Arthrokinematic Motion: "Aka Joint surface movement" - Takes place within the joint at the joint surfaces. It is the way adjoining joint surfaces move on eachother during osteokinematic joint movement.
Types of Arthrokinematic Motion:
- Roll - Rolling of one joint surface on another
- Sliding or Gliding - Linear movement of a joint surface parallel to the plane of the adjoining joint surface
- Spinning - Rotation of the moveable joint surface on the fixed adjacent surface
- Example: All three types of arthrokinematic motion occur at the knee joint, which is necessary for full range of motion. During weight bearing the femoral condyles roll on the tibia, and spin because the media femoral condyle is larger.
Convex - Concave Law: states that: The Concave joint surfaces move in the same direction as the joint motion, aka concave member moves in the same direction as the swing of the bone. Inversely, Convex joint surfaces move opposite the direction of the moving body segment, aka convex member moves opposite the direction of the swing of the bone.
- This concept can be demonstrated and applied to the glenohumeral joint (shoulder).
- The head of the humerus is convex
- The glenoid fossa is concave
- During shoulder flexion as the arm (humerus) moves upward the convex humeral head moves (rotates) downward.
Joint Surface Shapes:
- The type of motion occurring at a joint depends on the shape of the articulating surfaces of the bones.
- Ovoid Joint - is a joint with a convex-concave relationship, most synovial joints are ovoid (example: glenohumeral "shoulder" joint)
- Sellar or saddle shaped joint - each joint surface is concave in one direction and convex in the other direction (example: carpometacarpal joint of the thumb)
Accessory Motion Forces: When applying joint mobilizations three main types of forces are used
- Traction = Distraction = Tension; Occurs when an external forces is exerted on a joint causing the joint surfaces to be pulled apart, this assists in improving the mobility of the joint. This type of accessory force can be achieved through manual traction techniques such as cervical spinal traction or through self traction techniques such as with a band (hip and shoulder) or simply hanging from a pull up bar.
- Approximation = Compression: When an external forces is exerted on a joint causing the joint surfaces to be pushed closer together. Used to assist in the stability of a joint