Table 3.

Frailty indices employed in the 29 clinical studies included in the systematic review.

	Frailty Index name	Frailty index acronym	Items	Frailty scale	Ref.
Accumulation of deficit model	Spinal tumor frailty index	STFI	1) Anemia; 2) congestive heart failure; 3) chronic obstructive pulmonary disease; 4) coagulopathy; 5) electrolyte abnormalities; 6) pulmonary circulation disorders; 7) renal failure; 8) malnutrition; 9) pathologic fractures	NF: 0; Mild Frailty: 1; Moderate frailty: 2; SF: ≥ 3	28
	Metastatic Spinal Tumor Frailty Index	MSTFI	1) Anemia; 2) Chronic lung disease; 3) Coagulopathy; 4) Electrolyte abnormalities; 5) Pulmonary circulation disorders; 6) Renal failure; 7) Malnutrition; 8) Emergent/urgent case; 9) Anterior or combined surgical approach	NF: 0; Mild Frailty: 1; Moderate Frailty: 2; SF: ≥ 3	29, 31
	Modified Frailty Index	mFI	1) Non-independent functional status; 2) history of diabetes mellitus; 3) history of chronic obstructive pulmonary disease; 4) history of congestive heart failure; 5) history of myocardial infarction; 6) history of percutaneous coronary intervention, cardiac surgery, or angina; 7) hypertension requiring the use of medication; 8) peripheral vascular disease or rest pain; 9) impaired sensorium; 10) transient ischemic attack or cerebrovascular accident w/o residual deficit; 11) cerebrovascular accident w/o deficit	NF: 0; PF: 0-0.21 F: ≥ 0.27	30, 31, 32, 37, 38-42, 46-48, 51, 52
	Adult spinal deformity frailty index	ASD-FI	1)Health deficits documented by physician: >3 medical problems; BMI <18.5 or >30 kg/m2; Cancer; Cardiac disease; Currently on disability; Depression; Diabetes; Hypertension; Liver disease; Lung disease; Osteoporosis; Peripheral vascular disease; Previous blood clot (DVT/PE/stroke); Smoking status. 2)Health deficits patient-reported: Bladder incontinence; Bowel incontinence; Deteriorating health this yr; Difficulty climbing 1 flight of stairs; Difficulty driving a car; Difficulty getting dressed; Difficulty getting in/out of bed; Difficulty sleeping >6 hrs; Difficulty walking 100 yards; Difficulty w/o light activity; Feeling downhearted/depressed most of the time; Feeling tired most of the time; Feeling worn out most of the time; General health: fair/poor; Inability to bathe w/o assistance; Inability to cheer up often; Inability to do normal work/schoolwork/housework; Inability to lift heavy objects; Inability to travel >1 hr; Inability to walk w/o assistive device; Leg weakness; Loss of balance; Not in excellent health; Personal care dependency; Restricted activity level; Restricted social life	NF: < 0.3; F: 0.3-0.5; SF: > 0.5	33-36
	Modified Frailty Index 5	mFI-5	1) history of severe chronic obstructive pulmonary disease; 2) congestive heart failure within 30 days before surgery; 3) functional health status prior to surgery (independent versus partially or totally dependent); 4) hypertension requiring medication; 5) diabetes mellitus with oral agents or insulin	NF: 0; PF: 1; F: ≥ 2	38, 49, 53
	Cervical deformity frailty index	CD-FI	1)Health deficits documented by physician: >3 Medical problems; Anxiety; BMI <18.5 or >30; Cancer; Cardiac disease; Cerebrovascular disease; Currently receiving disability benefits; Dementia; Depression; Diabetes; Liver disease; Lung disease; Neuromuscular disease; Osteoporosis; Pancreatic disease; Rheumatoid arthritis; Smoker; Vascular disease; Venous disease; Unsteady gait. 2)Health deficits patient-reported: Bladder incontinence; Bowel incontinence; Difficulty driving; Difficulty getting dressed; Difficulty reading; Difficulty sleeping >6 h; Difficulty walking without assistive device; Feeling anxious or depressed most of the time; Feeling tired most of the time; Feeling weak most of the time; Feeling worn out/exhausted most of the time; General health <50; Inability to concentrate; Inability to do normal work/schoolwork/housework; Inability to engage in normal recreational activity; Inability to lift heavy objects; Inability to perform normal activities; Inability to walk; Leg weakness; Personal care dependency	NF: < 0.2; F: 0.2-0.4; SF: > 0.4	43, 45
	Modified cervical deformity frailty index	mCD-FI	1)Lung disease; 2) BMI <18.5 kg/m2 or >30 km/m2; 3) Diabetes; 4) Depression; 5) Liver disease; 6) Rheumatoid arthritis; 7) Venous disease; 8) Unsteady gait; 9) Bladder incontinence; 10) Leg weakness; 11) Comorbidities; 12) Anxiety; 13) Bowel incontinence; 14) Difficulty sleeping >6 h; 15) Inability to walk	NF: < 0.3; F: 0.3-0.5; SF: >0.5	44
	Frailty Index	FI	1) Help Bathing; 2) Help Dressing; 3) Help getting in/out of Chair; 4) Help Walking around house; 5) Help Eating; 6) Help Grooming; 7) Help Using Toilet; 8) Help up/down Stairs; 9) Help lifting 10 lbs; 10) Help Shopping; 11) Help with Housework; 12) Help with meal Preparations; 13) Help taking Medication; 14) Help with Finances; 15) Lost more than 10 lbs in last year; 16) Self Rating of Health; 17) How Health has changed in last year; 18) Stayed in Bed at least half the day due to health (in last month); 19) Cut down on Usual Activity (in last month); 20) Walk outside; 21) Feel Everything is an Effort; 22) Feel Depressed; 23) Feel Happy; 24) Feel Lonely; 25) Have Trouble getting going; 26) High blood pressure; 27) Heart attack; 28) CHF; 29) Stroke; 30) Cancer; 31) Diabetes; 32) Arthritis; 33) Chronic Lung Disease; 34) MMSE; 35) Peak Flow; 36) Shoulder Strength; 37) BMI; 38) Grip Strength; 39) Usual Pace; 40) Rapid Pace	NF: 0.15; PF: 0.15-0.24; F: ≥ 0.25	55
Phenotypic model		FRAIL scale	1)fatigue over the past 4 months; 2) ability to climb a flight of stairs unassisted; 3) ability to walk two blocks unassisted; 4) medical comorbidities; 5) loss of weight	NF: 0; PF:1-2; F: 3-5	54
		FRIED criteria	1) weight loss; 2) exhaustion; 3) physical inactivity; 4) slowness; 5) handgrip strength	NF: 0; PF:1-2; F: ≥ 3	50, 56
	Frailty Phenotype criteria	FP criteria	1) Slow gait (3-m timed walk); 2) Weakness (grip strength); 3) Low activity (energy expenditure); 4) Involuntary weight loss; 5) Exhaustion	NF: 0; PF: 1-2; F: ≥ 3	55