Ergonomic Aspects of Different Handles for Minimally Invasive Surgery - An Emg Based Study

Various studies have been performed to test different instrument handles in minimally invasive surgery (MIS). Although criteria for ergonomic handles have been suggested, to date it remains unresolved which handle design is best suited to various needs. The comparison of electromyogram (EMG) activities in different muscles provides information about the force developed by each muscle and allows to assess its contribution to a functional movement. The aim of the present study was to evaluate different types of handles for a simple grasping maneuver with respect to the force required in the main forearm muscles. Four different types of handles (axial handle, ring handle, shank handle, Hirschberg handle) were tested by 12 volunteers while manipulating a 0.1 N micro switch in a standard arm position. To test the handle with forces used during surgical procedures measurements were repeated with a 2.5 N micro switch. During the test the EMG activity of five forearm muscles was recorded and normalized with respect to the maximum voluntary activity of the respective muscle. The axial handle required significantly more EMG activity than the remaining handles in four of the five muscles tested. Similar results were obtained for both micro switches used but EMG activity increased with the switch force applied. The surgeon requires significantly more EMG activity and thus muscle strength when using the axial handle compared to the remaining handles. With the functional model of the Hirschberg and the ring handle the task can be performed with lower activity.

Group I afferent pathway contributes to functional knee stability

The hamstring reflex response has been suggested to play a substantial role in knee joint stabilization during anterior tibial translation. The present study was performed to determine which afferent pathways contribute to the hamstring reflex as well as the potential effects of specific afferent pathways on functional knee stability. Short- and medium-latency hamstring reflexes (SLR and MLR) were evoked by anterior tibial translation in 35 healthy subjects during standing with 30 degrees knee flexion. Nerve cooling, tizanidine, and ischemia were employed to differentiate afferent pathways. Two hours of thigh cooling (n = 10) resulted in a significant increase in MLR latency and, to a lesser extent, SLR latency. No significant changes were recorded in reflex sizes or maximum tibial translation. The ingestion of tizanidine (n = 10), a suppressor of group II afferents, strongly reduced the MLR size while SLR size or latency of both reflex responses was not significantly affected. Maximum tibial translation was unchanged [5.3 +/- 1.9 to 4.8 +/- 2 (SD) mm; P = 0.410]. Ischemia in the thigh (n = 15) led to a highly significant depression in SLR size (89 +/- 4%; P < 0.001) but only a slight and not significant decline of MLR size. In these subjects maximum tibial translation increased significantly (6.9 +/- 1.6 to 9.4 +/- 3.2 mm; P = 0.028). It is concluded that the hamstring SLR is mediated by Ia afferents, while group II afferents mainly contribute to the MLR. Suppression of SLR may increase maximum anterior tibial translation, thus indicating a possible functional role of Ia afferents in knee joint stabilization.

Effect of a whole-body vibration session on knee stability

The aim of the study was to investigate the effect of WBV on stretch reflexes involved in knee joint control. We evoked stretch reflexes of the hamstring muscles by inducing an anterior tibial translation during standing in 23 healthy subjects which were divided into a control and an intervention group. WBV with a frequency of 30 Hz and a vertical amplitude of 4 mm was induced by an uniformly oscillating platform. The WBV session lasted 60 seconds and was repeated twice. Short (SLR) and medium latency responses (MLR) of the hamstring muscles and maximum tibia translation were assessed using surface EMG and linear potentiometers. While there were no significant changes in latency, the size of the lateral and medial hamstring SLR was significantly increased after WBV (p = 0.039 and p = 0.043, respectively). No significant differences were found for the hamstring MLR size after WBV. Maximum tibial translation was significantly decreased after WBV (p = 0.031). Our results suggest that single WBV exposure has a positive effect on knee joint stability as a short-term adaptation on neuromuscular level. This appears to be directly associated with an increase of hamstring SLR size in response to the anterior tibial movement which may cause the decrease in anterior tibial translation.

Cortical and spinal adaptations induced by balance training: correlation between stance stability and corticospinal activation

AIM

To determine the sites of adaptation responsible for improved stance stability after balance (=sensorimotor) training, changes in corticospinal and spinal excitability were investigated in 23 healthy subjects.

METHODS

Neural adaptations were assessed by means of H-reflex stimulation, transcranial magnetic stimulation (TMS) and conditioning of the H-reflex by TMS (Hcond) before and after 4 weeks of balance training. All measurements were performed during stance perturbation on a treadmill. Fast posterior translations induced short- (SLR), medium- and long-latency responses (LLR) in the soleus muscle. Motor-evoked potential- (MEP) and Hcond-amplitudes as well as Hmax/Mmax ratios were determined at SLR and LLR. Postural stability was measured during perturbation on the treadmill.

