Cartilage

Disadvantages of cartilage

There are several diseases and processes that can affect cartilage. As mentioned before, the ECM is paramount in opposing shear, tensile, and compressive forces normally. Therefore, when this ECM is affected, it can lead to damage or injury. This can happen through physical mechanical forces, where excessive friction and applied forces wear down the cartilage (e.g. due to overuse or traumatic injury during athletics). Damage or injury can also happen through pathologic states, where ossification or breakdown of cartilage occurs due to dysfunction of cartilage-specific cells or synovial cells, or imbalances in the microenvironment surrounding the cartilage.

Cartilage has limited reparative capacities for a number of reasons:

• chondrocytes are bound in lacunae and cannot migrate to damaged areas
• cartilage does not have a blood supply so deposition of new ECM is very slow
• damaged hyaline cartilage is often replaced by fibrocartilage scar tissue with different biomechanical properties

Therefore, the standard treatments often involve total joint replacements (arthroplasty) or clever bioengineering techniques to regenerate articular cartilage through scaffolding and stem cell engineering.

Osteoarthritis

While osteoarthritis is a disease that affects the whole joint, one of the most affected tissues is the articular cartilage, which is thinned or completely worn away. This results in “bone against bone” grinding within the joint that leads to reduced range of movement, loss of proprioception, and pain. Since osteoarthritis affects the joints exposed to the highest stress (knees, elbows, and hips), this condition is considered less of a disease and is rather regarded as a result of “wear and tear”. Treatment involves arthroplasty and chondroitin sulfate or glucosamine sulfate supplements.

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a disease process where the body’s immune system attacks synovial cells, and therefore the lining of joint capsules, which is a tough membrane that encloses joints. RA frequently affects wrists, fingers, hips, knees, feet and ankles on both sides of the body (unlike osteoarthritis). It is a progressive and chronic autoimmune disease that triggers inflammation and results in damage to joint tissue, nearby bone and other organs, therefore indirectly affecting cartilage. RA progresses normally from various small to larger joints of the body, and damage to hands and feet is more likely to develop before damage to larger joints such as the hips or knees.

Treatment often involves various anti-inflammatory medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin or ibuprofen, or other COX inhibitors for symptomatic relief. More powerful immune system suppressing agents such as methotrexate and cyclosporine are sometimes used. Other medications aim to specifically inhibit inflammatory cytokines, such as tumor necrosis factor alpha, which helps drive inflammation in RA. Oftentimes, many of these medications are used in combination. Finally, treatment can also involve surgery or more progressive gene therapy drugs.

Achondroplasia

Achondroplasia is an autosomal dominant disease usually related to a mutation in the FGFR3 gene, which causes abnormal endochondral ossification to convert cartilage to bone, and results in dwarfism.

Costochondritis

Costochondritis is a cause of chest pain resulting from inflammation of cartilage connecting the ribs to the sternum.

Chondromas/Chondrosarcomas

Tumors made up of cartilage tissue can also occur, but can be either benign or malignant in nature. While these tumors usually appear in bone, and rarely in pre-existing cartilage, they can invade cartilage. Benign tumors are called chondromas, and the malignant tumors are called chondrosarcomas.