Table 1.

Characteristics of studies included in qualitative analysis

Author	Inclusion criteria	Exclusion criteria	Diagnostic criteria	Groups	Treatments	Outcome measures	Results (as reported by the authors)
LBP without radicular pain—comparison: different traction types
Tanabe et al, 2020, Japan	- Age >20 to <64 - Nonspecific LBP - More than 3 months duration - More than 70° at SLR test - Negative femoral nerve stretching test - No superficial sensory deficits - No muscle weakness	- Radicular pain or neurological deficits - Tumor, infection, or fracture - Previous back surgery - Severe osteoporosis - Psychiatric disorders - Liver and renal dysfunction - Pregnancy - Medication for cardiac failure - History of cerebrovascular accident and/or myocardial infarction within 6 months	Symptoms+physical exam	95 patients randomly assigned into 2 groups which received the same 2 treatments but in reverse order (ITV to ITO first n = 49; ITO to ITV first n = 46)	Patients were treated for a period of 2 weeks, 3 days a week, switching treatment mode after 1 week. They received 10’ traction with 30″ hold 5″ rest, with 40% bw traction force	6 check-points were conducted during the 2 weeks of observation, assessing each time	Both treatments significantly improved the JLEQ score compared to pre-treatment
LBP with or without radicular pain—comparison: different traction forces
van der Heijden et al, 1991, The Netherlands	- 25 to 65 years - Chronic LBP (more than 3 months), with or without radiation	- Previous lumbar traction treatment - Ongoing psychiatric or psychological treatment - Inguinal hernia - Pregnancy - Malignancy - Scheuerman, Bechterew, or Ehier–Danlos syndrome - Osteoporosis - Previous thoracic, lumbar, or pelvic fracture, surgery or dislocation - Hemiplegia - Local acute inflammation - Lower limb dysmetria (more than 5 cm) - Cardiac or bronchial disorders - Previous lumbar disc herniation - Spondylosis, spondylolostesis - Hemilumbarization, hemisacralization - Congenital hip dysplasia	Not specified	25 patients, randomized into 2 groups: - High dose (30% to 50% bw) group (n = 13) - Low dose/sham (max 25% bw) group (n = 12)	During a 4-week period, at most 3 times/week (10 to 12 sessions), patients underwent a 20-minute continuous mechanic lumbar traction treatment in supine position. Every patient also received an LBP-management pamphlet for at-home self-treatment	At baseline, at the end of treatment, and 1 month after: - Pain (VAS) - ADL impact (VAS) - Disability (Roland and Morris Disability Questionnaire (RMDQ))	- Better VAS score compared to placebo, no statistically significant difference - ADL impact has better score at end of treatment in placebo groups; both groups have the same improvement at FU assessment, with no statistically significant difference compared to baseline - Both groups have little improvement with no significant difference inter and intra-group at RMDQ score
Schimmel et al, 2009, The Netherlands	- LBP for more than 3 months - Bulging disc - Lumbar degenerative disc disease	- Previous surgical treatment with dynamic stabilization, fusion or disc replacement - Radicular leg pain - Malignancy - Pregnancy - Osteoporosis	Symptoms+physical exam	60 patients randomized into 2 groups: - Intervertebral Differential Dynamics Therapy with 50% bw+4.45 kg traction weight (n = 31) - Sham Therapy with 4.45 kg traction weight (n = 29)	20 traction sessions during 6 weeks, combining - 25’-30’ intermittent traction with the patient in supine position - Massage, heat, blue relaxing light, and music during the treatment session The traction treatment was held 5 times/ week for the first 2 weeks, thrice/week the second 2 weeks, twice/week for the last 2 weeks - 2 weeks after the start of the traction sessions, a standard graded activity program was added (1 h training 2 days/week for 12 weeks, always on different days compared to the