Chapter 27: Joint Pathology

Joint Pathology begins with Osteoarthritis (OA), the most common form of arthritis, defined as a degenerative joint disease involving the breakdown of articular cartilage due to wear and tear, aging, and biomechanical stress, typically affecting weight-bearing joints like the knees and hips. The summary details key pathological features of OA, including eburnation, subchondral bone sclerosis, loose bodies known as joint mice, and osteophytes, specifically identifying Heberden nodes at the distal interphalangeal joints and Bouchard nodes at the proximal interphalangeal joints. The text contrasts OA with Rheumatoid Arthritis (RA), a systemic autoimmune disorder linked to HLA-DR4 and HLA-DR1 genetics, characterized by inflammatory synovitis, pannus formation, and symmetrical involvement that includes morning stiffness improving with activity. Major complications of RA are explored, such as ulnar deviation, swan neck and boutonniere deformities, Baker cysts, and extra-articular manifestations like rheumatoid nodules, Sjögren syndrome, Felty syndrome, and Caplan syndrome. The discussion then moves to Seronegative Spondyloarthropathies, a group of HLA-B27 associated disorders lacking rheumatoid factor, notably Ankylosing Spondylitis with its classic bamboo spine, and Reactive Arthritis which presents with the triad of conjunctivitis, urethritis, and arthritis. Metabolic arthropathies are examined through crystal deposition, distinguishing Gout, caused by hyperuricemia and negatively birefringent monosodium urate crystals leading to podagra and tophi, from Pseudogout, which involves positively birefringent calcium pyrophosphate crystals often seen in older adults. The chapter also covers Infectious Arthritis, detailing suppurative agents like Staphylococcus and Gonococci, as well as Lyme disease caused by Borrelia burgdorferi transmitted by deer ticks. Finally, the summary concludes with Neuropathic Arthropathy (Charcot joint), describing joint destruction secondary to sensory neuropathy in conditions like diabetes mellitus, syringomyelia, and tabes dorsalis.