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DIABETIC FOOT

Cameron M. Akbari, M.D., F.A.C.S., and Frank W LoGerfo, M.D., F.A.C.S. .

Evaluation and Management of the Diabetic Foot

Surgeons caring for diabetic patients are faced with a diverse spectrum of foot disease.1,2 The clinical presentation may range from the asymptomatic patient who requires nothing more than preventive foot care to the unstable and critically ill patient in whom both loss of limb and death are imminent threats. This wide range of disease severity, coupled with inappropriate and untimely use of diagnostic testing, contributes to the clinical confusion that often leads to delays in diagnosis and treatment and, ultimately, to limb loss. It is important, therefore, that surgeons caring for diabetic patients develop a simple but comprehensive and orderly approach to diabetic foot problems that (1) can be implemented for any such problem, (2) recognizes the pathogenic roles of neuropathy, ischemia, and infection, and (3) emphasizes the initial clinical assessment at the bedside.3

Clinical Evaluation

Evaluation of any diabetic foot problem begins with a complete history and a careful physical examination. Broadly speaking, such evaluation should address the healing potential of the foot, the details of the foot problem (e.g., ulcer, gangrene, infection, or osteomyelitis), the systemic consequences of diabetes, and any immediate threats to life or limb.With this information in hand, the surgeon can usually make an accurate diagnosis and start a comprehensive treatment plan without having to order further diagnostic tests, which are liable to be both costly and time-consuming.

HISTORY

The history of the foot problem can yield valuable insights into the potential for healing, the presence of coexisting infection or arterial occlusive disease, and the need for further treatment. Whenever a patient presents with a foot ulceration or gangrene, possible underlying arterial insufficiency should immediately be suspected, even if neuropathy or infection is present. It is helpful to be aware of the event that incited the foot problem. In a patient with diabetes and arterial insufficiency, the inciting event for a foot ulcer may be a seemingly benign action, such as cutting a toenail, soaking the foot in a warm bath, or applying a heating pad. Unfortunately, because of the broad microneurovascular and macrovascular abnormalities associated with diabetes, these relatively innocuous actions can progress to a nonhealing ulcer and gangrene. Similarly, failure to heal after any podiatric procedure is strongly suggestive of underlying unrecognized arterial insufficiency. The duration of the ulcer also provides important clues, in that a long-standing, nonhealing ulcer is strongly suggestive of ischemia. Certainly, an ulcer or gangrenous area that has been present for several months is unlikely to heal without some further treatment, whether it be offloading of weight-bearing areas, treat-

ment of infection, or, most commonly, correction of arterial insufficiency. In some cases, the present ulcer has already healed at least once, and the current episode represents a relapse. A history of intermittent healing followed by relapse raises the possibility of underlying untreated infection (e.g., recurrent osteomyelitis) or an uncorrected architectural abnormality (e.g., a bony pressure point or a varus deformity). In view of the many vague and unsupported therapies advocated for the diabetic foot, it is helpful to know the type and duration of any treatments the patient has already undergone for the current problem. For example, a patient with an ischemic ulceration may have completed several different courses of antibiotics without success. Thus, if antibiotic therapy is contemplated for a current infection, possible antibiotic resistance must be taken into account in choosing the appropriate agent. It is also helpful to know which treatments were not previously offered to the patient and to look critically at why they were not offered. For example, many diabetic patients with correctable foot ulceration and limb ischemia are told that their only option is limb amputation, usually because of the physician's inherited pessimism or his or her inadequate knowledge of the advances made in limb and foot salvage. No patient should be denied an opportunity for limb salvage on the basis of a previous medical or surgical opinion without a new comprehensive evaluation being performed. Inquiries should be made about any previous foot and limb problems--for instance, whether the patient had other ulcers on the same foot that healed spontaneously, how long such healing took, and whether foot surgery was ever performed on that side. A history of recent ipsilateral ulceration or foot surgery that healed in a timely and uncomplicated manner suggests, but does not prove, that the arterial supply is adequate. Problems and procedures more remote in time, however, are less useful indicators. A history of previous leg revascularization (including percutaneous therapies) is also an important clue to possible underlying arterial insufficiency. Because of the predilection for mirror image­type atherosclerotic occlusive disease, the contralateral leg must be considered as well: previous revascularization in the opposite leg is often associated with arterial insufficiency on the affected side. Other cardiovascular risk factors, such as cigarette smoking and hyperlipidemia, must also be taken into account: their presence increases the likelihood that ischemia is contributing to the current foot problem. Although claudication and rest pain have traditionally been associated with vascular disease, they may be obscured by diabetic neuropathy; hence, their absence in the diabetic patient certainly does not rule out ischemia. Because even moderate ischemia precludes healing in the diabetic foot, the absence of rest pain is not a reliable indicator of an adequate arterial blood supply; moreover, many patients may not be walking long enough distances for vasculogenic claudication to develop. Conversely, some patients with true ischemic rest pain are dismissed for years as having "painful neuropathy."

