Joints

Joint types

Joint types

• Synarthroses: Immoveable, Fibrous

  • Suture

  • Syndesmosis

• Amphiarthroses: Slightly moveable, Cartilaginous

  • Symphysis

  • Synchondrosis

• Diarthroses: Freely moveable, Synovial

  • Gliding

  • Hinge

  • Pivot

  • Condyloid

  • Saddle

  • Ball & socket

Suture

• Bone sheets mate closely

• Held by fibers

• Ex: skull (lambdoid and coronal suture)

Syndesmosis

• Held by ligaments

• Ex: Midradioulnar, mid-tibiofibular

Synchondrosis

• Held by thin layer of hyaline cartilage

• Ex: 1st sternocostal, epiphyseal plate

Symphysis

• Thin plate of hyaline cartilage separates disc of fibrocartilage from bone

• Ex: Vertebral, pubic symphysis

Gliding (arthrodial)

• Nonaxial gliding (rubbing) only

• 0 DOF

• Ex: Intermetatarsal, intercarpal, intertarsal, facet joints (vertebrae)

Hinge (ginglymus)

• Matching convex/concave (ML axis)

• 1 DOF

• Ex: Humeroulnar (elbow), interphalangeal

Pivot (trochoid)

• Rotation around the longitudinal axis

• 1 DOF

• Ex: Proximal & distal radioulnar, atlanto-axial

Condyloid (ellipsoidal)

• Ovular convex vs. matching concave

• 2 DOFs

• Ex: Radiocarpal

Saddle (sellar)

• Shape of riding saddle

• 2 DOFs

• Ex: Carpometacarpal joint of the thumb

Ball & socket (spherodial)

• Spherical convex & concave

• 3 DOFs

• Ex: Hip (acetabulofemoral) and shoulder (glenohumeral)

Typical elements of a synovial joint

• Structure

  • Articular cartilage

  • Articular capsule

  • Synovial membrane

  • Synovial fluid

• Additional Structures

  • Bursa

  • Tendon sheath

  • Lubrication and reduction of friction between tendon and bone

Synovial joints vs. DOFs

0 DOF

• Gliding

1 DOF

• Hinge

• Pivot

2 DOF

• Condyloid

• Saddle

3 DOF

• Ball and Socket

Bursa and tendon sheath? Their main mechanical functions?

The mechanical function of the bursa and tendon sheath are to lubricate and reduce friction between the tendon and bone

Joint stability? Factors affecting joint stability?

• Ability to resist dislocation

• Prevents injuries to surround ligaments, muscles, and tendons

• Determining factors

  • Contact area between articulating bones

  • Strength of connective tissues

Shoulder vs. hip stability

• Hip is more stable

  • Higher contact area

  • Deeper socket for head of femur to insert into

  • Stronger ligaments and muscles surrounding the acetabulofemoral joint

• Glenoid cavity is much flatter

The best way to improve joint stability?

Strengthening of the surrounding tissues

Joint flexibility

Range of motion allowed at a joint

Importance of joint flexibility

• Important in terms of injury and performance

• If a muscle has low flexibility it can increase the chance of a rupture

Factors affecting joint flexibility

• Shapes of articulating bone surfaces

• Intervening muscle or fatty tissue

• Laxity of the joint

• Extensibility of the collagenous tissues and muscles

• Fluid contents in cartilaginous disc

• Temperature of collagenous tissues (warm-up)

The best way to improve joint flexibility

• Regular stretching → increase in flexibility

• Active vs. Passive Stretching

• Ballistic vs. Static Stretching