Thorax and chest wall

Biomechanics of Thorax and Chest

1. biomechanics of thorax and chest wall - viresh v

2. Anterior View Posterior View 1 st rib Manubrium Sternal Angle Costochondral Joint Body of Sternum Costal Cartilage Xiphoid Process Introduction : The Thorax consists of

3. GENERAL STRUCTURE AND FUNCTION RIB CAGE It is a closed chain Kinematics that involves many muscles. Borders of the Rib cage: Anterior – Sternum Lateral – are the ribs Posterior – Thoracic vertebrae superior – Jugular notch of the sternum, 1 st costocartilage, 1 st ribs and 1 st thoracic vertebrae inferior – Xiphoid process, ribs 7 – 10, inferior portions of 11 th and 12 th also.

4. sternum The sternum is an osseous protective plate for the heart and is composed of the manubrium, body, and xiphoid process . The manubrium and the body form a dorsally concave angle of approximately 160 deg.

5. RIB

6. There are 12 thoracic vertebrae that make up the posterior aspect of the rib cage. One of the unique aspects of the typical thoracic vertebra is that the vertebral body and transverse processes have six costal articulating surfaces- four on the body - a superior and an inferior costal facet, (or demifacet) on each side. one costal facet on each transverse process It also includes 12 pairs of ribs. Thoracic Vertebrae

7. The rib cage also includes 12 pairs of ribs. The ribs are curved flat bones that gradually increase in length from rib 1 to rib 7 and then decrease in length again from rib 8 to rib 12. The posteriorly located head of each rib articulates with thoracic vertebral bodies; and the costal tubercles of ribs 1 to 10 also articulate with the transverse processes of a thoracic vertebra.

8. Anteriorly, ribs 1 to 10 have a costal cartilage that joins them either directly or indirectly to the sternum. The first through the seventh ribs are classified as vertebrosternal (or “true”) ribs because each rib, through its costocartilage, attaches directly to the sternum. The costocartilage of the 8th through 10th ribs articulates with the costocartilages of the superior rib, indirectly articulating with the sternum through rib 7. These ribs are classified as vertebrochondral (or “false”) ribs. The 11th and 12th ribs are called vertebral (or “floating”) ribs because they have no anterior attachment to the sternum. T R U E ribs F A L S E ribs FLOATING RIBS

9. Articulations of the Rib Cage The articulations that join the bones of the rib cage include the Manubriosternal (MS) joint , Xiphisternal (XS) joint , Costovertebral (CV) joint , Costotransverse (CT) joint , Costochondral ( CC) joint Chondrosternal (CS) joint , Interchondral joint.

10. Manubriosternal Joint The manubrium and the body of the sternum articulate at the MS joint . This joint is also known as the sternal angle or the angle of Louis and is readily palpable. The MS joint is a synchondrosis . The Hyaline cartilage – covers the articulating ends of the manubrium and sternum. The MS joint has a fibrocartilaginous disk between the articular surfaces.

11. Xiphisternal Joint The Xiphoid process joins the inferior aspect of the sternal body at the XS joint. The XS joint is also a synchondrosis that tends to ossify by 40 to 50 years of age.

12. Costovertebral Joints The typical CV joint is a synovial joint formed by the head of the rib, two adjacent vertebral bodies, and the interposed inter vertebral disk. Ribs 2 to 9 have typical CV joints. The heads of these ribs each have two articular facets, or so-called demifacets (superior and inferior costovertebral facets ) . The demifacets are separated by a ridge called the crest of the head of the rib.

13. Adjacent thoracic vertebrae have facets corresponding to those of the 9 ribs that articulates with them. The head of each of the second through ninth ribs articulates with an inferior facet on the superior of the two adjacent vertebrae and with a superior facet on the inferior of the two adjacent vertebrae. The inferior and superior facets on the adjacent vertebrae articulate, respectively, with the superior and inferior facets on the head of the rib. The 1st, 10th 11th, and 12th ribs are atypical ribs because they articulate with only one vertebral body and are numbered by that body. A fibrous capsule surrounds the entire articulation of each CV joint.

14. The typical CV joint is divided into two cavities by the Interosseous or Intra - articular ligament. This ligament extends from the crest of the head of the rib to attach to the Annulus fibrosus of the intervertebral disk.