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Diabetic patient has foot problem Obtain history: inciting event, duration, healing, previous treatment (including surgery), vascular disease and risk factors, overall health, functional status. Perform physical examination: signs of infection, diabetic neuropathy, pulses, arterial perfusion. Assess clinical findings to determine direction of subsequent workup and treatment.

Evaluation and Management of the Diabetic Foot

Infection is absent

Infection is present, and patient is medically stable

Start antibiotics, correct metabolic abnormalities, and drain and debride as indicated.

Assess salvageability of foot.

Foot is salvageable Evaluate foot for ischemia.

Ischemia is absent

Ischemia is present Obtain arteriogram of entire lower extremity.

Perform revascularization.

Provide continued wound care: dressings, debridement as necessary, adjunctive measures, correction of metabolic abnormalities, antibiotics as needed. Determine whether secondary (definitive) foot surgery is needed.

Secondary foot surgery is indicated Proceed with foot operation.

Foot is not healed Reevaluate for infection (see above), and run through algorithm again.

Foot is healed Provide preventive foot care.

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Patient is in a septic state and is medically unstable

Guillotine amputation is not indicated

Guillotine amputation is indicated Correct metabolic abnormalities, and stabilize patient.

Foot is not salvageable

Perform formal below- or above-the-knee amputation.

Secondary foot surgery is not indicated Continue wound care.

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a

b

Figure 1 Shown is a benign-appearing gangrenous eschar (a) on the foot of a diabetic patient. Plain x-ray (b) reveals extensive subcutaneous air in soft tissue, consistent with severe necrotizing fasciitis.

Both the systemic effects of the foot problem and the systemic consequences of diabetes itself should be assessed. Because unrecognized infection in the diabetic patient may rapidly progress to a life-threatening condition, attention should be directed toward detecting the subtle manifestations of an infected foot ulcer. The patient should be asked about worsening hyperglycemia, recent erratic blood glucose control, and higher insulin requirements. As a consequence of the microvascular and neuropathic abnormalities in the diabetic foot, classic symptoms of infection (e.g., chills and pain) are often absent, and hyperglycemia is often the sole presenting symptom of undrained infection. Faced with ongoing infection and hyperglycemia, the surgeon should strongly suspect impending ketoacidosis or nonketotic hyperglycemic hyperosmolar coma, with the attendant symptoms of weakness, confusion, and altered mental status. Because a patient with a diabetic foot problem often needs some type of operative intervention, the history should also include a comprehensive assessment of overall health status to help stratify perioperative risk [see ECP:6 Risk Stratification, Preoperative Testing, and Operative Planning]. For example, knowledge of previous cardiac events (e.g., myocardial infarction or revascularization) and current cardiac status (e.g., New York Heart Association [NYHA] class or anginal severity) can help determine whether perioperative cardiac monitoring or preoperative cardiac testing is indicated and what form such monitoring or testing should take. Similarly, in a patient with suspected infection and ischemia, a history of worsening renal function or impending need for hemodialysis can help determine the choice and dosage of antibiotics and may alter plans for standard contrast arteriography.The essential point is that diabetes may affect virtually every organ system, often in an indolent pattern; thus, in the evaluation of any diabetic patient with foot disease, attention must be paid to all of these systems. Functional status also becomes an important consideration at this point, and the history should carefully determine the patient's

ambulatory and rehabilitative potential. Many different methods of quantifying functional status have been suggested. One simple approach is to classify functional status as a point on a continuum. One end of the continuum might be a fully ambulatory patient; almost all surgeons would recognize that such a patient should be offered every attempt at limb salvage. The other end might be a completely bedridden patient with multiple comorbid conditions; most surgeons would adopt a far less aggressive approach to such a patient. In practice, many patients fall somewhere between these two extremes, in which case a more thorough evaluation of functional and social status becomes imperative before any firm decisions can be made regarding limb salvage.

