This study aimed to summarize evidence on peripheral nerve enlargement in patients with diabetes, with and without diabetic sensorimotor polyneuropathy (DSP), compared with healthy controls. PubMed and Embase were systematically searched for ultrasound studies measuring the cross-sectional area (CSA) of peripheral nerves in patients with diabetes with and without DSP. The primary outcome was the weighted inter-group mean difference in CSA at all reported upper- and lower extremity sites. Forty-seven studies were identified, of which 41 were included in the meta-analyses. Patients with diabetes without DSP showed significantly larger CSA values than healthy controls at 3 of 11 anatomical locations, all located in the lower extremity. Patients with diabetes and DSP demonstrated increased CSA compared with controls at 9 of 14 sites, particularly at distal compression sites of the median and tibial nerves. Compared with patients with diabetes without DSP, those with DSP had significantly larger CSA values at 14 of 21 sites, with the greatest difference observed 4-5cm proximal to the medial malleolus (pooled mean difference+5.26mm2, 95% CI 0.94-9.57). In conclusion, peripheral nerve CSA is increased in diabetes and further enlarged in the presence of DSP, with the largest effects at distal compression sites.

Intraneural ganglion cysts (IGCs) can arise in different nerves but are uncommon in the tibial nerve (TN) and its branches near the ankle. According to the unified articular theory, a joint connection is always present in IGCs. This study aimed to identify joint connections of tibial-region IGCs and characterize their clinical, radiological, and propagation patterns. A prospectively collected international database of >1100 IGCs was reviewed to identify tibial and medial plantar nerve (MPN) and lateral plantar nerve (LPN) IGCs around the ankle. Sixty-two ankle region IGCs were identified: 29 involving the TN (46.8%), 25 the MPN (40.3%), and 4 the LPN (6.4%); in 4 cases, the parent nerve was indeterminate. Thirty-one (50%) cases demonstrated joint connections. Of these, all TN at/distal to the tarsal tunnel (n = 4/4, 100%), MPN (n = 16/16, 100%) and LPN IGCs (n = 2/2, 100%) had a connection to the subtalar (ST) joint. A tibial IGC just proximal to the tarsal tunnel was connected to the tibiotalar (TT) joint in 75% of cases (n = 3/4) and the ST joint in 25% of cases (n = 1/4). Surgical ligation/disconnection of the articular branch was associated with markedly lower recurrence (0/13, 0%) compared with incision or resection of cyst without ligation (8/29, 27.6%; P = .04). Our findings support the unified articular theory. All IGCs in the ankle primarily ascend. Two distinct propagation patterns emerged: (1) those that ascend and enter the parent nerve proximal to the tarsal tunnel continue to ascend in the leg, without affecting the plantar nerves, and (2) those that ascend and enter the parent nerve at/distal to the tarsal tunnel have the potential to undergo crossover at the TN bifurcation and subsequently descend down the plantar nerves seen only in ST-origin cysts. Recognizing these pathways enhances diagnostic accuracy, directs identification of the joint of origin, and guides articular branch disconnection to reduce recurrence.