15. The Radiate ligament is located within the capsule , with firm attachments to the anterolateral portion of the capsule. The radiate ligament has three bands : The superior band, which attaches to the superior vertebra; The intermediate band, which attaches to the intervertebral disk The inferior band, which attaches to the inferior vertebra. The atypical CV joints of ribs 1 and 10 through 12 are more mobile than the typical CV joints because the rib head, articulates with only one vertebra. The interosseous ligament is absent in these joints; therefore, they each have only one cavity. The radiate ligament is present in these joints, with the superior band still attaching to the superior vertebra. Both rotation and gliding motions occur at all of the CV joints

16. Costotransverse Joints The CT joint is a synovial joint formed by the articulation of the costal tubercle of the rib with a costal facet on the transverse process of the corresponding vertebra. There are 10 pairs of CT joints articulating vertebrae T1 through T10 with the rib of the same number. The CT joints on T1 through approximately T6 have slightly concave costal facets on the transverse processes of the vertebrae and slightly convex costal tubercles on the corresponding ribs. At the CT joints of approximately T7 through T10, both articular surfaces are flat and gliding motions predominate. Ribs 11 and 12 do not articulate with their respective transverse processes of T11 or T12.

17. The CT joint is surrounded by a thin, fibrous capsule. Three major ligaments support the CT joint capsule - lateral costotransverse ligament, the costotransverse ligament, and the superior costotransverse ligament. The lateral costotransverse ligament is a short, stout band located between the lateral portion of the costal tubercle and the tip of the corresponding transverse process. The costotransverse ligament is composed of short fibers that run within the costotransverse foramen between the neck of the rib posteriorly and the transverse process at the same level. The superior costotransverse ligament runs from the crest of the neck of the rib to the inferior border of the cranial transverse process.

18. Costochondral joint The CC joints are synchondrosis. The CC joints are formed by the articulation of the 1 st through 10th ribs antero laterally with the costal cartilages The CC joints have no ligamentous support.

19. Chondrosternal Joints The CS joints are formed by the articulation of the costal cartilages of ribs 1 to 7 anteriorly with the sternum Rib 1 attaches to the lateral facet of the manubrium, Rib 2 is attached via two demi facets at the manubriosternal junction, Ribs 3 through 7 articulate with the lateral facets of the sternal body. The CS joints of the first, sixth, and seventh ribs are synchondrosis. The CS joints of ribs 2 to 5 are synovial joints.

20. The CS joints of the first through seventh ribs have capsules that are continuous with the periosteum. Ligamentous support for the capsule includes : Anterior and Posterior radiate Costosternal ligaments. Sternocostal ligament. Costoxiphoid ligament.

21. The Sternocostal ligament is an intra-articular ligament, that divides the two demi facets of the second CS joint. The Costoxiphoid ligament connects the anterior and posterior surfaces of the seventh costal cartilage to the front and back of the Xiphoid process.

22. Interchondral Joints The Interchondral joints are synovial joints and are supported by a capsule and Interchondral ligaments. The 7th through the 10th costal cartilages each articulate with the cartilage immediately above them. For the 8th through 10th ribs, this articulation forms the only connection to the sternum

23. Kinematics of the Ribs and Manubriosternum

24. The movement of the rib cage is an amazing combination of complex geometrics governed by: 1. The types and angles of the articulations 2. The movement of the Manubriosternum 3. The elasticity of the costal cartilages.

25. The anterior articulation of rib 1 is larger and thicker than that of any other rib. The first costal cartilage is stiffer than the other costocartilages. Also, the first CS joint is cartilaginous (synchondrosis), not synovial, and therefore is firmly attached to the manubrium. Finally, the first CS joint is just inferior and posterior to the sternoclavicular joint. For these reasons, there is very little movement of the first rib at the anterior CS joint. Posteriorly, the CV joint of the first rib has a single facet, which increases the mobility at that joint. During inspiration, the CV joint moves superiorly and posteriorly, elevating the first rib.

26. There is a single axis of motion for the 1st to 10th ribs through the center of the CV and CT joints. This axis for the upper ribs lies close to the frontal plane, allowing thoracic motion predominantly in the sagittal plane. The axis of motion for the lower ribs is nearly in the sagittal plane, allowing for thoracic motion predominantly in the frontal plane The axis of motion for the 11th and 12 th ribs passes through the CV joint only, because there is no CT joint present. The axis of motion for these last two ribs also lies close to the frontal plane.

