Reconstruction of the radial collateral ligament of the metacarpophalangeal joints of the fingers
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Metacarpophalangeal joint
Little finger
Numerical digit
Middle finger
The control of whole hand grasping relies on complex coordination of multiple forces. While many studies have characterized the coordination of finger forces and torques, the control of hand muscle activity underlying multi-digit grasping has not been studied to the same extent. Motor-unit synchrony across finger muscles or muscle compartments might be one of the factors underlying the limited individuation of finger forces. Such “unwanted” coupling among finger forces, however, might be desirable when a high level of force coupling is required to prevent object slip during grasping. The goal of this study was to quantify the strength of synchrony between single motor units from extrinsic hand muscles as subjects held a device with a five-digit grasp. During the hold phase, we recorded the normal force exerted by each digit and the electrical activity of single motor units from each of the four divisions of the muscle flexor digitorum profundus (FDP) and one thumb flexor muscle, m. flexor pollicis longus (FPL). The strength of motor-unit synchrony was quantified by the common input strength index (CIS). We found moderate to strong motor-unit synchrony between FPL and the index FDP compartment [CIS: 0.49 ± 0.03 (SE)] and across most FDP compartments (0.34 ± 0.02). Weak synchrony, however, was found between FPL and the middle, ring, and little finger FDP compartments (0.25 ± 0.01). This difference might reflect the larger force contribution of the thumb-index finger pair relative to other thumb-finger combinations in five-digit grasping.
Numerical digit
Little finger
Motor unit
Middle finger
Hand strength
Hand muscles
Motor Control
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Kito, Munehisa MD; Yoshimura, Yasuo MD, PhD; Aoki, Kaoru MD, PhD; Uchiyama, Shigeharu MD, PhD; Uehara, Takeshi MD, PhD; Kato, Hiroyuki MD, PhD Author Information
Metacarpophalangeal joint
Middle finger
Finger joint
Little finger
Metacarpus
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Numerical digit
Little finger
Middle finger
Independence
Phalanx
Hand muscles
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Ring finger
Middle finger
Little finger
Hand strength
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Individual intra-digit somatotopy of all phalanges of the middle and little finger of the right and left hand was studied by functional magnetic resonance imaging in 12 healthy subjects. Phalanges were tactilely stimulated and activation in BA 3b of the human primary somatosensory cortex could be observed for each individual phalanx. Activation peaks were further analysed using the Direction/Order (DiOr) method, which identifies somatotopy, if a significantly high number of subjects exhibit ordered distal-to-proximal phalanx representions along a similar direction. Based on DiOr, ordered and similar-direction-aligned intra-digit maps across subjects were found at the left hand for the little and middle finger and at the right hand for the little finger. In these digits the proximal phalanges were represented more medially along the course of the central sulcus than the distal phalanges. This is contrasted by the intra-digit maps for the middle finger of the right hand, which showed larger inter-subject variations of phalanx alignments without a similar within-digit representation across subjects. As all subjects were right-handed and as the middle finger of the dominant hand probably plays a more individual role in everyday tactile performance than the little finger of the right hand and all left-hand digits, the observed variation might reflect a functional somatotopy based on individual use of that particular digit at the dominant hand.
Numerical digit
Phalanx
Middle finger
Little finger
Central sulcus
Left handed
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Summary Complex dislocations of the metacarpophalangeal joints are rare injuries. When they, occur, they are relatively common in the thumb, index and little fingers. Isolated complex dislocation of the metacarpophalangeal jont of the middle finger is extremely rare because of the inherent anatomical stability in that joint. We are reporting a case of isolated complex dorsal dislocation of the middle finger.
Metacarpophalangeal joint
Middle finger
Little finger
Ring finger
Finger joint
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Locking of the metacarpophalangeal (MCP) joint is commonly caused by hyperextension of the thumb or moderate flexion of the index or middle finger. We report a rare case of vertical locking of the MCP joint of the little finger in a 16-year old female after blunt trauma to the little finger. The MCP joint was locked when positioned at approximately 90-degree-flexion and could not extend actively or passively. A manual reduction was easily achieved and no immobilization was applied. Vertical locking of the MCP joint can be easily reduced, and immobilization is unnecessary after reduction. Correct diagnosis prior to reduction and differentiation from other types of locking are essential to prevent overtreatment.
Metacarpophalangeal joint
Middle finger
Little finger
Finger joint
Ring finger
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To determine whether other digits move when normal humans attempt to move just one digit, we asked 10 right-handed subjects to move one finger at a time while we recorded the motion of all five digits simultaneously with both a video motion analysis system and an instrumented glove. We quantified the independence of the digits to compare (1) the different digits, (2) the right versus the left hand, and (3) movements at a self-paced frequency versus externally paced movements at 3 Hz. We also quantified the degree to which motion occurred at the proximal, middle, or distal joint of each digit. Even when asked to move just one finger, normal human subjects produced motion in other digits. Movements of the thumb, index finger, and little finger typically were more highly individuated than were movements of the middle or ring fingers. Fingers of the dominant hand were not more independent than were those of the nondominant hand. Self-paced movements made at approximately 2 Hz were more highly individuated than were externally paced movements at 3 Hz. Angular motion tended to be greatest at the middle joint of each digit, with increased angular motion at the proximal and distal joints during 3 Hz movements. Simultaneous motion of noninstructed digits may result in part from passive mechanical connections between the digits, in part from the organization of multitendoned finger muscles, and in part from distributed neural control of the hand.
Numerical digit
Little finger
Middle finger
Independence
Motor Control
Finger joint
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Citations (416)
Most trigger digit (TD) patients complain that they have problems using their hand in daily or occupational tasks due to single or multiple digits being affected. Unfortunately, clinicians do not know much about how this disease affects the subtle force coordination among digits during manipulation. Thus, this study examined the differences in force patterns during cylindrical grasp between TD and healthy subjects. Forty-two TD patients with single digit involvement were included and sorted into four groups based on the involved digits, including thumb, index, middle and ring fingers. Twelve healthy subjects volunteered as healthy controls. Two testing tasks, holding and drinking, were performed by natural grasping with minimal forces. The relations between the force of the thumb and each finger were examined by Pearson correlation coefficients. The force amount and contribution of each digit were compared between healthy controls and each TD group by the independent t test. The results showed all TD groups demonstrated altered correlation patterns of the thumb relative to each finger. Larger forces and higher contributions of the index finger were found during holding by patients with index finger involved, and also during drinking by patients with affected thumb and with affected middle finger. Although no triggering symptom occurred during grasping, the patients showed altered force patterns which may be related to the role of the affected digit in natural grasping function. In conclusion, even if only one digit was affected, the subtle force coordination of all the digits was altered during simple tasks among the TD patients. This study provides the information for the future studies to further comprehend the possible injuries secondary to the altered finger coordination and also to adopt suitable treatment strategies.
Numerical digit
Ring finger
Middle finger
Little finger
Hand strength
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The first and most medial of five miniature long bones located in the palm of the hand, which articulates proximally with the trapezium of the carpus at the carpometacarpal joint and distally with the thumb phalanx at the metacarpophalangeal joint.
Numerical digit
Metacarpophalangeal joint
Phalanx
Metacarpus
Carpometacarpal joint
Proximal phalanx
Metacarpal bones
Little finger
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