The Foot in Diabetes - part 7 docx

chamber held in contact with the skin. The TcP O 2 is measured using a probe to measure the P O 2 in the solution. A low TcP O 2 re¯ects the degree of tissue ischaemia and increases with successful intervention. In diabetes, TcP O 2 is lower than in the matched arteriopathic patients, a TcP O 2 of less than 40 mmHg is associated with failure of wound healing, and increased TcP O 2 after intervention predicts success of angioplasty and wound healing more accurately than changes in ABPI 9 . Doppler Waveform Analysis In peripheral vascular disease, the normal, triphasic, waveform detectable using Doppler waveform analysis is damped distal to haemodynamically signi®cant lesions. In diabetes, damping of the waveform may indicate PVD; however, diabetic neuropathy has been shown to be related to abnormalities of Doppler waveform in the dorsalis pedis artery in the absence of PVD 10 . Colour Duplex Sonography (CDS) Ultrasound of the peripheral vascular system has been greatly enhanced by duplex-Doppler imaging. Ultrasound imaging, enhanced by colour ¯ow representation and Doppler waveform analysis, can be used to detect and characterize haemodynamically signi®cant lesions in larger vessels with 90% accuracy and predicts ®nal surgical intervention as accurately as does angiography. It has therefore been suggested that CDS may replace contrast angiography in the investigation of PVD 11 . Ultrasound resolution at present limits its use in assessing distal vessels for limb salvage procedures; however, no single modality can accurately identify foot vessels as suitable for a distal anastomosis. Contrast Angiography Non-invasive investigation, using a combination of modalities, can in most cases detect clinically signi®cant ischaemia and will identify most lesions of the larger vessels that are amenable to intervention. At present, however, despite full non-invasive investigation it is impossible to exclude surgically correctable lesions because of the problems of imaging disease in, and determining patency of, distal vessels. Angiography offers a further imaging modality which may help with the assessment of the distal vasculature but also provides a ``road map'' for planning surgical intervention. It is therefore indicated in cases of delayed ulcer healing as well as those in which preliminary vascular assessment has Peripheral Vascular Disease and Vascular Reconstruction 221 identi®ed signi®cant ischaemia. Best quality images are obtained with intra- arterial digital subtraction angiograms, with antegrade studies if necessary. Magnetic Resonance Angiography (MRA) The developing technology of magnetic resonance imaging is now beginning to offer accurate vascular imaging as an alternative to contrast angiography. The development of gadolinium enhancement and protocols for time-of- ¯ight analysis has resulted in high-resolution MRA which may, in the future, replace angiography 12 . MRA can now accurately detect haemodynamically signi®cant stenoses and occlusions and can resolve images of digital vessels and run-off vessels 1 mm in diameter. Availability of MRA currently prevents its routine use; in selected cases, however, it may offer an important imaging modality and increasing use seems likely. PRE-OPERATIVE ASSESSMENT One of the aims of the St Vincent Declaration on diabetes care made by the World Health Organization and International Diabetic Federation in 1991 was a reduction in rates of major lower limb amputation for diabetic gangrene 13 . Achieving this goal requires a rigorous approach to limb salvage based on medical, paramedical and surgical intervention and care. The elderly diabetic population in whom diabetic foot diseases occur are affected by many other medical problems. Assessment and control of these factors is important for successful limb salvage and patient survival after vascular reconstruction. Ischaemic Heart Disease Pre-operative assessment of patients for peripheral vascular reconstruction should routinely include assessment of cardiac status, including history of hypertension, angina and myocardial infarction (MI) and ECG. In diabetic patients, previous symptomatic ischaemic heart disease (IHD) carries a four-fold risk of cardiac complication. However, previously asymptomatic individuals contribute signi®cantly to the 5% overall risk of MI or cardiac death 14 . Previous ``silent'' MI may produce an unsuspectedly poor cardiac reserve, and slow post-operative recovery may re¯ect a peri-operative ischaemic event. Cerebrovascular Disease Previous severe disabling stroke would be a relative contra-indication to major vascular reconstruction for limb salvage for patients who would 222 The Foot in Diabetes return rapidly to their usual state of wheelchair mobility by considering primary amputation. Renal Impairment Impaired renal function as a result of renal artery or small vessel disease