27. Closed chain kinematics

28. The excursion of the Manubrium is less than that of the body of the sternum because the first rib is the shortest, with the caudal ribs increasing in length until rib 7. The discrepancy in length causes movement at the MS joint. The motion of the upper ribs and sternum has its greatest effect by increasing the Anteroposterior (AP) diameter of the thorax. This combined rib and Sternal motion that occurs in a predominantly Sagittal plane has been termed the “ Pump - handle” motion of the thorax. “Pump – handle Movement”

29. Elevation of the upper ribs at the CV and CT joints results in anterior and superior movement of the sternum there by increasing AP diameter is referred to as the “pump-handle” motion of the thorax.

30. The lower ribs have a more angled shape (obliquity increases from rib 1 to rib 10) and an indirect attachment anteriorly to the sternum. These factors allow the lower ribs more motion at the lateral aspect of the rib cage. The elevation of the lower ribs has its greatest effect by increasing the transverse diameter of the lower thorax. This motion that occurs in a nearly frontal plane has been termed the “Bucket - Handle” motion of the thorax. Elevation of the lower ribs at the CV and CT joints results in a lateral motion of the rib cage and thereby increasing transverse diameter is referred to as “ Bucket Handle ” motion of the thorax. “Bucket – Handle Movement”

31. Let’s watch a video on Pump - handle and Bucket handle movement

32. The 11th and 12th ribs each have only one posterior articulation with a single vertebra and no anterior articulation to the sternum; therefore, they do not participate in the closed-chain motion of the thorax.

33. Muscles Associated with the Rib Cage

34. The muscles that act on the rib cage are generally referred to as the Ventilatory muscles. The Ventilatory muscles are striated skeletal muscles that differ from other skeletal muscles in a number of ways: (1) The muscles of ventilation have increased fatigue resistance and greater oxidative capacity; (2) These muscles contract rhythmically throughout life rather than episodically; (3) The Ventilatory muscles work primarily against the elastic properties of the lungs and airway resistance rather than against gravitational forces; (4) Neurologic control of these muscles is both voluntary and involuntary (5) The actions of these muscles are life sustaining

35. Primary Muscles of Ventilation The primary muscles are those recruited for quiet ventilation. These include the diaphragm, the Intercostal muscles (particularly the parasternal muscles), and the scalene muscles. These muscles all act on the rib cage to promote inspiration

36. DIAPHRAGM The diaphragm is the primary muscle of inspiration during quiet breathing. Origin : arise from the sternum, costocartilages, ribs, and vertebral bodies. The fibers travel superiorly to insert into a central tendon. Functionally, the muscular portion of the diaphragm is divided into the Costal portion, which arises from the sternum, costocartilage and ribs. Crural portion, which arises from the vertebral bodies The vertical fibers of the diaphragm, which lie close to the inner wall of the lower rib cage, are termed as the zone of apposition.

37. The Crural portion of the diaphragm arises from the anterolateral surfaces of the bodies and disks of L1 to L3 and from the aponeurotic arcuate ligaments. The medial arcuate ligament arches over the upper anterior part of the psoas muscles and extends from the L1 or L2 vertebral body to the transverse process of L1, L2, orL3. The lateral arcuate ligament covers the quadratus lumborum muscles and extends from the transverse process of L1, L2, or L3 to the 12th rib.

38. During tidal breathing, the fibers of the zone of apposition of the diaphragm contract, causing a descent of the diaphragm. As the dome descends, the abdominal contents compress, increasing intra-abdominal pressure. With a deeper breath, the abdomen, now compressed, acts to stabilize the central tendon of the diaphragm.

39. With a continued contraction of the costal portion of the diaphragm against the central tendon that is stabilized by abdominal pressure, the lower ribs are now lifted and rotated outwardly in the bucket-handle motion. Indirectly, the action of the crural portion results in a descending of the central tendon, increasing intra-abdominal pressure. This increased pressure is transmitted across the apposed diaphragm to help expand the lower rib cage.

40. The resultant increase in thoracic size with descent of the diaphragm results in the decreased intrapulmonary pressure that is responsible for inspiration. Exhalation shows a decrease in thoracic size. As the diaphragm returns to its domed shape, the abdominal contents return to their starting position.

