The implications of thumb movements for Neanderthal and modern human manipulation.

Much research has debated the technological abilities of Neanderthals relative to those of early modern humans, with a particular focus on subtle differences in thumb morphology and how this may reflect differences in manipulative behaviors in these two species. Here, we provide a novel perspective on this debate through a 3D geometric morphometric analysis of shape covariation between the trapezial and proximal first metacarpal articular surfaces of Neanderthals (Homo neanderthalensis) in comparison to early and recent humans (Homo sapiens). Results show a distinct pattern of shape covariation in Neanderthals, consistent with more extended and adducted thumb postures that may reflect habitual use of grips commonly used for hafted tools. Both Neanderthals and recent humans demonstrate high intraspecific variation in shape covariation. This intraspecific variation is likely the result of genetic and/or developmental differences, but may also reflect, in part, differing functional requirements imposed by the use of varied tool-kits. These results underscore the importance of holistic joint shape analysis for understanding the functional capabilities and evolution of the modern human thumb.

The Flexor Pollicis Longus Tendon Does Not Lie Parallel to the Thumb Metacarpal.

BACKGROUND: Repair of the flexor pollicis longus (FPL) tendon by tendon retriever can be challenging because of uncertainty of the optimal direction. This study aims to describe the FPL tendon path in the thenar eminence. METHODS: In 18 hands of 9 cadavers, the angle of the FPL tendon was, after dissection, measured in relation to the axis formed between the metacarpophalangeal (MCP) joint of the thumb and the dorsal carpometacarpal joint (MC1-axis) and the axis formed between the second MCP joint and the distal edge of the trapezium (MC2-axis). RESULTS: The FPL does not follow the angle of the thumb metacarpal. The FPL runs ulnarly from the MC1-axis at a median of 32.5° in abduction and 30.6° in adduction. In relation to the MC2-axis, it runs at a median of 47.5° in abduction and 25° in adduction. CONCLUSIONS: The FPL tendon path can be preoperatively marked using: (1) the MC1-axis from which it runs ulnarly approximately at an angle of 30° in both abduction and adduction; or (2) the MC2-axis from which it runs radially at an angle of 47.5° in abduction and at an angle of 25° in adduction. We conclude that the FPL tendon path can be preoperatively marked using these axes and does not parallel the metacarpal axes of the thumb.

A Cadaveric Study of the Mean Distance of the Radial Artery During the Approach to the First Carpometacarpal Joint.

Multiple surgical procedures have been described to treat first carpometacarpal (CMC) arthritis. Although the superiority of one procedure over the others continues to be a controversial topic, they all approach the trapezium and require careful attention to the surrounding structures. One potential complication is injury to the radial artery, which lies in close proximity to the trapezium and is often encountered during surgical approach. Using cadaveric specimens, the authors dissected to identify and isolate the radial artery as it travels in the forearm, wrist, and hand while being careful not to disturb its native course. The authors then measured the shortest distance interval from the radial artery to the first CMC joint and from the radial artery to the scaphotrapeziotrapezoidal joint. Descriptive statistics were calculated from these measurements and averaged over the various specimens. The mean distance of the radial artery to the closest segment of the volar CMC joint was 11.6±2.5 mm. The mean distance of the radial artery to the closest segment of the volar scaphotrapeziotrapezoidal joint was 1.6±1.8 mm. A precise understanding of nearby anatomy is paramount to a successful surgical treatment for first CMC arthritis and to avoid iatrogenic complications. The authors describe the mean distance from the radial artery to 2 major landmarks used during surgical treatment and provide insight to surgeons who perform these CMC reconstruction procedures to decrease the risk of intraoperative radial artery injury. [Orthopedics. 2018; 41(4):e541-e544.].

Trapezium anatomy as a radiographic reference for optimal cup orientation in total trapeziometacarpal joint arthroplasty.

In trapeziometacarpal arthroplasty, correct implant position may be necessary to prevent complications such as dislocation, component loosening and premature wear. The metacarpal stem more easily fits anatomically. However, the cup in the trapezium is not anatomical and guidelines for its orientation are not uniformly defined. We determined the centre of the range of motion of the trapeziometacarpal joint in 30 healthy patients on postero-anterior and lateral radiographs and its relationship to the proximal articular surface of the trapezium. Our study suggests that in thumb carpo-metacarpal total joint arthroplasty, the prosthetic cup in the trapezium should be placed parallel to the proximal articular surface of the trapezium and combined with a metacarpal neck with 7° palmar offset. This should optimize arthroplasty ranges of motion and may minimize the risk of postoperative complications. Our study provides a reference for the surgeon to check correct cup alignment intra-operatively with fluoroscopy.

