Arthrokinematics refers to the small, subtle movements between joint surfaces that occur during osteokinematic (gross bone) motion. These are not usually visible, but they’re crucial for smooth, pain-free joint movement.
There are three primary types of arthrokinematic motions:
🔹 1. Roll
- Definition: When new points on one bone surface meet new points on the opposing surface—like a tire rolling on a road.
- Direction: Usually in the same direction as the bone’s movement.
- Common in: Hinge and ball-and-socket joints.
🧠 Example:
The femoral condyles rolling on the tibial plateau during knee flexion.
🔹 2. Glide (Slide)
- Definition: One point on the moving surface contacts many points on the fixed surface—like a car tire skidding.
- Direction: Depends on whether the moving surface is concave or convex (follows the concave-convex rule).
🧠 Example:
The humeral head glides inferiorly in the shoulder joint during abduction.
🔹 3. Spin
- Definition: A single point on one surface rotates around a single point on the other surface—like a top spinning on a table.
- Occurs when: Rotation happens with no roll or glide.
🧠 Example:
The radius spinning on the capitulum of the humerus during forearm pronation/supination.
🧩 Often, these motions happen together, not in isolation.
- For example, in knee flexion, the femur rolls and glides to maintain proper joint contact and avoid impingement.
📊 Summary Table
| Arthrokinematic Motion | Description | Example |
|---|---|---|
| Roll | New surface points contact new points | Femur rolling on tibia (knee) |
| Glide | Same surface point slides over new area | Shoulder joint during abduction |
| Spin | Rotation around a fixed axis | Radius during pronation |