Innervation of the human sternoclavicular joint.

The sternoclavicular joint (SCJ) functions as the basal joint of the entire upper limb and must move in the proper pattern for normal scapular motion. Afferent sensations from joints, such as proprioception and pain sensation, are important for maintaining the proper motion and condition of joints. Detailed anatomical data are useful for discussing injuries or surgeries that impair the afferent nerve to the SCJ. Nerve branches to SCJs were examined on 12 sides, and the subclavian nerve was investigated on six sides to clarify whether it innervates this joint. On seven of the 12 sides, the SCJ was innervated by two nerves, (1) a branch from the medial supraclavicular nerve that ran medially along the clavicle and (2) a branch from the lateral pectoral nerve that innervated the clavicular head and upper part of the sternocostal head of the pectoralis major. This branch ran medially behind the clavicular head of the pectoralis major and reached the SCJ. In the remaining five sides, the SCJ was innervated solely by the branch from the medial supraclavicular nerve. Subclavian nerves ended within the subclavius muscle or periosteum of the clavicle and were separate from the SCJs. Our data on the route of nerve branches to the SCJ suggest that injury or surgery, such as clavicle fracture or resection of the clavicular head of the pectoralis major for myocutaneous flap transfer, can impair the SCJ's afferent nerve supply.

Morphological differences between the dorsal and palmar septa of the first extensor compartment in relation to the brachioradialis and pronator quadratus.

BACKGROUND: The first extensor compartment of the wrist is known as a frequent site of stenosing tenosynovitis, referred to as de Quervain's disease. De Quervain's disease occurs more frequently in the dorsal part of the first extensor compartment than in the palmar part; however, the anatomical reason why the dorsal part is worse remains poorly elucidated. This study clarified the morphological differences between the dorsal and palmar parts by examining their relationship with the surrounding structures. METHODS: In this study, a total of 35 wrists from 23 Japanese cadavers were used. Twenty-five wrists were randomly assigned for macroscopic analysis, and the remaining 10 wrists were used for histological analysis. RESULTS: The palmar septum of the first extensor compartment was connected to the brachioradialis tendon and superficial head of the pronator quadratus and was histologically stout compared to the dorsal septum. Despite several anatomical variations, such as the septum between the abductor pollicis longus/extensor pollicis brevis and the multiple tendons of these muscles, the aforementioned characteristics of the fibrous sheath in the first extensor compartment were identical in all specimens. CONCLUSION: In contrast to the fragile structure of the dorsal septum, the stout structure of the palmar septum could be related to the low occurrence of symptoms of de Quervain's disease. The present results could play a role in revealing the pathogeny and establish the precise treatment for de Quervain's disease and provide an anatomical basis for kinesiological/biomechanical studies.

Muscle-tendon arrangement and intramuscular nerve distribution of flexor digitorum superficialis in the siamang (Symphalangus syndactylus), western lowland gorilla (Gorilla gorilla gorilla), western chimpanzee (Pan troglodytes verus), and Japanese macaque (Macaca fuscata).

Flexor digitorum superficialis (FDS) shows diverse muscle-tendon arrangements among primates. The intramuscular nerve distribution pattern is a criterion for discussing the homology of FDS. In this study, the muscle-tendon arrangement and intramuscular nerve distribution of FDS were examined in the siamang, western lowland gorilla, western chimpanzee, and Japanese macaques. The FDS had muscle bellies to digits II-V. FDS had proximal belly and intermediate tendon except for siamang. Distal belly to digit II (in the western lowland gorilla and western chimpanzees) or distal bellies to digits II and V (in Japanese macaque) originated from the intermediate tendon. In all specimens, nerve branches within digit III belly extended into digit IV belly, and nerve branch(es) within digit IV belly extended into digit V belly. This consistent pattern suggested that each muscle belly to digits III-V is interspecifically homologous. The digit II belly in the siamang and the distal belly to digit II in the western lowland gorilla, western chimpanzees, and Japanese macaques could be homologous based on their similar innervating patterns. The proximal belly was innervated by branches from the communicating nerve between median and ulnar nerves in the western lowland gorilla or branches from median and ulnar nerves in western chimpanzees. In the siamang and Japanese macaque, the whole FDS was innervated by median nerve. The proximal belly in the western lowland gorilla, western chimpanzees, and Japanese macaques could be classified into different groups from the other part of the FDS.