Men and women have similarly shaped carpometacarpal joint bones.

Characterizing the morphology of the carpometacarpal (CMC) joint bones and how they vary across the population is important for understanding the functional anatomy and pathology of the thumb. The purpose of this paper was to develop a statistical shape model of the trapezium and first metacarpal bones to characterize the size and shape of the whole bones across a cohort of 50. We used this shape model to investigate the effects of sex and age on the size and shape of the CMC joint bones and the articulating surface area of the CMC joint. We hypothesized that women have similar shape trapezium and first metacarpal bones compared to men, following scaling for overall size. We also hypothesized that age would be a significant predictor variable for CMC joint bone changes. CT image data and segmented point clouds of 50 CMC bones from healthy adult men and women were obtained from an ongoing study and used to generate two statistical shape models. Statistical analysis of the principal component weights of both models was performed to investigate morphological sex and age differences. We observed sex differences, but were unable to detect any age differences. Between men and women the only difference in morphology of the trapezia and first metacarpal bones was size. These findings confirm our first hypothesis, and suggest that the women have similarly shaped trapezium and first metacarpal bones compared to men. Furthermore, our results reject our second hypothesis, indicating that age is a poor predictor of CMC joint morphology.

Dimensions of the trapezium bone: a cadaver and CT study.

PURPOSE: The primary purpose of this study was to define the size of the trapezium bone through measurements on cadaver specimens and CT scans of living subjects. The secondary purpose of this study was to determine if any correlation existed between the size of the trapezium and local anatomical parameters. METHODS: The radio-ulnar length (L), dorsopalmar width (ℓ) and height (h) of the distal surface of the trapezium were measured by two independent observers on 20 cadaver specimens. The same measurements were carried out by two other observers on anonymized CT scans from 18 patients. The inter- and intra-observer agreement was determined using the intraclass correlation coefficient. RESULTS: In the cadavers, the mean length, width and height of the trapezium were 22.8, 15.5 and 15.2 mm, respectively. On the CT scans, these same dimensions were 19.2, 11.4 and 11.6 mm. Inter-observer agreement was statistically significant in both parts of the study. DISCUSSION: The dimensions of the trapezium bone were about 3.33 mm larger in cadavers than on CT scans. These differences can be explained partially by a systematic under-sizing error on the CT scans and the fact that the cartilage layer cannot be directly visualized. CONCLUSION: This study was able to define the dimensions of the trapezium bone. It may be possible to predict the trapezium height from the length of the forearm or the width of the radial epiphysis. Our data can be used to adjust the size of trapezium implants to the dimensions of the patient's bone.

Polar histograms of curvature for quantifying skeletal joint shape and congruence.

The effect of articular joint shape and congruence on kinematics, contact stress, and the natural progression of joint disease continue to be a topic of interest in the orthopedic biomechanics literature. Currently, the most widely used metrics of assessing skeletal joint shape and congruence are based on average principal curvatures across the articular surfaces. Here we propose a method for comparing articular joint shape and quantifying joint congruence based on three-dimensional (3D) histograms of curvature--shape descriptors that preserve spatial information. Illustrated by experimental results from the trapeziometacarpal joint, this method could help unveil the interrelations between joint shape and function and provide much needed insight for the high incidence of osteoarthritis (OA)--a mechanically mediated disease whose onset has been hypothesized to be precipitated by joint incongruity.

Three-dimensional quantitative comparative analysis of trapezial-metacarpal joint surface curvatures in human populations.

