A 61-year-old F presents to the ED from the orthopedic clinic with acute right knee pain. She endorses that while a physical exam was being performed, she had sudden onset knee pain. Denies any trauma to the knee, radiation of pain, numbness, tingling, or swelling. The above knee radiographs were obtained (Images courtesy of John Kiel, DO).
13-year-old M presents to the ED with acute left knee pain that occurred about 2 hours prior to arrival while playing football. No direct trauma. Reports two audible “pops” followed by knee instability. Radiograph as pictured (Image 1. Plain film of the left knee. Image courtesy of John Kiel, DO).
Patellar subluxation. This patient likely had a spontaneous dislocation and relocation (the two “pops”). There is a very small avulsion fracture noted along the lateral femoral condyle.
It is very important to complete a full neurovascular exam. As well as performing a thorough musculoskeletal exam, assessing the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), lateral cruciate ligament (LCL), medial cruciate ligament (MCL), and patella. View the ALiEM 2 minute knee examination.
If there is an abnormal neurovascular exam or unstable knee examination, pursue further workup such as a CT scan. As an outpatient, further imaging that can be considered is an MRI knee. See below for images from this case.
Image 2. Knee MRI – Sagittal cut showing large knee effusion. Image courtesy of John Kiel, DO.
Image 3. Knee MRI – Axial cut showing the osteochondral defect of the patella. Image courtesy of John Kiel, DO.
This is one of the few times a knee immobilizer is appropriate. However, close follow-up with sports medicine or orthopedics should be stressed as atrophy and contractions can occur if the patient remains in the knee immobilizer for an extended duration. Provide crutches and ask the patient to be non-weight bearing. Anti-inflammatories as needed are appropriate and encourage icing and movement.
An urgent follow-up is needed with sports medicine or orthopedics for further evaluation [3]. In the case of this patient who already had an MRI, he will typically require chondroplasty of the patella and MFPL reconstruction as an outpatient. Post-operatively, he will undergo standard physical therapy with an emphasis on range of motion and quadriceps strengthening.
29-year-old F presents to ED with acute onset knee pain. Reports hearing an audible “pop” after twisting her leg while running down the stairs at home. She explains that her right knee is stuck, and she can neither flex nor extend it. An image is shown below (courtesy of Andrew Murphy, Radiopaedia.org)
