Sprains and Strains, Knee

History: The individual will most often relate a traumatic event. Sometimes the incident will have seemed insignificant at the time of occurrence. The mechanism of injury will provide valuable clues to the direction of impact and amount of force to the knee, as will information about the timing of onset of pain and swelling; immediate swelling is most often associated with acute ligament tears. Individuals may relate a history of pain in partial ligament tears, but pain is often absent in complete tears. Individuals also may complain of the knee "giving way." Many individuals with ACL sprain report a "popping" sound in the knee. Any history of prior knee injury and treatment will be noted.

Physical exam: The examiner may touch (palpate) ligament and tendon insertion areas to elicit pain in any affected structures. Areas of localized swelling (edema) also may be felt on palpation. The joint itself may be filled with blood from the injury or with reactive synovial fluid (effusion). Pain along the course or attachment to bone (insertion) of a tendon usually indicates a strain, whereas such pain on palpation in a ligament area often indicates a sprain. Instability or excessive motion of the knee joint often is noted, although sometimes compensatory tightening of the surrounding muscles (physiologic splinting) may prevent detection of this loosening or instability. The individual may walk with a noticeable limp, as well as a "giving way" of the knee. Edema and bruising (ecchymosis) about the knee joint may be visible. The uninjured (contralateral) leg may be compared with the injured one to detect any relevant anatomical differences, such as the position of the kneecap (patella), and to determine a baseline level of normal laxity.

Tests: Knee arthrometer measurements may be done to quantify the degree of laxity. Routine knee x-rays rule out fractures, dislocations, patella-femoral abnormalities, and loose bodies. Stress x-rays may be done. MRI may be ordered to examine the ligaments and articular surfaces. MRI is especially useful in detecting accompanying (concomitant) injury, as well as in examining the severity of ligament damage. MRI also can detect bone bruises (injury to the tissues covering the bone) that may not be evident on routine x-rays, an advantage that can be important in treating a patient with persistent pain. Draining fluid from the knee (joint aspiration) may be done to decrease pain and evaluate the fluid. Blood in the fluid (aspirant) indicates torn tissue or an intraarticular fracture; fat in the bloody fluid indicates a possible bone injury. Examination of the interior of the knee with an arthroscope (a device used to look inside of joints) may be necessary to confirm a diagnosis.