Back in the day, he was known as “The Rocket,” a nickname bestowed on him by his basketball-playing pals because of his speed dashing up and down the court.

But New York executive Mark Kamen isn’t quite as speedy as he once was, thanks to double-knee replacement surgery last year.

“It’s the best thing I’ve ever done from a health point of view,” said Kamen, 56, who has spent a lifetime playing basketball, tennis and skiing.

His basketball days are behind him now, because of his surgery in early 2010, but he still has hopes for resuming other activities. He’s already playing golf, and walking the course.

“I want to be able to ski with my family again, to play tennis with my family,” he said.

Kamen is one of hundreds of thousands of Americans who are opting for knee replacement surgery each year. Traditionally, most patients were over the age of 60, but increasingly younger Baby Boomers, like Kamen, are going under the knife, too.

The University of Michigan Health System, for instance, says the number of boomers – those born between 1946 and 1964 – is growing exponentially. The university said the total number of people getting new knees has risen to 500,000 per year, and could well be headed for 3.2 million each year in a decade.

The leading culprit that is prompting that rush to the surgical suite is arthritis in all of its forms, osteo, rheumatoid, and arthritis that follows a knee injury.

That is the case that led to Kamen’s condition. He said he has known for years that he had arthritis in his knees. He would play basketball, but then suffer afterwards.

“My knees hurt,” he said, and packing them in ice and taking anti-inflammatory medication had ceased working.

His lifestyle echoes that of  a generation that tends to jog, play sports and do other strenuous physical activity well into middle age, putting real stress on knees, hastening the onset of osteoarthritis, the most common form of that condition.

Even then, boomers may be able to hold off surgery with some lifestyle changes. Is it time to quit running, for instance, or like Rocket, stay off the basketball court?

That could well be, if your knees are aching, and you’re having trouble getting up and down stairs.

Many doctors recommend switching to exercise like cycling, swimming, playing golf, or hitting the treadmill.

Also available, instead of surgery, are anti-inflammatory medications, injections of corticosteroids and physical thereapy.

If none of that works, however, surgery is an option, and one that has a fairly low rate of serious complications, 2 percent.

What goes wrong that led you to this point?

Think of your knee as a kind of intersection of your thigh bone, the tibia in your lower leg and your knee cap.  Normally, you’re protected from knee pain by cartilage and a thin membrane. But arthritis can damage that protection, and you end up with aching, or worse, knees.

Knee replacement surgery typically takes about 2-hours.

During that time, a surgeon will cut your knee open, and move your knee cap out of the way. The doctor will then cut the end of each leg bone, and shape the knee cap so there will be room for the metal and plastic artificial parts that will be fitted in your knee.

While the surgery is considered low risk, there are some risks – the new joint could become dislocated, and infection could set it, the new joint could loosen, you could have an allergic reaction, nerve or blood vessel damage, or blood clots.

Typically, you’ll be in the hospital for 3 to 5 days, but that’s really just the beginning of your recovery. Full recovery can take up until a year.

A relatively new procedure, called minimally invasive knee replacement, may shorten some of that healing time to 1 to 3 days in the hospital, and extended stay for rehabilitation may be shortened.

Kamen, who had traditional surgery, spent a week in a rehabilitation hospital after his operation, using light weights and being hooked up to a machine that worked his knee joint for him.

Kamen is well on his way to full recovery, marked for him by an important step.

“I can walk to work now,” from his bus stop to his Manhattan office.

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