Study design and settings
The present study is a Scientific Research Ethics Committee-approved retrospective analysis of patients treated with OLIF-PETD and MIS-TLIF for LDH complicated with lumbar instability at our institution (single-surgical team) between 2017 and 2019. All patients had symptoms of low back pain, accompanied by lower limb pain or numbness. All patients underwent X-ray, CT three-dimensional reconstruction and MRI examinations before surgery.
Participants and eligibility criteria
All patients with a diagnosis of LDH with lumbar instability who underwent spinal surgery at our hospital between 2017 and 2019 were potentially to be eligible for this study.
Inclusion Criteria: ① The patient was diagnosed with LDH complicated with lumbar instability (L2-L5): lumbar hyperextension and flexion lateral radiographs with sagittal displacement > 4 mm or intervertebral angle greater than 10° [7]; the symptoms involve lumbago and back pain combined with unilateral lower limb nerve compression symptoms, and strict conservative treatment is ineffective, requiring surgical intervention; ② OLIF with LSF and PETD or MIS-TLIF was used for treatment; ③ the main outcome measures were clinical efficacy and radiological measurement.
Exclusion Criteria: ①Complicated with spondylolisthesis or lumbar spondylolisthesis (Meyerding Grade ≥ 2); ②Complicated with a history of lumbar surgery; ③Complicated with spinal tumor, tuberculosis, infection, vertebral fracture or deformity; ④Complicated with severe osteoporosis.
Surgical method
OLIF + PETD: the PETD procedure was performed first, with the patient lying prone on the operating table under local anesthesia. Under G-arm fluoroscopy, the guide needle was punctured into the vertebral superior articular process, and the angle of 15–30° was the safe area. The skin cut was made (8 mm), the incision was dilated by a dilator and working channel. Intervertebral foramen plasty was performed with a ring saw, and a spinal endoscope was inserted (SPINENDOS GmbH, Munich, Germany). Different types of nucleus pulposus forceps are used to remove the herniated nucleus pulposus. At the same time, bipolar radiofrequency ablation (SPINENDOS GmbH, Munich, Germany) was used for hemostasis and to form the annulus fibrosus. After decompression, the endoscopic working sleeve was removed (Fig. 1).
The patient was then placed in the right decubitus position under general anesthesia for OLIF. Under G-arm fluoroscopy, the intervertebral space and anterior edge of the responsible vertebral body were located. Expose the intervertebral space and lateral side of the vertebral body. The insertion channel will be properly extended to open the intervertebral space. The anterior 1/3 annulus fibrosus was incised, and nucleus pulposus forceps and reamers were used alternately to remove intervertebral disc tissue. After discectomy and exposure of the bony endplate, a suitably sized cage was inserted and filled with allogeneic bone and bone repair materials. The multiaxial universal screw was screwed in the lateral side of the vertebral body with the screw passing through the contralateral cortex as far as possible. The longitudinal connecting rod and tail cap were placed (Fig. 2). Finally, the incision was closed layer by layer.
MIS-TLIF: under general anesthesia, the patient was placed in the prone position. Under G-arm fluoroscopy, the pedicle of the responsible vertebral body was marked on the body surface. A puncture needle was used to locate the vertebral space on the line of the pedicle marker point on the side of the disc herniation. A longitudinal incision was made (4 cm) and the working channel was inserted step by step. The nerve roots and thecal sac were exposed with osteotome and rongeur. A thorough discectomy was performed to expose the bony endplate. Then a cage filled with autogenous bone and bone repair materials was inserted. The pedicle screw guide needle was placed bilaterally, the hollow universal screw was screwed, and the prebent connecting rod was placed. A drainage tube was placed in the wound, and the incision was closed.
Outcome measures
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1.
Demographic data: Age, sex, and intraoperative parameters, including fusion level, operative duration, incision length, hospital stays, intraoperative blood loss, postoperative drainage, and complications.
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Clinical efficacy evaluation:
Visual analog scale (VAS): Assess the overall pain in the waist, lower extremities, and surgery. VAS scores were independently filled in by patients after the doctor's brief explanation, with 0 being no pain and 10 being very pain.
Japanese Orthopedic Association assessment of treatment score (JOA): Lumbar function was assessed at preoperative and postoperative follow-up. The total lumbar JOA score was 29, including symptoms, physical signs and bladder function. JOA improvement rate = (follow-up score — preoperative score)/(29 — preoperative score) × 100%.
