Does screw length for primary two-level ACDF influence pseudarthrosis risk?

Area of Science:

• Spine surgery
• Orthopedic biomechanics
• Fusion outcomes

Background:

• Pseudarthrosis is a common complication after anterior cervical discectomy and fusion (ACDF), impacting patient outcomes.
• While factors like smoking and osteoporosis are known risks, the optimal screw length relative to vertebral body diameter (VB%) for successful fusion remains understudied.

Purpose of the Study:

• To investigate the impact of ACDF screw length, specifically the screw length relative to vertebral body diameter (VB%), on the risk of pseudarthrosis.

Main Methods:

• A review of prospectively collected data from 85 patients undergoing primary two-level ACDF.
• Screw length and vertebral body diameter (VB%) were measured; radiographic pseudarthrosis (interspinous motion [ISM] ≥1 mm) and patient-reported outcomes (Neck Disability Index [NDI]) were assessed up to 2 years post-surgery.

Main Results:

• Overall fusion success was 92.9% at 1 year.
• Patients with any screw VB% <75% had significantly lower fusion success (64.3%) compared to those with VB% ≥75% (98.6%).
• A VB% <75% was an independent risk factor for radiographic pseudarthrosis (OR 77, p<.001) and associated with worse NDI scores.

Conclusions:

• A vertebral body percentage (VB%) of less than 75% for screws in primary two-level ACDF is strongly associated with increased radiographic pseudarthrosis.
• This VB% <75% threshold serves as a valuable intraoperative guide to help surgeons avoid unnecessarily short screws and improve fusion success.