An active, 50-year-old male, gym teacher, who had undergone total hip replacement 4 years previously, presented with a history of increasing limp, one dislocation, and episodes of subluxation in his right hip. Physical examination demonstrated a positive Trendelenburg sign and abductor lurch on walking. ROM was normal compared to the uninvolved left side. Patient had weak to nonexistent abductor strength when testing in the left lateral decubitus position. Preoperative radiograph is demonstrated in Figure 82.1A. Intraoperative findings demonstrated muscle necrosis and avulsion of the gluteus medius from the greater trochanter and the typical appearance of adverse local tissue response (ALTR) (Fig. 82.1B). The hip was reconstructed with a constrained liner and a modular tapered stem to prevent further instability (Fig. 82.1C). Attempt was made at the time of surgery to tenodese the medius muscle into the iliotibial band.

Not only is there physical trauma from dislocation following total hip replacement, there is also psychological trauma to both the patient and the surgeon. Historical review of dislocation before the new millennium demonstrated reports of dislocation following primary arthroplasty to range between 0% and 10% depending on the series and depending on the diagnoses at the time of surgery with rates following total hip replacement for fracture of the femoral neck among the highest (1,2,3). In revision surgery, the rates of dislocation following the procedure ranged from 3% to 20% (4). Although there have been many additional options (techniques and devices) for the surgeon to potentially decrease the incidence of the occurrence of dislocation (including larger heads, better head neck ratios with smaller modular tapers, anteverted and modular neck and femoral body designs), the rates of dislocation remain substantial. Evaluation of the 1998 to 2007 Medical National Sample (5%) database demonstrated 3.92% early dislocations and 1.15% late dislocations. Encouraging is the fact that the rate of early dislocation decreased from 4.2% in 1998 to 2.14% in 2007 and dislocation risk was lower by 35% for early dislocation between 2004 to 2007 and 1998 to 2003 as well as by 43% for late dislocations (5). The revision burden for the treatment of dislocation is also substantial. Bozic et al. (6) reported that revision for dislocation and instability was the most common reason for revision at 22.5% versus 19.7% for mechanical loosening, 14.8% for infection, 6.6% for periprosthetic osteolysis, and 6.2% for periprosthetic fracture. Fortunately, two-thirds of the dislocations can be treated closed (3), but the cost for the treatment of dislocation is also substantial. The cost of a closed reduction is 19% of the cost of a primary procedure and the cost of revision for dislocation is 148% of the cost of a primary procedure (7). Finally in this regard, revision for dislocation is not always successful with 39% failure reported by Daly and Morrey (8) and 15% failure in more recent series (9).

There is also a cumulative risk of dislocation with time (10). It is important for both the surgeon and the patient to be aware of this phenomenon. Twenty percent to 30% of dislocations occur late, after 2 to 5 years depending on the study (1,11), with an increased prevalence of 1% every 5 years and 7% after 25 years. It is also related to head size with a cumulative risk of 3.0% and 6.9% for 28-mm heads through the anterolateral and posterior approach, respectively, and 2.4% and 3.6% for 32-mm heads (12).

Understanding the epidemiology of the occurrence and treatment of dislocation outlined in the introduction of this chapter allows for those of us performing total hip replacements to recognize that prevention is better than treatment (Fig. 82.2). To prevent the occurrence, the surgeon needs to understand the causes of dislocation. Dorr outlined the reasons for dislocation to include patient compliance issues, soft tissue tensioning issues, component positioning
issues, and impingement issues both of components and bone (13,14,15).

Concerning patient-specific issues, the most anecdotal issues are related to alcohol and drug abuse, as well as dementia. Kelley et al. (16,17) have documented the relationship of alcohol abuse and dislocation and the studies of total hip replacement for hip fracture allude to the dementia issue (2). Other diagnoses such as Parkinsonism (18) have been reported to have higher rates of dislocation in some studies but not others. Recognition of patients in these high-risk groups should prompt the surgeon and the hip replacement team to add appropriate counseling, preoperative teaching, and documentation of the increasing risk in these groups. The surgeon may modify the approach and the prostheses in some of these situations.

The issues related to soft tissue tensioning, impingement, and component positioning will be addressed under various aspects of prevention discussed below.