Department of Orthopaedics, Columbia University Medical Center, The Och Spine Hospital at New York-Presbyterian, New York, NY, USA.
Department of Orthopaedics, Columbia University Medical Center, The Och Spine Hospital at New York-Presbyterian, New York, NY, USA.
Spine J. 2020 Nov;20(11):1752-1760. doi: 10.1016/j.spinee.2020.07.002. Epub 2020 Jul 13.
Pseudarthrosis remains a major complication for patients undergoing anterior cervical discectomy and fusion (ACDF; 0%-15% at 1-year follow-up). Potentially modifiable risk factors are known in literature, such as smoking and osteoporosis. Biomechanical studies suggest that plates with locking screws can enhance the fixation rigidity and pull-out strength. Although longer screws are known to be correlated with increased pull-out strength, deeper screw depths can increase the risk for intraoperative complications. An important factor that has yet to be studied is the minimum screw length relative to the diameter of the vertebral body (VB) necessary to achieve successful fusion. In this study, we hypothesize that screws with shorter depths relative to the VB will increase the risk for radiographic pseudarthrosis and result in poor patient reported outcomes (PROs).
To examine the impact of ACDF screw length on pseudarthrosis risk.
A review of prospectively collected data.
A total of 85 patients were included in this study. The mean age ±standard deviation was 58.9±10.3 and 42.4% of patients were female. The mean follow-up was 21.6±8.3 months.
The neck disability index (NDI) was used to assess PROs up to 2-years after surgery. For each ACDF level, the screw length and VB% (screw length divided by the anterior-posterior VB diameter) were measured. Radiographic pseudarthrosis (interspinous motion [ISM] ≥1 mm) was recorded at 6-weeks, 6-months, and 1-year for each patient. The positive and negative predictive values (PPV, NPV) for ISM ≥ 1mm were measured for different VB% thresholds. A VB% of <75% was found to have the highest PPV (93%) and NPV (70%) for radiographic pseudarthrosis. This threshold of <75% was then assessed in our bivariate and multivariate analyses.
We reviewed a database (2015-2018) of adult (≥18 years old) patients who underwent a primary two-level ACDF with or without corpectomy. All ACDF constructs involved fixed angle screws. The minimum follow-up period was 1 year. Multivariate analyses were performed to determine if screw VB% was an independent risk factor for radiographic pseudarthrosis.
By 1-year, overall fusion success was achieved in 92.9% of patients. The 1-year revision rate was 4.7%. Patients with any screw VB% <75% had substantially worse fusion success (64.3%) than those who did not (98.6%) at 1-year. The VB% <75% increased the risk for radiographic pseudarthrosis at every follow up period. In comparison to other time-points, patients with radiographic pseudarthrosis at 6 weeks had significantly worse NDI scores by 2-years (p=.047). The independent risk factors for radiographic pseudarthrosis at 6-weeks included any screw VB% <75% (OR 77, p<.001), prior/current smoker (OR 6.8, p=.024), and corpectomy (OR 0.1, p=.010). Patients with ISM≥1 mm had a higher rate of revision surgery at 1-year (5.9% vs. 3.9%), but this was not statistically significant (p=.656).
In primary two-level ACDF, VB% <75% is significantly associated with increased ISM (≥1 mm) at all time points for this study. As an intraoperative guide, spine surgeons can use the screw VB% threshold of <75% to avoid unnecessarily short screws. This threshold can be easily measured pre- and intraoperatively, and has been found to be strongly correlated to radiographic pseudarthrosis in the early postoperative period.
在接受前路颈椎间盘切除融合术（ACDF）的患者中，假关节仍然是一个主要的并发症（1 年随访时为 0%-15%）。文献中已知有一些潜在的可改变的危险因素，如吸烟和骨质疏松症。生物力学研究表明，带有锁定螺钉的板可以增强固定的刚性和拔出强度。虽然较长的螺钉与拔出强度的增加有关，但更深的螺钉深度会增加术中并发症的风险。一个尚未研究的重要因素是，为了实现成功融合，相对于椎体（VB）的螺钉长度需要达到最小值。在这项研究中，我们假设相对于 VB 的螺钉深度较短会增加影像学假关节的风险，并导致患者报告的结果（PROs）较差。
检查 ACDF 螺钉长度对假关节风险的影响。
对前瞻性收集的数据进行回顾。
共有 85 名患者纳入本研究。平均年龄±标准差为 58.9±10.3，42.4%的患者为女性。平均随访时间为 21.6±8.3 个月。
使用颈部残疾指数（NDI）评估术后 2 年的 PROs。对于每个 ACDF 水平，测量螺钉长度和 VB%（螺钉长度除以前后 VB 直径）。记录每位患者在 6 周、6 个月和 1 年时的影像学假关节（ISMs≥1mm）。对于不同的 VB%阈值，记录 ISM≥1mm 的阳性和阴性预测值（PPV、NPV）。发现 VB%<75%与影像学假关节的最高 PPV（93%）和 NPV（70%）相关。然后，在我们的双变量和多变量分析中评估了这一 VB%<75%的阈值。
我们回顾了一个（2015-2018 年）接受一期双水平 ACDF 手术的成年（≥18 岁）患者数据库，包括或不包括椎体切除术。所有 ACDF 结构都涉及固定角度螺钉。最低随访期为 1 年。进行多变量分析以确定螺钉 VB%是否是影像学假关节的独立危险因素。
在 1 年时，92.9%的患者总体融合成功。1 年的翻修率为 4.7%。与没有达到 VB%<75%的患者（98.6%）相比，任何螺钉 VB%<75%的患者融合成功率（64.3%）在 1 年时明显较差。VB%<75%增加了在每个随访期发生影像学假关节的风险。与其他时间点相比，在 6 周时出现影像学假关节的患者在 2 年时的 NDI 评分明显较差（p=.047）。6 周时影像学假关节的独立危险因素包括任何螺钉 VB%<75%（OR 77，p<.001）、当前/曾经吸烟者（OR 6.8，p=.024）和椎体切除术（OR 0.1，p=.010）。ISMs≥1mm 的患者在 1 年时的翻修手术率更高（5.9% vs. 3.9%），但无统计学意义（p=.656）。
在一期双水平 ACDF 中，VB%<75%与本研究所有时间点的 ISM（≥1mm）显著相关。作为术中指导，脊柱外科医生可以使用螺钉 VB%<75%的阈值来避免不必要的短螺钉。这个阈值可以在术前和术中很容易地测量，并且已经发现与术后早期的影像学假关节有很强的相关性。
