Keith Roach, M.D., syndicated columnist

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

However, since this time, my brother still cannot bend his knees more than 90 degrees without excruciating pain. The surgeon’s post-surgery remarks indicate that new knees were necessary, but do you have any insight as to what might be causing his continued inability to bend them? — B.R.

ANSWER: Knee replacement surgery is generally chosen because of osteoarthritis. It’s usually pain that is the major problem, but sometimes it’s because of limitations in the range of motion. Flexion is being able to bend your knee, with your heel moving toward your buttocks, and extension is being able to straighten the knee.

These are routinely limited before surgery but are generally much better afterward, as the damaged part of the knee is literally removed and a prosthesis placed in.

Limitations in knee flexion are common, although newer surgical techniques and prostheses have improved this. Several factors can lead to 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 that you have the worst case they have ever seen), I suspect that his quadriceps (the muscles in the front of the thigh that extend the knee) may have lost flexibility due to not being able to fully stretch for the years he 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. He will need to do this many times per day, and ideally, he would work with a physical therapist who is experienced in patients who have had knee replacements.

Over time, nearly everyone will have improvement in their ability to bend without pain.

Occasionally, the problem is due to scar tissue, and the surgeon performs a manipulation of the knee under anesthesia to break up the scar tissue. Personally, I’ve never had a patient who needed to have this done when they are compliant with their physical therapy.

DEAR DR. ROACH: What does it indicate if your anti-TPO level is high and your TSH level is normal while on levothyroxine? — S.R.

ANSWER: Thyroid peroxidase is an enzyme used to make thyroid hormone. It’s necessary for the thyroid gland to work properly. Antibodies against this enzyme are found in autoimmune thyroid disease, especially Hashimoto’s thyroiditis, but they may also be found in Grave’s disease.

The fact that your TSH level is normal on thyroid replacement means that the dose of thyroid hormone is likely adequate.

With these results, the most likely diagnosis is Hashimoto’s thyroiditis with correctly treated hypothyroidism.

EDITOR’S NOTE: Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.