RESULTS

Balance training improved postural stability. Hmax/Mmax ratios were significantly decreased at LLR. MEPs and Hcond revealed significantly reduced facilitation at LLR following training. A negative correlation between adaptations of Hcond and changes in stance stability was observed (r = -0.87; P < 0.01) while no correlation was found between stance stability and changes in Hmax/Mmax ratio. No changes in any parameter occurred at the spinally organized SLR and in the control group.

CONCLUSION

The decrease in MEP- and Hcond-facilitation implies reduced corticospinal and cortical excitability at the transcortically mediated LLR. Changes in cortical excitability were directly related to improvements in stance stability as shown by correlation of these parameters. The absence of such a correlation between Hmax/Mmax ratios and stance stability suggests that mainly supraspinal adaptations contributed to improved balance performance following training.

Changes in Stretch Reflex Excitability Are Related to “Giving Way” Symptoms in Patients With Anterior Cruciate Ligament Rupture

A rupture of the anterior cruciate ligament (ACL) usually leads to an altered stretch reflex excitability of the thigh muscles that stabilize the knee. The purpose of this study was to quantitatively assess reflex activity in the m. semitendinosus/semimembranosus after anterior tibial translation in 21 patients with isolated ACL ruptures. The patients were divided into a group with “giving way” symptoms (noncopers, n = 12) and a group without “giving way” symptoms (copers, n = 9). While the patients were standing upright with 30° knee flexion, a force of 300 N was applied to the knee to induce posterior–anterior tibial translation. Activity of m. semitendinosus/semimembranosus was measured using surface electromyography (EMG). A linear potentiometer was placed on the tibial tuberosity and measured maximum tibial translation during standing (i.e., functional condition). In addition, knee laxity was assessed with a KT1000 arthrometer under passive conditions. After ACL rupture, the short-latency response (SLR) latency remained unchanged ( P = 0.21), whereas for the medium-latency response (MLR) it was significantly longer ( P < 0.001). Significantly longer MLR latencies were noted for noncopers compared with copers ( P < 0.01), whereas SLR latencies were similar. Significant differences between healthy and injured legs were noted after tibial translations using KT1000 ( P < 0.001) and during stance ( P < 0.001). Mechanical knee instability was found to be unchanged between copers and noncopers (KT1000: P = 0.97; tibial translation: P = 0.31). These results indicate that ACL rupture is associated with altered stretch reflex excitability, which may lead to “giving way” symptoms, and that altered stretch reflex excitability may be more important for the development of “giving way” than the mechanical instability of the knee.

Modulation of soleus H-reflexes during gait in healthy children

During locomotion spinal short latency reflexes are rhythmically modulated and depressed compared to rest. In adults this modulation is severely disturbed after bilateral spinal lesions indicating a role for supra-spinal control. Soleus reflex amplitudes are large in the stance phase and suppressed in the swing phase contributing to the reciprocal muscle activation pattern required for walking. In early childhood the EMG pattern during gait underlies an age-dependent process changing from co-contraction of agonists and antagonists to a reciprocal pattern at the age of 5-7 years. It is unknown whether at this stage apart from the EMG also reflexes are modulated, and if so, whether the reflex modulation is fully mature or still underlies an age-dependent development. This may give important information about the maturation of CNS structures involved in gait control. Soleus Hoffmann H-reflexes were investigated in 36 healthy children aged 7-16 years during treadmill walking at 1.2 km/h and 3.0 km/h. At 7 years old a rhythmic modulation similar to adults was observed. The H-reflex size during the stance phase decreased significantly with age while the maximum H-reflex (H (max)) at rest remained unchanged. At 3.0 km/h H-reflexes were significantly larger during the stance phase and smaller during the swing phase as compared to 1.2 km/h but the age-dependent suppression was observed at both walking velocities. In conclusion H-reflex modulation during gait is already present in young children but still underlies an age-dependent process independent of the walking velocity. The finding that the rhythmic part of the modulation is already present at the age of 7 years may indicate that the supra-spinal structures involved mature earlier than those involved in the tonic reflex depression. This may reflect an increasing supra-spinal control of spinal reflexes under functional conditions with maturation.

In humans Ib facilitation depends on locomotion while suppression of Ib inhibition requires loading

The role of force feedback during gait is still a matter of debate. From work on cats, it is known that input from Golgi tendon organs from triceps surae does produce Ib facilitation during locomotion instead of autogenic inhibition. In humans, Stephens and Yang (Stephens, M.J., Yang, J.F., 1996. Short latency, non-reciprocal group I inhibition is reduced during the stance phase of walking in humans. Brain Res. 743, 24-31) found that voluntary contraction results in a reduction of Ib inhibition. During gait, they even observed Ib facilitation in a subset of subjects. This raises the question whether the crucial elements involved in these changes are either loading of the leg or locomotion. To examine this question, Ib reflexes were investigated during sitting, lying supine, lying supine with 300 N pressure applied to the foot sole, standing, and a rhythmic loading and unloading task called "reduced" gait. Ib inhibition was obtained during sitting and lying supine. This inhibition was significantly reduced or disappeared during standing and when lying supine but loaded. During the stance phase of "reduced" gait, the inhibition disappeared in eight subjects, and even a facilitation was observed in six subjects. It is concluded that the decrease in Ib inhibition from gastrocnemius to soleus occurs during a load-bearing condition and does not require locomotion. In contrast, Ib facilitation requires locomotion at least in a rudimentary form.

Intraoperative Direct Mechanical Stimulation of the Anterior Cruciate Ligament Elicits Short- and Medium-Latency Hamstring Reflexes

The anterior cruciate ligament (ACL) has not only a mechanical but also a sensorimotor function. Patients with injuries of the ACL frequently complain of knee instability despite good mechanical stabilization after surgical reconstruction. Compared with healthy subjects, their latencies of hamstring reflexes after anterior tibia translation are considerably increased. There is evidence for the existence of a reflex arc between the ACL and the hamstrings. The aim of this study was to determine if there is a direct reflex response after an isolated mechanical stimulation of the ACL in humans. In 10 patients who underwent arthroscopy, hamstring electromyographic (EMG) responses were assessed intraoperatively after applying an isolated load on the ACL. Latencies, amplitudes, and integrals of the EMG responses were analyzed. In four patients, the measurements were repeated after injection of local anesthetics into the ACL. In all subjects, responses with mean latencies of 42 ± 4.4 (SD) ms corresponding to a medium latency response (MLR) were found. In seven subjects, they were preceded by responses with a short-latency (SLR) of 24 ± 2.7 ms. The maximum amplitude was 8.6 ± 7 mV, the integral 0.064 ± 0.05 mV*s. The injection of local anesthetics reduced the amplitude by 34 ± 12% and the integral by 50 ± 20%. Direct mechanical stimulation of the ACL evokes considerably smaller SLRs and MLRs than anterior tibia translation during standing. It is argued that latency changes observed in patients with ACL ruptures may be rather due to changes in the sensorimotor integration of the afferent input from the knee joint than to the absence of the direct ACL reflex.

Differentiation of hamstring short latency versus medium latency responses after tibia translation

After injuries to the anterior cruciate ligament (ACL) a functional instability is frequently observed which has been attributed to a disturbed sensorimotor function. In light of the clinical importance of ACL injuries and the resulting functional instability, it is of enormous clinical interest to elucidate the role of sensorimotor pathways that involve the ACL. In animals and humans a direct reflex pathway between the ACL and the hamstrings has been shown. The onset latencies of responses reported after ventral tibia translation were around 40-50 ms (range 17.9-65) and were regarded as medium latency responses (MLR). However, ventral tibia translation should also induce a stretch of the hamstring muscles and evoke a short latency response (SLR). Before any muscle response after ventral tibia translation can be ascribed to anatomical structures, it is crucial to analyze the obtained muscle responses carefully. The aim of the present study was the development of an algorithm to differentiate SLR and MLR responses after ventral tibia translation. In ten healthy subjects reflex responses of the hamstrings after anterior tibia translation and after tendon taps on the biceps femoris tendon were evaluated. To investigate the influence of skin afferents, control experiments were performed after lidocain injection of the dorsal calf. The mean onset latency of the tendon jerk reflex was 21.9 +/- 3.1 ms (range 17.3 - 28.7 ms). Both SLR responses (mean onset latency: 20.3 +/- 3.5 ms; range 15.4 - 25.8) and MLR responses (mean onset latency: 38.9 +/- 4.2 ms; range 32.9 - 46.7) were obtained in all subjects. Skin afferents from the calf do not play a major role. The development of an evaluation algorithm is presented that allows a safe differentiation between these partly superimposed SLR and MLR components. It is demonstrated that by measuring the first part of the SLR from the onset to the first peak the end of the SLR can be predicted and that the onset latency of the MLR component can be assessed reliably. Possible reasons are discussed why previous studies only reported responses at MLR latencies. The fact that both SLR and MLR components can be observed after anterior tibia translation underlines the necessity to differentiate the responses before they can be ascribed to any anatomical structures. As a basis for future work the algorithm presented may become a useful tool to differentiate which afferent pathways play a role in initiating hamstring activity.

