Muscle variations and abnormal branching and course of the ulnar nerve in the forearm and hand

During dissection of the right forearm of a 27-year-old female cadaver, variations in the form and insertion of the palmaris longus muscle were observed. The tendon of the palmaris longus muscle, which demonstrated a centrally placed belly, split into two tendons: one inserted into the palmar aponeurosis and the other into the proximal part of the flexor retinaculum. Additionally, we found an accessory muscle extending between the flexor retinaculum and the tendon of the abductor digiti minimi muscle. This accessory muscle was located deep to the ulnar artery but superficial to the superficial and deep branches of the ulnar nerve at the wrist. Finally, an aberrant branch of the ulnar nerve was identified in the forearm; it traveled distally alongside the ulnar artery and in the palm demonstrated communications with common palmar digital nerves from the ulnar and the median nerves. No variations were observed in the contralateral upper limb.     

Anatomic variations of the median nerve within the carpal tunnel

Two hundred seventy-five consecutive carpal tunnel releases were reviewed to identify anomalies of median nerve anatomy. High division of the median nerve was observed in nine cases; in two of these the nerve divided proximally and then rejoined distally as a “closed loop.” In 42 cases the motor branch passed through the flexor retinaculum. Multiple motor branches were present in 13 cases. The palmar cutaneous branch passed through the flexor retinaculum in seven cases. In three cases, the distal communicating sensory ramus between the medial and ulnar nerves arose proximal to the superficial arch. Median nerve anomalies within the region of the carpal tunnel are common. Knowledge of such anomalies is important to avoid iatrogenic injury.     

Definition of a safe-zone in open carpal tunnel surgery: a cadaver study

Carpal tunnel decompression is one of the most common surgical procedures in hand surgery. Cutaneous innervation of the palm by median and ulnar nerves was evaluated to find a suitable incision preserving cutaneous nerves. A morphometric study was designed to define the safe-zone for mini-open carpal tunnel release. Sixteen fresh-frozen (8 right, 8 left) and 14 formalin-fixed (8 right, 6 left) cadaveric hands were dissected. Anatomy of the palmar cutaneous branch of the median and the ulnar nerve, motor branch of the median nerve, superficial palmar arch were evaluated relative to the surgical incision. We also identified the motor branch of the median nerve. Detailed measurements of the whole palmar region are reported in this study. The motor branch of the median nerve was extraligamentous as 60%, subligamentous as 34%, transligamentous as 6%. The palmar cutaneous branches of the median and the ulnar nerves in the palmar region were classified as Type A (34%), Type B (13%), Type C (13%), Type D (none), Type E (40%) according to forms of palmar cutaneous innervation originating from the ulnar and median nerves. Injury to the palmar cutaneous branch of the median nerve (PCBMN) is the most common complication of the carpal tunnel surgery. Various techniques were described to decrease post-operative morbidity. Based on these anatomic findings mini incision between the superficial palmar arch and the most distal part of the PCBMN in the palmar region is the safe-zone for carpal tunnel surgery.     

Biometric study of the relationships between palmar neurovascular structures, the flexor retinaculum and the distal wrist crease

During surgical exposure of the carpal tunnel it is possible to injure the neurovascular structures closely related to the flexor retinaculum, such as the superficial palmar arch and the communicating branch between the ulnar and median nerves. Because of the importance of these structures and with the purpose of increasing knowledge of anatomical details concerning to their location, a biometric study was performed on the retinaculum and the communicating branch, and between the communicating branch and the distal wrist crease, as well as between the retinaculum and the superficial palmar arch. We dissected 56 hands from 28 Brazilian formalin‐preserved cadavers of both sexes (24 male) at the Federal University of São Paulo–Escola Paulista de Medicina, Brazil. The communicating branch was observed in 96.4% of cases and the superficial palmar arch in 78.6%. The communicating branch was found between the common palmar digital nerve of the 4th interosseous space (from the ulnar nerve) to the homonymous nerve of the 3rd interosseous space (from the median nerve). In males, the distance between the distal wrist crease and the site where the communicating branch originates from the ulnar component had an average of 33.9±5.5 mm on the right side and 30.2±8.2 mm on the left. The distance between the distal wrist crease and the junction of the communicating branch with the common palmar digital nerve of the 3rd interosseous space was 43.6±6.9 mm on the right and 40.2±6.2 mm on the left side. Conversely, in 14.8% of cases (1 female), the communicating branch was observed to emerge from the common palmar digital nerve of the 3rd interosseous space. The distance between the retinaculum and the superficial palmar arch in the axial line of the 4th metacarpal bone was on average 7.3±4.3 mm on the right and 8.3±3.5 mm on the left side. At the same level, the distance between the retinaculum and the communicating branch was 6.2±3.7 mm on the right side and 5.1±2.8 mm on the left. These results can be used as a reference during surgical procedures in the palmar region.     

