Cartilage is a type of connective tissue found in the body. When an embryo is developing, cartilage is the precursor to bone. Some cartilage remains and is dispersed throughout the body, especially to cover the joints. Cartilage also composes most of the outer ear.
Cartilage is a unique tissue type because it doesn’t have blood vessels or nerves. Instead, cartilage cells (known as chondrocytes) are found in a gel-like “matrix” that provides nourishment to the cells. Cartilage has a unique structure that makes it a strong but flexible tissue.
Three types of cartilage exist in the body: hyaline, fibro, and elastic cartilage. Below is an explanation of each.
Elastic
Elastic cartilage is found in the ear and epiglottis (located in the throat) as well as parts of the nose and trachea. This cartilage serves to provide strength and elasticity to organs and body structures, such as the outer ear.
Fibro or fibrous
Fibro cartilage is found in special pads known as menisci and in the disks between your spinal bones, known as vertebrae. These pads are vital to reducing friction in joints, such as the knee.
Doctors consider it the strongest of the three cartilage types. It has thick layers of strong collagen fibers.
Hyaline
Hyaline cartilage is the most common type in the body. This cartilage type is found in the larynx, nose, ribs, and trachea. A very thin layer of cartilage is also present on bony surfaces, such as over joints, to cushion them. This hyaline cartilage is known as articular cartilage.
The term hyaline comes from the Greek word “hyalos,” which means glassy. Hyaline cartilage appears slightly glassy under a microscope. This cartilage type has many thin collagen fibers that help to give it strength. However, hyaline cartilage is considered the weakest of the three cartilage types.
Cartilage can become damaged after an injury or through degeneration, which is wearing down over time. Some of the common conditions related to cartilage degeneration include:
Chondromalacia patellae
This condition, also referred to as runner’s knee, occurs when the articular cartilage over the kneecap breaks down. Factors such as injury, overuse, poor alignment, or muscle weakness can all lead to the condition. Chondromalacia can cause bone to rub against bone, which is very painful.
Costochondritis
This condition occurs when the cartilage that connects the ribs to the breastbone becomes inflamed. While the condition is usually temporary, it can become chronic. The condition causes uncomfortable chest pain.
Herniated disk
When the gel-like material inside the cartilage disk protrudes through the outer cartilage, it’s known as a herniated or slipped disk. This condition is usually due to degenerative changes that occur as a side effect of aging. Other times, a person may have a severe accident or back injury that can cause a herniated disk. This condition causes severe pain in the back and often down the legs.
Unfortunately, cartilage breakdown can be a part of the body’s natural degenerative process. Steps like maintaining a healthy weight, practicing flexibility and strength-training exercises, and avoiding overtraining may help to reduce the rate at which cartilage breaks down.
While cartilage is very beneficial to the body, it does have a drawback: it doesn’t heal itself as well as most other tissues. The cartilage cells known as chondrocytes do not often replicate or repair themselves, which means damaged or injured cartilage will not likely heal well without medical intervention.
Over the years, doctors have found some methods that can stimulate new cartilage growth. These techniques are usually used for articular cartilage on the joints. Examples include:
Abrasion arthroplasty
This procedure involves using a special high-speed instrument called a burr to create small holes below damaged cartilage to stimulate cartilage repair and growth.
Autologous chondrocyte implantation
This cartilage repair technique requires two steps. First, a doctor removes a healthy piece of cartilage from a person and sends the cartilage sample to a laboratory. In the laboratory, the cells are “cultured” and stimulated to grow.
The person then goes to surgery where the damaged cartilage is removed and replaced with the newly grown cartilage. A surgeon also performs other repairs. Because this approach requires multiple surgical procedures, doctors usually only perform it on younger individuals who have a single injury that is 2 centimeters or greater.
Microfracture
This surgical technique involves removing damaged cartilage and then making small holes just beneath the cartilage in an area of bone known as the subchondral bone. This creates a new blood supply that will ideally stimulate healing.
Drilling
The drilling approach is similar to microfracture. It involves making small holes in the subchondral area as a means of stimulating healing and new cartilage growth by increasing blood supply.
Osteochondral autograft transplantation
This approach involves taking a piece of healthy cartilage from a non-weight-bearing area of the body and applying it to a damaged area. This type is usually only used on a small area of damage because a surgeon cannot take an excess of healthy tissue.
Osteochondral allograft transplantation
Unlike the other tissue grafts, an allograft comes from a cadaver donor, not the person themselves. The allografts can usually treat larger areas of injury than an autograft.
Although doctors can perform these procedures to promote healing, the cartilage may grow at a slow rate. Doctors will likely recommend physical therapy and other techniques in the meantime to promote mobility.
Researchers are exploring new ways of healing and treating damaged cartilage besides increasing blood supply and performing cartilage grafts. Examples include trying to use stem cells to grow into healthy cartilage and attempting to create a microgel like the matrix that nourishes cartilage.
However, these approaches are still in the clinical trial stages and will take time and testing before new techniques emerge.