41. Let’s watch a video

42. Clinical Aspect Chronic hyperinflation of the lungs results in a resting position of the diaphragm that is lower (more flattened) than normal. Consequently, with more severe disease, an active contraction of the diaphragm pulls the lower ribs inwardly more than pulling the diaphragm down. With an active contraction of the diaphragm in severe COPD , there is less of a reduction in thoracic size and a decreased inspiration. Chronic obstructive pulmonary disease (COPD)

43. COMPLIANCE Compliance is a measurement of the distensibility of a structure or system. Compliance = Compliance = Change in volume per unit of pressure During diaphragm contraction, the abdomen becomes the fulcrum for lateral expansion of the rib cage. Therefore, compliance of the abdomen is a factor in the inspiratory movement of the thorax. ▲ Volume ▲ Pressure

44. Increased compliance of the abdomen, as in spinal cord injury in which the abdominal musculature may not be innervated, decreases lateral rib cage expansion as a result of the inability to stabilize the central tendon. (Without stabilization of the central tendon, the costal fibers of the diaphragm cannot lift the lower ribs.) Decreased compliance of the abdomen, as in pregnancy, limits caudal diaphragmatic excursion and causes lateral and upward motion of the rib cage to occur earlier in the Ventilatory cycle.

45. Intercostal Muscles: The External and Internal Intercostal muscles are categorized as ventilatory muscles. The internal and external Intercostal and the subcostalis muscles connect adjacent ribs to one another.

46. The Internal Intercostal muscles arise from a ridge on the inner surfaces of the 1st through 11th ribs, and each inserts into the superior border of the rib below. The fibers of the Internal Intercostal muscles lie deep to the external intercostal muscles and run caudally and posteriorly. The internal intercostals begin Anteriorly at the Chondrosternal junctions and continue posteriorly to the angles of the ribs, where they become an aponeurotic layer called the posterior intercostal membrane. Internal intercostal muscles are also called as Parasternal muscles

47. The External Intercostal fibers run caudally and anteriorly, at an oblique angle to the Internal Intercostal muscles. The external intercostal muscles begin posteriorly at the tubercles of the ribs and extend anteriorly to the costochondral junctions, where they form the Anterior Intercostal membrane. Both internal and external inter costal muscles are called as lateral inter costal muscles.

48. The Subcostal muscles are also inter costal muscles but are generally found only in the lower rib cage. The Subcostal muscles are found at the rib angles and may span more than one Intercostal space before inserting into the inner surface of a caudal rib. Their fiber direction and action are similar to those of the internal Intercostal muscles.

49. External Intercostal muscles tend to raise the lower rib up to the higher rib, which is an Inspiratory motion. The internal Intercostal muscles tend to lower the higher rib onto the lower rib, which is an Expiratory motion. The external intercostal muscles are active during inspiration and the internal intercostal muscles are active during exhalation, both sets of intercostal muscles may be active during both phases of respiration as minute ventilation increases. Minute ventilation is the amount of air that is breathed in (or out) in one minute: Minute ventilation (VE) = [TV] x [Respiratory rate (RR)]

50. The action of the Parasternal muscles appears to be a rotation of the CS junctions, resulting in elevation of the ribs and anterior movement of the sternum. The primary function of the Parasternal muscles, however, appears to be stabilization of the rib cage. This stabilizing action of the Parasternal muscles opposes the decreased intrapulmonary pressure generated during diaphragmatic contraction, preventing a paradoxical, or inward, movement of the upper chest wall during inspiration. The function of the lateral (Internal and External) inter costal muscles involves both ventilation and trunk rotation.

51. Scalene Muscles The scalene muscles are also primary muscles of quiet ventilation. The scalene muscles attach on the transverse processes of C3 to C7 and descend to the upper borders of the first rib (scalenus anterior and scalenus medius) and second rib (scalenus posterior).

52. Their action lifts the sternum and the first two ribs in the pump-handle motion of the upper rib cage. Activity of the scalene muscles begins at the onset of inspiration and increases as inspiration gets closer to total lung capacity. The scalene muscles also function as stabilizers of the rib cage. The scalene muscles, along with the Parasternal muscles, counteract the paradoxical movement of the upper chest caused by the decreased intrapulmonary pressure created by the diaphragm’s contraction.

