Does Screw Length for Primary Two-level ACDF Influence Pseudarthrosis Risk?

Abstract Background Context : Pseudarthrosis remains a major complication for patients undergoing 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 necessary to achieve successful fusion. In this study, we hypothesize that screws with shorter depths relative to the vertebral body will increase the risk for radiographic pseudarthrosis and result in poor patient reported outcomes (PROs). Purpose : To examine the impact of ACDF screw length on pseudarthrosis risk Study Design : A review of prospectively collected data Patient Sample : 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. Outcome Measures : The neck disability index (NDI) was used to assess PROs up to 2-years after surgery. For each ACDF level, the screw length and vertebral body (VB) % (screw length divided by the anterior-posterior vertebral body diameter) were measured. Radiographic pseudarthrosis (interspinous motion (ISM) ≥1mm) 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 Methods : 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. Results : 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% Conclusions : In primary two-level ACDF, VB%