Chapter 2D - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
The Choice Between Limb Salvage and Amputation: Infection
John H. Bowker, M.D.
The vast majority of limb-threatening infections occur in the foot, mostly in patients with long-standing diabetes mellitus. A number of risk factors for infection exist in this group. The most widely recognized risk factor, sensory neuropathy leading to ulceration, appears to be directly related to the duration of the diabetic condition. Neuropathic patients are unsure that properly sized footwear really fit their feet and will tend to wear shoes that are too tight, thus inducing ulcer formation. They also may see no harm in walking without shoes, at least in the house, and thereby expose themselves to penetrating wounds from various objects left on the floor. Motor neuropathy may affect the foot and toe dorsiflexors and allow a rapid uncontrolled descent of the forefoot following heel strike. This slapping gait can result in damage to the skin under the metatarsal head area. This effect will be aggravated by paralysis of the foot intrinsics, which leads to shifting of the metatarsal fat pad distally as the toes go into a clawed position, thus leaving the skin under the metatarsal heads with little protective fat padding. In addition, autonomic neuropathy results in extremely dry skin, which then develops fissures that provide sites of entry for bacteria.
In the absence of normal pain sensation, it is quite common for diabetics to exhibit marked denial even in regard to open sores. They can also become quite depressed, especially if they have experienced chronic problems with their feet. While many are naturally quite fearful of amputation as an outcome, because of denial they may fail to come in during the early stages of an infection. A displaced locus of control is manifested by an inability to take responsibility for the care of their feet and/or diabetic state in general. All of these basically psychological difficulties may lead to poor compliance with a preventive foot care regimen. Infection in diabetic patients is further complicated by decreased chemotaxis and phagocytosis by leukocytes, especially in hyperglycemic states.
Other infections in the lower limb may also lead to amputation. Calf abscess, usually seen in immunosup-pressed patients, should be treated aggressively by wide incision and debridement if the foot is viable. This may be followed by later split-thickness skin grafting. Chronic osteomyelitis secondary to open tibial fracture usually presents with a long-standing draining sinus. A preoperative sinogram will determine the origin and full extent of the sinus, while an intraoperative injection of methylene blue mixed with a small proportion of hydrogen peroxide will assist in complete removal of the sinus by staining all passages and loculations. All sinus tissue should be carefully examined microscopically for evidence of carcinomatous change.
MANAGEMENT OF ACUTE PROBLEMS
The approach to management of foot lesions in the diabetic patient is greatly simplified by use of the Meg-gitt-Wagner foot lesion grading system (FIG 2D-1.).This is based on the presumption that most of these problems, other than dry gangrenous changes related to proximal arterial occlusion, are secondary to a penetrating lesion, either beginning in an ulcer or by direct puncture of the foot. Grade 1 and 2 lesions are ulcers that have not involved bone and joint. Although frequently colonized with bacteria, they are not overtly infected and may be readily treated by various non-weight-bearing devices including total-contact casts for ulcers in any plantar location or a hindfoot shoe for forefoot lesions (FIG 2D-2.). Due to a lack of compliance, the use of crutches or a walker is much less effective in insensate patients. In this discussion, however, we are primarily concerned with grade 3 lesions, i.e., ulcers penetrating bone and joint.
The extent of penetration and involvement of bone beneath an ulcer is easily determined by probing the wound. If bone is exposed in the depths of the wound, osteomyelitis with or without septic arthritis is usually present. Plain radiographs are useful in determining the extent of bony involvement as opposed to bone scans, which are not necessary in the usual penetrating lesion. On occasion, however, neuroarthropathy (Charcot joint) and an ulcer may coexist and lead to an erroneous diagnosis of osteomyelitis. Magnetic resonance imaging (MRI) rather than bone scans is best able to make the distinction.
The wound should be cultured and the patient initially given intravenous antibiotics that cover a wide range of organisms, including gram-positive, gram-negative, and anaerobic bacteria. Definitive antibiotics will be determined by culture sensitivities. Gentle probing will also give a good idea of the extent of any abscess that has developed in the forefoot.
Prior to embarking on a definitive surgical solution, the patient's potential for healing a wound should be evaluated. This includes evaluation of blood flow to the foot, nutritional status, and immunocompetence. There are a number of methods available that will give an indication of blood flow to the distal part of the foot, but the simplest reliable bedside test remains the Doppler ultrasonic evaluation. This can be done very simply by first applying the cuff just above the malleoli and determining systolic pressure over the dorsalis pedis and posterior tibial arteries and then moving the cuff to the midfoot and determining pressures at the level of the metatarsal necks (FIG 2D-3.). If the ischemic index (foot systolic pressure divided by the brachial systolic pressure) is 0.5 or more, foot salvage is attempted. If the ischemic index is below 0.5 and the problem is one of low-grade infection or distal dry gangrene, the patient should be referred to a vascular surgeon regarding the possibility of vascular reconstruction prior to limited distal amputation (see Chapter 2C). When accurate Doppler data are unobtainable due to severe vessel calcification, transcutaneous oxygen measurements will give reliable information regarding local tissue perfusion, especially when tested during inhalation of 100% oxygen. Nutritional status is considered adequate with a serum albumin level of 3.5 g/dL or above, while a total lymphocyte count of at least 1,500/mm is considered evidence of immunocompetence.