is an important factor in vascular assessment. Contrast arteriography carries with it signi®cant risks of renal failure or increased renal impairment, particularly in patients with existing impaired renal function and diabetes. For these patients it is particularly important to maintain good urine output, using intravenous ¯uids to maintain hydration. Diuretics are used in some regimens for renal protection; however, loop diuretics have been linked to adverse effects on renal function in some studies. MRA and CO 2 arteriography 15 may, in the future, be important modes of investigation in patients at particular risk of renal complications. Close operative monitoring of renal function is also essential in this group of patients. Proliferative Retinopathy Diabetic retinopathy may in¯uence decisions regarding the use of thrombolysis to salvage occluded grafts. Thrombolysis carries a risk of sight-threatening occular haemorrhage. Diabetic Control In the presence of signi®cant sepsis, diabetic control is frequently lost and some patients are at potential risk of developing diabetic keto-acidosis. The acute presentation of the diabetic foot may also be heralded by development of uncontrolled diabetes. Methods of diabetes control in the peri-operative period vary and several methods can be utilized. In the setting of poor glycaemic control due to sepsis, a regimen of intravenous dextrose and potassium with an intravenous sliding scale of insulin based on blood glucose measurements is frequently employed. Risk of Infection Some of the factors that contribute to the development of foot ulcers also result in increased risks of complications following surgical intervention. Long-standing diabetes is associated with poor wound healing, which may be related to poor nutrient transfer due to small vessel disease. Additionally, diabetes, particularly when poorly controlled, is associated with increased susceptibility to wound infection. The combination of poor wound healing and susceptibility to wound infection may require an Peripheral Vascular Disease and Vascular Reconstruction 223 alternative antibiotic policy and extra vigilance for wound-related complications. The risks of wound-related complications are also important with respect to the use of prosthetic graft materials for reconstruction. VASCULAR SURGERY FOR THE DIABETIC FOOT General Considerations Major vascular reconstruction requires prolonged anaesthesia and repre- sents a signi®cant risk of major postoperative morbidity and mortality, particularly in patients with other long-term complications. Surgical planning should therefore include consideration of the minimal interven- tion that will achieve successful healing and control of symptoms and, if vascular reconstruction is indicated, whether the probability of success and risk of complications are acceptable. Planning surgery should attend particularly to the arterial in¯ow to the limb, the availability of a suitable distal out¯ow vessel for anastomosis, and the surgery required to remove devitalized or infected tissue from the distal extremity to allow healing. Consideration should also be given to the alternatives to general anaesthesia that are available in high-risk patients. Techniques of regional anaesthesia, including spinal and epidural methods, may be suitable for selected patients and selected operations, although not when cephalic and basilic veins are to be obtained and used as a graft conduit. An important aspect of planning surgical intervention is the immediacy of the clinical situation. The presentation ranges from chronic ulceration to fulminant limb-threatening infection. In chronic cases, vascular reconstruc- tion may only be a consideration if more conservative methods fail to achieve ulcer healing. More acute presentations will require a rapid assessment of the prospect for limb salvage, the role of tissue debridement and vascular intervention. The Emergency Diabetic Foot For patients presenting with rapidly progressive tissue loss due to infection and/or ischaemia, the disease process represents a signi®cant risk of limb loss and mortality. A rapid assessment is required of whether the degree of necrosis and infection can be controlled by local debridement or minor amputation and, second whether ischaemia is an aetiological factor. In the acute situation, the diagnosis of ischaemia may not be possible before intervention to control localized infection and, if major amputation is not required due to extensive necrosis of the weightbearing areas, drainage and debridement can be undertaken as a primary procedure. 