Osteomyelitis: Part 3
Treatment: from a Clinician's Point of View
For the last several months, we have been discussing one of the more difficult complications of the diabetic foot, that of chronic osteomyelitis (OM). Once we have diagnosed the bone infection from a clinical and imaging perspective, we need to develop a treatment plan based not only on clinical experience, but also on the best available evidence. Unfortunately, there is no clear cut path of evidence to follow. Two camps exist in this regard: one supports the notion that osteomyelitis, in most cases, can be cured with systemic antimicrobial therapy, and the other believes that bone infection can only be cured with surgical intervention. Still, another school of thought has evolved somewhere in the middle of these two contrasting approaches. I am of the latter position, after having had many arguments with my medical colleagues who believe that OM can be cured with antimicrobial therapy. I have found that most patients do best with a combination of surgery and antimicrobial therapy directed at pathogens isolated from bone cultures. But I have also learned, to my surprise I must say, that there are indeed some cases of osteomyelitis in the diabetic foot that can indeed be resolved with prolonged antimicrobial therapy (and supportive wound care). Specifically, those patients who might have bone exposed at the tip of a toe or under an ulcer (my diagnostic criterion for likely osteomyelitis) but do not have any soft tissue necrosis, peripheral arterial disease (PAD), or bone erosions visible on radiographs can indeed be initially treated with even oral antibiotics for several months. Sometimes, they will certainly resolve the wound and underlying evidence for bone infection. In other cases, they will not.
As mentioned earlier, there is no consensus on the best way to treat OM. There have been no published comparative trials contrasting medical with primarily surgical therapy. In fact, many patients will not submit to surgery when advised to do so. This makes randomization difficult for clinical trials in this regard. Furthermore, there is no concrete data that supports any specific antibiotic or route of administration (intravenous or oral), nor is there good evidence on the duration of required therapy. We are all aware of the classic 6 weeks of intravenous therapy that every textbook espouses. However, there is no evidence to support this therapy. It is more a matter of custom than anything else that we engage in such protocols. In this sense, the equipoise and lack of consensus actually gives us great latitude in the approach to management of this difficult condition.
It is best to approach diagnosed or suspected OM in a diabetic foot from a rational perspective. If the patient is not acutely infected but has clinical osteomyelitis based on your evaluation, time is on your side and that of the patient. [ Figure 1 ] In this setting, after obtaining your deep tissue or, optimally, a bone culture, treatment can easily commence with prolonged culture directed oral therapy. At least 3 months of therapy should be planned for, recognizing that longer periods are often required depending upon response to therapy. If the associated wound heals and there are no local signs of inflammation, the odds are good that a “cure” or resolution has taken place. In contrast, if x-rays progressively worsen or if the infected wound fails to improve on clinical grounds, surgical intervention needs to be contemplated (or antimicrobial therapy needs to be changed- or both). Granted, long term therapy places the patient at risk for development of antibiotic related complications or resistant organisms. However. It can also cure the condition. In most cases, no harm is done during this period and, at the very least, the progression of the bone infection has been thwarted. Surgical debridement or excision of infected bone (i.e. a phalangectomy or metatarsal head resection) at that point can often be limited in nature with good outcomes.
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Figure 1: Stable ulcer that probes to bone without X-ray changes. This could be treated with culture guided antibiotics and good wound care initially.
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Figure 2: Chronic osteomyelitis of 1st MTP joint with destructive changes seen on plain radiographs. Joint resection or amputation is usually required in this situation.
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On the other hand, primarily medical therapy will not generally be successful in more advanced cases, where a good deal of bone destruction has already taken place, or in the presence of a severe infection or peripheral arterial disease. [ Figure 2 ] For these more severe type of cases, surgical intervention is best done earlier rather than later. Of course, adjunctive antimicrobial therapy based upon bone cultures will also be necessary. Where a local curative procedure has been performed in this setting (i.e. toe or ray amputation, joint resection, partial calcanectomy, etc.), our aim is to convert the bone and soft tissue infection into just a residual soft tissue infection. In this regard, a limited postoperative antibiotic course will be required (perhaps for two additional weeks or so). If signs of infection, inflammation, or wound healing failure become evident, it is likely that more bone excision will be required. Occasionally, we implant antibiotic impregnated beads (vancomycin, gentamicin, tobramycin) against the bone prior to wound closure. The beads will elute high concentrations of antibiotic locally without having the complications of high serum levels. Although there are no comparative trials supporting the efficacy of antibiotic bead implantation in resolving OM, we will often use such therapy for difficult cases. Unless they are absorbable, the beads will generally be removed in 3 to 6 weeks.
Above all else, your clinical acumen is required to successfully manage this challenging complication of the diabetic foot. Pay attention to the basics of wound care: debridement, offloading, restoration of perfusion for patients with PAD, diabetes control, culture guided antimicrobial therapy, etc. When things are not progressing the way they should, step back and reassess. Take another culture and another x-ray. Be suspicious and be thorough. Osteomyelitis in the diabetic foot is more difficult to resolve than in persons without diabetes, but it is indeed curable without the routine need for partial foot amputation. Your persistence will pay off in the long run.
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References are provided below that can expand upon many of the points made above. We welcome your opinions, concerns, and suggestions. If you have an interesting case or a troubling circumstance that you would like to share with fellow PRESENT Diabetes members, please feel free to comment on eTalk.
Best regards,
Robert Frykberg, DPM, MPH
PRESENT Editor,
Diabetic Limb Salvage
REFERENCES
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