Introduction

The xiphoid process is the most distal edge of the sternum or the breastbone. The sternum contains 3 major portions: the manubrium, the body, and the xiphoid process. Its name comes from the Greek word "xiphos," which means straight sword.[1] The xiphoid process articulates with the distal portion of the sternum and is termed the xiphisternal joint. Externally the xiphoid process can be located in the epigastric region of the anterior thoracic wall.[1] It is about 2 to 5 cm in length and is triangular. At birth, the xiphoid is pure cartilage. The xiphoid process is made up of 2 types of cartilage. It contains hyaline cartilage in the proximal portion and contains elastic cartilage in the distal portion.[2] As humans age, the xiphoid process ossifies, although there are variations in when this process begins.[1]

Structure and Function

The main function of the xiphoid process is to serve as a muscular attachment. It serves as an attachment on its anterior surface for the rectus abdominis muscle as well as an attachment for the aponeurosis of the internal and external oblique muscles of the abdomen. Posteriorly there are attachments to the linea alba with the inferior portion. There are some attachments to the diaphragmatic muscle bundles (slips) posteriorly; these are muscular fibers of the diaphragm that extend from the central tendon.[3] There are also costoxiphoid ligaments between the ribcage and the xiphoid. [1]

Embryology

There is great variation in the maturation and development of the sternum and xiphoid process.[4] There is a large variation in the size and shape of the xiphoid process, from deviations in the location of the xiphoid process to ventral curving the process itself. As stated above, it is commonly formed from 2 types of cartilage.[2] The xiphoid process starts out as a cartilaginous structure but begins to ossify, with age, from the superior portion to the inferior portion of the structure.[1] The xiphoid process commonly has1e and rarely has 2 foramina that have little to no significance to the purpose or function of the xiphoid process.[1] There is a facet located on the superior portion of the xiphoid process that articulates with the seventh costal cartilage.[5]

Blood Supply and Lymphatics

The blood supply to the xiphoid process is derived from perforating branches from the internal thoracic artery, once known as the internal mammary artery.[1] The internal thoracic artery is a branch from the subclavian artery superiorly around the midclavicular line.

Muscles

There are multiple muscular attachments to the xiphoid process. The main muscle attachment to the anterior portion of the xiphoid process is the rectus abdominis. The aponeurosis of the internal and external oblique abdominal muscles also attach to the anterior portion of the xiphoid process. The posterior portion contains attachments of the diaphragm, transverse thoracis, and ligaments from the costal cartilage termed costoxiphoid. The linea alba also attaches inferiorly to the xiphoid process. [1]

Surgical Considerations

The xiphoid process is an important landmark for cardiac surgeons when opening the sternum during open heart surgery. It gives an indication of the midline and provides a location where the surgeon should place the mechanical saw when opening the breastbone. Once the xiphoid process is removed, the surgeon can place the finger under the sternum and bluntly dissect away the pericardial attachments. It is vital that these attachments from the xiphoid be dissected bluntly away before the surgeon inserts the saw. Otherwise, it can lead to injury to the diaphragm, lungs, or even the heart. The xiphoid is also used as a landmark to determine the location of the hands during cardiopulmonary resuscitation (CPR). It is important for the person performing CPR not to compress at the xiphoid as the bone is very soft. Compression of the xiphoid cannot only lead to fracture of the xiphoid but can lead to serious trauma to the liver, spleen, heart, and diaphragm. During pericardiocentesis, the health care provider usually feels for the xiphoid and directs the needle underneath the xiphoid pointed toward the left shoulder.[6] Other surgical considerations of the xiphoid process include xiphoidectomy, the removal of the xiphoid process, and it is commonly used to increase visualization during a total gastrectomy. It has been shown to improve safety during the surgery due to increased visualizations of important structures.[7]

Clinical Significance

The xiphoid process has many anatomical variants, but this does not have any functional or aesthetic significance. In some cases, it may be flat, and in others, it may be protruding at the distal end of the sternum. The xiphoid is a rudimentary bone, and it is often without harm to the patient.[8]. Cardiopulmonary resuscitation (CPR) is an imperative procedure that is performed on a patient whose heart has stopped beating. Through the process of CPR, the sternum and ribs are at an increased chance of fracture that can lead to further injury of internal organs such as the liver or lungs. The xiphoid process being at the distal tip of the sternum is also at an increased chance of possible fracture and dislocation leading to further internal organ injury or laceration. The liver is a common organ that can be injured with CPR and fracture with the dislocation of the bony structures during the procedure. Knowledge of proper CPR techniques and the possibility of these fractures are imperative to all medical providers and staff.[9]. 

Xiphoid syndrome is an uncommon diagnosis that presents as a painful swelling and discomfort located over and around the xiphoid process. There are limited research and case presentations related to xiphoid syndrome, but it has been described in several case studies of individuals with tenderness to light pressure over the xiphoid process and should be considered in patients presenting with epigastric tenderness upon palpation of this region.[10]

Xiphodynia is an uncommon syndrome described mainly in chiropractic literature. It is used to describe a correlation of symptoms ranging from upper abdominal pain, chest pain, throat, and arm pain all deriving from pain in the xiphisternal joint or radiation from structures attached to the xiphoid process. Often this syndrome can go undiagnosed for many years. Several case reports discuss the used of local injections around the xiphoid process that improve the symptoms of xiphodynia.[5]