Monitor position in laparoscopic surgery

BACKGROUND

One of the key problems in laparoscopy is the ergonomic positioning of the monitor. In this study we tested task performance and muscle strain of subjects in relation to monitor position during laparoscopic surgery.

METHODS

Eighteen subjects simulated laparoscopic suturing by threading tiny pearls with a curved needle. This was repeated in three monitor positions (15 min each): frontal at eye level (A), frontal in height of the operating field (B), and 45 degrees to the right side at eye level (C). Subjects were not allowed to turn their heads during these sessions. After the test they were asked for their preferred monitor position. During all tests the electromyographic (EMG) activity of the main neck muscles was recorded and the number of pearls was counted.

RESULTS

The EMG activity was significantly lower for position A compared to positions C and B (p < 0.05). No significant difference was found between positions B and C. The number of threaded pearls as an indicator for task performance was highest for position B. The difference was statistically significant compared to position C (p = 0.0008) but not between positions A and C (p = 0.0508) or A and B (p = 0.0575). When asked for the preferred monitor position, nine subjects chose two monitors in the frontal positions A and B. No subject preferred the monitor at the side position (C).

CONCLUSION

Regarding EMG data, the monitor positioned frontal at eye level is preferable. Reflecting personal preferences of subjects and task performance, it should be of advantage to place two monitors in front of the surgeon: one in position A for lowest neck strain and the other in position B for difficult tasks with optimal task performance. The monitor position at the side is not advisable.

Ergonomic aspects of five different types of laparoscopic instrument handles under dynamic conditions with respect to specific laparoscopic tasks: An electromyographic-based study

BACKGROUND

The ergonomic deficiencies of various minimally invasive surgery (MIS) instrument handles are well-known. In the past, many studies have been performed to gain a better understanding of ergonomics in MIS. The current study investigates muscle strain during various dynamic tasks with different instrument handles.

METHODS

Five different handle designs were tested: the axial handle (Aesculap), the vario handle (own model), multifunctional and ring handles (both Karl Storz), and the shank handle (Wilo). Ten subjects without any surgical training tested the following instrument functions: precise dynamic movement, rotation of the closed instrument, and simultaneous opening and closing of the effector. During these three trials, task performance (errors/duration) and the electromyographic activity of the hand and lower arm muscles were measured.

RESULTS

Regarding the errors and the time required to carry out the tasks, the five handles showed similar results. The muscle activity was lowest for the precise dynamic movement task and highest during the rotation task. The axial handle required significantly more muscle activity than all other handles.

CONCLUSION

On the basis of these data, it was possible to construct characteristic muscle activation patterns for each handle. However, these patterns were not task specific. Accordingly, they may form a basis to improve the ergonomics of MIS handles with regard to muscle strain.

Effect of chronic bilateral subthalamic nucleus (STN) stimulation on postural control in Parkinson's disease

Postural instability is one of the most incapacitating factors in Parkinson's disease (PD). The underlying deficits and the effects of treatment are still not well understood. The aims of the present study were: (i) to identify abnormalities of postural control in PD patients during unperturbed stance and externally perturbed stance (anterior-posterior tilts of the support surface and of the visual scene); (ii) to assess the effects of L-dopa medication and subthalamic nucleus (STN) stimulation on posture control; and (iii) to characterize potential differential or additive effects of both treatments. Eight PD patients under chronic STN stimulation were investigated and compared with 10 normal controls. The assessment was performed in a crossover design (+/- STN stimulation, +/- L-dopa). During unperturbed stance, we recorded measures of spontaneous sway in terms of displacement, velocity and frequency of the centre of pressure (COP), lower body (LB) and upper body (UB) excursions. In addition, inter-segmental UB-LB coupling was investigated as a measure of axial stiffness. All these measures were abnormally large in patients OFF treatment. Under L-dopa treatment, the velocity, frequency and coupling measures were reduced, whereas sway amplitude increased. Very similar effects were obtained under STN stimulation, and these effects became more pronounced in the combined treatment condition. In these data, reduction of inter-segmental coupling correlated with increase in sway amplitude. The finding suggests that axial stiffness reduction under treatment revealed a treatment- resistant deficit in the sensorimotor postural control loop. However, these two effects did not correlate with the motor subscores of the unified Parkinson's disease rating scale (UPDRS), which indicates that they are of minor functional relevance for posture control. A frequency peak in the COP excursions at 0.7-1.1 Hz, which we take to indicate a resonance behaviour of the postural control loop, became reduced under therapy. The reduction of this peak did correlate with most improvements in the UPDRS under therapy. Support surface tilt revealed that an UB righting on the LB segment, which is present in normal controls, is missing in the patients. The postural responses to visual tilt were abnormally large in patients, independent of whether the support was stable or slightly moving, while the control subjects clearly profited from a stable support. This finding suggests that PD patients lack the ability of normal subjects to use sensory or cognitive information when suppressing the destabilizing effect of visual tilt. These abnormal tilt reactions of the patients were resistant to treatment with L-dopa, STN stimulation and a combination of the two. Overall, the effects of STN stimulation on posture control essentially paralleled those of L-dopa during both unperturbed and externally perturbed stance.

