Episode 91 Occult Knee Injuries Pearls and Pitfalls

This is EM Cases Episode 91 Occult Knee Injuries Pearls and Pitfalls. There are a whole slew of very important occult knee injuries - those that have a normal or near normal x-ray – that can cause serious morbidity if you miss them, and for the catchall soft tissue injuries there are some subtleties in diagnosis and management that will make a real difference to our patients. Arun Sayal and Hossein Mehdian answer questions such as: When should we suspect a spontaneously reduced knee dislocation? Do all patients suspected of a spontaneous knee dislocation require a CT angiogram to rule out vascular injury? Which patients with a low energy mechanism are at risk for knee dislocation and vascular complications? How can you increase the accuracy of the active straight leg raise in assessing for quadriceps and patella tendon rupture? What is an easy way to identify patella baja and patella alta? What are the indications for ultrasound of the knee? What are the true indications for a knee immobilizer and how can knee immobilizers kill our patients? and many more... Podcast produced and edited by Anton Helman, voice editing by Richard Hoang, sound design by Anton Helman. Written Summary and blog post by Anton Helman January, 2017 Cite this podcast as: Sayal, A, Mehdian, H, Helman, A. Occult Knee Injuries Pearls and Pitfalls. Emergency Medicine Cases. January, 2017. https://emergencymedicinecases.com/aortic-dissection-em-cases-course/. Accessed [date]. General Principles of Occult Knee Injuries A) A normal X-ray does not rule out a serious knee injury. There are several important diagnoses that you should consider in a patient who comes in with knee pain and has a normal x-ray of the knee.  Quads/patellar tendon rupture Lateral tibial plateau fracture Dislocation w reduction Locked knee Hip injury with referred pain Compartment syndrome Septic knee B) Mechanism of Injury: Direct blow vs valgus strain vs sudden deceleration vs twisting Direct blow – patella fracture, knee dislocation, tibia fracture Valgus strain – MCL tear and/or lateral tibial plateau fracture Sudden deceleration – ACL tear Twisting - Meniscus tear C) Age - The same mechanism in patients of different ages can lead to different injuries (e.g., with a valgus force injury to the knee you should consider a distal femur fracture in a child, an MCL injury in a young adult and lateral tibial plateau fracture in an older person) Physical exam pearls for occult knee injuries Many patients with acute knee injuries in the ED will experience a lot of pain and often clinicians short-change their examination of the knee because they don't want to cause more pain. However, there are several tips to help the patient relax enough to do provocative testing and the essential maneuvers: Patient must be supine on a stretcher (not sitting in a chair) with both knees fully exposed. Place a pillow or roll under the distal femur so that the knee is relaxed at about 20 degrees of flexion to allow for provocative knee testing. Always perform an active straight leg raise to assess for extensor mechanism function (quadriceps or patella tendon rupture). "The lateral joint line is the dark corner of the knee exam" - examine the lateral joint line in addition to the medial joint line to assess for the possibility of a lateral tibial plateau fracture in the setting of a valgus mechanism of injury. Occult Knee Dislocation About 20-50% of all knee dislocations spontaneously reduce before the patient arrives at the ED. A significant minority of occult knee dislocations will have neurovascular injuries which...