An anatomical study of the palmar cutaneous branch of the median nerve

We present an anatomical study of the palmar cutaneous branch of the median nerve emphasizing its frequency, origin, perforation point at the transverse carpal ligament, point of emergence in the palm, width, length, divisions and innervation territory. For this purpose, fifty cadaver hands were dissected under a stereomicroscope and/or magnifying glass. The origin of the palmar cutaneous branch (PCB) was on the average 4.56 cm proximal to conventionally named "zero point" on the most distal transverse volar wrist crease. Perforation of the aponeurosis occurred on average 0.79 cm from the mentioned point and its emergence in the palm at 0.76 cm. The nerve had an average length of 5.24 cm. PCB's divisions in the palm resulted in a medial branch in 42%, a lateral branch in 92% and an intermediate branch in 100% of the hands studied. In six specimens PCB presented a deep branch which was directed toward the thenar eminence or made communication with the superficial branch of the palmar digital nerve or still penetrated between the first or second metacarpal. In 4% of the cases there was a communicating branch between the superficial branch of the radial nerve and the PCB. These anatomical results should be considered in the evaluation of the best surgical techniques for decompression of the median nerve in the carpal tunnel.     

尺动脉腕上皮支降支小鱼际皮瓣的解剖学基础

目的 为尺动脉腕上皮支降支小鱼际皮瓣修复手掌心皮肤缺损提供临床解剖学基础。 方法　自2018年5月至2019年5月,采用42侧上肢新鲜标本,其中28侧经肱动脉灌注红色乳胶并进行解剖,14侧经肱动脉灌注ABS后制作铸型标本,解剖观察尺动脉腕上皮支降支在小鱼际区的分支、走行、分布、交通和吻合形式,测量其外径。 结果 从豌豆骨到环、小指指蹼间画一连线,并将其分成3等份。结果显示每侧尺动脉腕上皮支降支发出14.5条分支,其中在远、中、近1/3段共发出皮支6.8支,交通支7.7支。各皮支在小鱼际浅筋膜内相互吻合,形成1~2级皮支链,皮支长(1.80±0.60)cm,直径(0.23±0.10)mm。交通支分别与深部的尺动脉掌深支、掌浅弓尺侧缘、尺侧指掌侧总动脉或小指尺掌侧动脉吻合,交通支长(1.60±0.50)cm,直径(0.16±0.06)mm。在近、远1/3段各有1~2支较大的交通支,是转位较理想的血管蒂。 结论 小鱼际皮瓣的尺动脉腕上皮支降支血管蒂位置恒定,皮瓣内皮支链丰富,皮肤结构与手掌心部位同源,是修复手掌心小面积皮肤缺损的较理想的供区之一。     

Anomalous flexor of the little finger

We report an anomalous palmar muscle belly of the flexor digitorum superficialis muscle (FDS) in the right hand of an 80-year-old female cadaver. The muscle originated from the center of the volar surface of the flexor retinaculum and inserted onto the palmar aspect of the base of the middle phalanx of the little finger. Its tendon of insertion divided into two bands, a pattern typical of the FDS tendon, between which the tendon of flexor digitorum profundus muscle to the little finger passed. The tendon of the usual antebrachial FDS to the little finger was absent. The anomalous muscle belly was innervated by a branch from the median nerve.     

