Colleen Sweeney, Akash Desai
A 55-year-old female with no pertinent past medical or surgical history was brought in by ambulance after a bicycle accident with left knee pain. She was unhelmeted while riding a bicycle going 10mph when she collided into an e-bike. Her left knee was caught in her handlebars; she denied head trauma and had no LOC.
Vitals: BP 168/120, HR 70, T 96.0F, RR 22, SpO2 95% on RA, BMI 24.41
Physical Exam:
General/Neuro: alert, in acute distress, diaphoretic
HEENT: normocephalic, atraumatic, EOMI
CV: normal rate
Resp: tachypneic
Abdomen: flat, soft, no tenderness
MSK: RLE normal
L knee: +swelling, +deformity. Skin intact, small ecchymosis to left lateral knee. Knee diffusely tender to palpation. Sensation intact to light touch throughout. Palpable popliteal, PT, and DP pulses. Able to wiggle toes. Compartments compressible. Patient unable to tolerate any movement of L knee secondary to pain.
L lower leg: +swelling from knee distally, no lacerations
L ankle/foot: normal pulse, sensation intact to light touch throughout
Radiographs were indicated and initially attempted at bedside, however were unsuccessful as the patient was unable to tolerate the pain. Radiography was delayed until two hours due to pain management and census. In the interim, a POCUS was performed
Xray findings: "Acute, comminuted, displaced proximal tibial fracture extending to the lateral and central tibial plateau. Acute, mildly displaced and impacted fibular neck fracture. No fracture or malalignment of the left ankle. "
The patient was admitted to the trauma surgery service. The next day, she underwent a left knee spanning external fixator for stabilization of the tibial plateau fracture. One week later, she had an ORIF for long-term fixation of the fracture as well as a hamstring tendon repair.
Discussion
POCUS is increasingly utilized in acute musculoskeletal trauma. The patient’s gross knee deformity after a traumatic event led to POCUS utilization to provide rapid clinical guidance. In this patient, ultrasound was complete half an hour prior to the first attempt at radiographs and over 2 hours prior to their completion, thus proving useful in differentiating the severity of a patient’s injury during prolonged wait times and facilitating early orthopedic surgery consultation.
Ultrasound, though not a primary diagnostic modality for acute fractures, offers sensitivity of 87% and specificity of 70% for proximal tibial fractures specifically in cadaveric models [3]. In Figure 3, the cortical break visible on the left side of the image corresponds to the proximal tibial fracture seen on X-ray.
Figures 1 and 2 both demonstrate lipohemarthrosis. The presence of hemarthrosis, rather than a simple joint effusion, raises the suspicion for an intra-articular injury or fracture, with ultrasound demonstrating a sensitivity of 90% and specificity of 86% for this finding [2]. When lipohemarthrosis is identified—most clearly visualized in Figure 2 as hypoechoic fat “bubbles” originating from the bone marrow—it is even more indicative of an intra-articular fracture, carrying 97% sensitivity and 100% specificity for such fractures [4]. In its early stage, lipohemarthrosis appears as scattered fat globules, which later settle into the characteristic triple-layer pattern of fat, serum, and blood products [5]. Recognition of hemarthrosis or lipohemarthrosis on ultrasound may help risk-stratify patients for joint aspiration, potentially reducing unnecessary aspirations and associated infection risk.
The presence of lipohemarthrosis is highly suggestive of a distal femur or proximal tibial fracture. Recognizing these findings early allows clinicians to maintain a high index of suspicion for periarticular fracture prior to radiographic confirmation, enabling prompt immobilization, consultation, and fracture management. This early identification facilitates more efficient triage and throughput in the ED and underscores POCUS as a worthwhile adjunct in knee trauma in addition to traditional imaging such as X-ray, CT, and MRI [6].
References:
- Stannard JP, Lopez R, Volgas D. Soft tissue injury of the knee after tibial plateau fractures. J Knee Surg. 2010;23(4):187-192. doi:10.1055/s-0030-1268694
- Taljanovic MS, Chang EY, Ha AS, et al. ACR appropriateness criteria® acute trauma to the knee. Journal of the American College of Radiology. 2020;17(5). doi:10.1016/j.jacr.2020.01.041
- Demers G, Migliore S, Bennett DR, et al. Ultrasound evaluation of cranial and long bone fractures in a cadaver model. Mil Med. 2012;177(7):836-839. doi:10.7205/milmed-d-11-00407
- Bonnefoy, O., Diris, B., Moinard, M. et al. Acute knee trauma: role of ultrasound. Eur Radiol 16, 2542–2548 (2006). Doi:10.1007/s00330-006-0319-x
- Levrini G, Reggiani G, Vacondio R, Zompatori M, Nicoli F. Post-traumatic knee lipohemarthrosis: Temporal evolution with progressive separation of the three layers of the joint effusion by ultrasonography and computed tomography. European Journal of Radiology Extra. 2006;60(1):37-41. doi:10.1016/j.ejrex.2006.06.011
- De Maeseneer M, Marcelis S, Boulet C, et al. Ultrasound of the knee with emphasis on the detailed anatomy of anterior, medial, and lateral structures. Skeletal Radiol. 2014;43(8):1025-1039. doi:10.1007/s00256-014-1841-6