PURPOSE: Trapezial-metacarpal (TM) joint surfaces appear to be shallower in Asian than in white postmortem specimens, and the frequency of TM osteoarthritis seems to be substantially lower in Asian TM joints. This study tested the hypothesis that there are significant differences among human populations in TM joint surface curvature and that populations of Asian descent have less curvature than those of recent European descent. METHODS: The sample included trapeziums and first metacarpals from skeletons of 80 individuals of recent European and Asian descent and from skeletons of 34 African and 9 Australian aboriginal individuals. We scanned the surfaces using a laser digitizer to generate 3-dimensional models of each articular surface. We calculated dorsovolar, radioulnar, and root mean square curvatures by fitting modeled quadric surfaces to the TM joint surfaces. We tested pairwise comparisons of mean curvatures between populations for statistical significance using a standard resampling method (ie, bootstrapping). We also made pairwise comparisons of mean curvatures between males and females for a combined African and European sample. RESULTS: Mean dorsovolar metacarpal curvature was significantly higher in the European sample than in the Asian, African, and Australian samples. Mean root mean square curvature of the trapezial surface was significantly higher in the European sample than in the Asian sample. The European sample had the highest root mean square and dorsovolar trapezial curvatures of all the populations. We found no significant differences between male and female specimens. CONCLUSIONS: A tendency toward higher mean dorsovolar curvature of both the metacarpal and trapezial surface in the European sample may help to explain the higher frequency of TM osteoarthritis reported in Europeans. CLINICAL RELEVANCE: The greater TM curvatures affect basal thumb joint mechanics in thumb opposition and therefore may be a factor in the development of osteoarthritis at this joint in Europeans.

Arthroscopic hemiresection for stage II-III trapeziometacarpal osteoarthritis.

Trapeziometacarpal osteoarthritis is a common problem, due to the anatomy of the first ray and the forces applied to the trapeziometacarpal joint throughout activities of daily living. Numerous treatment options exist, and continue to be developed, for this problem. The current goal is to eliminate pain and restore function and strength in a timely manner. New advances allow for earlier return to function with minimally invasive techniques. Arthroscopic hemitrapeziectomy combined with interposition arthroplasty and/or suspensionplasty is a treatment option for Stage II and III trapeziometacarpal arthritis that uses a minimally invasive technique and allows for earlier return of function.

Bone-preserving arthroscopic options for treatment of thumb basilar joint arthritis.

While trapeziectomy with or without interposition arthroplasty and ligament reconstruction or suspensionplasty have been demonstrated to have a high rate of satisfactory outcomes, recent interest has focused on arthroscopy because of its perceived limited invasive nature as well as its versatility. In addition, using the arthroscope, other options are available that preserve all or part of the trapezium to limit subsidence of the thumb axis, preserve grip and pinch strength, and retain later options for joint reconstruction, should that become necessary.

Scaphotrapezial ligament: normal arthro-CT and arthro-MRI appearance with anatomical and clinical correlation.

The purpose of our study was to demonstrate and describe the MR and arthro-CT anatomic appearance of the scaphotrapezial ligament and illustrate some of the pathologies involving this structure. This ligament consists of two slips that originate from the radiopalmar aspect of the scaphoid tuberosity and extend distally, forming a V shape. The ulnar fibers, which are just radial to the flexor carpi radialis sheath, inserted along the trapezial ridge. The radial fibers were found to be thinner and inserted at the radial aspect of the trapezium. Twelve fresh cadaver wrists were dissected, with close attention paid to the scaphotrapezio-trapezoidal (STT) joint. An osseoligamentous specimen was dissected with removal of all musculotendinous structures around the STT joint and was performed with high-resolution acquisition in a 128-MDCT scanner. Samples of the wrist area were collected from two fetal specimens. A retrospective study of 55 patients with wrist pain that were submitted to arthrography, arthro-CT, and arthro-MRI imaging was performed (10 patients on a 3-T superconducting magnet and 45 patients on a 1.5-T system). Another ten patients had high-resolution images on a 3-T superconducting magnet without arthrographic injection. MR arthrography and arthro-CT improved visualization and provided detailed information about the anatomy of the scaphotrapezial ligament. Knowledge of the appearance of this normal ligament on MRI allows accurate diagnosis of lesions and will aid when surgery is indicated or may have a role in avoiding unnecessary immobilization.

Anatomía quirúrgica de la arteria dorsal de la escápula: su participación en la irrigación del colgajo miocutáneo de trapecio / Surgical anatomy of the dorsal scapular artery: its participation in the blood supply to the miocutaneous trapezius flap

