Anatomic investigation for direct reparative and reconstructive surgery of spondylolysis

Objective To provide data through anatomical study to facilitate the interspinous-transverse process cable and translaminar screw reparative and reconstructive surgery of spondylolysis.Methods Structures including transverse process, lamina and pars interarticularis in intact vertebrae specimen of L4 and L5 levels from 31 normal adult corpuses were anatomically measured.Results ① Transverse process: The thickness and width of transverse process at the starting point, medial one fourth point and midpoint of L5 level were greater than those of L4 level.At the same measured point, the L5 transverse process had a cross sectional area two times as that of the L4 transverse process. ② Lamina: The average thickness of the upper border of L5 lamina was 3.21 mm, which was greater than the 2.75 mm of L4 lamina.And the average thickness of the inferior border of L5 lamina was 5.71 mm, which was slightly larger than the 4.93 mm of L4 lamnina. At L5 level, the distance from the midpoint of the boundary of the lamina and the base of pedicle to the starting point of the anterior border of the transverse process on the other side was 45.78 mm,far greater than the 37.89 mm of L4 level.From the superior view, the angle between the screw path and the sagittal plane was about 55°~56°at both L4 and L5 levels. From the posterior view, the angle between the screw path and the sagittal plane was about 65°~66°at L4 level, and about 72°~73°at L5 level.③ Pars interarticularis: There was no significant difference in the height and thickness of pars interarticularis between L4 and L5 levels. The inferior border of pars interarticularis was distinctly thicker than the superior border. The thickness of central part of pars interarticularis was about 6.5～7 mm.Conclusions ① The transverse process of L4 is weaker,and less tensile strength can be exerted when binding the cable. ② The screws used for L4 level should be smaller than the ones used for L5 level. The screw path should be through the central or inferior portion of the lamina. ③ Serious attention should be paid to bone grafting.