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You are watching: Why do bone injuries heal much more rapidly than injuries to cartilage

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Cartilage has plenty of functions, including the capacity to resist compressive forces, enhance bone resilience, and provide support ~ above bony areas where over there is a need for flexibility. The primary cell that makes cartilage is the chondrocyte, which lives within the lacunae. The matrix of cartilage consists of fibrous tissue and also various combinations of proteoglycans and glycosaminoglycans. Cartilage, when synthesized, lacks lymphatic or blood supply and also the movement of waste and also nutrition is chiefly via diffusion to and also from adjacent tissues. Cartilage, prefer bone, is surrounded by a perichondrium-like fibrous membrane. This class is not efficient at regenerating cartilage. Hence, its recovery is slow after injury. The absence of active blood circulation is the major reason any kind of injury to cartilage takes a lengthy time to heal. Cartilage has no nerve innervation, and hence there is no sensation when it is hurt or damaged. As soon as there is calcification that cartilage, the chondrocytes die. This is adhered to by the instead of of cartilage through bone-like tissue. Unlike bone, cartilage go not have calcium in the matrix. Instead, it includes high quantities of chondroitin, i beg your pardon is the material that offers elasticity and flexibility.


Structure and Function

Several varieties of cartilage are discovered in the human body, and their structure and also relevant function depend ~ above this variation. 

Hyaline Cartilage

Hyaline cartilage is the many copious type that cartilage in the person body.<1> It has a pale blue-white color and also is smooth come the touch. That is primarily composed of form II collagen and also proteoglycans. The surface ar is normally moist, yet with age, the cartilage becomes dry, thinner, and also more yellow. Hyaline cartilage is usually discovered in the trachea, nose, epiphyseal development plate, sternum, and ventral segment of the ribs. Hyaline cartilage produce a long lasting surface through minimal friction. It additionally has wonderful ability to stand up to compressive forces at web page of bone articulation.<2>

Elastic Cartilage

This cartilage appears a dull yellow and is most typically found in the larynx, ear, epiglottis, and also eustachian tube. A perichondrium-like layer also surrounds it. It offers flexibility and also is durable to pressure.<3>

Fibrocartilage

This is abundant in kind 1 collagen and contains significantly less proteoglycan than hyaline cartilage. It deserve to resist high levels of tension and compression. It is commonly found in tendons, ligaments, intervertebral discs, articular surfaces of some bones, and in menisci. Unlike various other cartilage, it has no perichondrium.<4>


Embryology

Cartilage is created from the mesoderm germ layer by the process known together chondrogenesis.<5> Mesenchyme differentiates right into chondroblasts, which are the cells the secrete the significant components of the extracellular matrix—the most crucial of these components for cartilage development being aggrecan and type II collagen. Once initial chondrification occurs, the immature cartilage grows mostly by occurring into a an ext mature state since it cannot prosper by mitosis. There is minimal cell department in cartilage; therefore, the size and mass that cartilage perform not change significantly after originally chondrification.


Blood Supply and Lymphatics

Cartilage is avascular. This characteristic of cartilage is paramount during the discussion and also management of diseases affecting cartilage. Because there is no straight blood supply, chondrocytes get nourishment via diffusion native the neighboring environment. The compressive forces that routinely act top top cartilage likewise increase the diffusion that nutrients. This indirect procedure of receiving nutrients is a major factor in the sluggish turnover that the extracellular matrix and lack that repair watched in cartilage.


Nerves

Cartilage does not contain nerves; the is aneural.<6> If any type of pain is linked with a pathology entailing cartilage, that is most frequently due to irritation of surrounding structures, such together inflammation that the joint and also bone in osteoarthritis.


Muscles

Fibrocartilage is a significant component of entheses, defined as the connective tissue between muscle tendon or ligament and also bone. The fibrocartilaginous enthesis is composed of 4 shift zones as it progresses indigenous tendon to bone.<7> These change zones are noted in order of progression native muscle to bone. 


Longitudinal fibroblasts and also a parallel setup of collagen fibers are found in the tendinous area
A fibrocartilaginous an ar where the main type of cells current transitions indigenous fibroblast come chondrocytes
A an ar called the \"blue line\" or \"tide mark\" because of an abrupt change from cartilaginous to calcified fibrocartilage
Bone

Clinical Significance

An immense selection of clinical pathology exists including cartilage, such together osteoarthritis, spinal disc herniation, traumatic rupture/detachment, achondroplasia, costochondritis, and also neoplasm, and many others. These result from a variety of degenerative, inflammatory, and congenital causes.

Osteoarthritis is a an illness affecting the whole joint; however, the articular cartilage (a subset of hyaline cartilage) within the joint is the most influenced tissue. Osteoarthritis is known as a \"wear and tear\" phenomenon due to it mainly affecting joints under greater amounts of stress. That results as result of articular cartilage gift thinned and wearing away. This eventually results in a decreased range of motion, \"bone against bone\" contact within the joint, and pain. The early clinical therapy is with anti-inflammatories and also corticosteroid injections intraarticularly. Both therapies duty to alleviate the inflammation reaction caused by the degenerative cartilage\"s relax of cytokines. Patients might also show innovation by shedding weight, exercising, and also efforts come decrease joint anxiety with rest and using a cane. Eventually, however, plenty of patients will develop pain and also symptoms that interfere with day-to-day life. At this point, joint replacement or resurfacing might be recommended. Arthroscopic surgical procedure is no much longer recommended as it walk not improve outcomes in knee osteoarthritis and can cause harm.

Another common degenerative condition of cartilage is spinal disc herniation. It is as result of degenerative changes of the outer ring that the intervertebral disc, called the annulus fibrosus. The annulus fibrosus is written of fibrocartilage. Trauma, straining, and also lifting injuries are also implicated in the weakening the the annulus fibrosis predisposing come disc herniation. When there is structural damages to the annulus fibrosus, the cell core pulposus included within the disc might herniate right into the spinal canal, leading to impingement that 1 or lot of nerves as well together induce inflammatory alters due to the damaged fibrocartilage.<9> Diagnosis is do by history, symptoms, and physical examination. In ~ some point in the evaluation, imaging studies room usually carried out to ascendancy out other causes such as tumors, spondylolisthesis, and space-occupying lesions. Although part patients warrant surgery due to the severity of symptoms, most cases do not call for surgical intervention as they fix with conservative actions such as anti-inflammatories and lifestyle alters for the patient.

In comparison to the degenerative illness of cartilage, Achondroplasia is a hereditary disorder the cartilage formation and is the most common cause of dwarfism. The pathology watched is because of a mutation ~ above chromosome 4 affect the fibroblast growth factor receptor 3 (FGFR3) gene, i m sorry normally features as a an unfavorable regulator that bone and cartilage growth. The mutation in achondroplasia results in a truncated dysfunctional protein that is constitutively active. This dysfunctional protein impede cartilage development and development by suppressing chondrocyte proliferation and calcification.

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<10> The diagnosis the achondroplasia is usually during pregnancy via prenatal ultrasound. Over there is currently no known cure because that achondroplasia as it is not affected by a hormone pathway that deserve to be pharmacologically manipulated, and corrective surgical procedure is controversial.<11>