Week 9
Costovertebral Articulations •The ribs and vertebrae articulate in two locations. The first is the joint complex between the head of a rib and the adjacent vertebral bodies, known as the costocorporeal articulation. •The second costovertebral articulation is between a rib and the TP, known as the costotransverse articulation. •In addition to allowing the movements of the ribs so important to respiration, the costocorporeal and costotransverse articulations, along with the rib cage, provide stability to the thoracic region of the vertebral column. •Whereas the articular processes of the thoracic region limit flexion and extension, the ribs and costovertebral (both costocorporeal and costotransverse) articulations limit lateral flexion and axial rotation. •The joint between the head of a rib and the adjoining typical thoracic vertebrae consists of articulations with the two adjacent vertebral bodies and interposed IVD . •The rib head articulates with the superior demifacet of the same-number vertebra and the inferior demifacet of the vertebra above (e.g., seventh rib articulates with superior demifacet of T7 and inferior demifacet of T6. •The crest of the rib head is attached to the adjacent IVD by an intraarticular ligament. •This short, flat ligament creates two distinct articular compartments (upper and lower) within the costocorporeal articulation. •Both of these compartments are surrounded by a fibrous articular capsule lined with a synovial membrane. •These synovial joints can best be classified as having ovoid articular surfaces, and the fibrous capsule extends around the ovoid articular surfaces of both the demifacet and adjacent articular half of the rib head
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Interspinous Ligaments •The interspinous ligaments pass between adjacent spinous processes, filling the gap along the anterior-to-posterior length of these processes. • Anteriorly each interspinous ligament is continuous with the left and right ligamenta flava, and posteriorly each is continuous with the supraspinous ligament. • Even though the thoracic interspinous ligaments are thin and membranous in structure, they are more fully developed in the thoracic than cervical region. Supraspinous Ligament •The supraspinous ligament limits flexion of the spine. It is classically described as forming a continuous band that passes from the spinous process of C7 to the sacrum. However, disagreement exists as to whether or not it extends all the way to the sacrum. •The supraspinous ligament in the thoracic region is actually composed of two layers, with the deeper fibers running between adjacent vertebrae and the more superficial fibers spanning several (up to four) vertebrae. • The deepest fibers of the thoracic supraspinous ligament become continuous with the interspinous ligaments.
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T1: •T1 possesses two characteristics associated with cervical vertebrae but not normally found on typical thoracic vertebrae: uncinate processes and superior vertebral notches above the pedicles. • In addition, the vertebral body of T1 resembles that of a cervical vertebra, being rectangular in shape instead of heart-shaped, with the transverse diameter greater than the anteroposterior diameter. T9: •When the tenth rib does not articulate with the T9 vertebral body, the result is the absence of the inferior demifacet on T9. The other characteristics of T9 conform to those of typical thoracic vertebrae. T10: •The vertebral body of T10 contains only a single facet on each side for articulation with the head of the left and right tenth ribs. •The single facet on T10 is usually oval or semilunar in shape. T11: •T11 also has only a single facet on each side for articulation with the head of the eleventh rib. However, this facet is located on the pedicle. •There is also no articular facet on the TP for articulation with the articular tubercle of the rib. Therefore the eleventh rib does not articulate with the TP of T11. •The vertebral body of T11 also resembles that of a lumbar vertebra. The spinous process of T11 is almost triangular in shape with a blunt apex. T12: •The vertebral body of T12 is large, but the TPs are small. In fact, each TP is actually replaced by three smaller processes. One process projects laterally and is the equivalent of a thoracic TP except that it is small. •The largest of the three processes projects posteriorly and superiorly and is the homologue of the mamillary process of a lumbar vertebra. However, this mamillary process is not as closely related to the superior articular process as it is in the lumbar region.
