Variant of the extensor pollicis tertius: a case report on a unique extensor muscle to the thumb

Variations on muscular and tendinous connections of the hand occur frequently in the human population and are often discovered during routine surgical procedures and cadaveric dissections. A knowledge of such anomalies is important to the physician in order to avoid unintentional damage to healthy tendons during surgical procedures. In addition, accessory tendons have the potential to be used in the repair or replacement of damaged tendons through surgical transfer or transplantation. Here we describe a unique variant of the extensor pollicis tertius muscle that has its origin at the proximal end of the extensor indicis muscle and inserts on the tendon of the extensor pollicis longus at the proximal shaft of the proximal phalanx of the thumb.     

Undescribed variant muscle – “Deep abductor-flexor” of the little finger, in relation to ulnar nerve compression at the wrist

During routine anatomical dissection in the hypothenar region of the left hand of a 64-year-old female cadaver, a number of variant structures were observed. The most prominent finding in our case was a supernumerary muscle hitherto unknown in the anatomical literature. This variant muscle had a muscular body formed by the connection of two deeply situated muscular bellies--medial and lateral. The lateral belly originated from the flexor retinaculum, the medial one--from the hamate bone. The common muscular body inserted to the antero-lateral surface of the base of the fifth proximal phalanx. Due to its location and possible function, we named the variant muscle "deep abductor-flexor" of the little finger. The flexor digiti minimi brevis muscle showed two proximal tendons--the medial tendon was attached to the hamulus of the hamate bone while the aberrant lateral tendon originated from the lateral part of the flexor retinaculum. Both, the aberrant lateral tendon of the flexor digiti minimi brevis and the lateral belly of the "deep abductor-flexor", passed over the palmar branch of the ulnar nerve, which define their possible clinical significance in ulnar nerve compression. Therefore, the variations of the hypothenar muscles are reviewed and their relation to the compression of the ulnar nerve is discussed.     

Anatomic variation of the 5th extensor tendon compartment and extensor digiti minimi tendon

Anatomic variation within the 5th extensor compartment may contribute to the development of tenosynovitis and limit the usefulness of the extensor digiti minimi (EDM) for tendon transfer. The purpose of this study was to assess the anatomic variation of the EDM tendon and its surrounding retinaculum, with particular attention to anatomical variation between specimens. Forty-one fresh cadaver hands were dissected. The length of the 5th compartment retinaculum was noted. The incidence of an intercompartmental septum was noted in each specimen as well as the type of tendinous attachments present between the EDM and extensor digitorum communis (EDC) tendons. The presence and length of any accessory retinacular bands distal to the edge of proper extensor retinaculum was also noted. Only one specimen contained a single EDM tendon, while 71% (n = 29) of specimens contained two slips and 23% (n = 9) had three slips; 24% (n = 10) of EDC tendons had no slip to the small finger, while 61% (n = 25) of specimens had a single slip to the small finger. The EDC's contribution to the small finger was found to be an independent tendon in 42% of cases (n = 17), while 34% (n = 14) of specimens were found to have a common EDC slip, which branched to both the ring and small finger. Three EDM tendons divided distal to the extensor retinaculum, while the remaining EDM tendons divided beneath or proximal to the extensor retinaculum. Seventy-three percent (n = 30) of the specimens had an accessory retinacular band surrounding the EDM tendon identified at the base of the 5th metacarpal. Eighty-eight percent (n = 36) of hands had a septum between the EDM slips. The surgeon should be aware of variability within the 5th dorsal compartment in cases of trauma and in cases of tendon transfer. In our series 30 of 41 specimens were noted to contain an accessory dorsal retinacular band surrounding the EDM and 36 specimens were noted to contain a septum within the 5th compartment. The presence of an accessory retinacular band surrounding the EDM at the level of the 5th metacarpal base is an anatomic finding that requires further investigation.     

