Random Information About Joints In The Skeletal System
Joints: n
A joint is the point of contact between two bones, between bone and cartilage, or between bone and teeth. Joints con tribute to homeostasis by holding bones together in ways · that allow for movement and flexibility. With fibrous joints,
. bones are held together by dense irregular connective tissue,
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lnterosseous membrane·.
A fibrous joint
‘–~– Periosteum
· rich in collagen fibers. Cartilaginous joints hold bones together with by cartilage. Synovial joints have a synovial cavity, which is a space bernieffithe articulating bones. They are united by the dense irregular connective tissue of an articular capsule, and often by accessory ligaments .
Eplphyseal (growth) plates
Epiphysis —-
Pubic—- symphysis ·
Epiphysis
Synchondrosis
Cartilaginous joints
Articular Ooint) capsule:
Articulating —- bone
Synovial ijolnt) cavity (contains synovlal fluid)
Articular – cartilage
Articulating – bone·
. ‘ _J
Typical synovlal Joint .
Fibrous membrane
Synoviai’ membrane
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. ‘
Tests, Procedures, and Techniques
111 Arthroplasty Joints that have been severely damaged by diseases such as arthritis, or by injury, may be replaced surgically with artificial joints in a procedure referred to as arthroplasty (AR-thrii-plas’ -te; arthr- = joint; -plast:y = plastic repair
· of). Although most joints in the body .can:b·e repaired by arthroplasty, the ones most commonly replaced are the hips, knees, and shonlders. About 400,000 hip replace ments and about 300,000 knee replacements are per formed annually in the United States. During the pro cedure, the ends of the damaged bones are removed and metal, ceramic, or plastic components are fixed in place. The goals of arthroplasty are to relieve pain and increase range of motion.
Partial hip replacements involve only the femnr. Total hip replacements involve both the acetabulum and head of the femur. The damaged portions of the acetabulum and the head of the femur are replaced by prefabricated prosthe ses (artificial devices). The acetabulum is shaped to accept the new socket, the head of the femur is removed, and the center of the femur is shaped to fit the femoral component. The acetabular component consists of a plastic such as polyethylene, and the femoral component is composed of a metal such as cobalt-chrome, titanium alloys, or stain less steel. These materials are designed to withstand a high degree of stress and to prevent a response by the immune system. Once the appropriate acetabular and femoral com ponents are selected, they are attached to the healthy por tion of bone with acrylic cement, which forms an interlock ing mechanical bond.
Hip bone
Reshaped acetabulum
— Head of femur removed
Shaft of femur
Tests, Procedures, and Techniques 31
Knee replacements are actually a resurfacing of carti lage and, like hip replacements, may be partial or total. In a total knee replacement, the damaged cartilage is removed o from the distal end of the femur, proximal end of the tibia, and the back surface of the patella (if the back surface of the patella is not badly damaged, it may be lefr intact). The · femur is reshaped and fitted with a metal femoral com ponent and cemented in place. The tibia is reshaped and fitted with a plastic tibia component that is cemented in place. If the back surface of the patella is badly damaged, it is replaced with a plastic implant.
In a partial knee replacement, also called a nnicom partmental knee replacement, only one side of the knee joint is replaced. Once the damaged cartilage is removed from the distal end of the femur, the femur is reshaped and a metal femoral component is cemented in place. Then the damaged cartilage from the proximal end of the tibia is removed, along with the meniscus. The tibia is reshaped and fitted with a plastic tibial component that is cemented into place.
Researchers are continually seeking to improve the strength of the cement and devise ways to stimulate bone growth around the implanted area. Potential complica tions of arthroplasty include infection, blood clots, loos ening or dislocation of the replacement components, and nerve injury.
In a partial knee replacement, also called a unicom partmental knee replacement, only one side of the knee joint is replaced. Once the damaged cartilage is removed 0 from the distal end of the femur, the femur is reshaped and a metal femoral component is cemented in place. Then the damaged cartilage from the proximal end of the tibia
Artificial acetabulum
Artificial femoral head
Artificial metal shaft
Hip bone
Artificial acetabulum Artificial femoral · head
Artificial metal shaft
Shaft of femur
Preparation for total hip replacement Compoiients of an artificial hip joint Radiograph of an artificial hip joint 0
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32 5 Joints
Femoral surfaces removed
Tibial surfaces removed
Patellar surface removed
Preparation for total knee replacement
Plastic spacer
~ -i .. te ..
