Surgical Perspective in Treatment of Diabetic Foot Ulce...

Surgical Perspective in Treatment of Diabetic Foot Ulcers

Surgical Perspective in Treatment of Diabetic Foot Ulcers
2001
Wounds
MedScape

Clinical Evaluation
The two main causes of foot ulcers in diabetic patients are atherosclerotic occlusive disease and diabetic peripheral neuropathy. Ischemic ulcers originate due to poor perfusion, are located over bony prominences, and result from minor trauma. Ischemia may present as gangrene, usually involving the toes.[14] These changes are due primarily to atherosclerotic occlusive disease. Neuropathic ulcers occur on the pressure points of the foot, and develop as a result of diminished sensation related to diabetic peripheral neuropathy.[15] These patients also develop a clawing deformity of their toes, thus predisposing them to pressure necrosis over the dorsal interphalangeal joints and the metatarsal heads on the plantar surface of the foot. Microorganisms may infect these ulcerated tissues and possibly lead to osteomyelitis or deep plantar abscesses. Infection, if treated inadequately, may result in limb loss.[16]

Charcot joints are bony deformities that develop as a result of diabetic neuropathy. The patient, due to a lack of sensation in the foot, has repeated episodes of minor trauma to the foot bones. The distal ends of the metatarsals and arch of the foot collapse, which leads to the classic appearance of a "rocker-bottom" foot.[14] The patient with Charcot joints typically is seen initially with local erythema and a deformity of the foot. The erythema may represent a true cellulitis, which indicates an invasive infection. Often, with an invasive infection, some portal of entry is present, either an ulcer or a skin crack.[17] Some patients do not have an infection, however, and only have an inflamed foot due to bone and joint trauma. In the early stages, patients complain of considerable pain in their feet, but this symptom dissipates as their neuropathy progresses. The pain is usually in the metatarsal or tarsal joints, and is often described as a dull ache. Plain x-rays demonstrate destructive arthropathy in more advanced cases.

As many of these patients have diffuse vascular disease, a thorough head-to-toe evaluation of the vascular system should be performed. A complete foot examination begins with assessment of blood flow to the foot. The presence and strength of pulses should be recorded and vessels auscultated for bruits. Capillary refill should be assessed as well. Patients with ischemia have feet that are cool to the touch. Pallor and dependent rubor are often noted in patients with severe occlusive disease. The ulcer, if uncovered, is unroofed so its true characteristics can be identified. The wound should be probed to determine whether it tracks into the deeper tissues. The size and characteristics of the ulcer should be noted.

Evaluation for patients first seen with a foot ulcer involves the use of simple, plain x-rays to rule out the presence of invasive soft-tissue infections or osteomyelitis, particularly in those with neuropathic ulcers. The presence of gas in the soft tissues suggests there may be a necrotizing soft-tissue infection with the presence of anaerobic organisms. It also suggests the presence of an abscess, which should be drained urgently. When the plain x-ray demonstrates lytic changes in bony tissues, the patient must be treated for osteomyelitis. X-ray bone changes, however, may not be obvious initially in the early stages of osteomyelitis.[18] A three-phase bone scan may be helpful in identifying areas of osteomyelitis.[19] Another test, magnetic resonance imaging (MRI), may be helpful in selected patients to identify occult soft-tissue infections, particularly in those with a Charcot's foot. Recent studies have shown that an MRI may be a more sensitive test than a bone scan in patients with diabetic foot problems.[20] Often, a combination of these tests is used to make an accurate diagnosis of osteomyelitis.

One simple test that can be performed is an ankle-brachial index (ABI), which involves measuring an arm systolic blood pressure followed by a calf systolic blood pressure. The equipment required for this test includes a blood pressure cuff and hand-held, continuous-wave Doppler. An ABI equal to or greater than 1.0 is considered normal; a change of 0.10 is considered significant.[21] An ABI of 0.50 is consistent with a diagnosis of claudication; less than 0.3 is consistent with severe ischemia. One confounding problem with this test is that many diabetic patients develop medial calcification of their peripheral arteries. Thus, these arteries are difficult to compress and the ankle pressure may be elevated factitiously.[22] Another population in which this finding may be noted is patients with chronic renal failure. Therefore, other noninvasive tests may be used in these two populations to assess the degree of peripheral ischemia.

A test helpful to assess foot perfusion in a diabetic patient with calcified vessels is the toe systolic pressure. The digital arteries tend to be spared of severe calcification and, therefore, are usually compressible. Specialized toe blood pressure cuffs and a photoplethysmograph sensor are required. The transducer emits infrared light reflected back to the sensor from the skin. The spectrum of the light changes with the amount of blood flow to the tissues. These flow changes are created with inflation and deflation of the toe cuff. A value greater than 30mmHg suggests adequate perfusion to heal a wound or local amputation.[23] A toe brachial index (TBI) of 0.75 is considered normal; less than 0.25 is consistent with severe peripheral vascular occlusive disease. Unfortunately, a 10mmHg variation in toe pressure may be noted when a change in skin temperature of 10[ring]C occurs.

One also may evaluate Doppler-derived, common femoral waveforms in patients who have a diminished or absent pulse on physical examination. An assessment of the common femoral artery Doppler waveform and velocities is performed with duplex ultrasound. In patients with diminished flow suggested by a monophasic waveform at the level of the common femoral artery, more extensive evaluation of the iliac system should be performed to rule out an aortoiliac lesion.

Another helpful, but qualitative, test is the pulse volume recorder (PVR). A segmental air plethysmograph should be used to assess blood flow at various levels of the limb. For this procedure, fitted blood pressure cuffs are placed on the thigh, calf, and over the metatarsal heads on the foot. The waveform created is similar to that derived from an arterial line. In the patient without peripheral vascular disease, there is a prominent dicrotic notch; however, as atherosclerotic occlusive disease worsens, the more dampened the waveform becomes. The value of this test is that it is not affected by medial wall calcification[24] and, therefore, is useful in the diabetic patient population for qualitative assessment of occlusive disease. Some limitations include cardiac dysfunction and foot edema.

Trancutaneous oxygen tension (TcO2) measurements also may be helpful in assessment of the patient with a nonhealing foot ulcer. Measurements are usually obtained from several sites on the foot. When the TcO2 level is greater than 30mmHg, it has been determined to be consistent with wound healing.[25] Some caveats of testing are that patients should not smoke or drink coffee within two hours of the test. The values should be measured when the patients have been at rest for 20 minutes, with the room temperature kept between 22[ring]C and 24[ring]C.[26] Also, measurements should not be taken directly over wounds or necrotic tissue, as these values may undermine the patient's true TcO2.

At our institution, the authors use magnetic resonance angiography (MRA) with gadolinium enhancement of three-dimensional images for evaluation of the peripheral circulation in diabetic patients with ischemia. MRA is particularly useful in the diabetic patient already at a higher risk of post-contrast nephropathy, because gadolinium is a nonnephrotoxic contrast material.[27] MRA also is useful for identifying potential target vessels for bypass. Recent studies have shown MRA is particularly helpful in patients with low flow to the foot, in which target vessels do not appear with standard contrast angiography.[28,29]

In selected patients, an angiogram may be required to better define the anatomy and extent of disease. Generally, the authors prefer to use hyposmolar contrast in this patient population because of its diminished nephrotoxic effects. Also it is very important to well hydrate these patients both pre- and post-procedure.

© 2001 Health Management Publications, Inc