A 33-year-old man is brought to the emergency department after being involved in a major motor vehicle accident. He is unable to move his legs and complains of severe pain in his mid to lower back. On physical examination, he is found to have exquisite tenderness over some of the bony prominence of his lower back, but no gross physical deformity can be appreciated. On neurologic examination, flaccid paralysis of both lower extremities and complete anesthesia to all sensory modalities below approximately the L3 dermatome are noted. Catheterization of his bladder yields approximately 700 mL of urine. Plain radiographs of the spine reveal compression fracture in the body of L3 with greater than 50% of loss in its height. A computed tomography (CT) scan through this area reveals a burst fracture of the body of L3. There are large fragments of bone driven dorsally with an 80% canal compromise. What is the cause of weakness?
A 33-year-old man is brought to the emergency department after being involved in a major motor vehicle accident. He is unable to move his legs and complains of severe pain in his mid to lower back. On physical examination, he is found to have exquisite tenderness over some of the bony prominence of his lower back, but no gross physical deformity can be appreciated. On neurologic examination, flaccid paralysis of both lower extremities and complete anesthesia to all sensory modalities below approximately the L3 dermatome are noted. Catheterization of his bladder yields approximately 700 mL of urine. Plain radiographs of the spine reveal compression fracture in the body of L3 with greater than 50% of loss in its height. A computed tomography (CT) scan through this area reveals a burst fracture of the body of L3. There are large fragments of bone driven dorsally with an 80% canal compromise. What is the cause of weakness?
💡 Explanation
**Core Concept**
The underlying cause of weakness in this patient is related to spinal cord injury due to a burst fracture of the body of L3, leading to significant canal compromise and compression of the spinal cord.
**Why the Correct Answer is Right**
The patient's symptoms, including flaccid paralysis of both lower extremities and complete anesthesia below the L3 dermatome, are consistent with a spinal cord injury. The burst fracture of L3, with large fragments of bone driven dorsally and an 80% canal compromise, is likely causing compression of the spinal cord. This compression is likely affecting the anterior spinal cord, specifically the anterior horn cells of the spinal cord, leading to motor weakness.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the patient's symptoms are not consistent with a radiculopathy, which would typically present with pain and weakness in a dermatomal distribution. The patient's flaccid paralysis and complete anesthesia suggest a spinal cord injury rather than a radiculopathy.
* **Option B:** This option is incorrect because there is no indication of a peripheral nerve injury. The patient's symptoms are not consistent with a nerve root injury, which would typically present with pain and weakness in a specific dermatomal distribution.
* **Option C:** This option is incorrect because the patient's symptoms are not consistent with a muscle injury. The patient's flaccid paralysis and complete anesthesia suggest a spinal cord injury rather than a muscle injury.
**Clinical Pearl / High-Yield Fact**
In cases of spinal cord injury, the level of injury can be determined by the sensory and motor function below the level of injury. In this case, the patient's complete anesthesia below the L3 dermatome suggests that the level of injury is likely at or above L3.
**Correct Answer:** C.
✓ Correct Answer: C. Compression of the cauda equina
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