Simulation of fatigue-initiated subacromial impingement: clarifying mechanisms

Abstract

Subacromial impingement in the shoulder precedes many cases of rotator cuff pathology. However, debate exists regarding the mechanism, and even existence, of fatigue-initiated impingement. The controversy centers on two primary impingement mechanisms: 1) superior humeral head migration and 2) scapular reorientation. A linked series of in vivo experiments and in silica simulations accomplishes the integration of stochastic, orthopedic, geometric, kinematic, physiologic, literature-derived, and experimental data sources to help resolve the mechanism debate. A major focus is the multi-scale modeling of relevant variability. The described techniques have direct implications for musculoskeletal modeling and simulation of the shoulder region, with specific application to assessing occupational and activities of daily living in diverse populations.

The Effect of Shoulder Muscle Fatigue on Acromiohumeral Distance and Scapular Dyskinesis in Women With Generalized Joint Hypermobility

“…Narrowing of the subacromial space is believed the beginning stage in rotator cuff pathologies that eventually result in tendon tearing. 48,49 However, Michener et al reported a minimal detectable change of 0.8 mm and Leong et al a minimal detectable change of 2.1 mm for AHD. 50,51 Assuming similar method in the sonography measurement of AHD as Michener et al, the AHD changes following fatigue would not be clinically significant.…”

“…Therefore, even small AHD changes may be very important. 48 Decreasing the subacromial space may result in shoulder impingement syndrome and compress the tissues occupied the space. Biceps tendon, subacromial bursa and of particular concern the supraspinatus tendon are within this space.…”

The potential role of upper extremity muscle fatigue in the generation of extrinsic subacromial impingement syndrome: a kinematic perspective

“…Thus, while research suggests that subacromial space integrity can be maintained even in the presence of muscle fatigue through scapular reorientation, an important consideration reported by several researchers is the considerable inter-subject variability that exists both in controlled and fatigued conditions. 61 This implies that the risk of SAIS is non-uniform across the population. As described, the subacromial tissues, notably the supraspinatus tendon, are highly susceptible to injury in seemingly benign healthy scenarios (i.e.…”