Surgical anatomy of the pectoral nerves and the pectoral musculature

The pectoral nerves (PNs) may be selectively injured through various traumatic mechanisms such as direct trauma, hypertrophic muscle compression, and iatrogenic injuries (breast surgery and axillary node dissection, pectoralis major muscle transfers). The PN may be surgically recovered through nerve transfers. They may also be used as donors to the musculocutaneous, axillary, long thoracic, and spinal accessory nerves and for reinnervation of myocutaneous free flaps. Thus, in this article, we reviewed the surgical anatomy of PN. A meta-analysis of the available literature showed that the lateral pectoral nerve (LPN) arises most frequently with two branches from the anterior divisions of the upper and middle trunks (33.8%) or as a single root from the lateral cord (23.4%). The medial pectoral nerve (MPN) usually arises from the medial cord (49.3%), anterior division of the lower trunk (43.8%), or lower trunk (4.7%). The two PN are usually connected immediately distal to the thoracoacromial artery by the so-called ansa pectoralis. The MPN may also show communications with the intercostobrachial nerve. In 50%-100% of cases, it may pass, at least with some branches, through the pectoralis minor muscle. The LPN supplies the upper portions of the pectoralis major muscle; the MPN innervates the lower parts of the pectoralis major and the pectoralis minor muscle. Among the accessory muscles of the pectoral girdle, the LPN may also innervate the tensor semivaginae articulationis humero-scapularis, pectoralis minimus, sternoclavicularis, axillary arch, sternalis, and infraclavicularis muscles; the MPN may innervate the pectoralis quartus, chondrofascialis, axillary arch, chondroepitrochlearis, and sternalis muscles.     

Bilateral asymmetric deficiency of the pectoralis major muscle

We observed a rare, bilateral congenital deficiency of the pectoralis major muscle in a 72-year-old female cadaver in our gross anatomy dissection laboratory. The outward appearance of the anterior thoracic wall, which included well-developed breasts, revealed no obvious abnormalities. Upon dissection, the following features were observed: 1) on the left side, the sternal portion of the sternocostal head of the pectoralis major muscle was absent, the costal portion of the sternocostal head and the clavicular head were both well developed, a normal pectoralis minor was present, and the deltoid and subclavius muscles were not hypertrophied as is often the case when the pectoralis major muscle is deficient; 2) on the right side, the entire pectoralis major muscle was absent and the pectoralis minor, deltoid, and coracobrachialis muscles were infiltrated with connective tissue and fat; and 3) on both sides, the lateral pectoral nerves were absent and the medial pectoral nerves were present. The absence of the lateral pectoral nerves suggests that the deficiencies in the pectoralis major muscles are congenital malformations resulting from a developmental failure of the embryonic muscles rather than a sequel to polio or Poland's syndrome.     

A study on the communication between the pectoral nerve and the extramural nerve branches of the intercostal nerves]

Kumaki et al. (1979) defined the extramural nerve as the rudimentary sensory nerve which appeared on the upper thoracic wall; it branched off the root of the lateral cutaneous nerve of the second, third or fourth intercostal nerve, ran inferomedially adhering to the fascia of the intercostalis externus muscle and ended supplying the membrane covering the adjacent rib. They also stated that the extramural nerve (Rxm) occasionally became a cutaneous nerve which pierced the pectoralis muscles and supplied the skin covering the thoracic wall similar to the lateral cutaneous nerve (Rcl) or the anterior cutaneous nerve (Rca). Further, they proposed that the muscular nerves to the obliquus externus abdominis muscle which are usually situated below the fifth rib might be considered a part of this Rxm series. Although the definition of Rxm is still not widely accepted, Rxm is thought to be a key morphological factor influencing the variations of peripheral nerve arrangement on the thoracic wall. In the student course of gross anatomy dissection at Iwate Medical University School of Medicine during the years 1987-1991, three cases of Rxm communicating with the pectoral nerve and supplying the pectoralis major muscle were observed. Some cases have been reported in which Rcl innervates part of the pectoral muscles. However, the communication between the pectoral nerve and Rxm has not yet been discussed. Therefore, to clarify the morphological significance of the communication between Rxm and the pectoral nerve, the branching pattern and the distribution of the pectoral nerves were extensively investigated and the intramuscular nerve supply of some pectoral nerves, especially the pectoral nerves which communicated with Rxm, was examined in detail under a stereomicroscope. The results are summarized as follows: 1. In the first case, Rxm of the second intercostal nerve originated from Rcl, ran inferomedially adhering to the fascia of the intercostalis externus muscle and pierced the origin of the pectoralis minor muscle at the third intercostal space. Then Rxm turned superolaterally to communicate with a pectoral nerve which originated from the loop composed of the lateral and medial pectoral nerves and passed inferior to the pectoralis minor muscle. After communication, the pectoral nerve with Rxm supplied the caudalmost part of the sternocostal portion of the pectoralis major muscle. In the second case, a similar branch of Rxm of the second intercostal nerve passed inferior to the pectoralis minor muscle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Anatomical study on 2 cases of the congenital partial defect of pectoralis major and minor muscles

