Impingement and Entrapment Syndromes

The term “impingement” can be variously defined as either “a sharp collision produced by striking or dashing against something,” “influencing strongly,” or just “encroaching.” This diversity in language is also reflected in the range of impingement syndromes evident in musculoskeletal disease.

Impingement within the musculoskeletal system is a fascinating area with the phenomenon being increasingly recognized in many different parts of the body. Our ability as radiologists to evaluate these conditions has also been enhanced in the last decade by the improvements in resolution of both magnetic resonance (MR) imaging and ultrasound technologies.

During the past 15 years, ankle impingement has moved from a little known clinical diagnosis of exclusion to a well-recognized singular cause of chronic ankle pain and functional impairment. Similarly, femoroacetabular impingement is a continuing clinical hot topic with radiological findings playing a crucial role in confirming diagnosis and planning treatment. Nerve and tendon entrapment has also become a more accessible radiological diagnosis with the improved resolution afforded by technological advances. For all these conditions, high-resolution ultrasound is increasingly described as a method to target areas of impingement for diagnostic and therapeutic effect.

In contrast, shoulder impingement is a long established clinical diagnosis. The two articles on shoulder impingement in this issue of Seminars in Musculoskeletal Radiology provide an elegant outline and update on the continuing controversies in pathogenesis for these conditions while illustrating and describing the pertinent anatomy and radiological features.

Finally I would like to thank the editors and publishers of seminars for inviting me to serve as guest editor, and I would also like to thank all my radiology and orthopaedic colleagues who have submitted such excellent articles for this issue. All the articles aim to provide an up-to-date review of current concepts, detailed anatomy, pathogenesis, and imaging features for each condition focusing on MR imaging but discussing high-resolution ultrasound where appropriate.