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Thoracic Vertebra: The thoracic region contains the most vertebrae (12) of any of the movable regions of the spine. Consequently, it is the longest region of the spine. However, because of its relationship with the ribs, which attach anteriorly to the sternum, the thoracic region has relatively little movement. •Many of the unique characteristics of the thoracic region result from its anatomic relationships with the ribs. The typical thoracic vertebrae are T2 through T8. •T1, T9 (occasionally), T10, T11, and T12 perhaps can best be described as unique rather than "atypical." •The size of the thoracic vertebrae generally increases from the superior to the inferior vertebrae, just as the load they are required to carry increases from superior to inferior. The normal thoracic curve is a rather prominent kyphosis, which extends from T2 to T12. It is created by the larger superior-to-inferior dimensions of the posterior portion of the thoracic vertebrae. •The size of the thoracic vertebral bodies is approximately the same in males and females of all races and of all adult ages. The vertebral bodies of the typical thoracic vertebrae (T2 to T8) are larger than those of the cervical region. The volume of the vertebral bodies increases from T1 to T12. •Thoracic vertebral bodies appear to be heart-shaped when viewed from above, primarily because of a marked concavity of the posterior aspect of the vertebral body in the region adjacent to the vertebral foramen. •The posterior edge of the superior surface of upper thoracic vertebral bodies exhibits small remnants of the cervical uncinate processes.
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Vertebral Canal: •The vertebral canal in the thoracic region is more rounded in shape than in any other region. •It is also smaller in the thoracic region than in either the cervical or the lumbar region. Compared to the other regions of the spinal cord, the thoracic spinal cord also is smaller. •The spinous processes of thoracic vertebrae generally are large. The upper four thoracic spinous processes project almost directly posteriorly. •The next four (T5 through T8) project dramatically inferiorly. The spinous process of T8 is the longest of this group. •The last four thoracic spinous processes begin to acquire the characteristics of lumbar spinous processes by projecting more directly posteriorly and being larger in their superior-to-inferior dimension •The IVFs in the thoracic region differ from those of the cervical region by facing directly laterally rather than obliquely anterolaterally. The lateral orientation of the thoracic IVFs is similar to that found in the lumbar region. •Unique to the thoracic region is that the T1 through T10 IVFs are associated with the ribs. The eleventh and twelfth ribs are not directly associated with IVFs. More precisely, the following structures are associated with the T1 through T10 IVFs: the head of the closest rib (e.g., T5-6 IVF associated with head of sixth rib), the articulation between the rib head and the demifacets of the vertebral bodies, including the associated ligamentous and capsular attachments with the vertebral bodies and the interposed IVD •Certain groups of cells throughout the spine, known as the costal elements, have the ability to develop into ribs and do so in the thoracic region. •The costal elements develop to become precartilaginous ribs, which, after undergoing chondrification and then ossification, become the ribs themselves. •The TPs of the thoracic vertebrae grow behind the proximal ends of the developing ribs and are united to them by mesenchyme. This mesenchyme forms the articulations and ligaments of the costocorporeal and costotransverse joints. The fully developed ribs serve to protect the underlying thoracic viscera while providing attachment sites for a wide variety of muscles.
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•A "first thoracic rib ligament" is found on at least one side of 80% of individuals (Matullo et al., 2010). The 3-cm-long ligament attaches to the inner surface of the neck of the first rib and then distally along the inner surface of the shaft of the first rib. •The T1 anterior primary division courses around the inferior surface of this ligament and then passes superiorly between the ligament and the shaft of the first rib to unite on top of the first rib with the anterior primary division of C8 to form the inferior (lower) trunk of the brachial plexus •Ranges of Motion in the Thoracic Spine •Vertebral Motion • •As stated, the facets of the thoracic vertebrae are oriented approximately 60 to 75 degrees to the horizontal plane. Therefore they are more vertically oriented than the articular processes of the cervical region. This vertical orientation dramatically limits forward flexion. Extension is limited by the inferior articular processes contacting the laminae of the vertebrae below and also by contact between adjacent spinous processes. •Rotation is the dominant movement in the thoracic region with the axis of rotation for each vertebra located in the midsagittal plane at the anterior aspect of the vertebral foramen (Molnar et al., 2006). •However, the vertebrae are a part of the entire thoracic cage and even this motion is limited considerably. The relationship to the thoracic cage may help to explain why the lower thoracic region, with its relation to floating ribs and ribs with only an indirect attachment to the sternum, is the most mobile part of the thoracic spine. Ranges of motion of the thoracic spine include the following: •Combined flexion and extension 34 degrees •Unilateral lateral flexion 15 degrees •Unilateral axial rotation 35 degrees
