Researchers from Germany have found that obesity can negatively affect outcomes after total hip arthroplasty (THA), and an inadvertent reduction in cup anteversion may be part of the problem. The research was published in the May 4, 2016 edition of The Journal of Bone & Joint Surgery.
Reduced Cup Anteversion Problematic in Obese Patients?
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According to the May 6, 2016 article in JB&JS Orthobuzz, “The authors retrospectively analyzed postoperative radiographs from 790 THA patients (all of whom were operated on via a direct lateral approach) within three BMI [body mass index] ranges: normal weight (BMI <25 kg/m2), moderately obese (BMI between 25 and 34 kg/m2), and morbidly obese (BMI of ≥35 kg/m2). Reduced cup anteversion significantly correlated with increasing BMI and younger patient age, with the morbidly obese group demonstrating a 3.4° anteversion reduction compared with the normal-weight group. The authors attribute the reduced anteversion to increased pressure applied to dorsal and ventral acetabular rim retractors to ensure adequate visualization during THA surgery in obese patients.”
“When the authors applied their findings to the Lewinnek “safe zone” for acetabular positioning, only 59% of the morbidly obese patients were in that zone. While this study was not designed to track subsequent dislocations (a common consequence of incorrect cup positioning), the authors claim that these findings are nevertheless clinically important.”
Steffen Brodt, M.D. and Georg Matziolis, M.D. told OTW, “Based on daily X-ray controls after total hip arthroplasty we supposed that cup positioning is less accurate in obese patients. A subsequent literature research revealed a missing consensus about this issue. Based on these findings we decided to test our hypothesis.”
“The most interesting result was, that obese patients are at risk of a reduced anteversion. We expected the contrary result. The second interesting result was, that no dislocations were observed in that population during a follow up of two years. All patients were operated through a lateral, transgluteal approach.”
Asked how will this affect orthopedic surgeons’ daily practice, Drs. Matziolis and Brodt commented, “In the manuscript an increased attention during cup placement is recommended in obese patients. Rim retractors should be slackened when implanting the definite cup implant. Additionally, a higher anteversion may be anticipated in obese patients in order to produce the desired cup position. We implemented these recommendations in our daily work.”
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This is a fascinating development. In my practice we've seen similar outcomes with the revised protocol. The key differentiator seems to be patient selection criteria. Has anyone else noticed the correlation with BMI thresholds?
Great point. I'd push back slightly on the conclusion, the sample size in the cited study is too small to draw population-level inferences. That said, the directional signal is compelling and worth a larger RCT.
We implemented a similar approach last year. Early results are promising but we're still gathering 12-month follow-up data. Happy to share our protocol if anyone is interested.
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