Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID)

Abstract Background It is well known that clinical improvements following surgical intervention are variable. While all surgeons strive to maximize reliability and degree of improvement, certain patients will fail to achieve meaningful gains. We aim to analyze patients who failed to reach minimal clinically important difference (MCID) in an effort to improve outcomes for minimally invasive (MIS) deformity surgery. Methods Data was collected on a multi-center registry of MIS adult spinal deformity (ASD) surgeries. Patient inclusion criteria were: age > 18 years, and coronal Cobb > 20°, pelvic incidence-lumbar lordosis (PI-LL) > 10o, or a sagittal vertical axis (SVA)>5 cm. All patients had minimum 2 years follow-up (N=222). MCID was defined as 12.8 or more points of improvement in the Oswestry Disability Index (ODI). Up to two different etiologies for failure were allowed per patient. Results We identified 78 cases (35%) where the patient failed to achieve MCID at long-term follow-up. A total of 82 identifiable causes were seen in these patients with 14 patients having multiple causes. In 6 patients, the etiology was unclear. The causes were sub-classified as neurological, medical, structural, under treatment, degenerative progression, traumatic, idiopathic, and floor effects. In 71% of cases, an identifiable cause was related to the spine whereas in 35% the cause was not related to the spine. Conclusions Definable causes of failed MIS ASD surgery are often identifiable and similar to open surgery. In some cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery.