Cadaveric study of anatomical variations of the median nerve and persistent median artery at wrist

Anatomical considerations of US-guided carpal tunnel release in daily clinical practice

Carpal tunnel syndrome is the most frequent compression neuropathy with an incidence of one to three subjects per thousand. As specific anatomical variations might lead to unintended damage during surgical interventions, we present a review to elucidate the anatomical variability of the carpal tunnel region with important considerations for daily clinical practice: several variants of the median nerve branches in and around the transverse carpal ligament are typical and must - similarly to the variant courses of the median artery, which may be found eccentric ulnar to the median nerve - be taken into account in any interventional therapy at the carpal tunnel. Unintended interference in these structures might lead to heavy arterial bleeding and, in consequence, even underperfusion of segments of the median nerve or, if neural structures such as variant nerve branches are impaired or even cut, severe pain-syndromes with a profound impact on the quality of life. This knowledge is thus crucial for outcome- and safety-optimization of different surgical procedures at the volar aspect of the wrist and surgical therapy of the carpal tunnel syndrome e.g., US-guided carpal tunnel release, as injury might result in dysfunction and/or pain on wrist motion or direct impact in the region concerned. For most variations, anatomical and surgical descriptions vary, as official classifications are still lacking.

Pilot Cadaveric Study of Anatomical Variations of the Median Nerve at the Wrist in the Lithuanian Population

INTRODUCTION

 Carpal tunnel syndrome (CTS) is known as one of the most common neurological disorders in the human body. Nowadays, the prevalence in the general population ranges between 1% and 5%. Due to its high prevalence and increasing incidence of carpal tunnel surgery, the anatomical variations of the median nerve at the wrist are important to know to avoid iatrogenic injury of the nerve.

PURPOSE

The objective of this study was to evaluate the anatomical variation of the median nerve at the level of the wrist in the Lithuanian population with a focus on its thenar motor branch based on the classifications of Lanz.

MATERIAL AND METHODS

A cadaveric study was performed, and 30 wrists of 15 adult Lithuanian cadavers ranging from 70 to 89 years of age were dissected and examined. Eight female and seven male cadavers were included in the study. Any anatomical finding was documented, and the results were compared with the classification of Lanz as well as with the data found in the literature.

RESULTS

All hands showed different patterns in comparison to the standard anatomical variation Lanz type 0. The most common result was dedicated to Lanz group 4A. Nineteen out of 30 hands (63%, p<0.01) had an accessory branch proximal to the carpal tunnel, while one of these hands showed a third thenar motor branch. Five hands (16%) were dedicated to Lanz group 2 with an accessory branch distal to the carpal tunnel. One hand (3%) showed a variation close to Lanz group 2, but in this case, the thenar motor branch had its origin under the flexor retinaculum instead of proximal to it. Two hands each (6%) were classified by Lanz groups 1B and 3A. Additionally, one variation showed a pattern of a combination of Lanz types 3A and 3B. The bifid median nerve had a connecting branch in between which started distal to the flexor retinaculum. Two anatomical variations (6%) were not described by the classification of Lanz.

Anatomical Variations of the Median Nerve: A Cadaveric Study

Objectives: Variations in the morphological anatomy of the median nerve such as formation, distribution, and communication have been well documented. All these variations should be taken into account when practicing any surgical approach for the treatment of injuries affecting the median nerve. Furthermore, they are of the utmost importance for interpretation of the clinical presentation. Methods: The objective of this investigation was to determine the anatomical variations in the formation of the median nerve in cadavers at the Forensic Pathology department in Central Clinical Hospital of the Academy of Sciences of the Russian Federation between January 2022 and April 2022. A descriptive, cross-sectional, and prospective information source study was conducted on 42 anatomical bodies (corpses) and 84 brachial plexuses. Results: After analyzing the results obtained in this investigation, we concluded that the median nerve presented variation in its formation in 22.6% of the investigated cases. These variations were more common in males (81.8%) than females (18.2%). The anatomical variation was unilateral in 7.1% and bilateral in 19% of all anatomical bodies examined. Conclusions: The median nerve presented a great number of variations in its formation in roughly 23% of the anatomical bodies, with male being the predominant gender. Furthermore, the most frequent region of formation was the axillary region (92.9%). For clinicians, it is important to remember these variations during surgical procedures in this area and during brachial plexus block.

