upper segment emerge first followed by the succeeding ones. More often than not, numerous centers fuse or join together to become a segment. In sporadic cases, the sternum’s upper part could be segmented by small cracks or crevices.

The different divisions of the sternum body start merging during an individual’s teenage years, and the unification is completed by 25. The xiphoid process generally links with the body when one is in his or her forties, though it sometimes connects when the person is 30. However, it could remain separate in some individuals even when they grow old.

Clinical Significance

Congenital Sternal foramina

Congenital sterna foramina or sternal opening is a relatively rare disorder that is genetically inherited. A single foramen or hiatus is present in the body of the sternum right from birth and usually is asymptomatic. The formation of the foramen usually covers the body’s 2nd, 3rd, and 4th subdivisions.

Bone marrow examination site

When it comes to conducting bone marrow diagnostic assay, the breastbone serves as a significant site as it is rich in bone marrow. Especially for patients who are excessively obese or overweight, extracting bone marrow is from this site. It is so because accessing the same from the usual sites becomes problematic owing to the dense layer of tissues.

Dislocation

Disarticulation or dislocation of the sternum, in most of the cases happens due to severe stress (trauma) but is somewhat rare. If someone with arthritis suffers an injury, even a minor one, he or she becomes vulnerable to chest bone disarticulation.

Fractures

Ruptures related to the human sternum or sternal fractures are infrequent as well. Although fractures are rare, when they happen, the bone pulverizes typically or becomes powdery. Such fractures occur during fatalistic car mishaps, participation in rugby, football, and soccer fixtures and during boxing matches. Fractures of the sternum often cause lung tissue and pulmonary contusions.

Resection

While performing surgery for the treatment of sarcoma or melanoma that typically involves ‘mediastinal lymphadenectomy’ (surgical excision of lymph nodes), the sternum is completely excised. This removal of the breastplate bone by a surgical method is called resection.

Sternal Cleft or Bifid Sternum

When the different parts or sections of the breastbone fail to fuse, it results in ‘bifid sternum’ or ‘sternal cleft.’ The sternal cleft is an inherited disorder that is extremely rare and since it is asymptomatic, diagnosing it can be tough. More often it is related to other congenital diseases, and if the anomaly is detected during birth, it should be treated surgically within a month.

Sternotomy

While carrying out a cardiothoracic surgery, an incision (median sternotomy) is made in the chest bone for accessing the ribcage.

Problems Related to the Sternum

The human sternum forms the hub of the thoracic region, serving as the junction and transitional point for many muscles, ligaments, cartilages, bones, and bone joints. These bone joints, muscles, and cartilages aid motion in the arms, neck, and head. Any damage or injury in the sternal area could cause numerous complications (some of which could be severe):

  • Sternal Fracture: Costal cartilages are linking the ribs to the sternal region also acts as a cushioned sheath safeguarding the chest bone from damages. Nevertheless, it can get fractured or disarticulated if excessive force is applied during CPR. It leads to xiphoid fracture or a part of it, in the majority of the cases.
  • Post Surgical Issues: After conducting a cardiothoracic surgery for operating a particular organ inside the ribcage, the sternum’s split halves are sutured using stainless steel wires. But there always runs the risk of it damages if the same is subjected to intense stress (like performing strenuous workouts or hauling heavy objects). Such stressful activities could lead to snapping of the steel wires resulting in the halves coming unstuck.
  • Sternal Pain: An injured, broken or fractured sternum could cause acute pain. And regardless of the extent of the damage, the pain is usually extreme owing to its central location. One would experience midsternal pain to some extent even during inhalation and exhalation.

What causes pain in the sternum area?

You could mistake sternal pain for an SCA (sudden cardiac arrest) or heart attack, particularly if you’re less than 40 years old. Due to sternum being at the core of the thoracic and abdominal cavities, you might experience pain in the breastbone and the adjacent region whenever something affects one or more of the linked organs.

