Peripheral nerve transfers for dysfunctions in central nervous system injuries: a systematic review

Abstract

Background: The review highlights recent advancements and innovative uses of nerve transfer surgery in treating dysfunctions caused by central nervous system (CNS) injuries, with a particular focus on spinal cord injury (SCI), stroke, traumatic brain injury, and cerebral palsy.

Methods: A comprehensive literature search was conducted regarding nerve transfer for restoring sensorimotor functions and bladder control following injuries of spinal cord and brain, across PubMed and Web of Science from January 1920 to May 2023. Two independent reviewers undertook article selection, data extraction, and risk of bias assessment with several appraisal tools, including the Cochrane Risk of Bias Tool, the JBI Critical Appraisal Checklist, and SYRCLE's ROB tool. The study protocol has been registered and reported following PRISMA and AMSTAR guidelines.

Results: Nine hundred six articles were retrieved, of which 35 studies were included (20 on SCI and 15 on brain injury), with 371 participants included in the surgery group and 192 in the control group. These articles were mostly low-risk, with methodological concerns in study types, highlighting the complexity and diversity. For SCI, the strength of target muscle increased by 3.13 of Medical Research Council grade, and the residual urine volume reduced by more than 100 ml in 15 of 20 patients. For unilateral brain injury, the Fugl-Myer motor assessment (FMA) improved 15.14-26 score in upper extremity compared to 2.35-26 in the control group. The overall reduction in Modified Ashworth score was 0.76-2 compared to 0-1 in the control group. Range of motion (ROM) increased 18.4-80° in elbow, 20.4-110° in wrist and 18.8-130° in forearm, while ROM changed -4.03°-20° in elbow, -2.08°-10° in wrist, -2.26°-20° in forearm in the control group. The improvement of FMA in lower extremity was 9 score compared to the presurgery.

Conclusion: Nerve transfer generally improves sensorimotor functions in paralyzed limbs and bladder control following CNS injury. The technique effectively creates a 'bypass' for signals and facilitates functional recovery by leveraging neural plasticity. It suggested a future of surgery, neurorehabilitation and robotic-assistants converge to improve outcomes for CNS.

Figure 1

Flowchart of primary database searching and number of publications retrieved and excluded from review. SCIs, spinal cord injuries.

Figure 2

Risk of bias assessment of included studies. The figure features histograms detailing scores across study types. (A) Per-item scores for observational cohort studies, indicating articles rated as ‘Yes’, ‘Unclear’, or ‘No’. (B) Aggregate JBI scores for observational cohort studies, with ‘Yes’ scored 1 point per item and ‘Unclear’ scored 0.5 points per item. (C-F) Case reports and series. (G) Per-item scores of Cochrane’s ROB for randomized controlled trials. (H) Per-item scores of SYECLE’s ROB tool for animal studies.

Figure 3

Nerve transfer to restore limb functions in spinal cord injuries. This schematic diagram reviews commonly used nerve transfer surgeries in spinal cord injuries. (A–C) Transfer of axillary nerve that supply the teres minor muscle to the triceps branches of the radial nerve, transfer of supinator branch to posterior interior interosseous nerve and transfer of the brachialis branch of the musculocutaneous nerve to the anterior interosseous nerve. (D) Nerve transfer surgeries for bladder controlling, including transfer of the ventral root of L5 and S1 to the ventral root of S2.

Figure 4

Nerve transfer to restore limb function in brain injury. This schematic diagram reviews commonly used nerve transfer surgeries used in this case series. (A) Contralateral C7 nerve transfer: C7 nerve of the nonparalyzed arm is directed to the C7 nerve of the paralyzed arm to restore its motor function. (B) Contralateral L5 nerve transfer: partial L5 nerve of the paralyzed lower extremity is directed to the S1 or/and S2 on the paralyzed side restore its motor function.

Figure 5

Neural plasticity-based rehabilitation techniques following nerve transfer. (A–E) ‘Point-line-plane’ strategy of noninvasive brain stimulation. (A) Modulating the activity of cortex by direct stimulation. (B) Modulating subcortical areas by stimulating cortical projection point. (C) Modulating cortical connectivity by paired cortico-cortical stimulation. (D) Modulating cortico-subcortical connectivity with one stimulation on the cortex while the other stimulating a cortical projecting point of the subcortical nucleus (E) Brain network modulation by neural oscillation (tDCS). (F) Rehabilitation with combined use of VR and robotic-assistance. (G) A BCI model with signals derived from both EEG and SMEG. BCI, brain computer interface; EEG, electroencephalograph; M1, primary motor cortex; PFC, prefrontal cortex; SMA, supplementary motor area; SMEG, surface electromyography; TMS, transcranial magnetic stimulation; tDCS, transcranial direct current stimulation; VR, virtual reality.