Background: Adjacent segment degeneration (ASD) is a common complication of lumbar interbody fusion; the paraspinal muscles significantly maintain spinal biomechanical stability. This study aims to investigate the biomechanical effects of proximal multifidus injury on adjacent segments during posterior lumbar interbody fusion (PLIF). Methods: Data from a lumbosacral vertebral computed tomography scan of a healthy adult male volunteer were used to establish a normal lumbosacral vertebral finite element model and load the muscle force of the multifidus. A normal model, an L4/5 PLIF model (PFM) based on a preserved proximal multifidus, a total laminectomy PLIF model (TLPFM), and a hemi-laminectomy PLIF model based on a severed proximal multifidus were established, respectively. The range of motion (ROM) and maximum von Mises stress of the upper and lower adjacent segments were analyzed along with the total work of the multifidus muscle force. Results: This model verified that the ROMs of all segments with four degrees of freedom were similar to those obtained in previous research data, which validated the model. PLIF resulted in an increased ROM and maximum von Mises stress in the upper and lower adjacent segments. The ROM and maximum von Mises stress in the TLPFM were most evident in the upper adjacent segment, except for lateral bending. The ROM of the lower adjacent segment increased most significantly in the PFM in flexion and extension and increased most significantly in the TLPFM in lateral bending and axial rotation, whereas the maximum von Mises stress of the lower adjacent segment increased the most in the TLPFM, except in flexion. The muscle force and work of the multifidus were the greatest in the TLPFM. Conclusions: PLIF increased the ROM and maximum von Mises stress in adjacent cranial segments. The preservation of the proximal multifidus muscle contributes to the maintenance of the physiological mechanical behavior of adjacent segments, thus preventing the occurrence and development of ASD.

BACKGROUND AND OBJECTIVES: Atlantoaxial dislocation (AAD) is a high-risk condition that can lead to significant mortality. Lateral mass fusion offers structural stability and reduction, yet no standardized fusion device currently exists for consistent atlantoaxial fixation. This study compares the clinical outcomes of a novel anatomic cage vs iliac crest autograft in treating AAD. METHODS: Radiographic, laboratory, and clinical outcomes were retrospectively compared between 2 surgical groups: one treated with an iliac crest autograft by a traditional posterior approach, the other treated with an anatomic cage using an intermuscular approach. Health-related quality-of-life factors were also analyzed. RESULTS: One hundred nineteen patients underwent fusion with iliac crest autograft and 105 with anatomic cages were finally included. The iliac crest group had a shorter operative time ( P = .043), but the anatomic cage group had significantly less intraoperative blood loss, shorter hospitalization, and fewer C2 neurological symptoms (all P < .05). Bony fusion was similar between 2 groups (3.3 [0.6] months vs 3.1 [0.4] months, P = .163). Compared with the iliac crest group, the anatomic cage group showed greater improvements in lateral mass interspace height (LMIH, P < .001). Inflammatory markers were significantly lower at postoperative day 3 in the anatomic cage group. Improvement in pain (Visual Analog Scale) differed significantly between groups (Δ P <.001). Regression analysis showed that age <55 years was independently associated with greater Neck Disability Index improvement ( P = .025), while C1-C2 Cobb angle and cervicomedullary angle correlated with postoperative Japanese Orthopaedic Association and Neck Disability Index scores. LMIH was significantly associated with C2 neurological symptoms ( P = .015). CONCLUSION: Lateral mass fusion using the 3-dimensional–printed anatomic cages by an intermuscular approach is a safe and effective treatment of AAD. It offers improved radiological outcomes, preserves C2 nerve root integrity, and reduces early postoperative inflammation. In addition, intraoperative restoration of LMIH may reduce neurological symptoms in patients with AAD.