Knee pain after total knee replacement (TKR) is the most common problem patients face when the kneecap (patella) isn't replaced. Surgeons aren't always sure why this happens. Uneven cartilage and abnormal patellar shape may be part of the cause. Pain can occur if the patella doesn't track normally up and down over the joint.
Inflammatory and arthritic changes seen on X-ray before the operation are usually a big sign that the patella must be replaced called resurfacing. But it's possible to have normal preoperative X-rays and a poor result afterwards. Scientists think their may be unseen changes present. The patella in an affected joint may look quite normal, yet still have pathology that dooms it to failure.
Talk to your doctor about this problem. A simple revision surgery may be all that's needed to replace the patella and eliminate the pain.