Each week, Osmosis shares a USMLE® Step 1-style practice question to test your medical knowledge. Today’s case involves a 21-year-old man who injures his left knee during a football game, experiencing a “pop” and medial pain after being tackled. After getting an MRI, can you identify which physical examination maneuver is most likely to support this patient’s diagnosis?
A 21-year-old man presents to the emergency department after an injury to the left knee. The patient was running during a football game when he was suddenly tackled and struck in the lateral side of the left knee. The patient heard a “pop” and then felt pain at the medial aspect of his left knee. He was able to walk following the incident but noticed his left knee felt “wobbly.” On physical examination, the left knee is swollen, and there is medial joint line tenderness. The patient subsequently undergoes an MRI of the left knee, and the findings are shown below.
Which of the following physical examination maneuvers is most likely to support this patient’s diagnosis?
A. Valgus stress test
B. Varus stress test
C. Lachman test
D. Thessaly test
E. Posterior drawer test
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
A. Valgus stress test
Correct: See Main Explanation.
Incorrect Answer Explanations
B. Varus stress test
Incorrect: Varus force applied at the knee joint would demonstrate increased gapping in the setting of a lateral collateral ligament injury. This patient’s clinical presentation is more consistent with a medial collateral ligament injury.
C. Lachman test
Incorrect: Lachman test is used to assess for anterior-cruciate ligament injury. It is not used to evaluate for medial collateral ligament injury. This patient’s medial knee pain and mechanism of injury are more consistent with a medial collateral ligament injury.
D. Thessaly test
Incorrect: Thessaly test is used to assess for meniscus injury. However, the MRI does not show evidence of meniscal injury.
E. Posterior drawer test
Incorrect: The posterior drawer test identifies injury to the posterior cruciate ligament, which usually occurs from an anterior force applied to a bent knee, not a lateral blow, as seen in this case. The posterior drawer test is not used to evaluate for medial collateral ligament injury, which this patient likely has.
Main Explanation
This patient presents to the emergency department following an injury that involved a valgus force to the lateral aspect of the knee. Knee MRI demonstrates evidence of injury to the medial collateral ligament. When a valgus stress test is used, and valgus force is applied at the knee, medial gapping and pain would indicate a positive test in the case of a medial collateral ligament injury.
Medial collateral ligament (MCL) and lateral collateral ligament (LCL) injuries are common injuries in athletes. These injuries often occur in isolation–without the involvement of concomitant ligamentous injuries. Injury to the medial collateral ligament is most often caused by a valgus force applied to the knee, such as forceful turning or twisting or direct blow to the lateral aspect of the knee. In contrast, lateral collateral ligament injuries occur due to a varus force on the knee, such as forceful twisting or turning or direct blow to the medial aspect of the knee.
Diagnosis of either injury is often clinical. In MCL injuries, patients will have increased gapping and pain at the medial knee when valgus force is applied. In LCL injuries, patients will have increased gapping and pain at the lateral aspect of the knee when varus force is applied. MRI is the definitive diagnosis and will demonstrate increased signal intensity at the ligaments with partial tears or visible full-thickness tears.
Major Takeaway
Medial collateral ligament (MCL) and lateral collateral ligament (LCL) injuries are common injuries in athletes and occur due to a valgus force on the knee in MCL injuries and varus force on the knee in LCL injuries. Valgus stress test will be positive with an MCL injury and a varus stress test will be positive with an LCL injury.
Want to learn more about this topic?
Watch the Osmosis video: Special tests for the lower limb
References
- Andrews, K., Lu, A., Mckean, L., Ebraheim, N. (2017) Review: Medial collateral ligament injuries. Journal of Orthopedics. 14(4), 550-554. Doi: 10.1016/j.jor.2017.07.017.
- Grawe, B., Schroeder, A.J., Kakazu, R., Messer, M.S. (2018) Lateral collateral ligament injury about the knee: Anatomy, evaluation, and management. The Journal of the American Academy of Orthopaedic Surgeons. 26(6):e120-e127. Doi: 10.5435/JAAOS-D-16-00028.
- Walls, R., Hockberger, R., Gausche-Hill, M. (2017) Rosen’s emergency medicine: Concepts and clinical practice. New York, NY: Elsevier. ISBN: 978-0323354790.
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