Classification of joints & joint mechanics

A brief description of types of joints in human body and joint mechanics.

1. Classification of Joints &
Joint Mechanics
Dr. Piyush

2. Introduction
❖A joint, also called an articulation, is any place where
adjacent bones or bone and cartilage come together
(articulate with each other) to form a connection.
❖Joints are classified both functionally and structurally.
❖Functional classification: basis is range of movement
possible.
❖Structural classification: basis is nature of the intervening
soft tissue.

3. ❖Functional classification:
❖Synarthroses - Immovable joints ex: sutures of skull
etc.
❖Amphiarthroses - Slightly movable joints ex: pubic
symphysis etc.
❖Diarthoses - Freely movable joints ex: hip joint,
shoulder joint etc.

4. ❖Structural classification:
❖Fibrous joint: Bones are joined by fibrous connective.
❖Cartilaginous joint: Bones are joined by cartilage.
❖Synovial joint: Joint cavity with synovial fluid present.

5. Fibrous joint
❖Participating bones are united by fibrous connective
tissue.
❖Subtypes:
❖Sutures
❖Gomphosys
❖Syndesmosis

6. Sutures
❖Immovable
❖Confined to skull
❖bones are separated by a layer of membrane derived connective tissue called
sutural ligament.
❖Sutural aspect of each bone covered by a layer of osteogenic cells (cambial
layer)
❖Cambial layer overlaid by a capsular lamella of fibrous tissue that is
continuous with the periosteum on both the endo and ectocranial surfaces.

7. ❖The region between the capsular coverings contains
loose fibrous connective tissue which decreases with
age, so that the osteogenic surfaces become apposed.
❖On completion of growth, many sutures synostose and
are obliterated.

8. ❖Types of sutural joint: basis is shape
of articular surface
❖Plane: median palatine suture
❖Serrate: saggital suture
❖Denticulate: lambdoid suture
❖Squamous: temporo parietal suture
❖Schindylesis : rostrum of sphenoid
and cleft between ala of vomer.

9. Gomphosis
❖A peg and socket junction between tooth and its socket
❖Two components are maintained in intimate contact by
the collagen of the peri-odontium connecting the dental
cement to the alveolar bone

10. Syndesmosis
❖2 adjacent bones connected via considerable amount of fibrous
connective tissue.
❖Connective tissue in form of interosseous membrane or ligament.
❖ex: middle radioulnar joint, middle and inferior tibiofibular joint,
posterior part of sacro-illiac joint, tympano-stepedial joint.

11. Cartilaginous joint
❖Participating bones are
united by intervening
hyaline or fibrocartilage.
❖2 subtypes:
❖Primary cartilaginous
(synchondrosis)
❖Secondary cartilaginous
(Symphysis)

12. Primary cartilaginous (synchondrosis)
❖Occur where advancing centres of ossification remain separated by an
area of hyaline (but non articular) cartilage.
❖They are present in bones that form from more than one centre of
ossification.
❖Since hyaline cartilage retains the capability to ossify with age,
synchondroses tend to synostose when growth is complete.
❖Ex:epiphyseal growth plate, 1st costosternal joint, Spheno-occipital joint .

13. Secondary cartilaginous (Symphysis)
❖An intervening pad or disc of fibrocartilage interposed between the
articular (hyaline) cartilage that covers the ends of two articulating bones.
❖All symphyses occur in the midline.
❖ex: mandibular, manubriosternal, pubic and intervertebral
❖The mandibular symphysis (symphysis menti) is devoid of fibrocartilage, so
is basically a misnomer.
❖All symphysis except mandibular resist synostosis so are permanent .

14. Synovial joints
❖Freely moving joints
❖The articulating bony surfaces covered by
hyaline cartilage and separated by a
cavity of viscous synovial fluid that
serves as a lubricant.
❖ Joint stability is provided by a fibrous
capsule and often by internal or external
accessory ligaments.
❖Synovial fluid, which also aids metabolite
transport to cells in the articular
cartilages, is synthesized by the synovial
membrane that lines the joint capsule.

