Table 1 Characteristics of 21 included studies

(Kukke and

Triolo, 2004)

Preliminary study

n = 4;

M = 3

 F = 1

35.2 ± 9.2

C7 - T8;

AIS A − 2

AIS B − 2

6.7 ± 6.8

Implanted functional electrical stimulation

Pulse duration 0-200 µs and increased to greatest amount until trunk extension was observed.

Intramuscular electrodes implanted between L1–L2 or T12–L1 spinal segments.

Motion capture system, bimanual reaching maneuvers, sagittal reaching length.

Improvement in seated posture and increased bimanual reaching distance.

(Yang 2005)

(2005)

Repeated measurement study

n = 12;

M = 10

 F = 2

41.6 ± 9.1

C6 - T10;

AIS A − 8

AIS B − 3

AIS C-1

17.5 ± 8.5

Functional electrical stimulation

Biphasic stimulation, frequency 30 Hz, pulse width 300 µs, amplitude 80 mA.

Abdominal and back muscles stimulated.

Electromyography, wheel chair propulsion, trunk flexion, maximum voluntary contraction.

Abdominal and back muscles were highly activated, trunk stability increased.

(Triolo et al. 2009)

(2009)

Case study

n = 1; M

40

C4

AIS - A

20

Implanted electrical stimulation

Biphasic stimulation, stimulus amplitude (0.1–20 mA), pulse duration (0-255 µs), frequency 14 Hz.

L1 and T12 spinal roots.

Forward bimanual reaching distance, seated stability, rolling in bed without assistance.

Improved forward reach, restoration of upright sitting and bed turning was also improved.

(Triolo et al. 2013a)

Case series

n = 6;

M = 4

 F = 2

46 ± 10.8

C6 - T10;

AIS A − 3

AIS B − 2

AIS C-1

8.6 ± 2.8

Implanted electrical stimulation

Biphasic stimulation, intensity 20 mA, frequency 20 Hz, pulse width 0-250 µs.

L1 - L2 spinal nerves.

Maximum forward trunk lean, pushrim kinematics (peak shoulder moment and propulsion)

Increase in forward reach by 19–26% stabilizing the trunk.

(Triolo et al. 2013b)

Case series

n = 8;

M = 6

 F = 2

46 ± 9.9

C5 - T10;

AIS A − 3

AIS B − 3

AIS C-2

11.5 ± 6.9

Implanted electrical stimulation

Biphasic stimulation, stimulus amplitude (2–20 mA), frequency 20 Hz, pulse width 0-250 µs.

L1 - L2 spinal nerves.

Trunk extension strength, seated stability, bimanual reaching.

Increase in trunk extension and forward reach distance with improved sitting posture.

(Audu et al. 2015)

Case series

n = 5;

M = 3

 F = 2

53.4 ± 7.7

C7 - T10;

AIS − 2

AIS B − 2

AIS C − 1

10 ± 4.3

Implanted functional neuromuscular stimulation

Frequency 20 Hz,

50 ms, interpulse interval.

Hip and back extensor muscles stimulated.

Seated balance under external perturbations (forward flexion),

trunk tilt, erect posture.

Improved forward trunk tilt flexion and erect posture.

(Momeni et al. 2016)

Case series

n = 3

21.0 ± 1.0

AIS - B

10 ± 3.5

Electrical stimulation

Biphasic pulses of

300 µs at 35 Hz,

Intensity increased till visible muscle contraction.

Rectus femoris, biceps femoris, gastrocnemius, and tibialis anterior.

Surface electromyography, 10-meter walk test.

Trunk muscle activation and improved trunk stability.

(Rath et al. 2018)

Non-RCT within-subject crossover study

n = 8;

M = 7

 F = 1

29.9 ± 7.7

C4 - T9;

AIS A − 6

AIS C − 2

7.5 ± 3.3

Transcutaneous electrical spinal cord stimulation

Monophasic rectangular 1ms pulses, frequency 30 Hz at T11, and 15 Hz at L1, carrier frequency 10 kHz, intensity 10 to 150mA

Between T11 and T12; and between L1 and L2 hereafter referred to as T11 and L1.

Electromyography of the trunk muscles, three-dimensional kinematics, and force plate data were acquired.

Elevated activity of the trunk muscles contributing to improved trunk control, and increased multi-directional seated stability.

(Armstrong et al. 2018)

Clinical trial

n = 4;

M = 2

 F = 2

48.7 ± 8.0

C7 - T4;

AIS A -2

AIS B − 2

13.0 ± 6.2

Functional neuromuscular stimulation

Pulse amplitudes (0 to 20 mA), pulse durations (0 to 250 µsec), frequency (0 to 20 Hz).

Inserted at T12-L2 spinal nerves to activate the paraspinal muscles.

Turning events, superior-inferior angular velocity and displacement of trunk and pelvis measured.

Activation of the paraspinal and hip muscles, recovery of upright sitting, restoring a stable and erect posture.

(Bergmann et al. 2019)

Non-RCT Crossover study

n = 5; M

39.2 ± 7.1

C5-C6;

AIS B − 4

AIS C − 1

10.8 ± 6.0

Functional electrical stimulation

Frequency 3–18 Hz, pulse width 275 µs, intensity increased till strong visible muscle contraction.

Erector spinae and

rectus abdominis muscles.

Muscle oscillation frequency, characterizing muscle tone, limits of stability, and characterizing sitting balance were measured.

Increased trunk muscle tone and improved dynamic sitting balance during flexion movement.