正中神经返支卡压及易损伤部位的解剖学基础

目的：探讨腕管综合征术后大鱼际功能恢复不良的原因与返支易损伤部位。方法：对20侧成人新鲜上肢标本进行显微解剖，观测正中神经返支走行中存在的卡压因素以及易损伤部位。结果：(1)拇短屈肌浅头尺侧存在腱弓及腱纤维束结构，对正中神经返支形成卡压；(2)住屈肌支持带远侧返支与掌腱膜关系密切，在此部位掌腱膜可对返支形成卡压或术中易误伤返支；(3)走行中返支与拇长屈肌腱和示指屈肌腱存在交叉走行关系。结论：(1)返支走行中存在易卡压因素，治疗腕管综合征时应常规探查松解返支；(2)涉及拇长屈肌腱，示指屈肌腱和掌腱膜手术时，应注意防止损伤返支。     

Applied anatomy of the superficial branch of the radial nerve

The superficial branch of the radial nerve (SBRN) is highly vulnerable to trauma and iatrogenic injury. This study aimed to map the course of the SBRN in the context of surgical approaches and identify a safe area of incision for de Quervain's tenosynovitis. Twenty-five forearms were dissected. The SBRN emerged from under brachioradialis by a mean of 8.31 cm proximal to the radial styloid (RS), and remained radial to the dorsal tubercle of the radius by a mean of 1.49 cm. The nerve divided into a median of four branches. The first branch arose a mean of 4.92 cm proximal to the RS, traveling 0.49 cm radial to the first compartment of the extensor retinaculum, while the main nerve remained ulnar to it by 0.64 cm. All specimens had branches underlying the traditional transverse incision for de Quervain's release. A 2.5-cm longitudinal incision proximal from the RS avoided the SBRN in 17/25 cases (68%). In 20/25 specimens (80%), the SBRN underlay the cephalic vein. In 18/25 (72%), the radial artery was closely associated with a sensory nerve branch near the level of the RS (SBRN 12/25, lateral cutaneous nerve of the forearm (LCNF) 6/25.) A longitudinal incision in de Quervain's surgery may be preferable. Cannulation of the cephalic vein in the distal third of the forearm is best avoided. The close association between the radial artery and first branch of the SBRN or the LCNF may explain the pain often experienced during arterial puncture. Particular care should be taken during radial artery harvest to avoid nerve injury.     

An unusual termination of the ulnar nerve in the palm.

During the dissection of the left forearm and hand of a 57-year old male cadaver fixed in 10% formalin, it has been noted that the medial proper palmar digital nerve to the little finger arose from the dorsal branch of the ulnar nerve, instead of the superficial branch of the same nerve. The dorsal branch, given off by the ulnar nerve in the forearm, coursed distally and dorsally deep to the flexor carpi ulnaris muscle. Some 2 cm proximal to the pisiform, it pierced the deep fascia on the posteromedial side of the muscle to become superficial. At this point, one of the three branches given off travelled distally on the palmar-ulnar side of the hand to the skin of the little finger. There were connections between this branch and the branches of the superficial branch of the ulnar nerve which innervated the skin of the hypothenar eminence. Further, another branch of the superficial branch of the ulnar nerve passed under the fibrous arch of the flexor digiti minimi brevis muscle origin and the opponens digiti minimi muscle to re-unite with its parent nerve.     

Can palmar creases serve as landmarks for the deeper neuro-vascular structures?

Purpose

The aim of this study was the examination of the superficial anatomy of palmar creases and their relation to deeper neuro-vascular structures.

Methods

Four creases: distal wrist flexion crease, thenar crease, proximal palmar crease and distal palmar crease were evaluated with reference to the following structures: palmar cutaneous branch of median nerve, palmar cutaneous branch of ulnar nerve, the nerve of Henle, transverse palmar branches from ulnar nerve, recurrent motor branch of median nerve, radial proper palmar digital nerve to the index and the ulnar proper palmar digital nerve to the thumb, Berrettini’s communicating branch, ulnar nerve and artery, superficial palmar arch. We performed dissections of 20 cadaveric upper limbs derived from a homogenous Caucasian group. In our study we measured the location of surgically important structures with reference to palmar skin creases.

Results

Among the other observations we noticed that the palmar cutaneous branches of the median and ulnar nerves were located at least 0.5 cm away from the thenar crease. The superficial palmar arch was found between the thenar and proximal palmar crease and never crossed the proximal or distal palmar creases.