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•A ridge on the head of each rib, known as the crest of the head, is located between the two articular surfaces of the rib head. The crest of the head of each rib has a ligamentous attachment (intraarticular ligament) to the intervertebral disc (IVD) between adjacent thoracic vertebrae. •A fibrous capsule surrounds each vertebral demifacet and continues to the rib surrounding the articular surface on the corresponding half of the rib head. •The capsule is lined by synovium, making the costovertebral joint (costocorporeal joint) a synovial joint (diarthrosis). The radiate ligament extends from the head of each rib to the adjoining vertebral bodies and the surface of the intervening IVD •The pedicles of the thoracic spine are long and stout. In fact, the pedicles in the lower thoracic region are larger than the pedicles of the upper lumbar vertebrae. • The T4 pedicles are the narrowest (left-to-right dimension) and then the pedicles of T5 to T12 become increasingly wider. •Unlike the pedicles of the cervical vertebrae, cancellous bone, rather than cortical bone, predominates in the thoracic pedicles. However, like the cervical pedicles, the cortical bone of the lateral wall of a typical thoracic pedicle is thinner than that of the medial wall. •The thoracic pedicles become larger along their inferior surface from T1 to T12. Also, unlike the cervical pedicles, which attach at a significant lateral angle with the cervical vertebral bodies, the thoracic pedicles form only a slight lateral angle in the transverse plane with the thoracic vertebral bodies (and T12 forms no lateral angle with the vertebral body in this plane, i.e., a 90º angle to the vertebral body).
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•Anterior And Posterior Longitudinal Ligaments •The anterior longitudinal ligament (ALL) in the thoracic region is thicker from anterior to posterior and thinner from side to side than in either the cervical or the lumbar regions. The ALL attaches firmly to the superior and inferior bony end plates of the thoracic vertebrae, but has only weak attachments to the remainder of the thoracic vertebral bodies. Firm attachments of the ALL to the thoracic IVDs have been found in more than 50% of spines. The firm attachments of the ALL to the IVDs may help prevent anterior protrusion of the IVDs in this region. Ossification of the posterior longitudinal ligament (PLL) is much less common in the thoracic region than in the cervical region; however, when it does occur, it can be severe and lead to paraplegia.
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•Confirming the work of Meyer (1972), Erwin and colleagues (2000) found large synovial folds protruding into the costocorporeal joints. In addition, they found that the synovial folds were innervated by free nerve endings and mechanoreceptors immunoreactive to substance P. •Substance P is associated with pain transmission and functions in the perception of pain, related reflex muscle responses (flexion reflexes), and reflex responses to pain of the autonomic nervous system and endocrine system. •Therefore the costocorporeal joints are similar to the Z joints with respect to being planar synovial joints with nociceptive (pain-sensitive) innervation of both the joint capsule and the synovial folds. The nerve endings are most likely sensitive to tissue strain or tissue damage of mechanical origin. Costotransverse Articulation •This joint is composed of the costal (articular) tubercle of a rib articulating with the transverse costal facet of a TP. •Recall that the eleventh and twelfth ribs do not articulate with the TPs of their respective vertebrae. • The joint surfaces of the upper five or six costotransverse joints are curved, with the transverse costal facet being concave and the articular tubercle convex. The remaining joints are more planar in configuration. • A thin, fibrous capsule lined by a synovial membrane attaches to the two adjacent articular surfaces. •A costotransverse foramen is found between the TP and the rib between the costotransverse and costocorporeal articulations. •This foramen is filled by the costotransverse ligament. The costotransverse ligament passes from the posterior aspect of the rib neck to the anterior aspect of the adjacent TP. •For example, the costotransverse ligament of the sixth rib attaches to the posterior aspect of that rib and to the anterior aspect of the TP of T6. •Sensory nerve endings also have been found in the costotransverse ligament, indicating that it is pain sensitive.
