Fundamentals of Biomedical Engineering

1.The site where two or more bones come together whether or not there is movement between them, is called a joint. The primary function of joints is to provide mobility to the musculoskeletal system. In addition to providing mobility, a joint must also possess a degree of stability. Different joints have different functions to perform. Therefore, the joints have varying degree of mobility and stability depending upon functions to be performed. Joints are formed to give required mobility. Mobility can be triaxial (motion in all three planes) or uniaxial (motion in only one plane). Shoulder joint (ball and socket) is a triaxial joint, Here high mobility is achieved at the cost of low stability. Elbow joint (pivot joint) is a uniaxial joint. It has less mobility (one plane only) but more stability (less vulnerable to dislocation). A joint may have no mobility, The connecting bones of the skull form such joints and they have extreme stability.

1.Joints can be classified according to tissues that lie between the bones.

(a) Fibrous joints: The articulating surfaces of the bones are joined by fibrous tissues. The joint has very little movement which depends on the length of the collagen fibers connecting the bones. The connecting bones of the skull form such joints.

Suture

Periosteum (fibrous tissue) (m embrane)

Bone

Fibrous Joint

(b)Cartilaginous joints : It can be primary or secondary. A primary cartilaginous joint is one in which the bones are united by a plate of hyaline cartilage (For this type of cartilage, refer chapter 1). The joint between the first rib and manubrium is a primary cartilaginous joint. A secondary cartilaginous joint is one in which the bones are united by a disc of fibrocartilage and the articulator surface of the bones covered with a thin layer of hyaline cartilage. Intervertebral joints are secondary cartilginous joints. The amount of movement possible depend on the physical qualities of the fibrocartilage.

Fibrocartilaginous disc

Intervertebral Joint (Cartilaginous Joint)

(c) Synovial joints : The articular surface of the bones are covered by a thin layer

Synovial Joint

of hyaline cartilage separated by a joint cavity. This arrangement permits great degree of freedom of movement. The cavity of the joint is lined by synovial membrane which covers the one end of the articular surface of the first bone to that of the second bone. The

synovial membrane is protected on the outside by a tough fibrous membrane which is called the capsule of the joint. The articular surfaces are lubricated by a viscous fluid which is called synovial fluid. In certain synovial joints like knee joint, discs or wedges of fibrocartilage are interposed between the articulating surfaces of the bones which are called articular discs.

2. Joints can also be classified according to the relative motion between the bones forming a joint, synarthrodial joint does not permit any motion and it is a fibrous joint. Amphiorthrodial joint allows slight relative motions between the bones and it is nothing but a cartilagious joint. Diarthrodial joints permit varying degree of relative motion and they are synovial joints.

TYPES OF SYNOVIAL JOINTS

1.Synovial joints can be classified according to the arrangement of articular surface and nature of movement that are possible by the joints. The joints are:

(a)Plane joint: In these joints, the articular surfaces of the bones are flat which permit the bones to slide one upon other. The sternoclavicular and acromioclavicular joints are plane joints.

Sternoclavicular Joint

Acrumiolavicular Joint

Sternum Clavicle

Scapula

Plane Joint

(b)Hinge joint : It is similar to the hinges on a door i.e. the bones fold & unfold

themselves. Flexion is folding of bones (coming nearer) and extension is unfolding of bones (moving away). Elbow, knee and ankle joints are hinge Joints.

Elbow Joint

Elbow Joint

m ovem ent

Humerus

Radius

Ulna

Hinge Joint

(c) Pivot joint : These joints are like a wheel on an axel. Rotation is the only movement possible in these joints. The atlanto–axial and superior radioulnar joints are pivot joints.

Atlas

(first cervical vertebrae )

Boney Pivot

Axis (second cervical vertebrae)

Pivot Joint

(d) Condyloid joints : The bones have two distinct convex surfaces which articulate with two concave surfaces in these joints. These joints permit flexion, extension, abduction, adduction with small rotational movement. The

knuckle joints or metacarpophalangeal joints are condyloid joints.

M etacarpal

Condyloid Joint

(e)Ellipsoid joints: There is an elliptical convex articular surface that fits into an elliptical concave articular surface in this type of joints. Flexion, extension abduction and adduction can take place in these joints. The wrist joint is a ellipsoid joint.

