Diabetic Foot Problems: Keys to Effective, Aggressive Prevention

About 21 million Americans have diabetes mellitus.¹ In 2002, an estimated $92 billion, or nearly 11% of health care costs in the United States, was spent on the treatment of diabetes and diabetic complications.² Approximately one fourth of this amount was used in the management of foot and leg problems.³ Diabetic foot wounds are the leading cause of lower extremity amputations in the United States.⁴ Yet, when effective preventive measures are implemented, many such wounds can be avoided. With prompt and aggressive therapy, most diabetic foot and leg wounds that do occur can be resolved.

Here we discuss the various causes of diabetic foot problems and describe interventions that can prevent wounds from occurring.

CAUSES OF DIABETIC FOOT PROBLEMSIndirect causes. Neuropathy and peripheral vascular disease are indirect causes of many diabetic foot wounds (Table 1). The absence of pain can result in a patient's failure to recognize a problem or to appreciate a problem's significance. Peripheral vascular disease can impair healing and promote infection; thus, a minor wound can progressively worsen, often to the point where it does not heal.

Many experts believe that sensory neuropathy is responsible for the majority of diabetic foot wounds; however, sensory neuropathy must be placed in perspective. Wound recurrences are rare in motivated patients who have been educated about diabetic foot care-regardless of the degree of neuropathy. Treatment failure and leg amputation most often result from severe peripheral vascular disease, not from neuropathy.

Other conditions that can contribute to treatment failures include uncontrolled edema, capillary basement membrane thickening (a component of microangiopathy), impaired red blood cell deformability, autosympathectomy, hypoxia at the microcirculation level that results in a chemically mediated reperfusion insult, and the osmotic and glycosylation effects of hyperglycemia. Vasoconstriction resulting from cigarette smoking also interferes with blood flow and wound oxygenation.

Direct causes.Deformities are the direct cause of most diabetic foot wounds and, in our experience, are found in the majority of affected patients. Deformities can develop for several reasons, including:

• Muscle imbalances secondary to neuropathy, stroke, injuries, hereditary conditions, or previous surgery.

• Direct trauma that results in fracture and/or wounds.

• Repetitive trauma.

• Improperly fitted shoes.

Examples of deformities include spurs, bunions, bunionettes, bosses, malunited fractures, and arthritic changes. These often result in hypertrophied bursae over bony prominences. If there is trauma to such areas, the skin ulcerates. Tracts may develop rapidly to the underlying bone and provide a route for infection to spread to the bone and joint.

Figure 1 – Hypertension of the metatarsal phalangeal joint (MTPJ) is seen in this clawed right hallux. Note the superficial ulcer (secondary to irritation from shoe contact) over the hyperflexed interphalangeal joint. The extensor tendon "bowstrings" (arrow) over the MTPJ because of joint hyperextension. An in-office percutaneous tenotomy with a 2- to 3-mm incision can eliminate the extensor force that is causing the deformity.

Clawed toes are frequently seen in patients with diabetes (Figure 1). Imbalances in the tone and strength of the intrinsic and extrinsic toe muscles cause hyperextension of the metatarsophalangeal joints and hyperflexion of the interphalangeal joints. This has a winch-like effect: the metatarsal heads are driven toward the sole of the foot, which results in increased contact pressure-and often in perforating ulcers. Ulcerations can also result when the hyperflexed proximal interphalangeal joints rub against the toe box of the shoe.

Heel pressure sores develop in a similar manner. When the bony contours of the heel rest against the bedding and the heel is used as a fulcrum to support the full weight of the lower extremity, perfusion is compromised and blisters form rapidly. Shear forces that result when the heel slides across the bedding accelerate skin breakdown. If tissues in the affected area are poorly perfused (as in patients with peripheral vascular disease), ischemia results; tissues die and slough, and ulcerations and osteomyelitis frequently ensue.

