title: Acetabular component orientation in total hip arthroplasty: the impact of obesity.
abstract: BACKGROUND
  Acetabular component position can be an important determinant of joint stability and bearing surface wear after THA. Nonetheless, the incidence of malpositioning is high. Patient obesity, low surgeon volume, and minimally invasive approaches are known risk factors for malposition. As the incidence of obesity continues to increase, it is important to recognise its effect on intraoperative component positioning in THA.
  
  
  OBJECTIVE
  Our goal was to assess the impact of obesity on component position for a high-volume surgeon using a standard postero-lateral approach.
  
  
  METHODS
  A consecutive series of 120 obese (BMI >30, mean BMI 34.4) and 120 non-obese patients (mean BMI 25.4), who had undergone primary THA by a single surgeon, were included in our retrospective study. AP pelvis and cross-table radiographs obtained at the first postoperative visit were analysed using EBRA software to determine inclination and anteversion angles. Optimal position was defined as 30-45º of inclination and 5-25º of anteversion.
  
  
  RESULTS
  Mean inclination and anteversion were 40.6 (+/-5.4º) and 16.6 (+/-5.5º) respectively, in the obese group and 39º (+/-5.0º) and 16.2º (+/-7.5º) in the non-obese group. In the obese group 89 (74%) patients were within the desired range for both measurements, 31 (26%) were out of range in at least one, compared to 91 (76%) and 29 (24%) in the non-obese group, respectively. The overall incidence of malpositioning was 25% for both groups. Among outliers, mean deviation from the optimal range was ≤3.8º in both groups.
  
  
  CONCLUSIONS
  The risk of component malpositioning in THA may be reduced when surgery is performed by an experienced, high volume surgeon utilising a standard posterolateral approach. In this setting the deleterious effect of obesity may be overcome.
authors.affiliation: 1 Mayo Clinic, Rochester, Minnesota - USA.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: McArthur
authors.forename: Ettore
authors.initials: E
authors.lastname: Vulcano
authors.forename: Michael
authors.initials: M
authors.lastname: Cross
authors.forename: Joseph
authors.initials: J
authors.lastname: Nguyen
authors.forename: Alejandro G
authors.initials: AG
authors.lastname: Della Valle
authors.forename: Eduardo
authors.initials: E
authors.lastname: Salvati
mesh_terms: D000077:Acetabulum; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D015992:Body Mass Index; D002983:Clinical Competence; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D015207:Osteoarthritis, Hip / Q000453:epidemiology*; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011859:Radiography; D012189:Retrospective Studies