Aims Implantable tibial nerve neuromodulation (ITNM) represents a minimally invasive intervention for urgency urinary incontinence (UUI). This study evaluated the 3-year cost-utility of ITNM with an external wearable battery (Revi System) versus conservative treatments (behavioral ± pharmacotherapy) from a US payer perspective. Materials and methods A cohort state-transition (Markov) model with annual cycles compared ITNM to conservative treatment modalities (behavioral ± pharmacotherapy). ITNM clinical parameters were derived from the OASIS pivotal trial (N = 150); parameter uncertainty was propagated via 20,000 Monte Carlo simulations. Health states captured responder and non-responder status with permitted transitions, rescue interventions (onabotulinumtoxinA, sacral neuromodulation, percutaneous tibial nerve stimulation), and downstream event modules (falls, urinary tract infection, incontinence-associated dermatitis, depression, cognitive decline/dementia, and nursing-home entry). Costs and quality-adjusted life-years (QALYs) were discounted at 3% annually and expressed in 2025 US dollars. Parameter uncertainty was assessed using probabilistic sensitivity analysis (PSA; 20,000 simulations) and tornado analysis. Results ITNM was both more effective and less costly than behavioral ± pharmacotherapy. Mean 3-year costs were $39,308 versus $43,737 (ΔCost = –$4,428), with mean QALYs of 2.188 and 1.940, respectively (ΔQALY = +0.249). The incremental cost-effectiveness ratio was –$17,818/QALY (dominant). Incremental net monetary benefit at $40,000/QALY was $14,369, with 100% probability of cost-effectiveness across thresholds from $20,000–$150,000/QALY. Key value drivers were responder utility and fall-related parameters. Limitations The analysis adopts a US payer perspective with direct medical costs only. Some event risks were applied from population-level sources and may not fully capture patient-level heterogeneity. The 3-year base-case horizon may miss longer-term durability effects, though extended-horizon scenarios support consistent findings. Conclusions Over 3 years, ITNM with an external wearable battery improves quality-adjusted survival and lowers overall payer costs compared with conservative therapies for UUI, supporting its inclusion as a value-consistent minimally invasive therapy.

Tibial Nerve Stimulation: Recent Progress and Challenges.

Peripheral nerve blockade of the lower extremity focuses on two major nerves: the sciatic and femoral. Both nerves lie near large vascular structures and can require significant volumes of injectate to produce a reliable analgesic blockade. Moreover, blockade of these nerves leads to corresponding muscle weakness that can be unnecessary or even undesirable for recovery following surgery.New-generation, high-resolution ultrasound (US) probes facilitate the visualization of selective nerves in the lower extremity. Therefore, blockade of these nerves can be performed at multiple locations that can be individualized for specific patients undergoing forefoot and midfoot surgeries. This article describes an educational approach for selective lower extremity blocks of the saphenous, tibial, sural, superficial peroneal, and deep peroneal nerves with corresponding clinical applications for common forefoot and midfoot surgeries. These techniques are presented in a stepwise approach with surface and corresponding US anatomy. Cadaveric dissections are also included with some of the described techniques to emphasize the anatomical relationships. Each of these techniques, in this educational review, begins with easily identifiable surface landmarks and follows a stepwise approach.Understanding of these lower extremity selective nerve blocks allows for targeted low-volume blockade of specific sensory distributions, individualized to each patient.

To compare the onset and spontaneous recovery from rocuronium-induced neuromuscular block between the adductor pollicis (hand) and flexor hallucis brevis (foot) muscles in pediatric patients younger than two years. Patients younger than two years undergoing elective surgery under general anesthesia were enrolled. A TetraGraph electromyography monitor was applied to each of the ulnar and posterior tibial nerves to monitor train-of-four (TOF) responses of the hand and foot. Spontaneous recovery following rocuronium 0.6mg/kg was observed until the end of surgery. Endotracheal intubation was performed when a TOF count (TOFC) = 0 was observed at the foot. The primary outcome was the time from administration of rocuronium to TOFC = 1. Secondary outcomes included onset time, other recovery parameters, and intubating conditions. Data were analyzed using the paired t-test, with statistical significance set at p < 0.05. No significant differences were observed in onset and recovery times to TOFC = 1, 2, or 4; or to a TOF ratio of 0.4, between the hand and foot. Intubating conditions, including the ease of laryngoscopy, position of the vocal cords, and reaction to insertion of the endotracheal tube, were rated as excellent in all patients. In patients younger than two years, neuromuscular recovery from rocuronium did not differ between the hand and foot. This finding suggests that the foot may be a reasonable alternative site for neuromuscular monitoring and that TOFC = 0 at the foot represents an appropriate timing for endotracheal intubation.