Charcot changes in the foot are commonly mistaken for acute osteomyelitis. Infection can be excluded in most cases on clinical examination by noting that patients with neuropathic arthropathy are not systemically ill and exhibit only moderate local skin warmth relative to the bony destruction seen on plain radiographs. In doubtful cases, MRI has been shown to be the most definitive test available to date.
The goal of any surgical procedure in the infected foot is the removal of all necrotic and infected tissue while preserving as much of the foot as possible. Rather than delay the opening of an obvious abscess if operating room time is not immediately available, the abscess should be widely opened to reduce its internal pressure while the patient is still in the emergency room. This may be accomplished by using ankle block anesthesia or, in many cases, no anesthesia at all due to the patient's sensory neuropathy. During both temporizing emergency room and formal operating room procedures, the surgeon should use longitudinal incisions to preserve as many neural and vascular structures as possible. Normal weight-bearing surfaces such as the heel pad, lateral portion of the sole, and metatarsal head areas should be respected. The surgeon should not unnecessarily compromise a later ablation, such as a Syme ankle disarticulation, by extending a midsole incision into the heel pad or a dorsal incision proximal to the ankle joint. It may be necessary to do multiple dorsal and plantar incisions to gain full open drainage of all abscess pockets. Tissues to be removed include grossly infected bone and soft tissue, as well as poorly vascularized tissues exposed in the area of infection such as tendon, joint capsule, and volar plates of the metatarsophalangeal joints. All wounds should be lightly packed with gauze to allow free wicking of the infective fluids to the surface.
In many chronic, nonpurulent cases of chronic osteomyelitis, following removal of necrotic tissue the possibility of loosely closing the wound primarily should be considered (FIG 2D-4A.). The surgeon should individually assess the feasibility of closed vs. open management for each case of this type. The criteria for this method include a wound presenting with minimal or no pus, remaining tissues that are not inflamed or necrotic, and a situation in which debridement results in a grossly clean wound.
The methodology originally described by Kritter is quite simple. A small polyethylene irrigation tube is placed in the depths of the wound and sutured to the skin. Skin sutures are placed only at wide intervals (FIG 2D-4B.). One liter of irrigation fluid is run through the wound each 24 hours for a period of 3 days. The fluid passes from the wound between the sutures and is absorbed by the dressing (FIG 2D-5.). The outermost wrap is changed every 4 to 5 hours. If pus formation occurs after discontinuation of the irrigation, the wound can be simply reopened and packed at the bedside.
The advantage is that primary healing of the wound will usually occur in a 3- to 5-week period. The alternative is the prolonged morbidity associated with several months of healing by secondary intention when the wound is packed and left open. Better cosmesis is also generally achieved by eliminating the need for skin grafting of residual defects. The Kritter irrigation system can be used to assist in the closure of minor foot-salvaging procedures such as toe and ray amputations. Amputations of a single toe, with the exception of the entire great toe, result in little loss of foot function. Amputation of only the distal phalanx of the great toe will also give a good result. Following disarticulation of the second toe alone, the first toe may go into a valgus position due to loss of the lateral support provided by that toe (FIG 2D-6.). Resection of the second ray (toe and metatarsal) will allow the foot to narrow and thus avoid secondary hallux valgus (FIG 2D-7.). Any single-ray amputation can result in an excellent functional result except for loss of the first ray. In this case, as much metatarsal length as possible should be left to allow for effective orthotic restoration of the medial arch. The removal of two or more central rays is less desirable. In this situation, a transmetatarsal amputation may give a better functional and cosmetic result.
REHABILITATION OF THE INFECTED FOOT
As noted above, the inability to loosely close the wound primarily over a wash-through system results in prolonged morbidity as the wound slowly granulates and shrinks. This process may go on for 3 to 6 months or more. At the end of that time, it may still be necessary to skin-graft the wound to obtain adequate durable coverage. If it has been possible to close the wound loosely over an irrigation system, the sutures may be removed at 3 weeks. The patient should probably be non-weight bearing for a minimum of 5 to 6 weeks. If minimal removal of forefoot bony structure has been possible, changes in footwear may be limited to simple fillers attached to an insole, combined when necessary with a fairly rigid rocker sole on an in-depth shoe. Properly designed shoewear should provide the partial-foot amputee with a stable platform, proper padding of bony prominences, and protection of the foot from external trauma.
In our facility, following the healing process the patient is referred to the Patient Family Education Clinic. This program, operated by master's level nurse-educators, provides long-term follow-up care, including nail and callus trimming, referral for proper shoe fitting, and counseling regarding self-care of the feet. It features a hotline so that patients can call in at any time regarding early treatment of incipient foot problems. They will be seen promptly and appropriately treatedand referred to avoid the long emergency department waits common to many large public hospitals. A great deal of attention is also paid to psychological reorientation to overcome denial, depression, and other problems affecting compliance.
The prevention of major lower-limb amputation by the salvage of all or most of the foot in patients with diabetic foot infections has become a reality in recent years. Success in this endeavor depends on timely presentation of the patient, control of infection and hyperglycemia by a combination of early and complete debridement and appropriate antibiotics and insulin. When gangrene or poor healing is related to vascular occlusion alone, a vascular surgeon should be consulted regarding the feasibility of vessel recanalization or reconstruction. Once healing is achieved, the patient should be actively engaged in a program devoted to prevention of further lesions by the use of proper footwear, tight control of diabetes, and education in foot care with emphasis on assumption of responsibility for self-care.
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Chapter 2D - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles