Table 2. Characteristics of studies evaluating predictive factors affecting outcomes following LLIF/XLIF/DLIF for lumbar degenerative disease.

Investigator (y) Study design CoE	Populationa	Condition	Surgical procedure	Follow-up (% followed)	Predictive factors evaluated	Outcomes evaluated
Kepler et al (2012) Retrospective cohort CoE: III	• N = 29 • Age (mean): 69 y (45–87) • Male: 41%	• DDD, spondylolisthesis, or degenerative scoliosis	• LTIF from L1–L5, with posterior instrumentation or standalone • Number of levels: mean 2.3 levels/patient	≥ 6 mo (% NR)	• Demographic factors: age, sex, BMI • Surgical factors: none • Other factors: preoperative sagittal alignment at instrumented levels (degrees)	Postoperative lumbar lordosis
Isaacs et al (2010) Prospective cohort CoE: II	• N = 107 • Age (mean): 68.4 y (45–87) • Male: 27%	• Adult thoracolumbar scoliosis, with back pain, radicular pain, combined back/leg pain, or neurologic deficits • Symptom duration: > 2 y (78% of patients)	• XLIF from T11-L5 or direct anterior/ AxiLIF/ posterior interbody approach at L5-S1 either standalone or with instrumentation (percutaneous posterior pedicle screws or lateral fixation) • Number of levels involved: mean 4.4 levels/patient	6 wks (% NR)	• Demographic factors: age, sex, BMI, comorbidities, severity of deformity • Surgical factors: inclusion of specific levels, number of levels treated, additional posterior decompression, type of fixation • Other factors: none	Perioperative complications
Rodgers et al (2010) Retrospective cohort CoE: III	N = 313 Obese group • N = 156 • Age (mean): 58.9 y (30–87) • Male: 41% • BMI (mean): 36.0 kg/m2 Nonobese group • N = 157 • Age (mean): 62.9 y (24–88) • Male: 45% • BMI (mean): 25.7 kg/m2	• Degenerative spine disease in lumbar and thoracic spine, including stenosis, spondylolisthesis, DDD, scoliosis, HNP, or postlaminectomy instability	• XLIF, range of levels NR • Number of levels involved: NR	3 mo (% NR)	• Demographic factors: BMI, age, sex, height and weight, smoking, comorbidities (including diabetes mellitus, coronary artery disease, chronic obstructive pulmonary disease, chronic steroid use) • Surgical factors: number of levels treated • Other factors: preoperative diagnosis	Early complications (within first 3 mo), including wound, nerve, cardiac, renal, GI, respiratory, vertebral body-related, and hardware-related

Abbreviations: AxiLIF, axial lumbar interbody fusion; BMI, body mass index; CoE, class of evidence; DDD, degenerative disc disease; GI, gastrointestinal; HNP, herniated nucleus pulposus; NR, not reported; LTIF, lateral transpsoas interbody fusion; XLIF, extreme lateral interbody fusion.

^aObese group included patients who were obese (BMI ≥ 30 kg/m² and ≤ 40 kg/m²) or morbidly obese (BMI > 40 kg/m²) (Rodgers et al, 2010).