Obesity, age, sex, diagnosis, and fixation mode differently affect early cup failure in total hip arthroplasty: a matched case-control study of 4420 patients.

BACKGROUND: Studies about the influence of patient characteristics on mechanical failure of cups in total hip replacement have applied different methodologies and revealed inconclusive results. The fixation mode has rarely been investigated. Therefore, we conducted a detailed analysis of the influence of patient characteristics and fixation mode on cup failure risks.
METHODS: We conducted a case-control study of total hip arthroplasties in 4420 patients to test our hypothesis that patient characteristics of sex, age, weight, body mass index, and diagnosis have different influences on risks for early mechanical failure in cemented and uncemented cups.
RESULTS: Women had significantly reduced odds for failure of cups with cemented fixation (odds ratio = 0.59; 95% confidence interval, 0.43 to 0.83; p = 0.002) and uncemented fixation (odds ratio = 0.63; 95% confidence interval, 0.5 to 0.81; p = 0.0003) compared with that for men (odds ratio = 1). Each additional year of patient age at the time of surgery reduced the failure odds by a factor of 0.98 for both cemented cups (odds ratio = 0.98; 95% confidence interval, 0.96 to 0.99; p = 0.016) and uncemented cups (odds ratio = 0.98; 95% confidence interval, 0.97 to 0.99; p = 0.0002). In patients with cemented cups, the weight group of 73 to 82 kg had significantly lower failure odds (odds ratio = 0.63; 95% confidence interval, 0.4 to 0.98) than the lightest (<64 kg) weight group or the heaviest (>82 kg) weight group (odds ratios = 1.00 and 1.07, respectively). No significant effects of weight were noted in the uncemented group. In contrast, obese patients (a body mass index of >30 kg/m(2)) with uncemented cups had significantly elevated odds relative to patients with a body mass of <25 kg/m(2) (odds ratio = 1.41; 95% confidence interval, 1.03 to 1.91) for early failure of the cups compared with an insignificant effect in the cemented arm of the study. Compared with osteoarthritis as the reference diagnosis (odds ratio = 1), developmental dysplasia (odds ratio = 0.52; 95% confidence interval, 0.28 to 0.97) and hip fracture (odds ratio = 0.38; 95% confidence interval, 0.16 to 0.92) were significantly protective in cemented cups.
CONCLUSIONS: Female sex and older age have similarly protective effects on the odds for early failure of cemented and uncemented cups. Although a certain body-weight range has a significant protective effect in cemented cups, the more important finding was the significantly increased risk for failure of uncemented cups in obese patients. Patients with developmental dysplasia and hip fracture were the only diagnostic groups with a significantly decreased risk for cup failure, but only with cemented fixation. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.