Denis Classification of Sacral Fractures

Denis et al classified sacral fractures into three zones. Zone I (extraforaminal) fractures are lateral to the sacral neural foramina. Zone II (transforaminal) fractures extend through the neural foramina, but do not involve the spinal canal. Zone III fractures involve the spinal canal.

They found that zone I fractures were only occasionally associated with partial damage to the L5 nerve root. Zone II fractures were frequently associated with sciatica but rarely with bladder dysfunction. Zone III fractures were frequently associated with saddle anesthesia and loss of sphincter function.

Zone I and II fractures can cause injury to the L5 nerve root in the lumbosacral tunnel (space between the lumbosacral ligament and the S1 sala). Zone II and III fractures can cause injury to the S1 nerve root or pudendal nerve. S1 nerve injury in this setting is usually not isolated and tends to be associated with a lumbosacral plexus injury.

More recent work by Sugimoto et al has found that the incidence of lumbosacral plexus injury was not related to the zone of sacral fracture. Instead they found that risk factors for lumbosacral plexus palsy included longitudinal displacement of the pelvis, transverse sacral fracture, and trauma from a suicidal jump were risk factors.

The image above shows a right zone I sacral fracture (pink arrow). The white arrow indicates the right L5 nerve root/lumbosacral trunk (L4 and L5 nerve roots join up close to this location) is located directly anterior to the fracture.

References

• Denis F, Davis S, Comfort T. Sacral fractures: an important problem. Retrospective analysis of 236 cases. Clin Orthop Relat Res. 1988 Feb;227:67-81.
• Sugimoto Y, Ito Y, Tomioka M, Tanaka M, Hasegawa Y, Nakago K, Yagata Y. Risk factors for lumbosacral plexus palsy related to pelvic fracture. Spine (Phila Pa 1976). 2010 Apr 20;35(9):963-6.