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If your knee swells after an injury see a doctor

Dr. Robert LaPrade
newsroom@vaildaily.com
VAIL CO, Colorado
Special to the DailyDr. Robert LaPrade
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Dear doc: I fell and twisted my knee after I hit a mogul on the hill yesterday. It has become quite swollen. What should I be concerned about?

– Mogul maven

Dr. Robert LaPrade: Swelling in the knee after an injury almost always indicates that there is something wrong within the deep structures. When swelling comes on rather suddenly, the swelling is almost certainly due to blood within the joint. The main exception to this is for someone who has arthritis, and knee swelling may be due to extra joint fluid when one overdoes activities and the joint lining compensates by making extra joint fluid.



The most common cause of swelling in one’s knee (when one is less than 40 years old) is a tear of the anterior cruciate ligament (ACL). This is true in almost 75 percent of people. In fact, sudden onset swelling in a young athlete is a torn ACL until proven otherwise. An ACL tear is cause for concern because the ACL is necessary for twisting, turning and pivoting activities (like skiing).

Other injuries to be concerned about in this age group include a meniscus tear, a patella (kneecap) dislocation, or damage to the cartilage within the knee. You should follow-up with a physician as soon as possible to be evaluated for X-rays and an MRI scan. One should avoid twisting, turning, or pivoting activities after the injury to avoid further damage to other important structures within the knee. About 75 percent of people who tear their ACL report hearing or feeling a pop. This pop is felt to be due to a bone bruise, which occurs when the joint partially dislocates and the ACL stretches and tears.



In patients who are 40 years of age or older, in addition to the above noted injuries, it is also important to rule out a fracture, which is most commonly of the tibia plateaus (the “shinbone”). One often hears a “pop” with these injuries, has a significant amount of swelling, and has difficulty bearing weight. Thus, the presentation is very similar to an ACL tear. Thus, X-rays should be taken to rule out a fracture and an MRI scan to see if there is a subtle fracture or significant bruise of the bone with a crack of the bone into the joint, which causes the swelling.

Any swelling that happens after an injury, especially while skiing, should be investigated further by a physician. One should not ignore the fact there is blood in their knee and a further evaluation is necessary to determine whether physical therapy, bracing or surgery may be necessary to restore one back to higher-level activities.

Robert F. LaPrade, MD, PhD, is a complex knee surgeon with The Steadman Clinic in Vail. He also serves as the director of the Steadman Philippon Research Institute Biomechanics Research Laboratory.


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