traction sessions)	At baseline, at the end of treatment, and 8 weeks after: - Back pain (VAS) - Leg pain (VAS) - Disability (Oswestry Disability Index) - Health Status (Short Form 36) - Kinesiophobia (Tampa Scale)	- LBP VAS score significantly decreased in both groups at the FU measurement, with no differences among them. No time × group interaction detected - ODI, SF-36, and leg pain VAS score significantly improved at the end of treatment in both groups, with no significant differences among them. - Tampa Scale score showed no improvement at the end of treatment and no differences among the groups
Beurskens et al, 1995, The Netherlands	- Nonspecific LBP for at least 6 weeks - 18 years old or more	- Previous lumbar traction treatment - Underlying diseases or anatomic abnormalities (malignancy, osteoporosis, etc.) - Significant improvement during the previous 2 weeks	Not specified	151 patients randomized into 2 groups: - High dose (35% to 50% bw traction force) group (n = 77) - Low dose/sham (20% bw traction force) group (n = 74)	5 weeks duration, 12 treatment sessions Patient on a traction table in semi-Fowler position, receiving 20’ continuous motorized lumbar traction Patients were allowed to continue taking pain medication they had used before entry into the study	At baseline and at the end of treatment - Main complaint (VAS) - Second main complaint (VAS) - Pain at the moment (VAS) - Pain during last week (VAS) - Functional Status (Roland and Morris Disability Questionnaire) - Severity of LBP (11 point scale) - Spine ROM (inclinometer)	- Both groups significantly improved in all of the items except for the back ROM, but no significant differences among them
Beurskens et al, 1997, The Netherlands	- Nonspecific LBP for at least 6 weeks - 18 years old or more	- Previous lumbar traction treatment - Underlying diseases or anatomic abnormalities (malignancy, osteoporosis, etc.) - Significant improvement during the previous 2 weeks	Not specified	151 patients randomized into 2 groups: - High dose (35% to 50% bw traction force) group (n = 77) - Low dose/sham (20% bw traction force) group (n = 74)	5 weeks duration, 12 treatment sessions Patient on a traction table in semi-Fowler position, receiving 20’ continuous motorized lumbar traction Patients were allowed to continue taking pain medication they had used before entry into the study	At baseline, at 12 weeks, and 6 months - Main complaint (VAS) - Second main complaint (VAS) - Pain at the moment (VAS) - Pain during last week (VAS) - Functional Status (Roland and Morris Disability Questionnaire) - Severity of LBP (11-point scale) - Spine ROM (inclinometer)	- Both groups significantly improved in all of the items except for the back ROM, but no significant differences among them
LBP with or without radicular pain—comparison: different traction positions
Beyki et al, 2007, Iran	- Chronic LBP (more than 3 months) - Discogenic origin of the pain cleared by clinical examination - Symptoms, signs, and clinical exam correlate with MRI	- Osseous stenosis - Unstable spine - Previous spinal surgery - Spinal pain due to tumors, infection, inflammatory diseases - Pregnancy - Formal therapeutic or medical intervention within the last 3 months - Cardiac or respiratory conditions, neurological disorders or organ disease - Long-term oral steroid intake - History of major psychiatric illness	Symptoms+physical exam	124 patients, randomized into 2 groups: - Prone group (n = 62) - Supine group (n = 62)	1-month duration, 6 sessions every other day and 4 sessions every 3 days - 15 minutes of TENS with Hot Pack - 15 minutes of prone or supine intermittent mechanic traction Traction force: 35% to 50% body weight	At baseline and after treatment - Pain (VAS) - Disability (ODI)	- VAS score significantly improved in both groups, with meaningful differences prominent in prone group - ODI score significantly improved in both groups, meaningful differences prominent in prone group
