Proper Foot Care Is No. 1 Strategy

By Laurie Umeh, NP

Lower extremity limb loss is a dreaded complication of diabetes at any age. For the older adult, limb amputation often has particularly far-reaching consequences: loss of mobility and independence. Amputation may be the one event that ultimately and prematurely forces someone into nursing home placement.

Diabetes mellitus (DM) increases the risk of lower extremity amputation 15-fold.¹ Older adults in general are particularly vulnerable; approximately 96% of amputations occur in people older than 45.² Survival statistics about amputation are bleak. The 5-year survival rate after amputation is only 27%.³

For the older adult who has had an amputation, rehabilitation may be limited by cardiovascular disease or other medical conditions. Many older amputees find a prosthetic limb heavy and uncomfortable and lack the stamina to ambulate with it.⁴ In one study, only 53% of patients older than 65 could be fitted with a prosthetic limb.⁵

The direct and indirect costs of amputations represent a major burden for the health care system. Yet 85% of lower extremity amputations can be prevented through programs for preventing and treating foot ulcers, preventing ulcer recurrence and educating patients about proper foot care.⁷

The cascade of events that ultimately culminates in limb amputation often begins with an innocuous-appearing ulcer on the foot. The mechanism of injury may seem trivial — a wrinkled sock, an improperly trimmed toenail or a foot that swelled in its shoe and led to skin breakdown. A tiny blister or shallow ulceration becomes a draining, infected wound. After months of immobility and heroic efforts to save the ailing limb, osteomyelitis sets in, and amputation often results.

As providers of primary health care in clinic and nursing home settings, nurse practitioners are perfectly positioned to champion primary and secondary prevention of diabetic ulcers and lower extremity amputation.

The ability to perform foot care has limits in the older person with DM. Understanding the disease process, acquiring a repertoire of effective wound treatments, and knowing when to refer may prevent the progression of injury to ulceration and ulceration to amputation.

Neuropathy a Major Risk Factor

The greatest independent risk factor for lower extremity ulceration is probably peripheral neuropathy, which results in loss of protective sensation.⁸ Neuropathy appears to increase with age and duration of disease. A classic study of 4,400 mostly older patients with type 2 DM documented that 8% had neuropathy at time of diagnosis, and approximately 45% had neuropathy after 20 to 25 years with DM.⁹

Motor neuropathy can cause an imbalance between flexor and extensor muscles in the foot. This can cause clawing of the toes and prominence of the metatarsal heads, which results in foot deformity and abnormal pressure points.¹⁰ Abnormal pressures can cause callus to form. Thick callus acts as a foreign body (like a pebble) and may cause injury to the underlying soft tissues.¹¹

Motor neuropathy may contribute to one of the most severe foot deformities, the Charcot foot. A foot with Charcot deformity (or Charcot's joint) is severely distorted by degenerative joint changes due in part to motor neuropathy and collapse of the normal structure of the foot. If left untreated, a Charcot foot may develop a "rocker bottom" (complete loss of the arch) with ulceration at this abnormal pressure point.¹²

The patient with sensory neuropathy may present with aching, burning, tingling or stabbing pain — or none at all. Distal neuropathy often develops asymptomatically and insidiously. Patients with sensory neuropathy may be unaware they have lost protective sensation, and the degree of insensitivity may be shocking. One patient was admitted to a skilled nursing facility for intravenous antibiotic therapy after he underwent calcanectomy for an infected heel ulcer that progressed to osteomyelitis. The patient, a retired physician, had dropped a vial of insulin into his shoe and did not discover it until he had walked on it for several hours.

Pain is a protective sensation. Its loss results in many of the problems that occur in the diabetic foot. It is possible that the person with an insensate limb loses a sense of connection with the limb, resulting in an unconscious neglect.

Although various tools can detect loss of protective sensation (for example, the 5.07 Semmes-Weinstein monofilament), it is probably safe to assume that most older patients with DM lack protective sensation to some degree.

