Anthony Luke MD, MPH
The knee is one of the more commonly injured joints, especially in running and jumping sports. The most common knee complaints typically involve the patellofemoral joint. The knee takes a lot of stress, especially when bending. Studies have shown that the forces at the knee joint can reach three times body weight when the knee is bent during activities such as going up stairs, and up to six to seven times body weight when in a full squatting position. Internal derangement of the knee refers to a variety of damaged structures that can be injured within the knee, including meniscal cartilage tears and loose bodies. Ligament tears often present with pain and instability during function. The higher the degree of tearing in the ligament, the greater the amount of instability symptoms. The knee serves as an important transmission between the ankle and the hip. As such, knee injuries are among the most common complaints encountered in sports medicine.
Knee Joint Articulation Instabilty:
The examination of knee should include an assessment of both posture and lower extremity alignment. The alignment at the knees can be quickly screened by having the patient stand with their ankles together, and observing at the knees. If there is a wide space between the knees when the patient stands with their feet together and they appear to be “bow-legged”, the patient has genu varum, indicating that the lower leg angles inwards after the knee (towards the midline). Similarly, if the patient appears “knock-kneed”, and has a difficult time putting their feet together due to the proximity of their knees, they have a genu valgus alignment. When looking at the patient with both feet together and pointing forward, if the kneecaps point inwards thy have “squinting patellae” which often represents a rotational malalignment at the hips called femoral anteversion, where the hips are angled such that the knees and lower leg rotate inwards. It is important to always check the hip joint when evaluating knee injuries, beacause the hip may refer pain to the knee.
During the examination, it is important to feel the anatomical structures of the knee to see if they have been injured. Damaged structures around the knee are typically tender to direct pressure. Such structures include the joint surfaces of the knee cap, the femur, the tibia, and the muscles and tendons around the knee.
Patellar mobility is determined by passive medial and lateral movement. The patella can by divided into quadrants. A patella is considered to be hypomobile when it moves less than one quadrant on medial or lateral glide. A hypermobile patella is illustrated by a glide of more than two quadrants (one half of patellar width). Any tilting or rotation of the patella when it is pushed medially or laterally should also be noted. If the medial structures are too tight, the patella will tilt up when pushed laterally. If the lateral structures are too tight, the patella will tilt up when pushed medially.
Range of Motion
Examination of the range of motion at the knee is most easily performed with the patient in lying position. Full knee flexion is considered to be approximately 135° (Range 120-150°). Hyperextension may occur, especially in women (Range 0° to 15°). A goniometer is a useful joint angle measuring tool that can be used to measure range of motion. The greater trochanter (hip reference), lateral joint line (knee), and lateral malleolus (ankle) are typically used as reference landmarks to check for the range of motion of the knee.
Worrisome signs while testing range of motion include a “locked” knee, which lacks full extension when compared to the contralateral side. This suggests internal derangement may be present, such as a large meniscus tear, a ligament tear, or a loose body/bone chip. Another concering sign is the inability to extend the knee against gravity while in the lying position. This is indicative of an injury to the extensor mechanism of the knee. Examples include a quadriceps tendon tear, a patellar fracture, or an injury to the patellar tendon.
Description: The Anterior Drawer test examines for any tearing or laxity of the anterior cruciate ligament (ACL).
Maneuver: Have the patient lying on their back with their knee bent as close to 90° as possible, with the foot resting on the table. Place both hands behind tibia and pull the tibia forward, using a force between 15-20 lbs. The test can also test be performed with the foot externally rotated (turned out) to 15°.
Tip: The Anterior Drawer test has reduced sensitivity, especially after an acute injury due to the protective spasm of the hamstring muscles. Also, any large swelling in the knee, and any effects of the posterior horn of the medial meniscus can cause a decrease in the sensitivity.
Positive Findings: Increased anterior movement of the tibia on the injured side compared to the non-injured side is considered to be a positive test. Up to 3 mm of forward movement of the tibia is considered normal. The Grading for the test is as follows: Grade 1 = 5 mm, Grade 2 = 5 to 10 mm, Grade 3 > 10 mm.
Description: The valgus stress test checks for medial joint laxity, which usually represents an injury to the medial collateral ligament (MCL).
