Hip Microinstability: Current Concepts in Diagnosis, Surgical Management, and Outcomes A Narrative Review.

Background: Hip microinstability-subtle, symptomatic femoral head translation without dislocation-compromises the labral suction seal and accelerates chondrolabral wear. Clinical overlap with femoroacetabular impingement syndrome (FAIS) and borderline dysplasia delays recognition. Purpose: To synthesize contemporary evidence on definitions, diagnosis, imaging, management, and outcomes in hip microinstability and to propose a phenotype-guided framework grounded in the labrum-capsule-ligamentum teres (LT) stability continuum. Study Design: Narrative review. Methods: Peer-reviewed literature (2000-2025) focusing on biomechanical investigations, comparative cohorts, meta-analyses, and consensus statements on microinstability, hip capsular management, borderline dysplasia, and LT pathology. Results: A four-pillar diagnostic approach improves accuracy. The Abduction-Hyperextension-External Rotation (AB-HEER) and Hyperextension-External Rotation (HEER) tests provide the highest single-test accuracy among exam maneuvers, whereas the prone instability test offers high specificity to rule in. The femoroepiphyseal acetabular roof (FEAR) index aids in risk stratification for borderline dysplasia but is position-sensitive. Arthroscopy with labral preservation and complete hip capsular closure improves patient-reported outcomes (PROs) and survivorship relative to non-closure. Iatrogenic cam over-resection can precipitate microinstability; femoral head-neck remplissage is a revision option to restore contour and sealing mechanics. In borderline dysplasia, both arthroscopy and periacetabular osteotomy (PAO) improve PROs when selection is phenotype-guided; PAO trends toward lower total hip arthroplasty (THA) conversion when undercoverage is the primary driver. Early postoperative circumduction is associated with lower rates of adhesion-related reoperation. Return-to-sport (RTS) decisions are criteria-based rather than time-based across successful programs. Conclusion: A seal-first, close-second strategy, situated within a stability continuum, underpins contemporary care. Standardized definitions, objective laxity metrics, multicenter registries, and microinstability-specific rehabilitation/RTS batteries are needed to refine indications and improve durability; evidence specific to labral augmentation in microinstability remains limited. Clinical Relevance: Precise phenotyping and capsular stewardship reduce the risk of revision hip arthroscopy and conversion to total hip arthroplasty, inform sport-specific counseling, and align with joint-preservation goals in young, active patients. Level of Evidence: V (Narrative Review).