Osteoarthritis
(OA) is the most common joint disease, affecting nearly 50% of those over 65
years of age and almost all individuals over age 75. OA affects primarily the
weight-bearing joints of the axial and peripheral skeleton, causing pain,
limitation of motion, deformity, progressive disability, and decreased quality
of life.1−5 Other names for OA include degenerative
joint disease and hypertrophic arthritis, but these terms have
shortcomings. OA implies lack of inflammation and excess materials in the
joint, degenerative joint disease suggests a wearing out of the joint, and
hypertrophic arthritis describes the
overgrowth
of bone and cartilage that is only one aspect of OA. Thus the term
“osteoarthritis” best reflects the degenerative changes that occur in the
metabolically active cartilage and bone within a joint. OA is characterized by
increased destruction of cartilage and subsequent proliferation of adjacent
bone. The regenerated articular surfaces do not possess the same qualities and
architecture as the original joint, and this change in structure leads to pain,
decreased or altered motion, crepitus, and possibly local inflammation.2 The
pain of OA typically worsens with use and improves with rest. Morning stiffness
lasting less than 1 hour and “gelling” of the joints after inactivity are also
common. The inflammation associated with OA is usually mild or localized, in
contrast to that of rheumatoid arthritis or other inflammatory diseases
affecting the joints.
EPIDEMIOLOGY:
PREVALENCE
BY AGE, SEX, AND RACE
Based
on prevalence data from the National Centers for Health Statistics, an
estimated 15.8 million adults, or 12% of those between 25 and 74 years of age,
have signs and symptoms of OA.4 The prevalence of OA increases with age. In
those under age 45, about one-fifth have OA of the hands, while for those aged
75 to 79 years, 85% have OA of the hands. OA of the knee occurs in less than
0.1% of those aged 25 to 34 years, but in 10% to 20% of those aged 65 to 74
years. The overall incidence of hip or knee OA is approximately 200 per 100,000
person-years. The incidence of hip OA is greater in women than in men, whereas
the rate for knee OA is similar between genders. In men, rates of knee and hip
OA increase with age, but in women
rates
remain stable.
ETIOLOGY:
OBESITY
Increased
body weight is strongly associated with hip, knee, and hand OA.3,12,13
Obesity often precedes OA and contributes to its development, rather than
occurring as a result of inactivity from joint pain. In a three-decade
Framingham Study, the highest quintile of body mass was associated with a
higher relative risk of knee OA (relative risk of 1.5 to 1.9 for men and 2.1 to
3.2 for women).
OCCUPATION,
SPORTS, AND TRAUMA
Those
participating in activities involving repetitive motion or injury are at
increased risk for developing OA.14 Workers exposed to repetitive stress of the
hands or lower limbs are at higher risk for OA of the stressed joints.
Lower-extremity OA in some professional sports is also increased, likely
secondary to repetitive motion, trauma to the joint, loss of ligament
integrity, or damage to the meniscus. Risk for OA depends on the type and
intensity of physical activity. The Framingham Study showed that heavy physical
activity increases knee OA risk, especially in the obese, whereas moderate or
light activity does not.15
GENETIC
FACTORS
Heredity
plays a role in osteoarthritis.3,17 Heberden’s nodes are 10 times more
prevalent inwomen than in men, with a twofold higher risk if the woman’s mother
had them. Genetic links also have been shown with OA of the first
metatarsophalangeal joint and with generalized OA. Premature development of OA
is associated with a defect in type II procollagen.
OSTEOPOROSIS
An
inverse correlation betweenOAand osteoporosis has been demonstrated, and both
men and women with OA have increased bone mineral density at numerous skeletal
sites.2,18 This relationship may derive from the influence of body
weight on both diseases, because heavy individuals have higher bone density as
well as increased risk of OA.