Peripheral Vascular Disease

Peripheral vascular disease (PVD) is more prevalent among people with DM. PVD is an important contributing factor in ischemia, delayed wound healing and the development of gangrene in the lower extremity.² The pattern of PVD in people with DM is different, progresses more rapidly, and is more diffuse. Vessels below the knee tend to be affected, and surgical bypass in this area is more difficult and less successful. Involvement of the microvasculature is common and causes basement membrane thickening and other abnormalities that are most prevalent in the distal parts of the lower extremities.¹³

Education Not Enough

Although intensive patient education in self-care is the cornerstone of illness management for patients with DM, it is unrealistic to expect that the majority of older adults are able to perform a thorough foot evaluation or appropriate foot care. Hand tremors, poor vision, obesity, prior hip or knee surgery, arthritis, stroke, dementia or generalized debility can make adequate foot care impossible.

One study assessed the ability of older adults with DM to perform foot care. While the study subjects had their eyes closed for "sensory testing," the researchers applied self-adhesive red dots to the plantar aspect of some of the toes and metatarsal heads to simulate foot lesions. Only 14% of the subjects had the visual acuity or joint flexibility to permit inspection of the foot and removal of the "lesions."¹⁴

Check Feet at Each Visit

A visual inspection of the feet at every health care visit is the minimum standard of care for patients with neuropathy.¹⁵ For all patients with diabetes, a comprehensive examination is needed annually and should include assessment of protective sensation, foot structure and biomechanics, vascular status and skin integrity.¹⁵ All patients with DM should remove their shoes and socks at each office visit to allow for inspection.

Unless an able-bodied caregiver can provide necessary foot care (inspection, cleaning, toenail trimming), you should stress to older patients the importance of regular visits to a podiatrist for routine foot care. Older patients with DM need to know that any foot crack, blister or open sore is an emergency and requires evaluation by a health care professional within 24 hours. The wearing of white socks can be helpful for older patients with DM so that drainage or blood on the sock can alert them to a problem.

Hospital and SNF Patients

Patients with DM who have become immobilized due to illness or surgery are, of course, susceptible to pressure ulcers at any bony prominence. Patients who have undergone hip surgery and are allowed to lie in a supine position without the operated heel floated off the mattress are particularly vulnerable to heel blisters due to pressure. Heel blisters may also result from friction when a bedridden patient digs heels into the mattress in an effort to reposition in bed. A diabetes patient in a nursing home should receive a careful foot evaluation at the time of admission to detect any beginning skin breakdown, tinea infection or toenail problem.

All nursing home patients who have experienced acute illness or surgery require heel protection such as pillows placed under the legs or special protective boots. Order foot cradles for a patient with any sign of pressure on toes or heels or a past history of ulceration. Cloth heel booties may create more problems than they solve by failing to relieve pressure and falsely suggesting that the feet are protected.

Diabetic Foot Ulcer

A blister is a stage 2 (partial thickness) pressure sore and may be the beginning of a monumental problem for a patient with diabetes. If pressure is promptly relieved, even a large bulla may sequester itself and become self-limiting.

Some providers recommend application of an agent such as tincture of benzoin at this point to toughen the skin. Monitor the blister carefully over the next few days. If the blister opens, remove the devitalized skin, and apply a petroleum jelly-impregnated dressing or foam dressing. If the epithelium dries and hardens into eschar and no periwound erythema or drainage develops, no further treatment other than continued pressure relief and careful observation may be necessary.

If the eschar is very thick, or if erythema or drainage is present, sharp debridement or an enzymatic debriding agent may be required. If you are not skilled in performing these interventions, refer the patient to a podiatrist. The ulcer should be probed deeply and necrotic callus and fibrous tissue sharply debrided back to bleeding tissue to detect sinuses or abscesses. Note that topical enzymes are only adjuncts to sharp debridement for a deep ulcer with necrotic tissue.

Rest, foot elevation and relief of pressure are essential components of treatment for a foot ulcer. Crutches or a wheelchair may be necessary to completely off-load the foot for the duration of the ulcer.

