Bone Infection – Osteomyelitis

Osteomyelitis is the medical term for a bone infection. From the greek words osteon (bone), myelo (marrow), -itis (inflammation).

Osteomyelitis

Osteomyelitis

Bone infections can start either through 1) the spreading of an infection elsewhere, like a bacterial pneumonia, or 2) spreading from the surrounding tissues to the bone. The most common route in the lower extremity is from the latter, usually an open wound/ulcer, a deep cut, a puncture wound, or after a foot/ankle surgery.

How bone infections grow?
Initially, the bacteria adhere to the bone and holds on tight by producing a polysaccharide or carbohydrate capsule. The carbohydrate acts as a “biofilm” protection for the bacteria from the body’s defenses and from antibiotics. Once well adhered to the bone, the bacteria produce proteins that will break down the bone. If there is hardware (screws and plates) in this weakened bone, it will not hold as firmly and may need to be removed.

Diagnosing bone infection
Pain, redness, and swelling in the involved area, or with a wound of some sort all raise the suspicion for a bone infection. Biopsy of the bone is the current gold standard for diagnosing bone infection, but the use of x-ray, bone scan, and MRI may also be effective methods used before the invasive removal of a piece of bone for the microbiology lab to analyze. X-ray findings may take 10-20 days to appear because the bacteria have to destroy bone enough for a change to be visible (usually 30-50%), which takes time. X-rays should always be taken as they will help as a baseline to monitor progression or regression of the infection. Bone scans look to see if an area is “hot” and shows where there is activity in the bone. It is not very specific because other reasons, like surgery or trauma may create a positive bone scan result as well. Yet, a bone scan, if negative, means that there is no infection in the bone. Other than bone biopsy, an MRI is most effective in diagnosing a suspected bone infection.

Close-up of Osteomyelitis

Close-up of Osteomyelitis

Treatment
In general, if the bone infection is caught in the acute or early chronic stages, there will be a better treatment outcome. A good blood supply to the bone will lead to a better result than if the bone is necrotic (dead). The bacterial survive much better with a food source like dead bone and spreads fasters in these situations. Each patient is different and many factors need to be taken into consideration. Many bone infections can be treated with a course of antibiotics. This can be very effective, yet it may require 6-12 weeks of antibiotics to be effective.

Do I need surgery to remove the bone infection?
If the patient is too sick for surgery or doesn’t desire an amputation, nonsurgical therapy may be the only option. One study showed that 81% of patients that had a bone biopsy to identify the bacteria healed with antibiotics alone versus 50% of patients who didn’t have a bone biopsy.1 This shows that surgery isn’t always necessary if you can get a bone biopsy, but surgery may be necessary for other reasons. Surgery may be more definitive and a quicker cure, and results in a shorter course of antibiotics. In the end, the decision is the patients, but the surgeon takes into account the location of the infection, how much bone is infected, which bacteria is causing the infection, how good of blood flow to the bone, and how long the infection has been present before treatment.

References:
1. Senneville E, Lombart A, Beltrand E, et al. Outcome of diabetic foot osteomyelitis treated non-surgically, a retrospective cohort study. Diabetes Care 2008;31:637-642
2. McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery, 4th ed. 2013.

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