Biomechanics &articulations 

What is a joint?

• The location where 2 bones or more connects

The function of a joint:

• Majority allow movement ( except for the joint found in the skull/ sacral, sternal, and pelvic bones ),
• Provide mechanical support

Joints are classified based on the?

• Their structure AND their functionality.

joints are classified based on their anatomy with the following:

• The joint complexity, The number of axes,   The joint geometry, The joint movement capability

Types of joints based on their movability:

• Immovable joints ( also known as Synarthroses),  Slightly moveable ( also known as Ampisrthroses ), Freely movable ( Diathroses / Synovial )

Examples of each type ( joints based on movability):

•  Immovable joints  ( in skull),  Slightly movable joints ( Spine),   Movable/freely movable joints ( Hands and hip)

The structural classification of joints :

·       Fibrous

·       Cartilaginous

·       Synovial

fibrous joints are divided into:

• Sutures ( which are immovable; eg coronal sutures)
• Gomphosis ( also immovable; eg dental alveolar joint)
• Syndesmosis ( slight movement; interosseous membrane of the forearm and leg )

Cartilaginous joints are divided into :

• Primary joints ( immovable hyaline cartilage; eg growth plates, 1st sternocostal joint )
• secondary :( permits slight movement Fibrocartrlidge; Pubic symphysis and intravertebral discs )

types of Synovial joints:

1. Plane
2. Hinge
3. Pivot
4. Condylar
5. Saddle
6. Ball and socket

Talk about Synarthroses Joints : [ syn: together, athron: joint]

• they are immovable
• fibrous joint
• function: attenuate force / absorb shock, permit little to no movement of the articulating bones
• found as: sutures, Gomphosis, Syndesmosis

Talk about Amphiarthros Joints : [ Amphi: on both sides, athron: joint]

• they are slightly moveable

• Cartilaginous joint

• function: attenuate force /, permit motion more the SYnarthroses joint

• found as: the hyaline cartilage known as the pubic symphysis. Sternocostal joints; hyaline cartilage.

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Talk about Diarthroses or synovial joints :

• they are freely movable with only slight limitation
• a joint is synovial if those are found: Articular cartilage , Articular capsule , synovial fluid )

great example is the knee ( which has: Joint cavity filled with synovial fluid, Joint capsule that includes the synovial membrane and the fibrous capsule, and the articular cartilage )

what is articular cartilage, Articular capsule, SYnovial fluid

Articular cartilage : is a protective layer of dense white connective tissue covering the articulating bone surfaces

Articular capsule: double layer membrane , surround the joint

Synovial Fluid: clear slightly yellow liquid; provide lubrication inside the articular capsule

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Types of Synovial Joints

Synovial joints are also categorized based on the number of axes allowed during rotation into : uniaxial , biaxial , triaxial , nonaxial

joints with limited motion around the axis is called nonaxial .

Joint motion is sometimes discribed with degrees of freedom which is related to the number of axises utlized in motion . for example : a uniaxial joint has 1 Degree of freedom.

Articular Cartilage

→ it is a dense white connective tissue , thick , coats the ends of bones that are articulating at synovial joints .

→ it is also a soft porous , permeable tissue that is hydrated

• function of Articular cartilage :

  1. reduces contact stress by spreading the load over a wide area
  2. minmizes friction and mechanical wear at the joint by providing protective lubrication [ the lubrication is the one that minimizes friction and wear ]
  3. they can reduce the maximum contact stress by 50% or more

• disadvantage of cartilage : it has little to no abiltiy to heal or regenerate on its own , so once damged the injuries progresses . the protective coating of the articular bone wore away : which results into fegenerative arthritis

FIbrocartilage :

→ soft tissue discs or menisici , found between the articulating bones

→ example : menisici of the knee , in the spine

• Funtions of fibrocartlilage

  1. Distrubting the loads over joint surfaces
  2. improving the fit of articulations
  3. limiting slip between bones
  4. protecting the joint periphery
  5. lubricating the joint
  6. absorbing shock at the joint

what are the Articular connective tissues :

• Tendons ( muscle to bone ) and ligaments ( bones to other bones )

• both of them are passive tissues

• composed mainly of collagen and elastic fibre

• they don’t have the ability to contract ( like muscle tissues )

• they are slightly extensible

• they are elastic ( they will return to the original length ) unless they are stretched beyond the length/ability

• if they are stretched beyond the limit; they will remain stretched unless restored by surgery

• response to changed mechanical stress: hypertriphying/ atrophying

• effect of exercise: increased size and strenght of both tendons and ligaments , increased strength of th junctions between them and the bone

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Joint Stability :

• it is the ability of an articulation to resist dislocation / displacement while preventing injury to other surrounding parts

• factors influcing stability : shape of the articulating bone surfaces , arrangment of ligaments and muscles ( as ligaments muscles and tendons affect the stability ) .

