A 70-year-old female with no past medical history was hit by a motor vehicle while crossing the street. She experienced no head strike or loss of consciousness, however she was unable to ambulate at the scene, and upon arrival to the ED, complained of left knee pain. The emergency physician noted moderate swelling on exam with intact skin and distal pulses. She was tender to palpation over the proximal tibia. Portable 2-view radiographs were obtained and interpreted as “no acute fracture.” On repeat examination, however, the patient continued to have pain and was now unable to bear weight on the affected extremity. Is there a role for point-of-care ultrasound (POCUS) in this situation?
After reviewing this case, you should:
- Understand the technique for performing an ultrasound evaluation of the knee in the setting of trauma.
- Be familiar with the ultrasound findings pathognomonic for a tibial plateau fracture.
POCUS in Musculoskeletal Trauma
Ultrasound can be used in traumatic musculoskeletal injury to look for:1
- Joint effusions
- Major tendon rupture
- Vascular occlusions
- Foreign bodies
In this case, the attending physician recommended POCUS to evaluate for possible effusion or ligamentous injury given the patient’s persistent pain, inability to bear weight, and negative plain films (Figure 1).
For this POCUS of the knee, the patient should be supine with their affected knee slightly flexed. The sonographer should use a linear transducer to evaluate the suprapatellar bursa (recess), and the probe is positioned parallel to the femur (Image 2). Larger patients may require a curvilinear probe.
Ultrasound Result and Case Conclusion
Plain film radiographs are often not read by radiology after-hours, and the initial read by the emergency and trauma surgery attending in this was no gross fracture. However, the POCUS revealed a moderate sized lipohemarthrosis (Image 3). This prompted the ED team to send the initial x-ray images to the overnight radiology service, who noted a subtle cortical discontinuity at the left lateral tibial plateau, along with a small volume lipohemarthrosis. These findings are consistent with a left tibial plateau fracture. Orthopedics was consulted with recommendations for a left knee immobilizer and non-weight bearing precautions.
Take Home Points
Tibial plateau fractures can present with subtle radiographic findings. Approximately 15% of intra-articular fractures are radiographically occult, which may delay the diagnosis.2 This may can lead to articular cartilage injury and long-term problems with mobility.
Bedside ultrasound may reveal lipohemarthrosis, suggesting a radiographically occult and subtle tibial plateau fracture. Lipohemarthrosis is layering of fat and blood, which is indicative of an intra-articular fracture involving the bone medulla. This finding is more specific for intra-articular fractures than serous joint effusions alone.3
Incorporating POCUS into the evaluation of acute traumatic knee pain increases the likelihood of discovering an occult fracture. The sensitivity for finding an occult fractures is 84% with plain radiographs, and 94% when combined with POCUS.4 This improved sensitivity may limit the need for CT, prevent delayed diagnosis, and improve the patient’s length of stay. This approach may be particularly useful in resource-poor areas, and limit the patient’s exposure to radiation. A protocol to perform bedside ultrasound as part of the first evaluation of extremity trauma may help us define the population for which further imaging is unnecessary and improve ED resource utilization.