Introduction

Diabetic foot disease is a sequel of diabetes mellitus that is a growing problem worldwide. It is estimated that 221 million people will be affected with diabetes globally in 2010.[1] Patients with diabetes suffer blindness, kidney complications, and peripheral arterial disease.[2] Peripheral arterial disease is a significant risk factor for diabetic foot disease that may lead to critical limb ischemia, limb loss, and lower-extremity wounds in many patients.[2] Surgical management includes bypass grafting, angioplasty, wound debridement, and when inevitable, amputation.[3] The Saint Vincent declaration[4] called for a multidisciplinary team approach with an objective to reduce the amputation rate in diabetics by 50 percent; this target has not been achieved in the United Kingdom.

Typically, a patient may have critical ischemia of the lower limbs with digital gangrene, loss of diabetic control, and underlying complications of the heart and kidneys. Another patient may have significant loss of nerve function in the feet and nonhealing wounds in the plantar surfaces that are complicated by infection that has tracked to the deeper foot tissues. There could be bone and joint deformities in the foot serving to complicate the condition. Multiple organ disease may also complicate the patient’s condition. In both instances, the viability of the foot must be evaluated in order to determine the best option for management. A surgical decision to amputate is based on assessment of the extent of necrotic digit/organ, the extent of tissue perfusion to sustain healing, and the general condition of the patient. The aim of this paper is to examine the objective measures of tissue viability available for clinical management.

Viability Assessment Methods

A patient presenting with symptoms of peripheral arterial disease, diminished or absent pedal pulses, will have Duplex ultrasonography followed by contrast angiography when indicated. These investigations that are widely available will yield reliable diagnostic information to manage the macrocirculation. In order to assess tissue viability objectively, there is a need to measure tissue perfusion and determine its functional status. Measurements of toe pressure and ankle-brachial pressure index (ABI) are direct and simple, though these merely indicate the need for surgical intervention without offering any guidance toward the management of tissue viability.[5] Tissue viability has been assessed by such direct methods as fluorescein angiography, thermography, radionuclide clearance techniques, as well as indirect methods, such as transcutaneous measurements of tissue oxygen and direct measurement of oxygen saturation.[6] The three former methods are imaging techniques. An injection of sodium fluorescein (NaF) permits the microcirculation to be visualized using an ultraviolet lamp in which perfused tissue appears green. This technique is qualitative and difficult to repeat, though it was widely used in clinical and animal studies. Thermography or imaging heat generated by tissues using highly sophisticated infrared camera systems can be used to assess tissue viability. Such systems generate thermal maps with a color to indicate “hot” spots and are incredibly helpful in managing soft tissue disease.

The clearance of radioisotopes injected into the blood stream causes specific energy levels of radioactivity to be emitted hence permitting tissue perfusion measurements. This methodology was used in clinical and animal experiments using xenon (Xe 133) and iodine (I 125) using bolus injections and intradermal transfer of the radioactive tracers, respectively.

Thermography and later the clearance of a radioisotope 4-iodoantipyrine (I 125) were successfully used to determine the viability of skin flaps for below-knee amputations. The combination of these techniques yielded a success rate of 93 percent for transfibial amputations.