Femoral component Tibial component Patellar component
Femur
Femoral component
Tibial component
Tibia
Components of artificial knee joint_ (isolated and in place)
Fibula
Radiograph of a total knee replacement
is removed, along with the meniscus. The tibia is reshaped and fitted with a plastic tibial component that is cemented into place. .
Researchers are continually seeking to improve the strength of the cement and devise ways to stimulate bone growth around the implanted area. Potential complica tions of arthroplasty include infection, blood clots, loos ening or dislocation of the replacement components, and nerve injury.
• Torn Cartilage and Arthroscopy The tearing of articular discs (menisci) in the knee, commonly called tom cartilage, occurs often among athletes. Such damaged cartilage will begin to wear and may cause arthritis to develop unless the cartilage is surgically removed by a procedure called a menisectomy (men’ -i-SEK-t6-me). Surgical repair of the torn cartilage is required because of the avascular nature of cartilage and may be assisted -by arthros<;opy (ar-THROS- ko pe; -scopy = observation), the visual examination of the interior of a joint, usually the knee, with an arthroscope, a lighted, pencil-thin instrument. Arthroscopy is used to determine the nature and extent of damage following knee injury and to monitor the progression of disease and
the effects of therapy. The insertion of surgical instru ments through the arthroscope or other incisions enables a physician to remove torn cartilage and repair damaged cruciate ligaments in the knee; to remodel poorly formed cartilage; to obtain tissue samples for analysis; and to per form surgery on other joints, such as the shoulder, elbow, ankle, and wrist. Ill
Arthroscopy
Disorders Affecting Joints
Ill! Ankylosing Spondylitis Ankylosing spondylitis (ang’ -ki-LO-sing spon’ -di-LI tis; ankyle = stiff; spondyl = vertebra) is an inflammatory disease of unknown origin that affects joints between ver tebrae (intervertebral) and between the sacrum and hip bone (sacroiliac joint). The disease, which is more com mon in males, sets in between ages 20 and 40. It is char acterized by pain and stiffness in the hips and lower back that progress upward along the backbone. Inflammation can lead to ankylosis (severe or complete loss of movement at a joint) and kyphosis (hunchback). Treatment consists of anti-inflammatory drugs, heat, massage, and supervised exercise.
!i’l Bursitis An acute or chronic inflammation of a bursa, called bursi tis, is usually caused by irritation from repeated, excessive exertion of a joint. The condition may also be caused by trauma, by an acute or chronic infection (including syphilis and tuberculosis), or by rheumatoid arthritis. Symptoms include pain, swelling, tenderness, and limited movement. Treatment may include oral anti-inflammatory agents and injections of cortisol-like steroids.
Gouty Arthritis Uric acid (a substance that gives urine its name) is a waste product produced during the metabolism of nucleic acid (DNA and RNA) subunits. A person who suffers from gout (GOWT) either produces excessive amounts of uric acid or is not able to excrete as much as normal. The result is a buildup of uric acid in the blood. This excess acid then reacts with sodium to form a salt called sodium urate. Crystals of this salt accumulate in soft tissues such as the kidneys and in the cartilage of the ears and joints.
In gouty arthritis, sodium urate crystals are deposited in the soft tissues of the joints. Gout most often affects the joints of the feet, especially at the base of the big toe. The crystals irritate and erode the cartilage, causing inflam mation, swelling, and acute pain. Eventually, the crystals _ destroy all joint tissues. If the disorder is untreated, the ends of the articulating bones fuse, and the joint becomes immovable. Treatment consists of pain relief (ibuprofen, naproxen, colchicine, and cortisone) followed by admin istration of allopurinol to keep uric acid levels low so that crystals do not form.
