Cartilage and Diseases of Cartilage
PKGhatak, MD
Gristle, that word may be more familiar than cartilage - the term used in biological science. Cartilage is a connective tissue like bone and tendon, connecting two pieces together forming a joint. Joints have a layer of cartilage covering the bony ends preventing bones from grinding and making the movement smooth and pain free.
Cartilage, bone and muscle originate from the same source called mesoderm. Distribution of cartilage in the body follows the same path as that of bone, except in the respiratory tract cartilage alone provides structural stability. Cartilage does not have nerve supply, so it is pain insensitive and neither does it have blood supply or lymph channels. Cartilage derives its nutrition from synovial membrane secretion. The synovial membrane is the innermost covering of a joint, the secretion also acts as a lubricant.
Structure and types of cartilage.
The cartilage is composed mainly of a dense extracellular matrix. Within the matrix a few sparsely distributed cartilage cells chondrocytes and collage fibers are present. The cartilage cells secrete the matrix. Matrix is made up of water, protein and proteoglycans. Chemically proteoglycan is a derivate of chondroitin sulphate compounded with carbohydrate and protein.
Types of cartilage.
Cartilages are Hyaline, Fibrous and Elastic types based on the amount of fibrous and elastic tissues present.
Hyaline. Cartilage. Hyaline means glass like. Hyaline cartilage is smooth, glistening, semisolid and homogeneous.
The skeletal structure of a fetus is made of hyaline cartilage and later cartilage is turned into bones. But a part of hyaline cartilage remains at the end of bones forming movable joints, called the articular cartilage and also called the growth plate. The longitudinal growth of the skeleton takes place by the rapid expansion of articular cartilage under the influence of the pituitary growth hormone followed by calcification.
Hyaline cartilage is the most abundant of cartilage, the distribution in the body is represented in the above diagram.
Fibrous cartilage. Fibrous cartilage joins ligaments and tendons to bones. The fibrous cartilage is made up of tough bundles of fibers and provides strength to the structure.
Elastic cartilage. The external ears (pinna) and epiglottis are made of elastic cartilage. Elastic cartilage is remarkably resilient and retains its original shape after rough treatment.
Diseases affect cartilage.
Acquired diseases of cartilage are few because of poor blood flow preventing microorganisms from reaching cartilage directly. Infection can spread to cartilage from the adjoining tissues. Damage to the cartilage from sporting accidents and wear and tear of weight bearing joints are the principal causes of disease.
A. Genetic cause of cartilage disease.
Dwarfism.
Under the term dwarfism 400 different conditions or syndromes are included. Dwarfs are discussed under Proportionate Dwarfs and Disproportionate Dwarfs.
Proportionate Dwarf. The adult dwarf is 4 feet tall. The limbs, face, skull and torso are proportional. The growth and development of a dwarf child is delayed and mental capacity is low. This is due to a lack of adequate Pituitary Growth hormone.
Disproportionate Dwarf. The limbs are shorter, the torso is average size, the fingers are short and the middle and ring fingers are widely placed. The disproportionate dwarf has a large head and face and the bridge of the nose is flat. The patients have normal mental capacity and intelligence. Under this group, several distinct entities are included. Among all causes of dwarfism Achondroplasia is the most common, occurs 1 in 15,000 to 40,000 births.
Achondroplasia is an inherited autosomal dominant disease. The mutant gene is located in chromosome number 4 and the fibroblast growth factor 3 receptor encoding gene (FGF3) is abnormal. The mutant gene has a 100% penetration. The adult achondroplasia individual is 4ft 6 inches tall, the torso and head are normal, and all four limbs are short. Sometimes, the reverse is true – short torso and normal limbs. The mental faculties are normal in both instances.
Pseudo-achondroplasia is a partial form of achondroplasia. Only the arms are shorter but the height is normal. The gene mutation is located in the Oligomeric matrix protein encoding gene.
Diastrophic Dysplasias (DD) and Spondyloepiphyseal (SAA) diseases.
The abnormalities are due to an autosomal recessive mode of inheritance. DD patients are shorter than average people and any growing bone may be affected. In SAA, the spine and long bones are shorter and in addition, they have visual and auditory abnormalities. A defective gene that codes Parathyroid Hormone related Protein (PhrP) is transmitted by autosomal recessive mode often associated with this condition. Many other congenital dwarfisms in combination with other organ abnormalities are known but they are just too many to mention here.
Most of the work in the field of dwarfism was conducted by Dr. Victor Mckusick of the Johns Hopkins University, Baltimore, MD.
Turner's syndrome. It is an important congenital disease and it is not rare. A female child with only one copy of the X chromosome. The newborn can develop fully and appear normal at birth. At age 5 the small stature becomes noticeable. It is due to the arrested cell division of the growth plate. Other distinguishing features are a webbed neck and failure of development of female characteristics and heart abnormalities.
B. Autoimmune disease of cartilage.
Relapsing Polychondritis is considered as an autoimmune disease, characterized by recurrent inflammation and degermation of any or all the cartilage of the body, often the external ear is the most prominent lesion. Pain, redness, swelling and loss of function of the involved cartilage are common symptoms. Shortness of breath and wheezing develop due to the cartilage of conductive airways showing inflammatory changes and the cartilage is various stages of damage. Rapid respiratory failure and death may soon follow.
Trecheobronchopatheia osteochrondoplastica.