PHYSICAL EXAMINATION

Fever and tachycardia are strongly suggestive of deep or undrained infection, with hypotension being a late manifestation of ongoing sepsis. It is important to remember, however, that these signs may be absent in diabetic patients with impending or progressive infection. A focused cardiopulmonary examination helps confirm the presence or absence of congestive heart failure, valvular abnormalities, or rhythm disturbances, which must be recognized in diabetic patients with poor underlying medical reserve. Evaluation of the diabetic foot ulcer should include a strong suspicion of infection and a thorough search for it. In a patient with cellulitis, the entire foot, including the web spaces and the nail beds, should be examined for any potential portals of entry, such as a puncture wound or an interdigital ("kissing") ulcer. Encrusted and heavily calloused areas over the ulceration should be unroofed and the wound thoroughly inspected to determine the extent of involvement. A benign-appearing dry gangrenous eschar often hides an undrained infectious collection [see Figure 1]. Cultures should be taken from the base of the ulcer; superficial swabs may yield only colonizing organisms.

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Findings consistent with infection include purulent drainage, crepitus, tenderness, mild erythema, and sinus formation [see Figure 2], though these findings may be entirely absent in the neuropathic foot. With more advanced and deep infection, edema may be present as a result of elevated pressures within one or more of the plantar compartments [see Figure 3]. If left untreated, this process may spread proximally along tendon sheaths to involve the ankle or even the calf. Close inspection of the ulcer and the use of a sterile probe may also confirm the presence of osteomyelitis, which occurs commonly even in conjunction with benignappearing ulcers. If bone is detected with gentle probing, osteomyelitis is presumed present. Because of its prevalence and its causative role in diabetic foot ulceration and limb loss, neuropathy should be assessed in every diabetic patient, and appropriate preventive measures should be taken to guard against foot ulceration in the high-risk neuropathic foot. Protective sensation may be evaluated by pressing a Semmes-Weinstein 5.07 monofilament against the skin; inability to feel the monofilament correlates well with an increased risk of foot ulceration. Advanced sensorimotor neuropathy will lead to the presence of a so-called claw foot (from gradual atrophy of the intrinsic muscles) or to Charcot degeneration with bone and joint destruction at the midfoot. Both of these conditions give rise to abnormal pressure points on the plantar prominences and the potential for foot ulceration. Assessment of the arterial perfusion in the diabetic foot is a fundamental consideration, in that the diabetic foot needs maximal perfusion to heal. In the presence of ischemia, all efforts at limb salvage will fail.Therefore, the physical examination must include a systematic approach to the assessment of arterial insufficiency. Simple inspection of the leg and foot, including the ulcer, often provides suggestive clues. For example, distal ulceration (on the

tip of a digit), ulceration unassociated with an exostosis or a weight-bearing area, and gangrene are all strongly consistent with underlying ischemia [see Figure 4].The presence of multiple ulcerations or gangrenous areas on the foot, the absence of granulation tissue, and the lack of bleeding with debridement of the ulcer should immediately be taken as signals of possible underlying arterial insufficiency. Other signs suggestive of ischemia are pallor with elevation, fissures (particularly at the heel), and the absence of hair growth. Poor skin condition and hyperkeratosis, though not always good indicators of arterial disease, should be noted because they may help confirm initial clinical impressions. The pulse examination, including the status of the foot pulses, is the single most important component of the physical examination. In the absence of a palpable pulse, ischemia is always presumed to be present. Although an accurate pulse examination of the lower extremities is not difficult, it is an acquired skill, and time should be devoted to practicing and perfecting the technique. The femoral pulse is palpated midway between the superior iliac spine and the pubic tubercle, just below the inguinal ligament. The popliteal pulse is palpated with both hands and with the knee flexed no more than 15°. Palpation of the foot pulses is somewhat more demanding, requiring close attention and a good knowledge of the usual locations of the native arteries. The dorsalis pedis is located between the first and second metatarsal bones, just lateral to the extensor hallucis longus tendon, and its pulse is palpated with the pads of the fingers as the hand is partially wrapped around the foot [see Figure 5]. If the pulse cannot be palpated, the fingers may be moved a few millimeters in each direction; the dorsalis pedis occasionally follows a slightly aberrant course. A common mistake is to place a single finger at one location on the dorsum of the foot. The posterior tibial artery is typically located in the hollow curve just behind the medial malleolus,

Figure 2 Purulent drainage is seen from a submetatarsal ulcer on the plantar surface of the foot of a diabetic patient.

Figure 3 Shown is wet gangrene with edema and undrained severe infection in the foot of a diabetic patient presenting with hyperglycemia and ketoacidosis.

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Figure 4 Shown is dry gangrene of several toes in a diabetic patient with femoropopliteal and tibial arterial occlusive disease.

approximately halfway between the malleolus and the Achilles tendon.The examiner's hand should be contralateral to the examined foot (i.e., the right hand should be used to palpate the left foot, and vice versa), so that the curvature of the hand naturally follows the contours of the ankle [see Figure 6].