Bifid median nerve as an anatomical risk factor for carpal tunnel syndrome: A meta-analysis

As the median nerve enters the carpal tunnel, it is a single nerve that soon bifurcates into lateral and medial branches into the hand. If the bifurcation is proximal to the carpel tunnel, a bifid median nerve results. Carpal tunnel syndrome is often associated with a bifid median nerve with or without a persistent median artery. Individual keywords and MeSH phrases were searched in the Google Scholar, SCOPUS, and PubMed databases. Full texts were then collected and assessed for suitability. The prevalence of bifid median nerve at the wrist joint in normal and carpal tunnel syndrome wrists (pre-canal part) and the mean difference between groups were recorded. Only human data were used to test the findings. The pooled odds ratio (with minimal heterogeneity) was 1.50 [1.17-1.93, 95% CI]. The bifid median nerve cross-sectional area (CSA) was significantly greater than that of a solitary median nerve in normal wrists. The mean difference in CSA between the two was 1.50 mm² [0.56-2.45 mm² , 95% CI] without heterogeneity (i²  = 0). Sex and laterality distributions scarcely differed between the two types of wrists. Owing to the insufficiency of data, the relationships with mean height and weight were not examined. There was a 50% greater incidence of bifid median nerves in carpal tunnel syndrome patients than in normal subjects. A bifid median nerve increases the mean CSA at the wrist joint by 1.5 mm² . These findings indicate that the bifid median nerve is an anatomical risk factor for carpal tunnel syndrome. This article is protected by copyright. All rights reserved.

The persistent median artery and its vascular patterns: A meta-analysis of 10,394 subjects

The presence of a persistent median artery (PMA) has been implicated in the development of compression neuropathies and surgical complications. Due to the large variability in the prevalence of the PMA and its subtypes in the literature, more awareness of its anatomy is needed. The aim of our meta-analysis was to find the pooled prevalence of the antebrachial and palmar persistent median arteries. An extensive search through the major databases was performed to identify all articles and references matching our inclusion criteria. The extracted data included methods of investigation, prevalence of the PMA, anatomical subtype (antebrachial, palmar), side, sex, laterality, and ethnicity. A total of 64 studies (n = 10,394 hands) were included in this meta-analysis. An antebrachial pattern was revealed to be more prevalent than a palmar pattern (34.0% vs. 8.6%). A palmar PMA was reported in 2.6% of patients undergoing surgery for carpal tunnel syndrome when compared to cadaveric studies of adult patients in which the prevalence was 8.6%. Both patterns of PMA are prevalent in a considerable portion of the general population. As the estimated prevalence of the PMA was found to be significantly lower in patients undergoing surgery for carpal tunnel syndrome than those reported in cadaveric studies, its etiological contribution to carpal tunnel syndrome is questionable. Surgeons operating on the forearm and carpal tunnel should understand the anatomy and surgical implications of the PMA and its anatomical patterns.

High Division of the Median Nerve with Unusually High Origin of the 3rd Space Common Digital Nerve

BACKGROUND

Median nerve (MN) variation in the carpal tunnel has been well documented by Lanz. Encountering rarely documented variants, that do not fit into existing classifications, increases the risk of iatrogenic injury.

METHODS

The random occurrence of two unclassifiable anatomical variants of the MN in the carpal tunnel gives motivation to search the literature for similar and identical cases.

CASE REPORTS

This article presents two cases of very rare anatomical variants of high division of the MN. First case is a pure high branching of the 3rd space common digital nerve (CDN). The second case is a high division of the MN to a thicker lateral component and a thinner medial component. The lateral component of the MN gives off the palmar cutaneous branch (PCB), the thenar motor branch (TMB), the 1^st and 2^nd space CDN's and contributes medially with a branch to the 3^rd space CDN. The medial component of the MN bifurcates distally into a medial and lateral branch. The lateral branch from the medial component of the MN distally unites with the medial branch of the lateral component of the MN to form the 3^rd space CDN. The medial branch from the medial component of the MN has a major contribution to the 4^th space CDN from the ulnar nerve. In both cases, the medial component of the MN has a transmuscular course through the flexor digitorum superficialis (FDS) muscle.

