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Intertubercular plane

The is a (transverse) anatomical landmark in human , defined as the line connecting the tubercles of the iliac crests on both sides of the , positioned approximately at the level of the fifth (L5). This plane plays a crucial role in dividing the into standardized regions for clinical and anatomical purposes, forming the lower boundary when combined with the superiorly and two vertical midclavicular lines laterally, resulting in the classic nine abdominopelvic regions: the epigastric, umbilical, hypogastric (suprapubic), right and left hypochondriac, , and iliac (inguinal) areas. It lies inferior to the (at the level of the upper border of the third (L3)) and inferior to the transumbilical plane (at the L3-L4 ), providing a consistent reference point roughly 5 cm posterior to the anterior superior iliac spines. Clinically, the intertubercular plane aids in localizing abdominal organs, such as the and in the lower regions, and is essential for describing , masses, or surgical sites with precision during physical examinations, , or procedures. Its position aligns with the upper border of L5, making it a reliable guide for correlating with underlying skeletal and visceral structures.

Definition and Anatomy

Definition

The intertubercular plane is a transverse (horizontal) reference line in human that connects the tubercles located on the iliac crests of the right and left pelvic bones. Posteriorly, it corresponds to the level of the body of the fifth lumbar vertebra (L5). This positioning makes it an important divider in abdominal , contributing to the demarcation of the nine abdominal regions when combined with other planes.

Anatomical Position and Landmarks

The intertubercular plane is a transverse horizontal plane that passes through the iliac tubercles, which represent the most prominent anterior projections on the iliac crests of the . These tubercles are located approximately 5 cm posterior to the anterior superior iliac spines (ASIS), serving as key palpable bony landmarks for identifying the plane's position on the anterior abdominal wall. The plane can be clinically approximated by palpating the iliac tubercles, located about 5 cm posterior to the ASIS on each side, and drawing a transverse line connecting them. The iliac tubercles lie slightly inferior to the crest's superior margin but define the plane's precise transverse level. Internally, the intertubercular plane corresponds to the level of the fifth vertebra (L5), specifically aligning with its upper border and approximating the between the fourth and fifth (L4-L5). This vertebral correspondence provides a reliable reference for correlating external with underlying skeletal structures in clinical assessments. As a in abdominal topography, it helps delineate the lower extent of the .

Role in Surface Anatomy

Division of Abdominal Regions

The intertubercular plane serves as the inferior horizontal boundary in the standard division of the into nine regions, demarcating the three upper regions—epigastric, right hypochondriac, and left hypochondriac—from the three middle regions (umbilical, right , and left ) and the three lower regions (hypogastric, right iliac, and left iliac). This plane is drawn horizontally across the level of the iliac tubercles, providing a consistent anatomical landmark for topographic mapping of the abdominal surface. In conjunction with the superior subcostal plane and the two vertical midclavicular planes, the intertubercular plane establishes the grid that subdivides the into these nine distinct regions, facilitating precise localization in clinical examinations and imaging. The runs along the inferior margin of the anterior thoracic cage, while the midclavicular planes extend vertically from the midpoints of the clavicles to the midinguinal points, intersecting the horizontal planes to form the boundaries. This system of abdominal division forms part of the classical topographic anatomy framework, as outlined by 19th-century anatomists such as in his seminal work Anatomy of the Human Body.

Relation to Other Planes

The intertubercular plane, also known as the transtubercular plane, is situated superior to the interspinous plane—a transverse line connecting the anterior superior iliac spines. This relative positioning arises from the anatomy of the , where the tubercles lie posterior and at a slightly higher elevation than the anterior superior iliac spines due to the crest's upward curvature. Inferior to the subcostal plane, which passes through the lowest margins of the costal cartilages at approximately the level of the lower border of the vertebra, the intertubercular plane aligns roughly with the body of the L4 or L5 vertebra. This separation reflects the vertical span across the epigastric, umbilical, and hypogastric regions of the anterior . As one of the standard transverse (horizontal) planes in anatomical description, the intertubercular plane is perpendicular to both the (dividing the body into left and right) and the (dividing into anterior and posterior). Its intersections with the bilateral midclavicular lines—vertical planes passing through the of the clavicles—define critical demarcation points for abdominal compartmentalization, including the nine-region used in clinical localization of viscera.

Clinical and Surgical Significance

Use in Abdominal Quadrants and Regions

The intertubercular plane serves as a key horizontal demarcation in the nine-region division of the abdomen, formed by two horizontal lines (subcostal superiorly and intertubercular inferiorly) intersecting two vertical midclavicular lines, creating regions such as the right and left iliac fossae below the plane and the hypogastric region centrally below it. In the four-quadrant system, which typically employs a transverse plane through the umbilicus at the L3-L4 vertebral level, the intertubercular plane—positioned at the L5 level through the iliac tubercles—approximates the inferior boundary of the lower quadrants while providing greater precision for identifying transitions into the pelvic cavity. This positioning enhances its utility in clinical assessments by distinguishing upper abdominal structures from lower pelvic ones during initial evaluations. Clinically, the intertubercular plane aids in localizing and by correlating symptoms to specific regions inferior to it; for instance, pain in the right iliac region often indicates due to of the located there, while discomfort in the hypogastric region may suggest ovarian , such as cysts or torsion, involving the ovaries and related structures. These regional associations facilitate rapid during physical examinations, where of the iliac tubercles helps confirm the plane's landmarks for accurate quadrant mapping. In , the intertubercular plane is emphasized in curricula for training students in abdominal , enabling quick mental visualization of locations to guide systematic physical exams and improve diagnostic efficiency in settings. This foundational teaching underscores its role in standardizing assessments across clinical scenarios, from emergency presentations to routine check-ups.

Applications in Procedures and Imaging

The intertubercular plane serves as a critical surgical landmark for incisions in the lower , particularly the , which is positioned transversely approximately 2 cm above the within the hypogastric region defined inferior to the plane, enabling optimal access to pelvic organs during gynecological and obstetric procedures such as cesarean sections and hysterectomies. This placement leverages the plane's role in delineating abdominal regions to minimize tissue disruption while providing excellent exposure to the , , and ureters, with studies indicating lower rates of wound complications compared to vertical incisions. In diagnostic imaging, the intertubercular plane standardizes axial slice acquisition at the level of the upper border of the fifth lumbar vertebra (L5), aiding precise evaluation of the lumbar spine, lower renal poles, and in and examinations. For instance, in , alignment with this ensures consistent assessment of vascular confluence at the common iliac veins. Note that while the anterior intertubercular plane aligns with L5, its posterior extension—the intercristal line—typically corresponds to the L4 spinous process (though variable across individuals), which is used in applications for preprocedural scanning in neuraxial blocks to approximate the L4-L5 interspace and reduce the risk of incorrect vertebral level identification.

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