Ill Lyme Disease A spiral-shaped bacterium called Borrelia burgdo,feri causes Lyme disease, named for the town of Lyme, Connecticut, where it was first reported in 197 5. The bacteria are trans mitted to humans mainly by deer. ticks. {Ixodes dammim). These ticks are so small that their bites often go urmoticed. Within a few weeks of the tick bite, a rash may appear at the site. Although the rash often resembles a bull’s-eye target, there are many variations, and some people never
Disorders Affecting Joints 33
develop a rash. Other symptoms include joint stiffness, fever and chills, headache, stiff neck, nausea, and low back pain. In advanced stages of the disease, arthritis is the main o complication. It usually afflicts the larger joints such as the _ knee, ankle, hip, elbow, or wrist. Antibiotics are generally effective against Lyme disease, especially if they are given promptly. However, some symptoms may linger for years.
ilil Osteoarthritis ·· ·· Osteoarthritis (OA) (os’-te-ii-ar-THRI-tis) is a degen erative joint disease in which joint cartilage is gradually lost. It results from a combination of aging, obesity, irrita tion of the joints, muscle weakness, and wear and abrasion. Commonly known as “wear-and-tear” arthritis, osteoar thritis is the most common type ohrthritis.
Osteoarthritis is a progressive disorder of synovial joints, particularly weight-bearing joints. Articular cartilage dete riorates and new bone forms in the subchondral areas and at the margins of the joint. The cartilage slowly degenerates, and as the bone ends become exposed, spurs (small bumps) of new osseous tissue are deposited on them in a misguided effort by the body to protect against the friction. These spurs decrease the space of the joint cavity and restrict joint movement. Unlike rheumatoid arthritis (described next), osteoarthritis affects mainly the articular cartilage, although the synovial membrane ofren becomes inflamed late in the disease. Two major distinctions between osteoarthritis and rheumatoid arthritis are that osteoarthritis first afflicts o tl1e larger joints (knees, hips) and is due to_ wear and tear, whereas rheumatoid arthritis first strikes smaller joints and is an active attack of the cartilage. Osteoarthritis is the most common reason for hip- and knee-replacement surgery.
lili Rheumatoid Arthritis Rheumatoid arthritis (RA) is an autoimmune disease in which the immune system of the body attacks its own tissues-in this case, its own cartilage and jo~t linings.
Gamma ray photograph of swollen joints (bright spots) due to RA
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34. 5 Joints
Photograph of an individual with severe RA
RA is characterized by inflammation of the joint, which causes swelling, pain, and loss of function. Usually, this form of arthritis occurs bilaterally: If one wrist is affected, the other is also likely to be affected, although often not to the same degree.
The primary symptom of RA is inflammation of the synovial membrane. If untreated, the membrane thickens, and synovial fluid accumulates. The resulting pressure causes pain and tenderness. The membrane then pro duces an abnormal granulation tissue, called pannus, that adheres to the surface of the articular cartilage and some times erodes the cartilage completely. When the cartilage is destroyed, fibrous tissue joins the exposed bone ends. The fibrous tissue ossifies and fuses the joint so that it becomes immovable-the ultimate crippling effect of RA. The growth of the granulation tissue causes the distortion of the fingers that characterizes hands of RA sufferers. II
Additional Clinical Considerations • Dislocated Mandible A dislocation (dis’-16-KA-shun; dis-= apart) or luxation (luks-A-shun; luxatio = dislocation) is the displacement of a bone from a joint with tearing of ligaments, tendons, and articular capsules. It is usually caused by a blow or fall, although unusual physical effort may be a factor. For example, if the condylar processes of the mandible pass anterior to the articular tubercles when you yawn or take a large bite, a dislocated mandible (anterior displace ment) may occur. When the mandible is displaced in this manner, the mouth remains wide open and the person is unable to dciseTCTliis may be corrected by pressing the thumbs downv.ca:rd on the lower molar teeth and pushing the mandible backward. Other causes of a dislocated man dible include a lateral blow to the chin when the mouth is open and a-fracture of the mandible.
1111 Knee Injuries The knee joint is the joint most vulnerable to damage because it is a mobile, weight-bearing joint and its stabil ity depends almost entirely on its associated ligaments and muscles. Further, there is no correspondence of the articulating bones. A swollen knee may occur immedi ately or hours after an injury. The initial swelling is due to escape of blood from damaged blood vessels adjacent to areas involving rupture of the anterior cruciate ligament, damage to synovial membranes, torn menisci, fractures, or collateral ligament sprains. Delayed swelling is due to excessive production of synovial fluid, a condition com monly referred to as “water on the knee.’1 A common type of knee injury in football is rupture of the tibial collateral ligaments, often associated with tearing of the anterior cruciate ligament and medial meniscus (torn car tilage). Usually, a hard blow to the lateral side of the knee while the foot is fixed on the ground causes the damage. A dislocated knee refers to the displacement of the tibia relative to the femur. The most common type is disloca tion anteriorly, resulting from hyperextension of the knee. A frequent consequence of a dislocated knee is damage to the popliteal artery.