Comparison of the soleus and plantaris muscles in humans and other primates: Macroscopic neuromuscular anatomy and evolutionary significance.

In humans, the soleus is more developed compared to other primates and has a unique architecture composed of anterior bipennate and posterior unipennate parts, which are innervated by different nerve branches. The anterior part of the human soleus was proposed to be important for bipedalism, however, the phylogenetic process resulting in its acquisition remains unclear. Providing insights into this process, the anterior part of the soleus was suggested to be closely related to the plantaris based on the branching pattern of their nerve fascicles. To reveal the phylogeny of the soleus and plantaris in primates, the innervation patterns of the posterior crural muscles were compared among a wide range of species. From their branching pattern, posterior crural muscles could be classified into superficial and deep muscle groups. The anterior part of the soleus and plantaris both belonged to the deep muscle group. In all the examined specimens of ring-tailed lemurs and chimpanzees, as well as in one out of two specimens of siamang, the nerve branches corresponding to those innervating the anterior part of the human soleus were found. The muscular branches innervating the anterior part of the soleus and plantaris formed a common trunk or were connected in all the specimens. These results indicate that the anterior part of the soleus is closely related to the plantaris across different species of primates. In turn, this suggests that the anterior part of the soleus is maintained among primates, and especially in humans, where it develops as the characteristic bipennate structure.

The ulnar nerve is surrounded by the tendon expansion of the flexor carpi ulnaris muscle at the wrist: an anatomical study of Guyon's canal.

The ulnar tunnel (Guyon's canal) is an osseofibrous tunnel for the ulnar nerve and artery. With regard to the proximal palmar wall (palmar carpal ligament) of the ulnar tunnel, detailed anatomical data such as attachment sites, fibrous continuity to surroundings, and variations have not been clearly described. In this study, topology of Guyon's canal was examined, especially to the palmar side of the ulnar nerve, focusing on the continuity of tendinous structures to reveal a more detailed constitution of Guyon's canal. The palmar wall of Guyon's canal was investigated in 113 forearms of 57 cadavers. The dorsal wall of the canal was also investigated in 25 subjects. The ulnar nerve passed lateral to the pisiform and the flexor carpi ulnaris tendon. At the level of the pisiform, except for one, the ulnar nerve passed dorsal to the aponeurosis expanding from the flexor carpi ulnaris tendon and the periosteum of the pisiform, and this aponeurosis laterally merged with the palmar aspect of the flexor retinaculum. Moreover, the ulnar nerve ran palmar to the pisohamate ligament and the flexor retinaculum extended from the same tendon. The present study suggests that the aponeurosis of palmar side to the ulnar nerve connected with the flexor carpi ulnaris tendon, the periosteum of the pisiform, and the palmar surface of the flexor retinaculum. These findings indicate that the ulnar nerve is surrounded by the aponeurotic portion expanding from the flexor carpi ulnaris tendon at the wrist, which is a new insight of Guyon's canal.

Muscle-tendon arrangement and innervation pattern of the m. flexor digitorum superficialis in the common marmoset (Callithrix jacchus), squirrel monkey (Saimiri sciureus) and spider monkey (Ateles sp.).