Assessment of Clinical Findings

Once the clinical evaluation is complete, the next step is to assess the findings from the history and the physical examination so as to determine the course and urgency of the subsequent workup and treatment. This assessment is made at the bedside, focusing on three main concerns: (1) the presence and severity of infection, (2) the salvageability of the limb, and (3) the presence of ischemia.

PRESENCE OF INFECTION

environment (e.g., hospitalized or outpatient). Certain general assumptions can be made about likely causative organisms. Mild localized and superficial ulcerations, particularly in outpatients, are usually caused by aerobic gram-positive cocci (e.g., Staphylococcus aureus and streptococci). In contrast, deeper ulcers and generalized limb-threatening infections are usually polymicrobial. In addition to gram-positive cocci, potential causative organisms include gram-negative bacilli (e.g., Escherichia coli, Klebsiella, Enterobacter aerogenes, Proteus mirabilis, and Pseudomonas aeruginosa) and anaerobes (e.g., Bacteroides fragilis and peptostreptococci). Enterococci may also be isolated from the wound, notably in hospitalized patients; in the absence of other cultured virulent organisms, they should probably be considered pathogenic. Currently, it is clear that resistant organisms, particularly methicillin-resistant S. aureus (MRSA), are playing a growing role in the development of skin and soft tissue infections.Traditionally arising in patients who had previously been hospitalized and those who had previously received antibiotic therapy, MRSA-associated infections are now frequently encountered in outpatient settings. Indeed, in many U.S. cities, these so-called community-acquired MRSA infections are the most common skin and soft tissue infections seen in patients presenting to the emergency department.6 Accordingly, in both outpatient and inpatient settings, it is advisable to assume that MRSA is present in a patient with a diabetic foot infection until the culture data suggest otherwise. Awareness of the increasing prevalence of resistant organisms is critical for current management of diabetic foot infections, especially with respect to the initiation of antibiotic coverage. Initially, the choice of antibiotics is made empirically on basis of these general assumptions. When the results of the initial cultures become available, antibiotic coverage may be broadened or narrowed as appropriate. In a compliant patient with a small ulcer and no evidence of deep space involvement or systemic infection, treatment may be delivered on an outpatient basis. A dual-antibiotic regimen (pending culture results) is instituted, typically consisting of a cephalosporin or a -lactam antibiotic (for activity against staphylococci and streptococci) and trimethoprim-sulfamethoxazole or a tetracycline (for activity against MRSA). A dual regimen consisting of fluoroquinolone and linezolid is an acceptable alternative that also provides adequate coverage. In addition, the patient is instructed to offload weight from the

Evaluation for and treatment of infection is the first priority in the management of any diabetic foot problem.4,5 Although radiographic tests may confirm initial clinical suspicions, the determination of the severity of infection is almost always made on the basis of clinical findings. Infection in the diabetic foot may range from a minimal superficial infection to fulminant sepsis with extensive necrosis and destruction of foot tissue. Accordingly, the treatment plan should address the choice of antibiotic (which requires knowledge of the microbiology), the need for drainage, the option of local or even guillotine amputation, and the patient's overall medical condition. The microbiology of the diabetic foot varies according to the depth and severity of the infection and the nature of the patient's

Figure 5 Illustrated is the correct technique for palpation of the dorsalis pedis pulse.

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Figure 6 Illustrated is the correct technique for finding the posterior tibial pulse.

involved extremity and is taught appropriate methods for changing wound dressings. Frequent follow-up is vital, and guidelines should be imparted by which improvement or worsening of the lesion can be determined. A more common presentation, unfortunately, is a patient with ulceration or gangrene who has a deep infection affecting tendon or bone and possible systemic involvement. For such patients, immediate hospitalization is indicated, including bed rest with elevation of the infected foot, correction of any systemic abnormalities, and broad-spectrum I.V. antibiotic therapy (which may be focused more tightly once culture results are complete). Because the clinical findings of impending sepsis may be subtle, these patients should undergo a complete laboratory workup aimed at detecting and correcting electrolyte and acid-base imbalances. The choice of antibiotic agent and the duration of therapy are dependent on the extent of the infection. For patients with deep or chronic recurrent ulcers, which are typically polymicrobial, or

