Here's a great paper on obesity and orthopedics that answers your question. Some highlights: "In obese patients, cast immobilization of the lower or upper limbs and temporary or permanent traction are very difficult to achieve. Obesity makes any indication for conservative treatment difficult thereby forcing the surgeon to perform internal fixation. For example, immobilizing a humerus fracture along the chest of an obese woman causes arm abduction, which could be detrimental to fracture alignment [27]." "Complication rates are higher in obese patients relative to patients with normal BMI. The complication risk is 6.8 times higher and the need for re-operation is 4.7 times higher in pelvic ring fracture patients having BMI > 30 kg/m2 relative to ones with BMI < 30 kg/m2[28]." Imagine performing a knee surgery on this. She's from the paper and I believe she needed knee surgery.