Absence of the flexor digitorum longus tendon: An MRI study

Flexor digitorum longus (FDL) is the primary flexor of the lateral four toes. It is a reliable source of tendon for transfer surgery. We present a case whereby a patient who required a reconstruction for adult acquired flatfoot deformity using FDL as a dynamic structure for transfer was found to have an absent FDL tendon at the time of operation, necessitating the use of flexor hallucis longus (FHL) instead. This unusual finding prompted us to investigate the frequency of absence of the FDL tendon. We reviewed our hospital MRI database of foot and ankle images specifically looking for patients with absence of this tendon. After randomization, 756 images were reviewed independently by two surgeons and a consultant musculoskeletal radiologist. No instances of an absent FDL tendon were identified. In conclusion, the frequency of absence of the FDL tendon is less than 1 in 750. Surgeons who require FDL for tendon transfer surgery need not image the foot preoperatively to anticipate the need for the use of FHL as an alternative. Clin. Anat. 25:1062–1065, 2012. © 2012 Wiley Periodicals, Inc.     

Isolated flexor muscles of the little toe in the feet of an individual with atrophied or lacking 4 head of the M. extensor digitorum brevis and lacking the 4 tendon of the M. extensor digitorum longus

While dissecting the body of a 75-year-old male we observed variations in the Mm. flexor digitorum brevis and longus of both feet. In the left foot, the 4th tendon of the M. flexor digitorum brevis was atrophied and the respective tendon of the M. flexor digitorum longus to the little toe was absent. In the right foot, the 4th tendons of both the Mm. flexor digitorum brevis and longus to the little toe were absent. The lacking deep flexor tendon to the little toe in the left foot was replaced by an isolated flexor muscle originating from the medial and lateral processes of the calcaneal tuberosity, which additionally had connections to the tendinous plate of the M. flexor digitorum longus and the M. quadratus plantae. The absent superficial and deep flexor tendons to the little toe in the right foot were replaced by an isolated flexor muscle arising from the M. quadratus plantae distal from the medial process of the calcaneal tuberosity. The tendon of both isolated flexor muscles inserted in the distal phalanx of the little toe. The left isolated flexor muscle for the little toe had connections to the M. flexor digitorum longus and the M. quadratus plantae. From these results it seems likely that the M. quadratus plantae could be regarded as additional flexor head (caput breve or plantare) of the M. flexor digitorum longus as is described in classic textbooks. In the individual's lifetime the described variation perhaps led to the possibility of an isolated flexion of the little toe.     

Peripheral and central control of flexor digitorum longus and flexor hallucis longus motoneurons: The synaptic basis of functional diversity

Summary The two long toe flexor muscles in the cat, flexor digitorum longus (FDL) and flexor hallucis longus (FHL), have essentially identical mechanical actions, yet are used very differently during locomotion (O'Donovan et al. 1982). We attempted to identify the origin of the synaptic drive responsible for this functional differentiation.The organization of peripheral and central synaptic drive to FDL and FHL motoneurons was examined using two basic paradigms. (1) In animals anesthetized with chloralose or after ischemic destruction of the brain, peripheral reflex circuits were studied by recording intracellular responses from -motoneurons produced by electrical stimulation of muscular and cutaneous nerves. (2) Fictive locomotion, the centrally generated rhythmic synaptic drive produced in paralyzed, decerebrate animals by stimulation of the mesencephalic locomotor region or intravenous injection of L-DOPA and Nialamide, was monitored by recording electro-neurograms from the central end of cut motor nerves.Despite their functional dissimilarity, FDL and FHL motoneurons received monosynaptic EPSPs from both FDL and FHL la afferents. Ipsilateral cutaneous afferents in the sural nerve and from the central plantar pad produced multiphasic PSPs which were not different in FDL and FHL cells. However afferents from the saphenous and superficial peroneal nerves did exert differential effects: the first component of the multiphasic PSP in most FDL cells was an EPSP, which was not present in most FHL cells. The central latency of this early EPSP in FDL motoneurons (0.8–1.5 ms) strongly suggests a disynaptic linkage. Cutaneous afferents from the ipsilateral forelimb produced IPSPs in most FHL cells but in only one of 18 FDL cells. Since some peripheral reflex circuits exerted differential effects on FDL and FHL cells, but others did not, the intracellular data did not demonstrate that the functional differences between FDL and FHL could be explained by differences in reflex organization.During fictive locomotion elicited by electrical or pharmacological stimulation, FHL motoneurons were coactive with ankle extensors during the extension phase of the fictive step cycle. In contrast, FDL motoneurons were most consistently activated in a brief burst at the onset of the flexion phase, showing much weaker and more variable coactivity with ankle extensors. These patterns were essentially identical to those reported for FDL and FHL motor pools during treadmill locomotion by O'Donovan et al. (1982).We conclude that the central pattern generator (CPG) for locomotion produces distinct and highly differentiated sets of instructions for FDL and FHL motoneurons. Peripheral and descending systems are important in initiating and biasing the activity of the CPG, but are not responsible for the intrinsic structure of the locomotor command signals.     

