Purpose: To determine whether body mass index (BMI) is associated with mis-seating of ceramic acetabular components, and whether any associations are independent of differences in case mix.

Method: All primary total hip arthroplasty (THA) cases using ceramic components, identified from a prospective database of total joint arthroplasties performed at one center among six surgeons between 1998–2006 were radiographically reviewed. The risk of mis-seating by BMI was calculated using logistic regression models.

Results: Of the 411 THAs, 77 (20.3%) were performed in patients with BMIs that were defined as underweight to normal BMI (29.9 BMI). THA mis-seating occurred in 80 cases (19.5%). Intra-operative characteristics differed significantly according to THA mis-seating status. Univariate analysis revealed that THA mis-seating was more likely to occur in procedures performed by certain surgeons (2 trend, p = 0.01) and procedures performed in more recent years (2 trend, p = 0.02). In comparison with patients who did not incur a mis-seated THA, those patients who did incur a mis-seated THA did not have a significantly different trend in BMI (c2 trend, p = 0.09). However, adjustment for case mix, THA type, surgeon and year of procedure revealed a significant association between BMI and risk of THA mis-seating. Those patients who were overweight at the time of THA (BMI of 25.0–29.9) were at increased risk of THA mis-seating (adjusted odds ratio (OR) 2.52, 95% confidence interval (CI) 1.24–5.12, p = 0.01).

Conclusion: THA mis-seating of ceramic acetabular systems was a frequent occurrence. Although incidence of mis-seated THAs did not differ significantly by patient sex, hip side, indication, or THA component type, mis-seating did differ significantly by surgeon and year of replacement. Furthermore, patients who were overweight were more than two times more likely to suffer THA mis-seating than those who were underweight, of normal weight or obese.