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Fitridge R, Thompson M, editors. Mechanisms of Vascular Disease: A Reference Book for Vascular Specialists [Internet]. Adelaide (AU): University of Adelaide Press; 2011.

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Mechanisms of Vascular Disease: A Reference Book for Vascular Specialists [Internet].

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26Pathophysiology and Principles of Management of the Diabetic Foot

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Introduction

The incidence of diabetes continues to grow at a staggering pace. The United States’ Centers for Disease Control and Prevention estimate that 23.6 million people or 7.8% of the U.S. population has diabetes, with 1.6 million new cases being diagnosed each year.1,2 These figures are even more astonishing when one considers worldwide estimates. Close to 4 million deaths in the 20–79 year old age group may be attributed to diabetes in 2010, accounting for 6.8% of global all-cause mortality in this age group.3 The number of people with diabetes worldwide is expected to reach 366 million people by 2030, more than double the estimated 177 million people affected with the disease in 2000.2 The increased disease prevalence is accompanied by an increase in associated comorbidities. The literature estimates that patients with diabetes have nearly a 25% lifetime risk of developing a foot ulcer with more than 50% of these ulcers becoming infected and requiring hospitalization.4 In fact, at least 20% of all diabetes-related hospital admissions are due to diabetic foot ulcers. Associated with foot ulcers and infection is the incidence of amputation. It has been conservatively reported that, worldwide, a major amputation takes place every 30 seconds with over 2500 limbs lost per day.5 At least 60% of all nontraumatic lower extremity amputations are related to complications of diabetes.1 people with diabetes who have had one amputation have a 68% risk of having another in the next 5 years and have a 50% mortality rate in the 5 years following the initial amputation.6 It is estimated that up to 85% of diabetic foot-related amputations could be prevented through prompt intervention and with centers directed at educating individuals about proper foot care.

The economic impacts on the patient, national healthcare system and economy also impose a great burden. Healthcare expenditures on diabetes are expected to account for 11.6% of the total healthcare expenditure in the world in 2010.3 The estimated global costs to treat and prevent diabetes and its complications are expected to total at least 376 billion USD in 2010, with some projections exceeding 490 billion USD. Between 22 and 27% of the total diabetes costs are attributable to lower extremity disease.3,7

Pathophysiology of the Diabetic Foot

Neuropathy

Neuropathy, or the loss of protective sensation (LOPS) of the lower extremity, is the predominant etiology for diabetic foot ulceration. The absence of this most basic nociceptive mechanism results in the patient’s inability to perceive local foot trauma both from intrinsic factors such as abnormal or faulty foot mechanics or deformity, as well as extrinsic factors such as foreign objects or improper footwear. These factors place the foot at increased risk for developing an ulcer, which can lead to amputation.

Neuropathy can be subdivided into sensory, motor, and autonomic categories.

Sensory neuropathy typically begins distally, moving proximally, and is symmetrical. It is often described as a ‘stocking-glove’ distribution.

Motor neuropathy results in intrinsic muscle wasting, causing a progressive deformity such as hammertoe, claw toe, and plantar flexion deformities of the metatarsals. These deformities can cause an increase in focal pressure at the areas of the interphalangeal joints of the digits and beneath the metatarsal heads, respectively, increasing the probability of ulcer formation.

Autonomic neuropathy is associated with pathology of the sympathetic nervous system. In the lower extremity, this usually results in the absence of sweat production causing drying and scaling of the skin, increasing the likelihood of cracking and fissuring. These cracks or fissures, especially in the heel, may then serve as a portal of entry for bacteria, creating an increased chance of infection.

Other factors precipitating diabetic foot ulcers have been identified and are listed in Table 26.1. A risk factor classification scheme has been developed based on LOPS and other comorbidities (i.e. vascular disease) (Table 26.2). This classification system provides treatment recommendations and suggested follow-up time.

TABLE 26.1. Risk Factors For Ulceration.

TABLE 26.1

Risk Factors For Ulceration.

TABLE 26.2a. American Diabetes Association Risk classification for The Diabetic Foot.

TABLE 26.2a

American Diabetes Association Risk classification for The Diabetic Foot.

