Long-term mechanical failure in well aligned adult spinal deformity patients.

BACKGROUND CONTEXT: Mechanical complications (MC) are frequently linked to suboptimal postoperative alignment and represent a primary driver of revision surgery in the context of adult spinal deformity (ASD). However, it's worth noting that even among those deemed "well aligned," the risk of experiencing MCs persists, hinting at the potential influence of factors beyond alignment.

PURPOSE: The aim was to assess the incidence of MCs among well-aligned patients and delving into the relevant risk factors and surgical outcomes that come into play within this specific subgroup.

STUDY DESIGN/

SETTING

A retrospective analysis was conducted using data from a prospective multicenter database dedicated to ASD.

PATIENT SAMPLE: The study focused on patients aged 55 years or older, who had a minimum follow-up period of 2 years, and exhibited a Global Alignment and Proportion (GAP) score of 2 points or less (excluding age) within 6 weeks of their index surgery.

OUTCOME MEASURES: Mechanical complications such as rod fractures, pseudarthrosis, or junctional kyphosis or failure.

METHODS

Patients who developed mechanical complications were identified. Comparative analyses were performed, encompassing both continuous and categorical variables. Furthermore, binary logistic regression tests were employed to pinpoint risk factors, and ROC curves were used to determine the optimal threshold values for these variables.

RESULTS

A total of 83 patients met the inclusion criteria for this study, with a mean age of 66 years. On average, they had 10 instrumented levels, and 77% of them had fusion extending to the pelvis. Additionally, 27% of the patients had undergone 3-column osteotomies (3-CO). Among them, 33 patients (40%) experienced at least 1 MC during an average follow-up period of 4 years, which included 14 cases of proximal junctional kyphosis (PJK) and 20 cases of nonunion or rod breakage. 15 patients (18%) required revision surgery specifically for MC. In univariable analyses, patients who developed MC were characterized by higher body weight, poorer baseline general health (as indicated by worse SF-36 scores), and less favorable preoperative coronal and sagittal alignment. They also had longer hospital stays, a greater number of instrumented levels, and achieved less favorable postoperative coronal and sagittal alignment. Interestingly, factors such as 3-column osteotomies, postoperative bracing, and the addition of an anterior approach did not significantly alter the risk of MC in well-aligned ASD patients. Binary regression models revealed that independent risk factors for MC included the residual coronal lumbosacral curve, the number of instrumented levels, and relative spinopelvic alignment (RSA). ROC curves identified an optimal threshold of a residual lumbosacral curve of ≤4° and RSA of ≤3°. Moreover, the rate of MCs showed a stepwise increase within the GAP-Proportioned group, with rates of 31% for GAP=0, 54% for GAP=1, and 75% for GAP=2, with RSA emerging as the most influential parameter. Lastly, patients with MC exhibited poorer functional and radiological outcomes at their last follow-up assessment.

CONCLUSIONS

The rate of MCs remains elevated in sagittally "well-aligned" ASD patients that can be attributed to suboptimal residual sagittal and coronal malalignment, which in turn leads to poorer functional outcomes. This study reaffirms the multifaceted nature of MCs and underscores the significance of achieving impeccable postoperative alignment, particularly in the presence of additional risk factors such as extensive surgical correction, a high lever arm (involving instrumented vertebrae), excessive body weight, and frailty (as indicated by SF-36 scores).