Kim et al, 2013, South Korea	- LBP in everyday life - Diagnosed after x-ray, CT, and MRI scans - Duration of the symptoms at least 12 weeks	- Past or present neurological, hypertension, cardiopulmonary diseases, etc. - Chronic diseases, surgery for LBP. - Abnormal ophthalmic artery pressure during inversion	Symptoms+physical exam	47 patients, randomized in 3 groups: - Supine group (n = 15) - Inversion -30° group (n = 18) - Inversion -60° group (n = 14)	8 weeks duration, 4 times per week - 20 minutes of intermittent inversion traction in supine position, lying on a motorized gravitational machine Traction force: not specified	At baseline and after treatment: - Pain (VAS) - Night pain (VAS) - Flexibility of lumbo-sacral joint (seat and reach test, back extension from prone position (cm)) - Isokinetic strength of trunk muscles at 60°/s (flexor and extensor peak torque (Nm))	- VAS score, Lumbar flexibility, Isokinetic torques at 60°/s significantly improved in both groups
LBP with or without radicular pain—comparison: different hold and rest time combinations
Santhumayor et al, 2016, India	- Age 18-45 - Lumbar IVDP stage of degeneration/protrusion confirmed by radiography - Acute and subacute IVDP (<12 weeks) - VAS score more than 3 on a 10-point scale	- Previous spinal surgery - Last stage of IVDP (sequestration) - Therapeutic or medical intervention within the last 3 months - Conditions as ankylosing, spondylitis, spondylolisthesis, RA, spinal stenosis, spinal fracture or tumor, osteoporosis - Any systemic condition - Long-term oral steroid intake - Pregnancy - Hip pathologies	Symptoms+physical exam	40 patients randomly assigned into 4 different groups	All patients received intermittent traction delivered through similar traction apparatus, once a day for 1 week, for 15-20 minutes per session	Before and 1 week after the intervention	Groups with longer hold and rest time (60/10, 80/20) showed greater improvement in lumbar mobility and SLR score, reduction in disability, and VAS score.
LBP with radicular pain—comparison: different traction forces
Isner-Horobeti et al, 2016, France	- Lumbar sciatica of less than 6 weeks duration secondary to disc herniation - Pain radiating down the leg, along the distribution of the sciatic nerve - SLR +	- Duration of symptoms more than 6 weeks - Signs of clinical neurologic deficit - Lumbar sciatica not caused by disc herniation - Presence of abnormalities on lumbar tomodensitometry - Pregnancy - Patients aged less than 18 years - Patients on medical leave for more than 3 weeks at inclusion - History of lumbar surgery or previous lumbar traction therapy	Symptoms+physical exam	17 patients randomly divided into 2 groups: - High-level (50% of BW, LT50) group (n = 8) - Low-level (10% of BW, LT10) group (n = 9)	Patients received 10 lumbar traction sessions (5 per week for 2 weeks) - They rested in Fowler position receiving a traction force that was progressively applied for 5’, and subsequently maintained at the target level continuously for 20’. At the end of the session, relaxation was done progressively for 5’ - Patients could take their usual medications	At baseline, at the end of treatment, and after 2 weeks: - Radicular pain (VAS) - Mobility of the lumbo-pelvic-hip complex (Finger-To-Toe test (FTT)) - Lumbar spine mobility (Schöber–Macrae test) - Signs of nerve root compression (SLR) - Functional impairment (validated French version of the Roland and Morris Disability Questionnaire)	- In both groups, a statistically significant improvement was found for all the outcome but the Schöber test. No statistically meaningful difference was found when considering the inter-group analysis - No interaction effect was noted for VAS, FTT, SLR or Roland and Morris score - No differences were observed within or between groups for Schöber–Macrae test.
