Frequency, anatomical properties and innervation of axillary arch and its relation to the brachial plexus in human fetuses

Anatomical Variations of the Axillary Arch and Implications in Breast Surgery

INTRODUCTION

Langer's axillary arch (AA), the most common anatomical variant in the axillary area of definite clinical significance. This is an updated review of the reported variations in the structure, highlighting its morphological diversity and its potential in complicating axillary lymph node biopsy, lymphadenectomy, or breast reconstruction.

METHODS

A review of the literature concerning the AA published between 1812 and 2020 was performed using the PubMed, Scopus, Embase, and Cochrane medical databases. The frequency, laterality, morphology, origin, lateral attachment points, vascularization, and neurosis of the AA were the parameters retrieved from the collected data.

RESULTS

The prevalence of AA ranged from 0.8% to 37.5%. It is more often unilateral, muscular in nature, and extending from the latissimus dorsi to the pectoralis major. It is vascularized by the lateral thoracic vessels or the subscapular artery and innervated by the thoracodorsal nerve.

CONCLUSIONS

Langer's AA, when present, may complicate surgical procedures in the area; therefore, every surgeon performing breast or axillary surgery should be aware of this entity and its variations to ensure maximal effectiveness and safety in the management of patients.

Risk factors for neonatal brachial plexus palsy attributed to anatomy, physiology, and evolution

The inherent variable anatomy of the neonate and the uniquely-shaped maternal birth canal that is associated with the evolution of human bipedalism constitute risk factors for neonatal brachial plexus palsy (NBPP). For example, those neonates with a prefixed brachial plexus (BP) are at greater risk of trauma due to lateral neck traction during delivery than those with a normal or postfixed BP. Compared to adults, neonates also have extremely large and heavy heads (high head: body ratio) set upon necks with muscles and ligaments that are weak and poorly developed. Accordingly, insufficient cranial stability can place large torques on the cervical spinal nerves. In addition, the pelvic changes necessary for habitual bipedal posture resulted in a uniquely-shaped, obstruction-filled, sinusoidal birth canal, requiring the human fetus to complete a complicated series of rotations to successfully traverse it. Furthermore, although there are many risk factors that are known to contribute to NBPP, the specific anatomy and physiology of the neonate, except for macrosomia, is not considered to be one of them. In fact, currently, the amount of lateral traction applied to the neck during delivery is the overwhelming legal factor that is used to evaluate whether a birth attendant is liable in cases of permanent NBPP. Here, we suggest that the specific anatomy and physiology of the neonate and mother, which are clearly not within the control of the birth attendant, should also be considered when assessing liability in cases of NBPP.

A meta-analysis on the anatomical variability of the brachial plexus: Part I - Roots, trunks, divisions and cords

INTRODUCTION

The brachial plexus is a complex anatomical structure that gives rise to all the nerves of the upper limb. Its variability is frequently observed and represents a challenge for interventions in the lower neck and axilla. The aim of this study was to present a comprehensive and evidence-based review with meta-analytic techniques on the variability of roots, trunks, divisions and cords of the brachial plexus.

MATERIALS AND METHODS

Major medical databases were searched to identify all anatomical studies investigating the variability in the formation of the brachial plexus. Data extracted consisted of demographic information, morphometric parameters, the arrangement of the brachial plexus at the level of the roots, trunks, divisions and cords and the relationship of the brachial plexus to the axillary artery and scalene muscles. The different configurations of the brachial plexus were put into a new classification, and the pooled prevalence of each case was calculated using a random effects model. A sub-analysis on age and geographical location was also performed.

RESULTS

A total of 40 studies (3055 upper limbs) were included in the meta-analysis. The regular arrangement of roots forming trunks was identified in 84% (95% CI 79-89%) of cases. The overall prevalence of the prefixed and postfixed brachial plexus was 11% (95% CI 6-17%) and 1% (95% CI 0-1%), respectively and in less than 0.1% of cases the brachial plexus received a branch from both C4 and T2. For divisions forming cords, the regular arrangement was observed in 96% (95% CI 93-98%) of cases. Additional communicating branches between the components of the brachial plexus appeared in 5% (95% CI 3-7%) of cases. The relationship of the brachial plexus to the axillary artery and scalene muscles was considered regular in 96% (95% CI 89-100%) and 86% (95% CI 66-98%) of cases, respectively. Analysis of the morphometric parameters revealed the proportional consistency between the components forming the plexus during aging.

CONCLUSIONS

Knowledge of anatomical variations of the brachial plexus is important for examinations and interventions in the lower neck and axilla. The variability was observed especially in the roots forming trunks, while divisions forming cords showed quite stable appearance. The results of this evidence-based review and meta-analysis can be applied in many different medical disciplines.