2 cases of the defect of pectoralis major muscle observed in male cadavers allocated for routine dissection were investigated anatomically, especially on the nerve supply for the defected muscles. In both cases, one on the left and the other on the right side, pectoralis major muscle was defected, the clavicular portion and a small part of sternocostal portion only persisting. Meanwhile, the ipsilateral pectoralis minor muscle was defected in the first case to be a string-like muscle band and was missing in the second case substituted by a membrane which seemed not to be the degenerated same muscle. Both the lateral and medial pectoral nerves supplied the pectoral muscles in the first case. One of rami of the medial pectoral nerve was distributed unusually to the most lateral part of the persisted sternocostal portion. Only the lateral pectoral nerve existed in the second case. In both cases nerves derived from 2 caudal segments, C8 and Th1, were lacking or poor. However, it was suggested that the defect of the muscles was not due to the nonparticipation of these nerves but due to the failure of caudal growth of the pectoral premuscle mass in a five-week embryo (Lewis 1901).     

胸小肌移植重建拇对掌功能的神经解剖学研究

目的为临床应用胸小肌移植重建拇对掌功能手术过程中神经吻接提供解剖学依据。方法解剖观测胸内侧神经及尺神经深支分支特点,比较相关神经有髓神经纤维数目,确定手术过程中神经吻接。结果胸内侧神经为胸小肌的主要支配神经,其在第3肋间隙近锁骨中线处入胸小肌,有髓神经纤维计数为(868±130)根;尺神经深支穿出内侧肌间隔后在第3、4掌骨间隙分别发出两明显肌支,其有髓神经纤维计数分别为(394±49)根、(708±78)根;P3L4(尺神经深支在第4掌骨间隙的分支,其分布于第3骨间掌侧肌和第4蚓状肌)与胸内侧神经、正中神经返支有髓神经纤维数目都比较接近。结论胸小肌移植重建拇对掌功能手术中,在切取胸小肌时以胸内侧神经作为供体神经,以第3肋间隙与锁骨中线交点为标记寻找该神经;尺神经深支中P3L4肌支与胸内侧神经吻合最匹配。     

Anatomic variation of the spinal origins of lateral and medial pectoral nerves

Lateral and medial pectoral nerves are distributed to the pectoralis major and minor muscles. The purpose of this study was to identify the spinal origins of lateral and medial pectoral nerves and to evaluate the participating amounts of each spinal nerve composing both pectoral nerves. Two types of spinal origins appeared in lateral pectoral nerves. The first type was composed of nerve fibers from C5, C6, and C7 with a frequency of 50.0% and the second type was composed of nerve fibers from C6 and C7 at a frequency of 50.0%. Regarding the average participating diameter to the lateral pectoral nerve, C7 was the thickest with a value of 1.60 +/- 0.35 mm (mean +/- SD), next was C6 at 0.83 +/- 0.18 mm, and C5 was the third at 0.42 +/- 0.24 mm. Three types of spinal origin appeared in the medial pectoral nerve. The first type was comprised of nerve fibers from C8 and T1 in 73.3% of cases. The second type was comprised of C8 only in 23.4% of cases, and the third type was comprised of T1 only in 3.3% of cases. The average participating diameter was 0.71 +/- 0.22 mm from C8 and 0.52 +/- 0.17 mm from T1. These results show that the spinal origins of the both pectoral nerves were various. Participating amounts of the lateral pectoral nerve appeared sequentially in the order of C7, C6, and C5. In the medial pectoral nerve, C8 participated more amounts than T1.     

