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Xiphisternal joint

The xiphisternal joint, also known as the sternoxiphoid joint, is a cartilaginous symphysis that connects the inferior margin of the sternal body to the superior margin of the xiphoid process, the smallest and most distal part of the sternum.^[1]^[2] This joint typically begins as a fibrocartilaginous articulation but often ossifies into a synostosis (bony fusion) by around age 40, reflecting age-related changes in the sternum.^[1] Located at the level of the T9-T10 vertebrae, the xiphoid process measures approximately 2-5 cm in length and consists initially of hyaline cartilage proximally and elastic cartilage distally.^[2] The xiphoid process itself develops embryologically from bilateral mesenchymal plates that fuse by the 9th-10th week of gestation, with ossification beginning around the 6th month and progressing variably through childhood into adulthood, sometimes as late as age 60.^[2]^[3] Functionally, the joint serves as an attachment site for key structures, including the central tendon of the diaphragm posteriorly and the rectus abdominis muscle anteriorly, contributing to respiratory mechanics, trunk stabilization, and protection of underlying thoracic and abdominal organs such as the heart and liver.^[2]^[3] Clinically, the xiphisternal joint is significant as a anatomical landmark in procedures like cardiopulmonary resuscitation (CPR), where it guides chest compressions, and in cardiothoracic surgeries such as pericardiocentesis.^[2] It can also be involved in pathologies, including fractures from trauma (e.g., during accidents or sports), which may cause chest pain mimicking cardiac issues, and rare conditions like xiphoid syndrome, characterized by painful swelling treatable with rest, anti-inflammatory medications, or surgical removal if severe.^[2]^[3] Variations in xiphoid morphology, such as perforations or bifurcations, occur in up to 40% of individuals (e.g., bifid forms in 20-42.9%) and are usually asymptomatic but may influence surgical planning.^[2]^[4]

Anatomy

Structure

The xiphisternal joint is classified structurally as a symphysis, a type of secondary cartilaginous joint in which the articulating surfaces are directly united by fibrocartilage.^[5] This joint connects the inferior border of the sternal body to the superior aspect of the xiphoid process, forming a stable cartilaginous union that maintains the integrity of the lower sternum.^[6] The fibrocartilage at this interface provides a firm yet slightly flexible connection during early development, though it typically undergoes ossification in adulthood.^[2] Ligamentous reinforcements contribute to the stability of the xiphisternal joint through the costoxiphoid ligaments, also known as chondroxiphoid ligaments. These are inconstant fibrous bands that extend from the anterior and posterior surfaces of the seventh costal cartilage to the corresponding surfaces of the xiphoid process.^[7] By anchoring the xiphoid process to the adjacent costal structures, these ligaments help distribute forces across the lower thoracic wall and prevent excessive displacement of the joint components.^[8] Functionally, the xiphisternal joint is categorized as a synarthrosis, meaning it permits little to no movement, in contrast to synovial joints that feature a fluid-filled cavity enabling greater mobility.^[9] This immobility arises from the direct adhesion of fibrocartilage without an intervening joint space or synovial membrane, ensuring rigid support for the thoracic cage while accommodating minimal deformation under respiratory or postural stresses.^[6]

Location and relations

The xiphisternal joint is situated at the inferior end of the sternal body, corresponding to the level of the T9-T10 vertebrae, within the epigastric region of the anterior thoracic wall.^[2]^[10] The joint forms a triangular interface between the distal sternum and the base of the xiphoid process, with the articulation area typically measuring 2-5 cm in length along the xiphoid involvement.^[2] It is positioned anterior to the diaphragm and liver.^[2] Posteriorly, it relates to the central tendon of the diaphragm.^[2] Laterally, the joint connects to the seventh costal cartilages through the costoxiphoid ligaments.^[2] The region overlies superficial epigastric vessels and is in proximity to intercostal nerves, though the joint itself lacks direct innervation.^[2]^[11]

