Anatomy, Thorax, Xiphoid Process (2024)

Introduction

The sternumconsists of 3 major parts;the manubrium, the body, and the xiphoid process, with the xiphoid process being the smallest and most distalpart of the three. The manubrium is the broad, quadrangular, and most superior segment and is characterized by its superior dip known as the suprasternal notch. The body is the middle and longest part and connects to the manubrium at the sternal angle. The xiphoid process is triangular in shape and is the most distal part of the sternum.[1]See Image.Sternum Anatomy.

The term xiphoid process comes from the word "xiphos," which is of Greek origin and means straightsword describing the morphology ofthis bone.[2]It is approximately 2 to 5 cm in length. The xiphoidvaries in shape and size; it is primarily triangular, with its base directed superiorly and thetip pointing inferiorly at the level of the T10 vertebra. The base of the xiphoid process articulates with the distal end of the sternal bodyformingthe xiphisternal joint. Unlike the suprasternal/ jugular notch at the superior end of the manubrium of the sternum, palpating the xiphoid process can sometimes be challenging.Externally the xiphoid processis located in the epigastric region of the anteriorthoracic wall.[2]

At birth, the xiphoid is purely cartilaginous and is made of 2 types of cartilage; hyalinecartilage in the proximal portion and elastic cartilage in the distal part.[3]With age, the xiphoidprocess ossifies; the ossification age is vastly variable.[2]

Structure and Function

The median location of the sternum in the thoracic cage and its attachment to the costal cartilage allow it to function as a protective bone to the underlying mediastinal structures.[1]The primary function of the xiphoid process is to serve as a point for muscular attachment; several muscles and ligaments attach toits different surfaces.

The anterior surface of the xiphoid process is primarily occupied by theinsertionof the flat longitudinal muscles of the anterior abdominal wall. The rectus abdominis muscle serves as a strong trunk flexor and stabilizer. The aponeurosis of the internal and external oblique muscles also attaches to the anterior portion of the xiphoid process. These abdominal muscles, together with other core muscles, function to stabilize the trunk and assist in increasing intra-abdominalpressure.[4]

The seventh costal cartilages attach to bilateral demifacets to form thecostoxiphoid/ chondroxiphoid ligament.These demifacets are located on the superior end of the xiphoid, precisely at the point where it articulates with the sternal bodyto form thexiphisternal joint.[6]In addition, the transverse thoracis muscle attachesto the posterior and sometimes anterior surfaces of the xiphoid process.[7]Besides these muscular attachments, the inferior surface or the tip of the xiphoid process also provides a point of attachment for the linea alba.[2]

Embryology

The embryological development of the sternum follows a highly variable pattern in terms of age and location of ossification.[1]The sternum develops from bilateral mesenchymal platesduring the early weeksof gestation. These sternal plates or bands eventuallyfuse in the midline around the 7th week of embryonic development. This fusion starts at the cranial end of the bands and is generally complete by the 9th to 10th weeks. Until this stage, the three sternal parts would not bevisibleyet; as the embryonic sternum develops, the body, manubrium, and xiphoid process start to take shape.

Ossification of these three different sternal parts starts and completes at varying timesfollowing a craniocaudal direction. The manubrium and body begin to ossifyaround the 6th month of gestation and continue through the 1st postnatal year.Similarly, the ossification process of the xiphoid cancontinueup to the early years of childhood or late teenage (5th to 18th year).[8]Likethe variation in shape and size of the adult form of the xiphoid process, its maturation and development vary considerably.[9][3]Interestingly, some literaturemarksthe age of xiphoid process ossification as late as 40 to 60 years.[1]

Blood Supply and Lymphatics

The sternum is considered a highly vascular structure, receiving most of its arterialsupply through perforating and sternal arterial brancheslocated around the intercostal spaces.[10]The blood supply to the xiphoidprocess is derived from multiple perforating branches originating from the internal thoracic artery,alsoknown as the internal mammary artery. The right and left internal thoracic arteries are located parallel to the sternum. Before bifurcating into thesuperior epigastric andmusculophrenicarteries at the levelof the 7th intercostal space,The internal thoracic artery gives off multiple perforating and sternal branches to supply the xiphoid process (and the sternum in general).[2]The internal thoracic artery is a branch of the first part of the subclavian artery and supplies the sternum and other mediastinal structures.[11]

The venous drainage of the xiphoid process follows a similar pattern and is collected back through the internal thoracic veins, which empty directly into the right and left brachiocephalic veins.[1]

Nerves

Due to its anatomical proximity to the intercostal spaces, the sternum, including the xiphoid process, is supplied by the intercostal nerves from the T1-T11 segments.[12]The xiphoid process is located at the level of the T6skin dermatome of theupper thorax.[13]