胸小肌构筑特点和肌内外神经分布及临床意义

目的　为胸小肌肌移植的临床应用提供解剖学依据。方法　用 2 0具成人尸体和 10具经甲醛固定的尸体分别进行胸小肌的肌构筑和肌内、外神经分支分布研究。结果　 (1)胸小肌肌重 (4 2 3± 10 1)g ,肌长 (15 5± 1 8)cm ,肌纤维长 (9 4± 1 4 )cm ,生理横切面积 (4 3± 1 4 )cm2 ,羽状角为 (11 5± 1 7)° ;(2 )支配胸小肌的胸内侧神经和胸外侧神经在肌腹中部形成一“U”型神经襻 ,胸小肌各肌齿均有细长的神经分支分布。结论　 (1)胸小肌为一羽肌 ,这种构筑特点使其在收缩力和动幅上均有增加。 (2 )Sihler′s神经染色技术使肌亚部的研究更加简捷     

Anatomy and surgical landmarks for the ansa pectoralis: application to pectoralis major nerve selective neurotomy

Background

Ansa pectoralis neurotomy is a surgical approach in the treatment of the pectoralis major muscle spasticity causing an attitude in adduction and internal rotation of the shoulder.

Objective

To establish the anatomical landmarks allowing an easier localisation of the ansa pectoralis during neurotomy.

Material and methods

Fifteen adult human cadavers (10 embalmed and 5 fresh) were dissected in order to determine anatomical landmarks allowing an easier localization of the ansa pectoralis during neurotomy.

Results

In all the cadavers, the lateral pectoral nerve arose from the lateral cord of the brachial plexus, 0.2 cm above to 1.5 cm below the inferior border of the clavicle with a mean distance of 0.76 cm for left and right side, whereas the medial pectoral nerve arose from the medial cord of the brachial plexus, 0.7–2.3 cm below the inferior border of the clavicle with a mean distance of 0.61 cm for the left side and 0.68 cm for the right side. We systematically found both the origin of pectoral nerves and the ansa pectoralis at the level of the middle third of the distance between the sternoclavicular and the acromioclavicular joints. Moreover, ansa pectoralis was constantly localized lateral to the thoracoacromial artery. In four cases, the division of the lateral pectoral nerve was not found. In one case, medial pectoral nerve did not exist.

Conclusion

Ansa pectoralis can be found by a curved incision made at the mid-third of the distance between the sternoclavicular and the acromioclavicular joints, the medial point being located just below the lower edge of the clavicle and the lateral point 2 cm below the inferior edge of the clavicle.     

Coexistence of a pectoralis quartus muscle and an unusual axillary arch: case report and review

A pectoralis quartus muscle and an unusual axillary arch were found on the left side of a female cadaver. The axillary arch was a musculoaponeurotic complex continuous with the iliacal fibers of the latissimus dorsi. The muscular part, together with the tendon of pectoralis major, inserted into the lateral lip of the bicipital groove of the humerus, whereas the aponeurotic part was formed by a fibrous band that extended deep to the pectoralis major to insert into the coracoid process between the attachments of the coracobrachialis and pectoralis minor. The pectoralis quartus originated from the rectus sheath, and joined the inferior medial border of the fibrous band of the axillary arch, at the lateral edge of the pectoralis major. The axillary arch muscle crossed anteriorly the axillary vessels and the brachial plexus. The clinical importance of these muscles is reviewed.     

