Biomechanics of the rib cage

1. 1

2. BIOMECHANICS OF THORAX
AND CHEST WALL
2

3.  Most important
functions of the
thorax and chest
wall :
 Ventilation of
lungs
 Protection of
heart, lungs and
viscera
3

4.  Ventilatory mechanism in humans has three
parts
 The ribcage
 The ventilatory muscles
 The abdomen
4

5. 5
Ribcage

6.  Truncated cone shaped
 Articulations of ribcage
 Manubriosternum
 Xiphisternum
 Costovertebral
 Costotransverse
 Costochondral
 Costosternal
 Interchondral
6

7. 7
Manubriosternal and xiphisternal joints -
manibriumsternum
xiphisternum
Synchondrosis variety of
cartilaginous joints

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 Sternal angle/angle of Louis corresponds to T4-T5
posteriorly.
 Bifurcation of trachea
 Aortic arch

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Costovertebral joint
 Typical costoverterbral
joint - synovial type of
joint
 2nd to 9th ribs - typical
costoverterbral joint
 1st, 10th, 11th and 12th
atypical ribs articulate
only with their
corresponding vertebra

10. 10
 The costovertebral joints are the articulations
that connect the heads of the ribs with the bodies
of the thoracic vertebrae. Joining of ribs to the
vertebrae occurs at two places, the head and the
tubercle of the rib. Two convex facets from the
head attach to two adjacent vertebrae. This forms a
trochoid joint, which is strengthened by the
ligament of the head and the intercapital
ligament.

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Costotransverse joint
 Synovial joint
surrounded
by thin fibrous
capsule
 Is present from T1
to T10 vertebra and 1st
to 10th ribs
 This articulation is
reinforced by the
dorsal costotransverse
ligament

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 Upper CT joints the
primary movement -
rotation
costal facet concave shape
and costal tubercle
convex shape
 T7 to T10 both articular
surfaces are flat and
gliding motion
predominates

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14.  Costochondral joints are synchondroses with no
ligamentous support
 1st through 7th ribs articulate anterolaterally with
costal cartilages forming costochondral joint
14

15.  Costosternal (CS) joints
are formed by
attachment of the costal
cartilages of ribs to
sternum anteriorly
 CS joints of 1st, 6th and
7th ribs are
synchondroses
 CS joints of 2nd to 5th
ribs are synovial joints
15
Interchondral
joints
costosternal

16.  Interchondral joints are formed when 6th through
10th costal cartilages articulate with cartilage
above them and this is only way by which 8th to
10th ribs are connected to sternum
 Interchondral joints are synovial type of joints
16

17.  Costovertebral and costotransverse form a joint
couple mechanically linked
 Common movement - rotation about an axis
passing through centre of each joint for 1st to
10th ribs
 11th and 12th ribs it passes through the CV
joints as CT is absent for these two ribs
17

18.  Axis of motion - more towards frontal plane for
upper ribs and towards saggital plane for lower
ribs.
 During inspiration - ribs elevate, in upper ribs
motion simulates that of pump handle due to
frontal plane orientation of axis of motion, this
increases the anteroposterior diameter of
ribcage
18

19.  Axis of motion lying nearly in the saggital plane,
movement takes place more in lateral part in the
lower ribs
 Movement of 11th and 12th ribs varies from the
rest of the ribs
 Quadratus Lumborum muscle depresses and
fixes these ribs to provide adequate
diaphragmatic muscle tension
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20. 20
Axis towards frontal
plane
Axis towards saggital
plane

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22. 22

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MUSCLES

24.  Muscles of the ribcage - ventilatory muscles
 Increased fatigue capacity and contract
rhythmically throughout life rather than
episodically
 Act primarily against the elastic properties of
lungs and airway resistance rather than
gravitational forces
24

25.  Neurological control of ventilatory muscles is
both voluntary and involuntary
 Recruitment of these muscles for ventilation
depends on the type of ventilation required
 Primary muscles of ventilation - Diaphragm,
Intercostals and scalenes
25