Structural abnormalities/gait abnormalities

Structural deformities of the foot and ankle can be a potential cause of increased pressure and subsequent ulceration. The development of foot ulceration is often based on a biomechanical abnormality.8,9 It is important to evaluate both feet of a patient for any potential problem areas. As described earlier, motor neuropathy can lead to the loss of intrinsic foot musculature causing a deformity (and subsequent overpowering of the intrinsics by the larger extrinsic muscles). Identification and management of any of the following will assist in prevention of potential ulceration: hammertoe, claw toe, bunion, tailor’s bunion (bunionette), hallux limitus/rigidus, flat feet, high arched feet, Charcot deformities, or any postsurgical deformities such as amputations. Limited joint mobility should also be evaluated as it can cause an increase in vertical and shear force in certain areas, particularly to the plantar hallux, and lead to tissue breakdown. The Achilles tendon should be evaluated for any type of functional shortening causing equinus deformity. It is common to find an increase in glycosylation of soft tissues and tendons causing contracture of the muscles in the posterior compartment of the leg.10-12 This will cause an increase in plantar pressures in the forefoot making this area more prone to breakdown.

Gait evaluation and muscle testing should also be conducted to evaluate any potential abnormality with ambulation and muscle strength. Testing of the muscles in the lower extremity should be done both actively and passively, weight bearing and non-weight bearing. Plantar foot pressures can also be assessed with the use of a Harris ink mat or pressure sensitive foot mat.

Angiopathy

In combination with the risk factors for ulceration discussed above, the presence of vascular occlusive disease increases the risk of potential amputation. Vascular disease is a common finding in individuals with long-standing diabetes. While vascular insufficiency alone is not usually the primary cause of ulceration, inadequate perfusion can inhibit ulcer healing, leading to further tissue necrosis and the inability to clear infection. Table 26.3 provides a list of other potential risk factors for amputation. Most cases of vascular disease in individuals with diabetes, interestingly, affect the infrapopliteal vessels with relative sparing of the pedal vessels. In many instances, this allows for a distal bypass to a pedal target artery in order to increase the blood flow to the foot (Figure 26.1). The vascular examination is addressed in further detail later in this chapter.

TABLE 26.3. Risk Factors for Amputation:

TABLE 26.3

Risk Factors for Amputation:

FIGURE 26.1. Dorsalis Pedis Bypass.

FIGURE 26.1

Dorsalis Pedis Bypass.

Diagnosis

History and rapid visual screening

A thorough history and physical examination of each patient presenting with diabetic foot pathology should include a history of pedal wounds, history of prior amputations, and lower extremity vascular interventions.13,14 physical examination should note the types of deformities present, neurological status, vascular status, and dermatological presentation. The patient should be instructed to remove both shoes and socks for their examination. A systematic approach should be taken in order to avoid missing any important aspects of the examination. All surfaces of the foot and ankle should be evaluated including the nails, digits, interdigital webspaces, the soles, and the heels, inspecting for cracks, blisters or bullae, hyper/hypopigmentation, fissuring, calluses, and ulcers. The footwear should also be inspected for signs of wear patterns, foreign bodies, and any irregularities. Any gross deformities as described above can be identified during this rapid visual screening.14

Neurological examination

As stated earlier, peripheral sensory neuropathy is the major risk factor for the development of a diabetic foot ulcer. There are many simple, noninvasive examinations that can be performed to test and monitor sensation. A simple history of neuropathic symptoms such as tingling, burning, numbness, the feeling of insects crawling on the feet (formication) can help to identify those patients at risk for developing foot ulceration.15

Monofilament testing

One of the most common methods used to assess neuropathy is the use of the Semmes-Weinstein monofilament (10-g) wire.14,15 The nylon monofilament is placed on ten different pre-determined locations on the foot and pressed down manually until there is a slight bend in the wire (Figure 26.2). The patient is instructed to say ‘yes’ if he or she thinks they feel slight pressure or sensation. If the patient is unable to feel the sensation at two or more locations then it is safe to assume that protective sensation is lost.

FIGURE 26.2. Proper use of S-W Monofilament when applied to the foot. Slight bend of the filament noted.

FIGURE 26.2

Proper use of S-W Monofilament when applied to the foot. Slight bend of the filament noted.

Vibration testing

Vibratory perception testing can be assessed utilizing several different modalities. The more traditional method of testing is by the use of a 128-Hz tuning fork. The tuning fork is struck and then placed on a prominent bony surface of the foot, such as the great toe or metatarsal head. The patient is instructed to identify when the vibration stops.