Costochondritis is behind most sternum pain complaints

Inflammation of the costal cartilages or ‘costochondritis, the leading cause of sternal pain. There is no specific etiology for costochondritis, but the condition usually results from stressful physical activity, chest injury or osteoarthritis. Though it is not a condition to worry about, consider consulting a physician in case the pain continues.

Other Musculoskeletal Conditions

  • Injury or damage to Sternoclavicular joint
  • Fractured or broken sternum
  • Injured or wounded clavicle (collarbone)
  • Cardiothoracic and cardiovascular surgeries
  • A hernia or muscle strain/Hiatal hernia

Other Gastrointestinal Conditions

  • GERD (gastroesophageal reflux disease)
  • Heartburn

Other Respiratory Conditions

  • Pleurisy
  • Pneumonia
  • Bronchitis

What other conditions cause sternum pain?

  • Depression or anxiety disorder that causes a panic attack
  • Peptic ulcer
  • Heart attack (especially if you are in your forties or above)

Symptoms of Sternum Pain

Pain and discomfiture in the middle of the chest is the most reported sternal pain symptom. Other common symptoms comprise:

  • Pain on the application of pressure on the chest
  • Experiencing pain in the ligaments, muscles, bones, and cartilages linked to breastplate bone while stretching or contracting
  • Pain while you’re eating or after completing a meal
  • Feeling pain when lifting weights, exercising, swimming, running, jogging, and performing other physically demanding activities
  • Excessive physical or mental stress
  • Discomfiture or pain in ribs
  • The pain felt during coughing or inhalation
  • Inflammation or soreness in upper chest
  • Collarbone swelling or bruising
  • Heartburn
  • Recurrent belching
  • Shortness of breath

Sternum Pain vs. Heart Attack

Most of us tend to assume chest pain, irrespective of its nature, as a symptom of a looming heart attack. It is so because many symptoms associated with heart attack overlap with sternal pain signs. Pain in the thoracic cavity (where the sternum is located) is not only indicative of a cardiac arrest but could point to other conditions as well.

Symptoms that are common to both sternum pain and heart attack include:

  • Dizziness
  • Difficulty in breathing
  • Nausea
  • Perspiration
  • Feeling of tightness, fullness or heaviness in the chest

A few symptoms that are exclusive to heart attack:

  • Gradual change in the pain process that lasts for a while
  • Burning, tightness, squeezing, pressure or pain sensation
  • Continuous midsternal chest pain
  • Diffusing pain felt in the neck, left arm, upper back or jaw
  • Feeling of pain while undergoing emotional stress, performing a physical activity or during rest

Specific treatment for different types of sternum pain

Treatment for sternum soreness

Compress the affected area with ice pack may help lessen tenderness.

Treatment for a sternal fracture

  • Visit your physician who might recommend a sternum x-ray
  • Dislocated or fracture might necessitate surgical intervention
  • Complete rest following surgery
  • No laborious activity until the operated area recuperates fully

Treatment for collarbone trauma

  • Consult a physician as soon as possible
  • The doctor will recommend you to put on a sling going around your neck and one of the shoulders. You may have to wear the brace for 5-8 weeks.

Heartburn treatment

  • Antacids help restore pH balance of stomach
  • Drink a glass of water with baking soda (one teaspoon)

Treatment for pleurisy

  • Rest sufficiently
  • Try resting on the side where you feel the maximum pain. Antibiotics will help assuage bacterial or pneumonic infection.

Treatment for Costochondritis

Application of ice pack or heat may help get relief from inflammation. Stay away from contact sports or any activity that is physically demanding.

Sternoclavicular dislocation or injury treatment

  • Abduction brace or shoulder sling (depends upon the extent of dislocation)
  • Cold therapy for restoring healthy blood circulation
  • Staying away from any strenuous physical activity
  • Surgical treatment if injury or disarticulation is severe

References

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