those with limb-threatening or life-threatening infections, appropriate empirical antibiotic options include (1) vancomycin plus a -lactam antibiotic with a -lactamase inhibitor (e.g., piperacillintazobactam) and (2) vancomycin plus metronidazole plus a quinolone (in cases of penicillin allergy). Subsequent culture results then dictate further antibiotic coverage, if any. In the absence of osteomyelitis, antibiotics should be continued until the wound appears clean and all surrounding cellulitis has resolved (typically, 10 to 14 days). If osteomyelitis is present, treatment should include both surgical debridement and a prolonged (4- to 6-week) course of antibiotic therapy (though the course may be abbreviated if the entire infected bone has been removed, as with digital or transmetatarsal amputation). Heel lesions often present with some degree of calcaneal destruction, and determination of osteomyelitis may be made by clinical examination either alone or in conjunction with other radiographic tests (e.g., magnetic resonance imaging) [see Figure 7]. In the presence of an abscess or deep space infection, immediate incision and drainage of all infected tissue planes is mandatory. Incisions should be chosen with an eye to the normal anatomy of the foot (including the various compartments) and the need for subsequent secondary (foot salvage) procedures [see Figure 8]. Drainage should be complete, with incisions placed to allow for dependent drainage, and all necrotic tissue must be debrided. Repeat cultures (including both aerobes and anaerobes) should be obtained from the deep tissues. Drainage incisions on the dorsum of the foot should be avoided. Abscesses in the medial, central, or lateral compartment should be drained via longitudinal incisions made in the direction of the neurovascular bundle and extending the entire length of the abscess. The medial and central compartments are drained through a medial incision, and the lateral compartment is drained through a lateral incision; both of these incisions are made just above the plantar surface of the forefoot [see Figure 9]. Web space infections may be drained similarly through the plantar aspect of the foot. In some instances, open amputation of the foot (e.g., an open toe or transmetatarsal amputation) may be necessary to allow complete drainage and resection of necrotic tissue. Strict adherence to textbook amputations may lead to unnecessary soft tissue removal and possibly to a higher amputa-

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Figure 7 Shown is heel ulceration with eschar (a) in a diabetic patient. MRI findings (b) are consistent with calcaneal osteomyelitis.

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tion during future closure; therefore, all viable tissue should be conserved. A patient with an ongoing undrained infection may present with an unsalvageable foot and fulminant sepsis, manifested by hemodynamic instability, bacteremia, and severe acid-base and electrolyte abnormalities. Such patients should undergo prompt open (guillotine) below-the-knee amputation [see 6:20 LowerExtremity Amputation for Ischemia].This type of amputation is usually performed at the ankle level, with the aim of removing the septic source while allowing for revision and closure at a later date. Administration of I.V. antibiotics, correction of dehydration and electrolyte abnormalities, and continuous cardiac monitoring are absolutely essential throughout treatment. Once the infection has been drained and tissues debrided, continued wound inspection and management are essential. Ongoing necrosis should raise the possibility of undrained infection or untreated ischemia, in which case further debridement and treatment may be necessary. Avoidance of weight-bearing should be continued. Neither whirlpool therapy nor soaks are beneficial. Medical Stabilization Concomitant with the measures outlined above to control infection, medical stabilization of the diabetic patient must be carried out, and the surgeon must be directly involved in this process. Hyperglycemia is almost always seen when infection is present; it should be gradually corrected. More advanced hyperglycemia leads to ketotic or nonketotic hyperosmolar states, which carry a 10% to 25% mortality. Serum concentrations of electrolytes, magnesium, and creatinine should be obtained and osmolality determined at frequent intervals; any abnormalities should be corrected[see 8:24 Disorders of Water and Sodium Balance and 8:8 Acid-Base Disorders]. Dehydration is common in hyperglycemic patients and should be corrected. A urinary catheter is mandatory to help guide the response to fluid therapy; in unstable patients, a central venous pressure catheter or a pulmonary arterial catheter may be needed [see 8:4 Cardiovascular Monitoring]. Continuous cardiac monitoring is essential in patients with the hyperglycemic hyperosmolar syndrome or ketoacidosis.

SALVAGEABILITY OF LIMB

Medial Intermuscular Septum

Metatarsal Head

Vascular Arch

Lateral Compartment

Medial Compartment

Lateral Intermuscular Septum Central Compartment

Calcaneus

While the infection is being treated and controlled, the surgeon should determine whether limb salvage is feasible.This determination is based largely on the patient's functional status and the degree of foot destruction. For example, primary limb amputation may be considered in a nonambulatory, bedridden patient or in a patient with severe Charcot destruction and degeneration, for whom no further reconstructive foot surgery is possible. Poor medical condition, by itself, is not necessarily an indication for primary limb amputation, given the high perioperative morbidity associated with amputation. Moreover, it is often possible to improve the patient's overall medical status while he or she is being treated for infection and evaluated for ischemia. Assessment of limb salvageability should be carried out simultaneously with treatment of infection because appropriate drainage and antibiotics can dramatically change the appearance and viability of the foot. If limb salvage is not deemed possible, the patient should undergo formal below-the-knee or above-the-knee amputation [see 6:20 Lower-Extremity Amputation for Ischemia].