As an alternative, a vibratory perception threshold monitor (VPT – Diabetica Solutions, San Antonio, Texas, USA) (Figure 26.3) can be used to test for vibration perception threshold and is useful in identifying those at high risk for development of an ulcer. The instrument consists of a hand piece with a testing probe on the end, a motor, rheostat, and voltmeter. The probe is held gently on the distal aspect of each hallux, or distal most prominent area. The rheostat is slowly increased until the patient senses the vibration. Once the patient identifies the sensation, the rheostat is then decreased until the sensation is no longer felt. The average value of the two numerical readings is taken and the level of sensation is documented to the location where the numbers were obtained. Average values above 25 Volts are considered positive for neuropathic changes.14

FIGURE 26.3. Vibratory Perception Threshold Monitor (VBT).

FIGURE 26.3

Vibratory Perception Threshold Monitor (VBT).

Dermatologic examination

Following assessment for any loss of sensation, evaluation of the integumen is a critical part of the foot screening. The skin can be evaluated for color, texture, turgor, quality, and presence of any areas of dryness or fissures. Calluses, if present, can be problematic as they indicate areas of increased pressure and an ulcer can form under the hyperkeratotic lesion, which may cause hemorrhage beneath the callus. Debridement of these areas is recommended in order to reduce a potential focus of pressure.16,17

Appearance of the nails should also be noted. If there are nails that are incurvated or ingrown, these could be a potential area for skin breakdown and possible infection. Other nail issues to be aware of are onychomycosis (fungal nails), dystrophic nails, atrophy or hypertrophy, or paronychia (infected ingrown nail), as all can be potential problems.

Evaluation for any ulceration to the foot or lower leg should be assessed. Important characteristics of ulcers are depth, size, presence of fibrotic or granulation tissue, location, and whether or not the area appears to be infected.

Anatomy of occlusive disease – vascular examination

For decades, clinicians incorrectly believed that ischemia in diabetes was due to microvascular occlusion of arterioles, so-called small vessel disease.18 However, this assumption has been disproven by subsequent study.19,20 Diabetic vascular disease is a macrovascular phenomenon, commonly affecting infrapopliteal arteries with calcified stenoses and occlusions. More than 90% of patients have sparing of at least one major artery at the ankle level. The peroneal artery is often the last infrapopliteal artery to occlude; it provides blood flow to the foot through anterior and posterior perforating branches to the tibial arteries. Bypass to an infrapopliteal artery usually provides adequate blood flow to the foot, although some patients appear to have more compartmentalized pedal flow. Some patients with heel ulcers remain slow to heal after dorsalis pedis artery bypass, suggesting inadequate pedal circulation.21 Thus, if possible, patients with ischemic ulcers should preferentially receive a bypass to the arterial bed directly supplying the ulcer; this axiom is especially pertinent to patients with large heel ulcers.

Prediction of wound healing: assessment of perfusion

Pedal blood flow should be assessed before any surgical intervention on the diabetic foot. Absence of pedal pulses, dependent rubor, pallor on elevation, and loss of hair are clinical signs of advanced peripheral artery disease. If there is concern for ischemia, noninvasive testing is an appropriate initial diagnostic choice. The ankle-brachial index (ABI), while nearly 100% specific for PAD in non-diabetics, can be falsely elevated (>1.3) in diabetic patients due to medial calcinosis of the affected arteries. More useful are the systolic toe pressure and the toe-brachial index, since digital arteries are seldom calcified in those with diabetes.22 Additional tests to assess foot perfusion include skin perfusion pressure,23,24 and transcutaneous oxygen pressure (TcPO2).25-27

Currently there is no single test or combination of tests that can always predict wound healing. Apelqvist and colleagues prospectively studied 314 consecutive patients with diabetic foot ulcers.22 Primary healing occurred in 85% of patients with a toe pressure greater than 45 mmHg, while only 36% of patients with a toe pressure of 45 mmHg or less healed without an amputation. No patients with an ankle pressure less than 40 mmHg healed primarily. Kalani and colleagues also prospectively studied 50 patients with diabetic foot ulcers over a 12-month period.26 A toe pressure of at least 30 mmhg had a 15% sensitivity, 97% specificity, and 67% positive predictive value for wound healing. In that same study, TcPO2 was also evaluated; a TcPO2 of at least 25 mmHg had an 85% sensitivity, 92% specificity, and 79% positive predictive value for wound healing. Likewise, Carter and colleagues reported that TcPO2 measurements correlated significantly with the risk of major amputation, with a relative risk of 2.55 for a TcPO2 of 20 mmHg of less and 2.22 for a TcpO2 of 30 mmHg or less.27 In addition, an ankle pressure of 50 mmHg or less had a 5.83 relative risk of major amputation. Skin perfusion pressure (SPP) has also been used to predict wound healing. Faris evaluated 61 diabetic subjects with wounds and found that only 5% healed with an SPP less than 40 mmHg, while 88% of patients healed with an SPP higher than 40 mmHg.23 Yamada and colleagues studied 211 subjects, half of who were diabetic, and compared SPP to other noninvasive methods to predict wound healing. They found that SPP was superior to ankle pressure, toe pressure, or TcpO2 for predicting wound healing. An SPP of 40 mmHg had a 72% sensitivity and 88% specificity for predicting wound healing.24 Furthermore, the accuracy of prediction increased when a toe pressure greater than 30 mmHg was combined with SPP.

