Microinstability of the hip: A review.

With the development of conservative hip surgery techniques, new entities such as microinstability have been identified. Microinstability is a painful supra-physiological mobility of the hip. It results from the association of architectural and functional abnormalities impairing joint stability. These risk factors concern hip joint bone architecture or peri-articular soft tissues. Bone abnormalities are identified on hip assessment parameters. Soft tissues also play a key role in the static and dynamic stability of the hip: the joint capsule, labrum, ligamentum teres and adjacent myotendinous structures affect joint coaptation; any abnormality or iatrogenic lesion concerning these structures may constitute a risk factor for microinstability. Diagnosis is based on interview, clinical examination and imaging. Findings of labral lesions or femoro-acetabular impingement do not rule out microinstability; they may be associated. Treatment is based first on physiotherapy for muscle reinforcement to improve joint coaptation. In case of failure, arthroscopic surgery is indicated for femoro-acetabular impingement and capsular plicature which is being evaluated. Periacetabular osteotomy or shelf acetabuloplasty may be indicated, according to the severity of joint bone architecture abnormality. Microinstability is a multifactorial entity. Lesions induced by microinstability may in turn become risk factors for aggravation. Diagnosis and indications for surgery are thus difficult to establish. Only full clinical examination and exhaustive imaging assessment allow microinstability and associated lesions to be identified.