DISCUSSION

Finding similar case reports from worldwide suggests the need to improve current classification of the MN variants in the carpal tunnel.

CONCLUSIONS

One cannot rely entirely on the existing anatomical classifications of the MN in the carpal tunnel. There is an underappreciated risk of iatrogenic injury, especially in endoscopic carpal tunnel release, and a chance of missing out on repair of important anatomical structures in trauma cases. There is a possibility of augmenting group 3 of Lanz's classification by adding subgroup "3D High division of the MN with the medial component having a transmuscular course through the FDS muscle", stating the different distal branching patterns.

Upper limb principal arteries variations: A cadaveric study with terminological implication

Although the variability of the upper limb arteries is a clinically important problem, the prevalence is varying across the existing studies and classification is rather complicated, not well established and sometimes even unclear for simple and direct understanding and usage. Multiple case reports appearing in the last years apply incorrect, inappropriate, and sometimes misleading terminology. We performed an anatomical cadaveric study of the variability of the arteries of the upper limb, namely, the axilla, arm, and forearm, in 423 upper limbs embalmed with classical formaldehyde method (Central European population). We proposed to apply the Equality system based on the common trunks for denomination of the axillary artery branches principal variations: Truncus subscapulocircumflexus (22.9%), truncus profundocircumflexus (13.75%), and truncus bicircumflexus (13.95%). Further, we proposed the terminology system developed by Rodríguez-Niedenführ et al. for the free upper limb principal arterial trunk variations based on the origin, location (in the arm only, or in the arm and forearm), and course (related to the forearm flexor muscles) of the involved artery: Arteria brachialis superficialis (9.5%), arteria brachioradialis superficialis (6.4%), arteria brachioulnaris superficialis (1.9%), arteria brachiomediana superficialis (0.5%), and arteria comitans nervi mediani manus (3.3%). Extensive development of the catheterization methods via the arteria radialis et ulnaris as well as surgical procedures using flaps based on perforating branches of these arteries (including arteria brachioradialis superficialis et brachioulnaris superficialis) necessitate thorough data on prevalence of the variant vessels for safe performance of these procedures to prevent any unexpected situations or to react adequately in such.

Recently increased prevalence of the human median artery of the forearm: A microevolutionary change

The median artery has been considered as an embryonic structure, which normally regresses around the 8th week of gestation. However, various prevalences have been reported in adults since the 18th century. Furthermore, in a study by Henneberg and George (1995; Am J Phys Anthropol 96, 329-334), has suggested that increasing prevalence of the median artery during the 20th century was a 'possible secular trend'. The present study, conducted nearly a quarter of a century later, is a continuation of that study. A total of 26 median arteries were found in 78 upper limbs obtained from Australians aged 51 to 101 years, who died in the period 2015-2016, a prevalence rate of 33.3%. Analysis of the literature showed that the presence of the median artery has been significantly increasing (p = .001) over time, from approximately 10% in people born in the mid-1880s to approximately 30% by the end of the 20th century. The significance of the prevalence increased to a p value <.0001, when the results of the present study and other studies conducted by our research team were combined. After removal of the studies that were possibly biased, because of their specific focus on the evolutionary aspects of the median artery, the significance remained at p = .018. The present study provides an example of microevolutionary changes in the internal anatomy of the human body. Second-order polynomial regression of the median artery's prevalence on dates of birth shows that it is now present in 35% of people and predicts that people born 80 years from now will all carry a median artery if the trend continues. When the median artery prevalence reaches 50% or more, it should not be considered as a variant, but as a 'normal' human structure.