Figure 8 The foot has three plantar compartments: medial, central, and lateral. The intrinsic muscles of the great toe are in the medial compartment, and those of the fifth toe are in the lateral compartment. The central compartment contains the intrinsic muscles of the second through fourth toes, the extensor flexor tendons of the toes, the plantar nerves, and the plantar vascular structures. The floor of each compartment is the rigid plantar fascia; the roof is composed of the metatarsal bones and interosseous fascia. The medial and central compartments are separated by the medial intermuscular septum, which extends from the medial calcaneal tuberosity to the head of the first metatarsal. The lateral and central compartments are separated by the lateral intermuscular septum, which extends from the calcaneus to the head of the fifth metatarsal.

PRESENCE OF ISCHEMIA

Evaluation of the diabetic foot for ischemia begins with the history and the physical examination. By the conclusion of the clinical evaluation, the surgeon can usually make an accurate assessment of the adequacy of the arterial circulation to the foot. As noted [see Clinical Evaluation, Physical Examination, above], the absence of a palpable foot pulse strongly suggests ischemia unless proved otherwise. Noninvasive arterial testing plays only a limited role in the assessment of diabetic patients with foot ulceration and should not be employed in place of the bedside evaluation. Certainly, for patients with poor healing or gangrene and absent foot pulses, noninvasive testing adds little additional useful information to the initial clinical

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evaluation and typically serves only to further delay vascular reconstruction. For selected patients, however, noninvasive testing, in conjunction with the clinical findings, may be useful. Patients who might benefit from such testing include those with absent foot pulses who have a superficial ulcer with evidence of healing or a previous history of a healed foot ulcer and those without any foot lesions who are scheduled to undergo elective foot surgery. The presence of diabetes imposes limitations on all of the noninvasive arterial tests currently available. Medial arterial calcinosis occurs frequently and unpredictably in patients with diabetes and can result in noncompressible arteries and artificially elevated segmental systolic pressures and ankle-brachial indices. Because calcification levels tend to be lower in the toe vessels, toe systolic pressures are sometimes obtained, but their value is often limited by the proximity of the foot ulcer to the cuff site. Segmental Doppler waveforms and pulsed volume recordings are unaffected by medial calcification, but evaluation of these waveforms is primarily qualitative rather than quantitative. In addition, the quality of the waveforms is affected by peripheral edema, and cuff placement is commonly affected by the presence of ulceration. Regional transcutaneous oximetry measurements are also unaffected by medial calcinosis, and this modality appears to be reliable for predicting ulcer healing and amputation levels. However, transcutaneous oximetry measurements are actually higher in patients with diabetes and foot ulcers than in nondiabetic patients, possibly because of the effects of arteriovenous shunting. Other limitations, including lack of equipment standardization, user variability, and a large gray area in the interpretation of the measurements, further limit the ability of this test to predict ischemia.Therefore, although these measurements have been used to predict healing in patients without diabetes, high values may not correlate with healing potential in the presence of diabetes. When a patient presents with absent foot pulses in conjunction with gangrene, nonhealing ulceration, or significant tissue loss, it can be assumed that ischemia is present and must be corrected if the limb is to be salvaged. In such patients, arteriography of the entire lower extremity should be performed. The decision to perform arteriography and vascular reconstruction should be made as

soon as infection has started to resolve and signs of systemic toxicity have disappeared; prolonged delays in making this decision may result in further tissue loss and make salvage impossible. For a complete assessment, the arteriogram should include the foot vessels in both lateral and anterior views. Concern over possible contrast-induced renal failure should not be considered a contraindication to high-quality angiography of the entire lower extremity.The incidence of contrast nephropathy is not higher in diabetic patients without preexisting renal disease, even when ionic contrast agents are employed. Selective use of magnetic resonance angiography (MRA), carbon dioxide angiography, and duplex scanning may help minimize the contrast dye load. In patients with preexisting renal disease, use of a nonionic contrast agent, in conjunction with appropriate hydration and judicious administration of kidney-protecting agents, should minimize the risk of contrast-induced nephrotoxicity. N-acetylcysteine, 600 mg twice daily, should be started on the day before the arteriogram and continued for 48 hours, and 0.45 N saline should be given I.V. at a rate of 1 mg/kg/hr, beginning 12 hours before the scheduled arteriogram.7

Management

REVASCULARIZATION

The goals of arterial reconstruction are to restore maximal perfusion to the foot and, ideally, to restore a palpable foot pulse. Possible approaches include endovascular techniques (angioplasty and stenting) [see 6:19 Endovascular Procedures for Lower-Extremity Disease], bypass grafting (with autogenous or prosthetic grafts), and some combination of the two. Ultimately, the choice of procedure in any given case is based on the individual patient's anatomy, the comorbid conditions present, and the results of the preoperative assessment, with the aim being to provide the

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Figure 9 Shown is an infection in the central compartment of the foot from a submetatarsal ulcer that has extended proximally to include the medial compartment (a). A plantar incision through the ulcer and both compartments (including the septum) allows complete dependent drainage (b).