Repetitive stress. Many patients with diabetes have abnormal gait patterns and/or abnormal pressure distributions in their feet when standing or walking. Causes include muscle weakness secondary to neuropathy; loss of strength, endurance, or coordination resulting from inactivity; peripheral vascular disease; other effects of diabetes (such as capillary basement membrane thickening and the glycosylation effects of hyperglycemia); and combinations of these factors.

An abnormal gait or pressure distribution in the feet often results in shear stresses. Repetitive shear stresses are one of the greatest challenges in the management of diabetic foot problems. The problem is compounded by obesity, joint contractures, muscle weakness, balance problems, peripheral edema, and peripheral neuropathy-all of which magnify the stresses to vulnerable structures.

Repetitive stresses that involve low contact pressures result in bursae. Eventually, tissue-protective responses are overwhelmed, leading to ulcerations-especially if the repetitive stresses occur at the site of previously existing bony deformities or bursae. When shear or direct stresses are associated with high contact pressures, wounds develop rapidly.

Peripheral vascular disease can impede the ability of injured tissues to repair themselves. Bacteria then proliferate in the compromised, ischemic wound, in which a progression to cellulitis, a penetrating ulcer, deep infection, or a combination of these is seen.

Another consequence of repetitive stress is the pathologic (stress) fracture. In a patient with diabetic neuropathy, such a fracture may go unnoticed until swelling, erythema, deformity, and/or instability develop.

Direct trauma. Because of weakness, decreased sensation and proprioception, joint stiffness, and poor vision, patients with diabetes frequently sustain overt foot injuries. Such injuries can be devastating in a patient with diabetic neuropathy. Even with optimal orthopedic surgical interventions, simple ankle fractures can result in displacement. When foot and ankle fractures heal with angulation, displacement, or malrotation, deformities result. Malunited fractures can alter the mechanics of the foot and make it more susceptible to the effects of repetitive and shear stresses. Displacement can also lead to infected, malaligned ankle joints that may eventually require lower limb amputation.

Charcot arthropathy is another injury-related problem. The cause is not always apparent, but frequently a history of trauma-albeit mild-can be elicited. When the foot is warm and swollen, cast protection and avoidance of weight bearing are required. Once the hypervascularity phase has passed, weight-bearing activity in protective footwear can be initiated. Later, in the remodeling stage, bone spurs and foot contractures or deformities may require surgical management and/or accommodative shoes.

Improper footwear. Selecting footwear can be a challenge for the patient with diabetes, especially if he or she must accommodate deformities and repetitive stress problems. Patients with diabetes often do not know how to select appropriate footwear; they may choose shoes that are the wrong size, have insufficient padding or toe box space, or are simply an inappropriate style. Because of neuropathy, they may not notice that a shoe is too tight; edema may lead them to buy shoes that are too large-and that will allow the feet to slide, subjecting them to shear stresses. High heels; shoes with pointed toes; slip-on styles, such as moccasins; and shoes with flexible soles are inappropriate for persons with diabetic neuropathy.

In addition, many persons with diabetes have dry skin, which can result from alterations in the autonomic nervous system, or atrophy of the soft tissue pads in the feet, which may be a consequence of glycosylation. Both problems may require special padding inside the shoe.

PREVENTION OF DIABETIC FOOT WOUNDS
The maxim that an ounce of prevention is better than a pound of cure is particularly applicable to diabetic foot infections. To heal a diabetic foot wound requires an oxygen and blood supply 20 times greater than that needed to maintain the foot in a healthy state.^5,6 In fact, if a patient has poor circulation, a problem foot wound may necessitate amputation, because blood flow cannot be sufficiently increased to meet the requirements of a healing wound.

Prevention of diabetic foot wounds requires the cooperation of the patient and, if possible, assistance from the family. An effective strategy for preventive foot care includes several key components (Table 2).

