Sonographic Visualization of Thenar Motor Branch of the Median Nerve: A Cadaveric Validation Study

Sonography of the Thenar Motor Branch of the Median Nerve: A Pictorial Review

The thenar motor branch (TMB) of the median nerve exhibits significant anatomical variability, making it particularly vulnerable to iatrogenic injury during procedures such as carpal tunnel surgery. Understanding the diverse courses and origins of the TMB is critical for minimizing surgical complications. Such knowledge not only aids in preoperative planning but also enhances the accuracy of nerve conduction tests, contributing to improved postoperative outcomes. The ability to visualize and assess the TMB using imaging modalities like ultrasound represents a significant advancement in diagnostic and surgical preparation. Ultrasound is an accessible, cost-effective, and dynamic imaging technique that allows for real-time evaluation of neural structures. It provides detailed visualization of the TMB and its anatomical variations, offering valuable information that can guide surgical approaches and reduce the risk of injury to this vital branch. This article aims to provide a comprehensive overview of the anatomy, anatomical variants, and clinical significance of the TMB, with a particular focus on its assessment via ultrasound. Using high-resolution imaging, we demonstrate the application of ultrasound to identify the TMB in various configurations. Notably, the Lanz classification of the TMB is illustrated with ultrasound images, some of which, to our knowledge, are being presented for the first time. By integrating anatomical knowledge with advanced imaging techniques, this work emphasizes the importance of precise TMB evaluation, paving the way for safer surgical practices and enhanced patient outcomes.

Ultrasound of the Median Nerve: A Pictorial Review. Normal Ultrasound Findings and Variations

This is the first of a two-part article in which we focus on the Ultrasound (US) appearance of the normal median nerve (MN) and its main branches. The detailed anatomy and US anatomy of the MN course are presented with high-resolution images obtained with the latest-generation US machines and transducers. Variations are discussed to avoid misinterpretation of normal findings.

Predicting thenar motor branch anatomy for a safer carpal tunnel release

PURPOSE

Anatomic variations of the thenar motor branch of the median nerve (TMB) that place the nerve more ulnarly in the palm can increase the risk for iatrogenic injury to the nerve during carpal tunnel release. This study examines the prevalence of an origin of the TMB that is more ulnar than its typical branching from the radial aspect of the median nerve and explores whether the appearance of the palmar intrinsic muscles at surgery can predict an unusual TMB origin prior to visualizing the TMB itself.

METHODS

A prospective study of patients undergoing carpal tunnel release surgery was undertaken to document the take-off point of the TMB along the circumference of the median nerve and the presence or absence of intrinsic muscle obscuring the distal transverse carpal ligament.

RESULTS

Forty-one hands were evaluated. Eleven (26.8 %) demonstrated transverse carpal muscle. The most common origin of the TMB was from the radial aspect of the median nerve (56.1 %). In approximately 20 % of nerves, the TMB originated near its anterior midline. There was a statistically significant relationship between the TMB originating more ulnarly and the presence of transverse carpal muscle.

CONCLUSIONS

This study introduces a new classification system for further defining anatomic variations of the TMB. When transverse carpal muscle is absent, the TMB is highly likely to arise from the radial aspect of the median nerve. In the presence of transverse carpal muscle, the origin of the TMB is unpredictable and is significantly more likely to arise from the median nerve more ulnarly than is typically seen. Under these circumstances, attempts should be made to identify the TMB prior to completing ligament division.

Fluorescence imaging of peripheral nerve function and structure

Peripheral nerve injuries are common and can cause catastrophic consequences. Although peripheral nerves have notable regenerative capacity, full functional recovery is often challenging due to a number of factors, including age, the type of injury, and delayed healing, resulting in chronic disorders that cause lifelong miseries and significant financial burdens. Fluorescence imaging, among the various techniques, may be the key to overcome these restrictions and improve the prognosis because of its feasibility and dynamic real-time imaging. Intraoperative dynamic fluorescence imaging allows the visualization of the morphological structure of the nerve so that surgeons can reduce the incidence of medically induced injury. Axoplasmic transport-based neuroimaging allows the visualization of the internal transport function of the nerve, facilitating early, objective, and accurate assessment of the degree of regenerative repair, allowing early intervention in patients with poor recovery, thereby improving prognosis. This review briefly discusses peripheral nerve fluorescent dyes that have been reported or could potentially be employed, with a focus on their role in visualizing the nerve's function and anatomy.

