Characterization of lumbar spinous process morphology: a cadaveric study of 2,955 human lumbar vertebrae

Background context Despite the interest in lumbar spinous process (SP)-based surgical innovation, there are no large published studies that have characterized the morphometry of lumbar SPs. Purpose To provide accurate level-specific morphometric data with respect to human lumbar SPs using a human cadaveric lumbar spine model and to describe the morphometric variation of lumbar SPs with respect to gender, race, and age. Study design An anatomic observational study. Methods This study used 2,955 cadaveric lumbar vertebrae from 591 adult spines at the Hamann-Todd Human Osteological Collection. Specimens were aged 20 to 79 years. Each vertebra was photographed in standardized positions and measured using ImageJ software. Direct measurements were made for the SP length, width, height, slope, and caudal morphology. Gender, race, and age were recorded and analyzed. Results Spinous process length was 24.8±4.6 mm (L5) to 33.9±3.9 mm (L3). Effective length varied from 19.5±2.6 mm (L1) to 24.6±3.3 mm (L4). Height was shortest at L5 (18.2±2.7 mm). Caudal width was greater than the cranial width. Slope, caudal morphology, and radius measures showed large interspecimen variation. Slope at L5 was steeper than other levels (23.7°±10.5°, p<.0001). Most specimens demonstrated convex caudal morphology. L4 had the highest proportion of convexity (80.7%). L1 was the only level with predominantly concave morphology. Measurements for female SPs were smaller, but the slope was steeper. Anatomic and effective SP lengths were longer for specimens from white individuals. Specimens from black individuals had larger width and height, as well as steeper slope. Black specimens had more convex morphology at L4 and L5. With increasing age, the SP length, effective length, and width increased. Height increased with age only at L4 and L5. Slope and caudal radius of curvature decreased with age, and increasingly convex morphology was noted at most levels. Conclusions This large cadaveric study provides level-specific morphometric data regarding the osseous dimensions of lumbar SPs relevant to techniques and devices targeting the lumbar SPs or the interspinous space. Of particular importance is the recognition that L5 has relatively different morphology when compared with more cranial levels. Potentially important differences were noted comparing women with men, black with white, and aging populations.