Abstract
ObjectiveThe screw path of lumbar pedicle screws in the vertebral body has certain variability. It is not clear whether the screw paths in different directions can obtain the same pull-out resistance. This study intends to use CT (Computed Tomography) to measure the Hounsfield unit (HU value) around the screw paths in different parts of the lumbar vertebral body to obtain the bone mineral density value of the corresponding parts which will provide some reference for the direction of lumbar pedicle screw placement.MethodsThis retrospective study included 200 patients with lumbar degenerative diseases selected randomly from the case base and the patient’s basic information was recorded. L1-L5 vertebral body was divided equally into the upper, middle and lower 1/3, which was consistent with the three sagittal entry directions of the pedicle screw head tilt, parallel endplate and caudal tilt, and the HU values were measured by CT cross-sectional scanning to indirectly reflect the local bone density values. The paired t-test (randomized block experiment) was used to compare the HU values of the upper, middle and lower 1 / 3 parts, with P < 0.05 being considered statistically significant.ResultsComparison of HU values in different parts of each vertebral body revealed that HU values in the middle 1/3 of the L1,L2 (163.88 ± 58.44 and 152.94 ± 59.45) and in the lower 1/3 of the L4 (149.86 ± 60.18) were higher than in the other two parts of the vertebral body of the same segment(P < 0.0001,P = 0.0069 and P = 0.0024, respectively); According to the results of each stratification, patients with younger age and better bone condition had higher HU values in the middle 1/3 of L1 and L2, and higher HU values in the lower 1/3 of L3, L4 and L5; With the increase of age, the decrease of bone condition and the difference of HU value in each vertebral body gradually decreased.ConclusionAlthough further follow-up studies are needed, based on the analysis of the statistical results, we speculate that from the perspective of obtaining the best pull-out resistance of the lumbar pedicle screws, the placement direction of L1 and L2 in the sagittal position may be as parallel to the endplate as possible; L3, L4, and L5 may be as appropriate as possible to the tail tilt theoretically.
Highlights
Posterior lumbar interbody fusion (PLIF) is a commonly used surgical method for spinal surgery to treat degenerative diseases of the lumbar spine, which can achieve better prognosis in patients [1, 2].Since the first operation was performed in 1940, the majority of cases worldwide have been performed using this method
According to the stratification of variables Gender In 103 male patients and 97 female patients, we found that the mean Hounsfield units (HU) values in the middle 1/3 of L1 and the lower 1/3 of L4 and L5 were significantly higher than the rest of the vertebral body of the same segment in both men and women (Male: L1: P < 0.0001, L4: P = 0.0156, L5: P = 0.0050; Female: L1: P < 0.0001, L4: P < 0.0001, L5: P = 0.0142)
The direction of screw placement for most surgeries is parallel to the endplate, due to the influence of many factors, such as the curvature of the patient’s lumbar spine, the model of the implanted fusion cage, etc., the trajectory direction of the screw head at the anterior aspect of the vertebral body has a certain degree of variability [21]
Summary
Posterior lumbar interbody fusion (PLIF) is a commonly used surgical method for spinal surgery to treat degenerative diseases of the lumbar spine, which can achieve better prognosis in patients [1, 2].Since the first operation was performed in 1940, the majority of cases worldwide have been performed using this method. With the aging of the population, osteoporosis has become one of the most common diseases in the elderly, affecting 200 million people on a global scale. In these patients undergoing posterior lumbar fusion surgery, it is necessary to select the appropriate method to avoid screw loosening as much as possible, and to enhance the screw pull-out resistance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
