The decision to do the anterior vs posterior hip replacement surgery may not be entirely dependent on BMI. In my case, the surgeon refused to do anterior surgery because the damage in my joint was extensive, my bones relatively small, and he felt the field of view in the anterior approach would not be sufficient to allow precise placement of the implant components. When I needed a revision some years later, the new surgeon told me his complication rate was smaller with the posterior approach than the anterior. He would do the anterior if I insisted, but preferred not to - so we did posterior again.

Just this summer, when I was seeing him for a different issue, I asked him if his opinion has changed after 12 years. His reply surprised me - he still prefers the posterior approach first, the robotic approach second, and the anterior approach last. He feels his experience is superior to the robotic process for most people. He also says long-term success is better for robotic & posterior because perfect placement is so important. He has done over 4500 hip replacements, and also teaches at our medical school.
Sue