Nerve entrapment syndromes: detection by ultrasound

Nerve entrapment syndromes are commonly encountered in clinical practice. Accurate diagnosis and management require a knowledge of peripheral neuroanatomy and the recognition of key clinical symptoms and findings. Nerve entrapment syndromes are frequently associated with structural abnormalities of the affected nerve. Therefore, imaging allows the evaluation of the cause, severity, and etiology of the entrapment. High-resolution ultrasonography can depict early and chronic morphological changes within the entire nerve course and is therefore an ideal modality for diagnosing various nerve entrapment syndromes in different regions. This review article presents some of the most common types of nerve entrapment, with special focus on ultrasound imaging and key findings.

Ultrasound Imaging and Guidance for Distal Peripheral Nerve Pathologies at the Wrist/Hand

Ultrasound has emerged as a highly valuable tool in imaging peripheral nerve lesions in the wrist region, particularly for common pathologies such as carpal tunnel and Guyon's canal syndromes. Extensive research has demonstrated nerve swelling proximal to the entrapment site, an unclear border, and flattening as features of nerve entrapments. However, there is a dearth of information regarding small or terminal nerves in the wrist and hand. This article aims to bridge this knowledge gap by providing a comprehensive overview concerning scanning techniques, pathology, and guided-injection methods for those nerve entrapments. The median nerve (main trunk, palmar cutaneous branch, and recurrent motor branch), ulnar nerve (main trunk, superficial branch, deep branch, palmar ulnar cutaneous branch, and dorsal ulnar cutaneous branch), superficial radial nerve, posterior interosseous nerve, palmar common/proper digital nerves, and dorsal common/proper digital nerves are elaborated in this review. A series of ultrasound images are used to illustrate these techniques in detail. Finally, sonographic findings complement electrodiagnostic studies, providing better insight into understanding the whole clinical scenario, while ultrasound-guided interventions are safe and effective for treating relevant nerve pathologies.

Comparison efficacy of ultrasound-guided needle release plus corticosteroid injection and mini-open surgery in patients with carpal tunnel syndrome

This retrospective study was to compare clinical outcomes of ultrasound-guided needle release with corticosteroid injection vs. mini-open surgery in patients with carpal tunnel syndrome (CTS). From January 2021 to December 2021, 40 patients (40 wrists) with CTS were analyzed in this study. The diagnosis was based on clinical symptoms, electrophysiological imaging, and ultrasound imaging. A total of 20 wrists were treated with ultrasound-guided needle release plus corticosteroid injection (Group A), and the other 20 wrists were treated with mini-open surgery (Group B). We evaluated the Boston carpal tunnel questionnaire, electrophysiological parameters (distal motor latency, sensory conduction velocity, and sensory nerve action potential of the median nerve), and ultrasound parameters (cross-sectional area, flattening ratio, and the thicknesses of transverse carpal ligament) both before and 3 months after treatment. Total treatment cost, duration of treatment, healing time, and complications were also recorded for the two groups. The Boston carpal tunnel questionnaire and electrophysiological and ultrasound outcomes at preoperatively and 3 months postoperatively had a significant difference for each group (each with P < 0.05). There were no complications such as infection, hemorrhage, vascular, nerve, or tendon injuries in both groups. Ultrasound-guided needle release and mini-open surgery are both effective measures in treating CTS patients. Ultrasound-guided needle release plus corticosteroid injection provides smaller incision, less cost, less time of treatment, and faster recovery compared with mini-open surgery. Ultrasound-guided needle release plus corticosteroid injection is better for clinical application.

