Arthrokinematic Movement: Types, Importance, and Clinical Applications

What is Arthrokinematic Movement?

Arthrokinematic movement refers to the small, involuntary motions that occur between the articular surfaces of bones within a joint, such as rolling, sliding (gliding), and spinning. These subtle movements are essential for optimal joint function, allowing for full range of motion, shock absorption, and nutrient distribution within the joint capsule.

Understanding Joint Motion: Osteokinematics vs. Arthrokinematics

To fully grasp arthrokinematic movement, it's crucial to distinguish it from osteokinematic movement, which is often what we perceive as "movement."

• Osteokinematic Movement: These are the gross, visible movements of bones relative to one another at a joint, occurring in anatomical planes. Examples include flexion, extension, abduction, adduction, and rotation. These movements are voluntary and can be measured with tools like a goniometer. When you bend your elbow, or raise your arm, you are observing osteokinematic motion.
• Arthrokinematic Movement: In contrast, arthrokinematic movements are the microscopic, accessory motions that occur within the joint capsule between the joint surfaces themselves. They are typically involuntary and cannot be performed in isolation by conscious effort. These subtle movements are vital for ensuring that the larger osteokinematic motions can occur smoothly, efficiently, and without pain. Think of them as the "behind-the-scenes" mechanics that facilitate the main show.

Without proper arthrokinematic motion, osteokinematic motion becomes restricted, painful, or mechanically inefficient.

The Three Fundamental Arthrokinematic Motions

There are three primary types of arthrokinematic movements:

• Roll: This occurs when multiple points along one articular surface come into contact with multiple new points on the opposing articular surface. Imagine a tire rolling across the ground – different parts of the tire's surface touch different parts of the ground. In the body, an example is the femoral condyles rolling posteriorly on the tibia during knee flexion.
• Slide (or Glide): This motion involves a single point on one articular surface contacting multiple new points on the opposing articular surface. Picture a non-rotating tire skidding across ice – the same part of the tire is in contact as it moves over different parts of the ice. An example is the anterior glide of the tibia on the femur during open-chain knee extension.
• Spin: This is the rotation of a single point on one articular surface around a fixed single point on the opposing articular surface. It's like a top spinning in place. A classic example is the rotation of the radial head on the capitulum of the humerus during forearm pronation and supination.

It's important to note that these movements rarely occur in isolation. Most joint movements involve a complex combination of rolling, sliding, and spinning, often simultaneously.

The Concave-Convex Rule: Predicting Motion

A fundamental principle in understanding arthrokinematics is the Concave-Convex Rule. This rule helps predict the direction of the accessory glide component of motion based on the shape of the articulating surfaces:

• Convex on Concave: If a convex joint surface is moving on a stable concave surface (e.g., humeral head moving on glenoid fossa during shoulder abduction), the convex surface will roll in one direction and simultaneously glide in the opposite direction.
• Concave on Convex: If a concave joint surface is moving on a stable convex surface (e.g., tibia moving on femoral condyles during open-chain knee flexion), the concave surface will roll and glide in the same direction.

Understanding this rule is critical for clinicians performing joint mobilizations and for designing effective rehabilitation exercises.

Why Arthrokinematics Matters in Movement and Health

The seemingly subtle nature of arthrokinematic movements belies their profound importance for overall musculoskeletal health and function:

• Optimal Range of Motion: Proper arthrokinematics ensures that joints can achieve their full, pain-free osteokinematic range of motion. Restrictions in arthrokinematic motion often manifest as limitations in gross movement.
• Joint Nutrition and Health: The accessory movements help distribute synovial fluid, which lubricates the joint surfaces and delivers nutrients to the avascular articular cartilage. This is crucial for maintaining cartilage health and preventing degeneration.
• Reduced Friction and Wear: By allowing surfaces to glide and roll optimally, arthrokinematics minimizes friction and excessive wear on the articular cartilage, thereby protecting the joint.
• Joint Stability and Congruency: These subtle motions help maintain the optimal fit and alignment (congruency) between joint surfaces throughout the range of motion, contributing to joint stability.
• Efficient Force Transmission: Proper arthrokinematics allows forces to be transmitted efficiently across the joint, reducing stress on surrounding tissues like ligaments and muscles.
• Injury Prevention and Rehabilitation: Understanding arthrokinematics is fundamental for diagnosing joint dysfunctions, designing targeted rehabilitation programs, and preventing injuries related to improper joint mechanics.

Clinical and Practical Applications

The principles of arthrokinematics are central to various aspects of physical therapy, athletic training, and exercise science:

• Manual Therapy: Physical therapists frequently use joint mobilization techniques, which are skilled, passive movements applied to joint surfaces. These techniques specifically target and restore restricted arthrokinematic motions (e.g., applying an anterior glide to a restricted shoulder joint to improve external rotation).
• Exercise Prescription: Knowledge of arthrokinematics guides exercise selection. For instance, open kinetic chain exercises (where the distal segment is free to move, like a leg extension) often involve different arthrokinematic patterns than closed kinetic chain exercises (where the distal segment is fixed, like a squat).
• Biomechanics Analysis: Analyzing athletic movements, occupational tasks, or gait patterns often involves considering the underlying arthrokinematic efficiency to identify potential sources of dysfunction or performance limitations.
• Post-Surgical Rehabilitation: Restoring specific arthrokinematic motions is often a primary goal in post-surgical rehabilitation to regain full joint function and prevent complications like adhesions or stiffness.

Conclusion

Arthrokinematic movement, though often invisible to the naked eye, forms the intricate foundation upon which all gross joint movements are built. Understanding the subtle interplay of rolling, sliding, and spinning within our joints is not merely an academic exercise; it is essential for appreciating the complexity of human movement, optimizing performance, preventing injury, and effectively rehabilitating musculoskeletal dysfunctions. For anyone serious about fitness, health, or the mechanics of the human body, a firm grasp of arthrokinematics is indispensable.