Unusual accessory tendon connecting the hallucal extensors

During routine dissection of an adult human cadaver, a suite of tendinous anomalies was discovered in the left hallucal region. Whereas the main tendon of the extensor hallucis longus muscle inserted normally, two accessory tendons were found coursing medial and lateral to the main tendon. The most lateral tendon originated from a supernumerary muscle belly and merged with the tendon of extensor hallucis brevis to form a composite tendon. The most medial tendon crossed the metatarsophalangeal joint and joined the composite tendon deep to the tendon of extensor hallucis longus. A terminal tendon, consisting of these three contributions, inserted upon the proximal hallucal phalanx. This variant likely arose due to atypical differentiation of the common extensor muscle mass during development, and is of particular significance to clinicians performing arthroscopy, tendon transfers, and other surgical procedures.     

Morphology and functional anatomy of the first dorsal interosseous muscle of the hand

The aim of this study, based upon anatomical and electrophysiological evaluation, was to identify the relationship between the morphology and physiology of the first dorsal interosseous muscle of the hand, which should be distinguished from the other dorsal interosseous muscles of the hand. Its morphology, distal attachments and physiology have been subject of numerous studies yielding conflicting results. The study reported herein was made on the basis of anatomical and electrophysiological investigation. Most of the dissections (20/34) were made on fresh specimens. Results of this study confirm the existence of the deep and superficial heads of the 1st dorsal interosseous muscle. The muscle is attached distally to the palmar plate of the metacarpophalangeal joint, the lateral tubercle of the base of the proximal phalanx of the index and the interosseous hood. Conversely, the muscle did not show any attachment to the oblique radial wing of the extensor apparatus in our dissections. The deep head of the muscle causes mainly flexion pinch between thumb and index superficial head abduction. Within the complex physiology of the various types of apposition of thumb and index, the dorsal interosseous muscle acts as a stabilizer. The results of electrophysiological study confirmed most of the interpretations deduced from morphological investigation.     

The fourth lumbrical muscle in the hand: a variation of insertion on the fifth finger

Usually the four lumbrical muscles arise from the tendons of flexor digitorum profundus and insert into the extensor expansions on the radial side of the corresponding fingers. This special case showed a very rare variation of a unipennate fourth lumbrical muscle of the right hand; the muscle fibre bundles originated on the radial side of the flexor digitorum profundus and coursed horizontal on its radial side, deep to the palmar aponeurosis and in front of the deep transverse metacarpal ligament over the fifth metacarpophalangeal joint. At the level of this joint, its tendon divided into one radial and one ulnar slips. Both heads surrounded the tendons of the flexor digitorum superficialis and profundus muscles, and found their insertion into the flexor digitorum superficialis tendon, as well as their bony attachment into the proximal and even more into the middle phalanx.     

An uncommon form of the rare extensor carpi radialis accessorius.

Two accessory muscles were found in the lateral compartment of the forearm while dissecting a 92-year-old female cadaver. One of these originated from the extensor carpi radialis brevis, became tendinous and travelled between the two radial extensor tendons. It inserted independently into the second metacarpal bone, and may be regarded as an extensor carpi radialis intermedius. The other accessory muscle originated from the extensor carpi radialis longus, passed superficially over the parent tendon and inserted into the abductor pollicis brevis. This variation appeared to be a rare extensor carpi radialis accessorius, an additional muscle, which usually arises from below the extensor carpi radialis longus and inserts into the first metacarpal bone. Various forms of the accessorius have been described previously, including one that inserts into the abductor pollicis brevis. The tendon of the accessory muscle described in this study passed through its own dorsal tunnel under the extensor retinaculum, making it an uncommon form of the rare accessorius.     

Extensor pollicis et indicis communis or extensor indicis radialis muscle

Anatomical variations of the fingers extensor tendons are not uncommon and have been described by several authors. Participation of intertendinous band of fascia in this kind of variation can change muscle functionality. However, this element is scarcely described in the literature. In this case report, we describe the finding of an accessory tendon located between the extensor digitorum communis muscle tendon, destined for the index finger, and the extensor pollicis longus tendon. In an anatomical analysis, we observed a connection between the radial portion of the accessory tendon and the ulnar portion of the extensor pollicis longus tendon by intertendinous fascia. This finding corresponds anatomically to the supernumerary muscle denominated extensor indicis radialis, but due to the fascial connections observed with the extensor pollicis longus, this muscle would behave functionally as a supernumerary muscle denominated extensor pollicis et indicis communis. This report suggests that participation of fascia in muscular variation in this anatomical segment is essential to establish the correct morpho-functional denomination of muscular variants.     