Muscles

Multiple muscles are attached to different surfaces of the xiphoid process. The anterior surface of the process is primarily occupied by theinsertionof the flat longitudinal muscles of the anterior abdominal wall, including the rectus abdominis muscle which serves as a strong trunk flexor and stabilizer. In addition, the aponeurosis of the internal and external oblique muscles also attaches to the anterior portion of the xiphoid process. These abdominal muscles, together with other core muscles, function to stabilize the trunk and assist in increasing intra-abdominalpressure.[4]

Theposteriorsurface of the xiphoid process serves as anattachment point for several structures; the most important is the attachment of the diaphragmatic muscular slips providing the diaphragm with its fundamental contractile function in respiration.[5][2]In addition, the transverse thoracis muscle attachesto the posterior and sometimes anterior surfaces of the xiphoid process.[7]

Physiologic Variants

The xiphoid process is considered a variable bone, and most commonly, it varies in shape. It has been reported in the literature that the xiphoid process can take differentshapes, from thin to broad. Its pointed distal end may also be curved or bifid. Some case studies have reported xiphoid foramina or a non-ossified xiphoid, which are considered unusual variations.In-depth knowledge and awareness of thesevariations are essential as they may lead to misdiagnosis, primarily due to their proximal anatomical relationship to vital structures in the thoracic and abdominal regions.[2]

Surgical Considerations

The xiphoid process is an important surgical landmark, especially in cardiac surgery. For example, in open-heart surgeries, thisthoracicbone is used as a landmark for locating the midline while determiningthe exact location to place a mechanical saw before cutting through the sternum. It is imperative that theattachments of the xiphoid process are detached before insertinga saw to avoid injury to the diaphragm, lungs, or even the heart. Once the xiphoid process is detached, surgeonsutilize a blunt dissection method to detach the sternal pericardial attachments by inserting afingerposteriorto the sternum and bluntly dissecting from inferior to superior.

During pericardiocentesis, healthcare providers usuallypalpatefor the xiphoid process andaim to insert the needle directly underneath the xiphoid, pointing toward the left shoulder.[14]

Other surgical considerations of the xiphoid process includexiphoidectomy, the removal of the xiphoid process,whichis commonly used to increase visualization during a totalgastrectomy. This procedure has been shown to improve safety during surgery due to increasedvisualization ofvital organs andstructures.[15]

Clinical Significance

The xiphoid process is used as a landmark to determine the correct location for hand placement during cardiopulmonary resuscitation (CPR). It is essentialwhile performing CPR not to compress at the xiphoid process as this boneis very soft, which may lead to fracture of the xiphoid and can lead to severe trauma tounderlying vital organs such as the liver, heart, and diaphragm.[16][17]Knowledge of proper CPR techniques and the possibility of these fractures are imperative to all medical providers and staff.[18]

Xiphoid syndrome is an uncommoncondition presenting as painful swelling and discomfort around the xiphoid process and the epigastric region. Thereare limited research and case presentations related to the xiphoid syndrome. However, case studies describing this syndrome have documented that patients complain of tenderness andlight pressure over the xiphoid process.[19]This uncommon syndrome is described mainly in the chiropractic literature as it is primarily considered to be associated with mechanical thoracic trauma or lifting heavy objects.It isusually described as a combinationof symptoms, including diffuse epigastric pain due to inflammation of the xiphoid process. Patients also present with discomfort and pain in various body regions, the upper abdominal region, the chest, and the xiphisternaljoint. The discomfort and pain can even radiate distally to the throat and the upper extremity.

The diffuse nature of pain in the xiphoid syndrome can be explained as pain referred from the inflamed joint itself, the xiphesternal joint, or radiating from the structures attached to the body of the xiphoid. Because xiphoid syndrome is an uncommon and under-describedsyndrome, patients can go undiagnosed for many years. Several case reports discuss the use of local anesthetic or steroidal injections around the xiphoid process leading toimprovement of the symptoms of xiphodynia.[6]

Review Questions

Figure

Sternum Anatomy. The sternum anatomy includes a jugular notch, manubrium, sternal angle, body, xiphoid process, clavicular notch, and facets for attachment of costal cartilages 1-7. Contributed by B Palmer

References

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: Disclosure: Bradley Anderson declares no relevant financial relationships with ineligible companies.
: Disclosure: Matthew Holme declares no relevant financial relationships with ineligible companies.
: Disclosure: Leena Alkhammash declares no relevant financial relationships with ineligible companies.
: Disclosure: Bracken Burns declares no relevant financial relationships with ineligible companies.