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most durable procedure with the least risk. For example, in rare patients with isolated iliac artery stenoses, angioplasty may be effective by itself, but in patients with multilevel disease, it may have to be combined with an infrainguinal bypass [see 6:17 Infrainguinal Arterial Procedures]. In patients who have previously undergone surgical revascularization, careful consideration should be given to the availability of an autogenous conduit (e.g., an arm vein or the lesser saphenous vein), given the superiority of autogenous vein over prosthetic grafts. As a rule, arterial bypass grafting is required for restoration of the foot pulse.8 Proximal bypass to either the popliteal artery or the tibial and peroneal arteries may restore foot pulses, and preference should be given to these vessels if they are in continuity with the foot. Often, however, because of the presence of more distal obstructive disease, bypass grafting to the popliteal or even the tibial artery will not restore the foot pulse. In such cases, restoration of pulsatile flow to the foot may be accomplished with autogenous vein bypass grafts to the paramalleolar or inframalleolar arteries (e.g., the dorsalis pedis).The vein graft can be prepared as an in situ graft, a reversed graft, or a nonreversed graft, without any significant difference in outcome; the choice of approach should be based on the patient's particular vascular anatomy. As noted (see above), the absence of an ipsilateral greater saphenous vein is not a contraindication to pedal bypass: comparable results may be obtained by using arm vein or lesser saphenous vein grafts. Prosthetic material should seldom, if ever, be used for dorsalis pedis or other extreme distal (inframalleolar) bypass grafts. Active infection in the foot is not a contraindication to pedal bypass, provided that the proximal dorsum of the foot is free of infection and that incisions can be placed in clean tissue planes. The foot should be free of cellulitis, lymphangiitis, and edema before any inframalleolar bypass. Current advances in endovascular therapy are allowing this approach to be used more frequently and successfully in the peripheral vasculature. Lesions determined to be favorable on the basis of arteriography (e.g., short-segment stenoses) may be treated with angioplasty and, possibly, stenting. Similarly, endovascular therapy may be preferred to surgical bypass grafting in high-risk patients and patients who have no suitable autogenous conduit. Ultimately, the goal of endovascular intervention should be the same as that of bypass grafting: to restore the foot pulse and maximal blood flow to the foot.

CONTINUED WOUND CARE

the diabetic foot is usually attributable to unrecognized ischemia, ongoing infection, or poor conventional wound care--not, as a rule, to the absence of more sophisticated wound therapy. Hyperglycemia and malnutrition are common in hospitalized diabetic patients with foot ulceration, and both adversely affect wound healing. Correction of these abnormalities should begin early and continue throughout the wound-healing period. Attention should also be directed toward preventing new foot lesions (e.g., decubitus ulcers on the heel from prolonged bed rest). Heel splints, air mattresses, and leg pillows are all valuable in this regard.

SECONDARY FOOT PROCEDURES

Once the foot is fully revascularized--or once it is clear that the foot was adequately perfused to begin with--care of the foot wound should be continued. Revascularization of a severely ischemic foot ulcer may result in an immediate paradoxical worsening of the infection, and frequent inspection is mandatory postoperatively. New-onset cellulitis, hyperglycemia, or fever should prompt concern regarding potential worsening of the foot infection. Frequent debridement to healthy, bleeding tissue is required more often than not. Wounds should be kept moist, with wet-to-dry dressings avoided in favor of normal saline wet-to-wet dressings. Various adjunctive wound treatments are available, including chemical enzymatic debriding agents, growth factors, and hyperbaric oxygen therapy. Some of these may offer a slight additional benefit in terms of improved healing, but they are expensive; blanket use of these costly modalities is therefore discouraged. Failure of wound healing in