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.     

Morphological description of combined variation of distal attachments of fibulares in a foot

An interesting case of peculiarity of the distal attachment of the three fibular muscles is reported in the left foot of a male adult cadaver of Indian origin. The fibularis brevis, just inferior to the fibular malleolus, gave off an additional slender tendon anteromedial to its main tendon. This was attached to the dorsal digital expansion of the little toe while its main tendon was inserted to the customary bone. The tendon of fibularis longus on the plantar aspect just medial to the cuboid tunnel received a prominent slip of attachment of the tendon of tibialis posterior. The fibularis tertius had two parallel-running tendons attached to the bases of the fourth metatarsal and the fourth and fifth metatarsals respectively. The combined variation of the three fibulares in a single foot has not been reported previously. The more distal attachment of the fibularis brevis in this case is a regression in evolution. Weakness of both the fibularis brevis and fibularis longus is found in pes cavovarus. The former can be used as a rotational graft in soft tissue loss of the leg.     

Tonic and phasic discharge patterns in toe flexor gamma-motoneurons during locomotion in the decerebrate cat.

To investigate the specificity of fusimotor (gamma) drive during locomotion, gamma-efferents were recorded from the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) nerves in a decerebrate cat preparation. These nerves innervate hindlimb muscles that differ in some aspects of their mechanical action. For both FHL and FDL two stereotyped patterns of gamma activity were distinguished. Tonic units fired throughout the step cycle and had less modulation, but higher minimum rates, than phasic units, which were mainly recruited with ankle extensor [soleus (SOL)] electromyogram (EMG) activity. Differences in the relative timing of these patterns were apparent. In FHL the activity of phasic and most tonic neurons peaked after EMG onset. With FDL, tonic units generally reached maximum rate before, while phasic units peaked after, the beginning of EMG activity. During locomotion FHL and FDL alpha activity were rhythmically recruited with SOL. However, consistent with previous reports, FHL and FDL differed in their patterns of alpha activity. FHL was stereotyped while FDL was variable. Both FHL and FDL had activity related to ankle extensor EMG, but only FDL exhibited a peak around the end of this phase. No corresponding gamma activity was observed in FDL. In conclusion, 1) FHL and FDL received tonic and phasic fusimotor drive; 2) there was no alpha/gamma linkage for the late FDL alpha burst; 3) phasic gamma-efferents in both muscles received similar inputs, linked to plantar flexor alpha activity; and 4) tonic gamma-efferents differed, to the extent that they were modulated at all. The FHL units peaked with the plantar flexor alphas. The FDL neurons generally peaked before alpha activity even began.     

骨间前神经综合征的局部解剖学研究

目的 搪塞骨间前神经综合征的解剖学基础。方法 解剖４８例（左右各２４侧）成人防固定标本。结果 骨间前神经主干邻近腱性结构有旋前圆肌纤维桥（５８．３％），尺骨头浅面腱膜（９３．７％），联合腱板（８３．３％）和指浅屈肌纤维弓（９１．２％），横过骨间前神经的拇长岂副头（６６．７％），及少 尺侧血管、小束肌肉或纤维结构。７７％骨间前神经干走在桡骨颈前方结论 骨间的神经主干邻近的腱性结构及距离桡骨颈近可能是     

The Tendinous Patterns in the Palmar Surface of the Lizard Manus: Functional Consequences for Grasping Ability

