The ligaments of the fingers. Anatomical study of the Cleland ligaments

The aim of this study was to establish a precise architecture of the retinacular ligaments of human digits. Sixty selected digits from human cadavers aged 40-70 years were used in this study. We were able to identify, under the dissecting microscope, two distinct ligamentous complexes: one proximal of greater importance and the other distal of lesser importance. Both structures extend from the periosteum as well as from the fibrous part of the digital sheath to the skin. There are many variations in size and in shape of these structures but they are not related to a particular digit. The role of these ligaments is to prevent the 'effet de doigt de gant', to stabilize and to maintain the neurovascular bundle of the digit at the moment of the digital flexion.     

Somatotopy of digital nerve projections to the cuneate nucleus in the monkey

Somatotopic arrangements of cells and fibers within the dorsal columns and the dorsal column nuclei have been mapped most precisely by electrophysiological recording methods. This study uses an anatomical approach to evaluate the precision of individual digital nerve projections to the cuneate nucleus (CN) in young macaque monkeys. Digital nerves supplying about one-half the palmar skin of a digit were surgically exposed, cut, and treated with wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) on 3 successive days. After 2 additional days, animals were killed and medullas were recovered for study of serial sections reacted to display axons labeled by transganglionic transport of label. Labeled afferent fibers from each digit were found within a circumscribed columnar zone extending through the caudal CN and rostrally throughout the pars rotunda of CN. At caudal levels, diffuse projections reach the dorsal edge of the CN; more rostrally, they shift into deeper parts of the nucleus and are heaviest along its ventral and medial edges at levels near the obex. Fibers from the thumb (digit 1) project lateral (and ventral) to those from digit 2, and projections from digit 3 are medial to those from 2. Each digital projection field is closely adjacent to that from the adjacent digit. Few fibers extend to the rostral CN. Projection fields of homologous digits are quite symmetrical on the two sides. Although there do seem to be some differences in the somatotopic arrangement of digital input in macaques compared to other nonprimate mammals studied previously, these observations (precisely organized, circumscribed fields for separate digits) define a system well designed for transmission of data encoding spatial relationships.     

Somatotopy of Digital Nerve Projections to the Cuneate Nucleus in the Monkey

Somatotopic arrangements of cells and fibers within the dorsal columns and the dorsal column nuclei have been mapped most precisely by electrophysiological recording methods. This study uses an anatomical approach to evaluate the precision of individual digital nerve projections to the cuneate nucleus (CN) in young macaque monkeys. Digital nerves supplying about one-half the palmar skin of a digit were surgically exposed, cut, and treated with wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) on 3 successive days. After 2 additional days, animals were killed and medullas were recovered for study of serial sections reacted to display axons labeled by transganglionic transport of label. Labeled afferent fibers from each digit were found within a circumscribed columnar zone extending through the caudal CN and rostrally throughout the pars rotunda of CN. At caudal levels, diffuse projections reach the dorsal edge of the CN; more rostrally, they shift into deeper parts of the nucleus and are heaviest along its ventral and medial edges at levels near the obex. Fibers from the thumb (digit 1) project lateral (and ventral) to those from digit 2, and projections from digit 3 are medial to those from 2. Each digital projection field is closely adjacent to that from the adjacent digit. Few fibers extend to the rostral CN. Projection fields of homologous digits are quite symmetrical on the two sides. Although there do seem to be some differences in the somatotopic arrangement of digital input in macaques compared to other nonprimate mammals studied previously, these observations (precisely organized, circumscribed fields for separate digits) define a system well designed for transmission of data encoding spatial relationships.     

Acute effects of total or partial digit denervation on raccoon somatosensory cortex

