Dowel Fibular Strut Grafts for High-Grade Dysplastic Isthmic Spondylolisthesis

PURPOSE: Complete reduction of high-grade dysplastic isthmic spondylolisthesis is not always feasible and safe. An alternative is partial reduction and placement of a dowel fibular strut from the 5th lumbar vertebra into the sacrum placed after reaming a channel over a K-wire. Literature regarding results with this technique is sparse. Last year, one center reported results in 12 patients. This study reports the radiographic and clinical results of patients with high-grade isthmic spondylolisthesis (Meyerding III or greater) treated with fibular strut grafting and partial reduction at one institution from 1987-1997.

METHODS: 17 consecutive patients with high-grade isthmic spondylolisthesis who were treated with posterior fusion and fibular strut grafts were studied. Radiographs were reviewed at 3 time points: preoperative, immediate (within 3 months) postoperative, and ultimate (>2 years) follow-up. Parameters measured included lumbar lordosis, slip angle, Meyerding and Neumann scores, and pelvic incidence. The anterior and posterior fusions were graded on a I-V scale and the implants (if used) were examined for failure. The fibular strut was judged as to the amount of remodeling. Clinical outcomes were measured with Oswestry and SRS outcomes tools.

RESULTS: A total of 17 (14 female, 3 male) patients were studied, mean age 20.3 years (range 9-56 years). Follow-up averaged 4.6 years (range 2-8 years). 7 cases were revision surgeries for patients presenting with pseudarthrosis and progressive listhesis. Most (15/17) patients were treated with an anterior fibular strut graft (placed anterior to posterior) in conjunction with posterior decompression, fusion, and instrumentation. Two patients had fibular struts placed from posterior to anterior. There were 11 allograft and 6 autograft fibulae. Radiographic examination showed an average improvement of 1.3 Meyerding grades with improvement in the slip angle from 32 to 18 degrees. Importantly, there was no loss of correction in either parameter over time. All but one of the fibular struts was intact at the latest follow-up with 16/17 remodeled. 16/17 patients were judged to have Grade I posterior and anterior fusions. Clinical evaluation of the 16 patients with an intact fibular strut showed postoperative Oswestry scores of mean 11.4 ±3.8 (maximum of 100 equaling worst result) and SRS postoperative scores of mean 37.3 ± 1.3 (maximum of 45 equaling perfect result). The last 3 questions on the SRS questionnaire that pertain to patient satisfaction were then scored separately; mean score was 14.1 ± 0.3 (maximum of 15 equaling perfect result). Complications included one case of a broken strut in a patient who had previously had a failed posterior in-situ fusion without instrumentation; this was then revised to an instrumented circumferential fusion. There were no cases of deep or superficial infection. There were no neurologic deficits at ultimate follow-up.

CONCLUSIONS: Fibular strut grafting is a useful surgical adjunct in high-grade spondylolisthesis that is partially reduced. It fulfills two important roles by increasing the fusion bed as well as providing immediate structural support to the surgical construct. Our experience shows that there is no significant difference between allo and autograft. All struts healed and remodeled by the ultimate follow-up and there were no instances of strut breakage except in one case that had a failed posterior in-situ fusion without instrumentation.