Edward Rainier G. Santos, Jonathan N. Sembrano, Benjamin Mueller and David W. Polly
The authors performed a study to determine the optimal iliac screw size, length, and trajectory that produce the highest insertional torques.
Ten fresh cadavers were used and 7.5 × 140–mm and 9.5 × 140–mm iliac screws were placed using 3D image guidance in a randomized fashion in 1 of 2 trajectories. The screws were inserted from the posterior superior iliac spine (PSIS) to either 1) supraacetabular bone or 2) the anterior inferior iliac spine (AIIS). Insertional torque was measured for each full revolution, and the concomitant depth for each torque measurement was recorded. Insertional torque was correlated with detailed bony anatomy.
There was no difference in mean peak insertional torque between the 2 trajectories (25.6 ± 16.4 in-lb [supraacetabular], 26.3 ± 18.2 lb-in [AIIS]; p = 0.8). However, there was a difference between the 2 screw diameters (21.1 ± 10.9 lb-in [7.5-mm-diameter screw], 33.7 ± 19.4 lb-in [9.5-mm-diameter screw]; p = 0.0003). The greatest mean peak insertional torques were observed at depths greater than 80 mm (12.7 ± 9.6 lb-in [≤ 80 mm], 23.7 ± 15.7 lb-in [> 80 mm]; p = 2.6 × 10−7). Insertional torque peaks correlated with engagement of the lateral iliac cortex and the superior iliac fossa.
Although the trajectory had no effect on insertional torque, increased torques are achievable by placing larger-diameter and longer screws in proximity to bony landmarks, most of which are at distances greater 80 mm from the entry point at the PSIS. Iliac screws longer than those commonly used in clinical practice can be safely and accurately placed using image guidance, and reproducible screw paths can be achieved.
Sharon C. Yson, Edward Rainier G. Santos, Jonathan N. Sembrano and David W. Polly Jr.
In this paper the authors sought to determine the segmental lumbar sagittal contour change after bilateral transforaminal lumbar interbody fusion (TLIF).
Between March 2007 and October 2010, 42 consecutive patients (57 levels) underwent bilateral TLIF. Standard preoperative and 6-week postoperative standing lumbar spine radiographs were examined. Preoperative and postoperative segmental lordosis was determined by manual measurements using the Cobb method. The difference between the preoperative and postoperative values were calculated and analyzed for statistical significance.
The mean preoperative segmental alignment was 8.1°. The mean postoperative alignment was 15.3°, with a mean correction of 7.2° per segment. The largest gain in lordosis was obtained at the L5–S1 level (10.1°). There was a significant difference between the preoperative and postoperative values (p = 5 × 10−9). There was no significant difference in mean segmental correction between levels. Improvement in lordosis was higher in multilevel fusions (9.8°) than in single-level fusions (5.2°) (p = 0.047). There was an inverse correlation between preoperative sagittal lordosis measurement and change in lordosis (r = −0.599).
A significant improvement in lumbar lordosis can be gained by preforming bilateral facetectomies in TLIF with posterior compression. This procedure provides an additional option to a spine surgeon's armamentarium in dealing with significant lumbar sagittal plane deformities.