Hisayo Nasu

An anatomic study of the structure and innervation of the pronator quadratus muscle

The pronator quadratus muscle is composed of the superficial and deep heads. However, to date there is no consensus on the variations of each head. To add to this enigma, the innervation patterns of each head have not been thoroughly studied. The present study was conducted to clarify the structure and innervation of the pronator quadratus muscle by minute dissection of 46 forearms from 26 cadavers. The origin, insertion, shape, and direction of the muscle fascicles in each head were observed. The intramuscular distribution and the innervation patterns to each head were investigated. The attachment of the deep head was examined using Masson’s trichrome staining technique. Each head consisted of various muscle fascicles which differed in shape and direction. The most distal muscle fascicle extended toward the head of the ulna. On microscopic study, this most distal fascicle was observed to reach the base of the ulnar styloid process. The nerves innervating the superficial head penetrated through the deep head and ran on the anterior surface of the radius from medial to lateral. This tendency was common to all of the forearms studied. We confirmed that each head of the pronator quadratus muscle consisted of various muscle fascicles. The attachment to the base of the ulnar styloid process is considered to be an important structure that prevents the head of the ulna from impacting against the carpal bones. Knowledge of the innervation pattern to each head is critical for preserving the function of the pronator quadratus muscle during surgery for distal radial fracture.

An anatomic study of structure and innervation of the serratus anterior muscle

BackgroundThe structure and function of the serratus anterior muscle are partitioned into three parts. If the morphological characteristics in each part can be demonstrated in more detail, the cause of dysfunction will probably be identifiable more accurately. The purpose of this study was to demonstrate the details of the structure and innervation in each part of the serratus anterior muscle.Materials and methodsThis macroscopic anatomic study was conducted using ten sides from five cadavers. The structure and innervation in each part of this muscle were examined.ResultsIn the superior part, the independent branch was divided from a branch innervating the levator scapulae muscle. In the middle part, the long thoracic nerve descended on one-third of the anterior region between the origin and insertion. In the inferior part, the long thoracic nerve which ramified into many branches and branches from the intercostal nerves were distributed on all sides.ConclusionThis study demonstrated that the innervation of the serratus anterior muscle was different in each part. The difference indicates that the superior part has an intimate relation with the levator scapulae muscle while the middle and inferior parts could be the actual serratus anterior muscle. Moreover, the distribution of branches from the intercostal nerves shows that the inferior part has a connection with some trunk elements. Understanding these characteristics of innervation is useful to identify the cause of dysfunction. In addition, we assert that the constant distribution of branches from the intercostal nerves is significant for the morphology.

An artery accompanying the sciatic nerve (arteria comitans nervi ischiadici) and the position of the hip joint: a comparative histological study using chick, mouse, and human foetal specimens

Birds and reptiles always carry a long and thick artery accompanying the sciatic nerve (i.e., the sciatic artery), whereas mammals do not. We attempted to demonstrate a difference in courses of the nerve and artery in fetuses in relation with the hip joint posture. Eight mid-term human fetuses (15-18 weeks), five mouse fetuses (E18) and five chick embryos (11 days after incubation) were examined histologically. Thin feeding arteries in the sciatic nerve were consistently observed in human fetuses in spite of the long, inferiorly curved course of the nerve around the ischium. The tissue around the human sciatic nerve was not so tight because of the medial and inferior shift of the nerve away from the hip joint. The fetal hip joint position differed among the species, being highly flexed in humans and almost at right angle flexion in mice and chicks. Because of deep adduction of the hip joint in the mouse, the knee was located near the midline of the body. The mouse sciatic nerve ran through the tight tissue along the head of the femur, whereas the chick nerve ran through the loose space even in the gluteal region. In birds, evolution of the pelvis including the hip joint without adduction seemed to make the arterial development possible. In mammals, highly flexed or adducted hip joint seemed to be one of the disturbing factors against development of the long and thick artery. A slight change in posture may cause significant arterial variation.

Distribution of the axillary nerve to the subacromial bursa and the area around the long head of the biceps tendon

PurposePatients with a shoulder disorder often complain of pain on the anterior or lateral aspect of the shoulder. Such pain has been thought to originate from the suprascapular nerve. However, taking into consideration the distinctive course of the axillary nerve, the axillary nerve is likely to supply branches to the structure around the shoulder joint. This study was conducted to clarify the division, course, and distribution of the branches which originate from the axillary nerve and innervate structures around the shoulder joint.MethodsThe division, course, and distribution of the branches which originate from the axillary nerve and innervate structures around the shoulder joint were examined macroscopically by dissecting 20 shoulders of 10 adult Japanese cadavers.ResultsThe thin branches from the anterior branch of the axillary nerve were distributed to the subacromial bursa and the area around the long head of the biceps tendon. The branches from the main trunk of the axillary nerve or the branch to the teres minor muscle were distributed to the infero-posterior part of the shoulder joint.ConclusionThe pain on the anterior or lateral aspect of the shoulder, which has been thought to originate from the suprascapular nerve, might be related to the thin branches which originate from the axillary nerve and innervate the subacromial bursa and the area around the long head of the biceps tendon.Clinical relevanceThese results would be useful to consider the cause of the shoulder pain or to prevent the residual pain after the biceps tenodesis.