When Is Minimally-invasive Too Invasive?: Establishment of Invasiveness Thresholds Considering Frailty and Deformity Status in Minimally-invasive Adult Spinal Deformity Surgery

Introduction: Minimally Invasive Surgery (MIS) techniques in ASD surgery may provide greater incrementally benefit to patients with increasing frailty and deformity states, though MIS-specific surgical invasiveness thresholds have yet to be established.

Methods: Operative MIS patients ≥18yrs with pre-(BL) and two-year (2Y) data included, and four groups created: Low/High frailty (LF/HF) and deformity (LD/HD) per mASD-FI and PI-LL ranked in halves. Binary regression and CIT determined thresholds for ≥ 1 major complication or not meeting 2Y ODI MCID using a novel Minimally-Invasive Spine Surgery Invasiveness Score (MISSIS). MISSIS (Total 100): Staged (+23), tubular decompression(+3), Percutaneous instrumentation (+10), facet osteotomy/level (+3), three-column osteotomy/level (+3), SPO/level (+3), ALIF (+13), TLIF (+5), LLIF/XLIF (+8), iliac fixation (+5), revision (+3), per 10° change in PI-LL (+5), per 2° change in PT (+3), per 1 cm change in C7-S1 SVA (+3), per 1° change in thoracic kyphosis (+13).

Results: 111 MIS (69.31±10.59 years, 55% female) patients were included. Mean cohort MISSIS: 394.44±192.56. 19.8% of patients were classified as LF/LD, 38.3% as HF/LD, and 24.7% as LF/HD, and 17.3% as HF/HD. LF/LD patients demonstrated the lowest mean MISSIS (177.86), followed by LF/LD (197.53), LF/HD (281.68), and HF/HD (341.41) (p < .001). CIT identified thresholds of 165 for HF/LD patients (OR: 1.014 [1.003 – 1.025], p=.010) compared to 197 for LF/LD patients (OR: 1.015 [1.005 – 1.024], p=.004). Similarly, thresholds were set at 271 (OR: 1.003 [1.000 – 1.005], p=.035) for HF/HD versus 281 for LF/HD patients (OR: 1.008 [1.002 – 1.011], p=.008).

Conclusion : Taking into account both frailty and deformity status, this study utilizes a novel Minimally-Invasive Spine Surgery Invasiveness Score (MISSIS) score and demonstrates that increased frailty is a primary driver in sustaining major complications or not meeting MCID in ODI by 2Y post-operatively. As such, utilization and optimization of MISSIS during surgical planning may improve patient safety and post-operative outcomes.