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•Each LF had two layers, superficial (posterior) and deep (anterior). The fibers of the superficial layer were oriented obliquely, and those of the deep layer were more organized and oriented in a sagittal plane. The superficial and deep layers were separated by a potential space that Viejo-Fuertes and colleagues (1998) called a "gliding space." •There are two functions of the LF—biomechanical and neurologic functions. • Biomechanically the LF decreases flexion and also helps with extension of the vertebral column. •The neurologic function of the LF was both proprioceptive and nociceptive in nature; the proprioceptive information received from the LF would be important in providing the central nervous system with information used for segmental muscle reflexes, and the nociceptive information would be important in relaying information related to tissue damage to the central nervous system.
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•Finally, a small process that is homologous to the accessory process of lumbar vertebrae projects posteriorly and slightly inferiorly. T12 also has a single facet on each side for articulation with the head of the corresponding twelfth rib. •The facet is circular and is located primarily on the pedicle but may extend onto the vertebral body. The small TP has no facet for articulation with the twelfth rib. •Thoracolumbar Junction •The left and right Z joints between the T12 and L1 vertebrae are unique. •At this joint the L1 mamillary process of each side overlaps the posterior aspect of the inferior articular process of T12. This usually occurs to a greater degree between these two vertebrae than at any other level. •The result is that each inferior articular process of T12 fits closely into the superior articular process and overlying mamillary process of L1, much like a well-made carpenter's joint (e.g., mortise and tenon joint). •This configuration prevents almost any movement except flexion from occurring at this articulation (Singer & Giles, 1990have shown large Z joint synovial folds protruding into this joint. They also emphasize that normally almost no rotation occurs at this articulation. Ligaments and Joints of the Thoracic Region •These include the ligamenta flava (LF), anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), and interspinous ligaments.
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•The capsule extends to the intraarticular ligament between the upper and lower compartments. The fibers of the fibrous capsule closest to the IVD blend with that structure, and the posterior fibers blend with the costotransverse ligament. In a fashion similar to that found in the Z joints, synovial folds, or menisci, protrude into the costocorporeal articulation, presumably to help lubricate the joint and help with the sliding and rotary motions of the joint. •The heads of the first, tenth (occasionally), eleventh, and twelfth ribs form single ovoid synovial articulations with their respective ribs. •The ligaments of this compound joint include the capsular, intraarticular, and radiate. • Each radiate ligament associated with typical vertebrae attaches to the anterior aspect of the head of the articulating rib and the two vertebrae to which the head attaches. In addition, the radiate ligament attaches by horizontal fibers to the IVD between the two vertebrae. •The superior fibers attach just above the superior demifacet and ascend to the vertebral body of the superior vertebra. Likewise, the inferior fibers attach just below the inferior demifacet and descend to the inferior vertebral body. •The radiate ligament of the first rib has some superior fibers that attach to C7. The radiate ligaments of the tenth through twelfth ribs attach to only the vertebra with which the rib head articulates. •In addition to allowing motion of the ribs, the costocorporeal joints provide stability to the thoracic region during motions in the sagittal (flexion-extension), coronal (lateral flexion), and transverse planes (axial rotation).
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•The folds are usually located in the inferior (caudal) aspect of the joints, although they have been identified in all regions of the joint. • The folds are smaller in the thoracic region than in the other regions of the spine, but as in the cervical and lumbar regions, the thoracic synovial folds are believed capable of becoming entrapped (i.e., trapped between the articular facets) or extrapped (i.e., trapped between the articular process and Z joint capsule), both situations being a theoretical source of back pain. •The laminae in the thoracic region are short from medial to lateral, broad from superior to inferior, and thick from anterior to posterior. • As with other components of thoracic vertebrae, the left and right laminae are asymmetric in superior-to-inferior length, with the right laminae being longer than the left. In addition, the laminae of males are larger (superior-to-inferior) than those of females Paraarticular processes are spurlike calcifications on the anterior and inferior aspects of the laminae of thoracic vertebrae. They also have been called "laminar spurs" or "spicules," and represent spur formations of the lateral-most attachment sites of the ligamentum flavum (LF). •Paraarticular processes are rarely found in the lumbar region, and they are almost never found in the cervical region. However, paraarticular processes are thought to be normal findings on thoracic vertebrae and are distinct from the condition known as ossification of the LF.