PATHOPHYSIOLOGYOPHYSIOLOGY
OA falls into two major etiologic
classes. Primary (idiopathic) OA, the mostcommontype, has no
identifiable cause. Subclasses
of
primary OA are localized OA, involving one or two sites, and generalized
OA, affecting three or more sites. Erosive osteoarthritis is used to
describe the presence of erosion and marked proliferation in the
proximal and distal interphalangeal joints of the hands. Secondary OA is
that associated with a known cause such as rheumatoid or another
inflammatory arthritis, trauma, metabolic or endocrine disorders, and
congenital factors (Table 90–1).2,19−21
To aid uniform reporting of rheumatic diseases, a classification scheme
and criteria for OA of the hip, knee, and hand were devised by the
American College of Rheumatology (ACR). Criteria include the presence of
pain, bony changes on examination, a normal erythrocyte
sedimentation
rate, and characteristic radiographs.1,2,22 For hip OA, a patient
must have hip pain plus two of the following: an erythrocyte sedimentation rate
of less than 20 mm/h, radiographic femoral or acetabular osteophytes, or
radiographic joint space narrowing. For knee OA, a patient must have knee pain
and radiographic osteophytes plus one of the following: age greater than 50
years, morning stiffness of 30 minutes’ or less duration, or crepitus on
motion. Improved understanding of articular cartilage physiology has transcended
the wear-and-tear theory of OA. Some changes in the OA joint may reflect compensatory
processes to maintain function in the face of ongoing joint destruction. As
such, the pathogenesis of OA involves not only biomechanical forces, but also
inflammatory, biochemical, and immunologic factors.19−21,23−26 To understand the pathophysiology of
OA, familiarity with the normal joint is essential. To this end, a review of
the biochemistry and function of normal cartilage and of the diarthrodial joint
is provided.
CLASSIFICATION OF OA
Primary
(Idiopathic) Secondary
Localized
Trauma—acute/chronic
Generalized
Underlying
joint disorder
Local
(fracture/infection)
Diffuse (rheumatoid arthritis)
Erosive
Systemic
metabolic or endocrine disorders
Wilson’s
disease
Acromegaly
Hyperparathyroidism
Hemochromatosis
Paget’s disease
Diabetes
mellitus
Obesity
Crystal
deposition disease
Basic calcium
phosphate crystal disease
Calcium
pyrophosphate dihydrate
Hydroxyapatite
Other
calcium-containing crystals
Monosodium urate
monohydrate
Neuropathic
disorders
Intra-articular
corticosteroid overuse
Avascular
necrosis
Bone
dysplasia
STRUCTURE
AND BIOCHEMICAL COMPOSITION
OF
CARTILAGE
Articular
cartilage is a hydrated (75% to 80% water), complex extracellular matrix (ECM)
with a small number of chondrocytes
(<5%).
The remaining 20% to 25% of matrix contains three types of molecules:
collagens, large aggregates of proteoglycans, and noncollagenous proteins.
Orientation of collagen fibers is critical: superficial fibers are parallel to
the surface, reducing friction and allowing forces to be dissipated; basal
layer collagen fibers are perpendicular to the surface to anchor cartilage to
the calcified zone or subchondral bony end plate. Cartilage undergoes continual
biochemical and structural remodeling controlled by chondrocytes, which
synthesize collagen and proteoglycans, and also play a role in their
degradation. Because adult
articular
cartilage is avascular, chondrocytes are nourished by synovial fluid. With the
cyclic movement and loading of joints, nutrients flow into the cartilage,
whereas immobilization reduces nutrient supply. Recent research has highlighted
the role of peptides and proteins regulating chondrocyte function and cartilage
metabolism.19−21,23−26
Insulin-like growth factor, epidermal growth factor, fibroblast growth factor,
and other agents enhance chondrocyte proliferation and proteoglycan synthesis.
By contrast, interleukin-1 and tumor necrosis factor-α promote
chondrocyte secretion of matrix metalloproteinases (MMPs), including
collagenase (MMP-1) and stromelysin (MMP-2). These proteinases in turn degrade
matrix proteins. Interleukin-1 and
tumor
necrosis factor-α also suppress proteoglycan and collagen synthesis in
the ECM. Biomechanical factors, including load and strain, also affect
chondrocyte function, and joint loading increases proteoglycan synthesis. The
following sections will review the components of the joint matrix, and the
pathologic changes in this matrix leading to OA.
Collagen
Five
types of collagen (II, IX, X, XI, and VI) are located in cartilage. Type II
collagen accounts for 90% to 95% of the total collagen in articular
cartilage.19−21,23−26
Type VI appears to attach chondrocytes to the matrix. Type IX collagen, a
proteoglycan, may link matrix molecules together. The cross-linked network of
type II collagen fibrils with other ECM proteins provides tensile strength and
maintains cartilage volume and shape.
