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Classification Systems in Biomechanics: Esoteric or Essential

Discussion in 'Biomechanics, Sports and Foot orthoses' started by drsha, Jun 15, 2012.

  1. drsha

    drsha Banned

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    I have copied this as part of the Residency Teaching Program for DPM's that lives on Present Podiatry.

    As the biased U.S. Patent holder for Functional Foot Typing, I believe Dr. Fitzgerald's installment gives thought that we should investigate classification systems in biomechanics as a cerebral exercise in practice.

    What is your opinion?


    Classification Systems:
    Esoteric or Essential?
    Ryan Fitzgerald DPM,
    Present Podiatry, Residency Insight

    In the context of studying for the upcoming American Board of Podiatric Surgery (ABPS) oral boards, I have been reviewing a variety of different topics - among them the many classification systems that exist in the management of foot and ankle conditions. I will freely admit that historically speaking I was not a strong believer in classification systems, although as I have progressed throughout my training and into clinical practice I have come to see a certain value in classification systems – or at least in certain classification systems.
    As a student and even into my residency it seemed as though classification systems existed largely to allow selected elder clinicians the opportunity to establish a vehicle to carry their names into perpetuity - a cynical point of view, I'm sure most would agree. Never the less, as I progressed through my residency training I have seen an increasing value in particular classification systems, and I have found myself utilizing them far more than ever expected when I was a naïve student and perhaps an even more naïve (if that's possible) resident.

    In the process of reviewing these many and varied classification systems, I have found myself critiquing the essential pros and cons, if you will, of each system. This, of course, got me thinking – in a procrastinating sort of way – about the value of classification systems and about what, indeed, makes them good or bad. Have you ever considered the purpose of a classification system at such a basic level? Generally speaking, classification systems:

    Make it easier to detect duplicate objects.
    Convey semantics (meaning) of an object from the definition of its kind, in which the meaning is not conveyed by the name of the individual object or its way of spelling.
    Allow users to impart knowledge and requirements about a certain kind of thing so that this knowledge can be applied to the members of the kind, allowing for rapid identification and translation.
    So what does this mean? Simply put, classification systems allow users to quantify like-objects/scenarios/clinical-presentations and to then correlate generalized information regarding these individual objects/scenarios/clinical-presentations to extrapolate certain further information from new scenarios that fit the appropriate system. Or viewed another way, classification systems allow us to establish truth in the unknown by comparing to that which is known and well understood.

    To be valuable, a classification should provide information to the user beyond esoteric description. Classifications should MEAN something to the user. They should provide the clinician with information that helps to provide guidance in regard to what to do next in a clinical encounter. While there are many classification systems from which to choose, Breslow's system for staging malignant melanoma serves as an excellent archetype for "good" classification systems because it does just that. Breslow's system correlates the depth, in millimeters, of neoplastic invasion, with potential 5-year survival rates, while at the same time providing the clinician with recommended margins for excision of the lesion.

    Figure 1: Breslows Staging System for Malignant Melanoma

    Depth in MM Excisional margins 5-year survival
    Stage 1 < 0.75 1cm 95 - 100%
    Stage 2 0.76 - 1.49 1cm - 2cm 90 - 95%
    Stage 3 1.5 - 4.0 2.0cm 60 - 75%
    Stage 4 > 4.0 > 2.0cm < 50%

    While Breslow's level has recently been replaced with the American Joint Commission on Cancer (AJCC) Depth staging system for malignant melanoma – a significantly more complicated system – many clinicians still routinely implement Breslow's level because it is simple to understand, translates well across language and training barriers, is reproducible, and provides prognostic data as well as clinical information regarding the appropriate treatment options moving forward.

    And isn't that the point - isn't that the value of a classification system, really? To be easily applied across training and language barriers while providing appropriate prognostic indicators and suggested treatment algorithms? Consider this, when you're calling your attending at 3am to describe the radiographic finding for an significant ankle fracture – isn't it valuable to be able to describe at PER 4 and have the attending know what you mean, and therefore what will be required?

    As clinicians involved in the management of conditions of the foot and ankle, we have the opportunity to utilize many classification systems. Frankly, some are more valuable than others, but there are those classification systems that provide each of us with significant value if we will choose to utilize them – and we SHOULD use them. I encourage each of you to critically evaluate the myriad of classification systems available to you, separate out those that seem to provide the greatest value to you, and then use them. Use them daily; make it a habit to try to classify the clinical findings that you're experiencing. It will make you better – and isn't that the point?
  2. blinda

    blinda MVP


    I wasn`t going to bite because you still haven`t had the courtesy to reply to the points raised with regard to your classification of nail dystrophy. However, I cannot let your or Fitzgerald`s (supported by your copying `n pasting), misinterpretation of classification and staging on malignant melanoma (MM) go without comment. This is way too serious a disease, which every practitioner should be aware of.

    Breslow did indeed write one of the first basic classifications of MM, then along came Clark`s. The two are described, and still used, as classification schemes with a view to prognosis based upon depth and level of the lesion. However, as with all cancers, the American Joint Committee on Cancer (AJCC) defined the staging of this potentially life threatening condition, utilising the nationally recognised Tumor, Node, Metastasis (TNM) system. That is, numbers I to IV to describe the extent the cancer has spread (see below). This system takes into account the size of a tumour, how deeply it has penetrated, whether it has invaded adjacent organs. It also includes any lymph node involvement and whether it has spread to distant organs. Staging of cancer is the most important predictor of survival, and cancer treatment is primarily determined by staging, not classification.

