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Physical Examinations III

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Knee Exam

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Due to its location, the knee is subjected to a variety of traumatic and degenerative forces, and its intricate structure makes knee examination quite complex.

Although the knee is the largest joint in the body, it has an inherently unstable structure held together by various ligaments, and supported by menisci, which increase the contact area of the joint, and act as shock absorbers. The patella, which is the largest sesamoid bone in the body, lies in front of the knee, attached to the quadriceps femoris tendon and the patella tendon. It acts as a fulcrum to allow forceful extension of the knee, which is needed for activities like running, making patella a common source of pain related to trauma or overuse.

Here, we will review the essential steps required to carry out a comprehensive knee examination, combined with relevant anatomical illustrations. We will also explain the diagnostic relevance of various findings that one may come across during knee assessment.

Like most musculoskeletal exams, let's begin with inspection and palpation. Before you start, make sure that the patient has removed enough clothing to expose their knees and lower legs. Ask the patient to walk back and forth, while you observe for limping, pain, swelling, effusion, ecchymosis and quad atrophy. Remember, if the patient has an injured knee then the non-injured knee should be used as the standard for evaluation.

The next step is palpation. Remember to wash your hands thoroughly before you touch the patient. Ask the patient to sit on the exam table and then have them lay down supine. Start by assessing for swelling around the kneecap. Milk down from above and below the knee and then push down on the patella with your finger to appreciate any fluid above and below it. Repeat the same on the other side. Swelling in front of the kneecap suggests pre-patella bursitis or infection, whereas presence of fluid behind the patella suggests a knee joint effusion and likely significant internal derangement.

Next, palpate the tibial tubercle for tenderness. This is the insertion site of the patella tendon. Bend the patient's knee and feel the roughened protrusion on the anterior surface of the proximal tibia. Tenderness at the tubercle may suggest Osgood Schlatter's disease in children and adolescent population. From there, palpate the patella tendon, which is broad rope-like structure beginning just above the tubercle and extending to the lower pole of the kneecap. Tenderness along the tendon indicates inflammation.

From there, palpate the region around patella, this time checking for tenderness. Start at the inferior pole, then palpate the medial and lateral sides, and lastly feel the top of the kneecap. Tenderness at the inferior pole may suggest Synding-Larsen disease in children and adolescents, around or under may indicate patellofemoral pain, and over the top may suggest pre-patella bursitis.

Next, feel the joint line. Put your finger and thumb on either side of the patella tendon, and then push along the lateral and medial side, checking for tenderness or pain at the joint line, which, if present, suggests a meniscus tear or osteoarthritis.

Finally, palpate the medial and lateral aspect of the knee. Start at the medial femoral condyle, the attachment site of the medial collateral ligament, which extends from the condyle to the proximal medial tibia. Next, check the pes anserine bursa located just below the anterior medial joint line for tenderness. After that, palpate the lateral femoral condyle, the start site for the lateral collateral ligament, which can be felt till it inserts into to the proximal lateral tibia and fibula. Lastly, palpate the iliotibial band that runs from the hip, along the lateral side, and attaches on the tibia at Gerdy's tubercle.

After the inspection and palpation portion of the exam is complete, move on to testing the knee's range of motion.

While in supine position have the patient fully straighten their leg and lift it up slightly to test extension. Normally, this should reveal a 0° angle. Next, check for knee flexion. Passively, bend the patient's knee by bringing their heel as close to their buttocks as possible. The range for this motion should be about 130°. If limited, it can indicate joint effusion or quadriceps spasm.

Next, have the patient transition into seated position and ask them to straighten their knee. This is to test the integrity of the extensor mechanism. Lastly, feel for crepitus -- the palpable grinding produced by motion -- by placing your palm over the knee, as it is either passively or actively, flexed and extended. This sign is rarely clinically significant, unless associated with pain, effusion, or limitation of motion.

After performing all the above-mentioned maneuvers, evaluate the structure of the knee by using a variety of special tests. The first of these is the Ligament Testing. These maneuvers assess pain and laxity in the medial and lateral collateral ligaments, and the anterior and posterior cruciate ligaments, abbreviated as the MCL, LCL, ACL and PCL, respectively.