26. 26

27. Diaphragm
27

28.  Diaphragm - accounts for 70% to 80% of quiet
breathing
 Functionally, muscle portion of diaphragm can be
divided as Costal and Crural parts
 Costal part - sternum, ribs (lower 6) and costal
cartilages
 Crural part - vertebral bodies (L1-L3)
28

29. 29

30. Diaphragm contracts and pulls central tendon down
increasing vertical diameter of thorax
Decrease in the pleural pressure
Decrease in intrapulmonary pressure responsible for inspiration
30

31.  Costal fibers of diaphragm run vertically from
their origin close to the ribcage before getting
inserted into central tendon
 Portion of diaphragm which is close to inner wall
of lower ribcage - “ZONE OF APPOSIOTION”
 During tidal breathing, descent of dome of
diaphragm causes only slight change in its
shape, maintaining most of zone of apposition
31

32. 32

33.  Crural portion has an indirect effect on
inspiration, it helps central tendon to descend
thus increasing pressure which is transmitted
through apposed diaphragm thus helping lower
ribcage to expand
33

34. 34

35.  Diaphragm increases all three diameters of the
ribcage
Vertical diameter by contraction of central
tendon
Transverse diameter by elevating the lower ribs
Anteroposterior diameter by elevating the upper
ribs with the help of sternum
35

36. 36
Intercostals
 Intercostal muscles - internal and external
intercostals
 Act as splints during inspiration and expiration, by
maintaining a constant tone
 Internal intercostal muscles run caudally and
posteriorly continuing dorsally where they become
posterior intercostal membrane at angle of the ribs

37. 37
 External intercostals run caudally and at an
oblique angle to internal intercostals till
costochondral junction where they become
anterior intercostal membrane

38. 38

39.  Anteriorly portion where only internal intercostals
are present - parasternal muscles
 Posteriorly only external intercostals are present
from the tubercle of ribs to the angle of ribs
 Laterally both external and internal intercostals
are present and are referred to as interosseous
or lateral intercostals
39

40.  Both set of intercostal muscles may be activated
during phases of respiration as minute ventilation
increases
 Activation of intercostals is from cephalic to
caudal end
40

41. 41

42.  Parasternal muscles - primary inspiratory
muscles during quiet breathing and
stabilizers of ribcage
 Scalene are one of the primary muscles of quiet
respiration, their activity begins with onset of
inspiration and increases as inspiration gets
closer to total lung capacity
42

43. 43
Accessory musclesof respiration
Inspiration
 Levatores costarum
 Pectoralis major/minor
 Rhomboids
 Anterior/medial/posterior
scalenes
 Serratus anterior and posterior
superior
 Subclavius, SCM
 Thoracic erector spinae
 Trapezius
Expiration
 Iliocostalis lumborum
 Transversus thoracis
Inspiration/Expiration
 Latissimus dorsi
 Quadratus lumborum
 Serratus posterior inferior
Maintenance of rib cage shape
 Intercostals

44.  Accessory muscles of ventilation
 When thorax is fixed, accessory muscles of
inspiration move vertebral column, arm or head on
the trunk
 Reverse muscle action
44

45. 45

46.  Sternocleidomastoid flexes the cervical spine
when acting bilaterally
 When cervical spine is fixed the muscle moves
the ribcage superiorly, which expands upper
ribcage in pump handle mechanism
46

47.  Pectoralis major elevates upper ribcage when
shoulders and humerus are fixed. It can act both
as an inspiratory and an expiratory muscle
 Pectoralis minor can help raise third, fourth and
fifth ribs during a forced respiration
47

48.  Upper Trapezius can be helpful in active
inspiration in fixing the head so that
sternocledomastoid can act as a muscle of active
inspiration
 Subclavius is between the clavicle and first rib,
when acting in reverse action it can assist in
raising upper chest for inspiration
48