Murat et al, 2018, Turkey	- Lumbar disc herniation diagnosed after clinical evaluation and MRI - Pain in the back of the leg - Duration of the symptoms between 2 weeks and 3 months	- Pregnancy - Previous lumbar spine surgery or traction therapy - Progressive neurological loss - Umbilical, hiatal, and inguinal hernia - Malignancy - Infectious disease - Inflammatory pathologies - Severe lung and cardiovascular disease	Symptoms+physical exam	61 patients randomized into 2 groups: - Traction group (n = 30) - Placebo traction group (n = 31)	2-week duration 10 daily sessions (5/week) combining: - 20’ of intermittent lumbar traction of 35% to 50% bw or 10% to 20% bw - 20’ of 250 watt infrared 50 cm from the area - PT program, exercises to strengthen abdominal and back muscles Patients were allowed to use up to 4000 mg of paracetamol tablets	At baseline, at the end of treatment, and 40 days after: - Pain at rest and during activities (VAS) - Disability (Oswestry Disability Index - ODI and Roland and Morris Disability Questionnaire (RMDQ)) - Quality of life (Short Form 36 (SF-36))	- VAS values at rest and exercise and RMDQ scores significantly improved between pretreatment and first control in both groups. - ODI scores significantly improved for the study group. - SF-36 scores showed statistically significant improvement in both groups. - No statistically significant difference between groups
Reust et al, 1988, Switzerland	- Lumbosciatalgia with or without neurological deficit	- Previous lumbar traction treatment - Rapid progressive neurological loss - Behavioral problems - Referred allergies to diclofenac, diazepam, or heparin - Previous gastroduodenal problems - Specific bone diseases at the origin of the symptoms (spondylolysis, osteoporosis with settlements)	Not specified	60 patients randomized into 3 groups: - Placebo (5 kg) traction group (n = 20) - Light (15 kg) traction group (n = 22) - Normal (up to 50 kg) traction group (n = 18)	12 days duration, with consecutive daily treatment combining - 10’ continuous mechanic traction, lying supine on a traction table - Lit Strict, diclofenac 3 × 50 mg/day, diazepam 5-5-10 mg/day, Heparin 3 × 5000 U sc/day - 20’ Lumbar parafango - 20’ Muscle relaxing massage therapy	At baseline and at the end of treatment: - Pain (VAS) - Back mobility (Finger-Floor distance) - Neural tension (Lasègue)	- Pain and Lasègue scores showed a statistically significant improvement in all 3 groups, no significant differences between them - Finger-To-Floor score significantly improved in placebo and light traction group (no significant difference between groups), but not in normal traction group
Weber H. 1973, Germany	- Radiating pain and neurological signs corresponding to a lesion in the L5 and/or S1 root - Positive radiculogram	- Bladder paresis - Strong persistent pain - Acutely occurring paresis - Considerable constraint of the spinal column	Symptoms+physical exam	72 patients randomly assigned into 2 groups: - Actual traction group (n = 37), traction force corresponding to 1/3 bw - Sham traction group (n = 35), traction force of 7 kg	Patients had to lie supine on a Tru-Trac traction table. Intermittent traction was administered 20’ a day, daily, for 5 to 7 days	At baseline and at the end of treatment: - Lumbar spine mobility in sagittal and frontal plane - Lasègue test - Achille’s reflex - Motility (isometric strength in plantar and dorsal flexion of the foot, extension of the big toe, eversion of the foot, flexion of the knee, abduction and extension of the hip) - Sensory function (pin pricking) - Need for analgesic - Back and leg pain (NRS)	- No effect on lumbar spine mobility, sensory function and need for analgesic - No definite differences between groups for Lasègue test and Achille’s reflex - General increase in strength in both groups, no systematic trend comparing the groups; no beneficial effect on the paresis - A certain reduction of pain was detected, with no differences among groups.