High-resolution sonographic study of the communicating branch of Berrettini: an anatomical feasibility study

Sensory changes are common manifestations of nerve complications of carpal tunnel surgery. Division or contusion of a superficial communicating branch between the median nerve and the ulnar nerve, the communicating branch of Berrettini, can explain these symptoms. The aim of this study was to describe the potential value of high-resolution sonography to examine this branch. We conducted a study on eight fresh cadaver hands. An ultrasound assessment of the communicating branch of Berrettini, accompanied by an injection of methylene blue, was performed by a senior radiologist. Subsequent dissections confirmed that the eight guided ultrasound injections allowed the methylene blue to be placed around the origin and termination of the communicating branch of Berrettini. This study extends the limits of ultrasound both in the postoperative diagnosis of potential nerve complications and its possible use in ultrasound-guided carpal tunnel release.

"Million dollar nerve" magnetic resonance neurography: first normal and pathological findings

OBJECTIVES

To evaluate prospectively the feasibility of magnetic resonance neurography (MRN) in identifying the anatomical characteristics of thenar muscular branch (TMB) of the median nerve, also known as the "million dollar nerve," in patients and controls.

METHODS

Thirteen patients affected by carpal tunnel syndrome (CTS) and four healthy controls had their hands scanned on a 3-T MR imaging scanner for TMB visualization. Median nerve anatomical variations were classified into four groups according to Poisel's classification system modified by Lanz. TMB signal intensity and diameter were assessed for the diagnosis of neuropathy.

RESULTS

TMB was successfully identified in all patients and subjects by using MRN. The most suitable pulse sequences to identify and measure nerve diameter were 3D DW-PSIF and T2-FS-TSE. The axial oblique and sagittal oblique planes are complementary in demonstrating its entire course. TMB had mostly an extraligamentous course with radial side origin (93.8%, each). All patients experienced increased T2 signal intensity (p < 0.001) and thickened nerves. Mean TMB diameters were 1.27 ± 0.21 mm (range, 1.02-1.74 mm) and 0.87 ± 0.16 mm (0.73-1.08 mm) (p = 0.008) in the patient and control groups, respectively.

CONCLUSION

MRN is a reliable imaging technique for identification and anatomical characterization of TMB in patients affected by CTS. This innovative imaging workup may therefore be included in the preoperative evaluation of patients scheduled for carpal tunnel release, especially in CTS with TMB involvement or even in isolated TMB neuropathy.

KEY POINTS

• Magnetic resonance neurography allows precise visualization of the thenar muscular branch of the median nerve. • Thenar muscular branch anatomical variations can be correctly identified. • Preoperative scanning can contribute to reducing the risk of iatrogenic injuries during carpal tunnel release, especially in carpal tunnel syndrome with thenar muscular branch involvement or even in isolated thenar muscular branch neuropathy.

Five Wrist Operations That Give the Best Results

LEARNING OBJECTIVES

After reading this article and viewing the videos, the participant should be able to: 1. Recognize the following five wrist operations as consistent options for different wrist injuries: carpal tunnel release, medial femoral condyle bone flap for scaphoid nonunion associated with carpal collapse and avascular necrosis, scaphocapitate arthrodesis for Kienböck disease, percutaneous screw fixation of nondisplaced scaphoid fracture, and four-corner arthrodesis. 2. Know the state-of-the-art of these five procedures. 3. State the indications of each operation. 4. List the surgical steps of these five procedures.

SUMMARY

The wrist is a complex joint that concentrates different types of tissues (e.g., bone, cartilage, ligaments, nerves, vessels) and a broad different spectrum of diseases. Treatment of wrist injuries has improved during recent years, mainly because of improvement in strategy, techniques, microsurgical equipment, understanding anatomy and improvements in technology. In this article, we present the five operations (i.e., carpal tunnel release, medial femoral condyle bone flap for scaphoid nonunion associated with carpal collapse and avascular necrosis, scaphocapitate arthrodesis for Kienböck disease, percutaneous screw fixation of nondisplaced scaphoid fracture, and four-corner arthrodesis) that have consistently given good outcomes in patients suffering from different wrist injuries/maladies.

Clinical Results of Ultrasound-Guided Carpal Tunnel Release Performed by a Primary Care Sports Medicine Physician

OBJECTIVES

The purpose of this study was to determine the safety and efficacy of ultrasound-guided carpal tunnel release (USCTR) in a consecutive group of patients treated by a single primary care sports medicine physician.