In lizards, distinct patterns of the tendinous structures associated with the forearm flexors have been described. In most lizards, the m. flexor digitorum longus ends in a tendinous plate with an embedded sesamoid, from which tendons run to the terminal phalanx of each digit. This structure is known as the flexor plate. In many polychrotid lizards, however, the flexor digitorum longus muscle is continuous with individual tendons running to each digit, and no complete flexor plate is present. In most geckos, the flexor plate is reduced to a tendinous plate without sesamoid. To evaluate the consequences of these differences in morphology on locomotion and grasping, we compared the use of the fore‐arm and hand in lizards exhibiting three different tendon patterns (Pogona vitticeps, an agamid with a well‐developed flexor plate; Gekko gecko, a gekkonid with a flexor plate, but without an embedded sesamoid; Anolis equestris, a polychrotid without flexor plate, but showing independent tendons running to each digit) while moving on different substrates. We found that the presence of a flexor plate with sesamoid bone prevents digital flexion and creates a rather stiff palmar surface in P. vitticeps. This configuration makes it impossible for P. vitticeps to grasp narrow branches and results in a strongly impaired locomotor performance on narrow substrates. Both G. gecko and A. equestris can flex the palms of their hands and their fingers more extensively, and do so when moving on narrow substrates. We suggest that the reduction of the flexor plate in both G. gecko and A. equestris allows these animals to move effectively on narrow substrates. Anat Rec, 292:842–853, 2009. © 2009 Wiley‐Liss, Inc.     

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.     

Pollical oblique ligament in humans and non-human primates

A morphological study of the oblique ligament in the thumb is presented. The ligament was consistently described in human specimens and compared with dissections of non-human primates from different species. The oblique ligament was found in some, but not all, specimens in each of the following species examined: chimpanzee, orangutan, gibbon, anubis baboon, hamadryas baboon, squirrel monkey, lemur and marmoset. A revised identity of the oblique ligament is proposed as a reinforced distal border of a fibro-osseous annular pollical flexor sheath and whose function is not independent of the flexor sheath. The constant presence and tendinous trait of the pollical oblique ligament in humans, when compared with non-human primates, supports the notion that the oblique ligament strengthens the pollical flexor sheath in humans for restraint of the flexor pollicis longus tendon during forceful precision pinching. A derivation of the pollical oblique ligament is considered as representing a vestigial radial limb of a flexor pollicis superficialis tendon in the thumb.     

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.     

Epifascial accessory palmaris longus muscle

In hand reconstructive surgery the palmaris longus muscle is one of the most utilized donor site for tendon reconstruction procedures. However, its anatomic position is variable and anatomic variations may be responsible for median nerve compression. We report the case of a 40-year-old, right-handed woman, who presented with numbness and paresthesias in the palm and in the flexor aspect of the first, second, and third fingers of her right hand for the preceding 5 months, coinciding with increase of office work (typing). The clinical examination and radiological investigations (ultrasound and magnetic resonance) revealed a subcutaneous mass (15 mm x 2.3 mm x 6 cm), with a lenticular shape and definite edges at the level of the volar aspect of the distal third of the forearm. The fine-needle aspiration biopsy revealed the presence of striated muscle fibers. During surgery, a muscle belly was found in the epifascial plane. This muscle originated from subcutaneous septa in the middle forearm and inserted on to the superficial palmar aponeurosis with fine short tendon fibers. Exposure of the antebrachial fascia did not reveal any area of weakness or muscle herniation. The palmaris longus tendon, flexor digitorum superficialis tendons, and flexor carpi radialis tendon showed usual topography under the antebrachial fascia. The accessory muscle was excised and histology revealed unremarkable striated muscle fibers, limited by a thin connective sheath. The presence of an accessory palmaris longus (APL) located in the epifascial plane could be ascribed to an unusual migration of myoblasts during the morphogenesis. Although extremely rare, APL is worth bearing in mind as a possible cause of median nerve compression and etiology of a volar mass in the distal forearm.     

Clinical significance of variations in the interconnections between flexor digitorum longus and flexor hallucis longus in the region of the knot of Henry

Tendon transfer of the flexor digitorum longus tendon (FDLT) or the flexor hallucis longus tendon (FHLT) into the tibialis posterior tendon is carried out in patients with tibialis posterior dysfunction. FDLT and FHLT are connected in the region of the knot of Henry. The present study has investigated the anatomical variations of this tendinous interconnection. The results could be used to determine which of the two tendons should be transected proximal to the region of the knot of Henry in the surgical treatment of tibialis posterior dysfunction. In over two-thirds of cadaver specimens investigated, tension applied solely to FHLT resulted in flexion of all digits and the hallux. On the basis of these results, we propose that identification of the tendon to be transected should be decided at the time of surgery depending on the anatomical pattern. Based on the evidence provided by 16 cadaveric dissections, transection of FDLT proximal to the region of the knot of Henry for the repair of tibialis posterior dysfunction would result in retention of function of the hallux and lesser digits in the majority of cases.     