Ultrasound imaging of the thenar motor branch of the median nerve: a cadaveric study

INTRODUCTION

Anatomic variations of the median nerve (MN) increase the risk of iatrogenic injury during carpal tunnel release surgery. We investigated whether high-frequency ultrasonography could identify anatomic variations of the MN and its thenar motor branch (MBMN) in the carpal tunnel.

METHODS

For each volar wrist of healthy non-embalmed cadavers, the type of MN variant (Lanz classification), course and orientation of the MBMN, and presence of hypertrophic muscles were scored by 18-MHz ultrasound and then by dissection.

RESULT

MBMN was identified by ultrasound in all 30 wrists (15 subjects). By dissection, type 1, 2 and 3 variants were found in 84%, 3%, and 13% of wrists, respectively. Ultrasound had good agreement with dissection in identifying the variant type (kappa =0.9). With both techniques, extra-, sub-, and transligamentous courses were recorded in 65%, 31%, and 4% of cases, respectively. With both techniques, the bifid nerve, hypertrophic muscles, and bilateral symmetry for variant type were identified in 13.3%, 13.3%, and 86.7% of wrists, respectively. Agreement between ultrasound and dissection was excellent for the MBMN course and orientation (kappa =1).

CONCLUSION

Ultrasound can be used reliably to identify anatomic variations of the MN and MBMN. It could be a useful tool before carpal tunnel release surgery.

KEY POINTS

• Ultrasound can identify variations of the motor branch of the median nerve. • Ultrasound mapping should be used prior to carpal tunnel release surgery. • All sub-, extra-, and transligamentous courses were accurately identified. • Type 3 variants (bifid nerve), hypertrophic muscles, and bilateral symmetry were accurately identified.

The Prevalence of Anatomical Variations of the Median Nerve in the Carpal Tunnel: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVE

The course and branches of the median nerve (MN) in the wrist vary widely among the population. Due to significant differences in the reported prevalence of such variations, extensive knowledge on the anatomy of the MN is essential to avoid iatrogenic nerve injury. Our aim was to determine the prevalence rates of anatomical variations of the MN in the carpal tunnel and the most common course patterns and variations in its thenar motor branch (TMB).

STUDY DESIGN

A systematic search of all major databases was performed to identify articles that studied the prevalence of MN variations in the carpal tunnel and the TMB. No date or language restrictions were set. Extracted data was classified according to Lanz's classification system: variations in the course of the single TMB--extraligamentous, subligamentous, and transligamentous (type 1); accessory branches of the MN at the distal carpal tunnel (type 2); high division of the MN (type 3); and the MN and its accessory branches proximal to the carpal tunnel (type 4). Pooled prevalence rates were calculated using MetaXL 2.0.

RESULTS

Thirty-one studies (n = 3918 hands) were included in the meta-analysis. The pooled prevalence rates of the extraligamentous, subligamentous, and transligamentous courses were 75.2% (95%CI:55.4%-84.7%), 13.5% (95%CI:3.6%-25.7%), and 11.3% (95%CI:2.4%-23.0%), respectively. The prevalence of Lanz group 2, 3, and 4 were 4.6% (95%CI:1.6%-9.1%), 2.6% (95%CI:0.1%-2.8%), and 2.3% (95%CI:0.3%-5.6%), respectively. Ulnar side of branching of the TMB was found in 2.1% (95%CI:0.9%-3.6%) of hands. The prevalence of hypertrophic thenar muscles over the transverse carpal ligament was 18.2% (95%CI:6.8%-33.0%). A transligamentous course of the TMB was more commonly found in hands with hypertrophic thenar muscles (23.4%, 95%CI:5.0%-43.4%) compared to those without hypertrophic musculature (1.7%, 95%CI:0%-100%). In four studies (n = 423 hands), identical bilateral course of the TMB was found in 72.3% (95%CI:58.4%-84.4%) of patients.

CONCLUSIONS

Anatomical variations in the course of the TMB and the MN in the carpal tunnel are common in the population. Thus, we recommend an ulnar side approach to carpal tunnel release, with a careful layer by layer dissection, to avoid iatrogenic damage to the TMB.