Prospective Study of Anterior Lumbar Interbody Fusion Augmentation with Posterior Pedicle Screws or Translaminar Facet Screws

Introduction: Stand alone anterior lumbar interbody fusion (ALIF) is biomechanically unstable. The addition of posterior fixation such as pedicle screws (PS) or translaminar facet screws (FS) significantly and equally increase the initial stability of the construct as shown in in vitro biomechanical studies. However the difference between PS and FS has not been studied clinically.

Purpose: This prospective study compares the clinical outcomes and radiological results of 360° fusion consisting of ALIF and supplemental with either FS or PS.

Study Design: This is a prospecetive study of clinical and radiographic results by an independent reviewer. All patients were treated surgically at one institution.

Methods: Inclusion criteria were adult patients with axial back pain and one or two level disc degeneration confirmed with MRI and provocative discography who had failed nonoperative treatment of at least 6 months. Excluded were patients who needed an extensive decompression at the time of surgery and patients with prior fusion procedures. All patients underwent an anterior lumbar interbody fusion with tricortical graft (TRI) or femoral ring allograft (FRA) followed by posterior fusion and instrumentation with pedicle screws or translaminar facet screws. The choice of anterior graft and posterior fixation was consistent within and dependant upon individual surgeons. Radiographs and functional outcome questionnaires were collected preoperatively and at 1 year and 2 year follow-up. Presently there are 50 patients with minimum 2 year follow-up; 43% male and average age of 43 years (18-70). There were 60 levels in 34 patients with supplemental PS fixation group (PS) and 27 levels in 16 patients with supplemental FS fixation group (FS).

Results: There was no difference between groups with regards to age, sex, smoking status, or number of levels fused. The radiographic and clinical results are summarizes in the table:

+ Reoperation or radiographic evidence

A higher pseudarthrosis rate in FS compared to PS was noted in the subgroup of levels with TRI (58% vs 14%, p=0.003). Number of levels fused did not effect the pseudarthrosis rate.

Intraoperative complications specific for the posterior approach included one laminectomy to verify screw position in the PS group. Postoperative complications were noted in 4 PS patients (11%; 2 screw/implant failures; 1 deep wound infections; and one misplaced screw with L5 nerve root symptoms) and FS patient (6%; retrograde ejaculation).

Statistically significant improvements (p<0 .05) in SF36 scores (physical subscales and physical composite score) were noted both the treatment groups. In groups, Roland-Morris improved on average 8 points from pre-operative to follow-up.

Conclusion: Despite biomechanical studies documenting that facet screw fixation has similar biomechanical properties with pedicle screws, there is a significantly higher pseudarthrosis rate with use of FS, possibly due to lack of stability from cyclical loading. Both groups had significant improvement in patient-rated functional outcomes.