Nonaxial Movement: Definition, Examples, and Biomechanical Importance

What is a Nonaxial Movement?

A nonaxial movement refers to a simple gliding or sliding motion between two articulating bone surfaces, occurring without rotation around an axis and without a significant change in the angle between the bones.

Understanding Joint Movements

In the intricate world of human anatomy and biomechanics, joints are the crucial intersections where bones meet, allowing for movement. These movements are broadly categorized based on their complexity and the axes around which they occur. While many movements involve a change in angle between bones, others are more subtle, yet equally vital for optimal function.

Defining Nonaxial Movements

A nonaxial movement, also known as a translatory or gliding movement, is the most basic type of joint motion. Unlike angular movements (like flexion or rotation), which involve a change in the angle between bones and occur around a specific axis, nonaxial movements are characterized by the following:

• Simple Sliding: One bone surface slides or glides over another.
• No Axis of Rotation: Crucially, there is no fixed axis around which the movement occurs. The movement is linear, not rotational.
• No Change in Angle: The angle between the two bones involved does not significantly change.
• Limited Range: These movements are typically small and subtle.

Think of it like a book sliding across a table – it moves, but it doesn't spin or change its orientation relative to the table.

Characteristics of Nonaxial Movements

Nonaxial movements possess distinct characteristics that differentiate them from other types of joint motion:

• Translation: This term directly describes the linear movement of one joint surface across another.
• Accessory Movement: Nonaxial movements are often considered "accessory movements" because they frequently accompany larger, angular movements, enabling the full range of motion by allowing joint surfaces to adjust their positions.
• Joint Congruence: They play a critical role in maintaining proper alignment and congruence between articulating surfaces, ensuring the joint functions smoothly and efficiently.
• Minimal Muscle Involvement (Directly): While muscles initiate many movements, nonaxial movements are often passive adjustments or are facilitated by the shape of the joint surfaces themselves, though muscle tension can influence their occurrence.

Where Do Nonaxial Movements Occur?

Nonaxial movements are characteristic of specific types of synovial joints, primarily those designed for gliding:

• Plane (Gliding) Joints: These joints feature flat or slightly curved articulating surfaces that allow for simple sliding or gliding movements in one or two planes. Examples include:
  • Intercarpal Joints: Between the individual carpal bones of the wrist.
  • Intertarsal Joints: Between the individual tarsal bones of the ankle.
  • Acromioclavicular Joint: Between the acromion of the scapula and the clavicle.
  • Vertebral Facet Joints: The small joints between the articular processes of adjacent vertebrae, allowing for minor gliding during spinal movements.
  • Sacroiliac Joints: Between the sacrum and the ilium.
• Other Joints (Accessory Gliding): While not their primary motion, many joints exhibit subtle nonaxial gliding that is essential for their full range of angular motion. For instance, the patella (kneecap) glides over the femur during knee flexion and extension.

Nonaxial vs. Axial Movements: The Key Distinction

Understanding the difference between nonaxial and axial (or angular) movements is fundamental in biomechanics:

• Axial (Angular) Movements: These movements occur around a fixed axis of rotation and result in a change in the angle between the bones. Examples include:
  • Flexion and Extension: Decreasing or increasing the angle between bones (e.g., bending and straightening the elbow).
  • Abduction and Adduction: Moving a limb away from or towards the midline of the body.
  • Rotation: Turning a bone around its own long axis (e.g., turning the head).
• Nonaxial (Translatory) Movements: These movements involve sliding without an axis of rotation and without a change in the angle between bones. They are purely translational.

The distinction lies in the presence or absence of an axis of rotation and the resulting change in joint angle.

Examples of Nonaxial Movements in Daily Life and Exercise

While often subtle, nonaxial movements are constantly occurring and are vital for efficient and pain-free motion:

• Wrist and Ankle Mobility: When you flex or extend your wrist, the individual carpal bones within the wrist joint glide slightly against each other. Similarly, the tarsal bones in your ankle perform subtle gliding motions during foot movements. These accessory glides are crucial for the full range of the wrist and ankle.
• Shoulder Girdle Movement: As you raise your arm, your scapula (shoulder blade) glides across the rib cage (protraction, retraction, elevation, depression). While these are often described with directional terms, the fundamental movement of the scapula on the thorax is a gliding motion.
• Spinal Flexibility: The small facet joints between your vertebrae allow for minor gliding as your spine bends, twists, and extends, contributing to the overall flexibility of your back.
• Kneecap Tracking: The patella glides smoothly within the trochlear groove of the femur during knee bending and straightening. Impaired patellar gliding can lead to knee pain and conditions like patellofemoral pain syndrome.
• Weight Distribution: When standing or walking, the bones in your feet (tarsals) and hands (carpals) subtly glide to distribute weight and absorb shock across their surfaces.

In exercise, while you don't typically "train" nonaxial movements directly, their proper function is critical. For example, during a squat, the knee joint needs proper patellar gliding, and the ankle joint needs subtle intertarsal gliding for optimal depth and stability.

Importance in Biomechanics and Exercise

Despite their understated nature, nonaxial movements are profoundly important for:

• Joint Health and Longevity: Proper gliding ensures that articular cartilage is evenly loaded and nourished, reducing wear and tear.
• Optimal Range of Motion: They are essential accessory movements that facilitate full, pain-free angular motion. Without adequate gliding, angular movements can be restricted or lead to impingement.
• Load Absorption and Distribution: Nonaxial movements allow joint surfaces to slightly adjust, distributing forces more evenly across the joint and protecting against excessive stress concentrations.
• Proprioception and Stability: The subtle movements contribute to the sensory feedback (proprioception) that the brain receives about joint position, aiding in balance and stability.
• Rehabilitation: In physical therapy, manual techniques often focus on restoring nonaxial gliding movements in stiff or hypomobile joints to improve overall function.

Conclusion

A nonaxial movement is a fundamental biomechanical concept referring to the simple, linear gliding or sliding of one joint surface over another, without rotation around an axis or a change in the angle between bones. While often subtle and occurring beneath our conscious awareness, these translatory motions are critical for maintaining joint health, enabling full ranges of angular movement, distributing forces, and contributing to overall stability. Understanding nonaxial movements provides a deeper appreciation for the intricate mechanics of the human body and their profound impact on our ability to move efficiently and pain-free.