ObjectivesTo evaluate the effects of transcutaneous tibial nerve stimulation (TTNS) associated with behavior therapy (BT) compared to BT alone in the treatment of Overactive Bladder Syndrome (OAB) in older women.Study designRandomized controlled clinical trial in two groups, G1 that received BT (n = 19) and G2 with the addition of TTNS (n = 19).Main outcome measuresThe variables analyzed were impact on quality of live (QOL) and degree of discomfort of the symptoms of OAB by International Consultation on Incontinence Questionnaire Overactive Bladder (ICIQ-OAB) and voiding habit by a 3-day voiding diary (VD). The assessments were conducted at the beginning and the end of the treatment.ResultsBoth groups showed a significant reduction in the impact of QOL by ICIQ-OAB. The G1 (BT) reduced the discomfort of nocturia symptoms and urgency urinary incontinence, while in G2 (BT+TTNS), it just did not present a reduction in the discomfort of urinary frequency by ICIQ-OAB. In the VD, despite G1 presenting an episode reduction of urgency urinary incontinence and nocturia, it showed no significant difference. In the G2, the same variables had significant reduction.ConclusionBehavioral therapy reduced OAB symptoms and discomfort in older women, but its combination with TTNS led to greater improvements, particularly in urgency and nocturia. TTNS was safe, well tolerated, and enhanced quality of life, although further studies with larger samples and longer follow-up are warranted. No adverse events or complications were observed, supporting the safety and tolerability of TTNS in older women with OAB.

Supercharge end-to-side (SETS) nerve transfer enhances motor recovery in proximal nerve injuries by providing early reinnervation. However, the optimal indications and mechanisms remain unclear. This study examined the role of donor nerves using rat models of varying injury severity to clarify the clinical indications for SETS. Eighty female Sprague–Dawley rats were assigned to five groups: Control, Mild-SETS(–), Mild-SETS(+), Severe-SETS(–), and Severe-SETS(+). The tibial nerve was transected, decellularized, and reconstructed with a 10 mm (mild) or 20 mm (severe) graft. SETS consisted of end-to-side coaptation of the donor peroneal nerve to the tibial nerve 5 mm distal to the graft. Assessments included the sciatic functional index (SFI; measured every 4 weeks), compound muscle action potentials (CMAPs), gastrocnemius weight, and immunostaining for neurofilament (NF)-positive axons and S100β-positive Schwann cells at 8 and 16 weeks. In mild models, SETS accelerated early recovery in CMAP amplitude and muscle weight without affecting long-term outcomes. In severe models, SETS showed significant increases in CMAP amplitude and muscle weight at 16 weeks. NF-positive axons and S100β-positive Schwann cells increased distal to the coaptation site at 8 and 16 weeks in mild models, whereas both distal and proximal increases were observed in severe models. Donor nerves in SETS enable early arrival of axons and Schwann cells, leading to faster motor improvement. In the long term, spontaneous recovery compensates in mild models, whereas severe models benefit from sustained donor support that promotes regeneration. SETS nerve transfer may therefore be particularly useful in selected mild cases where rapid recovery is desired, and especially in severe cases where spontaneous regeneration is insufficient.