224 The Foot in Diabetes After local control of infection, and because of the dif®culties of diagnosing ischaemia non-invasively, an intensive vascular assessment will frequently be indicated. Colour duplex ultrasound may satisfactorily identify lesions suitable for angioplasty in many situations; however, angiography will be more readily available and will, in any case, be required to perform angioplasty and assess the arterial system for reconstructive surgery. Depending upon the patient's premorbid condition, the extent of the necrosis and infection, and the pattern of any arterial disease, a decision can be made as to the best combination of angioplasty, stent insertion, debridement, endovascular and vascular surgical recon- struction. Planning Vascular Surgery (Table 16.2) In¯ow Planning vascular surgery in suitable patients follows the basic principle of correction of haemodynamically signi®cant proximal lesions before more distal disease. The success of any reconstruction below the inguinal ligament is largely dependent on satisfactory in¯ow and in some cases, even with signi®cant distal arterial disease, improved in¯ow to a limb may be suf®cient to allow healing. Radiological intervention, such as percutaneous transluminal angioplasty (PTA) and stenting of iliac lesions, is dealt with in Chapter 15. Surgical approaches to in¯ow disease are divided into those designed to improve ¯ow through native vessels and operations that bypass diseased or Peripheral Vascular Disease and Vascular Reconstruction 225 Table 16.2 Cascade of surgical and radiological intervention for PVD (proximal before distal) Focal lesions stenosis/short segment occlusion Optimization of in¯ow and limb perfusion by radiological intervention Iliac disease without iliac in¯ow Aorto-(bi-)iliac Aorto-(bi-)femoral Axillo-(bi-)femoral Iliac disease with ipsilateral in¯ow Ipsilateral iliofemoral Iliac disease with contralateral in¯ow Contralateral iliofemoral Femoro-femoral cross-over Femoral artery bifurcation disease Profundaplasty Endarterectomy Femoropopliteal disease Femoropopliteal (AK) Femoropopliteal (BK) Popliteal trifurcation disease SFA/popliteal±crural Femorocrural Crural disease SFA/popliteal pedal Femoropedal SFA=super®cial femoral artery. occluded vessels. Focal stenosis due to atheroma can reduce ¯ow through native vessels and may not always be suitable for radiological intervention. This commonly occurs at the bifurcation of the common femoral artery into profunda femoris and the super®cial femoral artery. In this position PTA risks occluding the branch arteries, which can worsen the situation. The stenosis can be corrected by a surgical angioplasty. The exposed and clamped artery is opened longitudinally over the stenotic segment, atheroma is removed from the three vessels by careful endarterectomy, and the arteriotomy closed using a patch of native vein or synthetic material such as dacron. The arteriotomy and patch closure can be extended onto the profunda femoris to perform a profundaplasty. Operations to improve in¯ow by bypassing iliac occlusive disease include iliofemoral bypass, contralateral or unilateral as appropriate, and femoro-femoral cross-over. Similarly, for bilateral disease, transabdominal aorto-(bi-)iliac or (bi-)femoral bypass represent major surgical interven- tions, whereas axillo-(bi-)femoral bypass offers a less invasive, but haemodynamically inferior, procedure. Improved proximal in¯ow may be suf®cient to promote healing and relieve symptoms. Once satisfactory in¯ow has been achieved, infra-inguinal reconstruction may be appropriate to improve more distal circulation. Infra-inguinal Reconstruction Bypass of arterial occlusions distal to the inguinal ligament requires a suitable in¯ow vessel, without any more proximal obstruction to ¯ow, and a suitable distal vessel for the out¯ow anastomosis. In diabetes, arterial disease may be isolated to the popliteal trifurcation or proximal tibial vessels and in¯ow may, therefore, more frequently be taken from the distal super®cial femoral or proximal popliteal arteries than in the general vascular population 16±19 . The longevity of the graft is partially dependent upon the level and quality of the out¯ow vessel (Figures 16.3, 16.4). The distal vessel may be identi®ed by dependent Doppler ultrasound, pulse-generated run-off or on arteriographic images and these all give information about the quality of the distal vessel and the run-off from it. The decision as to the level of the distal anastomosis depends upon the level and quality of the available distal vessels. Patency is better for grafts to more proximal vessels. This observation, however, may re¯ect the more limited disease pattern seen in patients with suitable vessels at this level. Anastomosis to a diseased vessel is technically demanding and risks early graft occlusion because of disease close to the anastomosis and, therefore, anastomosis to a healthy, more distal vessel is essential if one is available (Figures 16.3, 16.4). For distal vascular reconstructions, an important 226 The Foot in Diabetes component of arterial run-off is the dorsal pedal arch. An angiographically intact arch is an important determinant of the success