Development

Embryonic origins

The xiphisternal joint originates from the sternal anlage, which arises in the lateral plate mesoderm during weeks 6-7 of embryogenesis.^[12] Mesenchymal cells from the somatic layer of this mesoderm migrate ventrally to form paired longitudinal bands, known as sternal bars, on either side of the midline.^[12] These bars chondrify independently and subsequently fuse in the midline, starting cranially and progressing caudally.^[2] The xiphoid component specifically develops from the caudal extensions of these paired ventral cartilage bars, which extend beyond the attachment of the seventh rib and fuse to form the distal sternal element.^[13] The initial cartilage formation occurs through the differentiation of these mesenchymal cells into chondroblasts, producing hyaline cartilage models that establish the foundational structure of the sternum.^[12] This process begins around the fifth to sixth week, with the paired models uniting to create a continuous cartilaginous plate by the seventh week.^[14] By the fetal stage, the xiphisternal articulation is defined as a synchondrosis, a cartilaginous joint united by hyaline cartilage, providing flexibility in the developing thoracic cage.^[15] At birth, the xiphoid process remains entirely cartilaginous, composed primarily of hyaline cartilage proximally and elastic cartilage distally, and is often palpable as a small, firm midline lump inferior to the sternal body in infants.^[2] This prominence is a normal finding and reflects the incomplete midline fusion and lack of early ossification in the region.^[3] Rare congenital variants, such as a bifid or absent xiphoid process, arise from disruptions in midline fusion and have been linked to altered Hox gene expression patterns, as demonstrated in developmental models where Hoxb5 and Hoxb6 mutations lead to similar sternal defects.^[16]

Ossification process

The ossification of the xiphisternal joint, which connects the xiphoid process to the body of the sternum, occurs through endochondral ossification, a process in which hyaline cartilage is progressively replaced by bone. This begins around the 5th to 6th month of gestation with the appearance of ossification centers within the cartilaginous xiphoid process, with postnatal progression variably from ages 5 to 18 years, though earlier in some cases.^[2]^[17] The mechanism involves chondrocyte hypertrophy, where cartilage cells enlarge and secrete matrix that calcifies, followed by vascular invasion that delivers osteoprogenitor cells to form bone tissue, ultimately creating a symphysis xiphosternalis—a secondary cartilaginous joint that may fuse into bone.^[18] The progression of ossification is highly variable, with centers expanding and merging irregularly in a craniocaudal direction, influenced by factors such as hormonal regulation (including sex hormones and parathyroid hormone) and mechanical stress from thoracic movements.^[2]^[19] In most individuals, complete synostosis or bony fusion of the xiphisternal joint occurs between ages 40 and 60, with mean ages around 45-46 years; fusion before age 37 is uncommon.^[2]^[20] Incomplete ossification may result in a persistent fibrous union, where the joint retains some cartilage or fibrous tissue rather than fully ossifying.^[2] Post-ossification, the joint typically becomes rigid, contributing to the stability of the thoracic cage in adulthood; however, if fusion remains incomplete, partial mobility may persist, potentially allowing slight movement under stress.^[18]^[2] This age-related rigidity enhances structural integrity but can vary based on individual developmental patterns.^[20]

Function

Structural role

The xiphisternal joint, classified as a synchondrosis, forms a cartilaginous articulation between the inferior margin of the sternal body and the superior aspect of the xiphoid process, contributing to the overall rigidity of the thoracic cage.^[2]^[15] This immovable connection ensures the sternum functions as a unified structure, enhancing the mechanical stability required for supporting the rib cage during various physiological demands.^[21] By age 40, the joint often ossifies into a synostosis, further solidifying its role in maintaining thoracic integrity.^[5] In its protective function, the xiphisternal joint reinforces the inferior sternum, shielding underlying organs such as the heart, liver, and diaphragm from potential trauma.^[21]^[2] It integrates with the costal cartilages, particularly the seventh, to strengthen the costal arch and preserve the rib cage's form during respiration and upright posture.^[21]^[2] This reinforcement distributes external forces across the thoracic framework, preventing deformation that could compromise organ protection.^[2] As a synarthrosis, the joint's immobility provides a fixed base for the sternum, limiting excessive thoracic flexion and promoting postural stability.^[21]^[15] It serves as the distal anchor point for the sternum, effectively distributing mechanical loads from the manubrium and sternal body to the lower thorax.^[2]^[21] This load-sharing mechanism minimizes stress concentrations, ensuring the thoracic cage withstands compressive and tensile forces encountered in daily activities.^[2]