Case reports on the pectoralis quartus and the pectoralis intermedius muscles

Each one case of the pectoralis quartus and the pectoralis intermedius muscles was found on the left thoracic wall in a 73 year old male and on the right thoracic wall in a 57 year old female respectively. The pectoralis quartus was a thin muscle of triangular shape, the base of which was the origin arising from the left thoracic wall at the level of the 6th rib between the pectoralis major and the latissimus dorsi, being separated from both margins of the muscles. The aberrant muscle ascended left-upwards about 10 cm to insert to the inner surface of the pectoralis major near its lower margin. The muscle was innervated by the most caudal pectoral nerve, passing around the lower margin of the pectoralis minor. The pectoralis quartus is extremely rare in man, and only two cases were reported by Bluntschli (1906) and Frey (1921). From the comparative anatomical point of view, the pectoralis quartus muscle was supposed to be a remnant of the ventral part of the subcutaneous trunci muscle in lower mammals, differing from the ordinary muscular arch of the axilla which was believed to derive from the dorso-cranial part of the muscle. The pectoralis intermedius was located in the deep layer of the right pectoralis major, lying about 2 cm below the lower margin of the pectoralis minor. It arose in the 4th and 5th ribs and extended right-upwards, running almost parallel with the pectoralis minor. The origin of the pectoralis minor shifted cranially to the 2nd and 3rd ribs.(ABSTRACT TRUNCATED AT 250 WORDS)     

An unusual innervation of pectoralis minor and major muscles from a branch of the intercostobrachial nerve

Variations of the branching pattern of the intercostobrachial nerve have been known to complicate dissection during mastectomy and other procedures involving the axilla. We present a unilateral case of a 73-year-old Caucasian female, in which the intercostobrachial nerve gives rise to an additional medial pectoral branch, which partially innervates the pectoralis minor muscle, as well as the abdominal head of pectoralis major muscle. Clinical consequences of such a variation may include motor losses, in addition to the commonly reported sensory losses, resulting from accidental or intentional dissection of the intercostobranchial nerve.     

Lateromedial and dorsoplantar borders among supplying areas of the nerves innervating the intrinsic muscles of the foot.

The branching patterns of nerves supplying the intrinsic muscles of the foot were analyzed as a basis to confirm the muscle layer structure. Thirty-eight feet of 20 Japanese cadavers were examined in detail in this study. The first dorsal interosseus was innervated by a branch from the deep peroneal nerve as well as a branch of the lateral plantar nerve in 92.1%, the second dorsal interosseus in 10. 5% and the third dorsal interosseus in 2.6%. In three specimens, branches from the deep peroneal nerve innervated the oblique head of the adductor hallucis or the lateral head the flexor hallucis brevis. In addition, branches from the medial and lateral plantar nerves and the deep peroneal nerve formed communication loops in three specimens. The first dorsal interosseus, the oblique head of the adductor hallucis and the lateral head of the flexor hallucis and their innervating nerve branches are closely related within the first intermetatarsal space. Since the tibial part of the first interosseus muscle primordium is occupied in the space during development, the variations of innervation patterns and formation of the communicating nerve loops may be explained by various combinations of the part and the other muscle primordia.     

Lateromedial and dorsoplantar borders among supplying areas of the nerves innervating the intrinsic muscles of the foot

The branching patterns of nerves supplying the intrinsic muscles of the foot were analyzed as a basis to confirm the muscle layer structure. Thirty‐eight feet of 20 Japanese cadavers were examined in detail in this study. The first dorsal interosseus was innervated by a branch from the deep peroneal nerve as well as a branch of the lateral plantar nerve in 92.1%, the second dorsal interosseus in 10.5% and the third dorsal interosseus in 2.6%. In three specimens, branches from the deep peroneal nerve innervated the oblique head of the adductor hallucis or the lateral head the flexor hallucis brevis. In addition, branches from the medial and lateral plantar nerves and the deep peroneal nerve formed communication loops in three specimens. The first dorsal interosseus, the oblique head of the adductor hallucis and the lateral head of the flexor hallucis and their innervating nerve branches are closely related within the first intermetatarsal space. Since the tibial part of the first interosseus muscle primordium is occupied in the space during development, the variations of innervation patterns and formation of the communicating nerve loops may be explained by various combinations of the part and the other muscle primordia. Anat Rec 255:465–470, 1999. © 1999 Wiley‐Liss, Inc.     

