Which term describes a herniation that penetrates the PLL?

Which term describes a herniation that penetrates the PLL?

• A. Subligamentous extrusion
• B. Transligamentous extrusion
• C. Extrusion
• D. Sequestration

Answer: (B)

The key idea is how the disc material relates to the posterior longitudinal ligament (PLL). The PLL acts like a barrier separating the posterior disc from the spinal canal. When herniated material breaches that barrier and passes through the ligament, you’re describing a transligamentous extrusion. The term literally means “through the ligament,” indicating penetration of the PLL into the canal. This distinguishes it from a subligamentous extrusion, where the herniation does not cross the PLL, and from a sequestration, where a fragment has broken away from the main disc and is free within the canal. If the material has crossed the PLL but remains connected to the parent disc, that’s extrusion; if it’s a free fragment, that’s sequestration.

The key idea is how the disc material relates to the posterior longitudinal ligament (PLL). The PLL acts like a barrier separating the posterior disc from the spinal canal. When herniated material breaches that barrier and passes through the ligament, you’re describing a transligamentous extrusion. The term literally means “through the ligament,” indicating penetration of the PLL into the canal.

This distinguishes it from a subligamentous extrusion, where the herniation does not cross the PLL, and from a sequestration, where a fragment has broken away from the main disc and is free within the canal. If the material has crossed the PLL but remains connected to the parent disc, that’s extrusion; if it’s a free fragment, that’s sequestration.