Medical and Surgical Considerations in the Care of Patients with Insensate Dysvascular Feet

John H. Bowker, MD

Introduction

Diabetes mellitus is the disease most often linked in the developed world with damage to the feet due to loss of protective sensation. In much of the developing world, insensitivity due to Hansen's disease-formerly known as leprosy-is more frequent. Another fairly common cause of insensate feet, seen worldwide, is alcoholism.

When studying the causes and prevention of foot ulceration, one must first consider the risk factors involved. The primary factor is peripheral neuropathy, which interferes with normal transmission of signals in peripheral nerves. Most healthcare professionals are now acutely aware of sensory neuropathy, in which loss of protective sensation results in damage to the feet.

Other forms of neuropathy, however, such as motor and autonomic neuropathy, can also play a significant role. Most commonly, motor neuropathy leads to a paralysis of the foot's intrinsic muscles, resulting in dorsal subluxation or clawing of the toes. As the toes subluxate dorsally, the plantar fat pad, which normally protects the metatarsal head area moves distally, leaving thinner skin (which is poorly suited for force dispersion) under the metatarsal heads. Motor neuropathy may also weaken the foot dorsiflexors, leading to a loss of controlled descent of the forefoot following heelstrike at the beginning of the stance phase of gait. Combined with loss of metatarsal head padding, the resultant slapping gait can cause rapid damage to the skin of the plantar forefoot.

Autonomic neuropathy causes dryness of the skin due to lack of normal sweat production. This condition may lead to fissuring of the skin, creating portals of entry for bacteria. Poor management of diabetes, resulting in chronic hyperglycemia, leads to glycosolation of collagen with diminished capacity to heal wounds.

Smoking is another risk factor of real significance. In the short term, vessels constrict, and over a longer period of time, smoking can enhance development of atherosclerosis. On a daily basis, healing is also impaired by the blood's decreased ability to deliver oxygen to tissues. (Carbon monoxide binds sites on hemoglobin, which normally carry oxygen.)

Development of foot ulceration is also related to the duration of diabetes. In a study of 119 diabetics in our clinic, those with ulcers had diabetes for an average of 16 years, while those without ulcers had diabetes only 11 years. The age at which patients developed ulcers was striking, averaging only 54 years. It is a major challenge to restore function to individuals at the height of their productive years. There were no significant differences in age, race or type of diabetes (i.e., insulin-dependent or noninsulin-dependent) among those who developed ulcers and those who did not.

We used a biothesiometer to obtain the Vibratory Perception Threshold (VPT) as a measure of sensory loss. Overall, those with a VPT greater than the normal upper limit of 25 had a tenfold increased risk of having ulceration compared with those patients with readings of less than 25. If the reading was more than 43, there was a thirty-fold increase in risk. In our series, the average VPT of patients with ulcers was 40. Those without ulcers averaged 23.5 (1).

It is sometimes thought ulceration must be related to lack of circulation. However, we determined the Doppler ischemic index at the ankle in 58 patients with ulcers and 42 without and found no significant difference.

Acute Management

To manage any disease process, lesions should be classified by a method that has therapeutic significance. For this reason, we triage our insensate foot lesions by the method of Meggitt and Wagner (2) (see Figure 1 ). Grade 0 is represented by a callused area over a bony prominence with no evidence of skin breakdown. Nonetheless, these insensitive feet are at risk. As local pressure builds up on skin squeezed between a prominent bone internally and the unyielding floor and hard callus externally, a superficial ulceration or Grade I lesion occurs. If weight relief and modified shoewear are not obtained, a Grade 2 lesion will supervene. Grade 2 ulcers are deep, penetrating to tendon or joint capsule, but do not enter the joint. The next stage is a Grade 3 lesion in which the joint has been violated, leading to septic arthritis and osteomyelitis. Further progression leads to a Grade 4 lesion or gangrene of the forefoot and to Grade 5, gangrene of the entire foot. Specific protocols have been developed for each grade of lesion.

As noted above, Grade 0 represents a foot at risk. Ordinarily, undue localized pressure can be relieved by custom inserts placed in shoes that comfortably accommodate both the foot and the insert. At times, this is not feasible and a prophylactic osteotomy is done to reduce or remove the offending bony prominence. Diligent foot care thereafter should prevent sores.

In Grades 1 and 2, provided that infection does not supervene, weight relief is necessary until the lesion is firmly healed. There are a number of non-weightbearing options. Using crutches or a walker is awkward at best, and these devices are frequently ignored by the patient because the ulcer causes no pain. They also make it difficult to carry objects and, therefore, are a nuisance. A wheelchair is sometimes useful for patients with lesions on both feet. Bed rest is to be condemned for its debilitating effect. Since their introduction by Brand, healing casts have been used for the healing of insensate ulcers in patients with Hansen's disease. They are extremely effective in distributing forces during weightbearing over the entire foot, thus reducing pressure over the prominent area. Recently, shoes have been introduced that bear major weight on the heel with little or none through the forefoot (see Figure 2 ). These are excellent for forefoot lesions but healing casts are still the best option for hindfoot lesions. Once healing has been achieved, protective shoes as described above should continue to be used.