After successful revascularization, secondary procedures on the foot may be performed for maximal foot salvage, with the aim of addressing both the acute problem and the underlying cause. The basic goals of such procedures are (1) to remove infected bone (if present), (2) to restore functional stability, and (3) to reduce the risk of subsequent ulceration. In the forefoot, digital, single metatarsal (ray), or transmetatarsal amputation [see 6:20 Lower-Extremity Amputation for Ischemia] may be performed, depending on the location of the ulcer. Tissue should be handled gently, forceps should not be used, and incisions should be carefully placed. Care must be taken to prevent dead spaces along tendon sheaths, bone splintering, and areas of residual necrosis, all of which can lead to failure of the procedure. If there is persistent infection or an abscess, the wound should be left open. Every effort, however, should be made to perform a closed amputation so as to avoid the time and cost associated with open wound care. This is a particularly important consideration in the occasional diabetic patient with unreconstructible foot ischemia, because open amputations rarely heal in the presence of ischemia. Underlying bony structural abnormalities in the diabetic foot are often the cause of ulceration. Such abnormalities may be corrected with hallux arthroplasty, metatarsal head resection, metatarsal osteotomy, or sesamoidectomy; if ulceration is present, these procedures may be combined with ulcer excision. Similarly, ulceration on a previous transmetatarsal amputation may be the result of an equinovarus deformity (from disrupted tendons and a decrease in calcaneal inclination).This problem should be treated with revision of the transmetatarsal amputation (perhaps in conjunction with ulcer excision) and biomechanical correction (e.g., Achilles tendon lengthening or, in more severe cases, posterior tibial tendon release). Heel lesions are particularly formidable, and there is considerable confusion regarding how best to manage them. Generally, dry eschars with no evidence of deep infection or abscess may be treated with offloading alone so as to allow healing beneath the eschar in the fully revascularized foot. In patients with chronic ulceration or osteomyelitis, partial calcanectomy may be considered.The presence of calcaneal osteomyelitis may be determined by means of probing or adjunctive studies such as MRI [see Figure 7]. Primary closure is occasionally possible, but given the relatively fixed nature of the heel, either secondary healing or some type of flap coverage is usually indicated. Both local and free flaps may be used in the fully revascularized foot. After any type of surgery of the diabetic foot, frequent postoperative observation of the wound is mandatory. Delays in

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ACS Surgery: Principles and Practice

7 DIABETIC FOOT -- 11

6 VASCULAR SYSTEM

healing or wound breakdown should immediately raise the possibility of infection or unrecognized ischemia and should trigger the appropriate workup.

PREVENTIVE FOOT CARE

Once the foot has healed, preventive measures should be initiated to prevent future ulceration. Foremost among these measures is patient education, focusing on general hygiene (e.g., daily washing and moisturizer use) and daily inspection of the feet. Walking barefoot, employing heat pads, wearing thong

sandals, and using caustic over-the-counter foot medications should all be strongly discouraged. Neuropathy continues to be the most common cause of diabetic foot ulceration, and its presence is a strong predictor of the likelihood of future ulceration. As noted (see above), inability to feel a Semmes-Weinstein 5.07 monofilament when it is pressed to the skin correlates well with an increased risk of foot ulceration. In addition, abnormal pressure points (secondary to mechanical deformity of the foot and motor neuropathy) can be identified by means of pedobarography, a procedure in which plantar pressure is measured on specialized contour plots as the patient walks on a pressure-sensitive platform. Identification of any high-pressure areas can facilitate the construction of specific, custom-molded orthotics and insoles to help in offloading.

References

1. LoGerfo FW, Coffman JD: Vascular and microvascular disease of the foot in diabetes. N Engl J Med 311:1615, 1984 13:671, 1996 5. Joshi N, Caputo GM, Weitekamp MR, et al: Infections in patients with diabetes mellitus. N Engl J Med 341:1906, 1999 Moran GJ, Krishnadasan A, Gorwitz RJ, et al: Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med 355:666, 2006 Tepel M, van der Giet M, Schwarzfeld C, et al: Prevention of radiographic-contrast-agent-induced reductions in renal function by acetylcysteine. N 8. Engl J Med 343:180, 2000 Akbari CM, LoGerfo FW: Distal bypasses in the diabetic patient. Current Techniques in Vascular Surgery. Yao JST, Pearce WH, Eds. McGraw-Hill, New York, 2001, p 285

2. Akbari CM, LoGerfo FW: Diabetes and peripheral vascular disease. J Vasc Surg 30:373, 1999 3. Caputo GM, Cavanagh PR, Ulbrecht JS, et al: Assessment and management of foot disease in patients with diabetes. N Engl J Med 331:854, 1994 Fox HR, Karchmer AW: Management of diabetic foot infections, including the use of home intravenous antibiotic therapy. Clin Podiatr Med Surg

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Acknowledgment

Figure 8 Tom Moore.

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