A critical look at Structural differentiation.
Rolf Walter, private practioner
CH-6834 Morbio Inferiore
The wish for structural differentiation is integral part of medical professions worldwide. Finding the anatomical structure driving the potential painful source of peripheral input may seem logical in situations where a distinct peripheral pain source is expected but observational and community based bias, false positives tests and mal interpretation of test results may occur (32). Several ways (instrumental, clinical) of structural, morphological differentiations have been historically used in the medical professions as well as in the so considered “alternative circuits” in health care. Reliability studies often demonstrate huge conflicting results no matter what procedures are being investigated (34). Therapeutic procedures aimed at anatomical and structural differentiation may lead to unidimensional proposals without considering psychosocial and physiological health factors which often are a key determinant part in therapeutically decision making and subsequent management.
Without doubt, there is importance in diagnosing structural lesions after acute trauma, differentiation procedures are mandatory to exclude potential level 1 diagnostic, red flag situations like fractures, arterial damage, vital organ damage. Less “vital”, level 2 diagnostic musculoskeletal lesions or sources may also be important to recognize. Ligamentous ruptures, peripheral joint damage and subsequent bleeding or edema, bone marrow lesions, soft tissue lesions and other structural lesions for which early diagnostic recognition may lead to optimum treatment modalities and management strategies, indicated to guarantee full recovery of function.
As an example; structural diagnostic differentiation may give indications for the type of lesion, for example knee ACL rupture, bone bruise in the tibia and clinical and theoretical evidence based literature on these topics may give indications for best treatment modalities and management strategies as well as healing times and prognosis but false positive findings like ligamentous ruptures and bone marrow lesions have been frequently found also in asymptomatic subjects (47).
Structural, musculoskeletal diagnostic differentiation may though also be misleading due to the multidimensional nature of many musculoskeletal disorders (24, 32). It is well known that structural, instrumental as well as clinical diagnosis represents huge amounts of false positives and potential false negatives (3,4,5,6,7,8,9,10,11,12,13,14,32), unreliable intra-tester interpretation of observations (1) and therefore diagnostic fallacies.
Sometimes structural differentiation does not seem to influence treatment and management decisions since a variety of active as well as passive treatments are showing a similar pattern of improvement (2). The therapeutic, “added value”, of some of the proposed differentiations has to be questioned therefore.
In literature pain provocation tests in musculoskeletal physiotherapy may have a better reliability than simple movement tests especially if cluster testing is applied (12,16, 29,31) but pain provocation may have its potential pitfalls (4). In a lumbar pain provocation study through discography (4) patients psychological, emotional profile and ongoing compensation issues were determinant and pain reproduction itself was found unreliable to confirm the localization of the nociceptive pain source. So how reliable is pain provocation to guide us to a specific patho-anatomical source? And is pain provocation or observation of pain behaviour in itself reliable as a response to our mechanical input? The community (for example the McKenzie group) based assumption that structural discogenic differentiation and diagnosis can be made by observing centralization or peripheralisation (41) of symptoms is criticized (42,43). Peripheralisation of symptoms has been related to spread of receptive fields (44) and is thus more related to the dorsal horn and central nervous system processing (45). Transduction of mechanically induced stimuli is not involving single structures therefore the evoked symptom may be due to many different structures at the same time. The mechanically induced stimulus, either pain provocative in nature, or non provocative in nature but firing into a sensitized central nervous system may give you the impression of a peripheral, tissue related problem since the symptom behavior may be similar (43). Spinal cord neurones now respond to normally non painful stimuli and give somatotopically inappropriate answers to input from distant healthy tissue (46). This definitely questions many of the differentiation procedures proposed in musculoskeletal therapy.
Sometimes the patient’s clinical presentation resembles a peripheral, tissue based problem but in hindsight, sometimes after several weeks/months have passed, it becomes clear that there must have been a multidimensional nature right from the beginning (27), unfortunately initial misdiagnosis and initial mismanagement may have occurred in the meantime.
Musculoskeletal physiotherapists hardly have insight in their patient’s psychological profile or have information about underlying ongoing compensation issues unless adequate filled in evidence based questionnaires on psychosocial profiles are available, therefore we should be aware of potential bias in pain reproduction with structural differentiations.
Another issue in symptom provocation might be the lack of monitoring of applied forces and time interval of exposed forces (15). Inconsistent application of forces due to individual clinician body weight, body height and individual force and experience may lead to false negatives as well as inconsistency of applied angles of force direction. The misbelief that we fully understand how mechanical applied forces lead to pain provocation (21) may create false interpretations.
Patients expectation and perception of pain (18, 19,20, 26), as well as clinician’s expectation (17) may be subject to powerful alterations of pain response. Impaired conditioned pain modulation (27) may play a role in what is mistakenly seen as a peripheral musculoskeletal disorder. Emotional and physiological even hormonal, responses may influence the pain response (28,30).
Anatomical blending may make structural selection by pain provocation tests groundless and several structures share the same innervation (35) making structural selection frequently impossible or at least highly questionable. Accurate structural diagnosis is further challenged by poor correlation between imaging findings and clinical symptoms (35). Physical inactivity as well as over-activity may lead to pain. (36,37,38). Anxiety and depression may both cause physically felt pain (39, 40).
It seems, for all the above mentioned multifactorial and multidimensional reasons, wise to be careful with the planning and the interpretation of structural differentiation and to link pain provocation through movement testing indistinctly to a musculoskeletal structure.
Summarizing; The many structure orientated treatment approaches based on hypothetical structural and or mechanical dysfunctions have been heavily criticized and should be reconsidered in a contemporary and multidimensional understanding of pain disorders (33). Clinical reasoning processes based upon symptom reproduction, as well as resistance assessment and subsequent structural differentiation have to be questioned for their added values at all times.
Max Zusman 1994:
“Provocative mechanical stimulation may not be an infallible means of accurately locating the pathological source of pain reported”
“The provocative mechanical manoeuvres used by therapists are, neurologically speaking, relatively crude. They do not have the necessary specificity to always distinguish between pathologically and non pathologically involved tissues and sites, Since their specific systemic effects have not been investigated, the responses produced with such stimuli are subject to variously influenced and informed interpretation”
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