A frequent and dangerous complication of an ulcer is infection.
And infected ulcer can cause systemic phenomena which make put at risk not only the possibility of saving the limb but even the patient’s life.
The first step is to distinguish whether an infected ulcer requires immediate measures beyond dressing or whether a dressing-based intervention is sufficient.
Compartmental infections (abscess) or infections caused by an aerobic (gaseous gangrene) or mixed germs (cellulitis or necrotising fascitis) require general and surgical treatment measures, which if not undertaken as a matter of urgency may have very serious consequences for the patient.
The infection sets up in most cases on an ulcer which has been open for a long period of time and which has not been adequately treated.
Very often the infection is the cause which in itself determines the need for major amputation, carried out at leg or thigh level.

It is possible to distinguish two types of infected wounds, depending on their characteristics of seriousness:

• Acute diabetic foot
• Chronic diabetic foot

The acute infection of the foot is defined as:

• limb-threatening infection: an infection which puts the leg at risk
• life-threatening infection: infection which puts life at risk.

Then there is chronic infection which, since that it is less "manifest" in comparison with the above examples is very insidious, since it can, if underevaluated or not correctly treated, develop into one of the two cases indicated above.
A very simple classification indicates 2 clinical pictures:

      A)    acute infected diabetic foot
      B)    chronic infected diabetic foot


A) Acute Infected Diabetic Foot
     (limb-threatening infection e life-threatening infection)

The acute diabetic foot which, as stated above, can endanger not only conservation of the lower limb but the patient's actual life, is a foot with an abscess or necrotising fascitis.
It is important to emphasise that, when faced with a patient with an "acute" foot, rapidity of intervention is the discriminating factor in relation to whether or not the foot and the patient can be saved.
In fact, the risks to which patients with these types of infection of the foot are subject is not only that of major amputation (leg or thigh) but also that of death caused by septic shock or other infective complications.
Therefore, delaying aggressive surgical treatment, even by a few days, means exposing the patient to the risk of a catastrophic outcome.
Intervening rapidly means removing any elements of infection which are present: surgical treatment allows us to drain (i.e. evacuate) the pus and allows us to carry out an intra-operative evaluation of how deep and extensive the infection is and therefore how many tissues are involved (tendons, muscles, bone).
From a purely clinical point of view there are three conditions which fall under the name of "acute diabetic foot" and which require urgent surgical intervention:

• Abscess and phlegmon ( Figure 35 e Figure 36)
  
  
• Necrotising fascitis ( Figure 37)
  
  
• Wet or gaseous gangrene ( Figure 38 e Figure 39)

Abscesses and Phlegmons
Abscess and phlegmon collection refers to the situation in which sacs of pus form in the internal tissues of the foot. These may be spontaneously evident (superficial fistulae) or be insidiously hidden at a deep level (purulent sacs).
In this case surgical treatment is essential, and may even require a very aggressive approach, which will allow us to evacuate these collections and remove the infected tissues present (refer to the section entitled Clinical Cases - Clinical Case 1 in this respect).
During drainage operations, in addition to collecting microbiological samples, a careful search for closed sacs will be carried out. These do not have any communication with the exterior and, if left in place, will allow the infection to remain active.
Surgical treatment for a purulent collection is almost always accompanied by the need for minor amputation (toe, ray, or extensive parts of foot).
This must be clearly borne in mind because often there is no trace of the gravity of the deep tissue infection on the visible face of the foot.

Necrotising fascitis
This is a serious infection which puts at risk both the affected limb and the patient’s own life.
It can be sustained both by germs referred to as aerobic and those referred to as anaerobic to (the most dangerous).
Within a few hours or a few days the infection can spread in a devastating manner through the band covering the muscles (in general the latter are not involved); the band usually appears grey and necrotic and the necrotic subcutaneous tissue splits away.
An immediate intervention, as well as intravenous antibiotic treatment, are essential.
Surgical treatment involves removing all the infected necrotic tissues present until healthy, bleeding tissue is reached.
In this case, and above all in the presence of anaerobic germs, hyperbaric oxygen therapy (HOT) may be an excellent ally.

Wet gangrene
Gangrene may be the most well known clinical picture affecting diabetics.
Gangrene (i.e. necrosis throughout the thickness of the soft tissues) may involve small parts (phalanges), more extensive sections (toe) or the majority of the foot (front of the foot, middle and back).
While dried gangrene is a matter of relative urgency, wet or gaseous gangrene is one of absolute urgency.
Once again we risk not only the loss of the limb but also the patient's life (sepsis).
Treatment is surgical and will involve removing necrotic and infected tissues.
At the same time intravenous antibiotic treatment is obligatory and, as in the previous case, some clinical pictures may benefit from assistance with hyperbaric oxygen treatment.

