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The labelling of non-traumatic shoulder pain related to the structures of the subacromial space has been debated for many years. Historically, labelling of shoulder diagnoses and exploring theories about the underlying causes of shoulder pain are interrelated. Many authors use the phrase ‘syndrome’ describing a combination of findings, often occurring together, with an unknown or heterogeneous underlying pathogenesis. As such, Dr Charles Neer introduced the diagnostic label of ‘subacromial impingement syndrome’ (SIS) of the shoulder in 1972. This label was based on the mechanism of structural impingement of the structures of the subacromial space. This concept has been the dominant theory of injury to the rotator cuff tendons and other structures in the subacromial space, and has served as the rationale for clinical tests, surgical procedures and rehabilitation protocols.
Controversy about the label ‘SIS’
However, the label of SIS is now controversial, as recent evidence suggests that this concept does not fully explain the mechanism.1–3 Until a few years ago, SIS was a widely accepted ‘umbrella’ term for a number of possible underlying structural or biomechanical causes. Throughout the years, the description progressed from SIS to ‘impingement related shoulder pain’, with the growing opinion that ‘impingement’ represents a cluster of symptoms and a possible mechanism for the pain, rather than a pathoanatomic diagnose itself. The recent tendency to expel SIS as a diagnostic label on the one hand allows us to critically review our perspectives on shoulder pain, but on the other hand leads to uncertainties about the ‘umbrella’ we used to classify patients.
Diagnostic labels based on tissue-specific pathology fail to accurately classify the patient into subgroups for clinical decision-making. Diagnostic labels are intended to guide treatment, to facilitate communication between health professionals and to provide homogeneous patient groups in treatment outcome studies.2 ,3 For that reason, clinicians as well as researchers continue the attempt to classify patients into subgroups underneath the umbrella of common shoulder symptoms. Many alternatives have been formulated, all with their opportunities and limitations. Referring to the subacromial conflict, terminology has shifted from SIS to subacromial pain syndrome (SPS).
SPS, rotator cuff disease, rotator-cuff-related shoulder pain—not a single label to satisfy everyone and everything.
The SPS label implies that the shoulder pain is attributed solely to subacromial structures (bursa, rotator cuff, structural abnormalities at the level of the acromial arch), but does not reflect many other causes of shoulder pain located outside the subacromial space. Others suggest the label of ‘rotator cuff disease’,4 which might cover rotator cuff-related shoulder pain,5 but these labels fail to take into account many other structures that possibly contribute to shoulder pain of the subacromial space, like the labrum or the biceps complex. Moreover, since many rotator cuff tears seem to be asymptomatic, it is likely inappropriate to attribute shoulder pain to structural damage of the cuff. Finally, the labels ‘anterolateral shoulder pain’ and ‘shoulder pain of unknown aetiology’ have been advocated. These labels are very ambiguous and are likely a heterogeneous group, and therefore useless in clinical practice.
What is the answer?
Maybe it is time to abandon the attempt to find ‘the perfect name’ for the problem, and abandon the concept of an ‘umbrella’ terminology. Shoulder pain probably can be caused by the bursa or rotator cuff via mechanical impingement against the acromion or internally in the joint, or by tendon failure due to loading, or central sensitisation mechanisms, or muscle imbalances to name a few. There is not a single label to cover all the mechanisms and pathologies associated with pain of the subacromial region. The search for mechanism(s) is constantly evolving, and depending on the research interest, expertise and background of the individual, different explanations are advocated. All of us find ‘mechanisms’ that could explain chronic non-traumatic shoulder pain, and a lot of mechanisms are implicated.6 Tendon-people find tendon-related causes for shoulder pain, scapula-people find scapula-related shoulder dysfunction, ultrasound-people find abnormalities in the tendon or subacromial space and so forth. We should acknowledge that non-traumatic shoulder pain is multifactorial.
‘We should not try to put all patients under the same umbrella—the umbrella will never be big enough to keep everyone out of the rain’. Better to create several umbrellas to put our patients under and keep them dry. The umbrellas (labels) should be meaningful to the healthcare providers, but still allow communication with other providers.
What about naming movement impairments?
An important point of consideration is that physiotherapists focus on movement-related impairments rather than structural anatomy.2 ,3 Indeed, physiotherapists cannot change the shape of the acromion, remove acromial spurs or restore the integrity of the labrum. Physiotherapists try to influence motor control, soft tissue strength and flexibility and functional osteokinematics and arthrokinematics. Rather than relying solely on an inferred structural diagnoses, physiotherapy strategies are based on the identified impairments, tissue irritability and patient-related goals and expectations.5 ,7 Structure-based diagnostic labels may be relevant for the prognosis and the possible limitation to full recovery in the case of substantial structural deficits, but do not primarily determine our treatment strategy. Considering the fact that impairments in the shoulder are often related to abnormal scapulothoracic or glenohumeral kinematics, muscle performance deficits or kinetic chain dysfunctions, the challenge will be to identify impairment patterns to classify patients based on movement dysfunction instead of pathoanatomic diagnoses, and to establish reliability and validity of these classifications.
Future classification labelling should consider both categories based on relevant impairments and pathoanatomical diagnostic labels.7 Surgeons will need to identify the pathoanatomy, in order to render a decision for surgery. Rehabilitation professionals will find pathoanatomy labels somewhat helpful, but may rely more on a broad categorical label and the use of impairments to drive treatment decision-making.
Classifying patients into subcategories like:
flexibility deficits versus muscle dysfunction,
high versus low irritability, glenohumeral versus scapulothoracic impairment,
strength deficits versus motor control impairment, and so forth,
will help the clinician to determine the treatment strategy. Moreover, over the course of an episode of care, patients may shift from one category to another, or be considered appropriate for two categories at the same time. It will be the challenge to find balance between researchers, focusing on homogenous labelling of patient selection for clinical studies and the individually based approach which is relevant for clinicians providing care.
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