Adjacent segment pathologies (ASP), including radiological adjacent segment degeneration (ASDeg) and adjacent segment disease (ASDis) after lumbar fusion surgeries have been troubling complications. The development of ASDis greatly reduces postoperative quality of life, and revision surgery may be required in severe cases. Several risk factors for ASP have been reported, such as age, sex, pre-existing adjacent degeneration, multilevel fusions, sagittal imbalance, the type of fusion, facet tropism and laminar inclination. Because multi-level degenerative imaging is common in lumbar degenerative disease, pre-existing adjacent degeneration makes challenge for the surgery strategy, sometimes it is difficult to determine the level at which fusion ends. Important pre-existing adjacent degeneration factors included discs degenerated, facets and ligamentum flavum tropism which could lead to spinal canal stenosis (SCS). Few studies have focused on asymptomatic pre-existing SCS as a risk factor for ASDis that requires additional surgery at an adjacent segment. But these studies only used the sagittal diameter or ratio to evaluate the degree of adjacent SCS. The status of neural tissues in the canal was neglected. Few studies also have focused on asymptomatic pre-existing degenerated disc as a risk factor for ASDeg. But these studies only used Pfirrmann grade to evaluate the degenerated disc. High-intensity zone (Hiz), vacuum sign were neglected.

This prospective study was limited to patients with the same preoperative pathology, the same fusion segments (L4-5 and L5-S1), the same fusion technique (PLIF). Dynamic X-ray and MRI examinations of lumbar will be completed to evaluate the imaging manifestations of the responsible and adjacent segments before surgery. The T2-weighted sagittal and axial MRI images are studied and the following parameters are recorded: grade of cerebrospinal fluid occlusion in L3/4 spinal canal at disc level, and the narrowest axial plane was used for grading; L3/4 disc degeneration by Pfirrmann grade; high-intensity zone (Hiz) and vacuum sign of L3/4 disc; L3/4 disc herniation quantificationally measured by MSU Classification; Patients will be divided into three groups according to the pre-existing status of L3/4 segment. Patients without pre-existing degeneration at L3/4 segment will be classified into control group (NS group). Patients with pre-existing disc factors (Pfirrmann grade≥3, Hiz or vacuum sign) at L3/4 segment will be classified into group D. Patients with pre-existing canal stenosis factors (cerebrospinal fluid occlusion≥1) at L3/4 segment will be classified into group C.

The patient's age, gender, preoperative body mass index (BMI), American Society of Anesthesiologists classification of anesthesia (ASA grade) will be recorded during the hospital stay. Surgical data including operation time, blood loss, perioperative complications (including cerebrospinal fluid leakage, wound infection, postoperative neurological dysfunction, and perioperative secondary surgery, cardiopulmonary complication, cerebral infarction/hemorrhage, etc.), and length of hospital stay are also recorded. Preoperative clinical function questionnaires, including visual analog scale (VAS) of low back, VAS of the legs, and Oswestry Disability Index (ODI) scores for patients were completed on admission for surgery without any assistance. All the patients enrolled will finished the follow-up from date of surgery at 1,2 and 5 years. The clinical outcomes and ASP will be recorded.