LBP with radicular pain—comparison: different traction positions
Bilgilisoy-Filiz et al, 2018, Turkey	- Age 18-65 years, - Chronic LBP with accompanying radiculopathy of L4-L5, L5-S1, or L4-S1 for more than 3 months - Moderate symptoms severity (pain threshold of 4/10 VAS)	- LBP due to neoplastic, inflammatory or infectious causes - Indication of urgent surgery (cauda equina syndrome, progressive motor deficit) - Previous spinal surgery - Pregnancy or early post-partum period (6 months) - Co-existing medical conditions (severe central or foraminal spinal stenosis with narrowing of the normal canal cross-sectional area by more than 2/3; osteoporosis, gross structural abnormalities such as spondylolisthesis or scoliosis, ankylosing spondylitis, spinal fracture, spinal tumor)	Symptoms+physical exam	125 patients randomized into 3 groups: - Supine traction group (n = 42) - Prone traction group (n = 41) - No traction group (n = 42)	Patients in traction groups received 15 sessions of treatment, 5/week for 3 weeks total, combining: -15’ intermittent mechanical lumbar traction, lying on a traction table in Fowler position or prone position. Traction force of 25% to 50% bw. - Standard PT program, with 20’ low-back HP, 10’ continuous ultrasounds, 20’ of low back TENS All patients asked to perform home exercises (strengthening of paraspinal and abdominal muscles, and stretching for back extensors, hamstrings, and calf muscles)	At baseline and at the end of treatment - Pain (VAS) - Back mobility (Schöber test) - Disability (Oswestry Disability Index)	- There were statistically significant improvements in all groups for all outcomes. - The between-groups analysis showed a greater improvement in all outcomes in the prone group compared to the other 2, statistically significant for ODI and VAS scores.
LBP with radicular pain—comparison: different traction types
Choi et al, 2015, South Korea	- Radiating pain caused by LBP (more than 3 months)	- Previous lumbar surgery - Malignancy - Intervertebral disc infection - Inflammatory diseases (e.g., rheumatism) - Fractures or other contraindications for manual therapy	Symptoms+physical exam	30 patients randomized into 2 groups: - Spinal decompression therapy group (n = 15), receiving intermittent traction from level 5 up to the maximum tolerated - General traction therapy group (n = 15), receiving the most traction tolerated, from 1/3 up to 50% bw (not specified whether continuous or intermittent traction)	During a 4-week period, patients underwent 3/week the following treatments: - Conservative physical therapy with 20’ HP, 15’ Interferential current therapy and 5’ ultrasounds - 20’ traction (through a spinal decompression or a traction device), both in supine position	At baseline and at the end of treatment - Pain (VAS) - Neural tension (SLR test) - Disability (Oswestry Disability Index)	- Both groups showed statistically significant improvement in VAS, ODI, and SLR scores. - The comparison between the 2 groups found no statistically meaningful differences
Güevenol et al, 2000, Turkey	- Complaint of LBP and lower extremity pain of not less than 1 month - Lumbar disc herniation diagnosed by CT	- Previous spinal surgery - History of cerebrovascular accident, thyroid disorders, hypertension, cardiac disorders - Previous hiatus hernia - Previous glaucoma, detachment of retina - Chronic obstructive and restrictive lung disorders - Osteoporosis and excessive joint laxity - Malignant, inflammatory, infectious, metabolic, congenital, and developmental disorders of the spine	Symptoms+physical exam	31 patients randomized into 2 groups: - Inverted traction group (n = 16) - Conventional traction group (n = 15)	Both groups received the treatments daily for 10 days, combining: - 20’ continuous traction (30 to 45 kg traction force) in supine position for the conventional traction group, or 5 to 10’ inverted gravitational traction in the inversion traction group - 15’ infrared radiation to heat superficial tissues - Abdominal and gluteal muscle exercises Patients were not allowed to take non-steroid anti-inflammatory drugs throughout the study. Analgesics were given as needed. Bed rest was required for all patients	At baseline, at the end of treatment, and 3 months