Arterial imaging

A number of techniques of arterial imaging are currently in use: arterial duplex scanning, computed tomographic angiography (CTA), magnetic resonance angiography (MRA), and digital subtraction arteriography (DSA). Duplex scanning is non-invasive and does not require administration of contrast. However calcification of the infrageniculate arteries can be problematic in many patients. Both CTA and MRA have the advantage of being noninvasive; however, both these studies are limited in diabetic patients with impaired renal function. CTA requires a large bolus of iodinated contrast, and the gadolinium-based contrast used in MRA has been associated with nephrogenic systemic fibrosis.28 In addition, MRA tends to overestimate the degree of arterial stenosis. Using selective catheterization techniques, DSA can produce high-quality images with low volumes of iso-osmolar contrast, thereby minimizing contrast-induced nephropathy. In addition, carbon dioxide can be selectively utilized as a ‘contrast’ agent; it is not nephrotoxic and quickly dissolves in blood before travelling to the lungs where it is readily expelled. DSA also has the advantage that angioplasty and stenting, if appropriate, may be performed at the time of diagnostic arteriography (Figure 26.4).

FIGURE 26.4. 56 year-old man with diabetes, renal insufficiency (serum creatinine 0.180mmol/L), absent foot pulses and non-healing dorsal foot ulcer for 6 weeks. Angiography showed normal arteries to the trifurcation and severe tibial artery occlusive disease with a long stenosis in dominant posterior tibial artery. Angioplasty markedly improved circulation and the wound healed with debridement, negative pressure wound therapy, and subsequent split-thickness skin graft placement.

FIGURE 26.4

56 year-old man with diabetes, renal insufficiency (serum creatinine 0.180mmol/L), absent foot pulses and non-healing dorsal foot ulcer for 6 weeks. Angiography showed normal arteries to the trifurcation and severe tibial artery occlusive disease with (more...)

Soft tissue imaging

Imaging studies should be conducted to evaluate any underlying bone or soft tissue deformity. The diabetic foot is prone to many common and uncommon infectious and non-infectious processes due to the combination of vascular and neurological impairments. Imaging studies may be difficult to interpret and may lack specificity; therefore, a ‘shotgun’ approach to imaging studies should be avoided. Appropriate imaging studies should be ordered to establish or confirm a suspected diagnosis in order to properly manage the patient. For example, it is very difficult to differentiate acute Charcot arthropathy from osteomyelitis on plain radiographs. The reliability of imaging studies is diminished in the presence of arterial occlusive disease, Charcot arthropathy or after recent surgery or trauma.29 A thorough history and physical examination and clinical overview by the treating physician must be correlated with the imaging studies in order to interpret them correctly.

Plain radiographs should be the initial study considered for patients that present with any signs or symptoms of foot problems. These studies help to identify osteomyelitis, fracture, dislocation, foreign bodies, soft tissue gas, arterial calcification as well as any other biomechanical or structural deformity. It should be noted that it might take time for acute osteomyelitis to be detected on plain film radiographs and serial radiographs or magnetic resonance imaging (MRI) should be considered if osteomyelitis is strongly suspected.

Computed tomography (CT) scans may be indicated if plain films fail to depict a suspected bone or joint deformity. CT offers higher anatomic detail and resolution in regards to bone and joints. 3-D CT reconstruction can be done to provide a 360-degree view and increased visualization of any suspected abnormality.

MRI is usually preferred over a CT scan for suspected osteomyelitis due to the increased resolution of the image. MRI scans also allow the physician to visualize the extent of the infection- osteomyelitis, deep abscess and septic joints, but also other soft tissue pathology such as tendon rupture.

