What is your diagnosis?

Comminuted fracture of the patella with a disrupted extensor mechanism. Comminuted fractures are common in multiple injured patients such as this one and a classic presenting mechanism is striking the anterior knee on the dashboard while in a flexed position [1].

• Pearl: In a trauma patient with altered mentation or other significant distracting injuries it can be easy to miss a disrupted extensor mechanism. Repeat assessments prior to discharge are keys to ensure no traumatic injury goes missed.

What is your management in the ED? Do I need to consult Orthopaedics?

Because this patient has a disrupted extensor mechanism they will require orthopaedic evaluation and likely operative repair of their patella fracture. While they are in the emergency department they can be placed in a knee immobilizer locked in extension [1,2].

• Pearl: If in a community setting, discharge in a knee immobilizer with urgent orthopaedic follow up is sufficient.

What is your disposition?

This patient requires evaluation by orthopaedic surgery and will likely require operative repair of their patella fracture. The indication in this scenario for operative fixation is the disrupted extensor mechanism. 

• Pearl: Patella fractures that are not significantly displaced (<3mm between fragments or articular step off of <2 mm) and have an intact extensor mechanism can be managed non operatively [1,2].

• Pearl: Testing the extensor mechanism can be done during the initial assessment of a trauma patient by having them hold a straight leg raise off of the hospital bed. Additionally the extensor mechanism can be tested by having the patient extend a partially flexed knee against gravity.

What imaging should be obtained?

X-ray imaging should suffice in diagnosing a patella fracture. We should obtain an AP, Lateral and oblique view of the knee. A sunrise view can be helpful but caution should be exercised as this view can cause further displacement of the fracture. We can also consider CT, Ultrasound or MRI however these are unlikely to change the emergency department disposition [2].

• Pearl: A normal variant to be aware of is the bipartite and tripartite patella. If there is suspicion that the patient has one of these normal variants, contralateral imaging should be obtained as these are usually bilateral. 

Image 2: Bipartite Patella. Image courtesy of Dr. Hanna Damtew Taddese, Radiopaedia.org, rID: 1357