Studies have shown that the height and width of the lumbar spinous process increased in elderly when compared with young people, and various anatomical parameters were in dynamic change with advancing age.In addition, the thickening of collagen fiber components of ligaments, cartilage metaplasia and calcification,even the formation of local interspinous ossification further resulted in the irregular shape of the spinous process and the narrowing of spinous process space in elderly patients.On the other hand, the function of extension and bending of spine was restricted because of degenerative changes of spine [11-13]. In summary, the difficulty of landmark-guided location caused by spinal degeneration may be a major reason for the low success rate of spinal anesthesia in elderly patients. Ultrasound has been successfully applied in spinal anesthesia for elderly with its’ advantages on non-invasiveness, non-radioactivity and low cost. Many studies have shown that preprocedural ultrasound technique could improve the accuracy of localization and the first-attempt success rate of lumbar puncturing as well as reduce the number of attempts in elderly patients[9,14,15,16]. Therefore, in order to improve the accuracy of location and reduce the effect of anatomical factors on results, we performed ultrasound-assisted location in all patients before anesthesia.As we can see,The difference between ultrasound-guided and landmark-guided location of intervertebral space was 30.4%, 24.5% and 16.3% in each group .
At present, midline technique and paramedian technique are widely applied for spinal anesthesia in elderly. The former is easy for residents to perform, but the needle tip is often stopped by bones and ligaments which results in a low success rate. The latter can bypass supraspinous ligament and interspinous ligament.But for residents, it is often difficult to grasp the optimal angel and depth to puncture. Previous studies have shown that two traditional approaches have their own advantages and disadvantages in clinical application, and there was a difference between resident physicians and senior physicians[10,17,18], which may be related to operators’ experience. Therefore, we set up a resident as anesthesia operator throughout the study.The results showed that the first-attempt success rate in elderly patients of groups M and P were 47.8% and 42.9%. There were no significant difference in first-attempt success rate, number of needle redirections,number of attempts,patient satisfaction and the incidence of postoperative adverse reactions,only the time taken to perform spinal anesthesia in group M was longer than group P. Rizk et al.  showed that under the premise of ultrasound-assisted localization and resident responsible for operation,compared with paramedian technique group, midline technique group has significantly a higher first-attempt success rate (73% VS 42%) ,fewer number of needle redirections and number of attempts and less puncturing time,which was different from the results of our study. This may lie in the different definitions of the first-attempt success rate and practical abilities of operators in the two studies.
As mentioned above, the trade-off between two traditional techniques sometimes fails to achieve satisfactory results. Therefore,it may be easier to look for a new technique to solve the clinical problem .For nearly ten years of clinical practice, we have found that even in the case of repeated failure for senior anesthesiologists to perform spinal anesthesia in elderly patients with midline technique and paramedian technique, the application of modified paramedian technique often gets success. What’s more,compared with midline technique,operators often feel a significant reduction in resistance in the process of needle insertion, especially in elderly patients. The reason may lie in that modified paramedian technique bypasses calcified supraspinal and interspinous ligament or the dense and tough part of ligaments of elderly patients which reduces the difficulty of puncturing. At the same time, it is especially suitable for residents with less experience. Because the insertion angle and depth of needle are easy to master.By reviewing previous literature[19-21], for modified paramedian, the needle tip can reach subarachnoid space smoothly theoretically by setting 0.5 cm lateral to the midpoint of L3-4 spinous process space as injection site with the needle perpendicular to skin.A study showed that compared with median sagittal and transverse images, ultrasound scanning in para-midsagittal position could obtain a larger intervertebral space and a clearer field of ligamentum flavum and epidural vessels, thus improving the overall visibility of all structures,which indicated that modified paramedian technique might be beneficial for spinal anesthesia. In conclusion, modified paramedian for lumbar puncture is supported by relevant anatomical theories.
Chen et al.  showed that compared with paramedian approach, modified paramedian approach had a higher first-attempt success rate and patient satisfaction, fewer number of attempts in pregnant,which was a feasible approach for residents.But it’s not clear if it’s be true for elderly.We firstly conducted the randomized controlled study on the application of preprocedural ultrasound modified paramedian technique for elderly, and compared it with two traditional techniques. The results showed the first-attempt success rate was higher significantly in group PM (77.6%) than groups M and P (47.8% and 42.9%). Compared with the latter, group PM had a fewer number of attempts and a higher patient satisfaction.When compared with group M, group PM had a significantly fewer needle redirections and a shorter procedure time.While compared with group P, there were no statistically significant difference.As we thought, modified paramedian technique was easy to learn and operate for beginners without an increasing of postoperative adverse reactions, which was consistent with the previous study. The reasons may be as follows:1)Compared to paramedian technique,the injection site of modified paramedian technique is closer to the midpoint of spinous process space, and the path of needle insertion is shorter. For residents with less clinical experience, the angle and depth of needle insertion are easier to grasp.2)Compared to midline approach, it bypasses the bony three-dimensional structure of lumbar spine to a certain extent, deviates from spinous process, and weakens the influence of intervertebral space stenosis on puncturing.3)The needle is walked superiorly on the lamina and advanced into the interlaminar space through the ligamentum flavum.As we all know,the distance of lamina space is larger than that of spinous process space in the horizontal direction, so the probability that the needle tip touches bones is reduced.In all,modified paramedian technique combines the advantages of two traditional techniques, making it more feasible to apply in spinal anesthesia for elderly.
In order to explore the effect of three techniques in patients of different age, all patients were divided into two groups according to age for subgroup analysis.We found that the puncturing time in group PM was significantly shorter than group M for all patients , and there was no significant difference between groups PM and P .For patients aged 65-74 years,the number of needle redirections in group PM was significantly fewer than group M,and the number of attempts was significantly fewer in group PM than group P. Compared to groups M and P, the first-attempt success rate was significantly higher in group PM. However, for the above indicators,there was no statistical difference among the three groups in patients aged ≥75 years. This may be related to the uneven distribution of the two age groups. Patients over 75 years old accounted for a small proportion(only about 30% of the total number of patients in each group),resulting in a small sample size. Although there were differences in some results, they were not statistically significant. The satisfaction score of patients in group PM was significantly higher than groups M and P in patients aged ≥75 years, but it wasn’t in patients aged 65-74 years, which may be related to the differences in patients' life experience, education level, psychological quality and other aspects. In addition, through intragroup comparison, we found that under the condition of using the same technique, the first-attempt success rate decreased with the increasing of age, while the number of needle redirections, number of attempts and puncturing time increased. This indicated that there was a certain correlation between age and the difficulty of lumbar puncture in elderly patients, which is consistent with previous research .
Our study has some limitations.Firstly, the injection site was 0.5cm lateral on the right of the midline in the test.Previous studies reported that the thickness and density of ligaments on both sides of the midline were different.Ligamentum flavum was significantly thicker on the right side[26,27].We did not explore whether it was better to identify the site as 0.5cm lateral on the left of the midline or not,which is worthy of a further study.Secondly,the study did not apply for real-time ultrasound guidance technique, which could be superior to ultrasound-assisted technique because of the advantages of full visualization.Thirdly,we felt the reduced resistance during the procedure of insertion, but we didn’t explore structures that the needle passed through. There has been no consensus in the reason up to now. Lastly,we only collected data about patients’ postoperative adverse reactions within 24 hours after surgery,the chance are that the collected values are less than actual values.