Hip Microinstability: New Concepts and Comprehensive Imaging Evaluation.

Hip instability is defined generally as extraphysiologic femoroacetabular motion classically observed as a sequela of prior trauma, hip arthroplasty, and developmental hip dysplasia. However, new concepts regarding subtle forms of hip instability have gained importance in recent discussions and literature with the emergence of the term microinstability. It can manifest as apprehension, especially while descending stairs, deep hip pain, and/or groin pain. Such patients commonly are evaluated by obtaining a detailed patient history and performing focused examination and radiographic imaging, although various internal derangement findings of hip microinstability are subtle and may not be evident on screening radiographs alone. Advanced MRI or MR arthrography can provide a more detailed assessment of chondrolabral injuries and capsular lesions or anatomic alterations and confirm the clinical suspicion of microinstability. However, when capsular laxity emerges as a primary cause of developmental alterations or conditions such as Ehlers-Danlos syndrome, dynamic examinations, such as leg traction MRI and dynamic US, can reveal increased femoral head distraction or translation in relation to the acetabulum. This article provides a comprehensive guide for the evolving concepts and definitions of hip instability, with a specific focus on microinstability, by discussing the role of various imaging modalities in this domain. The radiologist should be able to apply this knowledge in their multidisciplinary hip practice to aid timely diagnosis and management of such disorders. ©RSNA, 2025 Supplemental material is available for this article.