Fibrocartilage is a type of connective tissue known for its toughness and resilience. It acts as a biological shock absorber, managing compression and reducing stress in joints. This tissue is a hybrid, possessing the flexibility of cartilage and the immense strength of dense connective tissue. This combination of properties allows it to withstand intense forces in demanding areas of the body.
The Unique Composition of Fibrocartilage
The durability of fibrocartilage comes from its microscopic structure. It is composed of dense, parallel bundles of Type I collagen fibers, which give it exceptional tensile strength to resist pulling and stretching forces. Fibrocartilage is the only cartilage type to contain significant amounts of Type I collagen alongside the more common Type II found in other cartilages.
Scattered within this fibrous network are cartilage cells called chondrocytes, which are responsible for producing and maintaining the surrounding matrix. These cells are situated in small chambers known as lacunae. The matrix itself contains molecules called glycosaminoglycans that help the tissue resist compression. This composite structure is comparable to reinforced concrete: the collagen fibers act like steel rebar for strength, while the matrix provides cushioning.
This composition varies slightly depending on its location and role. For instance, the fibrocartilage in spinal discs is engineered for higher tensile strength and elasticity compared to the fibrocartilage in joint sockets, which is built to be more resistant to repetitive stress.
Where Fibrocartilage is Found and What It Does
Fibrocartilage is strategically placed in areas subjected to high pressure and friction. Its primary locations and functions include:
- Intervertebral discs: The outer layer of each spinal disc, the annulus fibrosus, is made of fibrocartilage. It acts as a tough cushion that absorbs shock and prevents vertebrae from grinding against each other.
- Knee menisci: In the knee, two C-shaped pieces of fibrocartilage sit between the thigh and shin bones. These structures distribute body weight evenly, absorb impact, and enhance joint stability.
- Pubic symphysis: This joint connects the left and right pelvic bones. Its fibrocartilage provides stability for the pelvic girdle during activities like walking, running, and childbirth.
- Other key areas: It is also found in the temporomandibular joint (TMJ) of the jaw, the labrum that deepens and protects the shoulder and hip sockets, and at junctions where tendons attach to bone.
Common Fibrocartilage Injuries and Conditions
Due to its role in high-stress joints, fibrocartilage is susceptible to traumatic injuries and gradual degenerative conditions. Traumatic injuries often occur from forceful twisting or impact. A classic example is a meniscus tear in the knee, which frequently happens during sports that involve sudden pivots. Symptoms often include pain, swelling, a clicking or popping sound, and a sensation of the knee locking or giving way.
In the wrist, the triangular fibrocartilage complex (TFCC) can be torn by a fall on an outstretched hand or by forceful twisting motions. A TFCC tear causes pain on the pinky side of the wrist, a clicking sound with rotation, and reduced grip strength. Similarly, the labrum in the hip or shoulder can tear, leading to joint instability, pain, and a catching sensation during movement.
Degenerative conditions develop over time as fibrocartilage wears down with age and repetitive use. Degenerative disc disease is a common condition where the intervertebral discs lose height and flexibility, which can lead to pain and stiffness in the spine. The fibrocartilage in the TFCC can also degrade with age or from inflammatory disorders, making it more prone to tearing from minimal force.
Healing Limitations and Treatment Approaches
Fibrocartilage injuries are challenging because the tissue has a limited capacity for self-repair. This difficulty is due to its avascular nature, meaning it lacks a direct blood supply. Without blood vessels, nutrients and the body’s healing factors cannot easily reach the site of damage, and the repair process is extremely slow and often insufficient to repair a significant tear.
When an injury does not penetrate the underlying bone, the potential for healing is limited. If an injury is deep enough to reach the bone, a blood clot can form and create repair tissue. However, this new tissue is mechanically inferior and less durable than the original cartilage that lines the joint surfaces.
Consequently, treatment focuses on managing symptoms and improving function. Conservative approaches are tried first and include physical therapy to strengthen surrounding muscles, which improves stability and reduces stress on the damaged tissue. Anti-inflammatory medications or steroid injections may also be used to reduce pain and swelling.
If conservative treatments fail or the injury is severe, surgical intervention may be necessary. For a torn meniscus, a surgeon might perform a meniscectomy to trim away the damaged tissue or attempt a repair if the tear is in a region with some blood supply. For significant cartilage defects, more advanced procedures like autologous chondrocyte implantation (ACI), where a patient’s own cartilage cells are grown in a lab and then implanted, may be an option for younger, active individuals.