It depends upon your definition of bad. Most studies have said somewhere around 90% of knee replacement recipients are satisfied, not equally numbers. If you mean 50% have pain during recovery, you are probably low in the other direction.

A TKR is a traumatic event. Even if the surgery is minimally invasive, the surgeon is still cutting off parts of two bones and attaching something artificial to them. If the surgery is traditional, as most still are, the surgeon also cut the tendon and muscle to gain access creating even more trauma. Once in there, the surgeon cuts and removes the ACL and often the PCL as well.

So one should expect some pain. But the end result is worth it. I recently had my six month checkup and my surgeon told me I had no limitations. Before the surgery I was in constant if endurable pain in my right knee and extreme pain if I stepped the wrong way from a nerve impingement caused by my severe misalignment. Now I can do things with my grandkids such as walking around the zoo for hours or going to a trampoline center with them.