To evaluate the relationship between the diabetic profile and human β-nerve growth factor (HβNGF), calcitonin gene-related peptide (CGRP), endothelin-1 (ET-1), and von Willebrand factor (VWF) in distinguishing painful from painless diabetic neuropathy. A case-control study. Department of Diabetic Foot, Baqai Institute of Diabetes and Endocrinology, Karachi, Pakistan, from October 2023 to August 2024. A total of 150 patients with Type I or II diabetes were recruited after IRB approval. Following informed consent, data on demographics, clinical examination, nerve conduction studies (peroneal, tibial, median, and sural nerves), and biochemical parameters (FBS, RBS, HbA1c, HβNGF, CGRP, ET-1, and VWF) were collected. Based on the NCS and DN4 questionnaire, participants were categorised into controls (no neuropathy), painless neuropathy, and painful neuropathy groups. Data were analysed using IBM SPSS version 23.0, with p <0.05 considered significant. Patients with painful neuropathy exhibited significantly lower VWF levels (p = 0.002) and higher fasting blood glucose (p = 0.01). Age, BMI, weight, and duration of diabetes differed significantly among the groups. Logistic regression identified duration of diabetes as the only independent predictor of painful neuropathy in both univariate (OR = 1.30) and multivariate analyses (OR = 1.47). FBS showed a positive correlation with diabetes duration (r = 0.188, p = 0.02). The duration of diabetes independently predicts painful diabetic neuropathy. Reduced VWF levels in patients with painful neuropathy suggest a potential role as a diagnostic biomarker. Further longitudinal studies are recommended. Diabetes mellitus, Diabetic peripheral neuropathy, β-Nerve growth factor, CGRP, Endothelin-1, von Willebrand factor.

This study investigates the relationship between National Cancer Institute Common Terminology Criteria (NCI-CTC) for grading bortezomib-induced peripheral neuropathy (BIPN) and objective motor/sensory nerve dysfunctions assessed by nerve conduction studies (NCS). It also evaluates the correlation between specific nerve conduction abnormalities and progression- free survival (PFS). Thirty-three patients with multiple myeloma developing peripheral neuropathy during bortezomib treatment were enrolled. Participants were grouped based on NCI-CTC toxicity scores (< 2, n=17; ≥ 2, n=16). Comprehensive NCS were performed, assessing compound muscle action potentials (CMAP), motor conduction velocities (MCV), sensory nerve action potentials (SNAP), and sensory conduction velocities (SCV) across ulnar, median, tibial, peroneal, sural, and superficial peroneal nerves. Correlation analyses were used to examine the association between NCS parameters and PFS. Patients with higher NCI-CTC grades (≥ 2) exhibited significant reductions in motor and sensory nerve conduction parameters. Notably, the peroneal nerve showed significant decreases in CMAP (p=0.0059) and MCV (p=0.0223). The superficial peroneal nerve displayed a significant reduction in SCV (p=0.0189). A strong positive correlation was found between median nerve SNAP and longer PFS (r=0.558, p=0.001). The findings indicate that higher clinical grades of BIPN (NCI-CTC ≥ 2) are associated with objective neurophysiological evidence of worsened nerve function, with the peroneal nerve being particularly affected. The correlation between median nerve SNAP and PFS suggests that NCS parameters could potentially serve as prognostic markers in patients with BIPN. Bortezomib-induced neurotoxicity leads to significant impairments in both motor and sensory nerve conduction. Median nerve SNAP shows promise as a predictor for PFS, underscoring the potential value of NCS in monitoring neurotoxicity and guiding clinical management in patients receiving bortezomib.

Neuromuscular ultrasound and nerve conduction studies as complementary tools for screening of diabetic peripheral neuropathy.

Current thresholds for motor conduction block on nerve conduction studies are primarily based on expert opinion and fail to consider individual patient- or nerve-specific characteristics. In this article, we aimed to improve diagnostic accuracy for identifying partial motor conduction block and determine the influence of latency difference (LD) between proximal and distal stimulation on amplitude decay in unaffected nerves. We developed the multivariate extrapolated truncated fit model to establish reference limits for amplitude decay depending on LD using existing nerve conduction studies data and compared these with existing literature values and with published thresholds for conduction block. A total of 67,266 investigations of the forearm or lower leg segments of the median, ulnar, peroneal, and tibial nerves were included. The mean multivariate extrapolated truncated fit upper limits (model +2SD) for amplitude decay in nerves with normal distal amplitude/decreased distal amplitude were: Median 14.3%/24.1%, Ulnar 17.5%/34.4%, Peroneal 27.7%/41%, and Tibial 46%/57.1%. For the four nerves, we observed 1.7% to 5.1% increases in amplitude decay per ms increase in LD. Contrary to the multivariate extrapolated truncated fit reference limits, existing thresholds for conduction block produced inconsistent positive rates between nerves with a high risk of false positive and negative results. Amplitude decay on nerve conduction studies was dependent on LD, and the multivariate extrapolated truncated fit model showed promise as a tool to create reference limits from large data sets. Reference limits adjusted for LD could improve diagnosis of inflammatory polyneuropathies and other conditions with conduction block.