15. Classification
1) On the basis of shape of
articular surface
❖Plane /gliding
❖Hinge / ginglymus
❖Pivot / trochoid
❖Ellipsoidal
❖Saddle
❖Ball and socket
❖Condylar

16. 2) On basis of number of articulating bone
❖Simple : 2 articulating bone
❖Compound : more than 2 articulating bone
❖Complex : joint cavity divided by articular disk

17. 3) on the basis of plane of movement
❖Uniaxial- hinge & pivot
❖Biaxial- ellipsoidal, saddle and condylar
❖Multiaxial- ball and socket

18. Plane synovial joint
❖Articular surfaces are almost flat
❖Movements are considered to be pure translations or
sliding between bones.
❖ex: intercarpal, intertarsal, intermetacarpal,
intermetatarsal, zygapophyseal joints of vertebrae

19. Hinge joint
❖Articular surfaces are pulley shaped
❖Movement takes place about a single stationary axis, and
so is largely restricted to one plane.
❖ex: Elbow, interphalangeal, knee and ankle

21. Condylar joint
❖Modified hinge joint
❖Predominantly uniaxial movements but a smaller
degree of movement possible with respect to an axis
perpendicular to main axis.
❖ex: Knee and temporo-mandibular joint

22. Pivot joint
❖Articular surface of one bone is round which rotates inside an
osteo-ligamentous ring.
❖These are uniaxial joints allowing rotation only around the
axis of the pivot.
❖Pivots may rotate in rings (e.g. the head of the radius rotates
within the annular ligament and ulnar radial notch), or rings
may rotate around pivots (e.g. the atlas rotates around the
dens of the axis).

24. Ellipsoid joint
❖Articular surface is elliptical and one is convex while
other is concave.
❖Movements possible in 2 axis (biaxial).
❖ex: radio-carpal (wrist), atlanto-occipital,
metacarpophalangeal and metatarsophalangeal joint

26. Saddle joint
❖Modified ellipsoid joint
❖Both articular surfaces are reciprocally concavoconvex.
❖Movements possible in 2 axis (biaxial).
❖ex: 1st carpometacarpal, sternoclavicular, calcaneocuboid,
incudomalleolar joint

28. Ball and Socket joint
❖Articular surface of one bone is round ball like which
fits in the socket like convexity of other bone.
❖Movement is multiaxial.
❖ex: hip, shoulder, incudo-stepedial joint.

29. Joint Mechanics
❖Degree of freedom: In mechanics, the position and orientation of a rigid body in space
is defined by three components of translation and three components of rotation, which
means that it has six degrees of freedom.
❖The three possible rotations are axial, abduction– adduction, flexion–extension.
❖Three possible translations are proximodistal, mediolateral and anteroposterior.
❖For most joints, translations are small and can be neglected.
❖A few joints have minor but pure translatory movements, but most joint motion is by
rotation.

30. Multi axial shoulder joint

31. Joint as a lever
❖Most motion at the major joints results
from the body’s structures acting as a
system of levers.
❖A lever is a rigid bar (bone) that turns
about an axis of rotation or fulcrum
(joint)
❖The lever rotates about the axis as a result
of a force (from muscle contraction)
❖The force acts against a resistance
(weight, gravity, opponent, etc.)
❖The relationship of the points determines
the type of lever.

32. Class I lever

33. Class II lever

34. Class III lever

35. Purpose of lever action

36. ❖Law of lever : load X load arm = effort X effort arm
❖Mechanical Advantage: the ratio of the force produced
by a machine to the force applied to it, used in assessing
the performance of a machine.
❖MA= Load/effort = effort arm/ load arm

38. ❖Joint function for movement is to do a work efficiently
❖Efficiency may be in terms of
❖Power : to lift a load with minimum effort.
❖Range /speed of motion
❖Power of a muscle depends on the number and
diameter of muscle fibres.

39. ❖Most muscles are inserted to the bones close to joints on
which they act, therefore they loose mechanical
advantage but they gain in speed and range of motion.

40. ❖Grays anatomy. 41st edition.
❖A. K. Dutta. Essentials of Human anatomy.
❖Biomechanical principles.
❖Cunnigham’s manual of Practical anatomy
BIBLIOGRAPHY

41. Thank You