Distal brachyphalangy of the thumb in mental retardation.
(49/402)
Distal brachyphalangy (DBP) of the thumbs is a hereditary autosomal anomaly found in 1 to 1.5% of whites and in less than 1% of blacks. It was found in 26 of 852 mentally retarded patients in the present study; a frequency of over 3%. The male:female ratio was 70:30. There was bilateral DBP IN 69.5% and unilateral DBP on the right hand in 19% and on the left in 11.5%. The 26 cases (100%) showed a subsyndromic aggregate of distal brachyphalangy of the thumb (DBT), short stature and mental retardation, 19 of them presented an abnormal head and 17 presented abnormal feet (nine of them also had convulsions). Six cases are discussed in detail; it is suggested that they belong to particular clinical categories. In addition to gene abnormalities (which is the most likely cause) a possible explanation of the aetiological factors could be found in some sort of anomaly of the hypopituitary-hypothalmic area, since in the five cases where it was investigated, the sella turcica was small in four cases and large in one. Almost all known syndromes of which the subsyndrome discussed here is a part also shown abnormal skulls, and this may add to the aetiology. (+info)
How safe is blood sampling? Anterior interosseus nerve injury by venepuncture.
(50/402)
All invasive procedures carry some degree of risk of damage to the normal structures in the proximity of the region where the procedure is performed. The risk is, however, minimal for venous cannulation. A case is reported of an injury to the anterior interosseus nerve sustained during venepunture for routine blood sampling at the cubital fossa. (+info)
Force enhancement following muscle stretch of electrically stimulated and voluntarily activated human adductor pollicis.
(51/402)
For electrically stimulated muscles, it has been observed that maximal muscle force during and after stretch is substantially greater than the corresponding isometric force. However, this observation has not been made for human voluntary contractions. We investigated the effects of active muscle stretch on muscle force production for in vivo human adductor pollicis (n = 12) during maximal voluntary contractions and electrically induced contractions. Peak forces during stretch, steady-state isometric forces following stretch, and passive forces following muscle deactivation were compared to the corresponding isometric forces obtained at optimal muscle length. Contractions with different stretch magnitudes (10, 20, and 30 deg at a constant speed of 10 deg s(-1)) and different speeds (10, 20, and 60 deg s(-1) over a range of 30 deg) were performed in triplicate in a random order, balanced design. We found three novel results: (i) there was steady-state force enhancement following stretch in voluntarily contracted muscles; (ii) some force enhancement persisted following relaxation of the muscle and (iii) force enhancement, for some stretch conditions, exceeded the maximum isometric force at optimal muscle length. We conclude from these results that voluntary muscle contraction produces similar force enhancement to that observed in the past with electrically stimulated preparations. Therefore, steady-state force enhancement may play a role in everyday movements. Furthermore, these results suggest that non-uniformities in sarcomere length do not, at least not exclusively, account for the force enhancement following active muscle stretch, and that the stretch magnitude-dependent passive force enhancement observed here may be responsible for the enhancement of force above the isometric reference force at optimal muscle length. (+info)
Early versus late mobilisation after simple excision of the trapezium.
(52/402)
We randomly selected 39 patients undergoing excision of the trapezium for osteoarthritis of the first carpometacarpal joint into two groups, with mobilisation either at one or at four weeks after operation. The patients were reviewed at a median of six months (6 to 8). The clinical details, the severity of the disease and the preoperative clinical measurements of both groups were similar. Excision of the trapezium resulted in significant improvement in objective and subjective function. Comparison of the outcomes of the two groups showed no differences except that patients found early mobilisation significantly more convenient. Although there was no significant difference in the range of movement between the groups, there was a small loss of movement at the metacarpophalangeal joint in the late mobilisation group. Our findings show that simple excision of the trapezium is an effective procedure for patients with carpometacarpal osteoarthritis of the thumb and that prolonged splintage is neither necessary nor desirable. (+info)
Prehension synergies: effects of object geometry and prescribed torques.
(53/402)
We studied the coordination of forces and moments exerted by individual digits in static tasks that required balancing an external load and torque. Subjects ( n=10) stabilized a handle with an attachment that allowed for change of external torque. Thumb position and handle width systematically varied among the trials. Each subject performed 63 tasks (7 torque values x 3 thumb locations x 3 widths). Forces and moments exerted by the digit tips on the object were recorded. Although direction and magnitude of finger forces varied among subjects, each subject used a similar multidigit synergy: a single eigenvalue accounted for 95.2-98.5% of the total variance. When task parameters were varied, regular conjoint digital force changes (prehension synergies) were observed. Synergies represent preferential solutions used by the subjects to satisfy mechanical requirements of the tasks. In particular, chain effects in force adjustments to changes in the handle geometry were documented. An increased handle width induced the following effects: (a). tangential forces remained unchanged, (b). the same tangential forces produced a larger moment T (t), (c). the increased T (t) was compensated by a smaller moment of the normal forces T(n), and (d). normal finger forces were rearranged to generate a smaller moment. Torque control is a core component of prehension synergies. Observed prehension synergies are only mechanically necessitated in part. The data support a theory of hierarchical organization of prehension synergies. (+info)
Importance of cutaneous feedback in maintaining a secure grip during manipulation of hand-held objects.