    AJCC groupings;
    • Stage 0: The melanoma is in situ, meaning that it involves the epidermis but has not spread to the dermis (lower layer).
    • Stage IA: The melanoma is less than 1 mm in thickness and Clark level II or III. It is not ulcerated, appears to be localized in the skin, and has not been found in lymph nodes or distant organs.
    • Stage IB: The melanoma is less than 1 mm in thickness and is ulcerated or Clark level IV or V, or it is 1.01-2 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.
    • Stage IIA: The melanoma is 1.01-2 mm in thickness and is ulcerated, or it is 2.01-4 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.
    • Stage IIB: The melanoma is 2.01-4 mm in thickness and is ulcerated, or it is thicker than 4 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.
    • Stage IIC: The melanoma is thicker than 4 mm and is ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.
    • Stage III: The melanoma has spread to lymph nodes near the affected skin area. No distant spread is present. The thickness of the melanoma is not a factor, although it is usually thick in people with stage III melanoma.
    • Stage IV: The melanoma has spread beyond the original area of skin and nearby lymph nodes to other organs, such as the lungs, liver, or brain, or to distant areas of the skin or lymph nodes. Neither the lymph node status nor thickness is considered, but in general, the melanoma is thick and has spread to lymph nodes.

    Staging is not;
    It is the next important step, after classification, to formulate the appropriate treatment plan. Many sites will concur that the TNM stages correspond with Breslow`s depth and Clark`s level measurements of MM and that both classifications are included in the AJCC staging guidelines for MM as a major prognostic factor (see here).

    I did that Dennis. As I said, still waiting for a reply.

  3. drsha

    drsha Banned


    I told you I would respond to you in private and I explained the reasons why. That offer still stands.

    As you cut and pasted my article in your thread on Classification of Dystrophic Toenails. I cut and paste Dr. Fitzgerald's installment for all to review.

    As you are not responsible for my article, I am not responsible for his.;)

    Here is the original thread if you wish to respond to Ryan personally:


  4. blinda

    blinda MVP

    Sorry Dennis, but you did not explain the reasons for not responding to my questions (after evaluating the paper to which you are a co-author) neither publicly or privately, other than stating that you refused to answer any of my questions that you considered were not pertinent to a thread which you had started.

    As I said, your copying `n pasting here is evidence of supporting the claims of Ryan Fitzgerald (not to mention satisfying your own desire to classify everything). When I quoted from your nail dystrophy article, it was in response to your invitation to critically evaluate it, not to take any responsibility for it. You have encouraged evaluation of classification systems; Therefore, I do not think it unreasonable to request justification of your example of using the Breslow system as an archetype classification system which, by your insinuation in imitation, has been replaced by a more "complicated system".
  5. blinda

    blinda MVP

    Maybe I`m missing something, as I am not a member of the forum, but I see no mention of the MM classification by Ryan Fitzgerald :confused:. From where did you copy `n paste your assertion that
    From the link you provided, Ryan simply states;

  6. drsha

    drsha Banned

  7. So let me get this right Blinda, the old classification system was replaced by the staging system because the staging system is a better predictor? But aren't they both classification systems?

    Is the key here that in order for a classification system to be of any use, it has to have demonstrable validity, reliability, specificity and sensitivity? Moreover, that the system needs to add clinical value in terms of the prediction of prognosis? That the reason the Breslow classification system was replaced was that it didn't?
  8. blinda

    blinda MVP

    Indeed, and yes they are. However, there is a difference between classification and staging.

    Taken from the AJCC website;

    Communication between both the patient and other Health Professionals involved in the patients care can only be achieved through `common language`(not an unknown classification system utilising terminology unrelated to the field of medicine). As the above quote indicates; staging of a disease certainly adds clinical value by allowing the practitioner to identify which clinical trials are relevant for each individual patient, thus informing the patient specific proposed treatment plan.
  9. Indeed, so when we have classification systems like the "foot posture index", despite having received reasonable attention in the literature regarding it's reliability and having minimal evidence to support its predictive nature, since its wider clinical use in predicting prognosis is pretty unclear, it has not been widely implemented within the medical community as a whole, despite that it uses language which should be understandable to all medical practitioners and explainable to patients.
  10. blinda

    blinda MVP

    Agreed. We can understand it`s descriptive classification but it`s clinical value as a predictive tool for prognosis, or pathology, remains very uncertain because it does not identify `state or stage of disease process`IMO.
  11. Nice. So to summarise, in order for a classification system of foot biomechanics to be of any value to the clinician on the coal face it needs to have demonstrable validity, reliability, specificity and sensitivity and to add clinical value in terms of the prediction of prognosis. It needs to be communicable between medical professional and to patients alike. Footy now though.
  12. blinda

    blinda MVP

    Yeah, I`d agree with that summary. But, I`m more of a rugger girl myself.
  13. I'd rather stick needles in my eyes than watch either. But the above points beside that are all excellent.
  14. blinda

    blinda MVP

    Actually. Right now, my left eye feels just like that.:boohoo:
  15. wdd

    wdd Well-Known Member

    I find them, almost always, essentially esoteric although in rare times of great need I find them esoterically essential.

    If I can help somebody as I travel on my way..............


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