Quantitative criteria to define MIS of spine: four major categories
| 1. Local zone of injury—less extensive collateral damage or muscle injury because of the approach |
| Less area or zone of injury as assessed by postoperative cross-sectional MRI |
| Less selective type II fiber atrophy on postoperative muscle biopsy |
| Lower physiologic cross-sectional area reflecting less muscle strength |
| Lower incidence of postoperative intracompartmental pressure, decreased perfusion, and lower oxygen saturation of the paraspinal muscle compartment |
| Less intramuscular edema |
| Less postoperative muscle atrophy of the multifidus, interspinales, intertransversarii, longissimus, and iliocostalis documented on muscle biopsy or less denervation by EMG |
| Postoperative muscle biopsy specimens showing a lower incidence of denervation, fibrosis, and fatty infiltration |
| Lower incidence of local neurologic injury (free-running EMG, MEP, SSEP) and less denervation of paraspinal musculature |
| Lower incidence of intercostal neuralgia, less decrease of sympathetic trunk function, and less development of reflex sympathetic dystrophies |
| Lower incidence of epidural scar formation |
| Reduced anterior abdominal dissection and less vascular retraction particularly with multilevel procedures |
| 2. Operative patient demographics that are directly dependent on the approach |
| Less intraoperative estimated blood loss |
| Shorter length of surgical time |
| Shorter fluoroscopy time and less radiation exposure |
| Lower amounts of wound drainage |
| Lower incidence of postoperative seroma formation |
| Fewer intraoperative complications or adverse events (dural tears, medical complications, and so on) |
| Greater preservation of spinal stability by preservation of anterior and posterior longitudinal ligaments |
| No or acceptable loss of sagittal or coronal balance |
| Smaller zone of muscle injury or necrosis measured by creatine kinase and aldolase levels. Is there a decrease in levels of inflammatory cytokines (IL-6, IL-8, IL-10, IL-1) compared with previous techniques? |
| Lower incidence of SSIs (Table 2) |
| 3. Patient and hospitalization demographics that are indirectly related to the approach |
| Shorter length of hospital stay |
| Shorter length of stay in intensive care unit |
| Shorter length of stay in rehabilitation hospital or skilled nursing facility |
| Shorter length of time in medically supervised physical therapy before transition to self-motivated physical fitness |
| Timing of neurologic decompression, particularly with staged front and back procedures |
| Outcome instruments (VAS, ODI, ZCQ, SF-36, ASIA score) |
| Fewer intrahospital complications, including medical and comorbidities |
| Lower incidence of reoperations |
| 4. Econometrics or global cost to society |
| Faster return to work with less economic expenditures |
| Improved QALYs with shorter estimated blood loss, LOS, and hospital time, without sacrificing patient outcome instruments (NDI, ODI, VAS, and so on) |
| More favorable incremental cost-effectiveness ratios (ie, change in cost/change in effectiveness or cost per QALY) |
| MIS is a procedure that requires more dependence on radiographic imaging and intraoperative navigation for intraoperative orientation for the surgeon |
| Lower cost of spinal instrumentation and spinal implants |
| Less costs for intraoperative surgical navigation |
| Cost of radiographic imaging and intraoperative CT scanning |
| Cost of optical magnification, endoscopes, and microscopes |
| Cost of patient being lost to the workforce |
| Lost opportunity costs |
| Learning curve of MIS and time spent adopting new MIS techniques in instructional cadaveric courses |
| Ability to expand indications to include additional surgical treatment groups, such as the elderly (higher BMI, more immunocompromised, more osteoporotic, more comorbidities) |
Abbreviations: ASIA, American Spinal Injury Association; BMI, body mass index; CT, computed tomography; EMG, electromyography; IL, interleukin; LOS; length of stay; MEP, motor evoked potentials; MRI, magnetic resonance imaging; NDI, Neck Disability Index; ODI, Oswestry Disability Index; QALY, quality-adjusted life-year; SF-36, Short Form 36; SSEP, somatosensory evoked potentials; VAS, visual analog scale; ZCQ, Zurich Claudication Questionnaire.