S(AD) SAD System The S(AD) SAD system evolved from the experience gained in trying to maintain a com- prehensive register of all ulcers managed in a single centre over a protracted period.
It was as a result of this process that it was progressively refined until just five features were identified: features that were thought to be key to distinguishing between groups of lesions.
It was from these five elements that the (rather ugly) acronym derives: Size, (Area, Depth), in- fection (Sepsis), ischaemia (Arteriopathy) and neuropathy (Denervation) (Table 7.7).
Like the UT system, this system has undergone some form of validation by seeking correlations without outcome.19 Unlike the UT system, however, the S(AD) SAD system was validated against a variety of end points (healing, failure to heal, amputation and death), rather than just against amputation.
The strength of the correlation between baseline measures and outcomes varied, with the strongest associations being found with ischaemia, area and depth.
The absence of strong association with infection conflicted with the results of the validation of the UT system, and this was almost certainly the result of the use of different end points and, to a lesser extent, different patterns of care.
In the United States, it has been usual to consider surgery early in the process of managing bone infection, whereas the unit in Nottingham has tended to favour a non-surgical approach.36,37 The absence of a strong association with infection when other outcomes are used suggests that its undoubted importance may be obscured by the effective- ness of appropriate antibiotic prescription.
Nevertheless, a weak correlation between infection and eventual outcome does not mean that infection is not a key factor distinguishing different types of lesions.
The main drawbacks of the S(AD) SAD classification (apart from its name) are the apparent complexity of a grid-based system and the irregularity (part ordinal, part nominal) with which
Table 7.7 The S(AD)SAD Classification
Size Grade Area Depth Sepsis Arteriopathy Denervation
0 Skin Intact Skin Intact. None Pedal pulses present Pin pricks intact 1 <1 cm2 Superficial (skin Surface Pedal pulses reduced Pin pricks reduced and subcutaneous or one missing tissue). 2 1, 3 cm2 Tendon, periosteum, Cellulitis Absence of both Pin pricks absent joint capsule. Pedal pulses 3 >3 cm2 Bone or joint space Osteomyelitis Gangrene Charcot
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104 THE DESCRIPTION AND CLASSIFICATION OF DIABETIC FOOT LESIONS
components (area, depth, infection, ischaemia and neuropathy) are subclassified, and the impre- cision of the clinical methods used. The system also includes the Charcot foot (as a grade of neu- ropathy), even though others have argued (with good reason) that the Charcot foot is a separate and highly complex condition that does not need to be included in any classification of ulcers.9
The PEDIS System The PEDIS system is the result of an attempt to reach international consensus, and has been published in preliminary form.10 It includes the same five components as the S(AD) SAD system, although using different terms to create the acronym: Perfusion (ischaemia), Extent (area), Depth, Infection, Sensation (neuropathy).
It differs from the UT and S(AD) SAD systems in being designed specifically for the purpose of population selection in prospective research.
As such, it abandons the symmetry of both UT and S(AD) SAD and uses strict definitions for the proposed grades of peripheral arterial disease and infection (Tables 7.4 and 7.5).
This gives the system the appearance of complexity, but that is not a major disadvantage if it is being used , as intended , only for the purposes of prospective research.
Those using it in research will be interested specialists who are studying rather smaller populations.
Having said that, those planning prospective research will inevitably consider their own criteria for inclusion and exclusion and would not necessarily feel the need to rely on the PEDIS framework.
The main value of this consensus work, however, lies in the formulation of working definitions for each of the parameters that might be classified.
IS IT POSSIBLE TO HAVE A SINGLE SYSTEM THAT MIGHT BE USED FOR ALL THREE PURPOSES?
The omission of neuropathy from the UT system means that it cannot be used for audit, and its place is effectively restricted to clinical care.
Even for this purpose, the UT system is limited by the lack of reference to ulcer area.
On the other hand, the S(AD)SAD system incorporates both neuropathy and area, and has a proven track record in clinical audit , even though its structure is far from ideal.
But as both UT and S(AD) SAD systems are based on much the same elements, it is not impossible that they could be combined, with the hybrid being based on the better points of each.
The PEDIS system is based on the same clinical elements and is not in competition , being concerned mainly with the clear definition of subgrades of the component parts.
Precise definitions, such as those explored in the PEDIS system, are desirable for implementation of any such new hybrid scheme.
Blueprint for a Hybrid
All three classifications variously use a combination of categorical (infection, ischaemia or both) and ordinal (area, depth) scales. In attempting to incorporate all of the features listed above, it will be apparent that , in addition to site and side , there are three that are categorical (binomial) and three that are semi-quantitative or ordinal. The three that are categorical (in- fection, ischaemia, neuropathy) are strictly all features of the limb or foot, whereas the three
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SUMMARY 105
Table 7.8 The SINBAD system for classifying foot lesions
Site and side Ischaemic ? Yes/No If Yes, is the ischaemia critical* ? Yes/No Neuropathy ? Yes/No If Yes, has the patient got Charcot? Yes/No Bacterial infection Yes/No If Yes, is there osteomyelitis? Yes/No 0 1 2 3 Area Skin intact <1 cm2 1, 3 cm2 >3 cm2 Depth* Skin intact Superficial Deep Bone
Categories as defined in UT, S(AD) SAD and PEDIS.
that are semi-quantitative are features of the ulcer (Table 7.8). The option exists for defining infection, ischaemia and neuropathy simply as binomial (Yes/No) options. Alternatively, it is possible to subclassify each, as shown in Table 7.8. Note that the issue relating to whether or not the system is used for ‘ulcer’ or for ‘lesions’ is not considered at this stage , despite its importance in using these systems in practice.
SUMMARY Clinical Care A system is needed for the routine description of foot lesions , whether the purpose is descrip- tion in routine in clinical practice, or more structured classification for audit and in population selection for prospective research.
Each of these has differing requirements and these determine the structure of any classification used , even though many of the components are shared.
Any system used in routine clinical practice must be simple enough to be remembered and easily applied, and the UT classification is suitable.
Its specificity would be improved by includ- ing reference to area and to neuropathy, but this would inevitably compromise its appealing two-dimensional structure and make it rather more complex and less easy to use.
Clinical Research The PEDIS system has refined the definitions that might be used when considering criteria for inclusion and exclusion for prospective research projects, and it emphasises the reliance of any working system on five specified criteria: area, depth, infection, neuropathy and ischaemia. It remains, however, in the development stage and has not yet been subjected to any form of validation.
Clinical Audit There is a great need for an agreed system for clinical audit because this will allow comparisons to be made between different centres, and the results of these comparisons will generate the hypotheses which will ultimately lead to improved clinical management. The specification of
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a system of audit presents, however, the greatest difficulty , since it needs to be simple enough to be applied easily to a large number of lesions in routine practice, and yet, it also needs to be precise enough to be meaningful.
The issues of timing and of clinical progression need to be addressed, as suggested by the introduction of the concept such as the ‘lesion narrative’.
The Nottingham (or S(AD) SAD) system has been shown to be both feasible and useful in routine practice, and the software is freely available (www.futu.co.uk).
Nevertheless, it is possible that the best features of both the UT and S(AD) SAD systems could be combined and used for both routine clinical care and comparing performance between different centres.
A new hybrid of the two, called the SINBAD system, is suggested.
The use of a single system for routine clinical description, for audit and , subject to the suggested definitions incorporated in the PEDIS system , for research, would have great advantages.