Minimum 5-Year Analysis of L5-S1 Fusion Using Sacropelvic Fixation (Bilateral S1 and Iliac Screws) For Spinal Deformity

• a - Medtronic Sofamor Danek

Objectives: To investigate clinical and radiographic outcomes for lumbosacral fusion (in spinal deformity patients) using a combination of bilateral sacral and iliac screws with minimum 5 year followup. Our hypothesis was that there would be a high percentage of clinical problems related to iliac fixation, including late sacroiliac joint arthritis and pain, and a high incidence of pseudarthrosis at L5-S1.

Background: Long-term results (>5-year followup) of bilateral S1 screw/bilateral iliac screw fixation have never been published or presented.

Materials and Methods: Total 67 consecutive patients (male 19, female 48, age 11-77, average 36.2 years) undergoing lumbosacral fusion bilateral sacral and iliac screws were analyzed for radiographic outcome and clinical course by outcome questionnaire analysis, collected prospectively. These 67 consecutive patients had surgeries at one institution between 1993 and 1998. Forty-four patients had anterior column support at L5- S1. 21 had previous surgery, 12 involved L5-S1 non-union on presentation to us. Follow-up period was minimum 5 years (5 to 9+8 years, average 6+3 years). Patients were divided into 2 groups. Group 1: 34 high-grade spondylolisthesis patients; group 2: 32 adult scoliosis patients fused from the thoracic spine to the sacrum. A true AP pelvis film was obtained in all patients to assess for sacroiliac joint arthritis, and standard spine radiographs. Patients were administered SRS, Oswestry and directed buttock pain questionnaires at latest followup. See attached demographic table.

Results: There were no cases of sacral screw failure (screw halo, partial screw pullout, or fracture of the sacral screw). There were 5 cases of non-union at L5-S1, which presented as either rod breakage between L5 and S1 or failure of pedicle screws at L4 or L5 (3 spondylos, 2 adult deformity). Four of the 5 did not have anterior column support at L5-S1. Three of the 5 were revised and subsequently achieved union. Iliac screws were removed electively on one or both sides in 23 of the patients (18 group 1; 5 group 2; p=0.0041) after 2 years postop, because of prominence. There were 7 cases of iliac screw breakage (4 group 1; 3 group 2). Iliac screw halos were observed in 29 patients. No sacroiliac osteoarthritis was observed on the true AP pelvis films. At ultimate follow-up, average Oswestry scores were 16.6 and 24.3, respectively in groups 1 and 2; SRS scores adding pain, function, and satisfaction were group 1 (50.34/ 60) and group 2 (45.11/60); indicating minimal pathology for the majority of patients at ultimate follow-up. On the directed buttock pain questionnaire, 48% of the patients reported no buttock pain. Of those who reported pain (52%) the mean VAS score for group 1 was 2.54±1.93 and group 2 was 3.67±2.77.

Conclusions: For high-grade spondylolisthesis and long adult deformity fusions to the sacrum a montage of bilateral S1 screws and iliac screws is effective in protecting the sacral screws from failure. There was a low incidence of pseudarthrosis at L5-S1. We saw no evidence of long-term effect of the iliac screws predisposing the sacroiliac joints to degeneration at follow-up ranging from 5-10 years.

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