Hip Microinstability: Understanding a Newly Defined Hip Pathology in Young Athletes

      Abstract: Microinstability is an increasingly recognized diagnosis in young athletes presenting with hip pain. Causes of microinstability may include abnormality of the hip bony anatomy, acetabular labral tears, joint capsule laxity or injury, and muscle dysfunction. Borderline hip dysplasia is an increasingly recognized factor predisposing to microinstability. The capsuloligamentous structures of the hip, particularly the iliofemoral ligament, provide important restraints to femoral head motion, and iatrogenic defects can predispose patients to instability after surgery. Injury to the acetabular labrum may disrupt its important hip-stabilizing properties including the suction seal and improved acetabular depth. Hip muscle weakness or imbalance may result in increased femoral head motion within the acetabulum. The diagnosis of hip microinstability can be challenging, and the history is often nonspecific. Physical examination maneuvers include the anterior apprehension, prone instability, axial distraction, and abduction-hyperextension-external rotation tests. Radiographic features may include borderline hip dysplasia, femoral head-neck junction cliff sign, and an elevated femoral-epiphyseal acetabular roof index. Magnetic resonance arthrography may demonstrate a capsular defect, capsular thinning, or labral pathology. Diagnostic intra-articular injection of anesthetic can confirm the intra-articular nature of the pathology. Management of hip microinstability focuses on strengthening the dynamic stabilizers of the hip through focused physical therapy. Surgery may be considered in recalcitrant cases where symptoms persist despite optimization of hip stabilizer strength. In such cases, addressing the primary source of instability through labral repair or reconstruction and capsular repair or plication can be considered. In highly selected cases, surgery can result in excellent outcomes.
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