Attachments and biomechanics

The inferior surface of the xiphoid process, part of the xiphisternal joint, serves as the origin for the central tendon of the diaphragm, facilitating its contractile role in respiration.^[2] Slips of the rectus abdominis muscle also originate from this surface, contributing to abdominal flexion and trunk stabilization.^[2] Nearby, the transverse thoracis muscle inserts on the posterior aspect of the xiphoid process, aiding in rib depression during expiration.^[22] The costoxiphoid ligaments attach the anterior and posterior surfaces of the xiphoid process to the seventh costal cartilage, providing lateral stabilization to the joint and connecting the thoracic cage to the xiphoid structure.^[22] In terms of biomechanics, the xiphisternal joint exhibits minimal movement when cartilaginous prior to ossification, allowing slight flexibility that supports thoracic expansion during breathing.^[2] Following ossification, often by around age 40, the joint becomes more rigid, transmitting forces from the upper sternum to the abdominal wall without significant displacement, which is essential during exertion such as coughing or Valsalva maneuvers to increase intra-abdominal pressure.^[2] This load distribution helps maintain structural integrity while integrating respiratory and abdominal mechanics.^[22]

Clinical significance

Associated disorders

Xiphoidalgia, also known as xiphodynia or xiphoid syndrome, is characterized by chronic pain and tenderness localized to the xiphisternal joint, often radiating to the chest, epigastrium, throat, arms, or head.^[23] This condition frequently mimics more serious pathologies, leading to misdiagnosis as cardiac issues such as angina or myocardial infarction, or gastrointestinal disorders like gastroesophageal reflux disease or peptic ulcer.^[24] Common causes include irritation from trauma (e.g., blunt chest impact or heavy lifting), inflammation due to arthritis (osteoarthritis or rheumatoid), incomplete ossification, or secondary factors such as obesity-induced displacement of the xiphoid process.^[23] In severe cases, the pain may worsen with movements like stooping or after meals, and it is more prevalent in occupations involving repetitive strain or in postpartum individuals.^[24] Fractures of the xiphoid process or disruptions at the xiphisternal joint typically result from high-impact blunt trauma, such as motor vehicle accidents involving seatbelts, falls, or aggressive cardiopulmonary resuscitation (CPR).^[25] These injuries can lead to subluxation or dislocation of the joint, particularly during rapid acceleration-deceleration forces, causing instability and persistent pain.^[25] Complications are rare but serious; a displaced xiphoid fragment may puncture the liver, resulting in laceration and hemoperitoneum, especially given the close proximity of the left hepatic lobe to the xiphoid during CPR compressions.^[26] Most cases are managed conservatively with pain control, though surgical fixation may be required for significant displacement.^[27] Anatomical variants of the xiphoid process, such as bifid (forked) or elongated forms, can predispose individuals to irritation and chronic pain at the xiphisternal joint, often contributing to xiphoidalgia by causing mechanical friction or palpation sensitivity.^[28] These variants arise from incomplete fusion of ossification centers and may be deflected anteriorly, mimicking epigastric masses or leading to soft tissue inflammation.^[22] Rare congenital anomalies, including xiphoid absence or the presence of foramina (holes) in the xiphoid, heighten vulnerability to complications like herniation of abdominal contents through weakened sternal structures, potentially causing incarceration or strangulation if untreated.^[29] Diagnosis of xiphisternal joint disorders relies primarily on clinical evaluation, with palpation of the xiphoid process reproducing characteristic tenderness while excluding mimics like costochondritis, which involves costosternal junctions rather than the xiphoid.^[23] Imaging plays a supportive role: plain X-rays detect fractures or gross variants, while computed tomography (CT) assesses joint alignment (e.g., xiphisternal angle narrowing) and rules out differentials such as Tietze syndrome or visceral pathology.^[30] A thorough history and exclusion of cardiac or gastrointestinal emergencies via electrocardiography or endoscopy are essential before confirming the diagnosis.^[24]

