Musculoskeletal Pathology

Part II

Joints, Tendons, Tendon Sheaths, Bursae & Muscles

Joint diseases

Congenital defectsDysplasia coxae congenitaTraumaDegenerative diseasesOsteoarthritisInflammationInfective arthritisLyme diseaseTuberculous arthritisRheumatoid arthritisGoutTumoursPigmented villonodular synovitis

Dysplasia coxae congenita

autosomal recessive congenital disorder

hypoplasia of hip joint with congenital subluxation or luxation

if left untreated → early secondary osteoarthritis

Trauma

disruption of synovial membrane – bleeding into the join cavity (haemarthros)

organization of haematoma – fibrous adhaesions limiting joint movements or ankylosis (joint space replaced by metaplastic bone)

haemarthros often complicates disorders of coagulation (haemophilia)

Osteoarthritis

most common of the joint diseases (14% of adult population)primary process is breakdown of the articular cartilageweight-bearing joints affected (hip, knee, intervertebral joints)

Clinical features: pain, joint deformity, limitation of movement, crepitus (creaking sound heard on movement of the joint)

Radiographic features: narrowing of joint space

Two main groups:Primary OA: no known associated condition

Secondary OA: degeneration of previously damaged joint (congenital disorders, inflammation, trauma)

Morphology

erosive changes of joint cartilage („fibrillation“), flaking off of small portions of cartilage, later complete loss of cartilage – polishing of the denuded bone (smooth ivory-like surface)

thickening of subchondral bone plate, synovial fluid under pressure enters into small defects in the bone → subchondral pseudocysts

bony outgrowths at the margins of the articular cartilage (osteophytes)

Infective arthritis

Staphylococcus aureus, Neisseria gonorrhoeae

blood spread (most common), direct penetration (trauma) and direct spread from a contiguous infected site (osteomyelitis)

hyperaemia and acute inflammatory infiltrate in the synovial membrane, exudate accumulation in the joint cavity (pyarthros)

lysosomal enzymes released from neutrophils → severe damage of the articular cartilage – secondary osteoarthritis

Lyme disease

spirochaete Borrelia burgdorferi transmitted to humans via tick bites

systemic disease: skin, nervous system heart, joints

Stage I: macular skin lesion (erythema migrans) + low-grade fever, headache, arthralgia, muscle pain, enlargement of regional lymph nodes

Stage II: early bloodstream dissemination of borrelia: nervous system (meningitis, meningoencephalitis, neuritis), heart (atrioventricular block, pericarditis)

Stage III: chronic disease (M or Y after the initial infection): arthritis (large joints, similar to rheumatoid arthritis), nervous system (encephalopathy), skin (acrodermatitis chronica atrophicans Herxheimer)

Tuberculous arthritis

children, haematogeneous dissemination

knee, hip, elbow and ankle

insidious development of pain, swelling and limitation of movement, other signs of inflammation mild or absent

synovial hyperplasia, tuberculous granulomas in 90% of cases, acid-fast bacilli seldom identified

Rheumatoid arthritis

common multisystem autoimmune disease

three times as common in premenopausal women as in males

small joints of the hands and feet, knees, hips, involvement frequently symmetrical

rheumatoid factor (IgM) positive in 95%

complication: secondary amyloidosis

Morphology

hyperplasia of synovial membrane with increased vascularity, cellularity and synovial fluid production

inflammatory infiltrate (lymphocytes and plasma cells), lymphoid follicles

pannus (proliferation of inflammed hypervascular granulation tissue)

degradation of articular cartilage, fibrous adhesions → joint movement severely limited, sometimes ankylosis (metaplastic bone), osteoporosis of adjacent bone

deformities of joints (ulnar deviation of the fingers)

periarticular rheumatoid nodules in 30% (central area of fibrinoid necrosis surrounded by macrophages and fibroblasts arranged in a palisaded fashion)

Variants of RA:

Juvenile rheumatoid arthritis (JRA): individuals younger than 16 years, large joints predominantly involved, rheumatoid factor often negative

Still’s disease (systemic JRA): fever, leucocytosis, enlargement of liver, spleen and lymph nodes