after - Pain cluster 1: morning pain, pain throughout the day, night pain, pain with Valsalva maneuver, radicular pain (VAS) - Pain cluster 2: flexion, extension, lateral flexion, rotation - Lumbar spine mobility (Finger-To-Floor distance) - Neural tension (SLR)	- A significant increment in SLR from pre- to post-treatment was obtained in both groups - Pain clusters 1 and 2 showed a meaningful decrement from pre- to post-treatment in both groups - There were similar changes from pre-treatment to follow up - No statistically significant difference between the post-treatment and the FU values was found in both groups - No statistically meaningful difference between any of the parameters tested comparing the groups was found
Kocak et al, 2018, Turkey	- Diagnosis of lumbar disc herniation - Protruding disc herniation according to the MRI - Longer than 3 months duration LBP	- Extruded and/or sequestrated LDH, spinal compression fracture, spondylolisthesis, vertebral infection - Lumbar spinal injection or lumbar surgery history, spinal fusion - Physical therapy and rehabilitation session during the past 6 months - Cognitive dysfunction - Neurological deficits, severe peripheral neuropathy - Pregnancy - Malignancy - Aortic aneurysms - Rheumatic diseases - Moderate-to-severe depression, as assessed by a Beck Depression Inventory (BDI) score of ≥19.	Symptoms+physical exam	48 patients randomized into 2 groups - Conventional motorized traction group (n = 24), with traction force of 25% up to a maximum of 50% bw - Non-surgical spinal decompression group (n = 24), with traction force of 50% bw—10 pounds up to 50% bw+10 pounds	20 sessions over 6 weeks (5 days/week during first 2 weeks, 3 days/week during the following 2 weeks, and 2 days/week during the last 2 weeks), combining: - 20’ HP and 20’ TENS - 30’ intermittent mechanical traction, applied to the patient in supine position - At the second week, patients were instructed on exercises to strengthen low back and abdominal muscles Patients could take paracetamol during treatment period	At baseline and at the end of treatment: - Pain (VAS) - Functional status (Oswestry Disability Index - ODI) - Quality of life (Short Form-36) - State of depression mood (Beck Depression Inventory - BDI)	- A statistically significant decline was found in the VAS, ODI, and BDI scores after treatment in both groups - Except for 2 subgroups (physical role restriction in the NSD group and pain in the CMT group), no significant changes were observed in the SF-36 Form. - No significant difference was observed in the evaluation outcomes after treatment between groups.

ADL, Activities of Daily Living; BDI, Beck Depression Inventory; BW, Body Weight; CMT, Conventional Motorized Traction; CT, Computed Tomography; FTT, Finger to Toe Test; FU, Follow Up; HP, Hot Packs; ITO, Intermittent Traction Only; ITV, Intermittent Traction with Vibration; IVDP, Acute Inter-Vertebral Disc Prolapse; JLEQ, Japan Low back pain Evaluation Questionnaire; LBP, Low Back pain; LDH, Lumbar Disc Herniation; MRI, Magnetic Resonance Imaging; Nm, Newton meter; NRS, Numerical Rating Scale; NSD, Non-surgical Spinal Decompression; ODI, Oswestry Disability Index; PT, Physical Therapy; RA, Rheumatoid Arthritis; RMDQ, Roland & Morris Disability Questionnaire; ROM, Range Of Motion; SF-36, Short-Form 36; SLR, Straight Leg Raising; TENS, Transcutaneous Electrical Nerve Stimulation; VAS, Visual Analogue Scale. ADL, Activities of Daily Living; BDI, Beck Depression Inventory; BW, Body Weight; CMT, Conventional Motorized Traction; CT, Computed Tomography; FTT, Finger to Toe Test; FU, Follow Up; HP, Hot Packs; ITO, Intermittent Traction Only; ITV, Intermittent Traction with Vibration; IVDP, Acute Inter-Vertebral Disc Prolapse; JLEQ, Japan Low back pain Evaluation Questionnaire; LBP, Low Back pain; LDH, Lumbar Disc Herniation; MRI, Magnetic Resonance Imaging; Nm, Newton meter; NRS, Numerical Rating Scale; NSD, Non-surgical Spinal Decompression; ODI, Oswestry Disability Index; PT, Physical Therapy; RA, Rheumatoid Arthritis; RMDQ, Roland & Morris Disability Questionnaire; ROM, Range Of Motion; SF-36, Short-Form 36; SLR, Straight Leg Raising; TENS, Transcutaneous Electrical Nerve Stimulation; VAS, Visual Analogue Scale.