Procedural and surgical applications

The xiphisternal joint serves as a key anatomical landmark in cardiopulmonary resuscitation (CPR), where guidelines recommend placing the heel of the hand on the lower half of the sternum, just superior to the xiphoid process, to optimize compression effectiveness while minimizing risks such as xiphoid or rib fractures and abdominal organ injury.^[31] This positioning, aligned with the inter-nipple line, ensures force is directed toward the heart without extending below the joint, as confirmed in studies evaluating optimal hand placement for hemodynamic outcomes.^[32] In pericardiocentesis, the subxiphoid approach utilizes the xiphisternal joint as the primary access point for needle insertion to aspirate pericardial effusions, particularly in cases of cardiac tamponade.^[33] The needle is inserted between the xiphoid process and the left costal margin and directed toward the left shoulder at a 30-45° angle to the skin or abdominal wall under ultrasound or fluoroscopic guidance, allowing safe entry into the pericardial space while avoiding vital structures like the liver or lungs.^[34] This method remains a standard emergent technique due to its direct path and lower complication rates when imaging is employed.^[35] During median sternotomy for cardiac procedures, the xiphisternal joint provides a critical inferior landmark for midline incision planning, with the xiphoid process dissected or divided to facilitate exposure of the heart and great vessels.^[2] The incision extends from the sternal notch to the xiphoid, ensuring symmetrical access while preserving diaphragmatic attachments.^[36] Additionally, xiphoidectomy—surgical removal of the xiphoid process—is employed in select open gastrectomies or hernia repairs to enhance visualization of the esophagogastric junction or abdominal wall defects, reducing operative time and improving field clarity without significant morbidity.^[37] The joint also guides other interventions, such as estimating insertion depth for central venous catheters via surface measurements from the xiphoid to the puncture site, aiding precise tip positioning in the right atrium.^[38] In upper abdominal laparoscopic surgery, a subxiphoid or epigastric port is commonly placed 2-3 cm below the xiphoid for instrument access and camera visualization during procedures like cholecystectomy or hiatal hernia repair.^[39]

References

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Xiphisternal joint | Radiology Reference Article - Radiopaedia.org
Nov 24, 2019 · The xiphisternal joint (or more rarely, the sternoxiphoid joint) is a symphysis between the inferior margin of the body of the sternum and the superior margin ...
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The xiphisternal joint is initially a synchondrosis, composed of hyaline cartilage connecting the sternal body to the xiphoid process. This joint typically ...
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Xiphisternal joint (Synchondrosis xiphosternalis); Image: Begoña Rodriguez ... The joint features include adjacent bone surfaces lined with hyaline cartilage and ...Missing: costoxiphoid | Show results with:costoxiphoid
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The XSJ is the synchondrosis which is temporary hyaline cartilage joint that is present during the growth phase of the skeleton. Often later in life this joint ...Missing: costoxiphoid | Show results with:costoxiphoid
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Jan 16, 2018 · The costoxiphoid ligaments, also known as the chondroxiphoid ligaments, are inconstant fibrous structures joining the anterior and posterior surfaces of the ...
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The xiphisternal joint is the anatomical junction between the xiphoid process and the body of the sternum. This joint is typically a synchondrosis.
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Three important regulatory variables include mechanical loading, sex hormones, and innervation/neuroregulation.Missing: sternum xiphoid
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### Summary of Xiphisternal Joint Role
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May 28, 2024 · A 1.2-cm incision is made three fingerbreadths below the xiphoid process and deepened into the subcutaneous fat. An 11-mm trocar is advanced ...Placement Of Ports And... · Exposure And Dissection · Mobilization And Removal Of...<|control11|><|separator|>