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive disorder caused by variants in the CYP27A1 gene, resulting in cholestanol accumulation in various tissues, including peripheral nerves. Polyneuropathy is common but often under-recognized in CTX. This study aimed to evaluate the cross-sectional area (CSA) of peripheral nerves in CTX. Six genetically confirmed CTX patients underwent clinical, electrophysiological, and ultrasonographic evaluations. Clinical severity was assessed using the Scale for the Assessment and Rating of Ataxia (SARA) and the Polyneuropathy Disability (PND) score. Nerve ultrasound was performed at standardized sites of the median, ulnar, tibial, and sural nerves, and at the supraclavicular brachial plexus. CSA values were compared with healthy controls. Nerve conduction studies (NCS) identified demyelinating polyneuropathy in three patients. However, ultrasound showed nerve enlargement in all six, including those with normal NCS. The supraclavicular brachial plexus was enlarged in every patient. In 5 adult patients, enlargement was most consistently observed in the median nerve (4 at the wrist and forearm; 5 at the cubital fossa and upper arm), the ulnar nerve at the upper arm (5), and the fibular nerve at the fibular head (4). This study demonstrates that nerve ultrasound can detect peripheral nerve enlargement in CTX, even in preclinical stages of polyneuropathy. Enlargement of peripheral nerves may be a sensitive marker of disease severity and peripheral nerve involvement. The role of nerve ultrasound as a diagnostic tool in CTX is promising, and future longitudinal studies are needed to determine its value in disease monitoring.

In a recent article published in Cell Research, Chen et al. reported that light flickering at 40Hz effectively counteracts chronic pain in Complete Freund Adjuvant (CFA)-treated mice and in mice whose tibial and common peroneal nerves were ligated (spared nerve injury, SNI) [1]. These mice served as models for inflammatory and neuropathic pain, respectively. After establishing that 40Hz light flickering exerted analgesia in both pain models, a systematic search started for the neuronal pathways involved and the conditions required for this effect. The combination of retrograde and anterograde tracing techniques indicated that retinal ganglion cells (RGCs) project monosynaptically to the central amygdala (CeA), and chemogenetic or optogenetic activation of this pathway simulates the effects of 40Hz light stimulation. Genetic sensors for adenosine expressed in the CeA proved that such a light stimulation caused an increase in the local concentration of adenosine, via the promotion of the equilibrative adenosine transporter-mediated outflow of the nucleoside from CNS cells. The enriched adenosine levels apparently stimulated A2A receptors (Rs) as proved by the abolition of 40Hz light flickering-induced analgesia by pharmacological blockade of A2ARs, or their genetic knockdown/knockout. The target neurons in the CeA were identified as belonging to the proenkephalin-containing type; their selective ablation abolished the effect of light stimulation. Finally, two capsaicin injections, 3h apart, the second one either combined with saline or the protein synthesis inhibitor anisomycin, showed that anisomycin deleted chronic pain memory traces. Hence, 40Hz light flickering may be a non-pharmacological manipulation for alleviating chronic pain in humans, without the cardiovascular and CNS side effects inherent to systemic adenosine application.

