Knowledge Representation

Patient information is interpreted by substantive diagnostic knowledge to produce a diagnosis. Substantive knowledge is mediated through a training programme, which is based on a variety of textbooks, many of which are strongly focused on biomedical or methodological knowledge. Maitland’s approach (for example) is strongly biased towards the procedure with advice to “make the

features fit” (Maitland, 1986p5s). The only support offered is by citing examples of specific cases.

However, it is rare for patient information to be clear and unambiguous (S ection 3.1 ). It often contains contradictions and incomplete information and is limited by the patient’s ability to remember and explain and by the therapist’s ability to observe and interpret.

Generally, it could be suggested that substantive diagnostic knowledge should be activated by positive reports of signs or symptoms. But, if the knowledge is represented inappropriately, it may remain inactivated, thereby failing to support problem solving (Larkin & Simon, 1987). Such a suggestion is supported by various other researchers, who postulate that knowledge undergoes re­ structuring during clinical education (eg Boshuizen & Schmidt, 1992, 1995; Schmidt & Boshuizen, 1993; Patel & Groen, 1986; Johnson, 1983). The revised structure of such knowledge may have a

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clinical orientation (Boshuizen & Schmidt, 1995).

In clinical practice, the reported signs and symptoms appear to be the triggers that recruit the anatomical, pathological or applied substantive knowledge, which can interpret the abnormality. A re­ description of substantive knowledge could take, as its starting point, the various tests prescribed by the procedure. If an abnormality is identified, then substantive diagnostic knowledge is activated and may produce a diagnostic hypothesis. For example, a common symptom may be pain on sitting. If the patient reports such a problem, inferences could be made about the structures that might be causing this symptom. Such structures could include (McKenzie, 1981p4_5) the discs (because sitting increases the intra-discal pressure), the joints (because the sitting posture often places them at the end of range of flexion) or the ligaments (because they are stretched). These inferences could be explicitly provided in an aid - perhaps in the form of questions (the trigger) and possible answers (the inference).

A way of supporting KS triggering could comprise a body of knowledge which explicitly provides the diagnostic inferences. The triggers (to activate the knowledge base) would, therefore, comprise signs or symptoms, identified during the information gathering part of the procedure. For example, at the beginning of the subjective, a patient may report the perception of stiffness in the morning on waking and rising. However, interpretation of this symptom may not be obvious, since it provides the trigger to (at least) three possible interpretations (Maitland, 1986p3s), depending on which specific KS was triggered. These hypotheses relate to the severity of the condition (triggering a testing KS), the class of structures causing the condition (triggering an anatomical KS) or the pathology (triggering a patho-physiology KS) . Representing these diagnostic hypotheses as production rules results in:

IF <early morning stiffness> THEN

[1] {condition may be severe} BECAUSE it interferes with function

[2] {condition may be mechanicai in origin) BECAUSE the joints have been maintained in one position during sleep

[3] {condition may be originating from an inflammatory joint disease} BECAUSE the duration of stiffness acts as an indicator of acuteness of inflammation

This example illustrates a common problem, since a single trigger {<early morning stiffness>) could activate three knowledge sources when considered with respect to the framework for modelling diagnosis (viz: KS® [l i f e s t y l e] KS® [j o i n tp a t t e r n] KS® [g e n e r a lp a t h o l o g y] ) . At this early stage in the

examination, there would probably be insufficient information available to identify which of the three KSs is the most relevant to the hypothesis. However, following further questioning, it might become obvious that the stiffness has a long duration (eg 4 hours). The duration is, therefore, added to the trigger of early morning stiffness and KS® is recruited. This combination of triggering factors enables

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the hypothesis to be refined as follows;

IF <early morning stiffness & long duration> THEN {condition is caused by an infiammatory joint disease}

Providing triggers and the possible inferences explicitly should cue the student to the relevance of that knowledge source, thus increasing the numbers of times the KSs are triggered. If, therefore, the knowledge sources are similar, but they are less efficiently triggered in students, an intervention which links the clinical presentation with the ‘textbook’ substantive knowledge (with which they are assumed to be familiar) could provide a solution to the difficulties. A key concern in the design of an intervention to support KS triggering, therefore, relates to the way the knowledge is structured. Such an intervention could take the form of, for example, prompts in the form of a checklist. These prompts could be brief on the assumption that they should cue existing knowledge. The prompts would represent the IF component of the production rules and could be expressed as questions. Alongside the questions would be the knowledge base, which provides possible diagnostic inferences (ie the answers to the questions). To extend the example given above, therefore, the trigger could be expressed as

1. Does the patient have early morning stiffness (EMS)? 2. How long does the EMS persist?

Assuming the first question is answered affirmatively and the answer to the second question is known, then the responses (in the knowledge base) could comprise:

Inflammatory joint disease is commonly associated with long (over 2 hours) periods of EMS.

