Dimensions of the spinous process and interspinous space: a morphometric study

Purpose: To measure the morphological dimensions of the spinous process (SP) and interspinous space, and provide a basis for the development of interspinous devices for the Korean or East Asian populations. Methods: We retrospectively analyzed the anatomical parameters of 120 patients. The parameters included height, length, and width of SP, interspinous distance (supine, standing, and dynamic), cortical thickness of SP, and spino-laminar (S-L) angle. Correlations between measurements, age, and gender were investigated. Results: The largest height, length, and cortical thickness and S-L angle were noted at L3. The largest width was observed at S1. The interspinous distance decreased significantly from L2–3 to L5–S1 and was significantly larger in the supine than in standing posture for L5–S1. Cortical thickness was gradually tapered from the anterior to the posterior position. The S-L angle at L2 and L3 was similar and significantly decreased from L3 to S1. An increased trend in width with aging and a decreased trend in distance (supine) were noted. A significant increase in height, length, and distance in males compared with females was also observed. Conclusions: The interspinous space is wider at the anterior, and the cortex is thicker anteriorly. Accordingly, it appears that the optimized implant position lies in the interspinous space anteriorly. The varying interspinous space with different postures and gradually narrowing with age suggest the need for caution when sizing the device. Gender differences also need to be considered when designing implantable devices.