Introduction to Osteomyelitis

Introduction

A pyogenic bone infection, osteomyelitis may be chronic or acute. It commonly results from a combination of local trauma—usually quite trivial but resulting in hematoma formation—and an acute infection originating elsewhere in the body. Although osteomyelitis may remain localized, it can spread through the bone to the marrow, cortex, and periosteum.

Acute osteomyelitis is typically a blood-borne disease that usually affects rapidly growing children. Chronic osteomyelitis, although rare, is characterized by multiple draining sinus tracts and metastatic lesions.

Incidence

The incidence of both chronic and acute osteomyelitis is declining, except in drug abusers. With prompt treatment, the prognosis for acute osteomyelitis is good; for chronic osteomyelitis, which is more prevalent in adults, the prognosis is still poor.

Causes
The most common pyogenic organism in osteomyelitis is Staphylococcus aureus; others include Streptococcus pyogenes, Pneumococcus, Pseudomonas aeruginosa, Escherichia coli, and Proteus vulgaris. Typically, these organisms find a culture site in a hematoma from recent trauma or in a weakened area, such as the site of local infection (for example, furunculosis), and spread directly to bone.
As the organisms grow and form pus within the bone, tension builds within the rigid medullary cavity, forcing pus through the haversian canals. This forms a subperiosteal abscess that deprives the bone of its blood supply and eventually may cause necrosis. In turn, necrosis stimulates the periosteum to create new bone (involucrum); the old bone (sequestrum) detaches and works its way out through an abscess or the sinuses. By the time sequestrum forms, osteomyelitis is chronic.

Signs and symptoms
Onset of acute osteomyelitis is usually rapid, with sudden pain in the affected bone, and tenderness, heat, swelling, and restricted movement over it. Associated systemic signs and symptoms include tachycardia, sudden fever, nausea, and malaise.
Generally, the signs and symptoms of both chronic and acute osteomyelitis are the same, except that chronic infection can persist intermittently for years, flaring up spontaneously after minor trauma. Sometimes, however, the only symptom of chronic infection is the persistent drainage of pus from an old pocket in a sinus tract.

Diagnosis
Patient history and physical examination reveal bone tenderness, swelling, and redness. The following laboratory tests help to confirm osteomyelitis:

• bone scan (indicates infected bone)
• bone lesion biopsy or culture (may reveal the causative organism)
• white blood cell count (shows leukocytosis
• erythrocyte sedimentation rate and C-reactive protein (CRP) (elevated; however, CRP appears to be a better diagnostic tool)
• blood cultures (identify the causative organism).
• X-rays don’t show bone involvement and alterations.

 Diagnosis must rule out poliomyelitis, rheumatic fever, myositis, and bone fractures.

Treatment
Treatment varies for acute and chronic osteomyelitis.
Acute osteomyelitis
Acute osteomyelitis should be treated before a definitive diagnosis. Treatment includes:

• administration of large doses of I.V. antibiotics after blood cultures are obtained
• early surgical drainage to relieve pressure buildup and sequestrum formation
• immobilization of the affected bone by plaster cast, traction, or bed rest
• supportive measures, such as administration of an analgesic and I.V. fluids.
• If an abscess forms, treatment includes incision and drainage, followed by a culture of the drainage. 
• Antibiotic therapy to control infection may include administration of a systemic antibiotic; intracavitary instillation of an antibiotic through closed-system continuous irrigation with low intermittent suction; limited irrigation with a closed drainage system with suction; or local application of packed, wet, antibiotic-soaked dressings.

Chronic osteomyelitis
With chronic osteomyelitis, surgery is usually required to remove dead bone (sequestrectomy) and to promote drainage (saucerization). The prognosis is poor even after surgery. Patients are usually in great pain and require prolonged hospitalization. Resistant chronic osteomyelitis in an arm or leg may necessitate amputation.
Some facilities also use hyperbaric oxygen to increase the activity of naturally occurring leukocytes.
Free tissue transfers and local muscle flaps are also used to fill in dead space and increase blood supply