Patient education. The primary care physician plays a key role in patient education, which has several facets. Impress on patients the necessity of examining their feet daily. If they have problems with flexibility, a mirror may be helpful. Tell patients to look for new onset of redness, swelling, breaks in the skin, blisters, calluses, and macerated areas. All of these conditions require prompt intervention. Patient education also includes a review of the "do's" and "don'ts" in the Box on page 248 and advice on activity modification.

An energetic, knowledgeable patient with diabetes should be encouraged to exercise. Profound sensory neuropathy of the feet is a relative contraindication for running activities; swimming, bicycling, calisthenics, and weight training are more appropriate forms of exercise.

For the debilitated patient, household ambulation with walking aids may represent the appropriate level of exercise. Joint range of motion and repetitive resistance exercises with light weights are highly desirable and may be the only reasonable exercise options for some debilitated patients; such exercises should be encouraged by and, if possible, supervised by family members or caregivers.

Skin and nail care. Daily skin and toenail care is essential for avoidance of diabetic foot problems.⁷ Foot skin care begins with a warm water soak. Tell patients not to use hot water, to avoid burning a neuropathic foot. Have them carefully test the water temperature with their hands-if no neuropathy is present-or have a family member or attendant test it. The feet can be soaked by bathing, showering, or using a foot or whirlpool bath, or by wrapping them in a moist towel. After towel-drying, have patients lubricate the entire foot, including the toes and intertriginous areas, with petroleum jelly or a similar agent; instruct them not to put the lubricant on open wounds. All residual lubricant, especially between the toes, must be wiped off because lubricant left in these areas can cause maceration.

The goal is soft, pliable, but not greasy skin that can tolerate reasonable pressure and shear stresses. A simple 0-to-2 rating scale can be used to quickly evaluate a patient's skin (Table 3).⁷ This scoring system can also be used as one component in an assessment of a patient's compliance with physician recommendations in general and with the foot skin care program in particular.

Figure 2 – Note the long, fungus-thickened toenails and the mildly dry and scaly skin. Appropriate management includes in-office filing and countouring of the toenails. Instruct the patient to perform daily foot skin care, including warm soaks and lubrication.

Nail care requires equal attention. Persons with diabetes, especially those whose feet show signs of dysvascularity, are particularly susceptible to fungal infections and dystrophic changes in the toenails. Thickened, fungus-infected nails (Figure 2) are often nearly impossible to trim with standard nail clippers. Surgical-quality, sterilized nail cutters or a rotary drum sander can effectively trim and contour such toenails. In fact, sanding a nail to tissue-paper thinness is an easy alternative to systemic or local fungicidal agents; the fungus cannot survive because of the drying effect of the air.

Many persons with diabetes have problems with vision and flexibility that prevent them from effectively trimming their own toenails. In such cases, the primary care physician or another caregiver trained in the management of diabetic foot problems can care for the patient's nails. As with the skin, a 0-to-2 rating scale can be used to evaluate the condition and care of toenails (see Table 3). Other helpful tips for foot skin and nail care in patients with diabetes are listed in the Box on page 248.

Appropriate footwear. Appropriate shoes for persons with diabetes range from quality walking or tennis shoes to orthotic walkers (Table 4). The cost progressively increases with the degree of customization. However, while prescription footwear can be expensive, the cost of such shoes is far less than that of the hospitalization and surgery required to manage a diabetic foot wound. In addition, Medicare authorizes reimbursement at customary rates for therapeutic footwear for persons with diabetes.⁸ The basic provision is for 1 pair of shoes and 3 sets of inserts per year, although this can vary under certain circumstances. Recommend that patients buy more than one pair of shoes if they can afford them.

Level 1: Quality walking or tennis shoes

Instruct patients to wear new shoes for only a few minutes a day at first. If there are no signs of pressure, then the periods of wear can be progressively lengthened. This break-in process may take 2 to 3 weeks to complete. Prescription shoes often require adjustments, which should be made by an orthotist or a pedorthist.