Anatomical study concerning the origin and course of the pectoral branch of the thoracoacromial trunk for the pectoralis major flap

The patterns of the feeding vessels to each muscle determine the extent of their safe transposition and the muscles value as a pedicled flap in reconstructive surgery. This study aimed to demonstrate the point of origin and the intra- and submuscular course of the pectoral branch of the thoracoacromial trunk (TAT) for pectoralis major (PM) flap surgery. Seventy sides of the PM were dissected based on a clinical reference line that has been used for several decades. The branching point of the TAT from the axillary artery was located lateral to the midclavicular line on the right-sided specimens (100%) and medial to the midclavicular line on the left sides (86%). The branching patterns of the pectoral branch to the PM muscle from the TAT were classified into three types. In type I the pectoral branches originated directly from the TAT (55 cases, 78.6%). In type II (11 cases, 15.7%) and type III (4 cases, 5.7%) the pectoral branch divided from the medial and lateral pedicle of the TAT, respectively. The course of the pectoral branch from the TAT in the PM was categorized into three patterns according to the degree of proximity to the midclavicular line. In 49 cases (70%), the pectoral branch in the PM ran within 1 cm of the midclavicular line. The other cases ran 2 cm (20 cases, 29%) and 3 cm (1 case, 1%) from the midclavicular line, respectively. These results provide topographic data of the pectoral branch based on anatomical landmarks, and will be useful in surgical planning as well as the procedure for PM flap surgery.H.-D. Park and Y.-S. Min equally contributed to this study     

Donor, recipient and nerve grafts in brachial plexus reconstruction: anatomical and technical features for facilitating the exposure

Forty three cadavers of adult and five patients were included in our study. Accessory, suprascapular, musculocutaneous and sural nerves were dissected. These widely used nerves in brachial plexus reconstruction have varying anatomy and still have no standard approach for surgery. Dissection of the accessory nerve in the upper part of the posterior neck triangle was quite complicated took a relatively long time and the nerve could easily be injured. It was found that these shortcomings could be diminished starting dissection of this nerve in the lower part of the posterior neck triangle near the anterior border of trapezius muscle 2 cm (0–3.5) above the clavicle. Accessory nerve entered inner surface of this muscle 3 cm (1–4) from this edge. The proximal portion of the suprascapular nerve was not difficult to identify if post-traumatic scarring is absent. Alternative approach was starting dissection from the junction of C5 and C6 into superior trunk. The suprascapular nerve diverged distally from this junction at 2 cm (0–2.5). The proximal portion of the musculocutaneous nerve was identified by cutting clavicle or tendon of major pectoral muscle. Quicker and less traumatic exposure of this nerve was starting dissection in the bed between biceps and coracobrachialis muscles. The first branches of the musculocutaneous nerve to the biceps brachii muscle took onset 4 cm (3.5–6) distally from the lower margin of the tendon of major pectoral muscle. First branch to the brachial muscle originated from the musculocutaneous nerve distally from the same tendon at 9.4 cm (6.1–10.5). Two main but controversial principles exist in sural nerve graft dissection: time saving and less traumatic approach. Long nerve graft is necessary during brachial plexus reconstruction when many interposition grafts are needed. Technique of multiple (4–7) transverse skin incisions let us to get sural nerve with both branches as long as 66 cm (average 47 cm). Total length of this nerve mainly depended on branching level, which was found to be 27.5 cm (9–35) measuring proximally from the lateral ankle.     

Unusual pectoralis major muscle: The chondroepitrochlearis

Presented herein is a case of an extremely rare muscle in the pectoral region. It involved an accessory muscular slip originating from the pectoralis major and inserting onto the medial epicondyle of the humerus and the medial intermuscular septum. According to the literature this muscle is defined as chondroepitrochlearis. The arterial and nervous supply to the muscle came from the lateral thoracic artery and the medial pectoral nerve, respectively. Clinical considerations of such a variation include ulnar nerve entrapment and functionally limited abduction of the humerus.     

