CLASSIFICATION OF JOINTS Human joints provide the structures by which bones join with one another and may be classified according to the histologic features of the union and the range of joint motion There are three classes of joint design ID: 920812
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Slide1
STRUCTURE AND FUNCTION OF BONE, JOINTS AND CONNECTIVE TISSUE
Slide2CLASSIFICATION OF JOINTS
Human joints provide the structures by which bones join with one another and may be classified according to the
histologic
features of the union and the range of joint motion. There are three classes of joint design:
(1) synovial or
diarthrodial
joints which articulate with free movement, have a synovial membrane lining the joint cavity, and contain synovial fluid;
(2)
amphiarthroses
, in which adjacent bones are separated by
articular
cartilage or a
fibrocartilage
disk and are bound by firm ligaments permitting limited motion (e.g., pubic
symphysis
,
intervertebral
disks of vertebral bodies, distal
tibiofibular
articulation, and sacroiliac joint articulation with pelvic bones);
Slide33)
synarthroses
, which are found only in the skull (suture lines) where thin, fibrous tissue separates adjoining cranial plates that interlock to prevent detectable motion before the end of normal growth, yet permit growth in childhood and adolescence.
The synovial joints are classified further according to their shapes, which include
ball-and-socket
(hip),
hinge
(
interphalangeal
), saddle
(first
carpometacarpal
), and
plane
(
patellofemoral
) joints. These configurations reflect the varying functions, as the shapes and sizes of the opposing surfaces determine the direction and extent of motion.
Slide4PRESENTING PROBLEMS IN MUSCULOSKELETAL DISEASE Pain in a single joint
Principal causes of acute
monoarthritis
in a previously normal joint
Septic arthritis
Crystal
synovitis
: gout,
pseudogout
Monoarticular
presentation of
oligo
- or
polyarthritis
Reactive, psoriatic or other
seronegative
spondarthritis
Erythema
nodosum
Rheumatoid arthritis
Juvenile idiopathic arthritis
Trauma: especially if associated with
haemarthrosis
Haemarthrosis
associated with clotting abnormality
Foreign body reaction (e.g. plant thorn)
Slide5Oligoarthritis
Oligoarthritis
affects 2-4 joints or joint groups (the wrist has many joints but counts as a single site).
Causes of inflammatory
oligoarthritis
.
Seronegative
spondyloarthritis
Reactive arthritis
Psoriatic arthritis
Ankylosing
spondylitis
Enteropathic
arthritis
Erythema
nodosum
Juvenile idiopathic arthritis
Oligoarticular
presentation of
polyarthritis
Infection, including
Infective
endocarditis
Neisseria
Mycobacteria
Causes of poly
arthritis
A-Rheumatoid arthritis (symmetrical, small and large joints, upper and lower limbs).
B-
Seronegative
psoriatic arthritis (asymmetrical, large > small joints, associated
periarticular
inflammation giving
dactylitis
).
C-
Seronegative
spondyloarthritis
(axial involvement, large > small joints, asymmetrical).
Slide8MATURE ARTICULAR CARTILAGE
Articular
cartilage is a specialized connective tissue that covers the weight-bearing surfaces of
diarthrodial
joints.
The principal functions of cartilage layers covering bone ends are to permit low-friction, high-velocity movement between bones, to absorb the transmitted forces associated with locomotion, and to contribute to joint stability.
Lubrication by synovial fluid provides frictionless movement of the articulating cartilage surfaces.
Slide9Chondrocytes
are the single cellular component of adult hyaline
articular
cartilage and are responsible for synthesizing and maintaining the highly specialized cartilage matrix macromolecules.
The cartilage extracellular matrix is composed of an extensive network of collagen fibrils, which confers tensile strength, and an interlocking mesh of
proteoglycans
, which provides compressive stiffness through the ability to absorb and extrude water.
The cartilage is
avasculare
and
aneural
.
Slide10Numerous other
noncollagenous
proteins also contribute to the unique properties of cartilage ,(Collagens,
Proteoglycans
, Other
Noncollagenous
Proteins (Structural), Or (Regulatory).
Proper distribution and relative composition of these proteins is required for the function of cartilage in protecting the
subchondral
bone from adverse environmental influences.
Slide11As the single cellular component in adult
articular
cartilage,
chondrocytes
are responsible for maintaining the ECM components in a low-turnover state. The composition and organization of matrix macromolecules, unique to this tissue, are determined during
chondrocyte
differentiation in embryonic and postnatal development of cartilage.
Adult
chondrocytes
exist in a hypoxic environment within
articular
cartilage. They are inactive metabolically, partially as a result of an absence of blood vessels and nerves, and display a rounded morphology that reflects their quiescent state.
Slide12Chondrocyte
culture models have been developed with the aim of maintaining differentiated phenotypes, characterized by the major collagen and
proteoglycan
constituents, type II collagen and
aggrecan
.
Chondrocytes
interact with specific ECM components via
integrins
,
annexins
, and CD44 on the cell surface.