Treatments for plantar fasciitis are often unsatisfactory. Dextrose exerts an analgesic effect through inhibiting transient receptor potential vanilloid receptor 1 (TRPV1)-mediated neuroinflammation. We reported the effectiveness of ultrasound-guided perineural tibial nerve (TN) 5% dextrose water (D5W) injection using the hydrodissection technique in treating plantar fasciitis. Two patients, a 52-year-old woman and a 60-year-old overweight man, presented with chronic left heel pain. Both had tried various treatments without sustained improvement. Ultrasound demonstrated an increase in the thickness of the plantar fascia, confirming the diagnosis of plantar fasciitis. Due to painful experience during previous intervention, they sought a less painful and more durable treatment option. We performed perineural TN ultrasound-guided D5W injection using the hydrodissection technique in two sessions, resulting in significant pain reduction and a less painful injection experience. A one-month follow-up showed sustained pain relief. Perineural TND5W injection using the hydrodissection technique appears to be an effective treatment option for plantar fasciitis.

There is limited data on the sensitivity and responsiveness of high-resolution imaging techniques in the longitudinal assessment of hereditary neuropathies. In this study, our aims were to investigate the ability of ultra-high field magnetic resonance imaging to detect longitudinal changes in the peripheral nerves of Charcot-Marie-Tooth (CMT) 1A patients, and to evaluate the potential benefits of doing so at the nerve fascicle level. We performed magnetic resonance imaging (MRI) to simultaneously obtain high-resolution anatomical and quantitative data at ultra-high 7 Tesla field strength in peripheral nerves of four patients with CMT1A disease at baseline and follow up. We compared the resulting measurements of T2 in sciatic, tibial, and fibular nerves within individual fascicles of the three nerve regions. Analyzing individual fascicle distributions, we demonstrated a significantly elevated T2 in the fibular nerve over the course of the study, with a mean increase of 3.55 ms (p = 0.01). Changes in the sciatic nerve were marginally significant (mean increase 1.42 ms, p = 0.05), and tibial nerve changes were not significant (mean increase 1.31 ms, p = 0.18). Combining fascicles across subjects showed significant changes in all three nerves over time. Our results indicate that longitudinal MRI assessment of individual nerve fascicles may serve as a quantitative biomarker of disease progression in patients with hereditary neuropathies. Further, our study demonstrates that the data provided by fascicle-level analysis may provide better analytical abilities than whole-nerve imaging.

Summary:Segmental peripheral nerve injuries, particularly those involving long nerve gaps, pose a significant challenge in reconstructive surgery. Conventional strategies, such as nerve autografts or processed allografts, are often limited by inadequate length or poor regenerative outcomes, especially in traumatized wound beds. Nerve flaps offer the theoretical advantage of enhanced axonal regeneration through improved perfusion and support of Schwann cell viability but are rarely used due to technical complexity and limited donor options. We present a unique case of a free sural nerve flap used to reconstruct a 7-cm segmental defect of the tibial nerve following blast trauma in a 23-year-old man. A composite flap consisting of the sural nerve and lesser saphenous vein was harvested with preservation of the bridging adipofascial tissue to maintain perfusion to the nerve. The lesser saphenous vein was anastomosed to the retrograde peroneal artery distally and ligated proximally, whereas the sural nerve was divided and used as a double-barrel cable graft across the defect. Intraoperative Doppler and SPY angiography confirmed perfusion of the nerve through the preserved adipofascial connections. The patient was recently seen in our clinic at 17 weeks postoperation. He demonstrated undetectable 2-point discrimination in all nerve distributions of his foot but is ambulatory. This case demonstrates the feasibility and potential utility of a free vascularized sural nerve flap for reconstructing extensive peripheral nerve defects, particularly in cases where standard techniques are inadequate.

