Osteomyelitis

By admin On Oct 4, 2023

Ovid: 5-Minute Sports Medicine Consult, The

Osteomyelitis

Alex B. Diamond

Basics

Description

Inflammatory process of bone and its components secondary to infection by pyogenic organism
Categorized as acute, subacute, or chronic
Other classification systems have emerged:
- Waldvogel: Hematogenous, contiguous, or chronic
- Cierny-Mader: Based on dynamic status of disease process
Acute osteomyelitis develops within 2 wks of disease onset:
- Predominantly in children
- Typically the result of hematogenous dissemination
- Metaphysis of long bones the most commonly involved location
Subacute osteomyelitis presents within 1 to several months of disease onset
- Diagnosis difficult, as characteristic signs and symptoms of acute form absent
- Brodie abscess most common type of subacute form:
  - Cavitary lesion in epiphysis or metaphysis characterized by small, localized lucency surrounded by reactive, dense-appearing bone
- Subacute form represents favorable host-pathogen response, as dependent on balanced interplay between infecting bacteria and host immune mechanisms
- Subacute form mimics various other conditions, which results in delayed diagnosis and treatment:
  - Most frequent incorrect diagnosis is that of tumor, either benign or malignant
Chronic osteomyelitis develops after few months of disease onset:
- May be recurrent or intermittent in presentation
- Direct contamination frequent cause of chronic form (open fracture, penetrating wound, surgical manipulation)
- Simultaneous presence of microorganisms and necrotic bone (sequestra) is hallmark

Epidemiology

Overall prevalence in children is 1 per 5,000
Overall incidence higher in developing countries
Most prevalent type is result of injury (associated with open fracture, surgical reconstruction of bone)
Males: Females = 2:1; no association with race
Special populations:
- Annual incidence in sickle cell patients is 0.36%.
- Prevalence after foot puncture in diabetic patients is 30–40%.
Incidence of subacute osteomyelitis has increased since use of antibiotics:
- Most common form in East Africa
Long-term recurrence rate of chronic osteomyelitis is 20–30%.
Secondary hematogenous infections more common in adults:
- Represent reactivation of quiescent focus of primary hematogenous osteomyelitis from childhood
Deep musculoskeletal infection incidence from open fracture as high as 23%
Spine becomes most common site of infection in patients >45 yrs old
Culture more likely positive if history of trauma, shorter duration of symptoms, higher WBC count and erythema, swelling or cellulitis overlying infected bone
Morbidity significant:
- Pain, disability, amputation, extension of infection and sepsis
- 10–15% with vertebral osteomyelitis develop neurologic symptoms or spinal cord compression
- 30% of pediatric cases may develop deep vein thrombosis.
Mortality low unless associated sepsis

Risk Factors

Open or compound fracture
Surgical manipulation (orthopedic, colorectal, genitourinary procedures)
IV drug abuse
Immunosuppression (AIDS, chronic steroid use)
Peripheral vascular disease (diabetes mellitus)
Sickle cell disease
Genitourinary or biliary tract infection
Chronic joint disease
Presence of prosthetic orthopedic device
Low socioeconomic status
Infancy
Elderly
Alcoholism
History of tuberculosis (Pott disease)

General Prevention

Timely diagnosis and treatment of primary infections to avoid seeding of bone
Appropriate wound management and possible use of prophylactic antibiotics with injury or manipulative surgery

Etiology

Normal bone highly resistant to infection unless result of very large inocula, trauma, or presence of foreign bodies
Microorganisms adhere to bone/devices; survive intracellularly in osteoblasts; express resistance to antimicrobial treatment (high failure rate of short courses of therapy); form inflammatory markers (potent osteolytic factors) and phagocytes (generate toxic oxygen radicals and release enzymes that lyse surrounding tissues); pus develops and spreads into vascular channels increasing intraosseous pressure and impairing blood flow; ischemic necrosis of bone
Infectious agents include bacteria, mycobacteria, and fungi.
Routes of infection include hematogenous, contiguous focus, and direct inoculation.
Primary hematogenous osteomyelitis occurs mainly in infants and children:
- Sluggish circulation at highly vascular metaphyseal-physeal barrier predisposes vessels to thrombosis and bone to localized necrosis and bacterial seeding.
- Metaphyseal arteries lack phagocytic lining cells and sinusoidal veins (in growth plate) contain functionally inactive phagocytic cells.
- Usually monomicrobial
Manifestations more localized, but can involve multiple organisms when result of contiguous or direct inoculation
Subacute osteomyelitis occurs in much wider variety of bones:
- Femur > tibia > remaining lower limb > upper limb
- Metaphyseal-equivalent locations (pelvis, vertebrae, calcaneus, clavicle, talus)
Chronic osteomyelitis characterized by sequestrum of necrotic bone harboring bacteria
Capability to persist or recur, regardless of initial cause/mechanism and despite aggressive intervention
Pathogen isolated in 35–40% of cases
Fungal agent usually result of catheter-related complication, use of illicit drugs, or prolonged neutropenia