Objetivo: confirmar y documentar la presencia deuna rama de la arteria dorsal de la escápula (ó dorsalescapular) como un pedículo constante, de diámetroadecuado y fuente principal de irrigación del colgajo detrapecio inferior.Alrededor de 1980 se utilizó el colgajo de trapecio inferior para cubrir defectos de la región posterior ylateral de cuello, cuero cabelludo y calota craneana (1).Sin embargo su uso fue disminuyendo al publicarse laalta incidencia de necrosis del colgajo. Una de las causas de los fracasos fue el desacuerdo respecto a suaporte arterial principal: la arteria cervical transversa(transversa colli) o la arteria dorsal de la escápula -ADE-(2,3). Esto incentivó la investigación para definir su anatomía vascular, así como comprobar el origen y la frecuencia de un vaso arterial que irrigue el segmento caudal del trapecio.Materiales y Método. Se utilizaron 44 cadáveres formolizados al 10% y 1 cadáver fresco; adultos, 24femeninos y 21 masculinos en la Cátedra de Anatomía Normal, Fac. de Ciencias Médicas, Universidad Nacio-nal de Córdoba.Resultados. En 89 especímenes (98,9%) se identificó un pedículo que irriga la porción inferior del trapecio: la rama trapecial de la arteria dorsal de la escápula.Este vaso fue identificado, documentado y utilizado comopedículo principal en los angiogramas de piezas anató-micas y en las cirugías reconstructivas realizadas.Conclusiones. El tercio inferior del trapecio tieneun pedículo vascular constante que es la rama trapecialde la arteria dorsal de la escápula, la cual emerge en laregión paraescapular medial entre el músculo romboidesmenor y mayor. Se compara y discute la literatura con los hallazgos anatómicos de este trabajo realizado en Córdoba.

Objetive: corroborate y record the presence of onebranch of the dorsal scapular artery as a constant pediclewith appropiate diameter and as the major contributor tothe blood supply to the lower trapezius flap. Around 1980,the lower trapezius flap was used to cover defects in backand lateral neck regions, scalp and skull cap. However,its usage decreased when the high incidence of flap ne-crosis was published. One of the probable causes offailures was the disagreement as regards its principalarterial contribution: the transverse cervical artery or thedorsal scapular artery. This motivated research to defineits vascular anatomy, and confirm the origin and thefrequency of an arterial vessel which irrigates the trapeziuscaudal segment.Materials and Method we used for this study 44bodies fixed in 10% formaldehyde and 1 fresh cadaver.All were adults , 24 female and 21 male, and thedissections were perform in the Cátedra de AnatomíaNormal, Facultad de Cs Médicas, Universidad Nacionalde Córdoba .Results: in 89 specimens (98,9%) we found apedicle that contribute to the irrigation of the lowertrapezius: the trapecial branch of the dorsal scapular artery.This vessel was identified, recorded and used as mainpedicle in the anatomical specimen ́s angiograms andduring the reconstructive surgeriesConclusions: the lower third of the trapeziusmuscle have a constant vascular pedicle: the trapeziusbranch of the dorsal scapular artery, wich arise in themedial para-scapular area, between the rhomboideusminor and rhomboideus major. The internationalliterature was com pared and discussed with theanatomical findings of this work carried out in Córdoba.

Sonography of the anterior oblique ligament of the trapeziometacarpal joint: a study of cadavers and asymptomatic volunteers.

OBJECTIVE: The purpose of this study was to evaluate the ability of ultrasound to identify and characterize the anterior oblique ligament of the thumb in cadavers and asymptomatic volunteers. SUBJECTS AND METHODS: The anterior oblique ligaments of four cadaveric hands were imaged with a high-resolution transducer. The ligaments were then injected with 0.1% methylene blue using ultrasound guidance. To confirm identification of the ligament, the base of the thumb was immediately dissected, revealing the exact location of the dye. The bilateral ligaments in 40 asymptomatic adult volunteers were imaged. RESULTS: Surgical dissection confirmed injection of methylene blue into all cadaveric ligaments. The proximal attachment of the anterior oblique ligament was well defined in all the hands, and the distal attachment was well defined in 94% of the hands. The mean thickness of the anterior oblique ligament at the metacarpal attachment (0.7 mm), midportion (0.98 mm), and trapezial attachment (0.65 mm) did not differ significantly with respect to sex, right and left side, or hand dominance and was weakly correlated with weight, height, body mass index, and age. The length of the ligament was statistically significantly different between the dominant (10.6 mm) and nondominant (9.6 mm) hands. The volar metacarpal translation with palmar abduction stress did not differ significantly between the dominant (0.7 mm) and nondominant (0.8 mm) hands. There was no association between the degree of translation and the biologic characteristics (weight, height, body mass index, and age). CONCLUSION: High-resolution ultrasound can be used to identify and measure the thickness of the anterior oblique ligament. Dynamic ultrasound imaging can depict volar translation of the metacarpal, which may facilitate diagnosis of ligamentous injury.