Oswestry disability index (ODI): The subjective function of the lumbar spine was assessed with a total score of 100, including pain degree, daily living, self-care ability, lifting, walking, sitting, standing, sleeping, sexual life, social activities, travel, etc. ODI = each score/total score × 100%.
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Degree of lumbar multifidus muscle injury
The multifidus muscle cross-sectional area (MF-CSA) of the affected side was measured before the operation and at the last follow-up on the MRI axial image of the lumbar vertebrae. The innermost fascia close to the outer edge of the spinous process and lamina was taken as the lateral boundary of the multifidus muscle, fat infiltration was excluded, and ImageJ software was used for measurement (Fig. 3). Atrophy rate = (preoperative CSA — last follow-up CSA)/preoperative CSA × 100%.
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Radiological measurement [8]
Lumbar spine lateral X-ray measurement indexes were as follows. Disc height (DH): The anterior vertebral height (AH) and posterior vertebral height (PH) of the fusion segment were measured in lateral X-ray, DH (mm) = (AH + PH)/2 mm; lumbar lordosis angle (LA): LA was measured on lateral X-ray with two measurement lines parallel to the L1 and S1 upper endplates; fusion stage angle (FSA): the angle between the upper endplate of the upper vertebral body and the lower endplate of the lower vertebral body of the fusion segment was measured by lateral X-ray (Fig. 4).
Lumbar spine computed tomography (CT) measurement indexes were as follows. Foraminal height (FH): the shortest distance between the lower edge of the upper vertebral pedicle and the upper edge of the lower vertebral pedicle, measured on lumbar CT sagittal image; foraminal cross-sectional area (F-CSA): measured on lumbar CT sagittal image, the area of the nerve root outlet region after excluding soft tissues such as discs, joint capsule and surrounding bone structures for the foraminal area (Fig. 5).
Lumbar spine magnetic resonance imaging (MRI) measurement indexes were as follows. Sagittal spinal canal diameter (SSCD): measured on MRI sagittal image of the lumbar spine, it is the anterior and posterior length of the spinal canal at the central level of the intervertebral space excluding the anterior intervertebral disc and posterior fat tissue, ligamentum flavum and other soft tissues; axial spinal canal diameter (ASCD): the length of the spinal canal in the horizontal direction measured on axial MRI images of the lumbar spine after excluding bony structures and soft tissues such as intervertebral discs, ligamentum flavum and fat tissue in the spinal canal; spinal canal cross-sectional area (SC-CSA): measured on axial MRI images of the lumbar spine, also excluding the bony structures and soft tissue such as intervertebral discs, ligamentum flavum and fat tissue in the spinal canal (Fig. 6).
Radiological measurement data were measured using ImageJ software. Radiological measurement data were independently performed by three authors (JM, LS and CD.).
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Fusion assessment at the last follow-up
A CT scan was performed at the last follow-up, and interbody fusion was divided into three levels according to BSF grading [9]. BSF-1: vertebral collapse, loss of vertebral space height, vertebral slippage, loosening of internal fixation or obvious absorption and subsidence of bone graft, visible light transmission around the fusion apparatus; BSF-2: continuous bone trabeculae connecting upper and lower endplates were seen in the fusion apparatus, and transparent bands were completely transverse; BSF-3: there were fully continuous bone trabeculae connected to the upper and lower endplates of the vertebral body inside or outside the fusion apparatus, and extensive osteogenesis existed at the horizontal position. BSF-2 and above are considered to indicate bony fusion.
Statistical analysis
SPSS 22.0 for Windows software was used for statistical analysis. The measurement data in accordance with a normal distribution are shown as the mean ± standard deviation. The VAS score, ODI index, JOA score and radiological measurement indexes of the two groups were compared with the analysis of variance of repeated measurement. If the spherical test was not satisfied, the Greenhouse‒Geisser method was used for correction. The general data, perioperative index, JOA score improvement rate, multifidus muscle atrophy rate and fusion rate between the two groups were compared with independent sample t tests. The α value of the test level is 0.05 on both sides. The counting data were expressed as rates, and the rank sum test or Fisher’s exact probability method was used for comparisons between groups. P < 0.05 was considered significant.