53. Accessory Muscles of Ventilation The muscles that attach the rib cage to the shoulder girdle, head, vertebral column, or pelvis may be classified as Accessory muscles of ventilation. They are : Sternocleidomastoid, Pectoralis major , Pectoralis minor, Serratus posterior superior, Serratus posterior inferior, abdominal muscles, Transverse Thoracis. These muscles assist with inspiration or expiration in situations of stress, such as increased activity or disease.

54. The accessory muscles of inspiration increase the thoracic diameter by moving the rib cage upward and outward. The accessory muscles of expiration move the diaphragm upward and the thorax downward and inward.

55. sternocleidomastoid Origin: Manubrium and superior medial aspect of the clavicle . Insertion : mastoid process of the temporal bone. Action : 1. Flexion of the cervical vertebrae. 2. With the help of the trapezius muscle stabilizing the head, the bilateral action of the sternocleidomastoid muscles moves the rib cage in the pump-handle motion.

56. PECTORALIS Major It has 2 portions: Sternocostal head & Clavicular head. The Sternocostal portion of the pectoralis major muscle can elevate the upper rib cage when the shoulders and the humerus are stabilized. The Clavicular head of the pectoralis major can be either inspiratory or expiratory in action, depending on the position of the upper extremity.

57. When the arm is positioned on the side of trunk ,the Clavicular portion acts as an expiratory muscle by pulling the Manubrium and upper ribs down. When the arm is raised, the muscle becomes an Inspiratory muscle, pulling the manubrium and upper ribs up and out.

58. Pectoralis Minor The Pectoralis minor can help elevate the third, fourth, and fifth ribs during a forced inspiration.

59. SUBCLAVIUS A muscle between the clavicle and the first rib, can also assist in raising the upper chest for inspiration.

60. Serratus Posterior Serratus posterior superior (SPS) & Serratus posterior inferior ( SPI) have been assumed to be accessory muscles of respiration. The presumed actions would be elevation the ribs by the SPS ( inspiration). and lowering of the ribs and stabilizing the diaphragm by the SPI (expiration).

61. Abdominal muscles They are : 1.Transversus Abdominis, 2. Internal Oblique Abdominis. 3. External Oblique Abdominis. 4. Rectus Abdominis Action : Expiratory muscles , help in forced expiration. Trunk flexors and rotators. By increasing intra-abdominal pressure, the abdominal muscles can push the diaphragm upward into the thoracic cage.

62. But during inspiration: First, the increased intra-abdominal pressure created by the active abdominal muscles during forced exhalation pushes the diaphragm cranially and exerts a passive stretch on the costal fibers of the diaphragm. These changes prepare the respiratory system for the next inspiration by optimizing the length tension relationship of the muscle fibers of the diaphragm.

63. Second, the increased abdominal pressure created by lowering of the diaphragm in inspiration must be countered by tension in the abdominal musculature. Without sufficient compliance in the abdominal muscles, the central tendon of the diaphragm cannot be effectively stabilized so that lateral chest wall expansion occurs.

64. Transversus Thoracis (Triangularis Sterni) Muscles These are a flat layer of muscle that runs deep to the Parasternal muscles. Origin : from the posterior surface of the caudal half of the sternum and run cranially and laterally, Insertion : into the inner surface of the costal cartilages of the third through seventh ribs. Action : These muscles are recruited for ventilation along with the abdominal muscles to pull the rib cage caudally. (force expiration)

65. Gravity acts as an accessory to ventilation in the supine position. Gravity, acting on the abdominal viscera, performs the same function as the abdominal musculature in stabilizing the central tendon of the diaphragm.

66. Scoliosis Increase in lateral curvature of spine. On the side of the convexity, with sufficient curvature, the Intercostal space is widened and the Intercostal muscles are elongated. On the side of the concavity, the ribs are approximated and the Intercostal muscles are adaptively shortened. Lung volumes and capacities are reduced.