Anomalous pectoral musculature

Anomalous disposition of pectoral muscles was encountered in an adult female cadaver on the left side. A prominent cleft separating the sternocostal and clavicular portions of the pectoralis major was noticed. The fibers of pectoralis major were partially fused with the deltoid, resulting in obliteration of the deltopectoral groove. Interestingly, cephalic vein was seen traversing superficial to the clavicular portion of the pectoralis major and pierced it to drain into the axillary vein. The pectoralis minor was inserted mainly on the coracoid process and few fibers were found blending with the coracobrachialis and short head of biceps brachii. Further, pectoralis minimus, a rare anatomic variant, was also observed lying superior to pectoralis minor. It was innervated by a twig from the lateral pectoral nerve at its superficial surface. Awareness of possibility of such anomalous muscles is important for surgeons operating on the chest wall.     

Danger of damaging the medial branches of the posterior rami of spinal nerves during a dorsomedian approach to the spine

Postoperative atrophy of the deep back muscles may be caused by denervation during a dorsomedian approach to the thoracolumbar spine; ensuing instability of the spine with poor clinical results, perhaps due to such muscle loss, has been observed in 11.7% of cases (Sihvonen et al., 1993, Spine 18:575--581). More specifically, this complication may be caused by damaging the medial branches of the posterior rami of the spinal nerves during lateral retraction of the muscles. To investigate the anatomic topography of the medial branches of the posterior rami of the spinal nerves, 18 carbol-formol-fixed specimens were dissected using an operation microscope; also, 3 fresh cadavers were cut in horizontal and vertical planes with a rotary cryotome to confirm the anatomic topography observed in the fixed specimens. In the thoracolumbar spine the medial branch of the posterior ramus of the spinal nerve is subject to ligamentous fixation by the strong fibers of the mammillo-accessory ligament, which extends between the mammillary process and accessory process infero lateral to the superior articular process. When the dorsomedian approach to the thoracolumbar spine is enlarged laterally to the articular processes by retracting the paraspinous muscles, the medial branches of the posterior rami of the spinal nerves are endangered. This may cause postoperative pain as well as dynamic instability beyond the corresponding segments. The results of our anatomic study suggest that the posterior surgical midline approach to the thoracolumbar spine should not be enlarged laterally to the articular processes to prevent injury to the medial branches of the posterior rami of the spinal nerves.     

Masticatory Muscles and Branches of Mandibular Nerve: Positional Relationships Between Various Muscle Bundles and Their Innervating Branches

The masticatory muscles, which are composed of four main muscles, are innervated by branches of only one of the cranial nerves, the mandibular nerve. This muscle group has a variety of very complex functions. We have investigated the origins and insertions of the masticatory muscles and the adjacent bundles of the main muscles, and closely examined the positional relationships between the muscle bundles and innervating branches. According to the findings of the nerve branching patterns, the masticatory muscles can be classified into two groups: the inner group consisting of the lateral pterygoid muscle, and the outer group consisting of the other muscles and adjacent muscle bundles. Further, the outer muscle group is sub-divided into the three other main muscles (the masseter, the temporalis, and the medial pterygoid muscle) and the adjacent various transitional muscle bundles. Anat Rec, 302:609–619, 2019. © 2018 Wiley Periodicals, Inc.     

足底内侧和外侧群肌的肌内神经整体分布模式及临床意义

目的 揭示足底内侧和外侧群肌的肌内神经整体分布模式,探讨其临床意义.方法 24具成年尸体,完整取下足底内侧和外侧群肌,采用改良Sihler染色显示肌内神经分布模式.结果 (足母)收肌的神经支从肌止端的深面入肌,而(足母)展肌、(足母)短屈肌、小趾展肌和小趾短屈肌的神经支常从肌起端的深面入肌.(足母)展肌中有1个半月形和...