Early mobilisation after conventional knee replacement may reduce the risk of postoperative venous thromboembolism.

We carried out an audit on the result of achieving early walking in total knee replacement after instituting a new rehabilitation protocol, and assessed its influence on the development of deep-vein thrombosis as determined by Doppler ultrasound scanning on the fifth post-operative day. Early mobilisation was defined as beginning to walk less than 24 hours after knee replacement. Between April 1997 and July 2002, 98 patients underwent a total of 125 total knee replacements. They began walking on the second post-operative day unless there was a medical contraindication. They formed a retrospective control group. A protocol which allowed patients to start walking at less than 24 hours after surgery was instituted in August 2002. Between August 2002 and November 2004, 97 patients underwent a total of 122 total knee replacements. They formed the early mobilisation group, in which data were prospectively gathered. The two groups were of similar age, gender and had similar medical comorbidities. The surgical technique and tourniquet times were similar and the same instrumentation was used in nearly all cases. All the patients received low-molecular-weight heparin thromboprophylaxis and wore compression stockings post-operatively. In the early mobilisation group 90 patients (92.8%) began walking successfully within 24 hours of their operation. The incidence of deep-vein thrombosis fell from 27.6% in the control group to 1.0% in the early mobilisation group (chi-squared test, p < 0.001). There was a difference in the incidence of risk factors for deep-vein thrombosis between the two groups. However, multiple logistic regression analysis showed that the institution of an early mobilisation protocol resulted in a 30-fold reduction in the risk of post-operative deep-vein thrombosis when we adjusted for other risk factors.

The Rowing Cycle: Sources of Variance and Invariance in Ergometer and On-the-Water Performance.

In a recent study of the kinematics of the drive phase of the rowing stroke, Lamb (1989) provided detailed evidence that ergometer performance simulates on-the-water performance closely. In the present experiment, Lamb's analysis was extended in an investigation of the timing of the complete cycle of the rowing action of 5 rowers under each of those performance conditions. The authors followed Beek's (1992) suggestion that the first task in the analysis of timing in skilled movement is to specify the sources of variance and invariance in each particular task by identifying the major temporal constraints and the key relative timing variables. In addition, the possibility that some simple mathematical relationship (e.g., Schmidt, 1985) might describe the relative timing between the stroke and recovery phases of the rowing action when performed at different speeds was investigated. Both an absolute and a relative variability criterion were used in assessing and comparing timing variability over 4 speeds of rowing and between on-water and ergometer rowing in 5 elite male subjects. Criteria outlined by Gentner (1987) were used in assessing relative timing between stroke and recovery. The results indicated that variability decreases dramatically as a function of increased rowing rate; however, when variability is expressed as a function of movement duration, those decreases appear much less dramatic. Overall variability of the rowing cycle was caused principally by variability in the recovery phase, whereas the stroke phase was relatively invariant under both rowing conditions. The changes in the relative timing of the rowing stroke across the 4 speeds studied followed a simple mathematical rule, best described as linear increments in the stroke proportion of the total rowing cycle with increases in rowing rate. Moreover, those changes were similar across the 2 rowing conditions. The present results are discussed in light of findings from other forms of propulsion, such as walking, running, and stair climbing, in which the movement constraints are quite different.

Amplitude Scaling Compensates for Serial Delays in Correcting Eye and Arm Movements.

Spatial and metrical parameters of the eye and arm movements made by human subjects (N = 7) in response to visual targets that were stepped unexpectedly either once (single step) or twice (double step) were studied. For the double-step, the displacement of a visual target was decreased or increased in amplitude at intervals before and during a movement. Provided the second target step occurred more than 100 ms before the onset of movement, the amplitude of the subjects' first response was altered in the direction of the new target location. But this amplitude scaling was not always sufficient to reach the new target location, and a second corrective response was required. The latency in producing this second response was greatly increased above reaction time latencies of movements to single-step targets, especially when the target change occurred 100 ms or more before movement onset. These findings suggest that even though serial processing limitations delay the production of a second corrective response, continuous parallel processing of visual information enables the amplitude of the first response to be altered with minimal delay. This enables some degree of real-time continuous control by the visuomotor control system.

Thermoregulation of paraplegic and able bodied men during prolonged exercise in hot and cool climates.

The purpose of this study was to compare the thermoregulatory responses of trained paraplegics (TP) and able bodied subjects (AB) performing submaximal exercise of the same relative intensity in both hot and cool conditions. Five TP (lesion range T12 to L3) and five AB subjects experienced in wheelchair use performed 60 minutes of constant load (55-60% of VO2 max) arm ergometry exercise in 37 degrees C and 15 degrees C climatic conditions. Heart rate (HR), sweat rate and rectal (Tr) and skin (Tsk) temperatures were recorded. In the hot climate the TP subjects recorded a significantly greater change in Tsk (delta Tsk) from 0 to 60 minutes of exercise than the AB subjects, because of greater thigh and calf temperatures, but no other significant differences were found between these groups. In the cool climate no significant differences were observed between the TP and AB groups. It was concluded that TP have a similar thermoregulatory ability to AB subjects who perform identical prolonged exercise in hot and cool conditions, although their lower limb skin temperatures are greater, probably because of venous pooling in the legs. While these results are a promising indication of the ability of TP to thermoregulate effectively while exercising in the, heat caution regarding their participation in endurance competitions in hot conditions should be expressed until data collected during wheelchair exercise (rather than arm ergometry) in the heat is available.

The muscle silent period following transcranial magnetic cortical stimulation.

Transcranial magnetic stimulation (TMS) of the motor cortex during tonic muscle contraction produces a motor evoked potential followed by a silent period in the electromyogram. We sought to characterize the TMS induced silent period and to compare it to the silent period induced by supramaximal peripheral nerve stimulation. TMS was delivered to the motor cortex using a 9 cm diameter circular coil and the surface electromyogram was recorded from the contralateral abductor pollicis brevis muscle in six normal subjects. Increasing TMS stimulus intensity from 10 to 50% above threshold resulted in an increase in the duration of the silent period from a mean of 50 ms to 185 ms. Increasing the level of tonic muscle contraction from 5% of maximum to maximum resulted in a decrease in silent period duration from a mean of 155 ms to 133 ms. In contrast, the duration of the silent period following supramaximal median nerve stimulation showed greater shortening under similar conditions, from a mean of 160 ms at 5% of maximum contraction to 99 ms at 75% of maximum contraction. The TMS induced silent period was present during a TMS induced increase in the reaction time for a ballistic movement, the onset of movement being delayed until the end of the silent period. Peripheral nerve stimulation did not produce a delay in movement onset. The present findings favour a cortical origin for the TMS induced silent period, probably on the basis of intracortical inhibition, rather than peripheral inhibition of spinal motoneurones which is considered to be the basis for the silent period following peripheral nerve stimulation.