Minimum 5-Year Follow-up of Anterior Column Structural Allografts in the Thoracic and Lumbar Spine

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Abstract
An analysis of consecutive adult patients treated surgically with anterior column structural allografts for sagittal plane abnormalities. To evaluate the effectiveness of anterior structural allografts in maintaining long-term sagittal plane correction when combined with posterior spinal fusion and posterior segmental spinal instrumentation and to assess anterior allograft incorporation into adjacent vertebral bodies a minimum of 5 years after implantation. There is no study in the literature in which incorporation and remodeling of anterior column structural allografts with minimum 5-year follow-up are assessed. Do they collapse or resorb or sustain stress fractures between a 2-year and 5-year follow-up? Twenty-three consecutive adult patients (mean age, 45 years; range, 25–63 years) had a combination of anterior structural fresh-frozen allograft plus posterior autogenous grafting and posterior segmental spinal instrumentation performed from June 1988 through August 1992. All patients had sagittal plane abnormalities, and all surgeries were performed by the same surgeon. Twenty of the 23 patients returned for follow-up examinations for at least 5 years (average, 7 ± 3 years; range, 5 ± 4–10 ± 3 years). Diagnoses included kyphoscoliosis (n = 8), spondylolisthesis (n = 3), degenerative disc disease (n = 3), and acute or chronic fracture (n = 6). The allografts spanned only disc spaces in 16 patients, and vertebral bodies and disc spaces in 4 patients. Forty disc spaces and four vertebral bodies were grafted, and 67 structural allografts were placed. Upright radiographs were analyzed before surgery, immediately after surgery, and at final follow-up examination to assess the degree of anterior allograft incorporation and maintenance of sagittal correction. A strict 4-point grading system was used. Two independent observers, not involved with surgical procedures, analyzed the radiographic results. Of the 67 structural allografts, 66 (98.5%) showed incorporation. Both observers concluded that none of the 67 structural allografts showed evidence of collapse. In all grafted levels and in any patient, there was no difference in sagittal plane measurements obtained immediately after surgery and those obtained at follow-up examinations 2 years and 5 or more years after surgery. Anterior fresh-frozen structural allograft works effectively in the long term to maintain correction of sagittal plane abnormalities if combined with posterior fusion and instrumentation. A minimumof 5 years after surgery, there is a high rate of structural allograft incorporation into the adjacent vertebral bodies.