(54/402)
Previous research has shown that grip and load forces are modulated simultaneously during manipulation of a hand-held object. This close temporal coupling suggested that both forces are controlled by an internal model within the CNS that predicts the changes in tangential force on the fingers. The objective of the present study was to examine how the internal model would compensate for the loss of cutaneous sensation through local anesthesia of the index and thumb. Ten healthy adult subjects (5 men and 5 women aged 20-57 yr) were asked to grasp, lift, and hold stationary, a 250 g object for 20 s. Next, the subjects were asked to perform vertical oscillatory movements over a distance of 20 cm at a rate of 1.0 Hz for 30 s. Eleven trials were performed with intact sensation, and 11 trials after a local ring-block anesthesia of the index and thumb with bupivacain (5 mg/ml). During static holding, loss of cutaneous sensation produced a significant increase in the safety margin. However, the grip force declined significantly over the 20-s static hold period. During oscillatory arm movements, grip and load forces were continuously modulated together in a predictive manner as suggested by Flanagan and Wing. Again, the grip force declined over the 30-s movement, and 7/10 subjects dropped the object at least once. With intact sensation, the object was never dropped; but with the fingers anesthetized, it was dropped on 36% of the trials, and a significant slip occurred on a further 12%. The mean correlation between the grip and load forces for all subjects deteriorated from 0.71 with intact sensation to 0.48 after digital anesthesia. However, a cross-correlation calculated between the grip and load forces indicated that the phase lag was approximately zero both with and without digital anesthesia. Taken together, the data from the present study suggest that cutaneous afferents are required for setting and maintaining the background level of the grip force in addition to their phasic slip-detection function and their role in adapting the grip force/load force ratio to the friction on initial contact with an object. Finally, at a more theoretical level, they correct and maintain an internal model of the physical properties of hand-held objects. (+info)
The effects of digital anesthesia on force control using a precision grip.
(55/402)
A total of 20 right-handed subjects were asked to perform a grasp-lift-and-hold task using a precision grip. The grasped object was a one-degree-of-freedom manipuladum consisting of a vertically mounted linear motor capable of generating resistive forces to simulate a range of object weights. In the initial study, seven subjects (6 women, 1 man; ages 24-56 yr) were first asked to lift and hold the object stationary for 4 s. The object presented a metal tab with two different surface textures and offered one of four resistive forces (0.5, 1.0, 1.5, and 2.0 N). The lifts were performed both with and without visual feedback. Next, the subjects were asked to perform the same grasping sequence again after ring block anesthesia of the thumb and index finger with mepivacaine. The objective was to determine the degree to which an internal model obtained through prior familiarity might compensate for the loss of cutaneous sensation. In agreement with previous studies, it was found that all subjects applied significantly greater grip force after digital anesthesia, and the coordination between grip and load forces was disrupted. It appears from these data, that the internal model alone is insufficient to completely compensate for the loss of cutaneous sensation. Moreover, the results suggest that the internal model must have either continuous tonic excitation from cutaneous receptors or at least frequent intermittent reiteration to function optimally. A subsequent study performed with 10 additional subjects (9 women, 1 man; ages 24-49 yr) indicated that with unimpaired cutaneous feedback, the grasping and lifting forces were applied together with negligible forces and torques in other directions. In contrast, after digital anesthesia, significant additional linear and torsional forces appeared, particularly in the horizontal and frontal planes. These torques were thought to arise partially from the application of excessive grip force and partially from a misalignment of the two grasping fingers. These torques were further increased by an imbalance in the pressure exerted by the two opposing fingers. Vision of the grasping hand did not significantly correct the finger misalignment after digital anesthesia. Taken together, these results suggest that mechanoreceptors in the fingertips signal the source and direction of pressure applied to the skin. The nervous system uses this information to adjust the fingers and direct the pinch forces optimally for grasping and object manipulation. (+info)
Cerebellar control of constrained and unconstrained movements. I. Nuclear inactivation.
(56/402)
The aim of this study was to determine in monkeys if inactivation of dentate and lateral interposed deep cerebellar nuclei preferentially impairs certain movements relative to others. Constrained movements of the digits were trained with digits, hand, and elbow constrained in a cast. Simple movements were flexion of Thumb or Index. A compound movement was simultaneous flexion of Thumb+Index. An unconstrained movement consisted of a reach to, pinch of, and retrieval of a small food reward (Reach+Pinch). In two monkeys we mapped the dentate and interpositus with 66 injections of muscimol (3 microl of 5 microg/microl). Thirty-two percent of the injections resulted in increased reaction times of Thumb, Index, and Thumb+Index (mean = 24, 24, 28 + 26, respectively). Fifty percent of the injections impaired Reach+Pinch, producing target overshoot, curved reach trajectory, missed target (X and Y errors), and clumsy pinch with dropped fruit bits. Inactivation impaired each and all of Thumb, Index, Thumb+Index, and Reach+Pinch in 27%, only Reach+Pinch in 23%, and only Thumb, Index, Thumb+Index in 5% of injections. In sum, all types of movement were impaired. Thumb+Index was no more impaired than Thumb or Index alone, suggesting that the lateral cerebellar nuclei are not specifically required for combining movements of the two digits when constrained. Reach+Pinch appeared so greatly impaired and Thumb, Index, Thumb+Index so little as to be consistent with the hypothesis that a principal role of the cerebellum is to control those interactions that occur between body segments in natural unconstrained movements. However, the fact that all movements were impaired shows that the cerebellum contributes to the control of all movements. (+info)