Effects of chronic median nerve compression at the wrist on sensation and manual skills.

The aim of this study was to analyse the functional impairments caused by chronic median nerve compression at the wrist on hand sensation and manual skill. Hand function was assessed in 11 patients (8 women and 3 men) with severe carpal tunnel syndrome (CTS) and compared with that of an age- and sex-matched control group. Apart from CTS, the subjects were healthy and the electrodiagnostic examination was normal. The pressure and vibration detection thresholds of the index finger were partially impaired and statistically different (P<0.05) when compared with controls, suggesting a reduction of tactile acuity in the territory of the median nerve. The thermal thresholds were identical in both groups, suggesting that the small-diameter fibres were not affected. When a small object was lifted and positioned in space, the coordination between the grip force and the vertical lifting force did not seem to be affected in our patients. They were able to modify their grip force according to the friction between the fingertips and the object, i.e. the more slippery the object, the higher the grip force. The unimanual Purdue Pegboard subtest results suggest that digital dexterity was also not significantly perturbed in our sample of CTS patients when compared with controls. Despite the severe abnormalities of median nerve conduction, our results suggest that chronic median nerve compression occurring in CTS induces partial impairment of tactile sensibility with minor impact on grasp force regulation and digital dexterity.

Impact of the surface slipperiness of grasped objects on their subsequent acceleration.

Seven subjects were asked to reach and grasp an object between the thumb and index finger, lift it about 30 cm high and 25 cm forward from one table to another, at their preferred speed. The perpendicular grip force and the tangential load force applied to the contact surface were digitized at 500 Hz and stored on a laboratory computer. The trajectory of the wrist and of the object was recorded using four infrared cameras tracking the movement of reflective markers attached to the distal styloid process of the radius and on the top of the object. The aim of this study was to demonstrate the influence of low friction (i.e. surface slipperiness) on the acceleration of the wrist. Friction was reduced by coating the smooth brass grasping surface with talc. The seven subjects had skin to surface coefficients of friction which ranged from 0.52-1.18 for dry brass and 0.24 0.34 for talc-coated brass. Two weights (418 and 1070 g) were used with each surface. The results indicated that with the slippery surface the necessary higher grip force/load force ratio was produced by an increase in the grip force and by a decrease in the wrist acceleration and a consequent reduction in the load force. This strategy was observed for both weights over a range of grip strengths between 21-98% of the individual's maximum voluntary contraction (MVC). This implies that even with adequate grip force reserves the reduction in acceleration is an acceptable and probable alternative solution to the force control problem. Our results also suggested that the loading rate and the object acceleration were planned and controlled together which emphasizes the role played by a predictive mechanism in organizing the kinematics of movements involving hand-held objects. This study shows that friction of the grasping surface not only affects the prehensile force dynamics, but it also influences the kinematics of the entire upper limb.

Long-term functional results of wrist arthrodesis in rheumatoid arthritis.

The purpose of this study was to evaluate the long-term effectiveness of wrist fusion on the relief of pain and also the functional capacities of the upper limbs in patients with rheumatoid arthritis (RA). Eighteen patients were assessed at a mean of 7 years after wrist arthrodesis and a mean of 17 years after the onset of RA. Radiological measurements, pain assessment and impairment rating of the upper limbs were made of the fused and non-fused sides. The average position of arthrodesis was 8 degrees of extension and 9 degrees of ulnar deviation. All patients were pleased with the procedure and had satisfactory pain relief. Impairment ratings did not detect any significant difference in the sensory and motor function of the hand when the fused and non-fused groups were compared. We conclude that in patients with rheumatoid arthritis, wrist arthrodesis is a reliable procedure that provides predictable pain relief and a high degree of satisfaction without additional functional loss in the upper limb.

Energy cost, mechanical work and muscular efficiency in swing-through gait with elbow crutches.

Crutches are widely used to assist ambulation in disabled people. Many authors have shown that the use of crutches increases the energy cost as compared to normal walking. In this study we have measured the energy consumed and the mechanical work performed during swing-through crutch gait in order to assess if the greater energy expenditure is accompanied by an equivalent increase of the work done to move the body. Our results show that, depending upon the speed, the energy expenditure is 2-3 times higher in swing-through gait than in normal walking. On the other hand, the mechanical work increases only 1.3-1.5 times. Thus the extra cost of swing-through gait cannot be explained solely by an increase of the mechanical work, but is due at least in part to a reduction in the efficiency of positive work production.