(Friederich et al. 2020)

Single-subject experimental design

n = 4;

M = 2

 F = 2

50.7 ± 8.3

C5-T4;

AIS A − 1

AIS B − 2

AIS C − 1

11.2 ± 6.9

Functional neuromuscular stimulation

Pulse width (0-250 µs), stimulus amplitude (2–20 mA), frequency 20 Hz.

Set of trunk muscles stimulated.

Electromyography, isometric muscle contraction.

Stimulated muscles were activated with increase in muscle force.

(Bergmann et al. 2020)

Non-RCT crossover study

n = 5; M

39.0 ± 7.0

C5 - C6;

AIS B – 4

AIS C − 1

10.8 ± 6.0

Functional electrical stimulation

Frequency 8–18 Hz, pulse width 275 µs, intensity increased till strong visible muscle contraction.

Placed on thoraco-lumbar area of the erector spinae and rectus abdominis muscles bilaterally.

EMG (maximum

voluntary isometric contraction), manual muscle test hand-held dynamometer.

Improved trunk muscle force generation and muscle fatigue reduced.

(Gill et al. 2020)

Clinical trial

n = 2; M

31.5 ± 7.8

T3 & T6

AIS - A

4.5 ± 2.1

Epidural spinal electrical stimulation

Frequency 20–25 Hz, pulse width 200–400 µsc, stimulation intensity 3.8–5.0 V.

T11 - L1 vertebral region.

Reaching performance, modified functional reach test.

Improved reaching performance and seated position, increase in reaching distance.

(Rahimi et al. 2020)

Randomised controlled trial

n = 16;

M = 13

 F = 3

37.0 ± 5.7

T5 - T12;

AIS - A

13.0 ± 5.7

Functional electrical

stimulation

Rectangular pulses, pulse width 400 µs,

frequency 40 Hz,

amplitude 20 to

200 mA increased to a visible contraction.

Quadriceps and gastrocnemius muscles.

Spinal Cord Independence Measure-III, quadruped unilateral reaching.

Improved ability to perform transfers, increased unilateral reaching.

(Keller et al. 2021)

Prospective within-subject design

n = 8;

M = 5

 F = 3

8.4 ± 3.9

Cervical-thoracic

NA

Transcutaneous electrical spinal cord stimulation

Frequency 30 Hz, intensity 134–140 mA.

T11 and L1 spinal levels.

Electromyography, trunk kinematics, center of pressure displacement, segmental assessment of trunk control.

Increased trunk extension, enabled upright sitting posture.

(Friederich et al. 2021)

Case study

n = 1; F

48 

C 7

AIS - B

22

Functional neuromuscular stimulation

Frequency 20 Hz, pulse 250 µs and amplitude set at 20mA.

Applied to nerves innervating the lumbar erector spinae, quadratus lumborum, adductor magnus, gluteus maximus, gluteus medius, and hamstring semimembranosus.

Trunk tilt, functional tasks in sitting, motion capture system.

Increased trunk movement and improved erect upright sitting posture.

(Tharu et al. 2022b)

Case series

n = 5;

M = 2

 F = 3

42 ± 13.7

C4 - C7;

AIS - A

9.3 ± 7.4

Transcutaneous electrical spinal cord stimulation

Biphasic stimulation, Frequency 20–30 Hz, pulse width 0.1-1.0 ms, intensity 90–115 mA.

T11-T12 and

L1-L2 spinal levels.

Functional reach test, trunk control test and function in sitting test, electromyography, motion capture system.

Improved trunk and sitting functions with increased static and dynamic balance.

(Kouwijzer et al. 2022)

Cross-sectional study

n = 11;

M = 10

 F = 1

41.6 ± 10.1

C4 - C7;

Complete − 8

Incomplete- 3

17.5 ± 13.3

Electrical stimulation

Biphasic pulses, frequency 30 Hz, pulse duration 300 µs, amplitude 30–100 mA.

Rectus abdominis, obliquus externus abdominis and erector spinae muscles.

Electromyography, trunk stability measured through reaching tasks, Isokinetic test on dynamometer.

Induced trunk muscle activation, trunk stability increased with increased reaching distance.

(Gorgey and Gouda 2022)

Case report

n = 1; M

25 

T3;

AIS - A

3.8

Epidural spinal electrical stimulation

Frequency 20 Hz, pulse width 240 µs, amplitude of the current gradually increased from 0–10 V.

T11–T12 vertebral region.

Electromyography, perturbation of trunk control.

Activation of abdominal muscles, immediate restoration of trunk control during seated position.

(Rowald et al. 2022)

Clinical trial

n = 3; M

34.0 ± 6.2

T4 - T7;

AIS A − 1

AIS B − 2

4.3 ± 4.1

Epidural spinal electrical stimulation

Frequency 70–80 Hz, single pulses (0.5 Hz) were delivered at increasing amplitude

to elicit muscle responses.

L1 and L2 spinal segments.

Inspecting muscular activity and kinematics, activity-specific stimulation programs, quantification of muscle mass.

Motor neurons innervating the trunk

and abdominal musculatures were activated and facilitated improved trunk posture.

(Friederich et al. 2022)

Feasibility study

n = 5;

M = 3

 F = 2

46.8 ± 9.0

C5 - T10;

AIS A − 3

AIS B − 1

AIS C − 1

13.2 ± 6.6

Functional neuromuscular stimulation

Frequency 40 Hz, pulse 250 µs and amplitude set at 20mA.

Applied to nerves innervating the erector spinae, quadratus lumborum, adductor magnus, gluteus maximus, gluteus medius, and hamstring semimembranosus.

Trunk angles measured using motion capture system, postural sway, reaching movements.

Postural sway reduced, reaching ability increased, time required for maintaining upright posture improved.