by Elizabeth Hofheinz, M.P.H., M.Ed.
For the degenerating spine, lateral retroperitoneal lumbar interbody fusion (LLIF) using percutaneous pedicle screw fixation can be quite successful. However, say a team of researchers from Kyoto, Japan, the exact mechanisms that determine segmental lordosis remain unclear. Their new retrospective study, “Analysis of the Factors Affecting Lumbar Segmental Lordosis After Lateral Lumbar Interbody Fusion,” was published in the July 15, 2020 of SPINE.
Co-author Bungo Otsuki, M.D., Ph.D. told OSN, “Because most of the lumbar kyphosis is coming from degenerative change of disc, not the collapse or deformation of vertebra, I started to think that most of the deformity can be corrected only making lordosis at disc level without osteotomies, which sometimes cause massive bleeding and longer operative time. So, I have studied what kind of factors affect the segmental lordosis in LIF [lumbar interbody fusion] and PPS [percutaneous pedicle screw] surgery.”
The team studied 69 patients (102 levels) who underwent LLIF with posterior pedicle screw fixation without posterior osteotomy (age range 16-85). CT scans were taken preoperatively and within 2 weeks postoperatively. Explanatory factors considered included segmental lordotic angle (SLA) before surgery, disc height before surgery, cage position, cage angle, cage height, cage height – disc height before surgery (amount of lift up), prior decompression surgery, and level fused.
The average segmental lordosis after operation (“Post-SLA”) increased significantly from the segmental lordosis before operation (Pre-SLA). “However,” wrote the authors, “there were no significant differences in the increased amount of lordosis across the spinal levels. Pre-SLA had a strong positive correlation with Post-SLA.”
“Cage position also had a strong positive correlation with Post-SLA, and Post-SLA was larger when the cage was located more to the anterior. Of note, 24 levels diminished the segmental lordosis after surgery, and the cages were located posteriorly at most of these levels. Average Post-SLA in each cage position was 10.68 in the anterior, 7.58 in the middle, and 3.28 in the posterior locations.”
“As for the cage angle, we compared the change in segmental lordosis before and after surgery (Pre-SLA and Post- SLA) between the two different CageAs [cage angles] (6° and 10°). Contrary to our expectation, there was no significant difference between the two groups…there was not any clear correlation between Post-SLA and LiftUp [amount of lift up of disc space].”
“The most important thing,” said Dr. Otsuki to OSN, “is that the segmental lordosis is decided by the position of the cage (not the angle of the cage) and the preoperative local segmental lordosis. Also, it is important to select the thin cage when the cage is located in the posterior.”
“I was surprised that the segmental lordosis after the surgery can be explained by only two factors, cage position and preoperative segmental lordosis, and these two factors explain 80% of all effects.”
“The difficult thing is to insert the cage to the appropriate position. We need more sophisticated methods and surgical instruments in the future.”