The immediate effects of total or partial denervation of single digits (0-16 hr after nerve transection) on primary somatosensory cortex were studied electrophysiologically. Comparisons of response properties and cortical somatotopy were made between intact raccoons and four groups of raccoons with transection of some or all of the nerves innervating the fourth or fifth digit. Animals with all four digital nerves cut (amputation of the digit) were most different from normal. Approximately half of the penetrations in the affected cortical region showed inhibitory responses to stimulation of adjacent skin regions. These consisted of a strong response to stimulus offset and/or a suppression of spontaneous activity during indentation. Since these responses were substantially different from those recorded several months after digit amputation, additional changes in connectivity and synaptic strength must occur with chronic denervation. These inhibitory responses were not seen in animals with one, two, or three nerves cut per digit. In the animals with partial denervation of a digit, the greatest disruption occurred when both ventral nerves to the glabrous skin were transected. This yielded cell clusters with abnormally large receptive fields, disruptions in somatotopic organization, and a decreased occurrence of low-threshold responses. If only one nerve to glabrous skin was transected, there was less change, even if it was combined with transection of both nerves to hairy skin. These results suggest that the release of inhibitory responses in a cortical digital region by amputation is prevented by the retention of even one ventral nerve. None of the denervation conditions produced large nonresponsive areas of cortex, which would have indicated a loss of all inputs.     

Acute Effects of Total or Partial Digit Denervation on Raccoon Somatosensory Cortex

The immediate effects of total or partial denervation of single digits (0-16 hr after nerve transection) on primary somatosensory cortex were studied electrophysiologically. Comparisons of response properties and cortical somatotopy were made between intact raccoons and four groups of raccoons with transection of some or all of the nerves innervating the fourth or fifth digit. Animals with all four digital nerves cut (amputation of the digit) were most different from normal. Approximately half of the penetrations in the affected cortical region showed inhibitory responses to stimulation of adjacent skin regions. These consisted of a strong response to stimulus offset and/or a suppression of spontaneous activity during indentation. Since these responses were substantially different from those recorded several months after digit amputation, additional changes in connectivity and synaptic strength must occur with chronic denervation. These inhibitory responses were not seen in animals with one, two, or three nerves cut per digit.

In the animals with partial denervation of a digit, the greatest disruption occurred when both ventral nerves to the glabrous skin were transected. This yielded cell clusters with abnormally large receptive fields, disruptions in somatotopic organization, and a decreased occurrence of low-threshold responses. If only one nerve to glabrous skin was transected, there was less change, even if it was combined with transection of both nerves to hairy skin. These results suggest that the release of inhibitory responses in a cortical digital region by amputation is prevented by the retention of even one ventral nerve. None of the denervation conditions produced large nonresponsive areas of cortex, which would have indicated a loss of all inputs.     

Somatotopy of digital nerve projections to the dorsal horn in the monkey

The dorsal horn projection patterns of finger nerves were investigated in four Macaca mulatta monkeys. Proper digital branches of the median nerves, serving the radial aspect of a digit on each hand, were loaded with wheatgerm agglutinin-horseradish peroxidase complex (WGA:HRP). The distribution of the lectin-enzyme complex was mapped in the right and left dorsal horns. The dorsal horn projections of the digital nerves were localized in segments C6-C8 in laminae I-VI, primarily in laminae I-IV. The wedge-shaped termination zones were somatotopically organized, in agreement with the projections of the digits in cats. The fingers are represented medially, as they are in the cat. This similarity suggests that there is a mediolateral gradient of dorsal horn organization similar to that of the cat, with distal skin represented medially and proximal skin represented laterally. The rostrocaudal trajectory of finger representation, with digit 1 most rostral and digit 5 most caudal, is also in agreement with the organization of hindlimb toe projections in the cat. There was a high degree of bilateral symmetry for homologous nerves, and little overlap of projections from nerves innervating adjacent fingers. The sample size was too small to permit us to assess interanimal variation. These results suggest a similar somatotopy of projections, and presumably of dorsal horn cell somatotopy, in monkey and cat.     

Somatotopy of Digital Nerve Projections to the Dorsal Horn in the Monkey

The dorsal horn projection patterns of finger nerves were investigated in four Macaca mulatto monkeys. Proper digital branches of the median nerves, serving the radial aspect of a digit on each hand, were loaded with wheatgerm agglutinin—horseradish peroxidase complex (WGA:HRP). The distribution of the lectin—enzyme complex was mapped in the right and left dorsal horns.

