High Body Mass Index

Indications/Contraindications

The most common indication for THA is osteoarthritis (OA). Several studies have shown that obesity is likely to play a role in the development of OA of the hip. Clinicians have postulated that “obese” (BMI, 30–39.9 kg/m ² ) and “morbidly obese” (i.e., BMI ≥ 40 kg/m ² ) patients undergoing THA pose greater technical difficulty for the surgeon, have more postoperative complications, and have poorer short- and long-term outcomes than “ideal weight” (BMI, 20–24.9 kg/m ² ) or “overweight” (BMI, 25–29.9 kg/m ² ) patients. In 1982, Sir John Charnley stated that obesity should be a contraindication to performing THA. Some surgeons advise obese patients to lose weight before undergoing THA, believing that THA in an obese patient would be technically demanding and would likely lead to increased postoperative morbidity. Possible concerns have included increased risk of infection, thromboembolism, and early implant failure (e.g., aseptic loosening, fatigue fracture).

Implant manufacturers today include some patient selection caveats in their precautionary statements to surgeons and include warnings in their product inserts, for example: “patients should be able to control their weight,” “excessive weight may adversely affect the implant,” “heavy patients can place high loads on the prosthesis which may lead to failure,” and “complications or failure may be more likely in heavy patients.” A study by Craik et al. found that 16% of 147,691 obese THA patients received implants against manufacturer recommendations that specifically listed obesity as a contraindication.

Some surgeons postulate that obesity should not be a deterrent to THA, with several studies reporting excellent functional outcomes, pain relief, and quality of life comparable to those seen in normal BMI patients. Regardless, a thorough discussion with the patient about the risks of THA and obesity is key.

Preoperative Planning

Preoperative planning for obese patients does not differ, in general, from planning for nonobese patients. Standard radiographic imaging should be performed. A radiographic marker may be more important for sizing because of increased distance between the hip and the radiographic plate. For those who prefer it, digital templating has been shown to be effective at predicting THA component sizes regardless of BMI. To facilitate postoperative evaluation and long-term follow-up, additional preoperative assessments can be valuable, for example, Harris Hip Scores (HHSs), the 12-Item Short Form Health Survey (SF-12) or 36-Item Short Form Health Survey (SF-36), HgA1c, percent body fat, albumin, and grip strength.

It is advisable to encourage obese patients to attempt to increase upper body strength preoperatively because they must use an overhead frame on the hospital bed to assist in achieving early mobilization. As with all THA procedures, early mobilization is important to avoid an overall decline in function, venous thromboembolism, and respiratory complications. In addition, preoperative plans for other accommodative equipment should be made, such as a wide bedside commode and a wide walker. Preoperative planning should also include pharmacologic consultation to ensure careful administration of narcotic pain medications because obese patients often cannot tolerate as much narcotic medication as simple calculations based on an increased BMI might suggest. Finally, consideration should be given to bariatric surgery and weight loss before elective primary THA for selected patients.

Description of Surgical Technique: Variations in Obese Patients

Few differences in operative technique have been described for obese patients undergoing THA. In general, a minimally invasive approach should be avoided in obese patients; however, any approach and incision that can achieve easy and adequate exposure while protecting the soft tissues is appropriate ( Fig. 86.1 ). The author prefers a straight lateral position on the operating table, which allows fat/excess skin to “fall away” ( Figs. 86.2 through 86.5 ), combined with an anterolateral or posterior approach and a cementless socket and stem. Several studies report increased surgical wound complications for the direct anterior approach (DAA) for THA, especially in obese patients. Therefore, it may not be ideal in these patients. Purcell et al., however, recently published a new and larger retrospective study showing no difference in superficial or deep infection rates between DAA and posterior approach (PA) hips in obese patients. For obese patients, a low-wear bearing with large diameter head is preferred in the absence of other contraindications. Dual-mobility implants should be considered in patients for whom instability is a concern.

Intraoperative radiographic evaluation allows the surgeon to determine proper cup placement. A study by Lambers and Jennings that tracked acetabular cup placement accuracy without fluoroscopy followed by immediate reposition of cups after imaging found that 57% of patients had an error of 5 degrees or more in at least one plane. A large retrospective study by Gosthe and Suarez recently demonstrated that with fluoroscopic guidance, acetabular components can be placed with accuracy comparable to those placed in nonobese patients. With obese patients, a tendency to place the cup in a more abducted position in the acetabulum should be avoided because this may result in increased wear. Similarly, strong traction caused by retractors in obese patients can lead to iatrogenic pelvic lift. It is recommended to release retractors prior to impacting the acetabular cup to allow the pelvis to tilt back to its neutral position if using a lateral transgluteal approach. Intraoperative radiographs allow the surgeon to assess the equality of leg length, which can be more difficult to determine in obese patients. At the conclusion of the operation, two drains are placed: one deep to the fascia and the other in the subcutaneous space. Then, a waterproof, occlusive dressing is applied in an effort to reduce wound complications and promote wound healing ( Fig. 86.6 ).