Diseases of musculoskeletal system

2. Infectious diseases of bone and joints

1. Osteomyelitis. 2. Septic arthritis.

ILOs Understanding definition, etiology, pathophysiology, laboratory findings, and complications of osteomyelitis. Identifying epidemiology, general and local risk factors, different types of bacteria, symptoms, treatment and prognosis of septic arthritis.

1. OSTEOMYELITIS *Def: inflammation of bone and bone marrow. *Classification: I. Acute osteomyelitis: Acute hematogenous osteomyelitis Acute non-hematogenous osteomyelitis. II. Chronic osteomyelitis: Chronic suppurative osteomyelitis Tuberclous osteomyelitis. Syphilitic osteomyelitis.

ACUTE HEMATOGENOUS OSTEOMYELITIS * Def: a blood borne infection of the metaphysis of the long bones in children and young adults. * Causative organism: staphylococcus aureus (in 90%). * Pathogenesis The 1ry source of infection is an abscess in upper respiratory tract or urinary tract. Bacteremia. The organism is localized in the metaphysis of long bones due to: frequent hematoma & slow blood stream.

The bone is inflamed and undergoes necrosis (due to bacterial toxins and ischemia) followed by suppuration. Pieces of the necrotic bone are separated (by osteoclasts) and form sequestrum. The pus spreads towards the cortex and periosteum. New Periosteal bone formation around the necrotic bone form involucrum, which shows holes to drain the underlying pus, called cloacae. Subperiosteal abscess is formed and spread to the skin and open by a sinus discharging pus.

* Complications: I. Spread of infection: A. Direct spread: Direct spread to muscles, tendons and nerves. Direct spread to joint cavity to produce sympathetic effusion. B. Blood spread: Toxemia, pyaemia and septicemia. II. Pathological fracture. III. Chronic suppurative osteomyelitis. Alteration of bone growth. 2ry Amyloidosis. IV. Malignancy on top of squamous metaplasia of the sinus tracts.

ACUTE NON-HEMATOGENOUS OSTEOMYELITIS * Def: acute suppurative inflammation of bones, commonly in adults. * Sites: Skull and long bones are common * Etiology: Direct spread from an adjacent septic focus; sinusitis, otitis media, mastoiditis. Compound fracture of bone. * Pathology: Similar to acute hematogenous osteomyelitis but; Affect diaphysis of long bones. No Subperiosteal abscess formation.

CHRONIC SUPPURATIVE OSTEOMYELITIS * Etiology: * Causative organism: Staph. aureus. Follow acute suppurative osteomyelitis. Starts as a chronic suppurative inflammation to form “Brodie’s abscess”. * Pathology: Affects metaphysis of long bones in children and young adults. The lesion consists of a circumscribed area of suppurative inflammation, which forms a cavity filled with pus and surrounded by a sclerotic bone.

* Complications: Pathological fracture. Effusion in a nearby joint. 2ry Amyloidosis.

2. Septic arthritis

Septic arthritis is an acute inflammation of one or more joints caused by pyogenic organisms e.g. Streptococcus, Staphylococcus, Pneumococcus, Gonococcus, or Meningococcus. * Predisposing factors: – Associates prosthetic joints. – Immunosuppression. – Follow fracture joints. – Complicates rheumatoid arthritis and SLE arthritis. – D.M.

* Symptoms: * Symptoms: include: chills fatigue and generalized weakness fever inability to move the limb with the infected joint severe pain in the affected joint, especially with movement swelling (increased fluid within the joint) hotness (the joint is red and warm to touch because of increased blood flow)

* Morphologically: * Morphologically: the joints are swollen, hot,, and pus-filled. * Treatment: * Treatment: includes antimicrobial drug therapy and drainage and rest of the joint.

At the slightest suspicion of septic arthritis, joint aspiration should be performed to evaluate the affected joint. If infected fibrinous deposits (cloudy aspirate) are present, arthroscopic irrigation should be performed repeatedly, every 2-3 days, until the infection resolves. If arthroscopic clearance is unsuccessful, consider open synovectomy.