Concave elliptical surface

Movements

Ellipsoid Joint

(f)Saddle joints: The joint resembles a saddle on a horse’s back. The articular surfaces are concavo-convex. Flexion, extension, abduction, adduction and rotation are possible in this joint. Carpometacarpal joint of the thumb is a saddle joint.

Concavo convex articular surface

(g)

Fill up the gaps

1.A site where two or more bones come together, whether or not there is a movement between them is called---------------

(a) skeleton (b) joint

2.The primary function of a joint is to provide

4.Motion in all time planes is called (a) trimotion (b) triaxial

5.Motion in one plane is called---------

(a) monomotion (b) uniaxial --------

10.Intervertebral joint is a -------- joint (a) cartilaginous (b) fibrous

11.Synovial joint has ------- degree of freedom of movement (a) greater (b) lesser

12.Amphiorthrodial joint permits------- relative motion between bones (a) slight (b) varying degree of

13.Diorthrodial joint permits ------- relative motion between bones (a ) slight (b) varying degree of

14.Synovial joint of plane variety has the articular surfaces of the bones which are

------- (a) flat (b) sliding

15.A joint which is like a wheel on an axel is

------ joint (a) hinge (b) pivot

6.The connecting bones of the skill form a

---- joint (a) fibrous (b) fixed

7.Cartilage joint has bones united by a -------

of fiberocartilage (a) ligament (b) disc

8.Synovial joint has articular bone surfaces separated by a --------- filled with synovial fluid (a) cavity (b) pouch

9.------- fluid reduces wear and tear of articular bone surfaces (a) lubricating (b) synovial

16.A saddle joint has reciprocally --------

articular surfaces (a) convex (b) concavoconvex

17. A ellipsoid joint has--------- articular surfaces (a) concavo-convex (b) elliptical

18.A condyloid joint has two distinct -------

surfaces which articulate with two distinct

------ surfaces

(a) flat, flat (b) convex, concave

INTRODUCTION

1.The vertical column is also known as spine, spinal column or back bone. It is the control axis of the body. It supports the body weight and transmits it to the ground through the lower limbs. It is the most complex part of the human muscleoskeletal system. Its principal functions are to protect the spinal cord, to support the head, neck and upper

limbs; to transfer loads from the head and trunk to the pelvis; and to provide flexibility to carry out a variety of movements. It can be divided into five regions viz. cervical (neck), thoracis (chest), lumbar (lower back), sacral and coccygeal regions. The thoracis and lumbar regions of spinal column form the trunk of the body while sacral and coccygeal regions join with pelvis and form parts of pelvic girdle.

C e rv ic al

V e rteb rae (7 )

ANATOMY OF SPINAL COLUMN

1.The vertical column is made up of 33 vertebraes which include 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal. In the thoracic, lumbar and sacral regions, the number of vertebrae corresponds to the number of spinal nerves and each nerve lying below the corresponding vertebrae. In cervical region, then are eight nerves, the upper seven lying above the corresponding vertebrae and the eight below the 7th vertebrae. In the coccygeal region there is only one coccygeal nerve.

2.The vertebrae are also grouped according to their mobility. The moveable or true vertebrae include 7 of cervical, 12 of thoracic and 5 of lumbar vertebrae which have intervertebrae disks in between for facilating rotating movement. Hence these are 24 movable (true) verterbrae and nine unmovable (false) verterbrae which are in sacrum and coccyx region. Twelve thoracic verterbrae have ribs attached to them.

3.There are 24 movable verterbrae and they form amphiarthrodial joints with the fibrocartilaginous interposed between each pair of vertebrae. The fibrocartilaginous discs perform following functions.

(1)Sustains loads transmitted from segments above

(2)Act as shock absorbers

(3)Eliminate bone to bone contact

(4)Reduce the effects of impact forces by preventing direct contact between the verterbraes. The intervertebrae disc permits articulation of each verterbrae with the adjacent verterbrae in these planes. Hence the entire spinal column functions like a single ball and socket joint. Flexion and extension, lateral flexion and rotation of body is possible due to the structure of spinal column.

4.At the superior end, spinal column has two important joints with head. The atlantooccipital joint is the joint between the first cervical vertebrae (called atlas) and the occipital bone of the head. This is a double condyloid joint (refer chapter 6) The joint permits movement of the head in the sagittal plane and lateral plane. The atlanto axial joint is the joint between the atlas and the axis (first and second verbetrae). This is a pivot joint which permits head to rotate in the transverse plane.

