Clinical Joint Mobilization and the Concave-Convex Rule

Indications and Factors Affecting Joint Motion

  • Primary Indications for Joint Mobilization:     * Decreased joint motion is a primary indicator for choosing joint mobilization techniques.     * Specific causes for decreased motion include:         * Fractures.         * Adhesions within the joint.         * Swelling (intra-articular edema).         * Malalignment of the joint structures.

  • Other Factors Influencing Joint Health:     * Muscle contraction and pain surrounding the joint.     * Hypermobility (joints that are too mobile).     * Deconditioned joint states.

Classification and Characteristics of Joints

  • Synarthrosis (Fused) Joints:     * Definition: Joints that are technically fused together.     * Perspective in Bodywork: Some practitioners, particularly those in craniosacral work, argue that even synarthrotic joints possess some degree of mobility.

  • Concept of "Inert" Tissue:     * Orthopedic technicians often use the term "inert" to describe certain tissues in the body.     * The speaker argues against the literal use of this term, stating: "If you're alive, there's nothing inert in your body. Everything has got contractility to it to some degree."     * Despite this philosophical disagreement, the term is used because it is standard in medical textbooks.

  • Synovial (Diarthrosis) Joints:     * These joints possess a high degree of movement.     * Shape and Function: The specific shape of the joint dictates the amount and type of movement allowed.     * Anatomical Features:         * They often feature a joint capsule.         * They contain synovial fluid within the joint space.     * Capsular Patterns: The joint capsule is critical because if it becomes restricted, it follows specific "capsular patterns" of movement limitation, as opposed to "noncapsular patterns."

Types of Synovial Joints and Planes of Movement

  • Gliding or Plain Joints:     * Example: Intercarpal joints.     * Movement: These joints slide well relative to one another and are easily moved.

  • True Hinge Joints:     * Example: The elbow.     * Movement: Characterized by spinning movement but notably lack gliding or sliding components.

  • Pivot Joints:     * Example: The proximal radioulnar joint.     * Movement: The bone spins or pivots on a central point.

  • Ellipsoid Joints:     * Example: The knee.     * Movement: Involves condylar surfaces moving relative to the flat tibial plateau.

  • Saddle Joints:     * Definition: A joint where a convex surface moves relative to a concave surface.     * Movement: These joints move in two different planes.

  • Ball and Socket Joints:     * Movement: These offer the greatest range, moving in three different planes.

  • Determining Planes of Movement:     * Shoulder Exemplar: Moves in three distinct planes of movement. Mobilization is performed to increase available movement in each.     * Elbow vs. Knee Comparison:         * The elbow has one plane of movement.         * The knee is often confused for a simple hinge like the elbow, but it has two planes of movement: up/down (flexion/extension) and a spinning motion during movement.

The Concave-Convex Rule

  • Metaphor for Importance: The speaker describes this concept as the "hole in the hull of a boat"—if a student does not understand this, their clinical practice will effectively "sink."

  • Defining Shapes:     * Concave: Shaped like a cave (inward curve).     * Convex: A rounded outward curve.

  • Functional Application (Shoulder Example):     * The scapula contains the glenoid fossa (concave) and is treated as the stable, fixated bone (e.g., when a patient lies on a table, the weight of the body stabilizes the scapula).     * The humerus (convex head) is the mobile bone.

  • The Rule for Moving a Convex Surface:     * If the mobile bone surface is convex, the glide and slide occur in the opposite direction of the bone's physiological roll/swing.     * Reasoning: If a convex bone rolls without sliding in the opposite direction, it will cause compression (which is undesirable). To prevent compression, the bone must slide/glide in the opposite direction of movement.

  • The Rule for Moving a Concave Surface:     * If the mobile bone surface is concave, the glide and slide occur in the same direction as the bone's movement.     * Reasoning: There is no risk of the concave surface "rolling into" or squishing the other bone structure during movement.

  • Specific Joint Application:     * Humerus on Scapula: Moving the humerus relative to the scapula (convex on concave).     * Knee (Tibia moving on Femur): Extending or flexing the knee involves the tibia (concave) moving relative to the femur (convex). During extension, the glide and slide of the tibia move in the same direction as the swing.

Joint Mobilization Techniques: Traction, Distraction, and Gliding

  • Traction (Long Axis Traction):     * Procedure: Pulling the bone along its longitudinal axis.     * Risk: Depending on the joint surface, pulling along the long axis can run a risk of compressing certain parts of the joint.

  • Distraction:     * Definition: Separating the articulating surfaces perpendicular to the treatment plane.     * Treatment Plane: An imaginary line drawn through the center of the concave bone and intersecting the center of the convex bone.     * Outcome: Creates equal space within the joint by pulling the mobile bone out.

  • Differences between Traction and Distraction:     * While both create space, distraction provides equal separation across the surfaces, whereas long axis traction follows the line of force of the bone and may cause unintended compression depending on the joint's curvature.

  • Gliding (Sliding):     * Definition: Movement that runs parallel to the treatment plane.

Questions & Discussion

  • Question (The Spine): Can distraction and traction happen at the same time in the spine? If you perform long axis traction on the spine, does it count as distraction because of the way vertebrae are shaped?     * Response: Pulling along the long axis of the spine decompresses the entire spine. However, it affects levels differently (e.g., $C_0$ on $C_1$ vs. $C_1$ on $C_2$). While it opens the spine without compression, the terms are applied differently than in peripheral joints. In the spine, one doesn't typically think of distracting vertebral bodies relative to necks in the same way, though the curvature (kyphosis/lordosis) plays a role. The primary distinction remains the avoidance of joint surface compression.

  • Question (The Shoulder): Is traction in the shoulder only pulling down in the anatomical position? Since you can change the long axis, does traction change?     * Response: Yes, you can change the long axis traction by changing the position of the arm. While you could pull the arm straight out (which might decompress), it is not as specific as distraction relative to the treatment plane.

  • Question (Saddle Joints): How is the concave-convex rule applied to saddle joints?     * Response: Saddle joints are complex because the mobile bone may be concave in one plane and convex in another. Applying the rule depends entirely on which bone is mobile and which specific plane of movement is being addressed.