Benign Synovial Neoplasms
For a long time, these pathologies were considered purely inflammatory, but current evidence confirms their neoplastic nature. Histologically, synoviocytes form cords accompanied by numerous macrophages, multinucleated giant cells, and hemosiderin deposits. Cellular atypia is typically absent, yet these neoplasms can erode adjacent bone and infiltrate soft tissues.
- Localized Nodular Tenosynovitis: Most commonly affects the tendon sheaths of the wrist and fingers. Macroscopically, it appears as a painless walnut-sized nodule. Microscopically, cells merge into a solid conglomerate.
- Giant Cell Tumor of the Tendon Sheath: An isolated lesion located in the same regions but reaching larger sizes. The tumor stroma frequently undergoes fibrosis and hyalinization. The prognosis is generally favorable, but a risk of recurrence persists.
Tumor-Like Joint Lesions (Cysts)
Tumor-like joint lesions primarily include two types associated with joint capsules and tendons:
- Tendon Sheath Cyst (Ganglion): A fluid-filled cavity 1–1.5 cm in diameter. Macroscopically, it resembles a firm, elastic nodule. It forms from connective tissue that has undergone cystic or myxoid degeneration. Smaller elements can coalesce. When located in the popliteal fossa, it is termed a Baker cyst. Occasionally, the cyst grows subchondrally (intraosseous ganglion), causing cortical erosion and bone deformation.
- Synovial Cyst: A herniation of the synovial membrane itself through defects in the joint capsule. The membrane becomes edematous and thickened, containing an infiltrate of lymphocytes, macrophages, leukocytes, and fibrin.
Bone Injuries: Pathogenesis of Fracture Healing
A fracture is a mechanical or pathological disruption of bone integrity. Healing is a complex cascade of reactions:
- Initial Stage: Vascular rupture leads to hemorrhage, hematoma formation, and acute inflammation.
- Days 2–3: The hematoma is organized and replaced by granulation tissue, establishing a primary fibrous connection.
- Weeks 2–3: Osteoblast precursors migrate from the periosteum and endosteum. Granulations transform into woven bone, forming the primary callus.
- Subsequent Weeks: The primary callus is resorbed and replaced by mature lamellar bone, forming the secondary callus.
Blood supply is a critical factor: adequate perfusion promotes bony trabeculae formation, whereas poor perfusion leads to cartilage formation (subsequently undergoing endochondral ossification). Finally, osteoclasts remove excess tissue, and newly formed osteons bridge the fracture line to restore normal structure.
Outcomes of Fractures
Bone tissue repair can proceed via several scenarios:
- Primary Healing: The ideal scenario. Lasts about 5 weeks, occurs without massive callus formation, and ends in complete structural restitution.
- Secondary Healing: Occurs when fragment mobility and poor apposition are present. It invariably includes a fibrocartilaginous callus stage.
- Pseudoarthrosis (Nonunion): An adverse outcome. Dense connective tissue proliferates between the ends of the broken bone. Due to metaplasia, it transforms into fibrocartilage containing foci of fibrinoid necrosis. Ultimately, a cavity lined by synovial-like cells is formed.
Hereditary Muscular Dystrophies (Myopathies)
Myopathies are primary inherited disorders of striated muscles characterized by the selective involvement of specific muscle groups and progressive weakness.
Duchenne Muscular Dystrophy is caused by an X-linked mutation in the dystrophin gene (a protein maintaining muscle fiber shape and contractility). It affects boys, manifesting at age 3–5. Pelvic and lower extremity muscles weaken first. Microscopy reveals fiber size variation, necrosis, macrophage phagocytosis, and compensatory satellite cell proliferation. Eventually, muscle tissue is replaced by fat and fibrosis; myocardial fibrosis leads to heart failure (with mortality typically occurring around age 20).
Becker Muscular Dystrophy shares a similar etiopathogenesis but has a much milder clinical course, later onset in boys, and less frequent cardiac involvement, allowing for a longer lifespan.
Myotonic Dystrophies (specifically the congenital form) are inherited in an autosomal dominant pattern. The hallmark symptom is myotonia (delayed muscle relaxation after contraction). Onset occurs in adolescence with foot drop, later accompanied by ptosis, facial muscle atrophy, and cataracts.