The muscle-tendon arrangement of the m. flexor digitorum superficialis (FDS) varies among different primate groups. Recent developmental investigations revealed that the primordium of FDS emerges in the hand region first and relocates to the forearm later. The relationship between the diverse muscle-tendon arrangement and the characteristic developmental process of FDS is important for understanding the evolutionary changes of the FDS. Moreover, the innervation pattern cannot go unremarked when discussing the muscle homology and evolution. We examined the muscle-tendon arrangement and intramuscular nerve distribution of the FDS in three genera of Platyrrhini: three common marmosets (Callithrix jacchus), two squirrel monkeys (Saimiri sciureus) and two spider monkeys (Ateles sp.). We observed that the FDS consisted of multiple muscle bellies. The origin of the muscle bellies to digits II and V varied, whereas muscle bellies to digits III and IV consistently originated from the medial epicondyle. The muscle-tendon arrangement of the FDS differed among the three genera owing to the different origins of muscle bellies to digits II and V. In all the examined specimens, the muscle bellies to digits II and/or III were innervated by the direct nerve branches from the median nerve. However, the muscle bellies to digits IV and V never received direct nerve branches from the median nerve. Nerve branches within the belly to digit III extended into the belly to digit IV, and one nerve branch within the belly to digit IV extended into the belly to digit V. These consistent nerve distribution patterns suggest that different patterns of FDS muscle-tendon arrangement have changed from that of a common ancestral condition. It is plausible that the diverse origins of muscle bellies in the FDS are attributable to the difference in the destination for the relocation of the muscle bellies during developmental processes.

Constant existence of the sensory branch of the nerve to the pyramidalis distributing to the upper margin of the pubic ramus.

Twenty-one sides of 11 adult Japanese cadavers were investigated, and 2 of 21 sides exhibited absence of the pyramidalis. We observed that all of the nerves to the pyramidalis included the sensory nerve branch, which distributed to the aponeurotic tissue in the upper area of the pubic ramus. To investigate the clinical relevance and developmental process of the pyramidalis, detailed innervation patterns of the pyramidalis and the lumber plexus were examined and compared with the case of absent pyramidalis. The nerves to the pyramidalis could be classified into five types by the derivative nerves and two subtypes by their courses associated with the funiculus spermaticus. In the cases of absent pyramidalis, similar sensory branches distributed close to the upper area of the pubic ramus. We deduced that the sensory branch extended along with the muscular branch to the pyramidalis after development of the pyramidalis and that only the sensory branch remained in cases in which the pyramidalis disappeared. The two subtypes might associate with descensus testis. Surgeons performing inguinal hernia repair using a mesh and tension-free surgical technique should preserve the nerves around the funiculus spermaticus to avoid diminished proprioception in the lower abdominal wall.

Anatomical Study of the Brachial Plexus in the Common Marmoset (Callithrix Jacchus).

To elucidate the forelimb phylogeny of primates, anatomical analysis of the brachial plexus in platyrrhines is beneficial. In the present study, six brachial plexuses and the surrounding arteries of four common marmosets were dissected. In five specimens, the brachial plexus consisted of five ventral rami from the fifth cervical nerve (C5) to the first thoracic nerve (T1). In one specimen, the ventral ramus of the fourth cervical nerve joined with the brachial plexus. In five specimens, the upper trunk was composed of C5 and the sixth cervical nerve (C6). In one specimen, the ventral division of C6 merged with the ventral branch of the middle trunk to constitute the lateral cord. The seventh cervical nerve constituted the middle trunk, and the eighth cervical nerve and T1 formed the lower trunk in all specimens. The lateral cord gave rise to the musculocutaneous nerve, and the remaining component merged with the medial cord. The confluence of the lateral and medial cords immediately bifurcated into the median and ulnar nerves. These branching patterns of the musculocutaneous, median, and ulnar nerves were consistent and similar to the human counterparts. In the dorsal division, the single posterior cord as observed in the human brachial plexus was not observed. The axillary artery did not pass between the medial and lateral roots of the median nerve, and the axillary artery bifurcated into the brachial artery and the superficial brachial artery. Anat Rec, 300:1299-1306, 2017. © 2017 Wiley Periodicals, Inc.

Anatomical observations of the human acromioclavicular joint.