An unique variation of the peroneus tertius muscle

Peroneus tertius (fibularis tertius) is a muscle unique to humans. It often appears to be a part of extensor digitorum longus, and might be described as its "fifth tendon". Although its insertion variation has been reported by many authors, variations of its origin points are not common. A variation of the peroneus tertius muscle was found during routine dissection of a 75-year-old male cadaver. The muscle originated from the extensor hallucis longus. The muscle belly of the extensor hallucis longus arose from the middle two-fourths of the medial surface of the fibula, medial to the extensor digitorum longus, and anterior surface of the interosseous membrane. It lay under the extensor digitorum longus, and lateral to the tibialis anterior muscle. The muscle belly of the extensor hallucis longus divided into medial and lateral parts 17 cm below its origin point. The lateral part, named as peroneus tertius, continued downward to reach the medial part of the dorsal surface of the base of the fifth metatarsal bone. The medial part ran also downward and divided into two tendons reaching the dorsal surface of the base of the distal phalanx of the great toe. This kind of variation may be important during foot or leg surgery.     

Multiple variations in the region of Mm. extensores carpi radialis longus and brevis.

While dissecting the body of an 80-year-old female we observed multiple variations in the right region of Mm. extensores carpi radialis longus and brevis. The M. extensor carpi radialis longus gave origin to an accessory head. The tendon of this accessory head passed through a separate tunnel in the extensor retinaculum and inserted in the middle of the first metacarpal bone. Concerning its function, this accessory head of the M. extensor carpi radialis longus could be regarded as an additional abductor pollicis. The M. extensor carpi radialis brevis had an accessory tendon lying underneath the main tendon of this muscle. The accessory tendon joined with the main tendon just when undercrossing Mm. abductor pollicis longus and extensor pollicis brevis. Afterwards the tendon lay in the second tunnel of the extensor retinaculum and inserted in the base of the third metacarpal. In her lifetime the individual's tabatière probably must have been conspicuously pronounced at its radial margin.     

手指伸肌腱Ⅰ区肌腱末节指骨止点与毗邻组织的应用解剖学研究

目的　通过对手指伸肌腱Ⅰ区肌腱末节指骨止点与毗邻组织的解剖研究，为骨性锤状指微型钢板内固定手术提供解剖依据。 方法　解剖观测10例成人尸体上肢手标本，观察指甲根部甲基质、甲根与伸肌腱Ⅰ区末节指骨止点的解剖关系，测量伸肌腱Ⅰ区末节指骨止点至甲根、甲基质、关节面距离，测量伸肌腱Ⅰ区末节指骨止点的宽度，测量末节指骨关节面水平的横径及纵径。显微镜下观察伸肌腱Ⅰ区末节指骨止点的形态及其与周围组织之间的联系。 结果　甲根近端未能完全覆盖甲基质，甲基质与伸肌腱Ⅰ区末节指骨止点相距（1.21±0.21）mm，两者之间平铺一层疏松结缔组织。伸肌腱Ⅰ区末节指骨止点宽度为（6.27±1.23）mm，在关节水平厚度为（1.02±0.21）mm。伸肌腱Ⅰ区末节指骨止点在肌腱掌侧面至末节指骨关节面（1.22±0.21）mm。末节指骨的关节面水平的横径为（8.00±2.21）mm，纵径为（6.22±1.21）mm。伸肌腱Ⅰ区与远侧指间背侧关节囊联系紧密，显微镜下解剖未见两者之间存在明显的解剖间隙。 结论　末节指骨背侧正中皮肤切口可充分显露伸肌腱Ⅰ区末节指骨止点周围组织结构；在应用微型钩状钢板固定骨性锤状指末节撕脱骨折块时，钢板远端与甲基质部分重叠，需要部分切开甲根及甲基质。伸肌腱Ⅰ区与远侧指间背侧关节囊联系紧密，该处伸肌腱终腱存在类似掌板样纤维软骨组织。     