Grade 3 and 4 lesions should be cultured aerobically and anaerobically. Coverage with broad spectrum antibiotics is given, pending the results of sensitivity testing, due to the polymicrobial nature of most diabetic food infections. Diabetic control should then be initiated. This may be difficult to accomplish in the presence of infection. Treating the infection with antibiotics, on the other hand, will be only partially effective because of the inhibitory effect of hyperglycemia on leukocyte functions. The interdependence of these factors reinforces the case for early excisional debridement of necrotic and infected tissue.

Determining the circulatory status of the affected limb will ensure surgery is performed at the appropriate level. Segmental systolic blood pressure measurement by Doppler is useful if peripheral vessels have not become overly stiffened from calcification secondary to diabetes. These values are compared to the systolic pressure in the brachial artery to obtain the ischemic index. This should be at least 0.45 to 0.5 in the affected area if reliable healing is to occur at that level. Pressures are recorded at the base of the toes with a cuff around the forefoot, as well as the ankle, with a supramalleolar cuff to provide information about the entire foot.

Grade 3 and 4 lesions will require excisional debridement of all infected and necrotic tissue. While the gangrenous tissue in Grade 4 lesions may be dry, more often it is wet due to infection. (Gangrenous changes occur due to thrombosis of local vessels surrounded by purulent material.) The patient must understand the procedure is somewhat exploratory in nature; and based on information acquired from the blood flow studies, the surgeon will be as conservative as possible in removing tissue.

However, the first priority is controlling the disease. Both the patient and surgeon must be willing to redebride the lesion as necessary, either at the bedside or more formally in the operating room if the patient's loss of sensitivity is not sufficient to permit this procedure without anesthesia. Following complete debridement, weightbearing must be limited until the wound is fully healed, whether it has been closed primarily or allowed to heal by secondary intention.

In instances where the wound can be closed primarily, the procedure consists of two parts. These are debridement of all necrotic and infected tissue, including bone, followed by reconstruction of the foot using all viable remaining tissue (provided the wound can be closed primarily according to criteria discussed later in this article). It is common to fashion nonstandard flaps using any residual noninfected viable tissue. In the case of osteomyelitis of the distal phalanx of the great toe, if sufficient skin can be salvaged to cover the proximal phalanx, the patient's gait definitely will be enhanced, as opposed to removing the toe at the metatarsophalangeal joint (see Figure 3a and Figure 3b ). Infection of the distal phalanx of the lesser toes also can be treated by removing only that phalanx. Removing the entire great toe produces some disability that will require shoe corrections. Removing only the second toe removes the support needed by the first toe to prevent bunion formation (see Figure 4 ). It is often better, therefore, to remove the entire second metatarsal down to its proximal metaphysis to allow the foot to narrow (see Figure 5 ). If one of the lateral three toes is removed, the others tend to shift and fill in the gap.

As Grade 4 lesions are gangrene of part or all of the forefoot, they require a partial foot amputation or Syme ankle disarticulation, followed by a prosthetic fitting and lifelong follow-up. Here we need to consider the role of transverse versus longitudinal amputations. With a longitudinal amputation, such as a single lesser ray resection, only the width of the residual foot lever is affected. Rollover function and overall foot balance during terminal stance should be minimally affected.

Ray resections are excellent examples of conservative forefoot amputations. The best ray resections, from a functional point of view, are those of single lesser rays. With barefoot walking, there is never a good first ray amputation (see Figure 6 ) because an intact medial column in forward propulsion is important. If the first metatarsal is infected, the length of the shaft of the first metatarsal should be preserved as much as possible. If sufficient length has been saved, an adequate custom-molded insert can be made to support the medial arch of the foot in proper shoewear. Removing two or more central rays is not good functionally or cosmetically (see Figure 7 ). If necessary, all lateral rays and portions of metatarsals can be removed in an oblique fashion and still provide a good functional result if the first ray remains intact (see Figure 8 ).

Transmetatarsal Amputation

Transmetatarsal amputation can be performed when all of the distal forefoot is involved transversely, and the blood flow to the soft tissues is sufficient to support the flap fashioned from the distal plantar skin. This procedure provides a reasonably long foot lever that can be quite functional in a shoe with a stiff sole or sole plate and rocker. Some patients, who are not too concerned about cosmesis, will elect a short shoe.

The Lisfranc and Chopart levels have considerably less to recommend them. If these are attempted in infected cases and fail, it is very difficult to salvage a Syme level. Patients also tend to develop equinus deformity and foot imbalance since insertions of the foot's extrinsic muscles are disrupted. Therefore, percutaneous fractional heel cord lengthening and proper balancing of the foot by reinsertion of extrinsic foot muscles should be done at the time of amputation. A post-operative cast is also helpful in maintaining the proper plantigrade position. In fitting transmetatarsal, Lisfranc and Chopart amputations, special care must be exercised to avoid excessive direct and shear forces at the interface of the prosthesis and residual foot.

