Diabetic foot is a complication that occurs when a foot ulcer appears resulting from a trauma (external or internal) in a diabetic patient with different stages of ischemia and neuropathy. All treatments for a diabetic foot aim at avoiding major amputation and the associated decrease in quality of life and the increased mortality rate. We must not forget that a patient who was submitted to a lower limb amputation has a 50% probability of having his contralateral limb amputated in the following 5 years. This is dramatic!
Infection is the main cause of diabetic foot amputation. Osteomyelitis (OM) is responsible for 20% of moderate infections and 50-60% of severe infections, which are associated with a high amputation rate. OM is a therapeutic challenge, and many times patients are offered inadequate treatment. Amputation is often immediately offered in cases of OM in a diabetic foot. Is this approach correct? Can we postpone amputation? Is not avoiding amputation the main objective?
I have treated diabetic foot since the very beginning of my surgeon’s life. While working at Hospital dos Covões, I was responsible for the “surgical diabetic foot consultation”, and treated many feet with superficial infection, deep plantar infection, osteomyelitis, and ischemia, for whom surgical revascularization was conducted. Many feet were amputated, but many more were saved. I currently treat this disease in Hospital Luz Aveiro and Hospital CUF Coimbra (“Diabetes Unit”).
This post follows three cases of diabetic foot osteomyelitis successfully treated without amputation. All patients presented a positive probe-to-bone test (one patient with limited bone exposure), with mild to moderate soft tissue infection, and one patient with a sausage toe. MRI confirmed the osteomyelitis. Vascular evaluation showed peripheral arterial disease with multiple atherosclerotic stenosis but without occlusions, mainly in the leg arteries. No revascularization was proposed. Since all patients had neuropathy, a mixed blessing could be responsible for the absence of vascular claudication. All patients started oral antibiotics for at least three months. In one patient, soft tissue debridement was performed. Three months later, the wounds were clinically better without soft-tissue infection. Re-evaluation MRI was performed. In one patient there were no signs of osteomyelitis, and in the remaining two patients’ improvement was evident. The first patient stopped the antibiotic, but the other two were kept on the same antibiotic for another three months. After this period, there were no signs of infection, and an MRI performed at 6 months of antibiotics showed no osteomyelitis. At two years (one patient) and 6 months (two patients) of follow-up, no recurrence was evident.
The challenge is to diagnose OM in a diabetic foot without clinical manifestations. The probe-to-bone (PTB) test should be used along with imaging findings. “A positive PTB test in an infected wound is highly suggestive of OM, whereas a negative PTB test does not exclude the diagnosis.” On the contrary, in an uninfected wound, a negative PTB test is suggestive of no OM. However, some authors advise the use of the PTB test as screening and not diagnosis. The reason why the PTB test must be interpreted along with imaging findings (ex. X-rays). I prefer using MRI because it is the most accurate imaging test for diagnosing OM, it can be used for treatment evaluation and follow-up. So, I use clinical evaluation (with PTB test) and MRI findings for OM diagnosis.
In the review paper from Lázaro-Martinez et al. from Madrid, Spain, it is stated that it is impossible to standardize treatment for diabetic foot osteomyelitis because it is a heterogeneous disease, “may have several clinical presentations and may or may be not associated with ischemia and soft tissue infection”. Guidelines are probably inaccurate to standardize treatment, and the best option to prevent amputation is probably the versatility of the surgeon. Clinical evaluation is paramount to choosing the best treatment (antibiotics only vs. surgery), which can be changed throughout the evaluation period.
According to the authors, medical treatment could be offered to:
ulcers in the forefoot
no soft tissue necrosis
bone and joint not visible through the ulcer
good vascularization (do not forget vascularization can sometimes be improved - ex. surgical bypass or endovascular treatment)
high surgical risk
Surgical treatment could be a good option in cases of:
bone and joint exposure in the ulcer
soft tissue necrosis
abscess (for surgical drainage – superficial dorsal infection vs deep plantar infection)
failed antibiotic treatment (90 days)
advanced bone destruction
high risk of antibiotic toxicity (renal disease)
Ultimately, all treatment options aim at avoiding amputation, so that more diabetic patients can walk on both feet. Many articles have concluded that most cases of OM (two-thirds) can be treated with oral antibiotics, with or without debridement. Some papers report a 66.9% success rate, while others report a cure rate of 88.2% following 6 months of oral antibiotics without bone resection. I believe this is very important, meaning doctors who treat diabetic foot osteomyelitis must be aware of the long-time antibiotic scheme and the huge amount of work it is to save a diabetic limb.
Although the aim is to save the limb, “surgery should always be considered if antibiotic therapy fails”. Conservative surgery (removal of infected bone only) without minor or major amputation can have a 50% success rate. The authors present studies comparing surgery and medical treatment, and both options have similar results in neuropathic ulcers without soft tissue necrosis. Conservative surgery decreases the time of antibiotics, gives us bone sampling, and removes necrotic bone and biofilm. However, it increases the risk of re-ulceration, foot instability, and morbidity.
So, clinical evaluation is crucial for treatment decisions. Vascular evaluation for deciding whether revascularization is indicated or not is very important. Why? While a neuropathic foot is well vascularized and heals well, in untreated ischemic foot wounds will not heal properly (including surgical wounds). Medical treatment and surgery should be complementary and offered to the patient according to a continuous evaluation by the surgeon. In the end, always remember (major) amputation is irreversible and increases morbidity and mortality. All efforts should be made to avoid any amputation. A good diabetic foot surgeon is the one who has a low amputation rate.
Link to PubMed:
Dr. Carlos Eduardo Costa Almeida
General Surgeon