Purpose of the study: Surgical strategies for high-grade spondylolisthesis are controversial. The main subject of debate concerns the indications for reduction or in situ fusion. We present mid-term results obtained in a series of patients with high-grade spondylolisthesis treated by posterior reduction and fusion.

Material and methods: Sixteen patient who had undergone surgery for spondylolisthesis of the superior isthmus > 50% were reviewed. Mean age was 12 years (range 9–16 years). Preoperatively, all patients were symptomatic with lumbalgia, truncated radicular pain, and gait anomalies. Surgical treatment consisted in a single posterior approach, L5 laminectomy, curettage of the L5-S1 disc combined with excision of the S1 dome, L4-S1 instrumented reduction, anterior L5-S1 and posterolateral L4S1 arthrodesis. Postoperative immobilization was achieved with a resin lumbar cast with crural stabilization for three months then a lumbar orthesis for three months. Clinical and radiographic outcome was assessed at 44 months on average (range 10–260 months).

Results: Clinically, 14 patients were pain free and had resumed their former activities. One patient complained of intermittent pain. No improvement was observed in one patient. Radiographic results were: displacement 78% (range 52–100%) preoperatively and 30% (8–95%) at last follow-up. The L5S1 displacement angle was 14° kyphosis (range 8–30°) preoperatively and 9° lordosis (range 3–12°) at last follow-up excepting one case with complications. The pelvic incidence was 85° (range 65–100°) preoperatively and 74° (range 50–90°) at last follow-up. Complications: There was one early infection treated by wash-out debridement and antibiotics without removing implants. Disassembly of the implanted material in one patient with a poor clinical result led to complete recurrence and lumbosacral kyphosis. Sacral screw fracture was diagnosed in six patients on average one year after surgery but without any progression or recurrence of the displacement. There were no neurological complications.

Discussion and conclusion: Posterior reduction enables restoration of a good sagittal balance. More than the reduction, it is particularly important to restore the lumbosacral junction in a lordosis position to guarantee long-term stability. This technique is a difficult surgical challenge and raises the risk of recurrence and potential neurological complications.