The dorsal horn projections of the digital nerves were localized in segments C₆-C₈ in laminae I-VI, primarily in laminae I-IV. The wedge-shaped termination zones were somatotopically organized, in agreement with the projections of the digits in cats. The fingers are represented medially, as they are in the cat. This similarity suggests that there is a mediolateral gradient of dorsal horn organization similar to that of the cat, with distal skin represented medially and proximal skin represented laterally. The rostrocaudal trajectory of finger representation, with digit 1 most rostral and digit 5 most caudal, is also in agreement with the organization of hindlimb toe projections in the cat. There was a high degree of bilateral symmetry for homologous nerves, and little overlap of projections from nerves innervating adjacent fingers. The sample size was too small to permit us to assess interanimal variation. These results suggest a similar somatotopy of projections, and presumably of dorsal horn cell somatotopy, in monkey and cat.     

Mechanical properties of pufferfish (Lagocephalus gloveri) skin and its collagen arrangement

Skin is a biological material the mechanical properties of which are dependent on the constituents from which it is assembled. Skin, the outer covering of animals is made up of collagen fibers arranged in more or less ordered arrays. Pufferfish skin provides a rigid framework to support the body contents and a flexible covering to allow whatever changes are necessary for the remarkable inflation mechanism. Here, we describe the structure and tensile properties of the dorsal and ventral skin of the pufferfish, Lagocephalus gloveri Abe and Tabeta, 1983. The ultimate tensile strength of ventral skin was found to be around two times higher than that of the dorsal skin. It was observed that the dorsal skin could resist more deformation than the ventral skin. The collagen fibers were arranged in different ordered arrays for ventral and dorsal skin and the concentration of fibers was found to be more in ventral than dorsal skin. This provides more stiffness to ventral skin. Scanning electron microscopy studies of the ventral skin showed a unidirectional arrangement of the collagen fibers, which provides more stretching capacity. Dorsal skin, on the other hand, has an orthogonal arrangement of fibers. The present study thus showed that the mechanical behavior of the skin of L. gloveri is strongly influenced by the concentration and arrangement of collagen fibers.     

Connective tissue reinforcing structures of the digital tendon sheaths of the human hand

At a greater number of humid preparated human hands, all the ligamentous supports of the digital tendon sheath were exposed and their dimensions were determined. The osteofibrous channels, which contain the long flexor tendons of the digits, were bounded on the one hand by transversely concave shaft areas of the phalanges and the palmar ligaments and on the other side by the fibrous parts of the tendon sheath. From the second to the 5th finger, it has a regular extension of length, which begins proximal at the heads of the metacarpal bones and runs distal to the base of the nail phalanx. In some cases, there is a continuous communication between the digital tendon sheath of the little finger and the carpal synovial sheath. The tendon sheath of the flexor pollicis longus muscle in comparison with it is always in an open communication with the radial synovial sac of the wrist. At the fibrous supports of the digital tendon sheath, one can find constant and inconstant ligamentous structures. Regular shaped ligaments consist of annular fibers (A1 to A5). The proximal complex of fiber supports is a formation of the A1 and A2 ligaments. The band A1 can be divided into 2 ligaments both of roughly equal length, which lay between the head of the metacarpal bone and the base of the proximal phalanx. The strongest fibrous support of the whole digital tendon sheath represents the band A2. It is attached to the midth of the proximal phalanx and increases in strength from proximal to distal. The middle length varies between 6.7 mm at the thumb and 18.7 mm at the middle finger. The distal margin is strengthened by fibrocartilage tissue to be in accordance with the important function as a pulley. The annular band A4 forms the distal supporting complex height above the shaft of the middle phalanx. At the 2nd to the 5th finger it is, with a middle length of 6 to 7 mm, very much shorter than A2 and restrains first of all the tendon of the flexor digitorum profundus muscle. In the area of the interphalangeal joints, we can find the annular bands A3 and A5, which fiber texture is formed variable. Both ligaments are attached on either both sides with the joint capsule and the palmar plate. The other inconstant supports of the digital sheaths are systematically recorded indeed (C1 to C3), but only in exceptional cases they exist of cruciform fibers (Lig. cruciatum).(ABSTRACT TRUNCATED AT 400 WORDS)     

Thermal Imaging of Aye-Ayes (Daubentonia madagascariensis) Reveals a Dynamic Vascular Supply During Haptic Sensation

