Rehabilitation strategies for abdominal wall reinnervation after intercostal nerve injury: A narrative review

Introduction

The abdominal wall is a complex, multilayered structure that provides mechanical stability and supports essential bodily functions. It is composed of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transversus abdominis (TrA), which act in combination with the fascia, connective tissue, and diaphragm to form a dynamic cylinder facilitating trunk stability, movement, and intra-abdominal pressure regulation.^1–4 In addition to enabling trunk flexion, rotation, and stabilization, it contributes to respiration, defecation, micturition, parturition, and protection of intra-abdominal organs.

Anatomy and physiology of the abdominal wall

The abdominal wall comprises four paired muscle groups—the RA, EO, IO, and TrA—each contributing to posture, movement, respiration, and intra-abdominal pressure regulation. The RA, oriented vertically, facilitates trunk flexion and assists in generating intra-abdominal pressure. The EO, running inferomedially, and the IO, oriented superomedially, coordinate rotational movements and lateral flexion. The TrA, the deepest of the abdominal muscles, acts as a stabilizing corset, providing segmental spinal support and playing a central role in regulating intra-abdominal pressure.

The abdominal wall musculature receives motor innervation from the ventral rami of ICNs T7-T12, which travel between the IO and TrA and supply the RA and provides cutaneous sensation, with additional contributions from the iliohypogastric and ilioinguinal nerves (L1).^2–4 Because this innervation is segmental, injury to a single ICN can cause localized muscle weakness, whereas multilevel injury can lead to broader impairments in trunk stability and respiratory function. Understanding this segmental distribution is critical for identifying patterns of weakness or dysfunction after ICN injury and guiding targeted rehabilitation.

From a respiratory function standpoint, the abdominal wall is critical during forced expiration, coughing, and sneezing as it generates intra-abdominal pressure to aid ventilation. It contributes significantly to ventilation, expiratory flow, and airway clearance. Recent anatomic studies have demonstrated that ICNs 7, 8, and 9 provide branches directly to the diaphragm. ² Consequently, abdominal wall dysfunction resulting from ICN injury can impair not only motor performance but also pulmonary health.

Due to the widespread roles and effect of the abdominal wall across multiple physiological domains, including but not limited to motor control and respiration, even partial denervation can result in profound impairment. Therefore, effective rehabilitation following an ICN injury must adopt a broad approach that addresses these diverse functions of the abdominal wall.

Consequences of an ICN injury

An ICN injury results in segmental denervation of the abdominal wall musculature, producing marked structural, functional, and quality of life consequences. Clinically, this manifests as asymmetric abdominal wall contouring, pseudohernia, visible bulging, weakness with trunk flexion and rotation, impaired coordination, and reduced postural stability, which may contribute to compensatory thoracic and/or lumbar spine pain and challenges in lifting, balance, and gait. Functional impairments also extend to activities requiring effective intra-abdominal pressure generation, including coughing, defecation, urination, and heavy lifting, with downstream respiratory and functional implications. In addition, visible deformity and chronic discomfort may lead to psychosocial distress, reduced activity participation, and diminished quality of life. These deficits can be quantified using objective imaging, electrodiagnostic, and functional assessments, which are described in detail below in the Functional Testing and Objective Outcome Measures section.

Functional testing and objective outcome measures

Objective assessment of abdominal wall function is crucial for both clinical care and research. Imaging modalities such as ultrasound can assess the muscle thickness of the TrA, IO, and EO at rest and during contraction. Reliability studies have demonstrated strong intra- and inter-rater agreements, confirming the robustness of ultrasound for longitudinal monitoring.^36,37 Panoramic imaging allows large field-of-view assessment of the RA, whereas elastography quantifies stiffness and contractile properties. Elastography, particularly shear wave elastography, has been shown to detect alterations in muscle stiffness that correlate with histologic, magnetic resonance imaging (MRI), and functional markers of muscle atrophy across experimental models, inflammatory myopathies, sarcopenia, and neuromuscular disease, supporting its role as a noninvasive tool for assessing muscle degeneration.^38–40