METHODS

The study group consisted of 35 USCTRs performed on 22 consecutive patients for whom clinical outcomes were available before USCTR and at 1 to 2 weeks, 1 month, and 3 months after USCTR. All procedures were performed by the same operator using a single USCTR technique. Outcomes included complications, Quick Disabilities of the Arm, Shoulder, and Hand scores, Boston Carpal Tunnel Questionnaire symptom severity and functional status scores, and a 5-point global satisfaction score.

RESULTS

The 22 patients included 13 female and 9 male patients (ages 31-82 years). Eleven patients (22 wrists) had bilateral simultaneous USCTRs; 2 patients (4 wrists) had staged bilateral USCTRs; and 9 patients had unilateral USCTRs. No complications occurred in any patient. Statistically and clinically significant reductions in Quick Disabilities of the Arm, Shoulder, and Hand scores and Boston Carpal Tunnel Questionnaire symptom severity and functional status scores occurred by 1 to 2 weeks after USCTR (mean 1- to 2-week changes, -29.23, -1.74, and -1.18, respectively), and further improvements occurred during the 3-month follow-up period (mean 3-month changes, -51.11, -2.29, and -1.91; P < .0001 for all values versus before USCTR). Mean global satisfaction scores at 1 to 2 weeks and 3 months were 4.63 and 4.66.

CONCLUSIONS

Ultrasound-guided CTR is a safe and effective procedure that can be performed by an experienced primary care sports medicine physician and typically results in significant improvements within the first 2 weeks after the procedure. Furthermore, bilateral simultaneous USCTRs are feasible and may provide significant advantages for patients who are candidates for bilateral CTRs.

Fluorescence Imaging of Nerves During Surgery

OBJECTIVE

This review details the agents for fluorescence-guided nerve imaging in both preclinical and clinical use to identify factors important in selecting nerve-specific fluorescent agents for surgical procedures.

BACKGROUND

Iatrogenic nerve injury remains a significant cause of morbidity in patients undergoing surgical procedures. Current real-time identification of nerves during surgery involves neurophysiologic nerve stimulation, which has practical limitations. Intraoperative fluorescence-guided imaging provides a complimentary means of differentiating tissue types and pathology. Recent advances in fluorescence-guided nerve imaging have shown promise, but the ideal agent remains elusive.

METHODS

In February 2018, PubMed was searched for articles investigating peripheral nerve fluorescence. Key terms used in this search include: "intraoperative, nerve, fluorescence, peripheral nerve, visualization, near infrared, and myelin." Limits were set to exclude articles exclusively dealing with central nervous system targets or written in languages other than English. References were cross-checked for articles not otherwise identified.

RESULTS

Of the nonspecific agents, tracers that rely on axonal transport showed the greatest tissue specificity; however, neurovascular dyes already enjoy wide clinical use. Fluorophores specific to nerve moieties result in excellent nerve to background ratios. Although noteworthy findings on tissue specificity, toxicity, and route of administration specific to each fluorescent agent were reported, significant data objectively quantifying nerve-specific fluorescence and toxicity are lacking.

CONCLUSIONS

Fluorescence-based nerve enhancement has advanced rapidly over the past 10 years with potential for continued utilization and progression in translational research. An ideal agent would be easily administered perioperatively, would not cross the blood-brain barrier, and would fluoresce in the near-infrared spectrum. Agents administered systemically that target nerve-specific moieties have shown the greatest promise. Based on the heterogeneity of published studies and methods for reporting outcomes, it appears that the development of an optimal nerve imaging agent remains challenging.

Ultrasound Imaging of Disorders of Small Nerves of the Extremities: Less Recognized Locations

Ultrasound is a well-proven imaging modality for showing peripheral nerve disorders and guiding perineural injections. The aim of this review is to focus on small peripheral nerve abnormalities, which are usually not recognized by sonologists. In fact, most of these small nerves have a tiny diameter (<2 mm), and their anatomy is less familiar. We describe the most common causes of small peripheral nerve disorders, providing an accurate description of their anatomic locations and relationships with adjacent structures; we also focus on technical hints that may help in their evaluation.

