this unit covered some of the basic ideas about arthrokinematics: the study of the motions that occur within joint spaces during bone movements. joints in the body are in general in a convex/concave relationship, which allows for greater surface area for the area of bone which are in contact with each other; increasing joint stability, dissipating contact forces, and providing more guidance for the motion.
the different motions possible in such a joint are: roll, slide, spin, distraction, compression, and longitudinal traction. rolling occurs when multiple points on one bone contacts with multiple points on the other, as in the femoral condyles on the tibial plateau. sliding occurs when a single point on one bone contacts multiple points on another, as in the carpal bones sliding on the facet joints. spinning is when a single point on bone rotates on a single point of another, such as the radial head rotating at the humeroradial joint during supination / pronation. distraction is the separation of joint spaces and compression is the reduction of space between the bones of the joint. longitudinal traction is distraction of the joint in a longitudinal direction; parallel to the length of the body.
convex on concave motion describes a joint in which the concave bone is fixed-- when the convex bone rotates, it also slides in the opposite direction so as to stay engaged in the joint. concave on convex motion describes the opposite scenario, where a convex bone is fixed and the concave rotation produces a sliding motion in the same direction.
most motions at real joints are actually dynamic combinations of the above mentioned motions. for example, at the glenohumeral joint, the rolling upward of the humerus during abduction is combined with spinning and sliding. likewise, at the knee joint, extension combines rolling, sliding, and spinning (which helps locks the knee at its fullest extension) and flexion also combines the same motions.
questions
1. what are the advantages to having a convex-concave joint configuration?
2. describe the "roll" motion in joints and give an example.
3. describe the "slide" motion and give an example.
4. describe the "spin" motion and give an example.
5. describe the "distraction and longitudinal traction" motions.
6. describe the "compression" motion.
7. what happens in convex-on-concave motion?
8. what happens in concave-on-convex motion?
9. what types of motions occur at the glenohumeral joint?
10. describe the motion that occurs at the knee in a "convex on concave" setting.
11. describe the motion that occurs at the knee in the "concave on convex" setting.
answers
1. the increased surface area for contact allows for greater stability, guided motion, and a dissipation of contact forces.
2. multiple points on one bone contact multiple points on another bone, such as the femoral condyles on the tibial plateaus.
3. few points on one bone contact multiple points on another bone, such as carpal bones on the facet surfaces.
4. one point on one bone rotating on one point on another-- like the head of the radius at the humeroradial joint during supination/pronation.
5. both refer to separating the bones within the joint / increasing the joint space. longitudinal traction is a type of distraction which moves the bone parallel to the body, longitudinally.
6. decreasing the space between the bones within the joint.
7. when the concave end is fixed, the convex end slides in the opposite direction of the rotation motion.
8. when the convex end is fixed, the concave end slides in the same direction of the rotation motion.
9. roll, spin, slide.
10. roll, slide, spin.
11. still roll, slide, spin.
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