Cervical Spine: Understanding Plane (Facet) Joints, Function, and Common Issues

What is the plane joint in the neck?

The primary plane joints in the neck are the zygapophyseal (facet) joints, which are synovial joints located between the articular processes of adjacent cervical vertebrae, allowing for gliding and sliding movements that facilitate and limit neck motion.

Understanding Joint Classification

To understand the plane joints of the neck, it's essential to first grasp the basic classification of joints. Joints, or articulations, are the points where two or more bones meet. They are classified based on their structure and the degree of movement they permit. Synovial joints are the most common type, characterized by a fluid-filled cavity that allows for a wide range of motion. Within the synovial joint category, there are several sub-types, including hinge, pivot, condyloid, saddle, ball-and-socket, and plane (or gliding) joints.

Plane (Gliding) Joints are characterized by two relatively flat or slightly curved articular surfaces that slide or glide over one another. While they allow for movement in multiple directions (multiaxial), the range of motion in each direction is typically limited. Their primary function is to permit small, translational movements and to guide other, larger movements.

The Cervical Spine: A Complex Structure

The neck is supported by the cervical spine, which consists of seven vertebrae (C1-C7). This segment of the spine is remarkably mobile yet also vulnerable, balancing the need for extensive head movement with the vital protection of the spinal cord. Each cervical vertebra has a body, an arch, and various processes, including the superior and inferior articular processes.

Identifying the Plane Joints: Zygapophyseal (Facet) Joints

The "plane joints" in the neck primarily refer to the zygapophyseal joints, commonly known as facet joints.

• Definition: These are synovial joints formed by the articulation of the superior articular process of one vertebra with the inferior articular process of the vertebra immediately above it.
• Location: There are two facet joints at each vertebral level (one on each side), extending from the base of the skull (C0-C1, though C0-C1 and C1-C2 have unique articulations) down to the thoracic spine.
• Articular Surfaces: The surfaces of the articular processes are covered with smooth articular cartilage (hyaline cartilage), which reduces friction during movement. Crucially, these surfaces are relatively flat or slightly curved, allowing for the characteristic gliding motion.
• Joint Capsule: Each facet joint is enclosed by a fibrous capsule lined with a synovial membrane, which produces synovial fluid to lubricate the joint.

Why Are They Plane Joints?

The facet joints are classified as plane joints due to the nature of their articular surfaces and the type of movement they facilitate:

• Gliding/Sliding Motion: The flat or slightly curved surfaces of the articular processes allow them to glide or slide past one another. This movement is not a rotation around an axis or a hinge-like flexion/extension, but rather a translation of one surface over another.
• Limited Range of Motion: While they permit movement in various directions (flexion, extension, lateral flexion, and rotation), the individual contribution of each facet joint to these movements is small. It's the cumulative effect of these small gliding movements across multiple vertebral levels that allows for the extensive range of motion observed in the neck.
• Guidance and Restriction: The orientation of the facet joints varies slightly throughout the cervical spine, influencing the primary movements permitted at each level. For instance, in the lower cervical spine, their orientation is more oblique, allowing for significant rotation and lateral flexion, while also helping to limit excessive motion and provide stability.

Role and Function of Cervical Facet Joints

The facet joints play several critical roles in the biomechanics of the cervical spine:

• Support and Stability: They contribute significantly to the structural integrity and stability of the cervical spine, helping to bear axial load and resist shear forces.
• Movement Guidance: They guide the direction and range of motion of the cervical spine, dictating how much flexion, extension, lateral flexion, and rotation can occur at each segment.
• Load Distribution: Along with the intervertebral discs, the facet joints help distribute forces transmitted through the spine, protecting the vertebral bodies and discs from excessive stress.
• Protection: By limiting excessive motion, they help protect the delicate spinal cord and nerve roots from injury.

Clinical Significance and Common Issues

Given their critical role, facet joints are a common source of neck pain and dysfunction.

• Osteoarthritis (Degenerative Joint Disease): Like other joints, facet joints can undergo degenerative changes, leading to cartilage breakdown, bone spur formation (osteophytes), and inflammation. This can result in chronic neck pain, stiffness, and reduced range of motion.
• Whiplash Injuries: Sudden, forceful hyperextension and hyperflexion of the neck, such as in a car accident, can strain or sprain the facet joint capsules and associated ligaments, leading to pain and dysfunction.
• Facet Joint Syndrome: This refers to pain specifically originating from the facet joints, often characterized by localized tenderness, stiffness, and pain that may worsen with certain movements (e.g., extension and rotation).
• Referred Pain: Pain from facet joints can sometimes be referred to other areas, such as the back of the head, shoulder, or upper back, mimicking other conditions.

Maintaining Cervical Spine Health

Understanding the function of your facet joints is key to maintaining neck health.

• Good Posture: Maintaining proper head and neck alignment (ears over shoulders) reduces undue stress on the facet joints and supporting structures.
• Regular Movement: Gentle, controlled range-of-motion exercises for the neck can help maintain joint mobility and prevent stiffness.
• Strengthening and Flexibility: A balanced exercise program that includes strengthening the deep neck flexors and extensors, as well as stretching tight upper trapezius and levator scapulae muscles, can support facet joint health.
• Ergonomics: Optimizing your workspace, especially for prolonged sitting, can significantly reduce strain on the cervical spine.
• Professional Guidance: If you experience persistent neck pain or stiffness, consult with a healthcare professional, such as a physical therapist or physician, for an accurate diagnosis and appropriate management plan.