DEAR DR. ROACH: My brother, who was extremely active and athletic in his youth, is now in his early 70s. His decision to have both knees replaced several years ago was not due to any general pain, but rather an inability to bend his knees more than 90 degrees. It was limiting his mobility and affecting his quality of life. Later, his surgeon commented that he had never seen knees in such bad condition.

However, since then, my brother still cannot bend his knees more than 90 degrees without excruciating pain. The surgeon’s post-operative comments indicate that new knees were necessary, but do you have any idea what might be causing your continued inability to bend them? -BR

ANSWER: Knee replacement surgery is usually chosen because of osteoarthritis. Pain is usually the main problem, but sometimes it is due to limitations in range of motion. Flexion is being able to bend the knee, with the heel moving toward the glutes, and extension is being able to straighten the knee. These are usually limited before surgery, but are usually much better afterwards, as the damaged part of the knee is literally removed and a prosthesis is placed.

Limitations in knee flexion are common, although new surgical and prosthetic techniques have improved this. Several factors can cause limitations in flexion. Postoperative scarring is a possible cause. However, given how bad his knees were before surgery (you never want to hear your doctor say you have the worst case they’ve ever seen), I suspect that his quadriceps (the muscles on the front of the thigh that extend the knee ) You may have lost flexibility because you were unable to fully stretch during the years you had arthritis.

The key to improvement is usually gradual exercises to flex the knee, not to the point of excruciating pain, but to the point of stretching the quadriceps. You will need to do this many times a day and, ideally, you would work with a physical therapist with experience in patients who have had knee replacements. Over time, almost everyone will improve their ability to bend without pain.

Sometimes the problem is due to scar tissue and the surgeon performs manipulation of the knee under anesthesia to break up the scar tissue. Personally, I have never had a patient who needed to have this done when completing their physical therapy.