Bilateral accessory flexor digitorum longus muscle in man

An accessory muscle (flexor digitorum longus accessorius) was encountered in the deep posterior compartment of both legs of a 57-year-old male cadaver. The muscle originated with two heads from the medial margin of the tibia, lateral margin of the fibula, posterior intermuscular septum and the deep fascia at the distal part of the leg. Both heads came together just posterior and superficial to the tibial nerve, and converged into a slender tendon which traversed the tarsal tunnel in the vicinity of the neurovascular bundle to reach the sole of the foot. It terminated by merging into the tendon of the quadratus plantae muscle. The potential of such an anomalous muscle to lead to misinterpretations of the radio-diagnostic examinations and the fact that it can be one of the causes of tarsal tunnel syndrome should be borne in mind.     

Recurrent collaterals of motoneurons projecting to distal muscles in the cat hindlimb.

1. Recurrent collaterals of motoneurons innervating muscles that have a role in control of the hindlimb digits were studied with neuroanatomic tracing methods to determine whether these motoneurons have simple recurrent collateral arbors in comparison with those of hip, knee, and ankle muscles. 2. Motoneurons innervating the hindlimb muscles plantaris (Pln), flexor hallucis longus (FHL), or flexor digitorum longus (FDL) were injected with 10% horseradish peroxidase. Recurrent collaterals were reconstructed from serial transverse sections. 3. No recurrent collaterals were observed in a sample of 10 FDL motoneurons. 4. FHL motoneurons had simple recurrent collateral arbors as assessed by number of first-order collaterals, number of collateral swellings, number of end branches, and the highest-order branch of individual collateral trees. Recurrent collateral arbors of Pln motoneurons were more complex than those of FHL motoneurons. Pln and FHL recurrent collateral arbors were less complex than those described for gastrocnemius-soleus, anterior tibial, and posterior biceps motoneurons. 5. These anatomic findings correspond well with electrophysiological results indicating that the recurrent inhibition produced by FHL motoneurons is weak and that FDL motoneurons do not produce recurrent inhibition. In addition, Pln motoneurons are reported to produce stronger recurrent inhibition than FHL motoneurons in many motor pools. 6. Consideration of these results with respect to the mechanical actions and patterns of motor activity observed in FDL, FHL, and Pln suggests that the complexity of recurrent collaterals of a motoneuron pool and the extent of its contribution to recurrent inhibition diminish with its involvement in the individualized control of the digits.     

趾长屈肌的亚部化研究及其临床意义

目的　探讨趾长屈肌的亚部划分，为临床外科“半肌”移位手术提供解剖学基础。 方法　大体解剖法、肌构筑法、改良Sihler’s 染色法。 结果　①可依劈开趾长屈肌肌内腱板，把该肌分为胫侧和腓侧两个亚部；②胫侧亚部各构筑学值大于腓侧亚部；③两亚部存在单独神经支配。 结论　①趾长屈肌可分为胫侧亚部和腓侧亚部，两亚部有独立的神经支配；②趾长屈肌的两个亚部均为半羽肌，胫侧亚部产生的肌力大于腓侧亚部。     

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.     

Toe flexor muscle spindle discharge and stretch modulation during locomotor activity in the decerebrate cat

In order to investigate the nature (i.e. static or dynamic) of fusimotor drive to the flexor hallucis longus (FHL) and flexor digitorum longus (FDL) muscles during locomotion we recorded Ia and group II muscle spindle afferent responses to sinusoidal stretch (0.25 and 1 mm amplitude, respectively, 4–5 Hz) in a decerebrate cat preparation. FHL Ia and group II afferents generally had increased discharge rates and decreased modulation to stretch throughout the step cycle, compared to rest, suggesting raised static γ drive at all locomotor phases. Although the modulation of Ia afferents was reduced during locomotion, most (13 of 18) showed a clear increasing trend during homonymous muscle activity (extension). This was consistent with phasic dynamic γ drive to FHL spindles linked with α drive. In agreement with previous reports, FHL gave a single burst of EMG activity during the step cycle while FDL α drive had two components. One was related to extension while the other comprised a brief burst around the end of this phase. Typically FDL Ia and group II afferents also had elevated firing rates and reduced modulation at all locomotor phases, again implicating static γ drive. Half the afferents (seven Ia, three group II) showed increased discharge during extension, suggesting phasic static γ drive. There was no γ drive associated with the late FDL α burst. In conclusion, the γ drives to FHL and FDL differed during locomotion. FHL, which has the α drive of a classic extensor, received γ drive that closely resembled other extensors. The γ drive of FDL, which exhibits both extensor and flexor α synergies, did not match either muscle type. These observations are compatible with the view that fusimotor drive varies in different muscles during locomotion according to the prevailing sensorimotor requirements.     

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.