Jo is an outpatient PT in a busy urban practice.  Sam, age 85, is one of her patients.  Sam's diagnosis is post-operative right hip arthroplasty with moderate pain.  Jo directs her aide, Sue, to apply a moist heat pad to Sam's affected area of discomfort.  Sue applies the hot pack, leaves a bell and 8-minute timer with Sam, and moves on to attend to other patients.  Jo and Sue become preoccupied with a patient  who has fallen to the floor while ambulating in parallel bars. Once that patient is checked out and stabilized, Sue returns to check on Sam, 22 minutes later.  Sue notes that she had forgotten to insulate Sam's treated area with towels.  A resultant 2^nd degree hot pack burn ensues.  Sue immediately calls Jo over to the scene and admits that she failed to use towels between the hot pack and Sam's skin.  Jo calls Dr. Tom, Sam's referring physician.  Dr. Tom orders Jo to transport Sam to the emergency room in a building adjacent to the PT clinic.  Jo complies. An exam by a physician assistant (PA) there reveals that Sam sustained a 2^nd-degree thigh burn from the hot pack.  The PA orders appropriate home treatment for Sam and places a one-week hold on PT.  By the evening, Sam's burn has developed into a 6-inch diameter blister, prompting Sam to return to the ER for follow-up.  The next morning, Sam and his attorney discuss pursuing legal action against Jo, Sue, the clinic and Dr. Tom.  

1. Identify and explain the four elements of proof of professional negligence that plaintiff-Sam must establish to find Jo liable for his burn