Felty’s syndrome: RA + splenomegaly + neutropenia

Gout

disorder of purine metabolism → hyperuricaemia

30 – 60 years, male preponderance

deposition of monosodium urate crystals into articular cartilage, synovial membrane and periarticular soft tissues (tophi, tophaceous gout)

Acute gouty arthritis: metatarsophalangeal joint of the big toe (70%), ankle, knee, wrist, elbow, the affected joint is red, hot, swollen, very painful and tender

Chronic gouty arthritis: follows recurrent episodes of acute gouty arthritis, progressive erosion of cartilage and bone – limited joint function

Pigmented villonodular synovitis

benign tumour rather than inflammatory condition

knee joint (80%)

mild pain, swelling, tenderness

brown-coloured nodular thickening of synovial membrane

villous synovial hyperplasia

diffuse proliferation of mononuclear cells resembling histiocytes

various number of osteoclast-like multinuclear giant cells

depositions of hemosiderin

Diseases of tendons, tendon sheaths and bursae

Ganglionarea of myxoid degeneration of connective tissue of tendon sheathextensor surfaces of hand and feetthin walled pseudocyst containing mucoid fluid

Tendovaginitis (inflammation of the tendon sheath)purulent, rheumatoid (serofibrinous), tuberculousTendovaginitis stenosans (deQuervain): stenosis of the tendon sheath by accumulation of fibrocartilaginous tissue – discontinual movement of the affected finger (digitus saltans)

Bursitisbursae around shoulder, elbow and kneeAcute bursitis (mechanical overload): serofibrinous exudateChronic bursitis (repeated traumatisation): fibrous thickening of the wall, hyperplasia of synovial lining and fibrin deposits

Diseases of skeletal muscle

Muscle atrophy

Muscle dystrophy

Myasthenia gravis

Inflammatory disorders (myositis)

Muscle atrophy

Generalized: malnutrition, hypopituitarism, immobilisation

Localized: immobilisation of one limb, denervation (trauma, neuritis, poliomyelitis)

Microscopic features: decrease in size of muscle fibers

Muscle dystrophy

heterogeneous group of genetically determined disorders

spontaneous progressive degeneration of muscle fibers

microscopic features: different size of muscle fibers (combination of atrophy and hypertrophy), degenerative changes (fragmentation of the sarcoplasma, necrosis), signs of regeneration (cells with basophilic cytoplasm and more nuclei), fibrosis, later lipomatosis

Duchenne-type dystrophy:

X-linked recessive disorder – males affected only

lack of dystrophin (immunohistochemistry)

early childhood (5 years), pelvifemoral groups of muscles (frequent falls, gait disturbances, difficulty in rising), progress to other muscle groups (wheelchair bound between the ages of 10 to 12 years), death usually before the age of 20 years (respiratory difficulties, pneumonia)

Becker-type dystrophy:

similar to the Duchenne-type dystrophy, but much milder clinical picture

dystrophin is produced, but is abnormal

Dystrophia myotonica:

autosomal dominant disorder

after the age of 20 years, sometimes congenital

clinical features: myotonia (prolongation of muscle contraction after voluntary effort has ceased), muscle weakness (facial muscles, distal muscle groups)

multisystemic disease: frontal baldness, cataract, cardiomyopathy, dementia, gonadal atrophy)

Myasthenia gravis

acquired autoimmune disorder: autoantibodies against acetylcholine receptors on the motor endplate → defect of neuromuscular transmission

hyperplasia of thymus (60%), thymoma (20%)

Clinical features: abnormal muscle fatiguability, muscle weaknessrespiratory muscles may be severely affected (patients may need mechanical ventilation)

Microscopic features: no light-microscopic abnormalities

Myositis (inflammation of muscles)

bacterial, viral (complication of systemic infections)

autoimmune myositis: dermatomyositis/polymyositis

Trichinosiseating meat containing viable cysts of Trichinella spiralis (improperly cooked pork products)larvae released after ingestion, and penetrate into blood throught duodenal mucosa → dissemination throughout the body (lung, heart, brain, skeletal muscles)larvae enclosed within the membrane (parasitic cysts), calcification of dead cysts

Myositis ossificanstumor-like lesion sometimes preceded by traumamust be distinguished from extraskeletal osteosarcomacentral area of plump, mitotically active fibroblasts surrounded by zones of immature woven bone and mature lamellar bone