5.The movement of head and neck is provided, controlled and coordinated by a muscle group viz. prevertebrals (anterior), hyoids (anterior) sternocleidomastoid (anterior lateral) scalene (lateral), levator scapulae (lateral) suboccipital (posterior) and spleni (posterior). The spine gets its stability from the inter vertebral discs and from the surrounding ligaments and muscles. The discs and ligaments provide passive stability while muscles give active support. The muscles of the spinal column exist in pairs. The anterior portion of spine is connected to abdominal muscles viz. the rectus abdominis, external obligue and internal obligue. These muscles can do flexion & maintain the spine in proper position. There are three layers of posterior trunk muscles viz. the erector spine, the semispinalis and the deep posterior spinal muscle groups. These muscles provide trunk extension as they are located at posterior position of the spine. The effect of gravity is also overcome by these muscles. The quadratus lumborum muscle helps in lateral trunk flexion. The pelvis and lumbar spine is stabilized by this muscle. The lateral flexion of the trunk is carried out by the abdominal and posterior muscles. The rotational movement of the turnk is controlled by the simultaneous action of anterior & posterior muscles.

ANALYSIS OF FORCE SYSTEM

1.When head flexes in meridian plane, exterior muscles exert force to support the head. There is also compressive force exerted on the first cervical vertebrae at the atlantooccipital joint.

F

b R Spinal cord

W

2.Let F is muscle force & R is reaction at the joint. We get a three forces system which is concurrent at joint O. Hence we can apply Lami’s theorem on the force system.

Where α is angle with horizontal of muscle force and β is angle of reaction of joint with horizontal.

Hence muscles must apply 50 N force to support the head and reaction force developed at the joint is 88 N.

MOVEMENTS OF NECK AND SPINE

1.Neck: It can rotate in horizontal plane. It can do lateral bending. It can also do flexion and extension in meridian plane.

Rotation

If we have W = 50 N, α = 30° & β = 60°

Flexion & Extension

Lateral B ending

2.Spine: Spine can do flexion and extension in meridian plane. It can also do lateral

bending. It can also have rotational movement in horizontal plane.

Fill up the Gaps

1.The primary function of spinal column is to protect the ----- of the body

(a) posture (b) spinal cord

2.Neck has ---- cervical vertebraes. (a) six (b) seven

3.Chest has -------- thoracic vertebrae (a) Thirteen (b) twelve

4.Back has ---- lumbar vertebrae (a) five (b) four

5.The spinal column has ---vertebrae (a) 24 (b) 33

MECHANICS OF THE SPINAL COLUMN

6.There are -------- movable vertebrae (a) 24 (b) 33

7.Each movable vertebrae has fibrocartilaginous --------- interposed between each pair of verterbrae.

(a) plate (b) disc

8.Movable vertbraes form -------- joints (a) amphiorthrodial (b) rotatable

9.Thoracic vertebraes have ------ attached to them. (a) ribs (b) abdomen

10.The interverbetrae disc permits ----- of each verbetrae with the adjacent vertebrae in three planes. (a) articulation (b) rotation

11.Entire spinal column functions like a single

------- joint. (a) ball and Socket (b) plane

12. The joint between first cervical vertebrae and the occipital bone of the head is -----

(a) ‘atlanto’ occipital (b) vertebro occipital

13.The atlantoaxial joint is between the first vertebrae and --------- vertebrae

(a) 3rd (b) 2nd

14.9 unmovable verterbraes are in -------

(a) Back (b) Pelvic girdle

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15.Chest is ------------ region (a) cervical (b) thoracic

16.Back is ---- region. (a) thoracic (b) lumbar

17.The thoracic and lumbar regions of spinal column form the ------ of the body.

(a) chest (b) trunk

18.Sacral and coccygeal regions join to form

------- (a) shoulder girdle (b) pelvic girdle

19.Ligament and discs provide ------- stability (a) active (b) passive

20.Muscles provide ------- stability (a) active (b) passive

21.The load from head to pelvis is conveyed by -------

(a ) chest bones (b) spinal column

22.The protection to spinal cord is provided by

------- (a) chest bone (b) back bone

23.Intervertebrae discs permit-------contacts between adjacent vertebrae.

(a) smooth (b) no

24.In coccygeal region, there is-------nerve/ nerves

(a) one (b) four