and survival of a graft to the distal vessels 20 . In diabetic patients, the prevalence of disease in the tibial vessels dictates a femorodistal approach more frequently than in the general population. Peripheral Vascular Disease and Vascular Reconstruction 227 Figure 16.3 Selection of out¯ow vessel for infra-inguinal reconstruction. The digital subtraction angiogram shows a patent below knee popliteal artery but with severely diseased run-off in all three tibial vessels (a) which occlude in the calf. Collateral vessels reconstitute just above the ankle in a peroneal artery with patent, but diseased, anterior and posterior branches. In this case a graft to the below knee popliteal is at high risk of occlusion due to poor run-off (b); however, the less than perfect ankle vessel makes a decision regarding distal anastomosis a dif®cult one The relative sparing of foot vessels from the atherosclerotic process in diabetes makes femoropedal surgery a relatively frequent option in reconstruction. Choice of ConduitÐAutogenous Vein Should be Used Whenever Possible Infra-inguinal bypass is technically feasible using either autogenous vein or synthetic materials, such as expanded polytetra¯uoroethylene (PTFE), as a conduit. General vascular surgical practice favours the use of autogenous 228 The Foot in Diabetes Figure 16.4 Healthy distal vessel for out¯ow anastomosis. In a limb displaying otherwise severe atheromatous disease, a patent and angiographically healthy anterior tibial/dorsalis pedis artery running into a patent pedal arch is available for distal anastomosis vein whenever possible because long-term patency is signi®cantly better for vein grafts. In diabetic patients, the preferential use of autogenous vein is particularly important because of an increased risk of occlusion 21 . Such patients are also at increased risk of prosthetic graft infection, which carries a signi®cant risk of amputation and death. The ipsilateral long saphenous vein (LSV) offers the ®rst source of autogenous vein; a satisfactory vessel may be used, employing in situ, reversed or non-reversed techniques, depending upon the quality and dimensions of the vessel and the anatomical bypass type. In the absence of a suitable vessel, however, the contralateral LSV, the short saphenous, basilic and cephalic veins or grafts spliced using vein from different sources are all available as sources of autogenous material before a synthetic graft must be contemplated. The result of these deliberations should be a planned procedure that will provide durable revascularization to the extremity and improve the rate and probability of healing of that extremity. The patient should understand the principles of the procedure, the potential bene®ts and also the risks associated with the surgery. Surveillance Occlusion of infra-inguinal bypass grafts leading to recurrent foot ischaemia requires major intervention. Thrombolytic therapy may achieve graft patency but there is a signi®cant risk of haemorrhagic complications locally and systemically, including fatal or disabling intracerebral bleeding. Patients in whom thrombolysis cannot be used or in whom it fails will require further bypass surgery or risk amputation 22 . In order to reduce graft failure rates, graft surveillance is undertaken to detect haemodynamically signi®cant lesions in in¯ow or out¯ow vessels or the graft itself. In the outpatient situation, repeated measures of the ABPI may detect a falling foot perfusion and indicate the need for further investigation. The gold standard for non-invasive graft surveillance, however, is duplex scanning 23,24 . A postoperative duplex scan performed in the ®rst week after operation followed by further scans at intervals of 4 weeks, 3, 6, 9 and 12 months, and 6 monthly thereafter, can be used to detect lesions requiring correction to prevent graft failure. Detected lesions are further investigated, frequently with angiography, and amenable lesions corrected by radiological or surgical means. Successful correction is followed by continued graft surveillance (Figure 16.5). Results of Infra-inguinal Reconstruction in Diabetics With close attention to pre-operative assessment, surgical planning, surgical technique and interventional graft surveillance, excellent rates of secondary Peripheral Vascular Disease and Vascular Reconstruction 229 graft patency (82±98%) and limb salvage (76±89%) can be achieved (Table 16.3). Graft patency and limb salvage rates are similar to those for non- diabetic patients 31±33 . ADJUNCTIVE PLASTIC SURGERY For the majority of patients undergoing peripheral vascular reconstruction, improved tissue perfusion and good nursing care will allow healing of an ulcer or minor amputation wound. Even in cases where a minor amputation 230 The Foot in Diabetes Figure 16.5 High grade stenosis in femoro-distal bypass graft. Three years after a femoro-dorsalis pedis graft using a composite vein graft a high grade stenosis, which required surgical intervention, was detected, on duplex surveillance, at the junction between the two segments of vein used [...]