Definition
A.Represents a wide spectrum of inflammatory bone disorders due to bacteria, mycobacteria, or fungi.
B.Multifaceted presentations of bone infection; no universally accepted system of classification.
C.Classification is most commonly based on the pathogenesis, chronicity, or location.
D.Known as a disease of the very young and the very old.
Incidence
A.The incidence of osteomyelitis in the United States is largely unknown. It may be as high as 16% after foot puncture (30%–40% in patients with diabetes). The rate of occurrence of vertebral osteomyelitis is estimated at 2.4 cases per 100,000. The prevalence of osteomyelitis is estimated as 1 case per 5,000 in children.
B.The prevalence of bone and joint infections in adults is increasing because of (1) longer life expectancy, (2) increasing use of bone fixation and prosthetic implants, and (3) higher rate of diabetes.
Pathogenesis
A.Hematogenous source: Spread by seeding from bacteria in blood.
1.Primary sources of initial infection: Urinary tract, skin and soft tissue, and intravascular catheters, as well as endocarditis.
2.Usually monomicrobial.
3.Most common in children due to seeding in the metaphysis of long bones, particularly the femur and tibia. Such osteomyelitis is rare in adults, but when it does occur it is most frequent in the vertebrae of the spine.
B.Contiguous source: Spread from adjacent soft tissues and joints.
1.Exogenous: Often spread following surgery or trauma with direct inoculation.
2.Generally polymicrobial, but can be monomicrobial.
3.Accounts for 80% of chronic osteomyelitis infection.
4.Bimodal age distribution with differing sources.
a.Older individuals: Decubitus ulcers, chronic soft tissue injuries, dental infections, and joint arthroplasties.
b.Younger individuals: Open fracture or bone surgery.
C.Secondary disease: From vascular insufficiency or peripheral neuropathy.
1.Most often related to diabetes.
2.Results from chronic, progressive deep skin/soft tissue infection, generally in the foot from diabetic foot syndrome.
D.Infectious causes: Multifactorial mechanisms in hosts at high risk.
1.Most commonly due to hematogenous seeding.
2.Intravenous drug abuse.
3.HIV infection.
4.Sickle cell disease: Accounts for about one third of cases.
E.Histological changes.
1.Infection: Results in bone edema and vascular congestion, leading to small vessel thrombosis.
2.Medullary and periosteal blood supplies: Compromised; bone becomes necrotic.
3.Sequestra: Fragments of dead bone that detach from living bone.
4.Dead bone: Becomes colonized by a biofilm of bacteria that is often resistant to antibiotics, so debridement in addition to antibiotics is necessary for chronic, well-established osteomyelitis.
F.Microorganisms: Often a function of the location of the osteomyelitis infection.
1.Staphylococcus aureus: Most frequent cause of all types of osteomyelitis.
2.Coagulase-negative staphylococci: Most common cause of prosthetic-associated infection.
3.Streptococci and other anaerobic bacteria: Associated with diabetic foot lesions and decubitus ulcers.
4.Aspergillus spp., Candida albicans, and Mycobacteria spp. most common in immunocompromised hosts.
Predisposing Factors
A.Compromised host.
B.Immunocompromise (HIV: High correlation secondary to unsterilized needles. The very young experience mostly in the long bones while the very old have more occurrences in the vertebrae).
C.Intravenous drug abuse or alcohol abuse.
D.Diabetes.
E.Malignancies.
F.Impaired circulation.
G.Liver cirrhosis.
H.Sickle cell disease.
I.Chronic steroid use.
J.Bone or joint surgery.
K.Traumatic injury involving the bone.
Subjective Data
A.Common complaints/symptoms.
1.Gradual onset of symptoms over several days.
2.Spinal osteomyelitis.
a.Pain: Determined by the location of the infection in the spine; generally dull pain with and without movement.
b.Fever (only in 64% of cases, due to degree of immunocompromise and age).
c.Local tenderness, warmth, erythema, and swelling.
d.Motor weakness or radicular pain.
e.Spinal deformity in patients with prolonged course of treatment.
3.Long bone and pelvis.
a.Acute osteomyelitis: Can present as septic arthritis because it affects the metaphysis to the joint.
b.Tenderness, warmth, erythema, and swelling.