Conclusions

These anatomical dissections will provide reference material for further ultrasound studies on the arrangements of neuro-vascular structures in reference to superficial palmar creases.     

Biometry of the muscular branches of the median nerve to the forearm

The aim of this study was to determine the biometry of the muscular branches of the median nerve to the forearm in ten embalmed upper limbs. We measured the length of the forearm and the level of origin of each muscular branch of the median nerve to the forearm from the middle of a line between the medial and lateral epicondyles. The level of origin of each branch was then calculated as a percentage of the length of the forearm. Mean length of the forearm was 25 ± 2.36 cm (range: 22-29 cm). Although the levels of origin of the proximal and distal nerves to pronator teres, and of the nerves to palmaris longus, flexor carpi radialis and flexor digitorum superficialis, were quite variable (coefficient of variation: CV > 48.61%), the level of origin of the anterior interosseous nerve (CV = 31.24%) and its branches (nerves to flexor pollicis longus and flexor digitorum profundus, CV = 20.06%) was less variable. These results suggest that the anterior interosseous nerve of the forearm is probably the nerve to connect in muscular free transfers in order to restore flexion of the fingers after damage to the flexor tendons to the forearm. We observed Martin-Gruber communications in six out of ten dissections. Clin. Anat. 11:239–245, 1998. © 1998 Wiley-Liss, Inc.     

Abnormal disposition of a branch of the ulnar nerve in the flexor retinaculum

The most frequent disposition of the structures within the ulnar tunnel is for the ulnar nerve to be located medial or posteromedial to the ulnar artery. The structures within the ulnar tunnel are closely related to the medial part of the flexor retinaculum. Lesions of the ulnar nerve and artery during endoscopic decompression of the carpal tunnel have been reported (Agee et al. 1992; Lee et al. 1992; Nath et al. 1993; De Smets & Fabry, 1995). An adequate anatomical knowledge of such structures and their variations is therefore important. During a study of the palmar region, we found that a special branch originated from the ulnar nerve in relation to the flexor retinaculum. Documentation of this variation will contribute to the knowledge of the anatomy of the ulnar nerve and its distal branches.     

A case of median nerve descended on the surface of the pronator teres muscle

We report a case in which the left median nerve passed downwards on the surface of the pronator teres muscle in a 70-year-old male cadaver examined during student dissection practice in 2001 at Nihon University School of Medicine. In the present case, the lateral cord of the median nerve is formed of only the middle trunk, C7 and did not include upper trunk, C5, 6. The upper trunk continued the musculocutaneous nerve, but it did not participate in the median nerve. In the cubital fossa, the median nerve descended on the surface of the pronator teres muscle. The pronator teres muscle had an additional head which arose from the medial intermuscular septum. The brachial artery passed between the humeral head and the additional head. It suggested the relevance that the first branch from the median nerve to the forearm flexor muscle group is the union covered with the common ensheathing epineurium. It consisted of the pronator teres muscle branch, the flexor carpi radialis muscle branch, and the branch to the proximal belly of the muscle bundle of the flexor digitorum superficialis muscle (FDS) for the second digit (II-p), which also supplies the palmaris longus muscle. The branch to the FDS for the third to the fifth digit and the anterior interosseous nerve branch arose from the back of the median nerve following the first branch, and the two branches connected mutually. And the median nerve had a branch to the distal belly of the muscle bundle of the FDS for the second digit (II-d) in its more distal part.     

Stratification of the flexor retinaculum and the course and distribution of the ulnar, median, and palmar digital nerves: an anatomical study

A gross anatomic study of 169 hands from 94 human adult cadavers was carried out to define the morphology of the flexor retinaculum and the relationship of the flexor retinaculum to the course of the median and ulnar nerves and branching of the palmar digital nerves. The following results were obtained. Three parts of the flexor retinaculum were arranged like overlapping tiles on a roof, and in all cases, the median nerve passed deep to the flexor retinaculum, whereas the ulnar nerve passed through various parts of the flexor retinaculum in 19% of cases irrespective of its proximal form and branching of the palmar digital nerves.     

