KIN 322 Kinesiology · Unit 1: Foundations and the axial skeleton · on Exam 1
1.2 Joint structure and arthrokinematics
Study notes for Joint structure and arthrokinematics in KIN 322 Kinesiology at Montana State University: the big ideas, a worked example, common mistakes and an exam tip. The same topic has endless practice questions and flashcards in Mathub.
Big ideas
- Structural classes: fibrous (sutures, the distal tibiofibular syndesmosis, gomphoses), cartilaginous (symphyses such as the pubic symphysis and intervertebral discs; synchondroses such as growth plates) and synovial (with a joint cavity). Functional classes: synarthrosis (immovable), amphiarthrosis (slightly movable), diarthrosis (freely movable).
- A synovial joint has hyaline articular cartilage, a capsule (fibrous outer layer, synovial membrane inside), synovial fluid and ligaments; many add menisci or discs, a labrum, bursae or fat pads.
- Six synovial types: plane (intercarpal, AC), hinge (humeroulnar, interphalangeal), pivot (proximal radioulnar, atlantoaxial), condyloid (radiocarpal, MCP), saddle (thumb CMC) and ball-and-socket (glenohumeral, hip).
- Arthrokinematics: surfaces roll, glide (slide) and spin. The convex–concave rule: when a convex surface moves on a fixed concave one, it rolls and glides in opposite directions; when a concave surface moves on a fixed convex one, they go the same direction.
- The close-packed position has maximal congruence and taut ligaments: most stable, least joint play (knee in full extension, glenohumeral in abduction with lateral rotation, humeroulnar in extension). The loose-packed (resting) position has the most play. Mobility and stability trade off: the shallow shoulder moves more than the deep hip.
Worked example
During shoulder abduction, which way does the humeral head glide on the glenoid, and why does it matter?
Show the solution
The humeral head is convex moving on the fixed concave glenoid, so it rolls superiorly and glides inferiorly, in opposite directions. Without that inferior glide the head would roll up into the acromion and pinch the tissues beneath it (impingement).
Common mistakes
- Calling the pubic symphysis fibrous. It is cartilaginous.
- Mixing roll (a tire rolling) with glide (a tire skidding).
- Applying the convex–concave rule without first asking which surface moves.
- Confusing close-packed (locked and stable) with the resting position.
Exam tipStart a table of every joint in the course: structural type, degrees of freedom, close-packed position and main ligaments. You will reuse it in every region.
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