The abductor pollicis longus: relation between innervation, muscle bellies and number of tendinous slips

The aim of this study was to assess the relation between the insertions of the distal tendinous slips, the muscle bellies and the innervation pattern of the abductor pollicis longus (APL) muscle and of the extensor pollicis brevis (EPB). The upper extremities of 31 frozen cadavers were dissected under magnifying lenses to describe the distribution of the posterior interosseous nerve (PION). The number and the distribution of distal tendinous slip insertions of the APL muscle were variable. Two superficial and deep distal tendon groups were noted. The separation into superficial and deep muscular parts of the APL was frequent (87%). The EPB muscle was generally constituted by one muscle belly and one tendinous slip (93.5%). The innervation by the PION to the APL and EPB muscles was classified into five types. The specific innervation between superficial and deep muscular parts of the APL muscle, the specific innervation of the deep muscle bellies and the independence of the superficial and deep distal tendon groups of the APL muscle are arguments in favor of a complex functional role of the APL motor unit in thumb mechanics. However, no independence of the tendinous slips in the two distal tendon groups and no correlation between the number of tendinous slips and muscle bellies or innervation were observed. These limit the functional role of the two independent superficial and deep musculotendinous APL motor units. The use of the APL tendon for interposition arthroplasty, for tendon transfer or tendon translocation seems logical, particularly if using one of the two distal tendon groups.     

Morphology of peroneus tertius muscle

Peroneus tertius (PT) muscle is peculiar to man, and man is the only member among the primates in whom this muscle occurs. The muscle is variable in its development and attachment. Because of functional demands of bipedal gait and plantigrade foot, part of extensor digitorum brevis (EDB) has migrated upwards into the leg from the dorsum of foot. PT is a muscle that evolution is rendering more important. In a total of 110 cadavers, extensor compartment of leg and dorsum of foot were dissected in both the lower limbs and extensor digitorum longus (EDL), and PT muscles were dissected and displayed. PT was found to be absent in 10.5% limbs, the incidence being greater on the right side. The remaining limbs in which the PT muscle was present had a very extensive origin from lower 3/4th of extensor surface of fibula (20% on right and in 17% on left), and the EDL was very much reduced in size. In approximately 12%, the tendon of PT was thick or even thicker than the tendon of EDL. In 4%, the tendon extended beyond fifth metatarsal up to metatarsophalangeal joint of fifth toe, and in 1.5%, it extended up to the proximal phalanx of little toe. In two cases (both on the right side), where PT was absent, it was replaced by a slip from lateral margin of EDL. We conclude that PT, which is preeminently human, is extending its purchase both proximally and distally.     

Force- and moment-generating capacities of muscles in the distal forelimb of the horse

A detailed musculoskeletal model of the distal equine forelimb was developed to study the influence of musculoskeletal geometry (i.e. muscle paths) and muscle physiology (i.e. force-length properties) on the force- and moment-generating capacities of muscles crossing the carpal and metacarpophalangeal joints. The distal forelimb skeleton was represented as a five degree-of-freedom kinematic linkage comprised of eight bones (humerus, radius and ulna combined, proximal carpus, distal carpus, metacarpus, proximal phalanx, intermediate phalanx and distal phalanx) and seven joints (elbow, radiocarpal, intercarpal, carpometacarpal, metacarpophalangeal (MCP), proximal interphalangeal (pastern) and distal interphalangeal (coffin)). Bone surfaces were reconstructed from computed tomography scans obtained from the left forelimb of a Thoroughbred horse. The model was actuated by nine muscle-tendon units. Each unit was represented as a three-element Hill-type muscle in series with an elastic tendon. Architectural parameters specifying the force-producing properties of each muscle-tendon unit were found by dissecting seven forelimbs from five Thoroughbred horses. Maximum isometric moments were calculated for a wide range of joint angles by fully activating the extensor and flexor muscles crossing the carpus and MCP joint. Peak isometric moments generated by the flexor muscles were an order of magnitude greater than those generated by the extensor muscles at both the carpus and the MCP joint. For each flexor muscle in the model, the shape of the maximum isometric joint moment-angle curve was dominated by the variation in muscle force. By contrast, the moment-angle curves for the muscles that extend the MCP joint were determined mainly by the variation in muscle moment arms. The suspensory and check ligaments contributed more than half of the total support moment developed about the MCP joint in the model. When combined with appropriate in vivo measurements of joint kinematics and ground-reaction forces, the model may be used to determine muscle-tendon and joint-reaction forces generated during gait.     