• when the area of contact is maximum : known as the close packed postion , where the joint stbaility is maximum , and it is the best fit for a joint moving through ROM .

• Loose packed postion : low area of contact, maximum mobility , and minmum stability.

• the acetabulum : deep socket for the head of femur > constant large contact area > considers one of the reasons the hip is a stable joint

• Should : relatively small socket > relative small contact area > one of the reasons the shoulder complex is relatively instable

• some people have joint that are more or less stable than others due to slight anatomical variations in shapes and sizes of the articulating bones .

• knee and should : the tension in the ligaments and muscle has a larger effect( by helping to hold the bone ends together ) as the anatomical structure doesnt offer enough stability .

• if the ligaments / tendons / muslces tissues are weak due to : disuse , lax from being strechted . the stability then is reduced

• the stronger the ligaments and muscles > the more stable the joint ( to enhance the stability of the knee > strengthen the quadriceps and hamstring groups )

Joint flexiblity

• it is a term used to describe the range of motion allowed in each plane of motion at a joint
• what is static flexiblity : it is the ROM present when a body segment is passivly moved ( clincian , excersice partner ..)
• what is Dynamic flexibility : ROM achieved by actively moving a body segment by virtue of muscle contraction.

Range of Motion :

• the angle through which a joint moves from anatomical postion to the extreme limit of segment motion in a particular direction
• ROM for flexion at the hip : individual supine
• tool used for joint ROM : goniometer

Main funtions of the joint : SUpport weight , provide range of motion

Joints are constantly subjected to both : acute and overuse injures ,plus infection and degenerative condition

Commen injuries : Sprains, dislocation , Bursitis ,Arthritis

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1. Sprains :

   • caused by abnormat displacement or twisting of the articulating bones >results in stretching or tearing of the ligaments , tendons and connective tissues crossing a joint
   • commenly seen in the ankle
   • different degrees of Sprains :
   1. first degree : the mildest , slight swelling , least loss of ROM for the joint
   2. Second degree : more damage to the present tissues , swelling, bruising , localized tenderness, moderate pain , some resistriction of ROM of the joint
   3. third degree : partial to complete tearing of the ligaments , swelling , pain , joint instability
   • Cure: sport message , cold therpay , ankel support , strenghing excersicce , mobility , strapping and taping , balance board excercises

2. Dislocations :

   • displacement of the articulating bones
   • common sites : shoulder , fingers , knees , elbows , jaw
   • symptoms include : visible joint deformity , intense pain ,swelling , some loss of joint movment capability
   • a dislocated joint >results in damage for the surrounding ligaments nerves and blood vessels
   • it is very importent to reduce nd properly relocate , a dislocated joint as soon as possible : to allivait the pain and to ensure blood supply to the joint is not impeded

3. Bursitis :

   • Bursae : sacs filled with fluid tht function to cushion points where muscles or tendons slide over the bone ( reduce friction and absorb shock)
   • normally : bursae creats a smooth , nearly frictionless gliding surfaces
   • with bursitis ( inflmation ) : movment around the affected area becomes painful . the more movemnt occur > more inflammation happens
   • treated with rest , ice and anti inflammatory medications

4. Arthritis :

   • pathaloy involving joint inflammation , accompained by pain and swellling
   • common with aging
   • over 100 differnt types of arthritis identified
   1. Rheumatiod arthritis
      • (Autoimmune disorder )involve the body immune system attacking healthy tissues
      • charcateristics include : inflammation and thickening of the synovial membrane , breakdown of the articular cartlilage > result in limitation of motion and eventuallt ossificaition/ fusing of the articulating
   2. Osteoarthritis :
      • common degenerative diseases of the articular cartilage
      • early strages : the joint cartilage loses its smooth , appearance > becomes rough and irrgular
      • eventually : the carilage > wears away completely , leaving the bone surface compmletely bare
      • Symptoms : pain , swlling , ROM restriction , stiffness .

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