Dry gangrene
Dry gangrene deserves a separate section in this section: we should not be complacent about this clinical picture; too many times we see patients who, having had dry gangrene for months, suddenly come to our centre with devastating infective clinical pictures because that the dry gangrene has turned into the wet form.
Frequently there has been an incorrect indication in these patients’ history: drying up the gangrene by having only one toe “drop off” (mummification).
In addition there is the second "bad practice" (malpractice) which we still see too frequently: surgical removal of dry gangrene (e.g. toe), it in patients with arteriopathies, without pre-operative re-vascularisation.
Once again in this case photographic images are worth a thousand words... ( Figure 34).

When faced with a so-called "acute" foot, generally the emergency operation allows us to stop the infection.
Depending on what is visible intra-operatively a decision will be taken about whether or not the surgical wound should remain open in the first instance or whether it is possible to carry out immediate surgical closure.
However it is a good thing to know that in many cases a second definitive intervention is necessary, which will be selected in accordance with the patient's clinical progress and with the mass of tissue lost either because of infection or because of the emergency surgical treatment.


B) Chronic Infected Diabetic Foot

These are the cases in which emergency treatment is not required, although medical treatment is however required, which is almost always surgical, even if not always radical.
The model example is chronic osteomyelitis ( Figure 40) secondary to an ulcerative wound which has extended in time (even for only a few months).
The case of ulcerative wounds of the foot which never manage to heal, in spite of being treated for months and months, more or less correctly, is fairly frequent.
Very often the cause is the presence of an infected underlying bone which does not allow the ulcer to close.
In these cases, the surgical option constitutes a definitive solution for the problem in addition to lengthy antibiotic treatment ( Figure 41).
The chronic infection may only involve the soft tissues in which case we will have the clinical picture of cellulitis, or may go right down to the bone in which case we will have the clinical picture of osteomyelitis.

Cellulitis
On account of its relatively benign characteristics, sometimes with the absence of systemic repercussions (fever, leukocytosis) requiring an emergency surgical intervention, cellulitis, which is actually an acute infection, is considered to be the equivalent of a chronic infection.
It is an infection which affects the soft tissues and which requires an oral or parental antibiotic treatment but no radical surgical intervention; however local debridement is important.
It is defined as mild or moderate on the basis of the surface of tissue involved: if the inflamed area is less than 2 cm we refer to mild infection, if greater than 2 cm we refer to moderate infection.
In the event of mild infection outpatient treatment can be carried out using oral antibiotics and dressing with antiseptics.
In the case of moderate infection hospital admission is preferable both to monitor the progress of the infection and to be certain that it does not become deeper (abscess or fascitis).

Osteomyelitis
As stated above, osteomyelitis is an infection which affects the bone.
In the diabetic foot it is always an infection caused by contiguousness: the germs reached the bone from an infected skin ulcer which has failed to heal rapidly.
The principal problem of osteomyelitis is the treatment decision, namely the choice between prolonged antibiotic treatment or surgical treatment.
We must emphasise how it is frequently possible to reduce a skin ulcer to minimum dimensions, with the illusion of being able to achieve a cure; in reality, if the infectious process remains in the bone, the skin wound, often of reduced dimensions, will require continuous dressing and antibiotic treatment ( Figure 42 e Figure 43).
Opinions on the most effective treatment for osteomyelitis are not all in agreement, even if literature indicates surgery as the most effective solution for eradicating the infection.
Our experience has led us to believe that it is possible to try a prolonged antibiotic treatment (> 6 weeks) only if the osteomyelitis is limited to the toe or parts of the metatarsals which are very close to the toes.
In the case of osteomyelitis affecting the base of the metatarsals we have no doubt about the need for surgical eradication of the whole of the infected bone.
This is because of the danger of the infective process extending from the bone in the middle of the foot to the bone in the back of the foot; when the heel is infected the risk of having to amputate the whole foot is extremely high ( Figure 44): the clinical case shown in fact reveals how the infection has spread from the metatarsal bones (X-ray) to the bone in the back of the foot (NMR) in spite of carrying out antibiotic treatment in accordance with the protocol for osteomyelitis.
Once again it is important to remember that the necessary condition for defining these wounds as mild or moderate, and therefore as a non limb-threatening infection, is the absence of arteriopathy.
In the presence of arteriopathy even a minor infection can rapidly become a destructive infection both in terms of preserving the leg and in terms of the patient’s life ( Figure 45).