OSTEOARTHRITIC
CARTILAGE
BIOCHEMICAL
CHANGES
Numerous
compositional differences have been noted between cartilage in OA and normal
individuals (Table 90–2).19−21,23−26 Early in OA, cartilage water content
increases, possibly as a result of a damaged collagen network that is unable to
constrain PGs, which subsequently gain water. As osteoarthritis progresses,
cartilage PG content decreases, possibly through the action of MMPs. Increased collagen
synthesis and altered distribution and diameter of the fibers are seen, but
collagen content does not appear to change until severe disease is present. Earlier
theories suggested that cartilage was passively eroded in OA, but in fact,
there is increased metabolic activity, suggesting a reparative response to
damage.19−21,23−26
Despite the increased matrix
synthesis
by chondrocytes, there is a net loss of PG, as degradation proceeds faster than
synthesis. Intense research efforts are directed toward understanding the roles
of MMPs and other collagen-degrading enzymes. MMPs are zinc-containing
proteinases falling into five related subgroups. MMPs are normally held in
check by tissue inhibitors of metalloproteinases
(TIMPs),
but there are also substances produced by chondrocytes that activate MMPs.23−26 Imbalance between activators and
inhibitors
of MMPs in synovial fluid or local tissues can lead to proteolysis of the ECM,
promoting osteoarthritic changes. Recent work showed that cartilage from
osteoarthritic human joints exhibited increased collagen-degrading activity
colocalized with increased levels of MMP mRNA.24 The subchondral bone adjacent
to articular cartilage also undergoes pathologic changes that may precede,
coincide with, or follow damage to the articular cartilage. Nevertheless, this
damage to subchondral
bone
is required and appears to permit continued damage to articular cartilage,
leading to progression to OA.25 This subchondral
bone
demonstrates increased bone turnover, with both increased osteoclast and
osteoblast activity. There is an associated release of vasoactive peptides and
matrix metalloproteinases, neovascularization, and subsequent increased
permeability of the adjacent cartilage.25,26 This sequence of events
leads to continued cartilage degradation, and eventually substantial loss of
cartilage, leading to a painful, deformed joint. In summary, the slow
progressive changes in OA consist of an increase in water content, loss of PG,
and reduction of PG aggregates of cartilage. The cartilage is subsequently
unable to repair itself. Alterations in metabolism of subchondral bone adjacent
to articular cartilage appear necessary for continued cartilage destruction.
Eventually,
progressive
loss of articular cartilage and increasing subchondral sclerosis lead to an
abnormal and painful joint.
PATHOLOGIC
CHANGES
Pathologic
changes in bone and cartilage accompany the biochemical changes just described.
These changes are noted in both weightbearing and non–weight-bearing joints,
and in both primary and secondary OA. A summary of the biochemical changes in
cartilage in OA follows.19,20
1.
Initial thickening of articular cartilage as ECM is damaged and water content
increases
2.
Proliferation of chondrocytes and an increase in ECM anabolic and catabolic
activity secondary to tissue damage or alterations in ECM structure
3.
Decline in response of chondrocytes to stabilize or restore tissue, resulting
in progressive cartilage loss
4.
Increased turnover of adjacent subchondral bone, leading to release of
vasoactive peptides and enzymes, causing cartilage degradation,
neovascularization, and increased leakiness of adjacent cartilage, likely contributing
to subsequent loss of articular cartilage
5.
Fibrillation or splitting of the noncalcified cartilage, likely related to the
biochemical changes described
earlier;
loss of cartilage exposes the underlying subchondral bone and may lead to
microfractures As cartilage is destroyed and the adjacent subchondral bone undergoes
pathologic changes, cartilage is eroded completely, leaving denuded subchondral
bone to become dense, smooth, and glistening (eburnation). A more brittle,
stiffer bone results, with decreased weight-bearing ability and development of
sclerosis and microfractures.19,20 Microfractures lead to callus and
osteoid production. New bone formations at the joint margins distant from
cartilage destruction are referred to as osteophytes, and may be an
attempt to stabilize the joint.