Arco axilar de Langer: serie de casos y revisión de la literatura

Introducción. El arco de Langer es una entidad infrecuente, cuya prevalencia depende de la técnica quirúrgica utilizada y usualmente no se asocia con síntomas de compresión vascular o neuronal. El objetivo de este estudio fue describir las características clínicas y morfológicas, y la proporción de síntomas de compresión neurovascular del arco de Langer, en mujeres con cáncer de mama llevadas a cirugía axilar. Métodos. Estudio descriptivo del arco de Langer en mujeres con cáncer de mama, llevadas a cirugía axilar en el registro personal de un cirujano, en Medellín, Colombia, entre el 1 enero de 2017 y el 15 agosto de 2020. Se evaluaron características clínicas, morfológicas y síntomas de compresión neurovascular. Las variables categóricas se agruparon según su frecuencia como porcentajes, y para las variables continuas se calculó la mediana y su rango intercuartílico. Resultados. Entre el 1 enero de 2017 y el 15 agosto de 2020 se realizaron 725 cirugías axilares, 479 biopsias de ganglio centinela y 246 linfadenectomías, encontrando 17 casos de arco de Langer, para una frecuencia de 2,3 %. Fue más frecuente encontrarlo en el curso de una linfadenectomía (n=11, 64,7 %). En 15 (88,2 %) casos se presentó riesgo de ocultamiento ganglionar y en 14 (82,3 %) generó dificultad quirúrgica. No hubo casos con síntomas de compresión vascular o neuronal. En ningún caso se realizó el diagnostico imagenológico prequirúrgico. La conducta quirúrgica predominante fue sección, en 88,2 %, sin presentar complicaciones quirúrgicas asociadas. Discusión. Es importante para el cirujano el conocimiento del arco axilar como una variante anatómica de la axila, que puede ocultar los ganglios o dificultar la disección axilar, por lo que la conducta más usada es la sección.

Variations of the musculofascial axillary arch with the adjacent lymph nodes

PURPOSE

This unique case gives the extent of knowledge in the axilla area with axillary arch (AA) and a discussion of its clinical importance.

MATERIALS AND METHOD

The anatomical anomaly was found during the dissection class for the brachial plexus. It was identified through the precise dissection of the structures bilaterally.

RESULTS

The cadaver had fascial and muscular AA bilaterally. The fascial AA was separated into the superficial and deep arch group. The superficial arch group connected to the clavipectoral fascia and the axillary fascia. The deep arch group attached to the subscapular fascia. The muscular AA had superficial and deep variations. The superficial muscular AA attached between accessory slip of latissimus dorsi muscle (LDa) and pectoralis quartus muscle (PQ). The deep muscular AA attached to the crest of lesser tubercle of the humerus from LDa. The adipose tissue with the level one central lymph node was located lateral to the pectoralis minor muscle expand from pectoral lymph node through between LDa and PQ.

CONCLUSION

This case showed the fascial and muscular AA together. The muscular AA had both complete and incomplete attachment types. It could give functional and neurological problems in the axilla, such as thoracic outlet syndrome. Additionally, the structures presented with the axillary lymph node. It helps to understand the patient's condition with the AA in the axilla and could provide.

Anatomic and histological analyses of chiasma plantare and long flexor tendons of the foot on human fetuses

PURPOSE

The aim of present study was to reveal slip transfers related to flexor hallucis longus (FHL) and flexor digitorum longus (FDL) by dissection and to investigate detailed structure of chiasma plantare composed of FHL-FDL tendons and quadratus plantae (QP), with precise composition of the long flexor tendons of lesser toes by histological sections in human fetuses.

METHOD

Slip transfers related to FHL and FDL tendons were identified and the related morphometric measurements were taken with dissection in 28 formalin-fixed fetuses (25-40 weeks). Composition and restoration of chiasma plantare and long flexor tendons of lesser toes were traced histological by analyzing movements of the tissues on the sequential coronal sections in five fetuses in the third trimester. The numbers of layers constituting chiasma plantare and the muscles that formed layers were specified. Each of two to five flexor tendons arising from the chiasma plantare was analyzed regarding its formation and contribution of FHL slip.

RESULTS

Slip transfers were found as FHL slip in 86% and cross-connections in 14%. The ratios of the slip width to that of FHL and FDL tendons were found higher than in adult literature. Variance in the involvement of slip to FDL and QP, formation and layering of chiasma plantare and formation of long flexor tendons from chiasma plantare were revealed and great similarities were found with data from dissection of adult in literature.

CONCLUSION

Slip transfers between FHL and FDL tendons, and layering properties of chiasma plantare were largely finalized during intrauterine period, while structural changes in slip seem to continue in the later stages of life, possibly by the effects of growth and usage of the extremity. In addition to individual variations, investigating the contribution of FHL slip, FDL and QP to long flexor tendons by different methods in literature is also suggested to be responsible for some diversities of our histological study.

The innervation of the axillary arch determined by surface stimulodetection electromyography

The axillary arch (AA) is a muscular anatomical variation in the fossa axillaris that has been extensively studied in cadaveric specimens. Within these dissections, different innervations of the AA have been proposed, but this has never been explored in vivo. Knowledge of the innervation of the AA is required in order to better understand its function (e.g. predisposition for certain sports and/or activities, understanding shoulder injuries in overhead sports). Here, we report on the use of surface stimulodetection electromyography (SSEMG) to resolve the innervation of the AA in 20 subjects (12 women, eight men - mean age of 21.3 ± 2.7 years) with a uni- or bilateral AA. SSEMG of each muscle [M. latissimus dorsi (MLD) and M. pectoralis major] was performed with a four-channel electrostimulation measuring system in order to determine the innervation of the AA. The results showed co-contraction of the MLD in 85% of the subjects after AA stimulation. In the remaining subjects, no specific localized response was observed due to non-specific nerve stimulation, inherent to the proximity of the brachial plexus in these individuals. Our findings demonstrate that SSEMG exploration offers a practical and reliable tool for investigating anatomical aspects of muscle innervation in vivo. Using this approach, we conclude that the AA receives the same innervation as the MLD (the N. thoracodorsalis), and may be considered a muscular extension of the latter.