What is Cartilage?
Cartilage is an important structure that lies within the joint in all four extremities.(1) Cartilages are also found between ribs and sternum, as well as between vertebral body. The stiff rings of trachea and bronchi are formed by cartilages.
Characteristics of Cartilage
Cartilage is a special type of connective tissue formed by chondrocytes.(2) Chondrocytes deposits collagen fibers, elastic fibers and proteoglycan. Cartilage is less solid than bones and flexible. It derives its nutrition with diffusion from other cells and tissues. Cartilage do not have sensory nerves, capillaries and lymphatic vessels. Thus, cartilage depends on diffusion from peripheral tissue to move oxygen and nutrients, as well as move waste substances from cartilage to adjacent soft tissue. Healing of cartilage takes longer than muscles and other soft tissues. The healing is prolonged because of restricted supply of nutrients and oxygen as well as lack of sensory nerve fibers.
Cartilage is found in joints of upper and lower extremities. The upper extremity joint that contains cartilage are shoulder, elbow, wrist, hand and finger. Similarly, lower extremity joint that contains cartilage are hip, knee, ankle, foot and toes. Cartilage, known as intervertebral disc, forms a link between adjacent vertebra. Similarly, cartilage connects ribs with sternum. Cartilage maintains firmness of nose, ear, larynx, trachea and bronchi.
Cartilage Injury and Recovery-
Cartilage does not have blood supply and sensory nerves. Cartilage often gets injured and injury is not diagnosed because of lack of sensory nerve. The injury is caused by wear and tear and repeated movements of joint as well as trauma. The regeneration of cartilage is extremely slow because of lack of direct blood supply and lack of sensory nerves.1 In several cases following cartilage tear the repair is followed by excessive calcium deposits and cartilage often turns in to bone. Such change interferes with function of cartilage.
What is the Function of Cartilage in a Joint?
- Maintain smooth joint movement
- Prevent friction between adjacent bone that forms a joint,
- Mechanical support to adjacent soft tissue in ear and nose,
- Functions as shock absorber when bones in joint collide against each other.
- Prevent damage of the end of bone.
- Prevent the separation of bone that forms the joint.
Types of Cartilage and Its Location and Function
There are three types of cartilages:
- Hyaline Cartilage
- Elastic Cartilage
Hyaline Cartilage2 – Hyalos means glassy in Greek language. Hyaline cartilages are smooth and glassy thus the cartilage is named Hyaline cartilage. The smooth shiny hyaline cartilages are found in nose, ear, larynx, trachea and bronchi. The rib cartilage that link rib to sternum is made up of hyaline cartilage. Hyaline cartilage is made up of thin fibers of collagen and is the weakest of all the three types. Hyaline cartilage is able to support weight bearing adjacent bone in joint of extremities. The cartilage is flexible and rubbery, but healing of torn cartilage is slow and takes several weeks.
Functions of Hyaline Cartilage- Maintains the Link Between Adjacent Bones In Joint- Cartilages adhere to adjacent bones and ligaments as well as tendons are attached to cartilages. Thus, cartilage prevents separation of adjacent bones.
Maintains Smooth Joint Movement- The smooth surface of hyaline cartilage helps to maintain smooth joint movement.
Reduces Friction Between Adjacent Bones- The cartilage smooth surface that is covered by synovial membrane prevents friction between adjacent bones.
Maintain the Anatomical Shape- Stiffness of cartilage maintains the anatomical shape of ear, nose and breathing passage like larynx, trachea and bronchi.
Fibrocartilage3 – Fibrocartilage is less flexible and more firm than elastic cartilage. The fibrocartilage is predominantly formed by collagen fibers. The fibrocartilage is tough and inflexible. Fibrocartilage is located at the front of the pelvic bone (pubic symphysis), intervertebral disc, shoulder joint, temporomandibular or jaw joint. The menisci that lies in front of knee joint is a tough fibro-cartilage and allows attachment of several ligaments.
The function of fibrocartilage are as follows-
Shock Absorber- Fibrocartilage that lies between vertebra known as intervertebral disc act like a shock absorber. The tough fibrocartilage that lies between adjacent vertebra prevents slippage of adjacent vertebra. The fibrocartilage protects adjacent vertebra from shock of rapid weight transmission when individual jumps or struck by direct impact.
Sustain Wear and Tear- Shoulder joint is also known as ball and socket joint. The ball of humerus and deeper socket of scapula forms shoulder joint. The cartilage that lines the socket and ball of humerus is fibrocartilage. The constant movement between ball and socket would cause constant wear and tear of joint cartilage. The fibrocartilage that lines shoulder joint prevents rapid wear and tear.
Support Tendons and Muscles- The tendon and muscles are attached to fibrocartilage in jaw, pelvis and vertebral column.
Elastic Cartilage – This type of cartilage provides higher flexibility and thus known as elastic cartilage. The cartilage lines the ear lobe, epiglottis and larynx. The elasticity and flexibility of cartilage helps to maintain change of position of ear lobe during sleep. Similarly, flexibility of cartilage helps in larynx and epiglottis when the voice box expands and narrows during breathing.
Functions of Elastic Cartilage-
Change of Shape and Size- The ear lobe often gets pinched during sleep under pressure. The shape returns to normal shape when pressure is removed. Allows Vibration- The cartilage of larynx (voice box) vibrates during speech and singing. The vibration or movements are caused by contraction and relaxation of attached muscles.
Muscle Attachments- The laryngeal muscles are attached to the elastic cartilages of voice box.
What Happens if Cartilage Wears Out or Gets Damaged?
Certain conditions can affect the cartilage resulting in improper functioning of cartilage or damage to joints or structures. Injury or trauma to the joint commonly occurring in sportspersons or after accidents, can result in tearing of the cartilage, which can further increase friction of the bones and cause joint pain. Osteoarthritis is a degenerative condition, in which the cartilage thins or wears off due to excessive usage or wear and tear causing pain and difficulty in moving the joint. Cartilage in ribs can get inflamed in costochondritis and cause rib pain. Cartilage cushion in spinal vertebrae, if damaged due to aging or trauma, can cause protrusion or herniation of spinal disc, causing back pain or nerve compression. Certain genetic conditions or autoimmune conditions affecting the cartilage or connective tissue can cause easy damage to the cartilage and result in specific complaints.
Iou-Ren Chang; Andrew Martin. Last Update: December 13, 2018.
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