Osteoarthritis is the most common articular disorder.
Obesity is a modifiable risk factor most closely associated with osteoarthritis.
The joints typically involved are: distal interphalangeal joints, proximal interphalangeal joints, first carpometacarpal joints, hips, knees, first metatarsophalangeal joint, cervical spine, and lumbosacral spine.
Typical radiologic findings include normal bony mineralization, nonuniform joint space narrowing, osteophytes, and sclerosis.
There are two indications for joint replacement surgery: pain unresponsive to medical therapy and loss of joint function.
Pathologic features of osteoarthritis:
Swelling of articular cartilage.
Loosening of collagen framework
Chondrocytes increase proteoglycan synthesis but also release more degradative enzymes
Increased cartilage water content.
Degradative enzymes break down proteoglycan faster than it can be produced by chondrocytes, resulting in diminished proteoglycan content in cartilage.
Articular cartilage thins and softens
Fissuring and cracking of cartilage. Repair is attempted but inadequate.
Underlying bone is exposed, allowing synovial fluid to be forced by the pressure of weight into the bone.
Clinical features of osteoarthritis:
Pain in involved joints.
Pain worse with activity, better with rest.
Morning stiffness (if present) <30 minutes.
Stiffness after periods of immobility.
Bony joint enlargement.
Limitation of joint mobility.
Periarticular muscle atrophy.
Laboratory findings are nonspecific:
Erythrocyte sedimentation rate (ESR) typically within normal limits, Rheumatoid factor (RF) is negative, Antinuclear antibodies (ANAs) are not present. Synovial fluid (normal viscosity, color is clear and yellow, white blood cell counts typically <1000/mm3 to 2000/mm3, no crystals and negative cultures)
Radiographic “ABCDES” of osteoarthritis:
A—No ankylosis. Alignment may be abnormal.
B—Bone mineralization is normal. Bony subchondral sclerosis. Bony spurs (osteophytes).
C—No calcifications in cartilage. Cartilage space narrowing that is nonuniform (occurs in area of maximal stress in weight-bearing joints).
D—Deformities of Heberden’s/Bouchard’s nodes. Distribution: involvement of typical joints
E—No erosions. (“Gull wing” sign in “erosive” osteoarthritis).
S—Slow progression over years. No specific nail or soft tissue abnormalities.
Vacuum sign in degenerative disc disease (a collection of nitrogen in a degenerated disc space).
--> Primary, idiopathic osteoarthritis,
Localized: Hands (DIP joints, PIP joints, and first CMC joints): nodal osteoarthritis. Hands (DIP joints, PIP joints, and first CMC joints): erosive, inflammatory osteoarthritis Feet (first MTP joint Hip. Knee, Spine.
Generalized (also called Kellgren’s syndrome).
Secondary osteoarthritis has the same clinical features as idiopathic osteoarthritis except that it has an identifiable etiologic factor and may have a different joint distribution. Atypical joint involvement (MCP joints, wrists, elbows, shoulders, ankles, MTP joints) or early age onset of osteoarthritis should prompt a search for an underlying disease process. A classic example is osteoarthritis seen in the MCP joints of the hands in association with hemochromatosis (young patients) and CPPD disease (older patients).