Review Question - QID 3454

Figure A shows an unstable bilateral pelvic ring injury. Percutaneous posterior iliosacral screw fixation places the L5 nerve root at risk as it courses across the sacral ala. Injury to the L5 nerve root would typically result in weakness in great toe extension and sensory changes on the dorsum of the foot. It is important to notice that L5 often partially innervates tibialis anterior along with L4, so weakness to ankle dorsiflexion may be present as well. Illustration A shows the post-operative films with bilateral iliosacral screws.

Routt et al examined the sacral slope and sacral alar anatomy in cadavers and a series of consecutive patients. They determined that the pelvic outlet and lateral sacral plain films provide the best plain radiographic views of the sacral ala. They recommended routine usage of these views intraoperatively to guide screw placement.

In another study, Routt et al reported on the early complications of percutaneous placement of iliosacral screws for treatment of posterior pelvic ring disruptions. While technically challenging, this technique leads to less blood loss and lower rates of infection compared to traditional open techniques.

Illustration B displays the root diagrams for sensation, reflex, and motor of the L4-S1 nerves.

Incorrect answers:
1: Weakness to knee extension would be caused primarily by an injury to the L4 nerve root.
2: Decreased patellar reflex would be caused primarily by an injury to the L4 nerve root.
4: Weakness in ankle plantar flexion would be caused primarily by an injury to the S1 nerve root.
5: Decreased Achilles reflex would be caused primarily by an injury to the S1 nerve root.