DEAR DR. DONOHUE: I have been involved in sports for many years, mainly tennis and skiing. I am in my late 60s, still very active and working full time. Last spring, behind my right knee, I developed a Baker’s cyst that broke and gave me six weeks of a very painful calf. A couple of months ago, I developed another Baker’s cyst behind my left knee. Eighteen years ago, I injured a ligament in that knee.

Should a Baker’s cyst be surgically removed? What other treatment is there for one? Have my skiing and tennis days come to an end? – I.M.

ANSWER: A Baker’s cyst is a fluid-filled swelling behind the knee. The cyst itself develops from a bursa in that region or from a bulge of the knee’s lining tissue. A bursa is a friction-reducing disc situated between a tendon and the bone over which the tendon glides. In either case, the fluid of a Baker’s cyst comes from the knee joint and almost always indicates there’s a disturbance in the joint. Either a knee cartilage is torn or the knee has developed arthritis. The injury in the knee promotes excess production of joint fluid.

A doctor can aspirate fluid from the cyst with a needle and syringe. Instilling cortisone after draining the cyst might prevent it from re-forming. An elastic wrap around the knee keeps the cyst from enlarging. Surgery is reserved for cysts that don’t respond to any other treatment.

However, the problem in the knee joint must be addressed.

If the cyst isn’t huge, isn’t painful and doesn’t interfere with knee motion, nothing need be done.

DEAR DR. DONOHUE: My teenage daughter plays volleyball. She loves it. She’s developed a painful knee. Her coach says it’s “jumper’s knee” and has her resting for a full week. She walks around without pain, but I’m worried about this. Is this a serious condition? – M.K.

ANSWER: It can become a serious condition if it’s ignored.

Jumper’s knee comes about from a degeneration of the tendon directly beneath the kneecap. It arises from too much use of that tendon with too little rest. When a person lands on the ground from a high jump, the tendon is subjected to great force, and some of the tendon components deteriorate. It repairs itself if given a rest.

The pain of jumper’s knee is felt below the kneecap. At first, pain is dull and arises after activity. Without rest, the tendon then begins to hurt at the start of activity. In the next stage, the tendon hurts both during activity and at rest.

An elastic knee support might be helpful when she resumes play.

During the off season, your daughter needs to start a program of thigh-muscle strengthening. Strong thigh muscles, especially the front thigh muscles, protect the tendon.

If things aren’t back to normal in a week, take your daughter to the family doctor. The numbers of potential knee injuries are great, and diagnosing the correct one requires a professional opinion.

DEAR DR. DONOHUE: I am a 72-year-old female and swim a half mile at least three times a week. I do the crawl stroke and swim nonstop for 70 minutes.

While I swim, I hold a buoyant dumbbell in each hand. They’re said to give 80 percent more resistance to the swimming stroke. I wear a similar product on my feet. Am I doing enough? I feel great. – J.H.

ANSWER: The experts tell us to exercise on most if not all days of the week. However, you’re putting in over an hour of swimming three times a week, and that’s more than most people do, including the experts. I believe you’re doing enough.

The buoyant dumbbells are a new twist. I had to look them up to see what they were. They add the benefit of stressing bones. Now swimming benefits not only your heart and blood vessels, but it’s helping you stave off osteoporosis.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.