49. 49
 Serratus anterior
 Serratus posterior
 Lat dorsi
 Sterno costalis

50.  Abdominal muscles –
 Tranversus abdominis
Internal abdominal oblique
External abdominal oblique
Rectus abdominis
50

51. Internal oblique
External oblique
Transverse
abdominis
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52. 52
Antagonismand synergismof diaphragm
and abdominal muscles :
 During inspiration – with diaphragmatic
contraction the central tendon descends down
increasing vertical thoracic diameter but this is
opposed by elongation of mediastinal elements
and also resistance of abdominal viscera.
At this time the abdominals relax allowing the abdomen
to bulge.
 This shows the synergistic activity of abdominals

53.  During expiration – diaphragm relaxes and
contraction of abdominal muscles lowers the
thoracic floor thereby decreasing simultaneously
the transverse and anteroposterior diameters of
thorax
 Also by pushing the viscera up abdominals
raise the central tendon
 This shows the antagonistic activity of
abdominals
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54. 54
 In normal breathing the respiratory muscles
should use less than 5% of the O2 taken in the
breath. If the diaphragm not working it is much
more.

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56. 56
Differencesassociated with neonates
 Healthy new born has an extremely compliant
chest wall because it is primarily cartilaginous
 Primary responsibility of ribcage stability on
ribcage muscles to counteract negative pleural
pressure of diaphragm during inspiration
 Ribs are also more horizontally placed this alters
angle of insertion of costal fibers of diaphragm

57.  Increased tendency of diaphragm fibers to pull
lower ribs inwards, thereby decreasing efficiency
of ventilation
 Only 20% of fibers of diaphragm are fatigue
resistance as compared to 50% in adults
 Accessory muscles are also at a disadvantage
57

58. 58
Differencesassociated with elderly
 Pulmonary changes that occur may
affect pulmonary function
 Costal cartilages ossify, which interferes with
their axial rotation
 Many articulations undergo fibrosis with
advancing age
 Synovial joints undergo morphological changes
reducing mobility

59. 59
 Chest wall compliance also reduces with age
 Lung tissue decreases in elasticity, thus
affecting elastic recoil property of lung and
outward pull of ribcage
 Results of these skeletal and tissue changes are
increase in functional residual capacity and
decrease in inspiratory capacity of thorax

60.  Loss of strength of skeletal muscles of
respiration
 Ventilatory muscles become more energy
expensive
 Resting position of diaphragm becomes less
domed with decrease in tone of abdominal
muscles
60

61. 61
Scoliosis
 In scoliosis, if the curve is structural it
affects chest wall biomechanics and hence ventilation
 Lumbar and cervical curves cause minimal
change in chest wall biomechanics but a thoracic
curve causes restriction in ventilatory capacity,
restriction proportional to severity of curve

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3 Types:
1. Nonstructural scoliosis
2. Transient structural scoliosis
3. Structural scoliosis (idiopathic accounts for 70–
80% of cases of scoliosis)

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64. 64
Kyphosis
An exaggeration of the normal posterior curve of the
spine.
 Results from change in structure and shape in
spine or posture.
 Fracture of anterior aspect of vertebral body –
Osteoporosis (OP).
 Scheuermann’s disease – Hereditary disorder that
results in kyphosis.

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COPD
 In COPD, major manifestation is hyperinflation of
lungs due to destruction of alveolar walls
 Resting position of thorax in more of inspiratory
cycle against the normal resting position in
expiration
 This leads diaphragm to adapt a more flattened
configuration in its resting state rather than
acquiring its usual dome shape

66.  Flattened diaphragm will pull lower rib cage
inward, actually working against lung inflation
 This also decreases the zone of apposition
 Majority of inspiration performed by accessory
muscles, particularly the parasternal and scalene
66

67. Pectuscarinatum
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Some patients develop a
rigid chest wall, in which
the AP diameter is
almost fixed in full
inspiration.
In these patients,
respiratory efforts are
less efficient.

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 Vital capacity is reduced
 Residual air is increased
 Alveolar hypoventilation may ensue, with arterial
hypoxemia and the development of cor pulmonale.
 As the lungs lose compliance, incidence of
emphysema and frequency of infection are
increased.

