Case #16: Knee Pain
Mitchell Kentor, M.D.
HPI: 75yo female presents to ED after fall onto her R knee 3 days ago. Patient has only been able to walk with a cane since that time and is unable to fully extend the knee since the fall.
Physical Exam/ Workup: The R knee appears purple and bruised. There is no obvious deformity. Patient has minimal ability to flex or extend the knee due to pain.
Bedside Ultrasound:
Diagnosis: Patellar Fracture
Treatment: If the extensor mechanism is intact, patient may qualify for non-surgical treatment. In this case, the knee should be immobilized and patient made non-weight bearing. The patient will need to follow up with orthopedics for definitive management. If the extensor mechanism is disrupted, the patient will need orthopedics for evaluation for surgical management.
Ultrasound Education: MSK Ultrasound in the ED
Trauma to the knee and inability to move the affected joint raises questions of injury to both bony structures and tendons. Physical exam may provide clues to the type of injury such as a high riding patella in patellar tendon rupture or a failed straight leg test indicating disruption of the extensor mechanism. Partial tears and fractures may be difficult to diagnose on exam alone. X-ray is helpful in identification of fractures but offers limited insight into damage to soft tissues. US of the patella, quadriceps tendon, and patellar tendon allows for quick imaging of the knee and key structures. Ultrasound can effectively visualize fractures along with damage to tendons.
How to perform MSK ultrasound of the knee
-A linear probe is used starting in the longitudinal plane
-The patella, patellar tendon and quadriceps tendon are superficial structures, making them easy to visualize. It is important to visualize the patella and tendon in the same image. You should be able to see the attachment of the tendon into the bone. The tendon will appear to have parallel echogenic lines running through the structure. One can then trace the length of the tendon looking for signs of injury.
-Signs of injury may include complete disruption of the tendon, hypoechoic areas within the tendon, surrounding edema and inflammation.
Conclusion: Bedside US in this patient made the diagnosis of patellar fracture without signs of damage to the tendon. Bedside US is a simple and effective tool in assessment and diagnosis of knee injury that offers information beyond that on standard x-ray.
Additional Resources:
-Blount, J (2016, November) Patella fractures. Up to Date
-Sonography of the patellar tendon and adjacent structures in pediatric and adult patients https://www.ajronline.org/doi/full/10.2214/ajr.176.6.1761535
-Tintinalli J et al. (2016) Tintinalli's emergency medicine: A comprehensive study guide (Eighth edition). New York: McGraw-Hill Education