... described Infection can also play a role in the pathogenesis of neuro-arthropathy, and the examiner may ®nd an infected neuropathic ulcer adjacent to the affected joint Clinical history should reveal whether the ulcer developed as a consequence of the deformity or if, in fact, the neuro-arthropathic joint resulted from a pre-existing infected ulceration The clinical ®ndings attendant on acute neuro-arthropathy... weightbearing on the injured foot, with consequent hyperaemic and in ammatory response to injury, resulting in increased blood ¯ow and massive oedema The insensitive joints are subjected to their extreme ranges of motion as capsular and ligamentous stretching or tearing result from the primary insult and subsequent joint effusions Instability increases as weightbearing continues, with progressive joint laxity... joint changes, and are all characteristic of active neuro-arthropathy Hypertrophic changes, which seem to predominate in the chronic or quiescent stages, are most evident in the solid bones of the midfoot and rearfoot (Figure 17. 7) These ®ndings have the appearance of an exaggeration of those found in advanced osteoarthritis, i.e cartilage 244 The Foot in Diabetes Figure 17. 6 Atrophic changes found in. .. restore stability to the involved joint(s)6 The fate of any neuro-arthropathic joint is greatly dependent upon the amount of destruction that has taken place during the acute process This is directly a function of the amount of trauma or weightbearing sustained by the joint while in the stage of development If such stress is continually introduced to the compromised neuropathic joint, the destructive cycle... range in age from their early 20s to late 70 s, depending again on diabetes duration There is no apparent predilection for either sex In the majority of patients only one foot is affected, although bilateral involvement can be expected in 9±25% of cases7,15, 17, 19,20 Usually the diabetes has been poorly controlled, regardless of treatment or type of diabetes Since neuropathic individuals might initially... ®nding with the acute neuro-arthropathic foot7 ,8,12,15 Almost invariably, the pulses will be bounding, a ®nding that, in association with the other clinical characteristics listed, makes the diagnosis probable, even prior to Charcot Foot Figure 17. 4 241 Neuro-arthropathic ankle with angular deviation radiographic examination A neurological examination should reveal the impaired sensory status of the. .. salvage in diabetic and non-diabetic patients Diabet Med 19 97; 14: 214±20 34 Mashiah A, Soroker D, Pasik S, Mashiah T Phenol lumbar sympathetic block in diabetic lower limb ischemia J Cardiovasc Risk 1995; 2: 4 67 9 The Foot in Diabetes Third Edition Edited by A.J.M Boulton, H Connor, P.R Cavanagh Copyright  2000 John Wiley & Sons, Inc ISBNs: 0-4 7 1-4 8 97 4-3 (Hardback); 0-4 7 0-8 463 9-9 (Electronic) 17 Charcot... ambulation Ulcer, infection Figure 17. 1 Acute Charcot joint Continued weightbearing Pathogenesis of the neuro-arthropathic (Charcot) foot 238 Figure 17. 2 The Foot in Diabetes Osteolysis following great toe amputation Eichenholtz14 has divided the disease process into three stages based on pathologic ®ndings The stage of development is characterized by the acute destruction of the joint, with debris... technetium, thereby reducing its utility Johnson, however, reports a 91% accuracy in detecting osteomyelitis, even in the presence of neuro-arthropathy, by combining technetium bone scans with indium-labelled leukocyte scans25 Magnetic resonance imaging (MRI) and CT scanning might also be of use in detecting early bone and joint changes, but the role of MRI in reliably distinguishing neuro-arthropathy... and 252 The Foot in Diabetes Figure 17. 13 Pattern IV neuro-arthropathy developed in same patient as in Figure 17. 12 after failing an initial subtalar arthrodesis Figure 17. 14 Pattern V osteopathy demonstrating the classical calcaneal insuf®ciency avulsion fracture of the posterior process Charcot Foot 253 although sometimes requiring internal ®xation, healing usually results in a stable foot with little . consistent ®nding with the acute neuro-arthropathic foot 7, 8,12,15 . Almost invariably, the pulses will be bounding, a ®nding that, in association with the other clinical characteristics listed, makes the. weightbearing on the injured foot, with consequent hyperaemic and in ammatory response to injury, resulting in increased blood ¯ow and massive oedema. The insensitive joints are subjected to their extreme. such as the hip or knee. Conversely, syringomyelia involves the joints of the upper extremities, i.e. the shoulder, elbow and cervical vertebrae. In diabetes mellitus, the joints of the foot and