Traumatic Sacral Spondylolisthesis Following Instrumentation for Spinal Deformity

TF Dwyer MD¹
MF O'Brien MD¹
C Dewald MD²
DG Gelb MD³
LB Flawn MD⁴
TG Lowe MD¹
RE Donnelly MD¹

Woodridge Orthopaedic and Spine Center, Wheat Ridge, Colorado¹
University of Colorado Health Sciences Center, Denver, Colorado¹
Rush-Pres-St. Luke's Medical Center, Chicago, Illinois²
Penn State Geisinger Health System, Hershey, Pennsylvania³
Austin Orthopedic Clinic, Austin, Texas⁴ USA

INTRODUCTION: Increased fracture rates amongst osteoporotic patients in proximity to instrumentation and prosthetic joint replacements is well documented in the literature. The authors have recently described burst fractures of the caudal end-instrumented vertebrae in adult scoliosis treated with fusion.

PURPOSE: To describe traumatic sacral spondylolisthesis, a newly recognized complication resulting from the surgical management of adult deformity after instrumentation to the sacrum and to suggest treatment options.

METHODS: Review of four patients with symptomatic spinal deformities and osteoporosis who were treated with surgical intervention. Each patient subsequently developed an insufficiency fractures and olisthesis of S1.

RESULTS: Four patients averaging 60 years of age (range: 36-78) underwent ASF-PSF to the sacrum averaging 9 levels (range: 3-13). Preoperative diagnoses included degenerative spondylolisthesis (n=2), degenerative scoliosis (n=1), and Charcot-spine (n=1). Insufficiency fractures of the sacrum were documented an average of 7 weeks post-op (range: 5-12). Minor trauma in the form of a fall was documented in 2 patients. Anterior olisthesis of the proximal fragment varied from 20-100%. Three patients did not progress and one patient with a 40% olisthesis progressed to a spondyloptosis. Intermittent urinary incontinence with urgency as a result of high-grade stenosis was identified in one patient with spondyloptosis. All patients had significant pain and one presented with the hallmark appearances of a high grade spondylolisthesis. The two patients with spondyloptosis elected surgical intervention. The patient with incontinence underwent partial reduction and extension of the fusion to the ilium. The other patient underwent extension of the fusion to the ilium without reduction. The remaining two patients were treated nonoperatively. All patients demonstrated clinical improvement at most recent follow-up.

DISCUSSION: ASF/PSF may create stress risers at adjacent levels. In the osteoporotic patient this may result in insufficiency fractures. Sacral insufficieny fractures as a consequence of spinal instrumentation have not been previously described. These fractures may present with painful instability and symptoms of neurologic compression similar to atraumatic spondyloptosis.

CONCLUSIONS: Developing a treatment plan for traumatic spondylolisthesis of S1 must take into consideration the degree of displacement, neurologic symptoms, and the general health and goals of the patient. In the osteoporotic patient preoperative consideration should be given to constructs which are shorter and less stiff in an attempt to decrease the magnitude of adjacent level stress risers.