Late Instability Following Total Hip Arthroplasty

Hi p pain due to underlying arthritis represents a common reason for individuals to seek medical attention.The symptoms of arthritis may be addressed by non-operative management delivered by primary care physicians; 1 however, for patients failing non-operative treatment, total hip arthroplasty (THA) is considered.THA is one of the most successful procedures in orthopaedic surgery that has effectively improved the quality of life of patients affected by osteoarthritis of the hip. 2 Unfortunately the outcome of THA is compromised by complications such as instability.3 Instability comprises two inter-related yet distinct conditions, dislocation and subluxation.Dislocation is a term reserved for situations in which the femoral head is completely out of the acetabulum, whereas subluxation is partial dislocation in which the femoral head is partially out of the acetabulum.Instability can present early or late after hip replacement.4,5 Late dislocation is considered if the event occurs five or more years after the primary arthroplasty, and in contrast to early dislocation, it appears to require operative intervention.Recent studies suggest that the incidence of late dislocation may be greater than initially appreciated 4,[6][7][8] and that the cumulative rate rises with longer follow up.9 In this article, we review the etiological factors for late instability.We also present our institutional experience on late instability due to polyethylene wear as the primary cause when no discrete reason for dislocation is identified. EtiologyThe etiology of hip instability is often multifactorial.Patient demographics, operative technique and implant design variables have been demonstrated to affect the risk of dislocation.There are multiple surgical and implant-related factors that predispose to dislocation, such as malorientation of the components, decreased head-to-neck ratio, proximal placement of the acetabular component, decreased femoral offset, posterior surgical approach, abductor insufficiency secondary to trochanteric migration, or abductor avulsion.3,5,[10][11][12] Patient risk factors for early dislocation after primary THA are female gender, older patients, neurological dysfunction or cognitive impairment, and a preoperative diagnosis of osteonecrosis of the femoral head, femoral neck fracture and/or inflammatory arthritis.3,9,10,12 The presumed etiological factors for late instability include long standing malpositioning of the components, trauma, deterioration in muscle mass, neurological status impairment and polyethylene wear 4,5,13 (table 1).