Infrared thermography (IRT) is used to visualize and estimate variation in surface temperatures. Applications of IRT to animal research include studies of thermofunctional anatomy, ecology, and social behavior. IRT is especially amenable to investigations of the somatosensory system because touch receptors are highly vascularized, dynamic, and located near the surface of the skin. The hands of aye-ayes (Daubentonia madagascariensis) are thus an inviting subject for IRT because of the prominent middle digit that functions as a specialized haptic sense structure during percussive and probative foraging. It is a vital sensory tool that is expected to feature a high density of dermal mechanoreceptors that radiate heat and impose thermal costs under cool temperatures. Here we explore this premise by acquiring IRT images of 8 aye-ayes engaged in a variety of passive and probative behaviors. We found that the middle digit was typically 2.3°C cooler than other digits when the metacarpophalangeal (MP) joint was extended, and that it warmed an average of 2.0°C when the MP joint was flexed during active touching behavior. These changes in digital surface temperature, which were sometimes as much 6.0°C, stand in sharp contrast with the profoundly invariant temperatures of the other digits. Although the physiological mechanisms behind these temperature changes are unknown, they appear to reveal a uniquely dynamic vascular supply.     

Hand biomechanics during simulated stone tool use

Human radial digits have derived features compared with apes, with long robust thumbs, relatively larger joint surfaces, and hypertrophic thenar muscles. Here we test the hypothesis that these features evolved in the context of making and using stone tools, specifically for producing large gripping forces and for countering large joint contact stresses. We used portable force plates simulating early stone tools to: 1) document and compare the magnitude of external/internal forces and joint stresses in the radial digits during hardhammer percussion and flake use, and 2) examine how variation in digit morphology affects muscle and joint mechanics during stone tool use. Force and kinematic data were collected from a sample representing normal variation in digit morphology (n = 25). The effects of digit size/shape on digit biomechanics were evaluated using partial correlations, controlling for tool reaction forces and impact velocities. Results show that individuals with longer digits require relatively less muscle force to stabilize digital joints, and are exposed to relatively lower joint contact stresses during stone tool use, due in part to an increase in the robusticity of metacarpals and phalanges in humans relative to chimpanzees. These analyses further suggest that Pan- or australopith-like pollical anatomy presents serious performance challenges to habitual tool use. Our data support the hypothesis that evolutionary increases in thumb length, robusticity, and thenar muscle mass enabled Homo to produce more force and to tolerate higher joint stresses during tool use.     

Organization of positional information in the axolotl limb

We have used the phenomenon of position-dependent growth stimulation, brought about by the confrontation of cells with dissimilar positional values, to reveal the organization of positional information in the center of the upper and lower arms of axolotls. When either humerus or radius was transplanted into either dorsal or posterior positions, extra growth leading to the formation of supernumerary digits occurred following amputation through the graft. However, transplants of humerus or radius into anterior or ventral positions did not lead to the formation of any additional digits. The ulna by contrast was capable of stimulating supernumerary digit formation when transplanted into anterior, posterior, dorsal, or ventral positions. We interpret these results to indicate that the humerus and radius are surrounded by symmetrically arranged anterior and ventral positional values, whereas the ulna is surrounded by a complete asymmetrical set of angular positional values. We use our proposed arrangement for the positional information in the limb center to explain a number of previous experimental findings. In addition, we provide an explanation, in terms of the underlying positional information, for the structural and developmental relationships between the different skeletal elements of the vertebrate limb, and in particular for the anatomical pattern known as Gregory's pyramid.     

Cruciate ligaments of the avian knee: Insight into a complex system

The avian cruciate ligaments were examined in Gallus domesticus, Anas platyrhynchos, Meleagris gallopavo, and Struthio camelus australis. The ligaments proved to be deviated around the intercondylar groove (cranial cruciate) and around the medial femoral condyle (caudal cruciate). Four functionally different fiber groups could be differentiated: fibers taut only in maximal extension, fibers taut only in maximal flexion, fibers taut in ranges from an intermediate position to an extreme position, and fibers taut throughout the entire range of motion (guiding bundles). Hence the cruciates serve the guiding of the joint and the restriction of motion, whereby the majority of the cranial cruciate fibers are taut in extension while those of the caudal cruciate are in flexion. No differences were found between the species examined with respect to fiber arrangement and function. The avian mechanical model proved to be more complex than the relatively simple mammalian four-bar link model as the avian guiding bundles change their shape due to deflection during motion. © 1992 Wiley-Liss, Inc.     