Electrodiagnostic studies provide complementary data. Needle EMG can identify increased spontaneous activity that confirm denervation, and the appearance of polyphasic motor units signals reinnervation. Electrodiagnostic testing of the ICNs in the setting of rib fractures has demonstrated reliability and utility in diagnosing and localizing lesions. ⁸

In the clinical setting, functional tests can capture outcomes relevant to patients. The timed leg-lowering task, in which a patient lowers their extended legs while in the supine position, maintaining posterior pelvic tilt, is sensitive to anterior abdominal wall endurance and control. ⁴¹ Core endurance tasks, such as plank holds, provide additional benchmarks. ⁴² Critically, cough peak flow provides a quantifiable respiratory outcome that reflects the combined contribution of abdominal and thoracic musculature. ⁴³ Clinically, these measures may be collected at baseline and reassessed periodically (early reinnervation and strengthening phases) to guide progression, with imaging and electrodiagnostic tools supporting the detection of reinnervation and functional tests reflecting meaningful clinical change.

Neuroplasticity and guided relearning

Cortical plasticity plays a central role in recovery after peripheral nerve injury. In the absence of input, cortical motor representations of denervated muscles shrink, limiting voluntary recruitment. Targeted interventions can maintain and even expand these representations, priming the brain to recruit newly reinnervated muscle fibers.

Mirror therapy provides visual feedback of movement on the unaffected side, engaging mirror neuron networks and strengthening cortical activation of the injured side. Motor imagery, in which patients mentally rehearse abdominal contractions, and action observation, in which they watch demonstrations of abdominal exercises, also stimulate motor networks without physical contraction. Biofeedback, using surface EMG or real-time ultrasound imaging, offers external confirmation of muscle activity, reinforcing voluntary recruitment once reinnervation begins. Early integration of these strategies primes the nervous system and enhances subsequent strengthening and functional reintegration.

Respiratory integration

The relationship between respiratory function and abdominal wall mechanics warrants focused discussion. The abdominal wall is essential for ventilation and airway clearance, working in concert with the diaphragm to regulate intra-abdominal pressure and optimize respiratory mechanics. During forced expiration, abdominal wall contraction compresses the abdominal cavity, elevates intra-abdominal pressure, and drives the diaphragm upward, thereby enhancing expiratory flow. Abdominal wall tension and the rapid generation of these pressures are essential for ventilatory mechanics, including an effective cough and airway clearance.^1,44,45

ICN injury is associated with clinically significant respiratory consequences due to impaired abdominal wall recruitment. ⁸ Resulting expiratory weakness diminishes cough efficacy and forced expiration, compromising airway clearance and increasing the risk of secretion retention, recurrent infections, atelectasis, and pneumonia. These risks are amplified in patients with concomitant pulmonary disease, spinal cord injury (SCI), or neuromuscular disorders, where baseline cough strength is already limited; in such populations, even minor deficits can lead to chronic morbidity and necessitate hospitalization.

Therefore, rehabilitation should directly address expiratory function. Inspiratory and expiratory muscle training with threshold devices has been shown to improve maximal inspiratory and expiratory pressures, enhance lung volumes, and increase cough effectiveness in patients with neuromuscular disease. Cough training through voluntary practice, manual assistance, or resisted expiration, is central in enhancing airway clearance, consistent with broader guidelines of respiratory management in patients with neuromuscular weakness.^6,46 This strategy reinforces abdominal wall activation in a functional context, whereas abdominal weight training further promotes muscle activation. These respiratory-focused strategies not only preserve pulmonary health but also provide task-specific training that accelerates the integration of reinnervated abdominal muscles. ⁴⁷