A rare anomaly of the extensor digitorum longus

We encountered the absence of the tendon to the fourth toe of the extensor digitorum longus muscle of the right leg in the body of a 73-year-old Japanese woman during the course of educational dissection at Nagoya City University Medical School. The tendon to the fourth toe of the extensor digitorum longus muscle was solely absent. To our knowledge, this anatomical variation has never been cited in the medical literature. We document the precise gross anatomical findings with some morphometric measurements. Moreover, we discuss the morphology of this anomaly in relation to previously described variations and anomalies of the extensor digitorum longus muscle.     

远节指骨的解剖学观察及其临床意义

目的：为人工肌腱修复指深屈肌腱或拇长屈肌腱固定方法和固定止点提供解剖学依据。方法：采用常规固定的16具成人手指标本(男、女各80个手指)。观察各指远节指骨长度，底和粗隆的宽度及厚度。结果：男性拇、示和中指远节指骨底的宽度为15．3、10．2、10．5mm，厚度分别为8．8、6．5、7．1mm。女性宽度分别为12．9、9．1、9．6mm，厚度分别为7．8、5．9、6．6mm。男性拇、示和中指远节指骨粗隆宽度为9．4、6．6、7．4mm，厚度分别为3．6、3．2、3．6mm。女性宽度分别为8．0、5．8、6．2mm，厚度分别为3．0、2．7、3．1mm。结论：用人工肌腱修复指深屈肌腱或拇长屈肌腱时，在远节指骨的底部可行螺丝固定，在粗隆可行钻孔固定。     

指深屈肌腱及指伸肌腱止点的解剖研究

目的　通过解剖研究指深屈肌腱及指伸肌腱在远节指骨基底掌侧和背侧止点平面的差别，为西摩骨折发生机制提供解剖学依据。 方法　手部残肢10具，其中左手3例，右手7例，均为男性患者，年龄24~58岁。2~5指分别有10指，全部手指无外伤手术史、无畸形。自远节指间关节水平掌侧及背侧分别切开，于末节指骨水平分离各指的指深屈肌腱及指伸肌腱，记录其与末节指骨掌侧及背侧关节面的距离，比较指深屈肌腱及指伸肌腱在末节指骨掌、背侧的止点水平。 结果　指深屈肌腱止点近端至关节面距离：示指（2.19±0.27）mm，中指（2.50±0.14）mm，环指（2.23±0.16）mm，小指（1.83±0.19）mm；指伸肌腱止点近端至关节面距离：示指（0.12±0.02）mm，中指（0.18±0.02）mm，环指（0.12±0.05）mm，小指（0.06±0.01）mm；各指差异有统计学意义（P＜0.05）。指深屈肌腱止点中点至关节面距离：示指（3.73±0.45）mm，中指（4.33±0.45）mm，环指（3.53±0.46）mm，小指（3.16±0.41）mm；指伸肌腱止点中点至关节面距离：示指（1.77±0.06）mm，中指（1.76±0.20）mm，环指（1.77±0.06）mm，小指（1.47±0.10）mm；各指差异有统计学意义（P＜0.05）。 结论　指伸肌腱在末节指骨基底的止点较指深屈肌腱的止点距关节面更近，为西摩骨折的发生机制提供了解剖依据。     

