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Concept: Thumb

161

Restoration of touch after hand amputation is a desirable feature of ideal prostheses. Here, we show that texture discrimination can be artificially provided in human subjects by implementing a neuromorphic real-time mechano-neuro-transduction (MNT), which emulates to some extent the firing dynamics of SA1 cutaneous afferents. The MNT process was used to modulate the temporal pattern of electrical spikes delivered to the human median nerve via percutaneous microstimulation in four intact subjects and via implanted intrafascicular stimulation in one transradial amputee. Both approaches allowed the subjects to reliably discriminate spatial coarseness of surfaces as confirmed also by a hybrid neural model of the median nerve. Moreover, MNT-evoked EEG activity showed physiologically plausible responses that were superimposable in time and topography to the ones elicited by a natural mechanical tactile stimulation. These findings can open up novel opportunities for sensory restoration in the next generation of neuro-prosthetic hands.

Concepts: Sensory system, Somatosensory system, Amputation, Star Trek: The Next Generation, Prosthesis, Proprioception, Hand, Thumb

28

The prevalence of sesamoid bones in the hands has been reported in some previous articles. Most of them, however, have reported sesamoid bones of the metacarpophalangeal joint of the hand and of the interphalangeal (IP) joint of the thumb. The present study investigates the prevalence of sesamoid bones of the IP joint of the thumb and fingers. A retrospective review of radiologic views of the IP joints in the thumb or fingers was performed, including a total of 650 patients (1,096 thumbs or fingers). Sesamoid bones were found in the IP joint of the thumb at 67% (212 of 318), while the index, middle, ring, little fingers had sesamoid bones in the proximal interphlangeal (PIP) joint at 0% (0 of 172), 0.4% (1 of 244), 0.5% (1 of 183), and 1% (2 of 179), respectively. None of the four fingers had sesamoid bones in the distal IP joint. Previous articles have described the similar prevalence to the present study, of sesamoid bones of the IP joint of the thumb, while some others reported the different prevalence. About the PIP joint, no previous articles have found a sesamoid bone. Because the lateral X-ray view is more accurate and suitable to evaluate sesamoid bones, we used the lateral one for the present study. The knowledge that sesamoid bones occurs at these rates in the thumb IP joint and finger PIP joints is helpful to differentiate chip fractures from sesamoid bones near the IP joint, including the PIP joint. Clin. Anat., 2012. © 2012 Wiley Periodicals, Inc.

Concepts: Bone, Skeletal system, Joints, Patella, Finger, Hand, Thumb, Sesamoid bone

28

The term ‘exploded hand syndrome’ refers to a specific type of crush injury to the hand in which a high compressive force excessively flattens the hand leading to thenar muscle extrusion through burst lacerations. Out of 89 crushed hands seen over a period of seven years, only five had exploded hand syndrome. They were all male industrial workers ranging in age between 24 and 55 years. All patients had thenar muscle extrusion. Other concurrent injuries included fractures/dislocations, compartment syndrome, and ischaemia. All patients were treated by excision of the extruded intrinsic muscles, as well as primary management of concurrent injuries. All patients had functional assessment including: motor power and sensory testing, range of motion of hand joints, and the quick DASH score. Objective testing showed reduced sensibility in the thumb, reduced grip strength (mean 52% of contralateral hand), reduced pinch strength (mean of 27% of contralateral hand), reduced thumb opposition (the mean Kapandji Score was 5 out of 10), and deficits in the range of motion of the metacarpophalangeal and interphalangeal joints of the thumb. The quick DASH score ranged from 11 to 49 and only two patients were able to go back to regular manual work.

Concepts: Injury, Hand, Median nerve, Hand strength, Grip strength, Thumb, Thenar eminence, Work hardening

28

Abstract Intraosseous epidermoid inclusion cysts of the phalanx of the finger are rare, and are regarded as reactive or post-traumatic pseudotumours. We describe a case of an epidermoid cyst in the distal phalanx of the fifth finger caused by chronic nail biting, which was successfully excised.

Concepts: Sebaceous cyst, Epidermoid cyst, Finger, Hand, Nail, Thumb, Distal phalanges

26

In this review, an international group of senior hand surgeons was asked to provide their currently used methods, views, and advice on thumb and fingertip repair. The basic requirements and methods of thumb and fingertip repair are first outlined, followed by descriptions of the methods favored by individual units or surgeons. More recent innovative methods and modifications are described and challenging topics are discussed. This review ends by illustrating and discussing a few exploratory treatments that hold promise of greatly changing future perspectives of this common clinical problem.

Concepts: Finger, Ring finger, Hand, Middle finger, Index finger, Phalanx bones, Thumb, Little finger

26

Phalangeal curvature is a commonly used morphological feature for the interpretation of extant and fossil primate locomotor behaviour. Here, we build on a recent biomechanical study (Richmond, 2007) in two ways: first, we use a 3D micro-FE model, which models the real internal microstructure (i.e., cortical thickness and trabecular bone structure) and, second, we model four siamang third proximal phalanges. We test identical 2D homogenized FE models and two 3D micro-FE phalanx models that are mathematically straightened to isolate the biomechanical significance of curvature. We further investigate how varying the loading configuration (e.g., boundary constraints) and modeling (e.g., 2D versus 3D) affects the biomechanical behaviour of the phalanx. Finally, we examine how intraspecific variation in external and internal bony morphology affects the biomechanical behaviour of the phalanx. Simulation results demonstrate that the general pattern of strain and displacement is similar between the 3D micro-FE and 2D homogenized FE models but the absolute values differ substantially. The biomechanical behaviour of the 3D FE models more closely match the relative strain patterns from the validation experiment than the 2D homogenized FE models, indicating the 3D microstructure model is preferable. Varying the loading configuration can have dramatic effects on the biomechanical behaviour of the phalanx depending on individual morphology, but overall a cantilevered beam model is an equally valid, if not better, configuration for modeling the phalanx as other previously-proposed models. Variation in flexor ridge morphology has a substantial effect on phalanx strain; the taller the ridge, the less strain incurred by other regions of the palmar shaft. Finally, phalangeal curvature reduces overall strain experienced by the phalanx, but does not necessarily reduce bending or increase the compression-to-tension ratio. These results confirm the adaptive role of phalangeal curvature during flexed-finger grasping postures and demonstrate that modeling variation in cortical thickness and flexor ridge morphology improves the behaviour of the FE model, which has important implications for the functional interpretation of phalanx form.