Bone scans can also provide some useful data when evaluating the diabetic foot. Technetium-99 methylene diphosphonate (Tc-99 MDP) as well as indium-111 bone scans can be useful in determining the presence of osteomyelitis. However, while bone scans and other scintigraphic techniques are certainly possible tools to employ, their lack of specificity often makes their specific utility problematic, particularly if used in isolation. Advanced imaging studies beyond plain radiographs should not be routine. Rather, they should only be obtained to answer specific clinical questions when the results will alter management (e.g. concern over deep space infection with equivocal clinical picture).

Classification Systems

Diabetes mellitus foot risk classification

Based on a thorough history and physical examination, each patient should then be classified and assigned to a specific foot risk category as outlined in Table 26.2a. These categories were designed to direct and expedite the referral process to the necessary specialist and should also serve as a guide for subsequent follow-up visits. Increased categorical levels are associated with increasing risk for ulceration, hospitalization, and amputation.

University of Texas wound classification system

While many wound classification systems exist, The University of Texas (UT) ulcer classification system was developed to provide a more uniform evaluation of diabetic foot wounds. Like other classification systems the UT wound classification system builds on the depth-ischemia classification however, the UT system also considers infection.30 The presence of infection and ischemia has been found to be more strongly predictive of outcome than the wound depth alone.31 the UT system uses a 4 by 4 matrix (classes A to D, wound depths 0 to 3) and evaluates 3 factors of ulceration, which include depth, infection, and peripheral arterial disease (PAD).32 the frequency and level of amputation increases in deeper wounds and in the presence of infection and PAD.30 Regardless of which specific classification is used, the key factors of depth, infection and ischemia should generally be communicated in some form. This classification is listed in (Table 26.2b).

TABLE 26.2b. The University of Texas (UT) Wound classification System.

TABLE 26.2b

The University of Texas (UT) Wound classification System.

Clinical Problems and Principles of Management

Ulceration

Initial presentation of the diabetic foot usually entails the presence of an open ulcer, located on the plantar aspect of a patient’s foot. Most patients will not suspect an ulcer on the bottom of their foot until they, or a loved one, notices blood either on the floor after walking or on a sock. Advising the patient that ambulation is contraindicated with an open ulcer is often challenging especially if the patient is neuropathic, as they have lost the ‘gift of pain.’33 However, reduction of pressure to the foot is essential for treatment. By effectively off-loading the area, the risk of continued trauma and resultant infection is decreased.

Epidemiology and risk factors

Ulceration of the diabetic foot is one of the single most common problems for which medical assistance is sought in a diabetic individual. Up to 25% of patients with diabetes will have a foot ulceration during their lifetime.4 Remarkably, at least 50% of those ulcerations will become infected, and in 20% of those cases an amputation is required.34 There are 81,000 major amputations performed on individuals with diabetes in the United States annually. Conservatively, 60% of all non-traumatic amputations occur in the diabetic patient.35 Studies have shown that after a major amputation the contralateral limb develops a serious lesion in 50% of cases.36 The 5 year adjusted mortality rate after a major amputation of a limb is 46%;6 this is alarming and is higher than the mortality rate for many forms of cancer. It has also been shown in more than 85% of lower extremity amputations a wound was a critical aspect of the causal pathway.8,34,37,38 The cost of treating diabetic foot ulcers is also growing at a staggering pace, reaching nearly $30 billion in the United States in 2007.39

Offloading

Numerous products are available to assist in redistributing pressure over a larger unit area (off-loading) on the foot. Some examples include removable cast walkers, non-weight bearing casts with crutch/walker assist, wedge sandals (either forefoot or heel wedge), healing sandals with a multilaminar, multidurometer foot bed. However, the choice of modality should be chosen with respect to the patient’s functional status. For example, if a patient presents with a plantar forefoot ulcer, a wedge shoe that does not allow the forefoot to bear weight would be an appropriate device. However, if the patient is not properly educated on use of the device and/or has issues with balance, the offloading modality could cause the patient be unstable when walking. In regards to diabetic shoes, whether custom-made or off the shelf, it is important to keep in mind one key fact. While diabetic shoes are effective in preventing ulcerations, they are (in general) not very effective in healing them.

For many years the gold standard in offloading an ulceration on the foot has been the total contact cast (TCC).40 This fully weight-bearing cast consists of a multiple layers of both fiberglass and plaster with minimal padding. When applied properly, the TCC allows the patient to be ambulatory. The TCC redirects pressure from the bottom of the foot, which is then redistributed over the bottom of the entire foot and up the cast. Some disadvantages of using a TCC is the time it takes to apply, the bulkiness for the patient, and the fact that the patient must wear the cast for 1 week intervals requiring weekly visits to the clinic. Newer TCC variants have reduced the time required for application of a traditional device whilst retaining many of the desirable therapeutic characteristics. An example of newer TCC variants can be seen in Figure 26.5.