Ectopic dermal ridge configurations on the interdigital webbings and postaxial marginal portion of the hindlimb in Hammertoe mutant mice (Hm)

The effects of the hereditary malformation of Hammertoe mutant mice (gene symbol Hm) on the digital pads and dermal ridge configurations on their hindlimbs were examined. In the wild‐type (+/+) mice with normally separated digits, dermal ridges developed only on the pads. Heterozygous (Hm/+) and homozygous (Hm/Hm) mutant mice, however, had a broad big toe, fused interdigital soft tissues, reduced claws, an extra rudimentary postaxial digit and camptodactyly. The dermal ridges appeared not only on the pads, affected in their number and configurations, but also on the ventral surface of the interdigital webbings and postaxial marginal area exhibiting an extra rudimentary digit and webbing. These aberrant configurations may be related to the abnormal occurrence of programmed cell death (PCD) in the interdigital zones and the postaxial marginal portion in Hm/+ and Hm/Hm mice. That is, the diminished cell death may fail to decrease the cell density in the interdigital zones and postaxial marginal portion and result in the webbing and an extra rudimentary digit and webbing, respectively. Simultaneously, it could also interrupt the migration of surviving cells of these areas toward the neighboring digits and the distal area of the sole and produce the ectopic dermal ridges on the way to the as yet unformed (presumptive) digital and plantar volar pads. The present findings suggest that normal interdigital and pre/postaxial PCD contributes not only to the separation of digits, the initial formation of individual digits of different sizes, and the inhibition of the extra digit but also to the development of the presumptive digital and plantar pads, including dermal ridges. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Anatomicohistologic study of the retaining ligaments of the face and use in face lift: retaining ligament correction and SMAS plication

Plastic surgeons have sought to improve nasolabial folds, jowls, jaw lines, and cervical contour with face-lifting procedures that are abundant in the literature. The retaining ligaments of the face support facial soft tissue in normal anatomic position, resisting gravitational change. As this ligamentous system attenuates, facial fat descends into the plane between the superficial and deep facial fascia, and the stigmata of facial age develop. In this study, surgical correction of the retaining ligaments and plication of the superficial musculoaponeurotic system (SMAS) to reposition the structures that have descended with gravitation are discussed. The anatomy of the facial retaining ligaments was studied in 22 half-faces of 11 fresh cadavers, and the localization, extension, and width of the ligaments were examined macroscopically and histologically. Surgical correction of the retaining ligaments and plication of the SMAS have been accomplished in 27 face-lift patients with this anatomicohistologic study taken into consideration. There was hematoma in one patient at the cheek region and a permanent dimple caused by postoperative edema in two patients, with a localization of one zygomatic and two parotidomasseteric ligaments. In one patient, hypesthesia in the mandibular nerve region was seen, which remitted at 14 weeks. There were no other complications, and with a follow-up of 24 months, excellent aesthetic results and a high level of patient satisfaction were encountered.     

The retaining ligaments of the cheek

The zygomatic ligaments (McGregor's patch) anchor the skin of the cheek to the inferior border of the zygoma just posterior to the origin of the zygomaticus minor muscle. The mandibular ligaments tether the overlying skin to the anterior mandible. Both these ligaments are obstacles to surgical maneuvers intended to advance the overlying skin. They also restrain the facial skin against gravitational changes, and they delineate the anterior border of the "jowl" area. The platysma-auricular ligament is a thin fascial sheet that extends from the posterosuperior border of the platysma and that is intimately attached to the periauricular skin; it serves as a surgical guide to the posterosuperior border of the platysma. The anterior platysma-cutaneous ligaments are variable fascial condensations that anchor the SMAS and platysma to the dermis. They can cause anatomic disorientation with dissection of false planes into the dermis. These four ligaments are useful as anatomic landmarks during facial dissections. The tethering effects of the zygomatic and mandibular ligaments must be interrupted if a maximum upward movement of the facial skin is desired.     

