The knee is a remarkable structure. The femur (thigh bone) and the tibia (shin bone) are long and thin, like two pencils balanced end to end, one on top of the other.
The knee joint holds the ends of these "pencil" bones together and allows them to move without falling apart.
The knee is able to run, jump, kick, dance and twist while keeping the pencils balanced perfectly end to end. This amazing feat is made possible mainly by four ligaments: one on each side and two in the middle of the knee. The ones on the sides (the "collateral" ligaments) keep the knee from bending side to side. The ones in the middle keep the tibia and femur from sliding too far backward or forward. These are called the "cruciate" ligaments because they "cross" each other.
A tear of the anterior cruciate ligament (ACL) is what causes the buckling and collapsing that were previously known as "trick" knees. Damage to the ACL allows the tibia to slide too far forward relative to the femur. This usually occurs during pivoting, twisting or cutting activities, and leads to buckling or giving way as the knee slips partially out of joint.
There are several ways to treat an ACL tear, depending on the patient's age, activity level and desires. One option is simply to give up the activities that cause the symptoms. This is often the choice of older, more sedentary persons. They can still participate in swimming, bicycling and other low-risk activities.
Specific exercises and bracing can be helpful for medium-risk activities such as softball and cross-country running, but usually are not sufficient for high-demand sports such as basketball, volleyball, tennis, soccer or football. Continuing these sports will usually require reconstruction of the ACL. It's been found that simply repairing the torn tendon is not an effective option because the tendon does not heal well.
There are several techniques of ACL reconstruction. The most common involve replacing the ACL with a section of the patient's own patellar or hamstring tendons. This is successful in allowing full activity about 90 percent of the time.
Recovery from this major knee surgery usually takes about six months to a year. Although some patients return to sports earlier, strenuous activity may risk injuring the newly transplanted ligament before it has chance to regain full strength.
There are a few other conditions that can cause the knee to catch, lock or buckle. These "trick knee" injuries can happen when the patella (knee-cap) slides out of place, a tear is made in one of the shock-absorbing cartilage pads within the knee (the meniscus), or a small piece of bone or cartilage comes loose and floats around in the knee, occasionally becoming pinched between the bones. These conditions can be treated very successfully with arthroscopic surgery or small incisions.
It's not as common anymore to hear someone complain about their "trick" knee because today's orthopedic surgeons are very good at diagnosing its cause and correcting the problem.
David A. Cook, M.D., is an orthopedic surgeon with the Tanner Clinic Orthopedic Center in Layton. Dr. Cook's specialty is helping patients find non-operative treatments.