How to Do an Olympic-Worthy Knee Exam
Have you been watching the Olympics this week? If you are like me, all you can think about as you watch the downhill skiing competitions is knee replacements. I get aches and pains just watching skiers barrel down the mountain conquering moguls with precise little hops. A skier myself, I know the feeling of a long day on the slopes and cannot imagine what making my little ski hobby a profession would do to my joints.
Working in the emergency department I treat a fair number of knee injuries, but the perfect knee exam seems to elude me. With knees there is so much more than “fractured” and “dislocated”. All those tendons and ligaments making up the knee pose potential problems in any knee injury. I would love to be able to diagnose a patient with tendon-specific accuracy, but most often in the ER I say something along the lines of “you may have torn a tendon or ligament and need to follow-up for an MRI”.
So today, in the spirit of the Olympics, I thought I would discuss the perfect knee exam. What do you need to look for in patients presenting with knee complaints? Which tests and maneuvers can help you pinpoint the patient’s exact problem?
Step 1: Consider the Injury…Or Not
Taking a thorough patient history is the start of any good knee exam. Was the patient injured or did the pain develop without any mechanism of injury? A direct blow to the knee, especially when the knee is flexed (common when the knee hits the dashboard in a car accident) can cause injury to the posterior cruciate ligament (PCL). Direct force applied to the side of the knee is likely to result in injury to the medial collateral ligament (MCL). Quick stops, turns and sharp cutting activities without a direct blow to the knee can sprain or rupture the anterior cruciate ligament (ACL).
Along with mechanism of injury, ask the patient about symptoms like locking, popping or clicking in the knee. Locking episodes suggest a meniscal tear while a popping sensation is suggestive of ligamentous injury. Episodes of the knee giving out can signal patellar subluxation or ligamentous rupture.
Step 2: Take a Quick Look
You can learn a lot from the most simple part of the knee exam, taking a basic look at the knee’s exterior. Is the knee swollen, discolored or bruised? Is there warmth, tenderness or effusion? If there is tenderness, is it medial, lateral or patellar? Placing your hands on both knees at the same time will help you detect temperature differences between the two joints. Slight warmth in the affected knee suggests inflammation.
Assess for fluid in the knee by applying pressure to the medial aspect of the knee. While pressure is applied, press on the lateral side of the knee feeling for fluid. No fluid collection is considered normal. The presence of fluid signals an effusion. Rapid onset of effusion, within two hours of injury, suggests ACL rupture or tibial plateau fracture. Slow onset of effusion, an onset within 24 to 36 hours of injury, is consistent with meniscal injury or sprain.
Step 3: Check Out the Patella
With the patient supine and the knee extended, observe the patella as the patient contracts the quadriceps muscle. The patella should travel in a relatively straight line. If the patella goes to one side, patella subluxation may be present. The patella apprehension test also examines for patellar subluxation. Place your fingers on the medial aspect of the patella and attempt to move it laterally. If this reproduces pain or a sensation of giving way, the patient may have a patellar subluxation.
Step 4: Look at the Ligaments
The anterior (ACL), posterior (PCL), medial (MCL) and lateral (LCL) ligaments are the most commonly injured in the knee.
To test the anterior cruciate ligament, use the anterior drawer test. Have the patient lay in the supine position with the knee flexed and hamstrings relaxed. Stabilize the foot and grip the proximal tibia. Apply anterior force to the tibia. Excess movement compared to the contralateral knee is a positive drawer test and signifies ACL tear. Lachman’s test can also be used.
To test the posterior cruciate ligament, use the posterior drawer test. The patient should lay supine with the knee flexed. Stand on the side of the table and assess for posterior displacement of the tibia. Then, apply posterior force to the proximal tibia. Excessive posterior movement compared to the contralateral knee is positive for PCL tear.
To test the medial collateral ligament, use the valgus stress test. With the patient supine and affected leg off the exam table, place one hand on the medial side of the knee with the other hand holding the patient’s foot and ankle. Apply lateral stress to the foot and ankle while observing the knee. Excess lateral mobility, an increase in the valgus opening, is seen in MCL injury.
To test the lateral collateral ligament, use the varus stress test. With the patient supine, and the patient’s leg off the exam table, place one hand on the lateral side of the knee and the other on the patient’s foot and ankle. Apply medial stress to the foot and ankle comparing the amount of medial movement in the affected knee to the contralateral knee. Excess medial mobility, an increase in the varus opening, is a sign of LCL injury.
Step 5: Manipulate the Meniscus
The McMurray test evaluates for meniscal tear. To perform the McMurray test, have the patient lay supine with the knee flexed. Rotate the tibia medially and extend the patient’s knee. A snap or a click accompanied by pain with this motion signals meniscal tear.
Step 6: Other Tests and Procedures
Most knee injuries are soft tissue injuries and therefor X-Rays will be normal. If fracture is suspected, an X-Ray should be ordered. The Ottawa Knee Rules can help you decide in a knee X-Ray is warranted.
While most injuries to the knee can be diagnosed clinically, MRI helps visualize the extent of injury and rule out multiple injuries to the ligaments and meniscus.
In cases of warmth, redness, painful effusion and pain with even slight motion of the knee, septic arthritis or acute inflammatory arthropathy should be suspected. Lab studies including CBC and ESR as well as joint fluid analysis are used to diagnose these conditions.
What types of knee injuries have you seen in your practice this Winter?