Phased rehabilitation strategy

Rehabilitation after a peripheral nerve injury is commonly conceptualized as a phased process aligned with the stages of reinnervation and functional recovery. Due to the limited literature specifically addressing abdominal wall reinnervation after ICN repair, the framework proposed below is derived primarily from principles established in peripheral nerve rehabilitation, respiratory rehabilitation, neuroplasticity research, and expert clinical opinion. Accordingly, this phased model should be interpreted as a conceptual rehabilitation framework intended to guide clinical decision making and future investigation rather than as a validated protocol (Table 1). Nevertheless, the integration of motor retraining, respiratory mechanics, and neuroplasticity-driven interventions may provide a useful structure for potentially optimizing functional reintegration of reinnervated abdominal musculature.

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Table 1.

Proposed phased rehabilitation framework following intercostal nerve repair or reconstruction.

Phase	Timeline	Primary goals	Example interventions	Proposed outcome measures
Phase 1: early postoperative/pre-reinnervation	0–6 weeks	Protect repair, preserve mobility, optimize respiration, and prevent maladaptive compensation	Diaphragmatic breathing, incentive spirometry, postural training, and gentle trunk mobility	Baseline ultrasound, EMG, and respiratory measures
Phase 2: early reinnervation	6 weeks to 6 months	Facilitate cortical recruitment and early activation	Motor imagery, mirror therapy, ultrasound biofeedback, and low-intensity activation exercises	Ultrasound muscle activation and EMG evidence of reinnervation
Phase 3: functional strengthening	6–18 months	Improve strength, endurance, and respiratory integration	Progressive trunk stabilization, resisted exhalation, cough retraining, and leg-lowering tasks	Functional core testing, cough peak flow, and endurance testing
Phase 4: return to function	>18 months	Restore dynamic function and task-specific performance	Advanced core exercises, lifting, gait stabilization, and sport/work-specific training	Functional testing, respiratory endurance, imaging, and EMG as indicated

EMG: electromyography.

Knowledge gaps and future directions

Despite the clinical importance of abdominal wall reinnervation, significant knowledge gaps remain. Much of the available literature consists of case reports, small case series, extrapolation from extremity peripheral nerve rehabilitation, and studies focused primarily on imaging, electrodiagnostic testing or surgical outcomes rather rehabilitation-specific interventions or functional recovery trajectories. Significant heterogeneity exists across patient populations, injury mechanisms, surgical techniques, timing of intervention, and outcome measures, limiting comparison across studies and preventing the development of evidence-based rehabilitation guidelines. Furthermore, prospective controlled investigations evaluating rehabilitation-specific interventions following ICN repair are currently lacking.

Combining ultrasound, electrodiagnostic testing, timed leg-lowering, and cough peak flow could standardize assessment and improve comparability across studies.^50–54 Future research should employ multicenter prospective trials, given the relative rarity of these cases, and use structured rehabilitation protocols with standardized outcome measures. Randomized studies are particularly needed to evaluate phased rehabilitation strategies, integration of neuroplasticity-driven interventions, and the role of respiratory muscle training. Systematic integration of these approaches will be essential for building an evidence base capable of informing consensus guidelines and standardizing care.

Conclusion

ICN injury with abdominal wall denervation represents a unique and often overlooked neuromuscular challenge that disrupts both motor stability and respiratory mechanics. Although surgical repair may restore the potential for reinnervation, rehabilitation strategies specific to abdominal wall recovery remain poorly defined. Existing evidence derived from peripheral nerve rehabilitation, respiratory muscle training, and neuroplasticity research suggests that a phased and integrated rehabilitation approach facilitates recovery; however, direct evidence supporting these interventions in abdominal wall reinnervation remains limited.

Accordingly, the rehabilitation framework proposed in this review should be considered a conceptual model intended to guide clinical reasoning and future research rather than an established evidence-based protocol. Prospective multicenter studies using standardized functional, imaging, electrodiagnostic, and respiratory outcome measures are needed to validate rehabilitation strategies and establish consensus guidelines for this underrecognized patient population.