Concepts: Computer graphics, Model, 3D computer graphics, Gibbon, Phalanx bones, Thumb, Cancellous bone, Siamang

25

Finger sucking is frequently found in children and sometimes in adults too. Often reasons are found to explain why certain children feel the need to suck their thumbs or fingers, but these explanations are always derived from clinical observation without any rational support, searching for motives for this bad habit from family life; strict parents, jealousy at the birth of a sibling, difficulty accepting the end of breastfeeding etc. Some think that a child should continue to suck after actual nutrition has ended and the substitution of the mother’s nipple with a thumb or finger could fill this need. Research however, using anatomical and neurophysiological data, explains why an infant forms the habit of thumb sucking from a neurological standpoint abandoning the psychological explanations proposed until now.

Concepts: Family, Scientific method, Medicine, Finger, Fingers, Thumb, Habit, Thumb sucking

24

Background: The trigger finger is characterized by the painful blocking of finger flexor tendons of the hand, while crossing the A1 pulley. It is a rare disease in children and, when present, is usually located in the thumb, and does not have any defined cause. Methods: We report 2 pediatric trigger finger cases affecting the long digits of the hand that were caused by an osteochondroma located at the proximal phalanx. Both children held the diagnosis of juvenile multiple osteochondromatosis. They had presented at the initial visit with a painful finger blocking. Surgical approach was decided with wide regional exposure, as compared with the trigger finger traditional surgical techniques, with the opening of the A1 pulley and the initial portion of the A2 pulley, along with bone tumor resection. Results: Patients evolved uneventfully, and recovered the affected finger motion. Conclusion: It is important to highlight that pediatric trigger finger is a distinct ailment from the adult trigger finger, and also in children is important to differentiate whenever the disease either affects the thumb or the long fingers. A secondary cause shall be sought whenever the long fingers are affected by a trigger finger.

Concepts: Medicine, Affect, Finger, Rare diseases, Phalanx bones, Fingers, Thumb, Exostosis

4

The human hand is unparalleled amongst primates in its ability to manipulate objects forcefully and dexterously. Previous research has predominantly sought to explain the evolution of these capabilities through an adaptive relationship between more modern human-like anatomical features in the upper limb and increased stone tool production and use proficiency. To date, however, we know little about the influence that other manipulatively demanding behaviors may have had upon the evolution of the human hand. The present study addresses one aspect of this deficiency by examining the recruitment of the distal phalanges during a range of manual transportation (i.e., carrying) events related to hominin behavioral repertoires during the Plio-Pleistocene. Specifically, forces on the volar pad of each digit are recorded during the transportation of stones and wooden branches that vary in weight and size. Results indicate that in most instances, the index and middle fingers are recruited to a significantly greater extent than the other three digits during carrying events. Relative force differences between digits were, however, dependent upon the size and weight of the object transported. Carrying behaviors therefore appear unlikely to have contributed to the evolution of the robust thumb anatomy observed in the human hand. Rather, results suggest that the manual transportation of objects may plausibly have influenced the evolution of the human gripping capabilities and the 3rd metacarpal styloid process.

Concepts: Force, Anatomy, Human anatomy, Finger, Hand, Metacarpus, Phalanx bones, Thumb

1

High resolution BOLD fMRI has the potential to map activation patterns of small neuronal populations at the scale of cortical columns. However, BOLD fMRI does not measure neuronal activity, but only a correlate thereof, since it measures blood dynamics. To confirm that BOLD activation maps reflect neuronal population activity patterns, a direct comparison with neuro-electrophysiological data from the same cortical patch is necessary. Here, we compare BOLD activation patterns obtained with fMRI at 7T to electrophysiological patterns obtained with implanted high density electrocorticography (ECoG) grids in the same patch of human sensorimotor cortex, and with similar resolution (1.5mm). We used high spatially sampled high-frequency broadband (HFB) power from ECoG, which reflects local neuronal population activity. The spatial distribution of 7T BOLD activation matched the spatial distribution of ECoG HFB-power changes in the covered patch of sensorimotor cortex. BOLD fMRI activation foci were located within 1 to 3mm of the HFB-power ECoG foci. Both methods distinguished individual finger movement activation within a 1cm cortical patch, revealing a topographical medial to lateral layout for the little finger to index to thumb. These findings demonstrate that the BOLD signal at 7T is strongly correlated with the underlying electrophysiology, and is capable of discriminating patterns of neuronal population activity at a millimeter scale. The results further indicate the utility of 7T fMRI for investigation of intra-area organization of function and network dynamics.

Concepts: Electrophysiology, Neuroscience, Cerebral cortex, Cortical column, Functional magnetic resonance imaging, Finger, Thumb, Electrocorticography