2.1 Study Design and Patients
This clinical research was a retrospective analysis of 52 patients who had undergone lumbar spinal surgery from May 2015 to December 2018 at our hospital. The study subjects were categorized into 2 groups: K-rod (n = 27; 21 men, 6 women) and PLIF (n = 25; 13 men, 12 women). The inclusion criteria of the study subjects were as follows: (1) patients who suffered from lumbar disc herniation (LDH), lumbar spinal stenosis (LSS), or lumbar spondylolisthesis and showed typical symptoms and signs consistent with the clear imaging manifestations; (2) patients who had no history of ineffective surgical treatment in the past ≥6 months as well as had no surgical contraindications; (3) patients with no history of spine-related diseases and surgery; and (4) patients who returned to the hospital regularly for professional examination after the operation and were followed up for >10 months.
2.2 Surgical procedure
All operations were conducted by the same experienced surgeon and in the prone position under general anesthesia. For example, in the L4/5 disc herniation surgery, the surgeon selected a suitable position for performing incision mark, routinely sterilize drapes, sticking the sterile film, making longitudinal incisions of appropriate lengths, and incising the skin, subcutaneous tissues, and back fascia in sequence.
K-rod internal fixation group: The paraspinal muscles was stripped along the side of the spinous process to the deep portion for exposing the L4-affected side vertebral plate to the facet joint. Using the C-arm machine, the surgeon could complete the preparation of the L4- and L5-affected side pedicle screw channels, selected the appropriate size channel system, and established the working channel. The ligamentum flavum was excised directly, the fenestrated lamina was drilled, and the spinal canal was exposed. An assistant pulled the dural sac and nerve root to the healthy side using the nerve root retractor on the opposite side. The protruding nucleus pulposus and intervertebral disc tissues were cleared under the vision and a probe was applied to ensure that the nerve roots and dura mater were not compressed. After achieving sufficient hemostasis, pedicle screws and peek rods were implanted and fixed. A drainage tube was then placed on the affected side, and the incision was closed layer by layer. No treatment was required on the opposite side.
PLIF group: The paraspinous muscles were stripped from the spinous processes using a subperiosteal technique along the laminar on both the sides and extended laterally to the articular processes. With the help of the C-arm machine, pedicle screws were routinely implanted. Then, cutting off the L4/5 and L5/S1 interspinous ligament, the L4 spinous process was bitten and complete laminectomy was performed to expose the spinal canal. The intervertebral disc tissue with nucleus pulposus and the final plate were accordingly removed. An appropriate sized cage filled with the harvested local bone and demineralized bone matrix was then inserted to the intervertebral space and a rigid connecting rod was applied to connect the pedicle screws, followed by compression and locking. The remaining procedure was the same as that for K-rod dynamic internal fixation.
2.3 Postoperative treatment and rehabilitation
Symptomatic and supportive treatments such as anti-infection, swelling, pain relief, and nerve nutrition were routinely performed after the surgery. The dressing was changed every other day, and the sutures were removed 12-14 days after the surgery. On the first day after the surgery, the patients were encouraged to raise their legs and turn over in the bed as an exercise. On the second day after the surgery, the catheter was removed when the drainage volume reached 30-50 mL or when the drainage fluid became clear. Patients were recommended to continue wearing the waist protection for 2-3 months after their discharge and to avoid heavy exercise in the first month of the surgery. Moreover, appropriate functional exercises were prescribed in combination with their self-recovery for 2-3 months after the surgery.
2.4 Postoperative follow-up and outcome measures
Lumbar spine X-rays were reviewed at our hospital 3 and 6 months after the surgery, while lumbar MRI were reviewed 1 year after the surgery. The surgical time, intraoperative blood loss, postoperative drainage volume, postoperative turning to the activity time on the ground, and postoperative hospital-stay duration were recorded for the two groups. The signs and symptoms were evaluated for low back pain based on the VAS score and ODI. At the final follow-up, MRI of the lumbar spine was obtained and the FCSA of the paraspinal muscles as well as the area of fatty infiltration were recorded.
2.5 Statistical analysis
All statistical data were analyzed using the SPSS22.0 statistical software (SPSS 109 Inc., Chicago, IL). Quantitative data were indicated as the mean value ± standard deviation (x̄ ±s ). The Shapiro-Wilk tests were performed to test the hypothesis of normal distribution. If the date was normally distributed, independent t-tests were performed on age, operation time, intraoperative blood loss, postoperative drainage, postoperative exercise time turning to the ground, postoperative hospital stay, VAS score, ODI, and paraspinal muscle FCSA of the two groups. The postoperative and preoperative VAS score and ODI were tested by paired t-test; the gender of the two groups was tested by c2 test; the grading change in the paraspinal muscle fatty infiltration of the two group was tested by Fisher’s exact test. P < 0.05 was considered to be statistically significant. Pearson’s product difference correlation coefficient analysis was employed to analyze the correlation between the VAS score of postoperative low back pain and the area of fatty infiltration and the area of paraspinal muscle atrophy.