指深屈肌腱及指伸肌腱止点的解剖研究

目的　通过解剖研究指深屈肌腱及指伸肌腱在远节指骨基底掌侧和背侧止点平面的差别,为西摩骨折发生机制提供解剖学依据。 方法　手部残肢10具,其中左手3例,右手7例,均为男性患者,年龄24~58岁。2~5指分别有10指,全部手指无外伤手术史、无畸形。自远节指间关节水平掌侧及背侧分别切开,于末节指骨水平分离各指的指深屈肌腱及指伸肌腱,记录其与末节指骨掌侧及背侧关节面的距离,比较指深屈肌腱及指伸肌腱在末节指骨掌、背侧的止点水平。 结果　指深屈肌腱止点近端至关节面距离：示指（2.19±0.27）mm,中指（2.50±0.14）mm,环指（2.23±0.16）mm,小指（1.83±0.19）mm;指伸肌腱止点近端至关节面距离：示指（0.12±0.02）mm,中指（0.18±0.02）mm,环指（0.12±0.05）mm,小指（0.06±0.01）mm;各指差异有统计学意义（P＜0.05）。指深屈肌腱止点中点至关节面距离：示指（3.73±0.45）mm,中指（4.33±0.45）mm,环指（3.53±0.46）mm,小指（3.16±0.41）mm;指伸肌腱止点中点至关节面距离：示指（1.77±0.06）mm,中指（1.76±0.20）mm,环指（1.77±0.06）mm,小指（1.47±0.10）mm;各指差异有统计学意义（P＜0.05）。 结论　指伸肌腱在末节指骨基底的止点较指深屈肌腱的止点距关节面更近,为西摩骨折的发生机制提供了解剖依据。     

Anatomical work-up of an individual with multiple muscular variants on both forearms

Muscular variants of the forearm are common and frequently cause neurovascular compression syndromes, especially when interfering with the compact topography of the carpal tunnel or the Canalis ulnaris. Here, we report on a male body donor with multiple muscular normal variations on both forearms. The two main findings are (1) an accessory variant muscle (AVM) on the right forearm originating from the M. brachioradialis, the distal radius, and the M. flexor pollicis longus. It spanned the wrist beneath the Fascia antebrachia and inserted at the proximal phalanx of the digitus minimus. (2) Moreover, we found a three-headed palmaris longus variant on the left arm with proximal origin tendon and a distal, trifurcated muscle belly, with separated insertions at the palmar aponeurosis, the flexor retinaculum, and, in analogy to the accessory muscle on the contralateral arm, at the base of the proximal phalanx of the digitus minimus. We found a considerable thickening of the left-hand median nerve right before entering the carpal tunnel indicative of a possible chronic compression syndrome adding clinical relevance to this anatomical case. We also discuss the notion that both, the AVM and the contralateral three-headed palmaris variant are developmental descendants of the M. palmaris longus. Additionally, we found a previously not recorded variant of the M. palmaris brevis on the left hand.

     

Common variations in muscles and tendons of the human hand

Common variations in muscles and tendons of the hand were determined by dissecting 40 pairs of hands (20 male, 20 female). Contrary to some anatomy textbooks which describe only three palmar interossei, with the thumb lacking one, this study found four palmar interossei present in 85% of hands and 90% of bodies. This first palmar interosseous typically arose from the base of the first metacarpal and inserted along with the tendon of the oblique head of adductor pollicis into the base of the proximal phalanx. Forty hands (50%) did not have the usual arrangement of lumbricals. Twenty-seven (34%) third lumbricals and four (5%) fourth lumbricals split at their insertions; four third lumbricals and four fourth lumbricals inserted on the ulnar side of the middle and ring fingers, respectively. The abductor pollicis longus inserted by 2 or 3 tendons in 91% of hands. The tendon of extensor digiti minimi split into 2 or 3 slips in practically all of the hands studied (96%). The tendon of extensor indicis split into 2 slips in more than a third (38%) of hands. In almost a third (30%) of hands there were accessory extensor muscles present deep to the tendons of extensor digitorum. Lastly, extra slips of origin of the abductor digiti minimi were present in 10% of hands. This study confirms the presence of a palmar interosseous muscle for the thumb and demonstrates that some variations occur more frequently than was expected. © 1993 Wiley-Liss, Inc.