Preventing ACL Injuries

What Your Knee Does for You-and How to Keep it in Good Working Order

By Charles B. Goodwin, MD

Illustration by Tony Christovich

Dr. Charles B. Goodwin is a sports medicine orthopedic surgeon who has worked with the US Tennis Association, the New York Knicks, and the NY Mets, among others. He can also play a mean game of squash. As always, contact your physician before starting any new treatment

Our knees are among the most mobile of the body's joints and it's a good thing they are, considering the extraordinary demands we make of them whenever we play squash or simply go about our day-to-day activities. Every time we walk up a flight of stairs, we increase the force on our knees by five times our body weight. Running will increase that pressure by as much as seven times our weight.

But the knee does more than just provide support; it also enables you to turn on a dime and then in the same instant run off again, at full speed without giving the matter a second thought. All in all, this modified hinge joint is our most versatile part of our physical equipment.

Even though the knee plays such a critical role in locomotion, balance, and shock absorption, and with its prominent knee cap appears to be quite solid and sturdy, sometimes all it takes is one wrong move to cause severe damage.

Here's what happened to a patient of mine. While playing squash one afternoon, the 30-year-old New York real estate developer sprinted to the corner of the court for a routine backhand. He planted his left leg and pivoted sharply on his right, just as he had done countless times before. But now something was different. 'When I turned, I was suddenly in pain. It felt like as if an electrical current was rippling through my right knee,' he recalls. 'This was no ordinary injury.'

He was right. The torquing motion of twisting his knee with his foot firmly planted on the squash court had severed his anterior cruciate ligament (ACL). This normally strong, rope-like 1.5-inch ligament crosses through the middle of the knee joint and keeps the shinbone from sliding too far forward on the thighbone.

Unlike the hip, with its deeply contoured ball-and-socket arrangement, the knee depends almost entirely on soft tissue'ligaments and tendons'for stability. The knee connects the two rounded surfaces (condyles) of the large thighbone (femur) with the lower leg bone (tibia). An elaborate system of ligaments, the anatomical equivalent of bungee cords, holds the joint together. Two ligaments (the collateral) bind the knee on the inside and outside borders, while anterior and posterior cruciate ligaments cross inside the joint to hold it in place.

In the course of any athletic movement when the knee is accidentally rotated too far and the ligaments are stretched even slightly beyond their length, they will often rupture with a sickening 'pop.' Most often it's the ACL, and such a devastating injury usually requires reconstructive surgery followed by extensive rehabilitation with weights.

A week after my squash-playing patient's injury, I performed surgery to reconstruct his ruptured ligament. He was placed in a knee brace and immediately started range-of-motion exercises. Later, he began leg-strengthening exercises. While some determined athletes are able to return to sports within four to six months, it's often a year or more for many before their injured knee is at full strength.

The Vulnerable Knee

A medical expert is needed to make the diagnosis of a ruptured ACL. The decision on surgical reconstruction is based on the age of the patient, the expected demands on the knee, and whether the patient has any unpredicted giving away of the knee.

While increased exercise and sports activity puts everyone at risk for knee injury, for a woman the risks are higher. The wider female pelvis, for instance, often produces thighs that angle inward, from hip to knee, at a sharper angle than in men. This Q-angle, or quadriceps angle, often predisposes a woman to more knee injuries than a man.

In addition, a woman's joints are slightly more lax than a man's. The joints typically have more hyper-elasticity or mobility; it's this hyper-looseness that predisposes a woman's ACL to more injury. Hormonal factors, leg strength, and the particular geometry of the female knee joint also may be factors to predispose one to increased risk of rupture.

Strengthen Supporting Muscles

In order to protect the delicate knee, improve stability and ensure maximal mobility, women and men should embark on preventative knee-conditioning programs. The key to preventing knee injuries is to make knee strengthening a regular part of your exercise routine. Building up the powerful muscles in the thigh and lower leg offers the best insurance currently available against most acute and chronic knee injuries.

While there are no guarantees that a rigorous strengthening program will afford complete knee protection'a direct blow can injure the knee of even the most well-muscled leg'stronger leg muscles do enhance stability and function. In addition, stronger legs take longer to fatigue, making them less prone to injury, while helping to recover faster from exertion.

Protecting the knee from chronic and acute injury entails maximally strengthening the specific muscles that help flex and extend the knee. These include the quadriceps (a grouping of four muscles in front of the thigh that cross the knee joint), hamstring muscles at the rear of the thigh (which pull the tibia backwards when they contract), and the gastrocnemius and soleus (which start behind and above the knee and inserts at the ankle).

The following leg exercises may be performed with or without weight equipment. If you chose to use weights for general conditioning, select a weight that will allow you to complete 8 to 10 repetitions. Gradually progress from one to three sets. Be sure to exercise both legs.

The Barbell Lunge
(for the quads and hamstrings)
Stand erect with the barbell (or broomstick, if not using weights) resting behind your neck on your shoulders, and your hands and feet slightly wider than shoulder-width apart. Inhale and slowly take a large step forward with the right leg, lowering your body until the thigh of this lead leg is parallel to the floor. The knee of the right leg should finish approximately over the ball of the same foot. Return to the starting position, exhale, and push off the floor with the right leg to return to the erect standing position. Repeat with the same lead leg. Perform an identical set with the other leg.

The Split Squat
(for the quads and hamstrings)
Stand erect with the barbell (or broomstick) resting behind your neck on your shoulders, and your hands and feet slightly wider than shoulder-width apart. Inhale, take a long step forward with the right leg, and descend slowly until the right thigh is just parallel to the floor. The knee of the lead leg should be directly over the foot at the lowest position. But rather than return to the starting position, maintain the open stance, exhale, and rise until both knees have straightened to complete one repetition. After the last rep, use small backward steps with the right leg to return to the starting position. Then take a long step forward with the other leg to perform the repetitions for the opposite leg.

Knee Extensions (for the quads)
Sit on a leg extension machine with your knees just over the edge of the seat and your hands holding the handles for support. Your knees shouldn't bend more than 30° to avoid joint stress. Inhale and slowly raise your leg(s) until completely straight. Hold this position for two seconds, exhale, and lowly return to the starting position.

This exercise can also be performed at home. Wearing ankle weight or a weighted iron boot (available at sporting goods stores), sit at the edge of a table or chair so your leg is dangling. Inhale and slowly raise the weights with your legs until they are completely horizontal. Hold this position for two seconds, exhale, and slowly return to the starting position.

Knee Curl (for the hamstrings)
Lie face down on a leg curl machine with your heels underneath the pads. Your kneecaps should be approximately two inches over the edge of the bench. Grasp the handles of the machine and inhale as you flex the knees and slowly curl the weights until the pads touch the buttocks. Exhale as you slowly return to the starting position.

To perform the exercise at home, use ankle weights and lie face down on the floor. Inhale as you flex the knees and slowly raise your leg until your heels touch your buttocks. Exhale as you slowly return to the starting position.