Iii Rotator Cuff Injury and Dislocated and Separated Shoulder
Rotator cuff injury is a strain or tear in the rotator cuff muscles and is a common injury among ·baseball pitchers, volleyball players, racket sports players, swimmers, and violinists, due to shoulder movements that involve vigor ous circumduction. It also occurs as a result of wear and tear, aging, trauma, poor posture, improper lifting, and repetitive motions in certain jobs, such as placing items on a shelf above your head. Most often, there is tearing of the supraspinatus muscle tendon of the rotator cuff. This tendon is especially predisposed to wear-and-tear because of its location between the head of the humerus and acromion of the scapula, which compresses the tendon during shoulder movements. Poor posture and poor body mechanics also increase compression of the supraspinatus muscle tendon.
The joint most commonly dislocated in adults is the shoulder joint because its socket is quite shallow and the bones are held together by supporting muscles. Usually in a dislocated shoulder, the head of the humerus becomes displaced inferiorly, where the articular capsl)le is least protected. Dislocations of the mandible, elbow, fingers, knee, or hip are less common.
A separated shoulder refers to an injury of the acro mioclavicular joint, a joint formed by the acromion of the scapula and the acromial end of the clavicle. This condi tion is usually the result of forceful trauma to the joint, as wherr.:lre· shoulder strikes the ground in a fall.
• Sprain and Strain A sprain is the forcible wrenching or twisting of a joint that stretches or tears its ligaments but does not dislocate the
bones. It occurs when the ligaments are stressed beyond their normal capacity. Sprains also may damage surrounding blood vessels, muscles, tendons, or nerves. Severe sprains may be so painful that the joint cannot be moved. There is considerable swelling, which results from chemicals released by the damaged cells and hemorrhage of ruptured blood ves sels. The lateral ankle joint is most often sprained; the lower back s.,~norher frequent location. A strain is a stretched or partialiji torn muscle or muscle and tendon. It often occurs when a muscle contracts suddenly and powerfully-such as the leg muscles of sprinters when they spring from the blocks.
!lll Tennis Elbow, Little-League Elbow, and Dislocation of the Radial Head
Tennis elbow most commonly refers to pain at or near the lateral epicondyle of the humerus, usually caused by an improperly executed backhand. The extensor muscles strain or sprain, resulting in pain. Little-league elbow typically develops as a result of a heavy pitching schedule and/or a schedule that involves throwing curve balls, espe cially among youngsters. In this disorder, the elbow may enlarge, fragment, or separate.
A dislocation of the radial head (nursemaid’s elbow) is the most common upper limb dislocation in children. In this injury, the head of the radius slides past or ruptures the radial annular ligament, a ligament that forms a collar around the head of the radius at the proximal radioulnar
Medical Terminology 35
joint. Dislocation is most apt to occur when a strong pull is applied to the forearm while it is extended and supi- nated, for instance while swinging a child around with o outstretched arms. . !Im _.,/
Medical Terminology
Arthralgia (ar-THRAL-je-a; arthr- = joint; -algia = pain) Pain in a joint.
Arthritis is a form of rheumatism in which the joints are swollen, stiff, and painful. It afflicts about 45 million people in the United States, and is the leading cause of physical disability among adults over age 65.
Bursectomy (bur~SEK-t6-me; -ectomy = removal of) Removal of a bursa.
Chondritis (kon-DRI-tis; chondr- = cartilage) Inflammation of cartilage.
Rheumatism (ROO-ma-tizm) is any painful disorder of the supporting structures of the body-bones, ligaments, tendons, or muscles-that is not caused by infection or injury.
Subluxation (sub-luks-A.-shun) A partial or incomplete dislocation.
Synovitis (sin’-6-VI-tis) Inflanunation of a synovial mem brane in a joint.
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