Hip instability: anatomic and clinical considerations of traumatic and atraumatic instability.

Hip instability is uncommon because of the substantial conformity of the osseous femoral head and acetabulum. It can be defined as extraphysiologic hip motion that causes pain with or without the symptom of hip joint unsteadiness. The cause can be traumatic or atraumatic, and is related to both bony and soft tissue abnormality. Gross instability caused by trauma or iatrogenic injury has been shown to improve with surgical correction of the underlying deficiency. Subtle microinstability, particularly from microtraumatic or atraumatic causes, is an evolving concept with early surgical treatment results that are promising.