Presentation
of Osteoarthritis
Age
Usually
elderly
Gender
Age <45
more common in men
Age >45
more common in women
Symptoms
Pain
Deep,
aching character
Pain
on motion
Pain
with motion early in disease
Pain
with rest late in disease
Stiffness
in affected joints
Resolves
with motion, recurs with rest
(“gelling”
phenomenon)
Usually
<30 minutes’ duration
Often
related to weather
Limited
joint motion
May
result in limitations activities
of
daily living
Instability
of weight-bearing joints
Signs,
history, and physical examination
Monarticular
or oligoarticular;
asymmetrical
involvement
Hands
Distal
interphalangeal joints
Heberden’s
nodes (osteophytes
or
bony enlargements)
Proximal
interphalangeal joints
Bouchard’s
nodes (osteophytes)
First
carpometacarpal joint
Osteophytes
give characteristic square
appearance
of the hand (shelf sign)
Knees
Patellofemoral
compartment involvement
Pain
related to climbing stairs
Medial
compartment involvement
Genu
varum (bowlegged deformity)
Lateral
compartment involvement
Genu
valgum (knock-knee deformity)
Transient
joint effusions
Typically
noninflammatory
synovial
fluid (WBC <2000/mm3)
Hips
Groin
pain during weight-bearing activities
Stiffness,
especially after inactivity
Limited
joint motion
Spine
L3
and L4 involvement is most common in
the
lumbar spine
Signs
and symptoms of nerve root compression
Radicular
pain
Paresthesias
Loss
of reflexes
Muscle
weakness associated with
the
affected nerve root
Feet
Typically
involves the first metatarsophalangeal
joint
Other
sites, less commonly involved
Shoulder,
elbow, acromioclavicular,
sternoclavicular,
and temporomandibular joints
Observation
on joint examination
Bony
proliferation or occasional synovitis
Local
tenderness
Crepitus
Muscle
atrophy
Limited
motion with passive/active movement
Deformity
Radiologic
evaluation
Early
mild OA
Radiographic
changes often absent
Progression
of OA
Joint
space narrowing
Subchondral
bone sclerosis
Marginal
osteophytes
Late
OA
Abnormal
alignment of joints
Effusions
Characteristics
of synovial fluid
High
viscosity
Mild
leukocytosis (<2000 WBC/mm3)
Laboratory
values
No
specific test
Erythrocyte
sedimentation rate and hematologic
and
chemistry survey are normal
PHYSICAL
EXAMINATION
Examination
of the affected joints reveals tenderness, crepitus, and joint enlargement.
Crepitus is a crackling or grating
sound
heard with joint movement that is caused by irregularity of joint surfaces.
Joint enlargement is related to bony proliferation or to thickening of the
synovium and joint capsule. Joint deformity may be present in the later stages
of OA as a result of subluxation, collapse of subchondral bone, formation of
bone cysts, or bony overgrowth. The presence of a warm, red, tender joint may
indicate the presence of an inflammatory arthritis such as gout.
HANDS
Hand
OA is associated with pain in specific joints and often with development of
bony enlargements (osteophytes). These usually develop slowly and painlessly,
appear on lateral and medial aspects of the joint, and are about 10 times more
common in women than in men.2,22 Occasionally, these nodes become red,
warm, swollen, and painful, usually as a result of trauma or use.
KNEES
The
knee is commonly affected in OA. It is important to localize the symptoms
because the joint has three separate articulations. Knee OA is associated with
pain, tenderness, crepitus, and limited range of motion. Limited joint motion
occurs from loss of articular surfaces, muscle spasm, capsular contracture, or
mechanical blockage secondary to osteophytes (bony enlargements). Weakness or
instability (the joint “gives way”) is frequently noted by patients with knee
OA. Such joint instability may lead to decreased activity and muscle atrophy.
HIPS
Hip
OA is common in the elderly, with a characteristic presentation. However, pain located on the lateral hip typically represents
trochanteric bursitis, while pain in the buttock region may indicate lumbar
spine OA or iliopsoas bursitis.
SPINE
Degenerative
changes involving the spine may occur in the intervertebral disks, vertebral
bodies, or posterior apophyseal articulations. Aside from pain and limitation
of motion, nerve root compression is a potential complication of arthritis .
LABORATORY
FINDINGS
No
specific laboratory abnormalities occur in primary OA.2 If secondary OA
is suspected, specific laboratory tests can help identify the cause.
RADIOLOGIC
EVALUATION
Radiologic
evaluation is an absolute necessity in the diagnosis of OA .
Bone erosions and unequivocal radiographic osteopenia are uncommon except in
erosive or secondaryOA. Finally, many patients who do not have clinical OA and
do not have pain may nonetheless exhibit radiologic changes typical of OA.28 Newer
techniques—computed tomography, magnetic resonance imaging, and ultrasound—have
been used, but are not suitable for routine use in diagnosing OA.
DIAGNOSIS
The
diagnosis of OA is easily made by history, physical examination, and
characteristic radiographic findings.2,6,22,28 The major
diagnostic goals are (1) to discriminate between primary and secondary OA, and
(2) to clarify the joints involved, severity of joint involvement, and response
to prior therapies, providing a basis for a treatment plan.
TREATMENT:
Oral
analgesics
Acetaminophen,
Tramadol
Topical
analgesics
Capsaicin
0.025% or 0.075%
Nutritional
supplements
Glucosamine
sulfate
Nonsteroidal
anti-inflammatory drugs
(NSAIDs)
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