Spine Center, Matsudo City General Hospital, 993-1 Sendabori, Matsudo, Chiba, 270-2296, Japan.
Spine Center, Matsudo Orthopaedic Hospital, 1-161 Asahi-cho, Matsudo, Chiba, 271-0043, Japan.
Neurosurg Rev. 2019 Sep;42(3):691-698. doi: 10.1007/s10143-018-1030-5. Epub 2018 Sep 5.
The disc angle at the fused segment is extended in operative prone position, but eventually returns to preoperative neutral position within 6 months to 1 year. This study aimed to assess pedicle screw (PS) shift without loosening to identify the mechanism of the change in disc angle after posterior fusion for degenerative lumbar spondylolisthesis (DLS). Sixty-three consecutive patients who underwent facet fusion for L4 single-level DLS were retrospectively reviewed using computed tomography (CT) immediately after surgery and 6 months postoperatively. Twenty-two patients (88 PSs) in whom the disc angle had decreased by more than 4° at 6-month postoperative radiographic follow-up were selected to more readily identify and quantify PS shift. Six patients with PS loosening and/or nonunion were excluded. We reconstructed a CT plane, vertical to the cranial endplate of the vertebrae and passing through the cannula used for percutaneous PSs. Angle α, which is formed by the cranial endplate and the cannula on this plane, was measured. A change in angle α of more than 2° between the immediate postoperative period and the 6-month follow-up was defined as a PS shift. Angle α did not change by more than 2° in any of the 44 PSs in the upper vertebrae of the fused segment. In the lower vertebrae, angle α changed by more than 2° in 22 of 44 PSs. The change in angle α in the lower vertebrae (average, 2.3°) was significantly greater than that in the upper vertebrae (average, 0.2°) (P < 0.0001). The change in the disc angle was not relevant to clinical outcomes assessed by the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire, the Roland-Morris Disability Questionnaire, and the visual analogue scale. The disc angle at the fused segment returned to preoperative neutral position due to PS shift without loosening, mainly in the lower vertebrae. PS shift is caused by bone remodeling in response to biomechanical load, similar to that in orthodontic tooth movement. As PS has limited ability to maintain a lordotic disc angle, even with the insertion of a cage, lumbar alignment will return to preoperative neutral position owing to cage subsidence or adjacent segment disease. These findings might indicate that it is not necessary to correct the spinal alignment for DLS.
融合节段的椎间盘角度在手术俯卧位时会延长，但在术后 6 个月至 1 年内最终会恢复到术前中立位。本研究旨在评估无松动的椎弓根螺钉（PS）移位，以确定退行性腰椎滑脱症（DLS）后路融合后椎间盘角度变化的机制。回顾性分析了 63 例因 L4 单节段 DLS 行关节突融合术的连续患者的 CT 资料，包括术后即刻和术后 6 个月的影像学随访。在术后 6 个月的影像学随访中，发现 22 例患者（88 枚 PS）的椎间盘角度下降超过 4°，选择这些患者更容易识别和量化 PS 移位。排除了 6 例 PS 松动和/或不愈合的患者。我们重建了一个 CT 平面，垂直于椎体颅侧终板并穿过用于经皮 PS 的套管。在该平面上，由颅侧终板和套管形成的角度α被测量。术后即刻和 6 个月随访时，角度α的变化超过 2°定义为 PS 移位。融合节段上椎的 44 个 PS 中，没有一个的角度α变化超过 2°。在下部椎的 44 个 PS 中，22 个的角度α变化超过 2°。下部椎的角度α变化（平均 2.3°）明显大于上部椎（平均 0.2°）（P<0.0001）。椎间盘角度的变化与日本矫形协会腰痛评估问卷、Roland-Morris 残疾问卷和视觉模拟评分评估的临床结果无关。由于无松动的 PS 移位，融合节段的椎间盘角度恢复到术前中立位，主要发生在下部椎。PS 移位是由于骨重塑对生物力学负荷的反应引起的，类似于正畸牙齿移动。由于 PS 维持腰椎前凸椎间盘角度的能力有限，即使植入 cage，也会由于 cage 下沉或相邻节段疾病而使腰椎对线恢复到术前中立位。这些发现可能表明，对于 DLS 不需要纠正脊柱对线。
