Spontaneous Spinal Arthrodesis in Stand-Alone Percutaneous Pedicle Screw Fixation Without in Situ Fusion in Patients With Lumbar Segmental Instability: Long-Term Clinical, Radiologic, and Functional Outcomes

No study to date has established how commonly spontaneous fusion occurs after stand-alone percutaneous pedicle screw fixation in adult population. In this retrospective single-center study, we investigated the effectiveness, long-term solidity and safety of stand-alone percutaneous pedicle screw fixation without in situ fusion and the influence of presence or absence of fusion on the clinical outcome of patients with low-grade lumbar segmental instability. Eighty-eight patients with symptomatic low-grade spondylolisthesis were treated with posterior stand-alone percutaneous pedicle screw fixation without bone graft. Radiographic evaluation was used to determine if spontaneous fusion or absence of fusion was present. The solid fusion and absence of fusion groups were analyzed clinically (visual analog scale and Oswestry Disability Index) and with a validated self-administered questionnaire. The average duration of follow-up was 70.5 months (range, 48–120 months). Radiologic signs of spontaneous fusion were present in 45.5% of the cohort and absent in 54.5%. Clinical outcome was excellent to good in 73.8% of the cohort (in 70.9% of cases with spontaneous fusion and in 67.5% of cases with absence of fusion). No significant differences in visual analog scale scores for residual back and lower limb pain between the 2 groups were seen at the final follow-up. At the final follow-up, 5 of 88 patients (5.6%) underwent revision surgery. Percutaneous pedicle screw fixation offers several advantages that help minimize approach-related morbidity, while achieving similar clinical outcome as seen with more traditional invasive procedures. A solid fixation without bone graft provides long-term clinical benefits. In our patients, the appearance of a spontaneous solid fusion and the absence of fusion after stand-alone pedicle screw fixation were correlated with similar improved clinical outcomes at long-term follow-up.