Ultrasound-Guided Surgery for Carpal Tunnel Syndrome: A New Interventional Procedure

Carpal tunnel syndrome (CTS) may be treated surgically if medical treatment fails. The classical approach involves release of the flexor retinaculum by endoscopic or open surgery. Meta-analyses have shown that the risk of nerve injury may be higher with endoscopic treatment. The recent contribution of ultrasound to the diagnosis and therapeutic management of CTS opens new perspectives. Ultrasound-guided carpal tunnel release via a minimally invasive approach enables the whole operation to be performed as a percutaneous radiological procedure. The advantages are a smaller incision compared with classical techniques; great safety during the procedure by visualization of anatomic structures, particularly variations in the median nerve; and realization of the procedure under local anesthesia. These advantages lead to a reduction in postsurgical sequelae and more rapid resumption of daily activities and work. Dressings are removed by the third day postsurgery. Recent studies seem to confirm the medical, economic, and aesthetic benefits of this new approach.

Minimally Invasive Ultrasound-Guided Carpal Tunnel Release: Preliminary Clinical Results

Ultrasound-guided carpal tunnel release was performed on 14 patients (18 wrists) using dynamic expansion of the transverse safe zone. Our patient population included able-bodied patients and those with impairments. The first 8 cases (12 wrists) underwent the procedure in an operating room, the remainder in an outpatient setting. No complications occurred, and all patients were able to immediately resume use of their hands without therapy. Improvements in the Quick Form of the Disabilities of the Arm, Shoulder, and Hand Index and Boston Carpal Tunnel Questionnaire at 3 months were comparable to results reported with mini-open and endoscopic release. Our results show that ultrasound-guided carpal tunnel release can be safely and effectively performed in an outpatient setting.

Indications for neuromuscular ultrasound: Expert opinion and review of the literature

Over the last two decades, dozens of applications have emerged for ultrasonography in neuromuscular disorders. We wanted to measure its impact on practice in laboratories where the technique is in frequent use. After identifying experts in neuromuscular ultrasound and electrodiagnosis, we assessed their use of ultrasonography for different indications and their expectations for its future evolution. We then identified the earliest papers to provide convincing evidence of the utility of ultrasound for particular indications and analyzed the relationship of their date of publication with expert usage. We found that experts use ultrasonography often for inflammatory, hereditary, traumatic, compressive and neoplastic neuropathies, and somewhat less often for neuronopathies and myopathies. Usage significantly correlated with the timing of key publications in the field. We review these findings and the extensive evidence supporting the value of neuromuscular ultrasound. Advancement of the field of clinical neurophysiology depends on widespread translation of these findings.

Anatomic Relationship Between the Hook of the Hamate and the Distal Transverse Carpal Ligament: Implications for Ultrasound-Guided Carpal Tunnel Release

OBJECTIVE

During ultrasound-guided carpal tunnel release, osseous landmarks may supplement direct visualization of the distal transverse carpal ligament (dTCL) to ensure a complete release. The purpose of this study was to determine the relationship between the apex of the hook of the hamate (aHH) and the dTCL within the transverse safe zone (TSZ) of the carpal tunnel.

DESIGN

Twenty unembalmed cadaveric specimens were dissected to determine the aHH-dTCL distance and the aHH-SPA distance (the distance between the aHH and the superficial palmar arch) at the ulnar and radial limits of the TSZ (the distance between the hook of the hamate or ulnar artery to the median nerve).

RESULTS

The aHH-dTCL distance averaged 11-12 mm across the TSZ (maximum, 18.2 mm), whereas the aHH-SPA distance was significantly greater on the radial side of the TSZ compared with the ulnar side (22.6 ± 3.6 mm vs. 14.0 ± 4.0 mm).

CONCLUSIONS

The dTCL lies approximately 11-12 mm distal to the aHH across the TSZ, with an upper limit of 18.2 mm. Along with direct sonographic visualization of the dTCL, the aHH can be used with other osseous landmarks to estimate the position of the dTCL during ultrasound-guided carpal tunnel release.