P.429

Bacterial agents:
- Most common include Staphylococcus aureus, coag-negative staph and aerobic gram-negative bacilli; others include strep, enterococci, and anaerobes
- Increasing MRSA
- Age of patient and inoculation method important factor in species prevalence:
  - Hematogenous: Children and adolescents: S. aureus (80%), group A streptococcus species, H. influenzae. Adults: Staph, occasional Enterobacter or strep species
  - Direct or contiguous: Generally staph (75% of cultures), Enterobacter, pseudomonas
- Puncture wound through sneaker typically staph, pseudomonas
- Chronic osteomyelitis most likely S. epidermidis or S. aureus, pseudomonas, serratia, E. coli
- Consider anaerobes if “fight bite” injury
- Staph and salmonella predominate sickle cell disease

Diagnosis

History

Children with acute hematogenous osteomyelitis may present with abrupt-onset high fever, chills, fatigue, irritability, lethargy, restricted motion and local pain, edema, erythema, and tenderness.
In a young child, inability to get to seated position, limp, and refusal to walk may be observed if the spine, pelvis, or lower extremity is involved; pseudoparalysis if upper extremity
50% of children and most adults present with vague complaints, nonspecific pain of involved limb, and minimal if any temperature elevation or constitutional symptoms.
Limitation of joint motion usually present if primary lesions particularly close to joint spaces leading to sympathetic effusions
Osteomyelitis due to contiguous focus often presents with painful or unstable joint, little or no fever
Subacute osteomyelitis presents with mild pain, minimal fever, and few constitutional symptoms.
In chronic osteomyelitis, there is local bone loss, persistent drainage through fistulas or sinus tracts, nonhealing ulcers, recurrent pain, possibly low-grade fever, and mild systemic symptoms (ie, chronic fatigue).
An insidious onset with history of acute bacteremic episode, local tenderness, erythema, and edema is common in vertebral osteomyelitis.

Physical Exam

Fever (temperature >100.4°F), but not always present
Tenderness to palpation, swelling, erythema, warmth over involved area
Fluctuance
Decreased use of extremity, refusal to bear weight
Limited movement of adjacent joint
Other possible foci of infection
Sinus tract drainage
Passive range of motion tolerated, unlike septic arthritis

Diagnostic Tests & Interpretation

Lab

CBC may reveal elevated WBC or left shift, but frequently normal
C-reactive protein (CRP) and erythrocyte sedimentation rate almost always elevated, but nonspecific tests:
- Changes in CRP detected sooner
Blood culture positive 50% of cases
Aspiration from affected site normal 25% of the time
Bone biopsy can be achieved by percutaneous needle, radiographic guided instruments, or open surgical procedure:
- Send for Gram stain and culture (aerobic, anaerobic, mycobacterial, and fungal)
- Obtain 2nd specimen for histopathology

Imaging

In early disease, x-rays may be normal or show only soft tissue swelling.
Osseous changes usually appear 7–14 days after symptom onset; 90% with changes on x-ray by 28 days:
- Include periosteal elevation and/or destruction of bone with radiolucency, fading cortical margins, and no surrounding reactive bone. Periosteal elevation followed by cortical or medullary lucencies.
In acute osteomyelitis in children, classic findings include deep, circumferential soft tissue swelling with obliteration of muscular planes.
In adults, plain radiographs are of less value because ∼50% of the bone matrix must be destroyed before lytic changes are visible.
Radioisotope bone scan (triple phase with technetium 99m) is highly sensitive and initial test of choice for early diagnosis of osteomyelitis, especially if x-ray studies are ambiguous (Termaat MF, et al. JBJS Am, 2005. LOE = III).
MRI effective in early detection and localization. Reported 90–100% sensitivity.
Consider MRI if bone scan is negative or when very minor destructive changes present. Spatial resolution of MRI makes it useful in differentiating between bone and soft tissue infection. Good for diagnosis and assessment of extension. IV contrast useful in differentiating vascularized and inflamed tissue from abscess.
CT scanning may play role in diagnosis and assisting the surgeon in operative planning. Most useful in evaluation of spinal vertebral lesions or other areas with complex anatomy (pelvis, sternum, calcaneous). May reveal small areas of osteolysis, gas, or foreign bodies.
US may show periosteal thickening and elevation, soft tissue abscess, or fluid collection. Provides direction for aspiration. May demonstrate changes earlier, but can't evaluate bone cortex.

