Bone and Joint Infections

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

• Usually bacteria causes infection in the bone. Staph aureus is the most common organism in adults.
• Leukocytes are attracted to the area and secrete enzymes in an attempt to kill the bacteria.
• Blood flow to the area is decreased and a devitalized necrotic bone is formed called a sequestrum.
• Sequestrum is a infected dead bone resulting from osteomyelitis.
• Haversian canals surround blood vessels and nerve cells throughout the bone.
• The sequestrum has no connection to the normal bone through haversian system.
• Because of the fact that the sequestrum is avascular (dead piece of bone) antibiotics cannot reach sequestrum or the bacteria.
• In fact the bacteria enters bone cells and hides there.
• Antibiotics alone may not help due to difficulty in penetrating the necrotic area.
• The involcrum is new bone formation around the sequestrum.
• The body tries to seal of the infection by forming new bone.
• The sequestrum drains through the sinus.
• Biopsy of sinus is not representative of the infection. Multiple deep samples preferably bone biopsy and cultures are needed.
• Biopsy of the sinus is important in longstanding cases of osteomyelitis to rule out the formation of squamous cell carcinoma.

• Patients with sickle cell anaemia may have osteomyelitis caused by salmonella, however staph aureus is the most common cause.
• Patients with  a history of iv drug abuse can have acromioclavicular or sternoclavicular joint infection due to Pseudomonas.
• Patients may also get Pseudomonas from puncture wounds through shoes.
• Immunosuppressed patients and patients on parental nutrition may get fungal osteomyelitis.

• In children, Eosiniphilic Granuloma, Ewing’s Sarcoma, and Acute Osteomyelitis may resemble each other.
• The patient may have pain, fever, tenderness of the area, and the patient may also have an increased sedimentation rate and leukocytosis.
• Osteomyelitis can also be confused with a benign or malignant tumor.
• Sometimes a biopsy is necessary for the diagnosis.
• Only 50% of chronic musculoskeletal infection will have elevated inflammatory markers.

• Treatment of osteomyelitis is usually a combination of surgical debridement of the necrotic, nonviable tissue plus administration of culture specific antibiotics.

• Body temperature more than 38 C
• WBC count more than 12,000
• Hematocrit less than 34%
• C-reactive protein more than 13.

• If  MRSA is identified, administer vancomycin or clindamycin
• In MRSA, you will have a  higher incidence of DVT than other causes of osteomyelitis.
• Older children, 8 years old or more, with MRSA osteomyelitis and CRP more than 6 has a 40% incidence of DVT on presentation.
• The presence of panton – valentine leukocidin(PVL) gene encoded in strains of MRSA bacteria may explain deep venous thrombosis(DVT)

• Do debridement first.
• Do dead space management (usually by putting cement spacer with antibiotics).
• Do soft tissue coverage.
• Later on, remove the cement spacer and deal with the bone defect, usually by adding bone graft.
• During this treatment, you can figure out the stability of the bone and add external fixator if needed.

• Antibiotic cement spacer followed by the soft tissue coverage, and then do staged bone graft at 6-8 weeks later (induced membrane then later do staged bone graft).
• The membrane secrets Bone Morphogenic Protein 2 (BMP-2) and Vascular endothelial growth factor (VEGF) as well as other growth factors, which peak around 4 weeks after membrane induction.