Anatomy of the percutaneous presacral space for a novel fusion technique

Lumbar fusion has been widely used to treat unstable spinal disorders. Methods are evolving from open procedures to less invasive methods to avoid soft tissue trauma. Recently, a soft tissue sparing method to access the axial lumbosacral spine has been developed. It is crucial to determine structures potentially at risk for injury during this fusion technique. The anatomy of the presacral space and safety of the paracoccygeal approach were evaluated through cadaveric dissection and radiographic studies. The objective was to evaluate the safety of a paracoccygeal approach to the axial lumbosacral spine and determine structures that could potentially be injured.

The paracoccygeal approach was performed on two cadavers, followed by dissection. Distances from the midline trajectory of the approach to surrounding vascular structures were determined. Similar distances were also measured on computed tomography (CT) and magnetic resonance imaging (MRI) of 12 patients, as well as CT images of two additional patients. A "safe zone" was determined using the sagittal length of the presacral space and the distance between the most medial internal iliac vessel on the right and left, respectively.

The coronal safe zone averaged 6.9 and 6.0 cm on MRI and CT, respectively. The mean distance from the anterior sacral margin to the rectum at the S3-S4 level was 1.2 and 1.3 cm on MRI and CT, respectively.

In this study, we defined the "coronal safe zone" within the presacral space. This "safe zone" may guide surgeons when utilizing the percutaneous paracoccygeal approach.