Diagnostic Procedures/Surgery

Histopathologic and microbiologic exam of bone is gold standard:

Requires 2 of 4:
- Purulent material on aspiration of affected bone
- Positive findings of bone tissue or blood culture
- Localized classic physical findings of bony tenderness, overlying soft tissue erythema, or edema
- Positive radiological imaging study

Pathological Findings

Principal histiologic findings in acute osteomyelitis include microorganisms, infiltrations of neutrophils, and congested or thrombosed blood vessels
Distinguishing feature of chronic osteomyelitis is necrotic bone

Differential Diagnosis

Acute leukemia
Acute rheumatic fever
Rheumatoid arthritis (adult or juvenile)
Acute gout, pseudogout
Cellulitis
Malignant bone tumors (Ewing sarcoma, osteosarcoma)
Septic arthritis
Multiple myeloma (elderly)
Sepsis
Deep vein thrombosis, thrombophlebitis
Intervertebral disc disorders
Fracture
Aseptic bone infarction
Neuropathic joint disease
Transient synovitis

P.430

Treatment

Immobilization of the affected part, hydration, fever control, and IV antibiotics directed by culture and sensitivity results (when available)
Involvement of specialists (orthopedic surgeon, infectious disease specialist)
Empiric treatment is guided by the age of the patient, severity of disease, and suspected organisms:
- Use broad-spectrum antibiotics until lab results, then tailor to culture and sensitivities
- Stengel D et al. Lancet Infect Dis, 2001. (LOE = II-III)
For children >4 yrs, nafcillin or oxacillin is recommended. If allergic to penicillin, use vancomycin or clindamycin. If community-acquired MRSA is suspected, use vancomycin or clindamycin as 1st choice. Add a 3rd-generation cephalosporin for gram-negative bacteria coverage if needed.
In adults >21 yrs, recommended antibiotics include nafcillin, oxacillin, or cefazolin. If allergic to penicillin, use vancomycin or clindamycin. Add a 3rd-generation cephalosporin or ciprofloxacin plus rifampin for gram-negative bacilli coverage.
For suspected Pseudomonas aeruginosa, administer ceftazidime or cefepime; alternatively, use ciprofloxacin, except in children.
Duration of treatment is usually 4–6 wks IV, but may be longer, depending on the clinical response and laboratory values
For sickle cell patients, use fluoroquinolone except in pediatric population. Alternative is 3rd-generation cephalosporin (ceftriaxone).
Possibility for children with Albright hereditary osteodystrophy to receive 2 wks IV therapy followed by 4 wks of PO antibiotics if responding well
Recommend treatment with IV antibiotics 6 wks from last debridement
Failure of symptoms to resolve after an up-to-6-wk course of antibiotics or worsening of the condition during treatment should lead to reevaluation and a definite tissue diagnosis, followed by surgical treatment and appropriate antibiotics.
Other indications for surgery are impending sinus formation, drainage into a synovial joint, and signs of subperiosteal pus or synovitis, which indicate that the subacute infection has transformed into an acute component.
Surgical drainage and debridement is needed for tissue culture identification of the offending organism, evacuation of abscesses, and removal of necrotic bone and nidus of infection.
Surgical decompression may release intramedullary and subperiosteal pus.
Chronic osteomyelitis requires primarily surgical treatment, as complete debridement of all devitalized bone and soft tissue is essential for cure (Simpson AH et al. JBJS Br, 2001. LOE = II).
Reconstruction of large bony defects may be required, and success entails both filling the space created by the loss of tissue due to debridement and revascularization of poorly perfused regions.
Grafting wounds (bone, soft tissue) and revascularization procedures are the best means of fighting recurrent infection.
Remove infected prosthetic devices and hardware.
Hyperbaric oxygen therapy has shown some promising results in treating chronic or refractory osteomyelitis, but no convincing evidence, especially in diabetic patients with vascular insufficiency (Goldman RJ. PMR, 2009. LOE = Moderate – High via GRADE criteria).
Provides oxygen to promote collagen production, angiogenesis, and ultimately wound healing
With skeletal tuberculosis, any bone can be involved.
Usually involves the metaphysis of long bones in children and adolescents
In adults, the axial skeleton most often is involved, followed by the proximal femur, knee, and small bones of the hands and feet.
Tissue for histologic examination is almost always required for diagnosis.
With fungal osteomyelitis, bone infections may be caused by coccidioidomycoses, blastomycosis, cryptococcosis, candidiasis, or sporotrichosis.
Most common presentation is a cold abscess overlying an osteolytic lesion.
Treatment involves surgical debridement and antifungal chemotherapy.
Vertebral osteomyelitis primarily in adults, rare disease overall
Involves 2 adjacent vertebrae and disc spaces between them
Focal neck or back pain, fever
Blood culture often negative; needle biopsy with multiple specimens is diagnostic procedure of choice
Biopsy and debridement cultures dictate choice of antibiotic(s).
Surgical intervention reserved for management of complications or for medical therapy failure.
Percutaneous transpedicular debridement and discectomy by removing infected necrotic bone accelerates healing and prevents progression of bone destruction and deformity in the early stages of vertebral osteomyelitis and spondylodiscitis.

