Predictive Analysis of Mechanical Failure in Adult Cervical Deformity Patients

Introduction: Mechanical complications may present a serious risk to patients undergoing cervical deformity (CD) surgery.

Methods: Operative patients with pre-(BL) and two-year (2Y) postop radiographic/HRQL data were categorized as having suffered mechanical failure (Failed) or not (Not Failed) after index surgery. Mechanical failure was defined as: instrumentation failure (rod fracture, screw failure), bony failure, pseudarthrosis, or junctional failure [DJK, DJF)]. Differences in demographics, radiographics, and complication rates were assessed via means comparison analyses. Conditional backstep binary regression analysis was used to identify predictive factors for mechanical failure. Conditional inference tree (CIT) determined thresholds for significant predictors.

Results: 115 CD pts met inclusion criteria (60.97±10.19yrs, 70%F, BMI:28.03±7.28kg/m2). 10.6% underwent 3-column osteotomy. By 2Y post-op, 18 (15.6%) of patients experienced mechanical failure, with 11.1% (n=2) of Failed patients suffering instrumentation failure. At BL, Failed patients had more comorbidities (p=.002), but were otherwise equivalent in BL radiographic markers (all p>.05). However, Failed patients did report significantly worse BL NSR pain scores (both p<.006) compared to Not Failed patients. Surgically, Failed patients were more likely to undergo combined approach (p=.023). BMP use was significantly higher in the junctional failure cohort (p=.020). By rod, instrumentation failure patients were implanted with 3.5 and 6.0 mm cobalt chrome rods, respectively, both of which fractured at 6M, requiring reoperation. Post-operatively, Failed patients demonstrated significantly increased upper extremity paresthesia at 6M (p=.012). By 2Y, no significant differences were noted in regional nor global alignment between Failed vs Not Failed patients (all p>.05). Though 4 (22%) of Failed patients required reoperation, 2Y reoperation rate was comparable between groups (p>.05). Regression analysis revealed six most significant predictors of mechanical complication overall to be BL BMI>28.6, undergoing PSO, VCR, or 3CO, as well as BL TS-CL>19°, and BL C2SS>50° (model p=.001, AUC=81.2%).

Conclusion : Instrumentation failure in the absence of junctional failure in cervical deformity surgery remains exceedingly rare. Predictive modeling revealed increased BMI, increased osteotomy grades, and severe baseline cervical radiographic parameters to be synergistically associated with mechanical failure within two years of surgery.