Bilateral superficial median arteries

A superficial artery may be present in the forearm, arising from the axillary, brachial or superficial brachial arteries and crossing over the origin of the flexor muscles of the forearm to reach the palm (Adachi, 1928; Bergman et al. 1988). When this superficial artery continues as the normal ulnar artery accompanying the ulnar nerve at the wrist, it is referred to as the superficial ulnar artery, with an incidence of ∼4%. When the artery passes below or superficial to the flexor retinaculum in the middle of the forearm, sometimes continuing to join the superficial palmar arch, it is called the superficial median artery, with an incidence of ∼1%. We have observed a relatively rare variation involving the presence of a superficial median artery in both upper limbs. We discuss the clinical importance and the developmental aspects of this arterial variation.     

A Case of the Bilateral Duplicate Palmaris Longus Muscles Coupled with the Palmaris Profundus Muscle

The palmaris longus muscle is one of the most variable muscles in human anatomy. During a routine anatomical dissection for medical students at Tottori University, we found duplicate palmaris longus muscles in the bilateral forearms together with the palmaris profundus muscle in the right forearm. The bilateral aberrant palmaris longus muscles were observed at the ulnar side of the palmaris longus muscle and their distal tendons were attached to the flexor retinaculum. The palmaris profundus muscle found in the right forearm was located at the radial side of the flexor digitorum superficialis muscle. The proximal tendon was originated from the anterior surface in the middle of the radius, while the distal tendon coursed radial to the median nerve through the carpal tunnel, finally inserting into the distal part of the flexor retinaculum. Both the palmaris longus and aberrant palmaris longus muscles were innervated by the median nerve. The palmaris profundus muscle was presumably supplied by the median nerve.     

The Muscular Branching Patterns of the Ulnar Nerve to the Flexor Carpi Ulnaris and Flexor Digitorum Profundus Muscles

The branching pattern of the ulnar nerve in the forearm is of great importance in anterior transposition of the ulnar nerve for decompression after neuropathy of cubital tunnel syndrom and malformations resulting from distal end fractures of the humerus. In this study, 37 formalin-fixed forearms were used to demonstrate the muscular branching patterns from the main ulnar nerve to the flexor carpi ulnaris muscle (FCU) and ulnar part of the flexor digitorum profundus muscle (FDP). Eight branching patterns were found and classified into four groups according to the number of the muscular branches leaving the main ulnar nerve. Two (Group I) and three (Group II) branches left the main ulnar nerve in 18 and 17 forearms respectively. The remaining two specimens had four (Group III) and five (Group IV) branches each. Usually one or two branches were associated with the innervation of the FCU. However, in 2 cases, three and in one, four branches to FCU were observed. The FDP received a single branch in all cases, except in four, all of which had two branches. In six forearms, a common trunk was observed arising from the ulnar nerve to supply the FCU and FDP. The distribution of the muscular branches to the revealed muscles was outlined in figures and the distance of the origin of these branches from the interepicondylar line was measured in millimeters. The first muscular branch leaving the main ulnar nerve was the FCU-branch in all specimens. The terminal muscular branch of the ulnar nerve to the forearm muscles arose at the proximal 1/3 of the forearm in all specimens. In 7 forearms, Martin-Gruber anastomosis in form of median to ulnar was observed.     

断掌再植的神经解剖学基础

目的：为断掌再植的神经修复提供解剖学基础。方法：对30侧成人手标本掌部浅、深两层的主要神经分支进行解剖。以远侧腕横纹为横坐标，以掌中线为纵坐标对掌部主要神经分支的起、止点进行坐标测量。将手掌部划分为64个正方形小区，按照掌部主要神经分支起、止坐标对各神经进行小区定位，确定各神经分支的体表投影。模拟不同平面断掌，确定各断掌平面应修复的神经。结果：R1T3、R1T4、R2T2、R2T3、R2T45个小区集中了正中神经返支、正中神经分叉处及尺神经深支的大鱼际肌段，此区域神经分支较多，是断掌时神经修复的重要区域。U2T1、U2T2、U3T33个小区有尺神经深支通过，通过此三小区的断掌应仔细修复尺神经深支。结论：本文结果可供对断掌及其他手掌外伤的神经损伤修复作出较为准确的定位，并根据预测结果对掌部损伤神经进行有目的的修复。