An articular disc is a flexible structure found within certain joints throughout the body. These discs are composed of tough fibrocartilage, a type of connective tissue. Serving as an intermediary between bones, the articular disc enables smooth and stable movement across a range of motion. It contributes to the overall function of the joints where it resides.
What Are Articular Discs and Where Are They Found?
Articular discs are thin plates made of fibrocartilage, a dense connective tissue. This composition allows them to be resilient and withstand mechanical stress within joints. These discs are positioned between articulating bones, effectively dividing the joint space into two separate compartments, each lined with its own synovial membrane.
The temporomandibular joint (TMJ), often referred to as the jaw joint, is a prominent location for an articular disc, which is biconcave and oval-shaped. This disc sits between the mandibular condyle, part of the lower jaw, and the glenoid fossa of the temporal bone in the skull. Other locations where articular discs are found include the sternoclavicular joint, which connects the sternum and collarbone, and the acromioclavicular joint, located between the collarbone and shoulder blade.
How Articular Discs Enable Joint Movement
Articular discs contribute to joint movement by facilitating smooth articulation between bone surfaces. In the TMJ, the disc is positioned between the mandibular condyle and the temporal bone, allowing for frictionless movement as the jaw opens, closes, and moves side to side. This arrangement helps prevent direct bone-on-bone contact, which would otherwise cause friction.
These discs play a role in distributing forces evenly across joint surfaces. By acting as a cushion, they absorb shocks and spread the load across a larger area, reducing excessive wear on the bones. For example, in the sternoclavicular joint, the disc absorbs and transmits forces, protecting the joint from impact. This even distribution of pressure contributes to the overall health of the joint.
Furthermore, articular discs enhance joint stability by increasing the congruence, or fit, between the articulating bones. In the acromioclavicular joint, the disc improves the congruency of the joint surfaces, which helps to stabilize the connection between the shoulder blade and collarbone. The disc’s attachments to the surrounding joint capsule and ligaments also provide additional support, ensuring proper alignment during various movements. This stability is particularly important in joints that undergo a wide range of motion.
Common Problems Affecting Articular Discs
Articular discs can be susceptible to various issues that disrupt joint function and cause discomfort. One common problem is displacement, particularly in the temporomandibular joint, often referred to as disc derangement. This occurs when the disc moves out of its normal position between the mandibular condyle and the temporal bone, which can lead to clicking or popping sounds during jaw movement. The disc’s attachments to the joint capsule and surrounding structures can be compromised, allowing it to slip forward or backward.
Degeneration of the articular disc is another frequent concern, where the fibrocartilage tissue begins to break down over time. This can result from aging, repetitive stress, or underlying conditions like osteoarthritis. As the disc degenerates, its ability to absorb shock and distribute forces diminishes, potentially leading to increased friction between joint surfaces and subsequent pain. Such changes can make everyday activities, like chewing or speaking, uncomfortable.
Tears in the articular disc can also occur, often due to trauma or sudden impact to the joint. These tears can vary in severity and may affect the disc’s structural integrity, impacting its ability to cushion and stabilize the joint. Symptoms associated with disc problems generally include pain in the affected joint, a limited range of motion, and audible sounds such as clicking, popping, or grinding during movement. These issues can significantly interfere with daily activities and overall quality of life.