Sagittal imaging study of the lumbar spine with the short rod technique

Purpose The short rod technique (SRT) is a novel method for lumbar pedicle screw placement to reduce surgical trauma and avoid damage to the facet joint and articular surface. The core concept is to change the entry point and angle of the screw on the vertebrae at both ends in the sagittal plane to shorten the length of the longitudinal rods. The purpose of this study is to determine the sagittal screw angle (SSA) and its safe Maximum (MAX) value on each lumbar vertebra for the SRT and to observe the shortening effect on the longitudinal rods. Methods A total of 152 healthy adults were investigated by measuring the lumbar spine lateral view images. The SSA and MAX-SSA were measured with SRT as reference to the conventional placement technique method. The distance between the entry points of the proximal and distal vertebrae was measured to compare the changes in the length of the longitudinal rods using the two screw placement techniques. Results + SSA increased from L1 to L4, and −SSA increased from L2 to L5, in which the −SSA of L2, L3, and L4 were significantly greater than those of + SSA ( P < 0.05). + MAX-SSA at L1–L4 was 23.26 ± 3.54°, 23.68 ± 3.37°, 24.12 ± 3.29°, and 24.26 ± 3.42°, respectively. −MAX-SSA at L2–L5 was 36.25 ± 3.26°, 38.26 ± 3.73°, 38.62 ± 3.63° and 37.33 ± 3.31°, respectively. Theoretical reductions by calculation for the 2-segment lumbar pedicles were: L1–2: 9 mm, L2–3: 9.29 mm, L3–4: 6.23 mm, and L4–5: 7.08 mm; And the 3-segment lumbar pedicles were: L1–3: 16.97 mm, L2–4: 16.73 mm, L3–5, and 18.24 mm, respectively. Conclusions The application of the SRT to lumbar pedicles is a safe screw placement method that can significantly shorten the length of the used longitudinal rods.