Osteomyelitis of the foot: diagnosing and treating bone infection

How a foot wound reaches the bone

Most diabetic foot infections begin at a break in the skin, usually an ulcer, and germs can spread deeper into tendons, joints and finally bone.⁠^[1] Nerve damage and poor circulation can mute the usual warning signs of redness, warmth and pain, and bone infection can be present even when a wound doesn’t look inflamed.⁠^[1]

Bone infection is more likely when a wound has been open for many weeks, is wide or deep, sits over a bony bump, shows bone at its base, or comes with a red, swollen “sausage” toe.⁠^[1] A red, swollen foot has other possible causes too; see a red, hot, swollen foot.

See also diabetic foot ulcers, heel ulcers and puncture wounds of the foot.

How bone infection is diagnosed

No single test is decisive, so guidelines suggest combining several.⁠^[1]

• Probe-to-bone test. A sterile, blunt metal probe is gently placed into the wound; feeling hard, gritty bone is a positive test. In a systematic review, it picked up about 87% of bone infections and correctly cleared about 83% of wounds without one.⁠^[1,4]
• X-rays. We take X-rays at the practice. Because bone changes can lag, a normal X-ray may be repeated in 2 to 3 weeks when suspicion stays high.⁠^[1]
• Blood tests. Inflammation markers (ESR, CRP or procalcitonin) help alongside the exam and X-rays, but none is reliable alone.⁠^[1]
• MRI. MRI is recommended when doubt remains. It maps how far infection reaches, which helps plan surgery, though bone swelling from injury, earlier surgery or Charcot foot can look alike.⁠^[1] We arrange MRI at an outside imaging center.
• A bone sample. Culturing bone is the most accurate way to confirm infection and identify the germ; in most studies, wound cultures match bone cultures less than half the time. Bone can be sampled safely with a needle or during surgery.⁠^[1] Dr. Ozturk performs bone biopsies when the result will guide treatment.

Swipe sideways to see the whole drawing.

See how a foot wound is evaluated and the Center for Lower Extremity Surgery’s guide to foot and ankle imaging (external site).

The foundation: antibiotics, wound care and blood flow

We choose antibiotics based on culture results. Many people take them by mouth at home; some start through a vein or need a hospital stay.⁠^[1] Without bone removal, guidelines suggest about 6 weeks of treatment.⁠^[1] In a randomized trial of 40 people treated without surgery, remission rates after 6 or 12 weeks of antibiotics did not differ significantly (60% and 70%), and fewer people on the shorter course had stomach and bowel side effects (15% vs 45%).⁠^[5]

Antibiotics need wound care alongside them, including debridement, offloading, a circulation check and steady blood sugar; without these, treatment is much more likely to fail.⁠^[1] Because bone infection counts as at least a moderate infection, guidelines suggest a removable boot for an infected ulcer on the ball or middle of the sole, so the wound can be checked often; a non-removable device suits ulcers with mild infection or none.⁠^[1,6] We fit the boot and see you regularly to clean and measure the wound (see wound care visits).

Infection combined with poor circulation makes healing much harder and raises the risk of amputation, so blood flow is checked early.⁠^[1] We start with noninvasive circulation testing at our practice; if flow is reduced, we arrange further imaging and treatment with a vascular specialist (see circulation tests for foot wounds).

Guidelines suggest against hyperbaric oxygen just to treat infection, as evidence that it clears soft-tissue or bone infection is lacking.⁠^[1] For its role in some slow-healing ulcers, see hyperbaric oxygen therapy.

Antibiotics alone are a reasonable option for a forefoot bone infection that doesn’t need urgent drainage, with no artery disease and no exposed bone.⁠^[1] In a randomized trial of people with forefoot bone infection and good circulation, 75% healed with 90 days of antibiotics and 86% with bone-sparing surgery plus 10 days of antibiotics, not a significant difference; 4 of 24 on antibiotics alone got worse and needed surgery.⁠^[3]

When surgery is the right step

Removing infected bone has long been the standard treatment; guidelines suggest it, combined with antibiotics, and advise considering surgery for every severe infection and whenever treatment without surgery is likely to fail.⁠^[1] Surgery is usually favored when:

• there is an abscess, spreading dead tissue or a fast-moving infection, which calls for urgent surgery (see diabetic foot infections)
• bone is exposed, or the infection is in the midfoot or heel, where evidence for antibiotics alone is thin
• artery disease is present; surgery is then planned with a vascular specialist, who restores badly reduced blood flow before or after the operation
• antibiotics alone haven’t worked⁠^[1,3]

What surgery adds:

• It removes the source. Guidelines favor limited bone removal, avoiding amputation where possible.⁠^[1] Bone-sparing operations remove part of a toe bone, an infected joint surface, a sesamoid bone or a metatarsal head. A review concluded that, when indicated, they are safe and effective, improving the chance of healing and lowering the risk of limb loss compared with more radical amputation, though its authors call for randomized trials.⁠^[2]
• It shortens antibiotics. Guideline tables list 2 to 5 days when all infected bone is removed, and up to 3 weeks when the edge of the remaining bone still shows infection.⁠^[1] In a randomized pilot trial of 93 people treated after surgical debridement, remission occurred in 84% with 3 weeks of antibiotics and 73% with 6 weeks; in this small trial, the shorter course was no worse.⁠^[7]
• It can fix the pressure point. If the pressure or deformity behind the ulcer isn’t corrected, infection can return at the same spot.⁠^[1] See surgery that takes pressure off ulcers.

For the infections that need it, Dr. Ozturk, a Foot and Ankle Surgeon board certified in wound care (FAPWH), removes infected bone from the toes to the heel, including metatarsal head resection and partial calcanectomy (taking away the infected part of the heel bone). He chooses the smallest operation that clears the infection; read more in surgery for bone infection.

If infection has damaged more of the foot, a well-planned partial foot amputation that saves as much of the foot as possible is still limb preservation, and a limb salvage second opinion can help you weigh your options.

Limits and risks

Evidence comparing surgery with antibiotics alone is thin: a systematic review found only six trials (308 people), two at low risk of bias, and concluded the evidence cannot yet show which approach is preferable.⁠^[8]

Wound infection after surgery is more common with diabetes. Among 1,465 foot and ankle operations in one study, it occurred in 9.5% of people with diabetes and 2.4% of those without; the authors tied the risk mainly to nerve damage, with Charcot foot and smoking also playing a part.⁠^[9] In the antibiotics-versus-surgery trial described earlier, 3 of 22 people in the surgery group needed a second operation.⁠^[3] If circulation is worse than tests suggest, an operation can leave a wound that won’t heal, one more reason we test blood flow before surgery.⁠^[1] If you smoke, read about smoking and foot surgery healing (external site).

Recovery and staying in remission

Because bone infection can return, specialists speak of “remission” rather than a final all-clear, judged at least 6 months after antibiotics end. Resolving skin infection, falling inflammation markers and X-rays showing no further bone loss are good signs.⁠^[1]

After a diabetic foot infection, most people stay at high risk of new foot problems, so lifelong foot checks are warranted.⁠^[1] See keeping your foot in remission.

When to seek care

See us within a day or two for any foot wound that isn’t healing, especially if you have diabetes.