Answer to Case 1.4
A 56-year-old man was brought to your ED after bring involved in a MVC. He was a restrained driver in a car that was traveling at 40 MPH and slammed into a tree. The patient denies loss of consciousness. A radiograph is seen below.
1. What is the abnormality on the radiograph?
2. Name the nerve(s) that are frequently injured in this type of injury?
3. What are the motor and sensory physical exam findings corresponding to these nerve(s)?
1. Left acetabular fracture. A MVC is a very common mechanism that causes acetabular fractures when the knee hits the dashboard causing the flexed hip to move posteriorly into the acetabulum.
2. The sciatic nerve is the most commonly inured nerve. Exam findings should be clearly documented on the chart. The femoral nerve can also be injured with a fracture of the acetabulum.
3. The motor component of the sciatic nerve is checked by testing the strength of the extensor hallucis longus. This is performed by having the patient resist downward pressure on the great toe while held in extension. The sensory component is examined by checking sensation over the dorsum of the foot and lateral calf.
The femoral nerve is less commonly injured than the sciatic nerve. The motor component is checked by extension of the knee as well as the patellar reflex. The sensory component is examined by testing for sensation over the anterior thigh and inner calf.
It looks like an acetabular fracture since it involves the superior pubic ramus at its lateral extent, near the acetabulum. A second fracture should be present and I believe is seen superior to the acetabulum – a slight break in the iliopubic line (arcuate line). By the radiograph, the fracture would be classified as an anterior wall fracture. A CT would show it well. A superior pubic ramus fracture would generally be in the midportion of the pubic ramus and when it’s this displaced would be associated with an inferior pubic ramus fracture, and, likely as well, a second break in the pelvic ring, e.g., a sacral wing fracture.
The Teardrop Sign
The radigraphic teardrop sign is a landmark present in normal pelvic radiographs and is often disrupted with acetabular fractures. However, if the patient is rotated, the teardrop sign may not be present. In addition, the presence of the teardrop sign does not exclude a fracture. Nonetheless, if the teardrop sign is absent in the right clinical setting, then you should be highly suspicious for an acetabular fracture.
Thank you for everyone who submitted an answer. Please stay tuned for next week’s radER.
radER is a weekly contest, hosted by Dr. Kerin Jones’ “Fracture”, consisting of a radiograph selected from various areas of emergency medicine that are central to the education of medical students and residents in training.
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