Socks. Selection of proper socks is also important. Socks must not interfere with circulation; tell patients to avoid those with elastic bands at the edge, which can compromise venous return. White socks are preferred because stains from skin damage, leaking blisters, bleeding, maceration, and so on, are more readily apparent.

Footwear needs to be examined daily. Instruct patients to check socks for wrinkles when they put them on. Have them inspect both shoes and socks-before putting them on and after removing them-for foreign objects, such as small stones, needles, nails, and slivers, as well as for stains.

Gait management. Abnormal gait patterns are often associated with foot deformities such as inversion, hyperpronation, splaying of the forefeet, and tilting of the heels. Partial foot amputations magnify problems with gait and shear stresses; the shorter the foot (secondary to forefoot or midfoot amputation), the more difficult these problems are to control.

Inserts, shoe wedges, lifts, molded plastic ankle-foot orthoses (AFOs), and double upright (Klenzak) braces can correct abnormal gait patterns and the resulting shear stresses. The plastic AFO is an excellent choice for patients with footdrop deformities; it is lightweight and can be adapted for use with a variety of footwear. However, patients with diabetic neuropathy who use a plastic AFO may fail to recognize repetitive stresses from the orthosis that can lead to pressure sores.

The Klenzak brace stabilizes and controls deformities of the foot and ankle because it is rigidly attached to a prescription shoe. Although heavy and cumbersome-looking, the brace can be very helpful for certain patients, especially those with tilt (valgus or varus deformities of the foot and ankle); it may be the only nonsurgical method for controlling shear stresses that result from abnormal gait. However, if the deformity worsens in such a patient, surgical correction or avoidance of weight bearing on the extremity involved is required.

Limiting ambulation is another option. Some patients do best relying primarily on a wheelchair and using their lower extremities only when transferring to or from a bed or chair or when using the bathroom. A physical therapist can help determine the appropriate level of ambulation and what walking aids, if any, are needed. However, final recommendations about ambulation are the decision of the physician.

Ulcer

Proactive surgeries. Certain corrective procedures can be performed in either the office or the operating room, with minimal risk of healing complications (Table 5).^9,10 I refer to these as "KISS" (Keep It Simple and Speedy) procedures. Although those interventions that are restricted to the operating room require formal training in foot surgery, most of the in-office procedures can be performed effectively by the primary care clinician.

CLINICAL HIGHLIGHTS

• Clawed toes often lead to foot wounds in patients with diabetes. Hyperextension of the metatarsophalangeal joints and hyperflexion of the interphalangeal joints that occur in this deformity can result in increased contact pressure and-often-perforating ulcers under the metatarsal heads, which are driven toward the sole of the foot. Ulcerations can also result when the proximal interphalangeal joints rub against the toe box of the shoe.

• Inserts, shoe wedges, lifts, molded plastic ankle-foot orthoses (AFOs), and double upright (Klenzak) braces can correct abnormal gait patterns and the resulting shear stresses. The plastic AFO is an excellent choice for patients with footdrop deformities; it is lightweight and can be adapted for use with a variety of footwear. However, patients with diabetic neuropathy may fail to recognize repetitive stresses from the AFO that can lead to pressure sores.

• Socks must not interfere with circulation; tell patients to avoid those with elastic bands at the edge, which can compromise venous return. White socks are preferred because stains from skin damage, leaking blisters, bleeding maceration, and so on, are more readily visible.

• Instruct patients to inspect both shoes and socks-before putting them on and after removing them-for foreign objects, such as small stones, needles, nails, and slivers, as well as for stains.

• Persons with diabetes are particularly susceptible to fungal infections and dystrophic changes in the toenails. Surgical-quality nail cutters or a rotary drum sander can effectively trim and contour thickened, fungusinfected toenails. In fact, sanding a nail to tissue-paper thinness is an easy alternative to systemic or local fungicidal agents; the fungus cannot survive because of the drying effect of the air.

References:

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