I'm guessing it varies. I just read a study dated March this year from the American Academy of Orthopaedic Surgeons:
In the study, "High-intensity versus Low-intensity Rehabilitation after Total Knee Arthroplasty: A Randomized Controlled Trial," researchers found that activating and exercising the quadriceps muscles as soon as possible after TKR may be the key to regaining optimal, post-surgical function in the knee and legs.
The quadriceps muscles in the front of the thigh are important for straightening and stabilizing the leg during movement. Most patients have difficulty fully activating i.e., contracting the quadriceps during the first month after surgery, which results in pronounced quadriceps weakness. Quadriceps activation may be improved through strengthening exercises or neuromuscular electrical stimulation, said senior author and orthopaedic surgeon Douglas Dennis, MD.
The study followed 162 patients at the University of Colorado who received a total knee replacement at Colorado Joint Replacement, the University of Colorado Hospital, or Panorama Orthopedics & Spine Center. Patients were divided into two groups for high and low-intensity therapy, with all patients receiving 25 physical therapy sessions over 12 weeks. Patients who activated more of their quadriceps or "quad" muscles earlier in their therapy showed better rehabilitation progress when it came to their abilities to climb stairs, a telltale sign of recovery after knee replacement.
"Quad activation is the biggest thing we have got to change to improve recovery and long-term function for knee replacement patients," said Dr. Dennis.
These findings may be especially important for patients under age 59--the fastest growing population undergoing knee replacement--who want to remain active after total knee replacement.
Naturally, no where in this study does it say push through excruciating pain. I think it's just common sense NOT to do that.