Method for the estimation of a double hinge kinematic model for the trapeziometacarpal joint using MR imaging.

In this paper, we propose a method to estimate the parameters of a double hinge model of the trapeziometacarpal joint (TMC) by MRI-based motion analysis. The model includes two non-orthogonal and non-intersecting rotation axes accounting for flexion-extension (F-E) and adduction-abduction (A-A). We evaluated the quality of the estimated model parameters in the prediction of the relative motion of the first metacarpal bone with respect to the trapezium. As a result, we obtained that: (a) the estimated location and orientation of the F-E and A-A axes were in agreement with previous in vitro studies, (b) the motion of the first metacarpal predicted by the 2 degrees of freedom (2DoF) model exhibits a maximum surface distance error in the range of about 2 mm and (c) four thumb postures at the boundary of the TMC range of motion are sufficient to provide a good estimation of the 2DoF TMC kinematic model and good reproducibility (~1.7 mm) of the real thumb motion at TMC level.

Imaging the ligaments of the trapeziometacarpal joint: MRI compared with MR arthrography in cadaveric specimens.

OBJECTIVE: The purpose of our study was to compare the normal ligamentous anatomy of the trapeziometacarpal joint in cadavers on conventional MRI and MR arthrography and review the most common diseases and abnormalities that affect this articulation. MATERIALS AND METHODS: MR images of seven trapeziometacarpal joints of seven fresh cadaveric hands were obtained before and after arthrography. The MR appearances of the ligaments around the trapeziometacarpal joint were analyzed and correlated with corresponding anatomic sections. The imaging planes that allowed best analysis of these structures were determined. RESULTS: Five ligaments around the trapeziometacarpal joint were generally recognized: the dorsoradial ligament; the posterior oblique ligament; the intermetacarpal ligament; the ulnar collateral ligament (UCL); and both portions of the anterior oblique ligament, the superficial anterior oblique and deep anterior oblique ligaments. The former three were attached to the dorsal aspect and the latter three to the volar aspect of the trapeziometacarpal joint. The dorsoradial ligament, posterior oblique ligament, intermetacarpal ligament, and superficial and deep anterior oblique ligaments were best visualized in the sagittal plane, whereas the UCL was best visualized in the coronal plane. MR arthrography mainly improved visualization of the intermetacarpal ligament, superficial and deep anterior oblique ligaments, and UCL. CONCLUSION: MR arthrography improves visualization of and provides detailed information about the anatomy of the ligaments around the trapeziometacarpal joint. Knowledge of the appearance of these normal ligaments on MRI allows accurate diagnosis of lesions of the trapeziometacarpal ligaments and of the adjacent structures and aid the attending physician if and when surgery is indicated.

The mend of the bend-flexor pollicis longus tendon has an additional pulley distal to its point of angulation.

The tendon of flexor pollicis longus angulates at the trapezio-metacarpal joint level. The degree of angulation varies with extent of radial/ulnar deviation (Rack and Ross [1984] J. Physiol. 351:99-110). We report a fibrous pulley at this level that helps stabilize the tendon and facilitates its action. The morphology of the pulley is described. We believe that it has an important role to play in the unique function of the tendon facilitating the movement of the thumb perpendicular to the plane of the thumbnail.

[Arthroscopy of the trapeziometacarpal joint: anatomical study on cadavers]. / Artroscopía de la articulación trapeciometacarpiana: estudio anatómico en cadáver.

INTRODUCTION: Osteoarthritis of the trapeziometacarpal joint is one of the most common degenerative diseases of the hand for which a variety of surgical procedures have been developed. Arthroscopic techniques offer good results, although they have not been standardized. OBJECTIVE: To identify the main anatomical structures in relation to arthroscopy portals from the trapeziometacarpal joint and to determine their security area. MATERIAL AND METHODS: We conducted a transversal and descriptive study in which the anatomy was analyzed in seven cadaveric specimens. Fourteen thumbs were dissected after the arthroscopic portals were made. In all of the specimens the distance between the radial artery, the articular line and the arthroscopy portals was measured. RESULTS: The radial artery was found dorsal to the Extensor Pollicis Longus (EPL), 4-5 mm proximal to the dorsal arthroscopic portal, 4-8 mm to the articular line and 8-11 mm to the Extensor Pollicis Brevis (EPB). In two cases sensitive branches of the radial nerve were found through the dorsal portal. CONCLUSION: The anatomical evaluation defined a secure area for the dorsal portal between the EPL and the EPB. The proximal radial zone to the EPL must be avoided so that the dorsal branch of the radial nerve is not damaged.