69. Pectusexcavatum
69
Unless severe does not
cause restriction in
breathing , but due to
altered biomechanics
–shallow breathing
and dyspnea on
exertion may be
present

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Flail chest

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 The characteristic paradoxical motion of the flail
segment occurs due to pressure changes associated
with respiration that the rib cage normally resists:
 During normal inspiration, the diaphragm
contracts and intercostal muscles push the rib cage
out. Pressure in the thorax decreases below
atmospheric pressure, and air rushes in through
the trachea. However, a flail segment will not resist
the decreased pressure and will appear to push in
while the rest of the rib cage expands.

72. 72
 During normal expiration, the diaphragm and
intercostal muscles relax, allowing the abdominal
organs to push air upwards and out of the thorax.
However, a flail segment will also be pushed out
while the rest of the rib cage contracts.
 The constant motion of the ribs in the flail
segment is painful, and, untreated, the sharp
broken edges of the ribs are likely to eventually
puncture the pleural sac and lung, possibly
causing a pneumothorax.

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Paralysisof diaphragm/hemidiaphragm

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Positioning

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TREATMENT TECHNIQUES

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Impaired Muscle Performance
Sources:
 Neurologic impairment or pathology
 Muscle strain or injury
 Disuse resulting in atrophy and general
deconditioning
 Length-associated changes resulting in altered
length-tension properties

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Treatment
• Neural input must be restored for muscle performance
to improve.
• Protect weakened muscles from overstretch with
proper support.
• Stretch short muscles to maintain extensibility and
prevent contracture.
• For example: Impaired respiration – Stretch short
muscles and apply manual or elastic band resistance to
facilitate strength.

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Stretch Lateral Trunk and
Intercostal Muscles

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Muscle Strain or Injury
 Address posture and movement patterns.
 Improve performance of underused synergists.
 For example, in the case of overuse of anterior
scalene during breathing, reduce anterior scalene
use by improving performance of deep anterior
cervical flexors and instruct in proper pump and
bucket handle diaphragmatic breathing.

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Disuse Resulting in Atrophyand General
Deconditioning
Caused by illness, immobilization, sedentary
lifestyle, subtle shifts in muscle balance.
Progressive resistive exercises for the upper body.
Initially, weight of limb is ample stimulus.
Progress in small increments.
Address balance between abdominal and spinal
extensors as well as thoracic multifidii.

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Length-Associated Changes
Subtle imbalances in muscle length lead to length-
associated strength changes and positional
weakness of one synergist compared with agonist
or antagonist.
• Strengthen weak overstretched muscle groups in
shortened range.
• Stretch adaptively shortened muscles.
• Supportive taping adjunctive.
• Correction of posture and movement patterns.

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Supportive Taping forThoracic Spine

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Impaired ROM, Muscle Length, and Joint
Mobility/Integrity
Optimal function of the thoracic region requires
full symmetrical cardinal plane motion and full
rib motion.
Consider symmetrical breathing patterns.
Diagnose restrictions that are joint versus soft
tissue origin.

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Establish the neutral spine

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Exercise to PromoteThoracic Extension

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Exercise Managementof Scoliosis
• Avoid symmetrical and spine flexibility exercises.
• Strengthen overstretched antagonist/synergist in
shortened range.
• Promote strength of the relatively weak muscle or
groups of muscles in the anterior thoracolumbar
region and the pelvic-hip complex.
• Trunk curl exercises or sit-ups are not indicated
methods of strengthening anterior thoracolumbar
muscles.

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Thoracic Outlet Syndrome
• Characteristically young, slender women with
drooping shoulders and poor posture
• Treatment aimed at improving muscle
performance and reducing stretch to upper and
middle trapezius
• Supportive taping to elevate scapula

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• Correct posture and movement relative to
neurovascular compression or stretching (i.e.,
depressed or anterior tilt scapula)
• Tape scapula into elevation to relieve compression
• Alter sleeping habits
• Improve diaphragmatic breathing
• Address associated physiologic/psychological
impairments

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Summary
Functions
Joints
Movements
Muscles
Differences associated with neonates and elderly
Chest wall deformities
Treatment and correction of thoracic mechanics

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