(MONEY Magazine) – Marie Greenwalt will never forget the day she thought her amateur soccer career was in jeopardy. ''I was practicing shots from about 30 yards out,'' says the 36-year-old billing clerk from Tualatin, Ore., ''when I felt something pop in my knee. I limped to the sideline and wrapped it in an Ace bandage. But when I got back on the field, I realized I couldn't run -- or even walk -- without severe pain.'' Her family physician diagnosed a torn anterior cruciate ligament and recommended surgery. But Greenwalt has had a horror of the knife ever since her brother endured two painful operations and was out of action for more than a year after a similar knee injury. Seeking a second opinion, she hobbled on crutches over to the Cook Clinic, a local sports medicine outfit that counts among its patients the Portland Trail Blazers basketball team. An orthopedist took X-rays, then deftly popped the kneecap back in place and sent her home with a brace and a program of special exercises to strengthen it. Three weeks later, winger Greenwalt was back in the game. Says she: ''I'll never go to a regular doctor again for something that happens in sports.'' Multiply Greenwalt's experience many times over and you get one indication of why sports medicine clinics have grown tenfold -- to more than 600 nationally -- during the past decade. Some 70 million Americans now exercise regularly, and the resulting bumps, sprains and strains contribute to an estimated 17 million sports injuries each year. The sports medicine specialist -- usually a physician or orthopedist with experience in athletic injuries -- aims to get patients off the bench faster than would the family doctor, who usually would either recommend rest or refer them to a specialist for a more comprehensive diagnosis. Still, the name ''sports medicine'' on the door is no guarantee that the treatment you get inside will cure your tennis elbow or jogger's knee. No specific license is required to practice sports medicine. As Dr. Lyle Micheli, head of the sports medicine clinic at Children's Hospital in Boston, concedes, ''Someone can graduate from medical school with a degree in dermatology and hang out a sports medicine shingle.'' And doctors have an incentive to do so: prices are high in this trendy field -- up to $75 for a first visit, compared with $50 or so for the typical internist and $35 for a family physician. How can you tell whether a sports medicine clinic is worth its price? If your whole mental well-being revolves around your athletic regimen, you might be willing to pay extra to cut your recuperation time. Dr. Peter Jokl, professor of orthopedics and head of the Sports Medicine Center at Yale University, reckons that ''for every day you're down, it will take three days to get back in condition.'' And Dr. Jokl and most other orthopedists now believe that putting the injured part to moderate and appropriate use may actually help it heal faster. This is true even of so-called overuse injuries that make up the majority of sports ailments: racquet elbow, shinsplints, persistent shoulder pain and the like. Another occasion to seek a sports specialist's attention: when your injury is more subtle, or more debilitating, than your family doctor seems to recognize. That was what drove Bill St. Armour of Phoenix to the Center for Sports Medicine and Orthopedics. St. Armour had hurt his back while picking up a tire last year, but his doctor of 14 years said it was all right for him to go back to his job as a mechanic and also to continue playing golf. But at the center, which also treats basketball's Phoenix Suns, doctors discovered a herniated disk -- a condition they said could have been aggravated either by his work or by an afternoon on the links. ''They had the ability to treat, diagnose and rehabilitate under one roof,'' says St. Armour, who has recently returned to the practice tee. If you decide you would like to consult a sports medicine doctor, the next step is to find a good one. The American Orthopaedic Society for Sports Medicine (70 W. Hubbard St., Suite 202, Chicago, Ill. 60610; 312-644-2623) can provide you with names of its members in your area. The American College of Sports Medicine (401 W. Michigan St., Indianapolis, Ind. 46202; 317-637-9200) provides a similar service, although, unlike the orthopedic group, not all of the college's members are M.D.s. You can also get the latest annual list of sports medicine clinics around the country by sending $15 to Physician & Sportsmedicine magazine (Editorial Department, 4530 W. 77th St., Minneapolis, Minn. 55435). If all of the above fail, call a few of the local sports teams and ask where they get their medical care. Once you've located one or more clinics in your area, ask the following questions before making a commitment: -- Who will treat you? You should be seen by an orthopedist or a physician, since many insurance companies won't cover care that isn't ordered by a doctor. -- What are the doctor's professional affiliations? It's best if he is a member of one of the medical societies mentioned above, which are the major players in the field. -- Does the clinic offer a full range of diagnostic and rehabilitative services? The most comprehensive facilities include an orthopedist, a podiatrist, a physical therapist and a trainer on the staff. Look for state- of-the-art isokinetic machines such as a Cybex or Biodex that speed recuperation. More exotic gear might include an Aquatrex underwater treadmill machine (pictured on page 171) that allows people with back or leg injuries to work out. -- How much will it cost? A sports medicine specialist should not charge more than a conventional orthopedist for a medical procedure. If you're in doubt about a quote, ask your insurance company what is the reasonable and customary fee for your particular ailment. For example, the surgeon's fee for diagnostic arthroscopy on your knee -- in which the doctor uses a fiber-optic wand equipped with a miniature camera to check for cartilage or bone damage -- should range between $500 and $800. Of course, the best way to avoid the high cost of sports medicine is not to get hurt in the first place. Ease up for a couple of days if your exercise is causing persistent pain. Try cross-training, in which you alternate your daily jog, for example, with bicycling, swimming or walking every other day to give the varying muscles and joints a chance to rest. Or hire a professional trainer to check out your regimen. As Dr. John Bergfeld, head of the Cleveland Clinic's section of sports medicine, puts it, ''If you're spending $40 to $50 an hour to come in here, it might be worth your while to spend that much beforehand on a coach.''