FIGURE 26.5. Anterior and lateral view of cast boot, which allows ambulation.

FIGURE 26.5

Anterior and lateral view of cast boot, which allows ambulation.

Recent studies have evaluated the use of a removable cast walker rendered irremovable. This technique has been termed the ‘instant total contact cast (iTCC).’ This can be fabricated by simply adding a layer of fiberglass, cohesive bandage, or plaster around the leg portion (Figure 26.6). The iTCC has proven to be an effective and easy offloading device that ensures patient adherence.41

FIGURE 26.6. Example of an instant total contact cast (iTCC) with fiberglass wrapped around the leg portion, of an off-loading walking boot, to make it irremovable.

FIGURE 26.6

Example of an instant total contact cast (iTCC) with fiberglass wrapped around the leg portion, of an off-loading walking boot, to make it irremovable.

In many instances, proper off-loading may be all that is necessary to achieve wound healing. However, if wound healing fails in the midst of proper off-loading, adequate blood flow, and satisfactory nutritional status, surgical intervention may be warranted.

Non-vascular surgical treatment

Surgical management of the diabetic lower extremity can be a challenging and frustrating task, but can be ultimately rewarding both to the physician and patient upon healing of an ulcer and correction of the underlying cause of the deformity. Surgery in the absence of critical limb ischemia is based on three fundamental principles: presence or absence of neuropathy (LOPS), presence or absence of an open wound, and presence or absence of acute limb-threatening infection.42

A classification system has been developed outlining non-vascular surgical treatment of patients with diabetes and has been divided into four categories and highlighted in Table 26.4 and is based on indications and perceived risk.42,43

TABLE 26.4. classification of non-vascular Diabetic Foot Surgery.

TABLE 26.4

classification of non-vascular Diabetic Foot Surgery.

Class I: Elective

The goal of elective surgery is to reduce or eliminate any pain associated with a particular deformity and improve function.42 Examples of these deformities include bunions, hammertoes and bone spurs, all in patients without peripheral neuropathy and with a low chance for ulceration. Basically any type of reconstructive surgical procedure can fall into this category with the exception of an amputation. Rarely are amputations done as an elective procedure. Only in the case of severe deformity or instability from a previous injury or surgical procedure, will an amputation be considered. Assuming good glycemic control, patients grouped to this class are not at any increased risk for the development of complications than corresponding patients without diabetes.43

Class II: Prophylactic

Procedures in this class are indicated to alleviate a deformity in a patient who is neuropathic however does not have the presence of an ulcer.42 The goal of prophylactic surgery is to reduce the plantar sheer and vertical stresses. Many procedures for prophylactic surgery would be considered elective if the patient did not suffer from neuropathy. Several examples of procedures in this class include a Charcot foot reconstruction, a metatarsal head resection, a Keller arthroplasty, an a chilles tendon lengthening or a hammertoe repair.

Class III: Curative

Curative surgery often is identical to prophylactic surgery with the exception that procedures in this class are designed to speed the healing rate of an open wound but also to eliminate any potential recurrence of the ulceration.42 Surgical procedures frequently utilized in this category may include exostectomy, digital arthroplasty, sesamoidectomy, single or multiple metatarsal head resection, joint resection or partial calcanectomy as well as Achilles tendon lengthening. Some surgeons may also elect to combine a plastic surgical flap and/or skin graft to help expedite healing.

Class IV: Emergency (Urgent)

Urgent procedures are performed to limit the spread of acute, limb and potentially life-threatening infection. Most often these procedures are done in the presence of significant ischemia. They require the removal of all infected and necrotic tissue to the level of viable soft tissue and bone and usually involve some level of amputation. When at all possible these procedures should be performed to allow for maximum amount of function to the extremity to be maintained.

With respect to any of the above classifications it is best to evaluate the vascular status of the patient to consider the necessity of any prior or subsequent arterial procedure that may be needed.42

Post-operative management

The management of the diabetic foot patient in the post-operative setting is much the same as a patient without diabetes. Adequate pain control, rest, elevation of the extremity and proper dietary intake are all recommended. One key difference is the timeframe for protected weightbearing or complete non-weightbearing. It is often stated that diabetics require twice the healing time as a non-diabetic. That means that if a simple bunionectomy in a non-diabetic requires 4 weeks of protected weightbearing, the same procedure in a diabetic may require 6-8 weeks of protected weightbearing. The same can be said for a procedure requiring non-weightbearing. Most surgical procedures done for class 1–3 can be managed with protected weightbearing.43 most class 4 procedures will require some period of non-weightbearing or protection. The same can be said for any type of surgical implant or skin closure technique. For example, leaving skin sutures in place for an additional 1–2 weeks is advantageous over early removal to allow for the tissue to heal.