The use of a dorsal-distal portal in trapeziometacarpal arthroscopy.

An accessory dorsal-distal portal (D-2) was developed to improve the visualization of the medial aspect of the trapezium during an arthroscopic trapeziectomy. This portal is ulnar to the extensor pollicis longus tendon and 1 cm distal to the V-shaped cleft at the juncture of the index and thumb metacarpal bases. The entry site is marked before the tourniquet is elevated to allow palpation or Doppler ultrasound of the radial artery in the anatomic snuffbox. A 22-gauge needle is inserted with proximal, radial, and palmar angulation to penetrate the joint space, which is viewed from either the 1-R or 1-U portal. A small skin incision is made and is followed by the insertion of a blunt trocar and cannula. An anatomic dissection of 5 cadaveric hands revealed that branches of the superficial radial nerve passed within 3.2 mm, the radial artery was 3.8 mm away, the first dorsal metacarpal artery was within 2.8 mm of this portal, and the cephalic vein was within 2.8 mm of this portal. On average, the D-2 portal was 17.2 mm from the 1-U portal (range, 12 to 20 mm). This study provides a safe, standardized approach to the D-2 portal for trapeziometacarpal arthroscopy, which is useful for evaluation of the dorsal capsular ligaments, provides access to medial osteophytes during an arthroscopic partial trapeziectomy, aids in the reduction of intra-articular metacarpal base fractures, and facilitates triangulation of the instruments.

Anthropometric characteristics of wrists joint surfaces depending on lunate types.

It is well known that the lunate presents with two main types: lunate type I has one facet of its distal surface only for capitates, whereas lunate type II has two facets of the same surface for capitate and for hamate. Our previous anthropometric studies showed that the lunate type II wrists are of greater size than the lunate type I wrists. The aim of the present study was to determine whether the lunate types and the presence or absence of hamato-lunate joint correlate with anthropometric characteristics of the joint surfaces of other wrists. Sixteen sets of macerated wrists with the lunate type I and 21 with the lunate type II were studied. Two-thousand-four-hundred-and-forty-eight anthropometric measurements were done (for 68 anthropometric indicators) and 864 anthropometric indices were calculated (for 24 anthropometric indices) separately for the wrist joint surfaces. The absolute value of the anthropometric indicators of the joint surfaces of the separated wrists were greater in the wrists with the lunate type II, except for the indicators "Greatest length of the dorsal joint surface of pisiform", "Width of the proximal joint surface, measured in the middle" and "Greatest width of the proximal joint surface" for the trapezoid and "Greatest height of the ulnar joint surface" for the capitate. The enlargement of the joint surfaces for the scaphoid was mainly in proximo-distal direction. The enlargement for the triquetrum and pisiform was mainly in radio-ulnar direction. The enlargement for trapezium, trapezoid and capitate was mainly in dorso-volar direction (except for the ulnar joint surface of capitate). The enlargement for hamate was mainly in radio-ulnar and dorso-volar directions (except for the joint surfaces for capitate and triquetrum). The calculated indices illustrate the quantitative proportions of the variations mentioned above. The anthropometric differences are a good reason to make a clear distinction between both types of wrist joint complexes-with or without a hamato-lunate joint.

Identification of two accessory muscle bundles with anomalous insertions in the flexor side of the right forearm.

During dissection practice held at Kyorin University School of Medicine in 2004, two anomalous muscles were observed on the Rt-forearm-flexor-side of an 83-year-old man. The results of this investigation are reported. One accessory muscle originated from the tendinous insertion of the biceps brachii and medial epicondyle. After passing through the deep layer of the pronator teres, it became tendinous, passing towards the trapezium and second metacarpal base. Its two origins fused superficial to the ulnar artery distal to the cubital fossa, and it merged with the deep region of the pronator teres. More distally, the accessory muscle formed a belly before again becoming tendinous and bifurcated, one branch attaching to the trapezium and the other fusing with the belly of the second accessory muscle. These findings suggested that this accessory muscle was similar to Gantzer's muscle. The other accessory muscle arose distal to the origin of the flexor pollicis longus and inserted onto the second metacarpal base. In addition, from the distal side of its origin, a small muscle bundle was formed and became tendinous. It fused with the insertion tendon of the first accessory muscle to the trapezium. The second accessory muscle was thought to be deep radial carpal flexor.