Introduction:
Adult spinal deformity (ASD) is a heterogeneous spectrum of abnormalities that affect both coronal and sagittal plane of the spine in adult patients.The aim of our study is to evaluate the predictive effect of some morphological and surgical parameters on mechanical and junctional failure in the surgical treatment of ASD with a minimum FU of 5 years.
Methods:
Patients and Design: Retrospective review of a consecutive single-center registry; patients that underwent correction of ASD from January 2008 to October 2016.
Inclusion Criteria: Patients > 18 y/o; minimum of 4 levels of Posterior Instrumented fusion; minimum FU of 5 years; no previous spinal surgical procedures; complete clinical and radiological data.
Exclusion criteria: Patient with neuromuscular or rheumatic disease or active tumor or infections.
Variable analyzed: Demographic data; clinical data were collected preoperatively and at the last available FU; spinopelvic parameters [Pelvic Incidence (PI), Pelvic Tilt (PT), Sacral Slope (SS), Lumbar Lordosis (LL), L4-S1 Lordosis (LL4-S1), Thoracic Kyphosis (TK), Global Tilt (GT), C7 sagittal vertical axis (SVA), odontoid to hip axis center angle (ODHA)] were measured preoperatively and at each follow-up; predictive variables: restoration of Roussouly type according to pelvis and spinal shape and GAP score was measured post-operatively, each subsection of GAP score and Roussouly was assessed, Schwab’s criteria were collected postoperatively. Data on mechanical complications (junctional failure and hardware failure) and revision surgery were collected.
Results:
212 patients were definitively enrolled, 32 males and 180 females, with a mean age of 64 y/o (SD 16) at the time of surgery. The average of FU was 8,3 years (SD 1,7). Mechanical complications were descripted in 40,5% (86/212), of which the 96,5% (83/86) had needed surgery. We had junctional failure in 20,3% (43/212) and hardware failure in 20,3% (43/212). Roussouly restoration seems to be correlated with the occurrence of mechanical failure [chi-square = 5,06, p = 0,024 & Log Rank (Mantel-Cox) = 4,36, p = 0,037]. AUC is 0,713 (IC 95%: 0,62-0,8) in the analysis of GAP score for junctional failure and the value that maximize the Youden Index is GAP score = 4,5, so we used this cut-off in order to create the Kaplan-Meyer curves and we obtained a Log Rank (Mantel-Cox) = 22,65, p = 0,000. We obtained a “scale effect” dividing our cohort in GAP score 0-2, GAP score 3-6, GAP score 7-12. No correlation was found for the other variables. The machine learning approach shows the GAP score is the most predictive variable for mechanical complications, and for the subsection of GAP and Roussouly Type the best predictors are Age, Lordosis Distribution Index (LDI) and Relative Spinopelvic Alignment (RSA).
Discussion:
Roussouly type restoration and GAP score are predictive variable for mechanical complication. The need to obtain a proper alignment in terms of global and segmental, together with the restoration of the original Roussouly Type are mandatory with the aim to reduce the risk of mechanical failure.