Maneuver: Have patient lie on their back. Position one hand at the joint line on the outer part of the knee. Have the other hand fixed on the ankle of the affected side. Flex the knee between 20° and 30° and apply a medial or valgus force to the knee. Approximately, 15 to 20 lbs of force should be applied during the test. In order to test the MCL, as well as the posterior medial capsule, the test can be repeated at 0° with the knee in full extension.
Tip: Fixing the ankle and pushing medially with the hand at the knee allows force to be easily applied to the knee due to the leverage of the long bone of the shin.
Positive Findings: A positive test demonstrates increased medial joint laxity compared to the unaffected side. A Grading system from 1 to 3 can be used which is based on the amount of joint space opening (Grade 1 = 5 mm, Grade 2 = 5 to 10 mm, Grade 3 > 10 mm).
Description: The varus stress test checks for joint laxity on the outside of the knee, which usually represents an injury to the lateral collateral ligament (LCL).
Maneuver: With the patient lying on their back, position one hand at the joint line on the outer part of the knee. Fix the other hand on the ankle of the affected side. Flex the knee between 20° and 30° and apply a lateral or varus force to the knee. This can be done either by reaching over the top of the knee, or by approaching the patient from the inside aspect of the knee with the leg off to the side. Approximately, 15 to 20 lbs of force should be applied during the test. The test can also be repeated at 0° with the knee in full extension.
Tip: Fixing the ankle and pushing laterally with the hand at the knee allows force to be easily applied to the knee due to the leverage of the long bone of the shin. If the leg opens on a varus stress testing, be extra careful when testing the ACL, PCL and posterolateral corner. The LCL is not commonly torn in isolation.
Positive Findings: A positive test demonstrates increased lateral joint laxity compared to the unaffected side. A Grading system from 1 to 3 can be used which is based on the amount of joint space opening (Grade 1 = 5 mm, Grade 2 = 5 to 10 mm, Grade 3 > 10 mm).
Description: The posterior drawer test is used to examine the Posterior Cruciate Ligament (PCL).
Maneuver: Have the patient lying on their back with their knee bent as close to 90° as possible with their foot resting on the table. Place both hands behind the tibia, and push backwards on the proximal shin/tibia looking for instability backwards. Use a force between 15-20 lbs
Tip: A PCL injury can give a false positive of ACL laxity, beacuse pulling the leg forward may actually reduce the knee from its new posterior position. Therefore, one should take special notice of any posterior sag sign in the knee before the test is performed. Applying a posterior force to the tibia with the knee flexed 80° and the tibia externally rotated 15° can also stress the posterolateral corner of the knee.
Positive Findings: : Upon application of a posterior force to the upper shin, an increase in backwards motion (posterior translation of the tibia) in comparison to the other side is indicative of a positive test.
Description: This test checks for meniscal tears and other internal derangement in the knee.
Maneuver: : With the patient supine, and their hip and knee bent to 90°, grasp the heel in one hand. Place the other hand over the knee, with the thumb and fingers on the joint line. Gently rotate the tibia with the heel internally rotated with a mild valgus force (for the lateral compartment) and externally rotated with a mild varus force (for the medial compartment).
Tip: The laterality of the test is non-specific, which means that the test can bother a mensical tear on either side of the knee when rotation occurs.
Positive Findings: Painful clicking along the joint line, or any pain over the joint line that reproduces the patient’s symptoms is considered to be a positive test.
Description: This functionally tests meniscus tears in the standing position. Since bending and twisting movements while weight bearing often reproduce pain from meniscus tears, this test recreates the exacerbating movements.
Maneuver: Have the patient stand on one foot with the foot flat on the floor. Hold the patients hand for support and have them initially bend on the standing knee to 5° of flexion. Ask the patient to twist at the knee, making sure they are internally and externally rotating at the knee rather than at the pelvis or back. Check for any reproduction of pain symptoms. Next, have the patient bend the knee deeper to 20°degrees and again actively twists on knee.
Positive Findings: The twisting movement will reproduce pain of a meniscal injury. The pain is typically localized to joint line, and patients typically have more pain with the knee bent at 20° rather than 5°.