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•The head of a typical rib articulates with two adjacent vertebral bodies (see Vertebral Bodies). Inferior and superior articular facets of the rib head articulate with the superior costal demifacet of the same-number vertebra as the rib and with the inferior costal demifacet of the vertebra above, respectively. The crest of the head is a ridge that runs between the two articular surfaces of the rib head. The crest is joined by the intraarticular ligament to the adjacent IVD. This creates the two separate components of the costocorporeal joints—one superior to the crest of the head of the rib and one inferior to the crest •The neck of a typical rib is located between its head and tubercle. The neck serves as the attachment site for the costotransverse ligament and superior costotransverse ligament. •The shaft of a rib begins at the articular tubercle and extends distally to the end of the rib at its articulation with the costal cartilage. The typical ribs curve inferiorly and anteriorly. •Much of this anterior curve is achieved at the angle of the rib. The angle of the rib is located a few centimeters distal to the articular tubercle and is where the shaft makes the sharpest anterior bend. •The tubercle of a rib is a process that forms the lateral boundary of the neck and the beginning of the shaft. It possesses an articular facet (articular portion) for articulation with the transverse costal facet on the TP of a typical thoracic vertebra. •The tubercle of a rib articulates with the same-number vertebra as the rib (e.g., fourth rib articulates with TP of T4). •The tubercle also contains a nonarticular part lateral to the articular portion. The nonarticular region serves as an attachment site for the lateral costotransverse ligament.
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•The left-right (lateral) width of the thoracic vertebral bodies is greater than the anterior-posterior (length) and superior-inferior (height) dimensions. The lateral width decreases from T1 through T3 and then gradually increases throughout the thoracic region (continuing into the lumbar region until L4-L5). •The decreasing width of the upper thoracic vertebral bodies may allow for increased lateral flexion (and possibly rotation) of the cervical region •The lateral width of a thoracic vertebra is smaller at the superior versus inferior vertebral margin of the vertebra and the lateral width of the inferior aspect of each vertebra is always larger than the superior width of the subjacent vertebra. •Consequently, in a coronal (frontal) section the vertebral bodies have a trapezoid shape (i.e., narrower superiorly) and the intervertebral discs have an inverted trapezoid shape (i.e., narrower inferiorly). • Typical thoracic vertebrae also are more flattened on their left than right surfaces because of pressure from the thoracic aorta. •The thoracic vertebral bodies are wedged-shaped, the superior-inferior height being smaller anteriorly than posteriorly. The wedging increases from T1 to T7 and then begins to decrease incrementally until L2. •The posterior aspect of a typical thoracic vertebra is approximately five times the height of the posterior aspect of the intervertebral disc immediately above the vertebra. •The superior-inferior height of the T1 and T2 vertebral bodies is greater than the anterior-posterior length. This ratio is reversed throughout the rest of the thoracic region. •Consequently, the T1 and T2 vertebral bodies are more rounded when viewed from the left or right sides. This configuration may help to accommodate the large amount of flexion and extension that occurs in the cervical region
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•The superior articular processes of the thoracic spine are small superior projections of bone oriented in a plane that lies approximately 60 to 75 degrees to the horizontal plane (25 to 40 degrees to the coronal [frontal] plane). •The inferior articular processes and their facets match those of the superior ones facing in the opposite direction—that is, anteriorly, slightly inferiorly, and medially, with matching asymmetry as well. The facet orientation and asymmetry are the same for males and females of all ages and racial origins •The orientation of the thoracic articular processes and their articulating facets allows a significant amount of rotation to occur in this region. •Flexion and extension are limited primarily by the orientation of the thoracic facets, and lateral flexion is limited partly by the orientation of the facets. •However, the firm attachments of the thoracic vertebrae to the relatively immobile thoracic cage, by means of the costocorporeal and costotransverse articulations, are the primary constraints to axial rotation and lateral flexion of the thoracic spine. •The zygapophysial (Z) joints are important structures clinically. These joints are thought to be the source of pain in 48% of the cases of chronic thoracic pain. •The capsules of the thoracic Z joints are similar to those of the cervical and lumbar regions. However, there are fewer mechanoreceptors in the Z joint capsules of the thoracic region than in the cervical or lumbar regions •Z joint synovial folds (meniscoids) have been found to protrude into approximately 62% of thoracic Z joints, which is a lower incidence than the cervical and lumbar regions. Some thoracic Z joints have more than one synovial fold.