P.431

Ongoing Care

Protection of the joint with traction or splinting and starting protected motion early is a consideration.
Limitation of weight-bearing until x-ray evidence of defect's partial healing due to risk of collapse
Follow-up based on response to therapy and overall health of patient after completion of treatment regimen.
Should continue for at least 2 yrs in subacute cases:
- Closely monitor at 1st for signs of response to treatment (clinical and laboratory).
- Then ensure compliance with antibiotic therapy for 6 wks. Clinical response is usually within a few days of initiation of treatment.
- For next 6 mos, monitor for signs of recurrence. Most recurrences occur within this time, but recurrence after up to 18 mos has been reported.
Radiologic healing is slower than clinical healing and usually occurs within 3–12 mos. Metaphyseal and epiphyseal cavities usually heal, leaving either a small area of sclerosis or a small, indistinct lucency in the cortex.
The purpose of follow-up after a year is for assessment of bone growth and alignment.

Prognosis

Variable, but markedly improved with timely diagnosis and aggressive treatment

Complications

Include bone abscess, bacteremia, fracture, loosening of hardware, overlying cellulitis, and draining soft tissue tracts
Sinus tract formation may be associated with neoplasms, especially with long-standing infection:
- Squamous cell carcinoma most common tumor associated with chronic osteomyelitis. Other tumors reported.
- Recalcitrant infection that does not respond should prompt biopsy evaluation for malignancy from multiple sites.
Despite localized transgression of the epiphyseal plate by subacute osteomyelitis, growth disturbances are exceedingly rare.
Most common complication is recurrence.

Additional Reading

Carek PJ, Dickerson LM, Sack JL. Diagnosis and management of osteomyelitis. Am Fam Physician. 2001;63:2413–2420.

Conterno LO, da Silva Filho CR. Antibiotics for treating chronic osteomyelitis in adults. Cochrane Database Syst Rev. 2009;CD004439.

Goldman RJ. Hyperbaric oxygen therapy for wound healing and limb salvage: a systematic review. PM R. 2009;1:471–489.

Lew DP, Waldvogel FA. Osteomyelitis. Lancet. 2004 Jul 24–30;364:369–379.

Lew DP, Waldvogel FA. Osteomyelitis. N Engl J Med. 1997;336:999–1007.

Pineda C, Vargas A, Rodríguez AV. Imaging of osteomyelitis: current concepts. Infect Dis Clin North Am. 2006;20:789–825.

Sharif I, Adam H. Current Treatment of Osteomyelitis. Pediatrics in Review. 2005;26:38–39.

Stengel D, Bauwens K, Sehouli J, et al. Systematic review and meta-analysis of antibiotic therapy for bone and joint infections. Lancet Infect Dis. 2001;1:175–188.

Codes

ICD9

730.00 Acute osteomyelitis, site unspecified
730.01 Acute osteomyelitis involving shoulder region
730.02 Acute osteomyelitis involving upper arm

Clinical Pearls

The most common pathogens implicated in development of osteomyelitis are MRSA, coagulase-negative staph, aerobic gram-negative bacilli
Often, abrupt high fever presents with acute hematogenous osteomyelitis. It is not uncommon to have no fever or a low-grade fever with the other forms of the disease.
The test of choice and gold standard for diagnosis of osteomyelitis are bone biopsy and histopathologic and microscopic examination.
Chronic osteomyelitis primarily requires surgical treatment for cure.
Recalcitrant infection that does not respond to treatment should spur biopsy evaluation from multiple sites for concern of malignancy development following long-standing infection.