Surgical and non-surgical complications in this patient population are to be expected. Joint dislocation, bone fracture, surgical incision dehiscence, new ulceration or re-ulceration, and infection are all commonplace, not infrequently leading to re-hospitalization. Proper management by use of off-loading, local wound care, antibiotics and patient education will all be beneficial when dealing with any potential complication. It should also be kept in mind that not all diabetic foot complications can be prevented, but all can be adequately managed.

Infections

The Infectious Diseases Society of America (IDSA) has produced a classification system for diabetic foot infections, which is based on clinical signs and symptoms (Table 26.5). The IDSA divides infections into four categories, uninfected, mild, moderate, and severe.44 These guidelines and classification system has become a reliable clinical predictor of the outcome of a diabetic foot infection.45 It is important that initial antibiotic therapy cover the broad range of potential aetiological organisms in the diabetic foot until targeted therapy can be instituted once appropriate cultures have been obtained.

TABLE 26.5. Infectious Diseases Society of America (IDSA) Diabetic Foot Infection classification.

TABLE 26.5

Infectious Diseases Society of America (IDSA) Diabetic Foot Infection classification.

Charcot arthropathy

Charcot arthropathy is defined as a progressive condition characterized by joint dislocation, pathologic fractures, and severe destruction of the pedal framework (Figure 26.7). It is typically seen individuals with neuropathy and can be easily confused with acute infection or osteomyelitis. A patient will often present with a red, hot, swollen extremity with no sign or history of ulcer or break in the skin (Figure 26.8). Usually all other constitutional signs of infection are absent and laboratory values are within normal limits.

FIGURE 26.7a & b. X-ray of acute Charcot arthropathy. This plain x-ray demonstrates degenerative changes in the tarso-metatarsal joints (Lis-franc joints) with joint space narrowing and subchondrial sclerosis, consistent with Charcot arthropathy. Also noted is bone destruction and pathological fracture of the proximal phalanx of the 4th toe, indicative of osteomyelitis of this bone.

FIGURE 26.7a & b

X-ray of acute Charcot arthropathy. This plain x-ray demonstrates degenerative changes in the tarso-metatarsal joints (Lis-franc joints) with joint space narrowing and subchondrial sclerosis, consistent with Charcot arthropathy. Also noted is bone destruction (more...)

FIGURE 26.8. a) Anterior view of acute Charcot. Notice the erythema and edema to the forefoot.

FIGURE 26.8

a) Anterior view of acute Charcot. Notice the erythema and edema to the forefoot. b) Lateral view of acute Charcot. Marked flattening of the medial arch with associated edema and erythema.

Pedal manifestations of Charcot foot result in a debilitating deformity frequently leading to an amputation. While not well understood, several theories regarding the development of the disorder exist with many authors believing it is caused by a combination of the neurovascular and neurotraumatic theories. Neuropathy and trauma seem to be the common event preceding the development of an acute Charcot foot. As a result of the trauma and associated autonomic neuropathy, blood flow to the foot increases causing osteopenia and weakening of the bony structure. Fracture is often associated with unrecognized injury or minor trauma that might otherwise appear innocuous.46,47 An unfortunate cycle continues as the patient ambulates, without pain, causing further destruction of the foot.

The initial diagnosis of acute Charcot is often clinically based on the characteristics listed above. It can become complicated as patients often present with a concomitant ulcer, which raises questions of possible osteomyelitis. Someone presenting with the previously mentioned characteristics and lack of an open ulcer are more pathognomonic of acute Charcot arthropathy. Routine laboratory values are often of little use in diagnosing Charcot. They are valuable, however, with respect to excluding potential infection. An elevated WCC with a left shift is often seen with acute infection and not with acute Charcot. Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level may also be elevated in acute infection but they often respond to any inflammatory process and thus are nonspecific. The most important diagnostic aid in determination of acute Charcot is the high index of clinical suspicion when a neuropathic patient presents with a deformed or swollen foot.