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•The superior-inferior height of most thoracic vertebral bodies is asymmetric with the right side usually greater than the left side. • This "left lateral wedging" is typically found in one or several (usually 3) contiguous vertebrae, "interrupted" by a single vertebra of symmetric left and right heights, followed by additional vertebrae with left lateral wedging. •The T2 vertebral body is somewhat cervical in appearance, being slightly larger in transverse than anteroposterior diameter. The body of the T3 vertebra is the smallest of the thoracic region; the vertebral bodies gradually increase in size below this level. •The vertebral bodies of T5 through T8 become more and more heart-shaped. This means that the concavity of the posterior aspect of the vertebral bodies becomes more prominent. •The heart-shaped appearance also is accentuated because the anteroposterior dimension of the vertebral bodies increases more than the transverse (lateral) dimension at these levels. •The T9 through T12 vertebral bodies begin to acquire lumbar characteristics (see the following discussion) and enlarge more in their transverse than anteroposterior dimension. The T12 vertebral body is similar in shape to that of a lumbar vertebra. •The thoracic vertebral bodies become stronger from upper to lower thoracic vertebrae. This results from an increase in bone density that is probably a response to the increase in compressive forces placed on the successively lower vertebral bodies. •Typical thoracic vertebral bodies have four small facets, two on each side, for articulation with the heads of two adjacent ribs. These facets are known as costal demifacets (literally, "half-facets") because the head of each rib articulates with both the superior demifacet of the vertebra with the same number and the inferior demifacet of the vertebra above.
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•The thoracic IVDs have the thinnest superior-to-inferior dimension of the spine. Also, the discs of the upper thoracic region are thinner than those of the lower thoracic region. •The upper thoracic region is also the least movable area of the thoracic spine (although the small amount of motion appears to support end range motion of the cervical region). •In contrast to the cervical and lumbar IVDs, which are thicker anteriorly than posteriorly, the thoracic IVDs are of more equal thickness. •Thoracic IVD protrusion is rather infrequent, accounting for only 0.15% to 1.8% of all disc protrusions (Alvarez, Roque, & Pampati, 1988; Bauduin et al., 1989). However, they may be more common than previously believed (Vernon, Dooley, & Acusta, 1993). When present, this condition usually affects the lower thoracic discs of individuals primarily between 30 and 60 years of age
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•The thoracic pedicles incline slightly superiorly in the sagittal plane (Marchesi et al., 1988). They also attach very high on their respective vertebral bodies; as a result, no superior vertebral notch is associated with typical thoracic vertebrae. T1, which is atypical, does have a superior vertebral notch. On the other hand, the inferior vertebral notches of the typical thoracic vertebrae are very prominent. •The transverse processes (TPs) of typical thoracic vertebrae project obliquely posteriorly. •They also lie in a more posterior plane than those of the cervical or lumbar regions, being located behind the pedicles, intervertebral foramina, and articular processes of the thoracic vertebrae. • The TPs also become progressively shorter from T1 to T12; therefore the distance between the tips of the left and right TPs is the greatest at T1 and then decreases incrementally until T12, where the TPs are very small. •Each thoracic TP possesses a facet for articulation with the articular tubercle of the corresponding rib (e.g., the TP of T6 articulates with the sixth rib). •This facet is appropriately named the transverse costal facet, or costal facet of the transverse process, and is located on the anterior surface of the TP. •The first six transverse costal facets are concave and face not only anteriorly but also slightly laterally. •The transverse costal facets inferior to T6 are more planar (flatter) in shape and face anteriorly, laterally, and superiorly. The forces applied to the ribs during movements, load carrying, or muscular contraction are transmitted through the TPs to the laminae of the thoracic vertebrae.
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