CORR Insights®: A Radiographic Abdominal Pannus Sign is Associated With Postoperative Complications in Anterior THA

Where Are We Now?

Anterior-approach THA has gained popularity, in part because of evidence it delivers faster and easier recovery than achieved with other approaches [8], and without any substantial difference in terms of the overall risk of complications compared with posterior or laterally based approaches [7]. Nevertheless, specific complications have been reported more commonly after anterior THA, particularly during the surgeon’s learning curve or in patients with difficult anatomy [1]. These include femoral perforations and fractures, femoral component loosening, superficial surgical site infection, and other wound complications [3]. The anterior approach is performed in the supine position, which facilitates fluoroscopic guidance and anesthesia care, but some have counseled caution when applying anterior approaches to patients with obesity because of concerns regarding surgical site complications [9, 12].

Severe obesity is associated with many challenges and complications in THA [11] and is commonly quantified using BMI. However, this metric ignores muscle mass, body fat percentage, and fat distribution, making BMI an imperfect surrogate for surgical risk. By contrast, excess body fat distributed over (or near) the area where a surgeon plans to make an incision will consistently render surgical exposure more difficult and prolong surgical time; it may also result in fat necrosis or impaired healing at the surgical site. Indeed, studies have shown adipose tissue thickness at the surgical site is a risk factor for surgical site complications in TKA [13] and spine surgery [4].

Obesity is associated with extended surgical times and an increased risk of complications in anterior THA [9]. Although it is unclear whether using the anterior approach for THA increases the risk of complications in patients with obesity, many surgeons choose other surgical approaches for THA in patients with severe obesity. Some do so by stratifying by BMI, while others evaluate for the presence and mobility of an abdominal pannus and the presence of intertriginous dermatitis or other signs of impaired skin integrity. Unfortunately, such assessments are subjective and thus vulnerable to bias, real and perceived. Potential bias is a concern when the results of an obesity assessment may be used to restrict a patient’s access to specific forms of surgical care.

The current study [10] introduces a novel, objective, and anatomically plausible radiographic parameter—what the authors call the “pannus sign” on an anteroposterior radiograph of the pelvis—to investigate how obesity influences surgical risk in THA. Based on their findings, the authors suggest that if THA is planned and the patient has a large abdominal pannus, an approach other than the anterior should be considered. This will remain my personal practice. I will also continue to consider the mobility of any pannus and the condition of the skin, issues not addressed in the current investigation, but the radiographic measurements introduced will add objectivity to the assessment. Others have suggested use of “bikini” anterior incisions that avoid the inguinal crease [6] and closed incision negative pressure dressings [2] to mitigate the risk of wound complications in patients with obesity who have a large abdominal pannus.

Where Do We Need To Go?

This study [10] uses readily available information to inform patient education and care. Like most important research, however, it raises more questions than it answers.

1. Is the measured risk directly related to the size and location of an abdominal pannus and distinct from the risks associated with an abnormal BMI, malnutrition, and diabetes mellitus and high American Society of Anesthesiologists classification? Or is the pannus sign simply another redundant way to measure established risks?

2. Would posterior or lateral surgical approaches actually reduce complications in patients who are identified as being at increased risk based on the pannus sign? Or are the measured risks relevant to any surgical approach, regardless of the proximity of the incision to an abdominal pannus?

3. How should we treat patients with obesity who have an abdominal pannus before hip surgery? Will medical weight loss, bariatric surgery, or panniculectomy reduce the risks of THA in general or anterior THA in particular? Will attempts at weight loss result in malnutrition and paradoxically increase these risks?

4. Can presurgical treatments of intertriginous areas, such as the use of antifungal powders, reduce the risk of wound complications when a large abdominal pannus is present?

5. Can “bikini” anterior incisions that avoid the inguinal crease reduce wound complications in patients with obesity [6]?

6. Can changes in incision management, such as use of subcutaneous drains or negative-pressure wound therapy [2], ameliorate the risk of infection and wound complications in patients with obesity?

How Do We Get There?

Further research is certainly warranted. A similar retrospective method could be applied to determine whether the pannus sign remains associated with surgical risk in posterior and laterally based THA or in anterior THA with bikini incisions. Studies could include data on BMI, American Society of Anesthesiologists classification, glycemic control, and nutritional status, with a multivariate analysis to explore whether pannus location is an independent risk factor for complications. Because of potential statistical collinearity between BMI and the described pannus sign, large cohorts will be necessary, likely requiring data from multiple centers. Such studies should seek to include centers or surgeons that perform their chosen approach in “all comers” to reduce, but not eliminate, the selection bias inherent in comparing surgical approaches retrospectively. Large randomized controlled trials (RCTs) would be desirable but are likely less practical for comparing THA approaches, given established patient and surgeon preferences and variations in surgical technique.

RCTs comparing obesity treatments before anterior THA may also be difficult to accomplish. Retrospective studies can compare complication rates in patients with an abdominal pannus who underwent medical weight loss treatments, bariatric surgery, or panniculectomy before anterior THA to rates in similar patients who did not receive treatment. A recent study found an increased complication rate in patients with obesity who lost weight before THA [5], confirming the need to validate recommendations for treating obesity as part of presurgical optimization.

RCTs are ideally suited for an investigation of several discrete treatment choices intended to modulate surgical risk. A recent RCT showed reduced complications when comparing negative-pressure and antimicrobial dressings in patients with obesity undergoing anterior THA [2]. These findings warrant confirmation, and similar study designs could be applied to the use of subcutaneous drains or preoperative skin treatments, incorporating measurements of abdominal pannus in addition to BMI to stratify people with obesity. Investigators should use the highest-quality study design that is practical, but we cannot wait for RCTs before making decisions for patients who show up next week.

Future patients will benefit the most from public health or other interventions that address the obesity epidemic itself. Successful prevention and treatment of obesity, without creating iatrogenic malnutrition, seems the ideal way to prevent the complications noted in this investigation [10]. Recommending diet and exercise rarely results in sustained weight loss, but bariatric surgery can result in malnutrition and may not reduce complications after subsequent THA. Some headway is being made with medical treatment, but obesity remains very common in western countries. Until medical science meets this need, orthopaedic surgeons will remain challenged to decide when to offer elective THA to patients with obesity who are at high risk of surgical complications and how to mitigate that risk.