Treatment of Charcot consists of immediate immobilization and stress reduction. Most physicians would recommend strict non-weight bearing to the affected limb. However, this then subjects the contralateral extremity to increased pressure thereby predisposing it to repetitive stress and the potential for ulceration or even acute Charcot.48 Nonetheless, non-weight bearing by means of a short leg plaster or fiberglass cast, or TCC remains the gold standard in the acute phase of the disease.40

Following the initial period of off-loading, skin temperatures and edema of the affected extremity will decrease. At this point protected weight bearing is permitted, usually with some sort of assistive device. This can be achieved through use of a Charcot restraint orthotic walker (CROW) (Figure 26.9), total contact cast, fixed ankle walker, bivalved casts or patellar tendon-bearing braces, to name a few. The average time of rest and immobilization in a patient that has undergone an acute Charcot event is 4 to 6 months before returning to permanent and proper footwear.

FIGURE 26.9. Charcot Restraint Orthotic Walker (CROW) boot. A patient is able to ambulate with this device once the acute phase has passed.

FIGURE 26.9

Charcot Restraint Orthotic Walker (CROW) boot. A patient is able to ambulate with this device once the acute phase has passed.

If offloading is unsuccessful or if the deformity is unstable, reconstructive surgery may be considered. The goal of surgical intervention in the Charcot foot is to provide a stable, plantigrade foot that may be appropriately accommodated with proper shoe gear.49 Most surgical interventions consist of an exostectomy for prominent plantar bony prominences or ‘rocker-bottom’ deformities that cause ulcerations and could lead to potential infection.50 Other, more complex procedures such as arthrodesis of the midfoot and hindfoot, use of external fixation, and intramedullary nail have also been used in the latent stage of the Charcot disease process.

Prevention

Diabetic foot care requires an interdisciplinary team approach given the progressive nature of the disease in the foot. It is unlikely that one individual medical or surgical specialty is able to manage all aspects of diabetic lower extremity disease and appropriately manage these patients. Recent evidence suggests a reduction in major amputation rates following the development of an interdisciplinary approach to limb salvage.51 The components of a limb salvage team are predicated on the pathology at presentation. The core of the team typically starts with clinicians caring for the structural aspects of the foot (podiatrists), along with clinicians caring for the vascular integrity of the lower extremity (Vascular Surgeons). Other specialties of the team, to add a more comprehensive care model may include Endocrinology, Infectious Diseases, Orthopaedic surgery, Physiotherapy, plastic Surgery, Nursing and Orthotics/Prosthetics.

Vasculopathy and neuropathy are two major contributors to diabetic foot disease and subsequent ulceration. Therefore, appropriate utilization of an interdisciplinary team approach, as stated above, will help to address the varying factors associated with lower extremity ulceration and reduce amputation. A diabetic rapid response acute foot team has been proposed in an effort to combine the knowledge of certain specialties to promote limb salvage.52 This is an interdisciplinary team model whose core involves the ability to rapidly diagnose and provide treatment to patients with lower-extremity complications of diabetes, utilizing seven basic skill sets (Table 26.6). AT the forefront of the team are members from podiatry (Toe) and members from vascular surgery (Flow). These specialties, with adjunctive teams added as necessary, combine to collectively posses the ability to perform the 7 essential skills, stated above, to be effective in promoting limb salvage. This model has been effective at the University of Arizona’s Southern Arizona Limb Salvage Alliance (SALSA) in which the Vascular Surgery/Podiatry team approach has been able to significantly reduce the number of major diabetes-associated lower-extremity amputations as well as provide a framework for prevention of diabetic ulcers. In fact, abundant data suggest that establishing such comprehensive diabetic foot care teams can significantly reduce the incidence of major amputation in both community and academic hospital settings.53

TABLE 26.6. Seven Essential Skills of a Diabetic Rapid Response Acute Foot Care Team (DRRAFT).

TABLE 26.6

Seven Essential Skills of a Diabetic Rapid Response Acute Foot Care Team (DRRAFT).

Conclusion

Treating the diabetic foot, but moreover the patient with diabetes, is an extremely challenging yet rewarding experience. As the incidence continues to grow worldwide the likelihood of people with diabetes constituting a significant proportion of a vascular and podiatric surgical practice is quite high. Common, seemingly trivial foot problems such as calluses, corns, ingrown nails, and dry scaly skin, may provide sufficient trauma to develop into limb-threatening problems. Early recognition and diagnosis of these factors combined with aggressive preventive measures and a multidisciplinary team approach will all be beneficial in the treatment of the diabetic foot with the ultimate goal of amputation reduction and prevention.

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© The Contributors 2011.
Bookshelf ID: NBK534268PMID: 30485022

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