The December issue of The Physician and Sports Medicine was devoted to the medical aspects of skiing, with articles on ski bindings, the physiological demands of downhill skiing, getting in shape, the mechanics of common skiing injuries and the role of instruction in preventing injuries.

Dr. Robert P. Mack, a physician for the U.S. National Ski Team, wrote about the performance of safety bindings and what you can do to maintain them.

Approximately 60 per cent of all ski injuries involve the legs, he said, and half of those are sprained knees, injuries to the knee ligaments or fractures of the tibia - the front bone in the lower leg. Safety bindings are a vast improvement over the old "bear traps" of 30 years ago, but, according to the periodical, 40 per cent of the leg injuries still result from failure of the bindings to release properly.

Cheap bindings should be avoided. Proper mounting is critical, so go to a reputable specialized shop. Silicone spray, maintenance of the bindings and proper adjustment are also vital, for even the best of bindings will not release properly if they're neglected.

Most knee injuries, 86 per cent of them, are incurred by external rotation of the lower leg at the knee. The cause is the familiar "skier's excuse" for any spill - "I caught and edge." An external rotation happens when you catch the inside edge of a ski, leaving the foot trailing and rotating outward! As momentum carries the body forward the knee is forced forward, downward and inward. As the strain on the knee increases, ligaments are torn and you may be off your "boards" for the rest of the season. The pressure of such a spill should force your bindings to release at the toe and perhaps at the heel, but the injury rate attests to their failure to do so.

More than half of all tibial fractures occur when the tibia is bent forward over a rigid object. Most fractures occur at the boot top level, which seems to point an incriminating toe at either the rigid plastics used in many modern ski boots or the failure of the heel piece of the binding to release properly.

Unfortunately, no binding is completely safe and no brand or model is the best under all circumstances. According to Dr. Mack, who tested bindings in 28 types of simulated ski accidents when he was director of the Sports Medicine Center at Case Western Reserve University, even the best bindings failed five of the tests. To select a binding you should read the relevant articles that appear in the ski magazines at the beginning of each seasons, and then have a good shop help you select bindings that are appropriate to the design of your boots, the level of your skiing and the condition of your leg muscles and knee tissue.

Vibrations, salt spray from roads, repeated use, ice and dirt adversely affected the function of each of the bindings tested by Dr. Mack. He recommends covering the bindings during transport to protect against salt spray. Most ski shops carry binding covers. Cleaning, frequent adjustment and an occasional dose of silicone spray protect against dirt, vibration and frequent use.

Icing consistently resulted in the greatest decline in performance. And freezing may occur when riding a lift or with any change in temperature. According to Dr. Mack, "Skiiers should be alert to this possibility and manually open or close bindings to remove any ice that could interfere with normal function."

To adjust bindings Dr. Mack recommends this method: With the ski boot on and inserted into the binding, the skier should flex his knee forward and inward, thus trapping the inner edge of his ski. He should then be able to cause his toe to release with further forceful rotation of the lower leg. To test the heel, the boot and binding should be on. With the ski flat on the snow or carpet and someone standind on the tail of the ski, the skier should be able to step forward with the other leg (no ski on) and pull the heel being tested upward, forcing a heel release with his own muscle strength.