Localized or diffuse submucosal calcified nodules overlying tracheobronchial rings is the main lesion. Patients are symptom free or have recurrent hemoptysis and shortness of breath.
Normal wear and tear and degernation.
Osteoarthritis is the most prevailing disease of the cartilage. The incidence of osteoarthritis (OA) is 1 in 4 adults. Overuse of weight bearing joints and genetic predisposition are the causes of OA. Obesity, gait disorder (acquired or congenital), osteoporosis, osteomalacia, lack of physical activity, metabolic disorders, and prolonged use of steroids are additional risk factors.
The name osteoarthritis is a misnomer because the lack of blood supply to the cartilage is the principal reason for the delayed repair of cartilage. When bone ends are exposed bones, the damaged bone cells release cytokines and initiate inflammation.
Understanding the basic avascular nature of the cartilage, damaged or diseased cartilage cannot be restored to health by taking vitamins, calcium, magnesium, chondroitin sulfate, proteins and other micronutrients, no matter the amount, because those will not simply reach the cartilage. If there are documented deficiencies then taking them will help bones and other tissue but not the cartilage.
For further information see the previous blog dated Nov.3,2022.
Loose bodies in joints. Osteochondritis Dessicants produce fragmentation of articular cartilage and pieces of cartilage fall in the joint space. These loose bodies interfere with joint movements and may lock up a joint and may require medical intervention to unlock the joint.
C. Cartilage damage from inflammatory joint diseases.
Rheumatoid arthritis, Juvenal rheumatoid arthritis, ankylosing spondylitis, SLE and other collagen vascular diseases secondarily produce damage to the cartilage. To add to this list are - Frostbites, insect bites, sunburns, and congenital syphilis that affects external ears. Granulomatosis with polyangiitis involves airways. Nosal cartilage is often infected with leprosy, Leishmania, and fungi. Epiglottis is affected by amyloidosis and sarcoidosis.
Pseudogout. Calcium monophosphate dehydrate crystal (calcium pyrophosphate) deposit disease is otherwise called pseudogout because similar to gout symptoms. Usually, people between 45 to 60 years old and both sexes are affected. Knees are mostly affected joints but all joints including the spine may be involved. Damage to cartilage is secondary to the chronic relapsing nature of the illness.
D. Inflammatory disease of cartilage.
Infective chondritis. Ear cartilage piercing may introduce infection into cartilage directly; usually, infection of ear cartilage spreads from infected subcutaneous tissues. Pain, swelling and fever follow. Pain is severe and the risk of necrosis is considerable due to the absence of subcutaneous space in between cartilage and skin. Occasionally infection spreads to blood and septicemia develops.
Costochondritis. The joints at the anterior ends of the ribs and sternum can be infected by viruses or other agents. Pain is felt in the chest. Chest pain produces anxiety of the patient mistaking the pain for a heart attack. The illness is self limited and leaves no lasting bad effects.
Tietze syndrome. A similar costochondral joint pain and in addition the joints are swollen. It is usually seen in younger people. The 3rd and 4th costochondral joints are most affected but any joint including neck and shoulder joints may be affected. The cause is unknown but repeated microtrauma may be responsible. Symptoms of Tietz syndrome last longer, at times for years. The swelling may not regress even when the pain disappears. Treatment is not very satisfactory.
E. Traumatic cartilage damage:
The external ear, nose and larynx are more prone to damage from various ways like wrestling matches, whereas, the right and left meniscus of the knee are tourn in sports related injuries.
The most life-threatening injury to cartilage is the fracture of laryngeal cartilage from cloak-holding by law enforcing officers and in professional wrestling events. Once the laryngeal wall becomes frail, it acts as a check valve preventing air movement and respiratory failure only hours away. An artificial tracheal opening is necessary for the long term solution. Choak-holding should be outlawed.
Knee menisci fracture.
When the foot is planted firmly on the ground and the body is twisting, the shearing force of the femoral condyle tears a piece of meniscus. In old people with worn out menisci minor physical activities may produce a tear. Previous minor tear predisposes a major injury in otherwise healthy athletes. The lateral 3rd of the meniscus has adequate blood supply but the inner 2/3 has none. The chance of complete healing is remote in a complete meniscus tear and treatment is surgical.
In recent years cartilage transplants have been tried with encouraging results. An outline of these methods are as follows-
1. Microfracture. Multiple small holes are drilled in the bone and bone marrow underneath the damaged cartilage. Bone marrow cells enter the cartilage through the small openings and start forming new fibrocartilage at the damaged site but not articular cartilage.
2. Osteochondral Allograft / Mosaicplasty. A small piece of healthy cartilage with attached bone is removed from the patient's non-weight bearing joint and inserted beneath the damaged cartilage through a small drilled hole. The new cartilage that forms are articular cartilage. The graft survives for a long time. The procedure is limited because cartilage can be harvested only from a few joints.
3. Osteochondral Allograft. In this procedure, cadaveric cartilage with attached bone is used like in the previous procedure. After initial healing, the new cartilage wears away sooner than expected.
4. Autologous Chondrocyte implant. Articular cartilage is harvested from the patient. The cartilage cells are allowed to grow in the laboratory. When the desired number of chondrocytes is grown, the new cartilage cells are transplanted into the damaged joint.
5. Matrix Autologous Cartilage implant. In this case, the cartilage cells are grown on a special collagen mesh, then the mesh containing new chondrocytes is implanted.
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