4.Chronic osteomyelitis.
a.Pain, erythema, and swelling.
b.Occasional draining sinus tract.
c.More likely with presence of prosthetic material, extensive tissue ulceration, or vascular insufficiency.
B.Common/typical scenario.
1.Complaints of pain, swelling, and possibly low-grade fever.
2.Symptoms develop over days to weeks.
C.Family and social history.
1.Past medical history: Comorbidities leading to increased risk.
2.Recent surgeries, implants, and so on.
3.History of diabetes with ulcers.
4.Decubitus ulcers.
5.Peripheral vascular disease.
6.Intravenous (IV) drug abuse.
7.Sickle cell disease.
8.Recent trauma.
9.Urinary tract infection (UTI) or pyelonephritis.
D.Review of systems.
1.Constitutional: Possible night sweats, fatigue, malaise, or lethargy.
2.Genitourinary: Signs and symptoms of UTI; loss of bowel or bladder control.
3.Musculoskeletal: Pain, swelling, or redness at site.
4.Skin: Purulent drainage from open wound.
5.Musculoskeletal: Weakness in lower extremities.
Physical Examination
A.Location of any skin lesions (in case of diabetic foot ulcers [> 2 × 2 cm] or exposed bone, osteomyelitis is likely).
B.Positive neurological examination with areas of weakness or sensory loss (particularly in suspected spinal osteomyelitis).
C.Presence of vascular and arterial insufficiency.
D.Probe to the bone in pedal ulcers using sterile, blunt metal tool.
1.Positive result: Hard, gritty surface of bone.
Diagnostic Tests
A.Laboratory studies: Generally nonspecific initially.
1.CBC.
a.Leukocytosis: Common in acute osteomyelitis but less common in chronic cases.
2.ESR greater than 70 mm/h: Indicative of osteomyelitis.
3.CRP elevated.
4.Blood cultures: Most useful when patient is febrile.
B.Imaging studies.
1.Accuracy dependent on intensity of the inflammation, chronicity of the infection, site, vascularity, and associated pathology.
2.Simply support or refute clinical suspicion.
3.Plain films generally used for the initial study.
a.Most sensitive but least specific of all the diagnostic modalities.
b.Cortical abnormality with periosteal new bone formation: Suggestive of osteomyelitis.
c.Most useful when symptoms have persisted for more than 2 weeks.
4.MRI: High negative predictive value and highly sensitive.
a.First choice for suspected spinal osteomyelitis.
5.Radionuclide bone skeletal scintigraphy (i.e., three-phase bone scan) combined with CT: May be used if MRI is not possible due to indwelling hardware.
C.Bone biopsy: Combined with histologic findings of inflammation and bone necrosis.
1.May be done using open or percutaneous approach, with open being preferable because the sensitivity of percutaneous biopsy is poor.
Differential Diagnosis
A.Spinal osteomyelitis with symptoms of backache.
1.Influenza, or virus with flu-like symptoms.
2.Pyelonephritis.
3.Pancreatitis.
4.Osteoporotic fracture.
5.Disc herniation.
B.Long bone osteomyelitis.
1.Septic arthritis.
2.Bone tumor.
3.Occult or pathological fracture.
4.Soft tissue infection.
5.Charcot arthropathy.
6.Bursitis.
7.SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, and osteitis).
8.Gout.
Evaluation and Management Plan
A.General plan.
1.Bone probing for foot ulcerations suspected of being osteomyelitis.
2.Prolonged duration of antibiotic treatment is necessary.
3.Bone biopsy: Open approach preferable to needle biopsy.
a.Identification of causative organism with gram stain and culture, including aerobic, mycobacterial, and fungal culture.
4.Surgical debridement: May be required for chronic osteomyelitis.
5.Removal of hardware: May be required.
6.Adjunctive therapies: Hyperbaric oxygen therapy.
B.Patient/family teaching points.
1.Prolonged duration of antibiotic treatment is necessary.
2.Recurrence is common.
C.Pharmacotherapy.
1.Antibiotic selection based on cultures identifying causative agent and susceptibilities. Empiric treatment against methicillin-resistant Staphylococcus aureus (MRSA) should be completed when culture data are available (piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate; penicillin allergic: clindamycin, metronidazole, ciprofloxacin, levofloxacin; if MRSA is suspected, vancomycin).