Osteomyelitis

The single most important predictor of amputation is the observation of fascia, tendon or bone at the initial wound assessment. An indolent foot ulcer can develop osteomyelitis at any time. Infected wounds are often minimally symptomatic, displaying only drainage, odor or mild discomfort. Failure to diagnose underlying infection often results in failure of wound healing. Infections that are not imminently limb threatening are those with no signs of systemic toxicity. They generally have less than 2 cm of cellulitis, no deep abscesses and no osteomyelitis or gangrene. Conversely, extensive cellulitis, deep abscesses, osteomyelitis or gangrene, especially in a limb that is ischemic, characterizes limb-threatening infections.¹⁶

In the clinically infected wound, cultures for aerobic and anaerobic organisms (taken by curettage of the cleansed ulcer or by aspiration of purulent secretions) are often helpful. Swab cultures and cultures of noninflamed neuropathic ulcers generally are not useful.¹⁶

X-rays are not a sensitive indicator of acute bone infection and may be falsely negative early on. Bone scanning has high sensitivity but low specificity. White cells studies have high specificity but low sensitivity. Magnetic resonance imaging is probably the most sensitive test. Ultimately, a bone biopsy may be necessary to rule out suspected osteomyelitis.¹⁷ C-reactive protein and estimated sedimentation rate may point toward infection, but they are more useful for monitoring response to treatment.

Referral

Consult a vascular surgeon when a patient presents with an ischemic wound or if an ulcer shows no progress despite appropriate wound management. Consider referral even though classic signs of PVD are not present. To illustrate this point, consider this story: An alert 56-year-old man with an infected foot wound was admitted to a skilled nursing facility for intravenous antibiotic therapy and wound care. The wound did not respond to treatment. Although the patient was instructed to elevate his feet at all times, he rarely complied and spent long hours sitting in his wheelchair. Staff nurses noticed that even when the patient was in bed, he hung his feet over the side. He was finally asked why he refused to elevate his feet. He stated that he had too much pain and that his feet felt better when they hung down. This is a symptom of arterial insufficiency. The patient was referred to a vascular surgeon and underwent femoral-popliteal bypass surgery. The ulcer healed rapidly after his surgery.

Proper Footwear

Patients who have no history of foot ulcers may wear all well-fitting shoe styles. The shoe needs to fit and not cause skin irritation. Proper shoe fit requires that the person be standing when measured. When standing, the ball of the foot (metatarsal heads) should correspond to the widest part of the shoe. Half an inch of space should be evident between the longest toe and the end of the shoe. Lace-up shoes provide the most adjustability and even pressure distribution. They also provide greater stability because they cover more of the foot than pumps or loafers. The heel of the shoe should fit securely to avoid friction that may cause a blister.

People who have a foot deformity or history of ulceration or amputation of any part of the foot should be referred to a podiatrist for custom shoes or orthotics. Medicare Part B pays 80% of the cost of special therapeutic shoes or orthotics for people with DM.¹⁸

Putting It Into Practice

The rate of lower extremity amputation in people with DM remains unacceptably high and represents a major public health problem with significant morbidity and mortality. Older adults are particularly vulnerable because they often lack protective sensation in their feet, are unable to monitor their feet for early signs of problems, and are unable to provide proper foot care themselves.

References

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10. Boulton AJ. The diabetic foot. Med Clin North Am. 1988;72(6):1513-1530.

11. Tierney LM, et al, eds. Current Medical Diagnosis & Treatment. New York, N.Y.: McGraw Hill; 2006.

12. Bell DS. Lower limb problems in diabetic patients. What are the causes? What are the remedies? Postgrad Med. 1991;89(8):237-244.

13. Thomson FJ, Masson EA. Can elderly diabetic patients cooperate with routine foot care? Age & Aging. 1992;21:333-337.

14. American Diabetes Association. Preventive foot care in diabetes. (Position statement.) Diabetes Care. 2004;27:s63-s64.

15. Consensus Development Conference on Diabetic Foot Wound Care. April 7-8, 1999, Boston, Mass. Diabetes Care. 1999;22(8):1354-1360.

16. Frykberg RG. Diabetic foot ulcers: pathogenesis & management. Am Family Physician. 2002;66(9):1655-1662.

17. Grainger KC, et al. Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. London, England: Churchill Livingstone; 2001: 2060.

Laurie Umeh is a gerontological nurse practitioner at Kaiser Continuing Care Services in Richmond, Calif.