A scanning electron microscopic study of differentiation of the digital pad in regenerating digits of the kenyan reed frog,Hyperolius viridiflavus ferniquei

Newly metamorphosed Kenyan reed frogs, Hyperolius viridiflavus ferniquei, are able to regenerate amputated digits. The terminal digital pad is also completely reformed. Differentiation of the regenerating digital pad was studied by scanning electron microscopy. External differentiation of the digital pad began late in the second postamputational week with the appearance of small patches of specialized epidermal cells on the ventral surface of the regenerating digit. The differentiation of the pad spread out radially until late in the fourth week, when its overall shape approximated that of the normal digital pad. The appearance of patches of digital pad epidermis on the ends of spike regenerates arising from the forearm was also confirmed.     

Fiber-based modeling of in situ ankle ligaments with consideration of progressive failure

Ligament sprains account for a majority of injuries to the foot and ankle complex among athletic populations. The infeasibility of measuring the in situ response and load paths of individual ligaments has precluded a complete characterization of their mechanical behavior via experiment. In the present study a fiber-based modeling approach of in situ ankle ligaments was developed and validated for determining the heterogeneous force-elongation characteristics and the consequent injury patterns. Nine major ankle ligaments were modeled as bundles of discrete elements, corresponding functionally to the structure of collagen fibers. To incorporate the progressive nature of ligamentous injury, the limit strain at the occurrence of fiber failure was described by a distribution function ranging from 12% to 18% along the width of the insertion site. The model was validated by comparing the structural kinetic and kinematic response obtained experimentally and computationally under well-controlled foot rotations. The simulation results replicated the 6 degree-of-freedom bony motion and ligamentous injuries and, by implication, the in situ deformations of the ligaments. Gross stiffness of the whole ligament derived from the fibers was comparable to existing experimental data. The present modeling approach provides a biomechanically realistic, interpretable and computationally efficient way to characterize the in situ ligament slack, sequential and heterogeneous uncrimping of collagen fascicles and failure propagation as the external load is applied. Applications of this model include functional ankle joint mechanics, injury prevention and countermeasure design for athletes.     

Birds have dinosaur wings: The molecular evidence

Within developmental biology, the digits of the wing of birds are considered on embryological grounds to be digits 2, 3 and 4. In contrast, within paleontology, wing digits are named 1, 2, 3 as a result of phylogenetic analysis of fossil taxa indicating that birds descended from theropod dinosaurs that had lost digits 4 and 5. It has been argued that the development of the wing does not support the conclusion that birds are theropods, and that birds must have descended from ancestors that had lost digits 1 and 5. Here we use highly conserved gene expression patterns in the developing limbs of mouse and chicken, including the chicken talpid(2)mutant and polydactylous Silkie breed (Silkie mutant), to aid the assessment of digital identity in the wing. Digit 1 in developing limbs does not express Hoxd12, but expresses Hoxd13. All other digits express both Hoxd12and Hoxd13. We found this signature expression pattern identifies the anteriormost digit of the wing as digit 1, in accordance with the hypothesis these digits are 1, 2 and 3, as in theropod dinosaurs. Our evidence contradicts the long-standing argument that the development of the wing does not support the hypothesis that birds are living dinosaurs.     

Evolution of digit identity in the three-toed Italian skink Chalcides chalcides: a new case of digit identity frame shift

SUMMARY Digit identity in the avian wing is a classical example of conflicting anatomical and embryological evidence regarding digit homology. Anatomical in conjunction with phylogenetic evidence supports the hypothesis that the three remaining digits in the bird wing are digits 1, 2, and 3. At the same time, various lines of embryological evidence support the notion that these digits develop in positions that normally produce digits 2, 3, and 4. In recent years, gene expression as well as experimental evidence was published that supports the hypothesis that this discrepancy arose from a digit identity shift in the evolution of the bird wing. A similar but less well-known controversy has been ongoing since the late 19th century regarding the identity of the digits of the three-toed Italian skink, Chalcides chalcides . Comparative anatomy identifies these digits as 1, 2, and 3, while embryological evidence suggests their derivation from embryological positions 2, 3, and 4. Here we re-examine this evidence and add gene expression data to determine the identity of the three digits of C. chalcides . The data confirm that the adult and the embryological evidence for digit identity are in conflict, and the expression of Hoxd11 suggests that digits 1, 2, and 3 develop in positions 2, 3, and 4. We conclude that in C. chalcides , and likely in its close relatives, a digit identity frame shift has occurred, similar to the one in avian evolution. This result suggests that changes in of digit identity might be a more frequent consequence of digit reduction than previously assumed.