Joint Pathophysiology PDF

# JOINT ## I. BASIC PRINCIPLES * **A.** Connection between two bones * **B.** Solid joints are tightly connected to provide structural strength (e.g., cranial sutures). * **C.** Synovial joints have a joint space to allow for motion. * **1.** Articular surface of adjoining bones is made of hya...

# JOINT ## I. BASIC PRINCIPLES * **A.** Connection between two bones * **B.** Solid joints are tightly connected to provide structural strength (e.g., cranial sutures). * **C.** Synovial joints have a joint space to allow for motion. * **1.** Articular surface of adjoining bones is made of hyaline cartilage (type II collagen) that is surrounded by a joint capsule. * **2.** Synovium lining the joint capsule secretes fluid rich in hyaluronic acid to lubricate the joint and facilitate smooth motion. ## II. DEGENERATIVE JOINT DISEASE (OSTEOARTHRITIS) * **A.** Progressive degeneration of articular cartilage; most common type of arthritis * **B.** Most often due to 'wear and tear' * **C.** Major risk factor is age (common after 60 years); additional risk factors include obesity and trauma. * **D.** Affects a limited number of joints (oligoarticular); hips, lower lumbar spine, knees, and the distal interphalangeal joints (DIP) and proximal interphalangeal joints (PIP) of fingers are common sites. * **E.** Classic presentation is joint stiffness in the morning that worsens during the day. * **F.** Pathologic features include * **1.** Disruption of the cartilage that lines the articular surface (Fig. 18.7); fragments of cartilage floating in the joint space are called 'joint mice.' * **2.** Eburnation of the subchondral bone * **3.** Osteophyte formation (reactive bony outgrowths); classically arises in the DIP (Heberden nodes) and PIP (Bouchard nodes) joints of the fingers ## III. RHEUMATOID ARTHRITIS * **A.** Chronic, systemic autoimmune disease * **1.** Classically arises in women of late childbearing age * **2.** Associated with HLA-DR4 * **B.** Characterized by involvement of joints * **1.** Hallmark is synovitis leading to formation of a pannus (inflamed granulation tissue). * **2.** Leads to destruction of cartilage and ankylosis (fusion) of the joint * **C. Clinical features** * **1. Arthritis with morning stiffness that improves with activity.** * **i.** Symmetric involvement of PIP joints of the fingers (swan-neck deformity), wrists (radial deviation), elbows, ankles, and knees is characteristic (Fig. 18.8); DIP is usually spared (unlike osteoarthritis). * **ii.** Joint-space narrowing, loss of cartilage, and osteopenia are seen on x-ray. * **2.** Fever, malaise, weight loss, and myalgias * **3.** Rheumatoid nodules - central zone of necrosis surrounded by epithelioid histiocytes; arise in skin and visceral organs * **4.** Vasculitis - Multiple organs may be involved. * **5.** Baker cyst - swelling of bursa behind the knee * **6.** Pleural effusions, lymphadenopathy, and interstitial lung fibrosis * **D. Laboratory findings** * **1.** IgM autoantibody against Fc portion of IgG (rheumatoid factor); marker of tissue damage and disease activity * **2.** Neutrophils and high protein in synovial fluid * **E.** Complications include anemia of chronic disease and secondary amyloidosis. ## IV. SERONEGATIVE SPONDYLOARTHROPATHIES * **A.** Group of joint disorders characterized by * **1.** Lack of rheumatoid factor * **2.** Axial skeleton involvement * **3.** HLA-B27 association * **B.** Ankylosing spondyloarthritis involves the sacroiliac joints and spine. * **1.** Arises in young adults, most often male * **2.** Presents with low back pain; involvement of vertebral bodies eventually arises, leading to fusion of the vertebrae ('bamboo spine'). * **3.** Extra-articular manifestations include uveitis and aortitis (leading to aortic regurgitation). * **C.** Reactive arthritis is characterized by the triad of arthritis, urethritis, and conjunctivitis. * **1.** Arises in young adults (usually males) weeks after a GI or Chlamydia trachomatis infection * **D.** Psoriatic arthritis is seen in 10% of cases of psoriasis. * **1.** Involves axial and peripheral joints; DIP joints of the hands and feet are most commonly affected, leading to "sausage" fingers or toes. ## V. INFECTIOUS ARTHRITIS * **A.** Arthritis due to an infectious agent, usually bacterial * **B.** Causes include * **1.** N. gonorrhoeae - young adults; most common cause * **2.** S. aureus- older children and adults; 2nd most common cause * **C.** Classically involves a single joint, usually the knee * **D.** Presents as a warm joint with limited range of motion; fever, increased white count, and elevated ESR are often present. ## VI. GOUT * **A.** Deposition of monosodium urate (MSU) crystals in tissues, especially the joints * **B.** Due to hyperuricemia; related to overproduction or decreased excretion of uric acid * **1.** Uric acid is derived from purine metabolism and is excreted by the kidney. * **C.** Primary gout is the most common form; etiology of hyperuricemia is unknown. * **D.** Secondary gout is seen with * **1.** Leukemia and myeloproliferative disorders - Increased cell turnover leads to hyperuricemia. * **2.** Lesch-Nyhan syndrome - X-linked deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT); presents with mental retardation and self-mutilation * **3.** Renal insufficiency - decreased renal excretion of uric acid * **E.** Acute gout presents as exquisitely painful arthritis of the great toe (podagra) * **1.** MSU crystals deposit in the joint, triggering an acute inflammatory reaction. * **2.** Alcohol or consumption of meat may precipitate arthritis. * **F.** Chronic gout leads to * **1.** Development of tophi - white, chalky aggregates of uric acid crystals with fibrosis and giant cell reaction in the soft tissue and joints (Fig. 18.9A) * **2.** Renal failure - Urate crystals may deposit in kidney tubules (urate nephropathy). * **G. Laboratory findings include hyperuricemia; synovial fluid shows needle-shaped crystals with negative birefringence under polarized light (Fig. 18.9B).** * **H. Pseudogout resembles gout clinically, but is due to deposition of calcium pyrophosphate dihydrate (CPPD); synovial fluid shows rhomboid-shaped crystals with weakly positive birefringence under polarized light.**