• Shinichi Inoue, Morsi Khashan, Takahito Fujimori, and Sigurd H Berven.
• Department of Orthopaedic Surgery, University of California, San Francisco, CA, USA, inoshin@hyo-med.ac.jp.
• J Orthop Sci. 2015 Jul 1; 20 (4): 609-16.

BackgroundLong fusion to the sacrum has been demonstrated to increase the mechanical failure rate after adult spinal deformity (ASD) surgery, and these mechanical failures are the most common etiology for reoperation. The purpose of this study was to determine the incidence and risk factors for mechanical failure associated with reoperation after spinal fusion to the sacrum in ASD.MethodsThe study included 76 patients with ASD who underwent spinal fusion surgery including the sacrum at a single institution between 2005 and 2010. The inclusion criteria were a minimum age of 20 years and fusion of ≥ 5 levels. The terminal event was defined as either the first reoperation for mechanical failure or a minimum of 2 years following surgery in patients who did not undergo reoperation.ResultsThe cumulative reoperation rate for mechanical failure was 37 % (n = 28). The procedure survival rate was 79 % at 1 year and 72 % at 2 years. Mechanical failures consisted of proximal junctional complications in 16 patients and pseudarthrosis in 12 patients. Proximal junctional kyphosis (PJK) was the most frequent cause (n = 15), and seven patients were diagnosed with fractures at the UIV or one level above the UIV. Multivariate analysis identified the following as independent factors predicting mechanical failure: three or more comorbidities, smoking, and a preoperative sagittal vertical axis of >95 mm. SRS-22r and ODI scores were lower in patients with mechanical failure.ConclusionOverall, 37 % of the patients who underwent ASD surgery involving the sacrum required reoperation for mechanical failure. The most frequent form of mechanical failure associated with reoperation was surgical PJK. Significant risk factors for mechanical failure included medical comorbidities, smoking, and severe preoperative sagittal imbalance. Critical mechanical failure may have a negative influence on health status.

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