For the MCL and LCL tests, first straighten the patient's knee by lifting it at the ankle with one hand, then use your other hand to flex it to about 20°. To assess the MCL, keep the knee in flexed position, and apply valgus stress by pushing the ankle outside. Then do the same with the knee extended. To check the LCL, switch hand positions, and apply varus stress by pushing the ankle medially with the knee extended and then flexed. In either case, score the ligament injury by pain and laxity as shown in this table.

The next couple of tests, namely the Lachman test and the Anterior Drawer test examine the ACL. For the Lachman test, request the patient to relax their legs, then flex their knee to about 20° angle. And while pulling forward on the proximal tibia with one hand, push down on the femur with the other. With this maneuver, you are feeling for an end point as the ACL gets stressed.

Next, conduct the Anterior Drawer Test. Ask the patient to bend their knee and lay their foot flat on the table. Then, sit on the foot so that it does not move. Place your hands just below the knee with both index fingers at the posterior joint line and pull to check if the tibia moves forward, which it should not.

Following two maneuvers - the Posterior Drawer test and the looking for Sag Sign -evaluate the PCL. For the Posterior Drawer test, have the patient bend their knee just like the Anterior drawer test, then put both your thumbs on either side of the patella tendon, and pull back and push posteriorly on the upper aspect of the tibia. Significant displacement may suggest a PCL injury.

Lastly, perform the Sag sign test. With the patient's knee flexed to 90° and foot flat on the exam table; note if the tibia sags or drops back with respect to the femur. It is a good approach to compare between sides. Presence of this sign may suggest a PCL tear with significant posterior laxity.

After ligament testing, perform the following maneuvers that check for meniscal injury. However, one should keep in mind that these tests are often nonspecific and require additional confirmation.

First of these tests, is the Bounce test. With the patient supine, lift the leg at the ankle and gently "bounce" the knee by forcing it into full extension. This maneuver will cause pain if the meniscus is torn. To assess the joint line tenderness palpate along the medial and lateral joint lines, where the meniscus is located. Any tenderness here may suggest either an injury to the meniscus or osteoarthritis.

Next, ask the patient to transition into prone position with both knees hanging just off the end of the exam table. This is the prone knee extension test. Difference in heel height may indicate a mechanical block to knee extension caused by a torn and displaced meniscus.

Subsequently, conduct the McMurray's test. First, bend the patient's knee and flex it fully, then internally rotate and extend it. Repeat the same by rotating it externally. A significant clunking sound during this test may indicate a displacing meniscal tear. This maneuver should be done with caution as one may cause a torn meniscus to displace and lock the knee joint.

Next, perform the Apley Compression test. With the patient prone, passively flex the knee to 90°, rotate the tibia internally, apply axial load, and flex and extend the knee continually to check for any clunking sound. Repeat the maneuver while rotating the tibia externally. Significant clunking may indicate a torn meniscus.

For the last meniscal test, called the Duck Walk Test. Request the patient to get into a full squat position and then walk. A patient is unlikely to have a significant cartilage or ligament injury if they are able to do this.

Finally, a few tests called the patella tests can be performed to evaluate for patellofemoral dysfunction, pain, or dislocation.

First maneuver in this group is called the apprehension test. Push the patient's kneecap in a lateral direction, and see if the patient becomes apprehensive that the patella may dislodge, which suggests a prior patella dislocation. Next, perform the patella grind test by pushing down on the patient's kneecap and grind it back and forth. Pain experienced by the patient during this maneuver may suggest patellofemoral dysfunction.

Finally, check the quadriceps- or the Q-angle. With the patient supine, estimate the angle formed by a line connecting the anterior superior iliac spine and the center of patella, with a line from the center of patella down the anterior tibia to the tibial tubercle. Angles greater than 10° in males and 15° in females suggest a predisposition to patellofemoral problems.

You have just watched a JoVE video detailing the knee assesment. In this video, we reviewed the essential aspects of this exam including inspection, palpation, range of motion testing, and additional special diagnostic maneuvers to narrow down the differential diagnosis associated with knee problems. As always, thanks for watching!

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