Following excisional debridement, with or without partial foot amputation, a decision must be made regarding primary closure vs. open management of the wounds created. Prior to the pioneering work of Kritter, these wounds were invariably left open. His studies led to a revolution in the management of these problems (3). By following his principles, primary healing can be achieved in three to four weeks in virtually all cases; this avoids lengthy healing by secondary intention that might take four to six months in many cases. It also avoids skin grafting, resulting in better cosmesis.

This method works well when certain criteria are met. Pus in the presenting wound must be either absent or minimal. When the debridement is complete, the wound should be clean with minimal inflammation of the remaining tissues. A 14- or 16-gauge polyethylene intravenous catheter, equipped with its own insertion needle, is passed through the skin into the depths of the wound. The needle is withdrawn and the catheter hub is sutured in place to the skin. A bag of normal saline is then attached to the catheter. Once the system has been noted to be running well, the skin is closed loosely with a few deep, widely spaced simple cutaneous sutures (see Figure 9 ). Widely spaced sutures let the fluid escape from the wound to be absorbed in a soft dressing. The wound is irrigated in this flow-through manner for three days at a rate of one liter of normal saline every 24 hours. Intravenous antibiotics are given concomitantly. At the end of three days, if there is any evidence of purulence, the wound can simply be opened and packed at the bedside. This rarely occurs, however, if the criteria described are met.

Long-Term Management

Once healing has been achieved, it is essential patients become involved in an effective program for the long-term management of their insensate/dysvascular feet. In general, the problems related to diabetes have not been approached from a holistic point of view, but rather from a fragmented one related to the various organ systems affected. Therefore, it is important to take a more organized approach in foot management if true preventive rehabilitation is to be achieved. A team dedicated to the prevention of foot loss is ideal and must be both interdisciplinary and interactive.

In our institution, orthopaedics and diabetology work closely together to ensure the proper overall care of the patient. The vascular surgeon is ready for consultation, as necessary, in cases where reconstruction or recanalization of vessels might be indicated. The dietician, physical therapist, psychologist and social worker all have major roles to play. The pedorthist plays a special role in providing the proper shoewear and shoe inserts. The patient is probably the most important member of the team because without his or her compliance, little can be accomplished.

The heart of our system, the Patient-Family Education Clinic, is run by master's-level nurse educators. In this clinic they try to instill concepts of foot self-care, arrange pedorthic care, closely monitor foot condition, trim nails and calluses as necessary and triage foot problems so patients receive the appropriate services in a timely fashion. The nurses also operate a hotline that encourages early reporting of foot lesions. This leads not only to early effective management, but also prevents the long emergency department delays commonly seen in large public hospitals such as ours. Use of the hotline also prevents inappropriate triage to services not used to handling these situations. The hotline is operated by the nurse educators at work from 7 a.m. to 3 p.m. Three nurses rotate call from 3 to 9 p.m. at home each evening. Specific instructions are given on shoewear-specifically avoiding tight, noncompliant materials, high heels and inward-facing seams. Favored features include roominess for toes and a high, wide toe box, pliant leather rather than rigid plastics and proper padding in the form of inserts depending on the individual conformation of the sole of the foot. We have found that well-fitted indepth shoes with custom-molded inserts meet most patients' foot protection needs. Patients are encouraged to check their shoes, socks and feet daily for problems and are warned to avoid barefoot walking.

Further preventive instructions are given about avoiding thermal injury, keratolytic callus removers and "bathroom surgery." Rational walking programs are stressed to prevent excessive weightbearing trauma.

Psychological risk factors include denial, depression and displacement of the locus of control. These all affect compliance with the foot care program and are addressed by the social worker and the psychologist. This counseling can be done in individual and group sessions in both inpatient and outpatient phases of care.

Summary

Peripheral neuropathy complicating diabetes mellitus is the leading cause of insensate foot problems in the developed world. The risk factors associated with this problem have been discussed. A systematic approach to the management of insensate foot lesions, based on the work of Wagner and Meggitt, is described. Proper application of the principles noted by all members of the interdisciplinary team, including the patient, should lead to prevention of major limb loss.

John H. Bowker, MD, is a professor of orthopedics and rehabilitation at the University of Miami School of Medicine and is Director of Insensate Foot and Amputation Service, U.M.-Jackson Memorial Rehabilitation Center, Miami, Fla.

References:

Boulton AJM, Kubrusly DB, Bowker JH. Gadia MT, Quintero L, Becker DM, Skyler JS, Sosenko JM. Impaired vibratory perception and diabetic foot infection. Diabetic Medicine 1986; 3 :335-337.
Wagner FW Jr. Orthopaedic rehabilitation of the dysvascular limb. Orthopaedic Clinics of North America 1978; 9:325-350.
Kritter AL. A technique for salvage of the infected diabetic foot. Orthopaedic Clinics of North America 1973; 4:21-30.