Pseudarthrosis in Primary Fusions for Adult Idiopathic Scoliosis: Incidence, Risk Factors, and Outcome Analysis

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Abstract

Study Design.

A retrospective study.

Objective.

To analyze the incidence, characteristics, risk factors, and Scoliosis Research Society Instrument-24 (SRS-24) outcome scores of pseudarthrosis in adult idiopathic scoliosis primary fusions.

Summary of Background Data.

The healing of spinal fusion is complex and difficult to study in a clinical setting. There are no detailed reports on pseudarthrosis in primary fusion for adult idiopathic scoliosis since the introduction of “modern” segmental fixation techniques.

Methods.

A retrospective chart and radiographic review of 96 patients (average age 42.2 years; range 18.2–62.9 years) with adult idiopathic scoliosis undergoing first time (primary) spinal instrumentation and fusion with a minimum 2-year follow-up (average 5.9 years; range 2–16.8 years) treated at a single institution between 1985 and 2001 were analyzed.

Results.

Sixteen patients had pseudarthroses (17%). Fifty-nine percent of the pseudarthroses occurred between T9 and L1, and 81% presented with multiple levels involved (2–6 levels). The site of crosslinks or dominoes correlated with pseudarthrosis site in 69%. Pseudarthroses were detected radiologically at 32.4 months (range 12–67 months) postoperatively. Patient age at surgery more than 55 years significantly correlated with pseudarthrosis (P = 0.007). The number of fused levels more than 12 vertebrae is also significantly correlated with pseudarthrosis (P = 0.03). Smoking history and comorbidity did not increase the pseudarthrosis rate (P = 0.71 and 0.19, respectively). A larger preoperative Cobb angle (≥70°) and a greater thoracic kyphosis (T5–T12 >40°) did not correlate with a higher pseudarthrosis rate (P = 0.76 and 0.73, respectively). Thoracolumbar kyphosis (T10–L2 ≥20°) correlated with a significantly higher pseudarthrosis rate (P < 0.0001). Preoperative global sagittal and coronal imbalance did not increase the pseudarthrosis rate (P = 0.45 and 0.62, respectively). Patients with pseudarthrosis had lower SRS-24 scores than those without (P = 0.01).

Conclusion.

The incidence of pseudarthrosis following adult idiopathic scoliosis primary fusion was 17%. The pseudarthrosis was most likely to occur at the thoracolumbar junction. Older patients (>55 years), longer fusion (>12 vertebrae), and those with thoracolumbar kyphosis (≥20°) demonstrated increased risk for pseudarthrosis. Patients’ outcomes as measured by the SRS-24 were “negatively” affected by the pseudarthrosis.

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