Subacromial Impingement Syndrome:
The Identification of etiologic Mechanisms (SISTIM)
- Pieter Bas de Witte, MD, BSc
- Arjen Kolk, MD
- Prof. J.L. Bloem, MD, PhD
- M. Reijnierse, MD, PhD
- A. Navas Canete, MD
- Dutch Arthritis Association (in dutch: Reumafonds)
- Department of Orthopaedics, Haga Hospital, The Hague
- Department of Orthopaedics, MCH, The Hague
- Department of Orthopedics, Rijnland Hospital, Leiderdorp
- Department of Rehabilitation, LUMC, Leiden
- Department of Radiology, LUMC, Leiden
Rationale: The subacromial impingement syndrome (SIS) is the most prevalent disorder of the shoulder in primary health care. Acromionplasty, as the main surgical treatment of SIS, is one of the most performed orthopedic surgeries.
The etiology of the primary SIS is not clearly understood, but surgical treatment is primarily focused at the extrinsic mechanism as described by Neer(1): the anterior part of the acromion painfully impinges on the subacromial tissues and therefore must be resected. Nevertheless, variable results of this frequently performed procedure have been reported (successful in 48- 90%), and there are numerous publications of successful (conservative) treatments without changing the coracoacromial shape.(1-8)
There is a lot of debate on the etiology of SIS. Several mechanisms have been described: i.e. narrowing of the subacromial space caused by cranial translation of the humerus in multidirectional instability, scapular dyskinesia, or intrinsic mechanisms such as primary degenerative tendinopathy of the rotator cuff.(9-12)
In theory, impingement (“narrowing of the subacromial space”) can be caused by several mechanisms. Our hypothesis is, that the extrinsic mechanism is only valid for a subgroup of patients; complaints of SIS can be caused by 1) a pathologic pattern of arm-scapula movements caused by a disrupted balance in muscle forces, leading to cranial translation of the humerus with respect to the scapula, or 2) narrowing of the subacromial space because of anatomic variations (i.e. a hooked acromion or humeral shape), or 3) a subacromial inflammatory reaction (i.e. caused by micro-trauma), or 4) secondary to an adjoining pathology (i.e. osteoarthritis in the acromioclavicular(AC)-joint).
Objective: Organization of distinct etiological mechanisms for symptoms clinically diagnosed as SIS, into several identifiable subgroups of patients (relative cranialisation of the humerus, structural narrowing of the subacromial space, subacromial inflammatory processes, other primary pathologies), in order to improve diagnostic and therapeutic strategies of SIS by designing concept diagnostics and treatment flow charts for each subgroup.
Hypothesis: The etiology of primary SIS is heterogeneous and the extrinsic mechanism and acromial shape play a substantial role in only a subgroup of patients. Therefore, acromionplasty is not a good treatment for at least a part of the patients clinically diagnosed with SIS. With new diagnostic methodologies, these subgroups can be identified.
Study design: Multicenter observational cohort study.
Study population: Patients clinically diagnosed with Subacromial Impingement Syndrome.
Main study parameters (categorized for etiological subgroups):
Relative cranial translation of the humerus: 3D arm-scapula motion registration (3D RoM), muscle activation parameters of shoulder and rotator cuff muscles (EMG), static acromiohumeral distance (sAH) on AP-radiographs ‘at rest’ and with exerted ab- and adduction moments (dAH), integrate bony 3D-shape with 3D RoM to describe dynamic AH (3DdAH).
Structural (bony) narrowing of the subacromial space: shape parameters of scapula (i.e. Bigliani acromion classification) and humerus, 3D kinematic analysis of scapulo-humeral motion by integration of bony 3D-shapes with 3D RoM.
Subacromial inflammatory processes and damaged tissues: MRI for rotator cuff and muscle quality (Goutallier score) and signs of bursitis, tendinitis and rotator cuff ruptures.
Other primary pathologies leading to SIS complaints: evaluation of MRI and radiographs for acromioclavicular-osteoarthritis, full thickness rotator cuff-ruptures, coracoid impingement and other subacromial pathologies.
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