The condition of the acromioclavicular joint (ACJ) is considered to be one factor in the etiology of shoulder impingement syndrome, but there are few supporting morphological data. Fifty-two sides of 35 cadavers were investigated macroscopically and histologically using Safranin O, Fast green, and Weigert's iron hematoxylin staining. The ACJs were classified into three major types depending on the presence or absence of the articular disk. In type 1, the articular disk divided the articular cavity completely (n = 2; 3.8%). In type 2, the articular disk was incomplete and divided the joint cavity incompletely (n = 13; 25%). Type 2 was further divided into subtypes 2a and 2b depending on the configurations of the articular facets. In type 3, no articular disk was found in the joint cavity (n = 37; 71.2%). Type 3 was further divided into subtypes 3a, 3b, and 3c depending on the configurations of the articular surfaces. Fewer than half of the ACJ specimens (22/52 or 42.3%) demonstrated an ellipsoid character in which axial rotation was limited. Histological observation revealed that the upper part of the articular disk of the ACJ comprised fibrocartilage while the lower part comprised dense connective tissue. In cases where the ACJ appears to be an ellipsoid joint, its limited axial rotation restricts posterior tilting of the scapula during arm elevation, which could contribute to shoulder impingement syndrome.

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes osteoclastogenesis via induction of and interaction with dendritic cell-specific transmembrane protein (DC-STAMP).

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes endochondral ossification. However, the role of CCN2 in the replacement of hypertrophic cartilage with bone is still unclear. The phenotype of Ccn2 null mice, having an expanded hypertrophic zone, indicates that the resorption of the cartilage extracellular matrix is impaired therein. Therefore, we analyzed the role of CCN2 in osteoclastogenesis because cartilage extracellular matrix is resorbed mainly by osteoclasts during endochondral ossification. Expression of the Ccn2 gene was upregulated in mouse macrophage cell line RAW264.7 on day 6 after treatment of glutathione S transferase (GST) fusion mouse receptor activator of NF-κB ligand (GST-RANKL), and a combination of recombinant CCN2 (rCCN2) and GST-RANKL significantly enhanced tartrate-resistant acid phosphatase (TRACP)-positive multinucleated cell formation compared with GST-RANKL alone. Therefore, we suspected the involvement of CCN2 in cell-cell fusion during osteoclastogenesis. To clarify the mechanism, we performed real-time PCR analysis of gene expression, coimmunoprecipitation analysis, and solid-phase binding assay of CCN2 and dendritic cell-specific transmembrane protein (DC-STAMP), which is involved in cell-cell fusion. The results showed that CCN2 induced and interacted with DC-STAMP. Furthermore, GST-RANKL-induced osteoclastogenesis was impaired in fetal liver cells from Ccn2 null mice, and the impaired osteoclast formation was rescued by the addition of exogenous rCCN2 or the forced expression of DC-STAMP by a retroviral vector. These results suggest that CCN2 expressed during osteoclastogenesis promotes osteoclast formation via induction of and interaction with DC-STAMP.

Macroscopic and histological observations on the human sternoclavicular joint disc.

To know the detailed morphology of the human sternoclavicular joint and its articular disc is essential to understanding the movement of this joint and the functional role of the disc. In the present study, 51 articular discs of the sternoclavicular joint of 29 Japanese cadavers were macroscopically examined and then embedded in paraffin to make a complete series of coronal sections for light microscopic observation. We classified the articular discs into three types, discoid, ring, and meniscoid. The discoid-type disc was flattened and round in shape, whereas the other two types had partial defects in the centers (ring type) or in the periphery (meniscoid type). We found the bony process that protruded from the sternal end of the clavicle and fitted into the defect part of the ring- or meniscoid-type discs. The mean values of this bony process of the clavicle adjacent to the articular disc were 2.1, 4.7, and 6.0 mm, respectively, in the three types of articular disc. The movement between the articular disc and the clavicle may be limited, because the articular disc was directly attached to the clavicle on its medial region. The present histological observation demonstrated that the sternal side of the disc was composed of fibrocartilage and dense connective tissue. The clavicular side of the disc was composed of only fibrocartilage. The clavicular side of the articular disc of the sternoclavicular joint has the function of resisting the compressive load to the clavicular surface.