A diagnostic hypothesis concerning the pathology of the condition could then be generated. It should be noted that the example is capable of application to any anatomical area affected by a musculo­ skeletal dysfunction.

To support practice, therefore, it could be suggested that the structure of substantive knowledge affects the ability of students to identify and interpret key parts of the examination findings. For example, a patient with an acute sprain of the ankle would present with signs and symptoms of swelling, bruising and pain, which was increased on stretching the structure. Interpreting these signs and symptoms should cue anatomical and pathological knowledge, including, for example, the structures of the ankle and foot (anatomy), inflammatory changes and degrees of severity of the injury (pathology). However, it is the clinical presentation of the signs and symptoms, which recruits the substantive knowledge and leads to the suggestion of a diagnostic hypothesis. On this view.

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knowledge required in diagnosis of any musculo-skeletal dysfunction should be represented in a clinically oriented form. Such a revision should contain explicit links between the clinical presentation and the possible diagnostic interpretation (which is based on substantive knowledge).

This discussion is justified by the way problems present clinically, but it is supported by the evidence offered in the literature. The form in which the substantive knowledge is structured has been identified as important to the effectiveness of the task. Novices in many areas use hypothesis generation and testing to problem solve - a factor underlying the choice of the blackboard framework in this research. On this view, providing a ‘knowledge base’, which contains explicit triggers and the inferences of abnormality, may support the student in treatment planning. Any re-description of substantive knowledge supporting diagnosis in musculo-skeletal dysfunction must relate to the requirements for support (Section 7.3) and those aspects identified as important, in the possibility of

supporting object level knowledge.

7.6 2.2 Knowledge Completeness

Reference was made earlier (Section 7.6.1) to the inherent problems of providing content that

was area specific^. Adopting the approach of supporting KS triggering should mean that the knowledge base and its triggers can be general (ie not area specific). The substantive knowledge in the aid must be capable of application across the area of diagnosis of musculo-skeletal dysfunctions, assuming that the diagnosis of dysfunctions is made by comparison with established norms of human function and structures (C hapter 3). If a case arises, which does not conform to this direction of

inference, then it is possible that the support will fail to fulfill its aims. However, as previously discussed (Sections 2.2; 3.2.3), physiotherapy knowledge is poorly documented and only rudimentary

disease classifications exist to support diagnosis. These difficulties (ie in guaranteeing that every conceivable case of musculo-skeletal dysfunction could be covered) must be acknowledged and, therefore, substantive knowledge should be expressed at as high a level as possible. It could be derived from textbooks and experts and should be re-structured to form the knowledge base’. Assuming the student already possesses the knowledge, but requires assistance to access it, should mean that high level prompts would cover the majority of cases - thus rendering it fit for purpose.

Diagnostic knowledge should be expressed at a high level in order to ensure it can be applied across musculo-skeletal disorders, although, in any specific case, the hypothesis should refer to the precise structures affected. On this view, a diagnosis relies on recruiting substantive knowledge from basic and applied biomedical knowledge. Using the examination procedure as a basis for specifying this knowledge assumes that the clinical findings will activate substantive knowledge, which produces

^ Area specific reports m ight consist o f (for exam ple) decreased range o f flexion at the shoulder joint. A m ore general transform ation would be to analyse the possible inferences resulting from the trigger <decreased range o f m ovem ent>

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the diagnostic inferences. Classroom based activities tend to focus on textbook knowledge, which is biased towards the procedure or the basic sciences. A set of general hypotheses should support knowledge recruitment in students faced with a diagnostic problem. Such a re-description of the substantive knowledge should appear in any re-configuration of the worksystem.