Slide13The
subchondral
bone plate beneath the calcified base of
articular
cartilage may have many effects on the cartilage above it. Its stiffness modifies the compressive forces to which
articular
cartilage is subjected, its blood supply may be important in cartilage nutrition ,and its cells may produce peptides that regulate
chondrocyte
function.
Slide14Several studies have suggested that the responses of the
subchondral
bone to mechanical stimulation may transmit signals into the
articular
cartilage.Tidemark
advancement with thickening of the calcified cartilage and thinning of
articular
cartilage is associated with fibrillation of the cartilage surface during aging.
Slide15Condrocyte
only 2%
Slide16SYNOVIAL FLUID AND NUTRITION OF JOINT STRUCTURES
The volume and composition of synovial fluid are determined by the properties of the
synovium
and its vasculature.
Fluid in normal joints is present in small quantities (2.5
mL
in the normal knee) sufficient to coat the synovial surface, but not to separate one surface from the other.
Tendon sheath fluid and synovial fluid are biochemically similar. Both are essential for the nutrition and lubrication of adjacent
avascular
structures, including tendon and
articular
cartilage, and for limiting adhesion formation, maintaining movement.
Slide17The synovial joint is uniquely adapted to responding to environmental and mechanical demands. The synovial lining is composed of two to three cell layers, and there is no basement membrane separating the lining cells from the underlying connective tissue.
The
synovium
produces synovial fluid, which provides nutrition and lubrication to the
avascular
articular
cartilage
Slide18SYSTEMIC REGULATION OF BONE REMODELING
CALCIUM METABOLISM
Calcium is crucial to many processes in the body, including most
signaling
cascades and synaptic
signaling
, creating a requirement for tight control of systemic calcium concentrations. the skeleton is the reservoir for calcium, and bone
remodeling
is one of the processes crucial to calcium regulation. Hormones involved in calcium homeostasis have profound effects on the skeleton.
Slide19Parathyroid hormone
The primary function of PTH is to maintain serum ionized calcium levels within a narrow physiologic range. PTH secretion increases as calcium levels decrease to less than 8 mg/
dL
, controlled by decreased binding of the calcium ion to the calcium receptor on the parathyroid
cell.When
a serum calcium value greater than 10 mg/
dL
accompanies a high level of serum PTH, a diagnosis of hyperparathyroidism can be made. Other circulating factors, such as vitamin D,
tumor
necrosis factor-α, and prostaglandins, also are involved in regulating calcium balance.
Slide20Vitamin D
Vitamin D has effects on bone
remodeling
and calcium homeostasis. A 10-minute exposure of the skin to ultraviolet light from the sun causes endogenous production of sufficient quantities of vitamin D
3
from 7-dehydrocholesterol to allow normal calcium balance. Vitamin D
3
is first
hydroxylated
to 25-hydroxyvitamin D in the liver, followed by 25-hydroxyvitamin D hydroxylation in the kidney. Often referred to as
calcitriol
, the active metabolite, 1,25-dihydroxyvitamin D, stimulates intestinal absorption of calcium, providing the mineral necessary to build bone.
Slide21supraphysiologic
levels induce bone
resorption
by stimulating the differentiation of
osteoclast
precursors.
This occurs through the effect of 1,25-dihydroxyvitamin D of increasing bone
stromal
cell production of M-CSF
and RANKL expression.
Besides the role of vitamin D in ensuring calcium acquisition from the intestine, vitamin D has subtle effects on the formation and
resorption
of bone.
Slide22STIFFNESS
Stiffness is a common complaint among patients with arthritis. What is meant by stiffness varies from patient to patient, however. Some patients may use the term
stiffness
to refer to pain, soreness, weakness, fatigue, or limitation of motion.
Rheumatologists generally use the term
stiffness
to describe discomfort and limitation on attempted movement of joints after a period of inactivity. This “gel” phenomenon occurs usually after an hour or more of inactivity. The duration of stiffness related to inactivity varies, with mild stiffness lasting minutes to severe stiffness lasting hours.
Slide23SYNOVIAL FLUID ANALYSIS
Slide24Example on each class
Slide25Cell Count
The WBC count and differential are among the most valuable diagnostic characteristics of SF. Normal SF contains fewer than 200 cells/mm3.
SF from
noninflammatory
arthropathies
may have WBC counts of up to 2000 cells/mm3 .
Noninfectious
inflammatory
arthropathies
have WBC counts that vary widely, ranging from 2000 to 100,000 cells/mm3 .
Although the autoimmune arthropathies
generally present with WBC counts of 2000 to 30,000 cells/mm3, cell counts of 50,000/mm3 or higher are not unusual in RA.
Slide26Patients with crystal induced arthritis, such as acute gout, usually have WBC counts of greater than 30,000 cells/mm3 and counts of 50,000 to 75,000 cells/mm3 are common.
The closer the WBC count gets to 100,000 cells/mm3, the greater the likelihood of a septic arthritis. Although a rare patient with crystal-induced
arthropathy
, RA, or even a
seronegative
arthropathy
may have a WBC count greater than 100,000 cells/mm3, such patients should be treated empirically for a septic joint until microbiologic data exclude infection.
A WBC count of less than 100,000 cells/mm3 does not preclude the possibility of infection.