Ph Hernigou (Créteil)
Obesity is associated with increased rates of dislocation after total hip arthroplasty (THA). However, in these patients with obesity, it is not known whether the risk is only postoperative or persists several years after surgery and whether having bariatric surgery prior to undergoing THA or/and receiving a specific device (dual mobility) is better to decrease dislocation is unclear. We asked: (1) what is the cumulative risk of dislocation in obese patients after THA in absence of dual mobility or constrained liner? (2) Does bariatric surgery before undergoing THA decrease dislocation’s risk in obese patients (3) Are dual mobility liners efficient in obese patients
Material and methods: We retrospectively reviewed 4 groups of THA to compare the dislocation rate between non-obese patients (BMI≤30 kg/m²) with standard cups, obese patients (BMI>30 kg/m²) with standard cups, previous obese patients with standard cups having bariatric surgery prior THA (with reduction of BMI<30 kg/m²), and obese patients who received dual mobility liners without bariatric surgery prior THA (BMI>30 kg/m²). All patients received the same implants except for diameter head (32-mm head with standard cups and 28-mm head with dual mobility or constrained liners). The patients were followed at routine intervals and were specifically queried about dislocation.
Results: With standard liners, more hips in patients with BMI> 30 kg/m² dislocated than did hips in non-obese (BMI<30) patients. The cumulative number of dislocations (first-time without recurrent dislocation) was at one year followup 6% [13 of 215] compared with 2% [4 of 215] in non-obese patients (odds ratio [OR], 3.4; 95% confidence interval [CI], 1.09 to 10.58; p = 0.03) and was at 15 years followup 13% [28 of 215] compared to 4% [8 of 215] in non-obese patients (odds ratio [OR], 3.9; 95% confidence interval [CI], 1.72 to 8.71; p = 0.001). When Bariatric surgery was performed before THA, BMI declined from 42.0 kg/m2 to 27.6 kg/m2, but with the same standard liners more hips after bariatric surgery dislocated at one year follow-up than did hips in obese patients without pre-operative bariatric surgery (13% [11 of 85] compared with 6% [13 of 215]; odds ratio [OR], 0.43; 95% confidence interval [CI], 0.18 to 1.01; p = 0.05). Dual mobility implants decreased the risk of dislocation, and less hips at 7 years followup had dislocated in obese patients with dual mobility than did hips with standard liners (2% [3 of 155] compared with 9% [20 of 215]; odds ratio [OR], 0.19; 95% confidence interval [CI], 0.05 to 0.66; p = 0.01) bringing this number in line with the number observed in non-obese subjects with standard cups.
Conclusions: With standard liners, the risk of dislocation is increased in obesity. Pre-op decrease of BMI (with bariatric surgery) in obese patients did not prevent the risk of dislocation with standard liners. Dual mobility liners in these patients is an effective technique to prevent post-operative hip dislocation.