Urinary dysfunction affects billions of individuals worldwide; however, the fundamental cellular and circuit properties that govern perineal motor control remain largely unknown, serving as a functional “black box”. Here, we describe several methods that, when used in concert, characterise cellular, synaptic, and motor unit properties underlying the control of urination in adult mice. High-density electromyography combined with real-time cystometry were used to study external urethral sphincter (EUS) motor units, which follow a hierarchical (“onion skin”) recruitment pattern during bladder filling. The transition to the voiding phase is marked by inhibition, followed by synchronised bursts. Furthermore, through concurrent recordings of ischiocavernosus (IC) muscles, the relationship between IC and EUS motor units could be studied to look for shared common inputs that could shed light on circuitry. Whole-cell patch-clamp recordings from retrogradely identified neurons revealed a fundamental biophysical divergence: urinary parasympathetic preganglionic neurons (PPGN) are significantly smaller and more excitable than somatic EUS and IC motoneurons and lack the recurrent excitatory and inhibitory circuits present in both EUS and IC motor pools. Finally, using a novel pressure-clamp preparation, we showed that acute tibial nerve stimulation (a widely used treatment for urinary dysfunction) evokes short-latency inhibition of EUS motor units. Collectively, these methods can be used to delineate patterns of motor unit recruitment, local recurrent microcircuit architecture, and distinct biophysical properties of the perineal motor system, providing mechanistic insights into urinary function.

Tarsal tunnel syndrome is an entrapment neuropathy caused by the compression of the tibial nerve and its terminal branches in the tarsal tunnel. Electrophysiological examinations are often used to diagnose tarsal tunnel syndrome. Surgical decompression of the tibial nerve is performed in patients who are resistant to conservative treatment. However, the preoperative electrophysiological findings that predict surgical outcomes remain unknown. This study aimed to clarify the preoperative electrophysiological findings that predict the surgical outcomes of tarsal tunnel syndrome. We reviewed 28 feet of 23 patients who underwent preoperative electrophysiological examinations between November 2021 and October 2024, were diagnosed with tarsal tunnel syndrome, and subsequently underwent surgery. Electrophysiological examinations included nerve conduction study and needle electromyography. We reviewed patient characteristics and electrophysiological findings prior to surgery. Sensory plantar symptoms, such as numbness and pain, were evaluated using the Numerical Rating Scale before and after surgery. Patients were divided into the improvement and non-improvement groups based on the Numerical Rating Scale improvement rate after surgery. A comparative analysis of patient characteristics and preoperative electrophysiological findings was performed between the improvement and non-improvement groups. In a motor nerve conduction study of the tibial nerve, the amplitude of the compound motor action potential evoked by stimulation at the ankle was significantly lower in the non-improvement group than in the improvement group. In tarsal tunnel syndrome, a low compound motor action potential amplitude of the tibial nerve on preoperative motor nerve conduction study may indicate poor symptomatic improvement after surgery. Electrophysiological examinations may be useful for predicting the surgical outcomes of tarsal tunnel syndrome.

Background/Objectives: The popliteus muscle (PM) plays a crucial role in stabilizing the posterolateral aspect of the knee. However, its layered structure and innervation are not well understood due to its location, size, and proximity to neighboring anatomical features. This study aimed to clarify the layered morphology, intramuscular innervation, and fiber-type composition of the PM, providing anatomical insights for clinical interventions. Methods: We examined 32 lower extremities from sixteen formalin-embalmed cadavers using a multimodal approach that included gross dissection, Sihler's staining, ultrasonography, and histochemical analysis. Results: On average, 2.8 ± 1.1 branches of the tibial nerve entered the PM, with a consistently high-density entry zone located at 56-64% of the muscle length. Sihler's staining and ultrasonographic analyses revealed a distinct separation between the superficial and deep layers across the central tendon, each exhibiting compartmentalized intramuscular branching territories. The superficial layer was primarily composed of type IIx fibers and exhibited a larger pennation angle, while the deep layer was richer in type IIA fibers with a smaller pennation angle. These findings illustrate that the PM functions as a dual motor unit rather than a uniform structure. Conclusions: The PM exhibits a distinct compartmentalized organization, functioning as a multifunctional motor unit. The identification of specific intramuscular entry zones and the organization of muscle layers provide strong anatomical evidence for improved targeting in neuromuscular-modulating interventions. This enhances the precision, safety, and efficacy of clinical strategies aimed at addressing posterior knee stability and pathologies related to the posterolateral complex (PLC).