67. Developmental Aspects of Structure and Function Differences Associated with the Neonate The newborn has a cartilaginous, and therefore extremely compliant (travel through the birth canal). Due to increased compliance, there is thoracic instability. The infant’s chest wall muscles must act as stabilizers, rather than mobilizers. Complete ossification of the ribs does not occur for several months after birth. Rib cage of an infant shows a more horizontal alignment of the ribs, with the angle of insertion of the costal fibers of the diaphragm also more horizontal than those of the adult. There is an increased tendency for these fibers to pull the lower ribs inward. Only 20% of the muscle fibers of the diaphragm are fatigue-resistant fibers in the healthy newborn. (diaphragmatic fatigue)

68. Until infants can stabilize their upper extremities, head, and spine, it is difficult for the accessory muscles of ventilation to produce the action needed to be helpful during increased ventilatory demands. As the infant ages and the rib cage ossifies, muscles can begin to mobilize rather than stabilize the thorax. As the infant gains head control, he is also gaining accessory muscle use for increased ventilation. As the toddler assumes the upright position of sitting and standing, gravitation forces and postural changes allow for the anterior rib cage to angle obliquely downward allowing a greater bucket handle motion of the rib cage.

69. Differences Associated with the Elderly Many of the articulations of the chest wall undergo fibrosis with advancing age. The Interchondral and Costochondral joints can fibrose, and the Chondrosternal joints may be obliterated. The Xiphosternal junction usually ossifies after age 40. The chest wall articulations that are true synovial joints may undergo morphologic changes associated with aging, which results in reduced mobility. The costal cartilages ossify, which interferes with their axial rotation. Overall, chest wall compliance is significantly reduced with age.

70. Aging also brings anatomical changes to the lung tissue that affect the function of the lungs. The airways narrow, the alveolar duct diameters increase, and there are shallower alveolar sacs. There is a reorientation and decrease of the elastic fibers. Overall, there is a decrease in the elastic recoil which allows the thorax to rest with an increased A-P diameter. An increased kyphosis is often observed in older individuals, which decreases the mobility. Decreased compliance of the bony rib cage, an increased compliance of the lung tissue, and an overall decreased compliance of the respiratory system as a result of the effects of aging.

71. Skeletal muscles of ventilation of the elderly person have a documented loss of strength, fewer muscle fibers, a lower oxidative capacity. The resting position of the diaphragm becomes less domed, with a decrease in abdominal tone in aging

72. Chronic Obstructive Pulmonary Disease The major manifestation of COPD is damage to the airways and destruction of the alveolar walls. Pathophysiology : As tissue destruction occurs with disease, the elastic recoil property of the lung tissue is diminished and becomes ineffective in removing air from the thorax. Air trapping and hyperinflation occur. The static position of the thorax changes as more air is now housed within the lungs at the end of exhalation. This affects the lung volume and ventilatory capacities

73. In COPD, there is an imbalance in these two opposing forces. (between the elastic recoil properties of the lungs pulling inward and the normal outward spring of the rib cage) As elasticity decreases, an increase in the A-P diameter (more of a barrel shape) of the hyperinflated thorax is apparent, along with flattening of the diaphragm at rest. The range of motion of the thorax is limited. The basic problem in COPD is an inability to exhale . Due to hyperinflation, the fibers of the diaphragm are shortened. Contraction of this very flattened diaphragm will pull the lower rib cage inward, actually working against lung inflation. The diaphragm has a limited ability to laterally expand the rib cage, and so Inspiratory motion must occur within the upper rib cage.

74. In a forceful contraction of the functioning Inspiratory muscles of the upper rib cage, the diaphragm and the abdominal contents actually may be pulled upward. This is a Paradoxical thoracoabdominal breathing pattern because the abdomen is pulled inward and upward during inspiration and is pushed back out and down during exhalation. the work of breathing, in COPD is markedly increased.

75. Some Important questions from the chapter: (from previous years question papers) Name any four accessory muscles involved in Ventilation. (2) Name the muscles involved in Normal Breathing. (2) Name the muscles of Ventilation. (2) Scoliosis (2) Movements of Rib – cage during breathing. Add a note on muscles of breathing. (5) Explain the movements occurring during breathing. (5) Mention in detail about muscles responsible for normal ventilation. (5) Explain in brief the kinematics of ribs and Manubriosternum. (5) Describe the biomechanics of respiration. (5) Explain Chest wall motions during normal breathing. (5) Explain the kinematics of Chest wall. (5) Pump Handle and Bucket handle movement. (5) Describe the mechanical of Normal breathing. (10) Explain chest movements associated with Ventilation. (10)