Ergonomic aspects of four different types of laparoscopic instrument handles with respect to elbow angle. An electromyogram-based study

BACKGROUND

Only few studies have tested different ergonomic aspects of the working posture assumed by laparoscopic surgeons. Although no experimental data are available for a laparoscopic setting, a working posture with a horizontal forearm or an elbow angle 90 degrees to 120 degrees has been recommended for performing minimally invasive surgery (MIS). The comparison of electromyogram (EMG) activities in different muscles provides information about the force developed by each muscle and allows assessment of its contribution to a functional movement. The current study aimed to investigate whether certain handles do not support this posture.

METHODS

For this study, 12 volunteers were postured in two different standardized arm positions, defined by elbow angles of 90 degrees and 120 degrees. They were manipulating a 0.1-N and a 2.5-N microswitch with four different types of instrument handle design: axial handle, ring handle, shank handle, Hirschberg handle. During the test, the EMG activities of five forearm muscles were recorded and normalized with respect to the maximum voluntary activity of the respective muscle.

RESULTS

Virtually no significant difference in EMG activity was found between the two elbow angles in any of five forearm muscles for a simple grasping maneuver. Thus, the muscle activity required to manipulate different types of MIS handles is similar for the elbow angles of 120 degrees and 90 degrees.

CONCLUSIONS

The current study did not show relevant differences between the two elbow angles for any of the four handles during a simple grasping maneuver with respect to the force required in the main forearm muscles.

Effect of bilateral subthalamic nucleus stimulation on gait in Parkinson's disease

The fundamental disturbance of the parkinsonian gait is the reduction in walking velocity. This is mainly due to reduction in stride length, while cadence (steps/min) is slightly enhanced. Treatment with L-dopa increases stride length while cadence is unchanged. Chronic stimulation of the thalamus has no effect on Parkinsonian gait. The efficacy of electrical stimulation of the subthalamic nucleus (STN) on gait in advanced Parkinson's disease has been clearly demonstrated clinically. The aim of the present study was to quantify the changes in gait measures induced by STN stimulation and L-dopa and to assess possible differential or additive effects. Eight Parkinson's disease patients (mean +/- SD age 48.1 +/- 7.3 years) with chronic bilateral STN stimulation (mean duration of disease 13.3 +/- 2.4 years, mean stimulation time 15.4 +/- 10.6 months) and 12 age-matched controls were investigated. Subjects walked on a special treadmill with a closed-loop ultrasound control system that used the subject's position to adjust treadmill speed continuously for the actual walking velocity. In an appropriate crossover design, spatiotemporal gait measures and leg joint angle movements were assessed for at least 120 stride cycles in four treatment conditions: with and without stimulation and with and without a suprathreshold dose of L-dopa. With STN stimulation, there were increases of almost threefold in mean walking velocity (from 0.35 to 0.96 m/s) and stride length (from 0.34 to 0.99 m). Cadence remained constant. The range of motion of the major leg joints also increased. L-Dopa alone had a slightly weaker effect, with an increase in walking velocity to 0.94 m/s and in stride length to 0.92 m at a similar cadence. These increased values were in the range of those for healthy age-matched subjects performing the same task. The combination of both treatments further increased the mean walking velocity to 1.19 m/s and stride length to 1.20 m at an unchanged cadence. However, not all patients receiving STN stimulation improved further when they also received L-dopa. These results demonstrate that chronic bilateral STN stimulation, like treatment with L-dopa, improves walking velocity by increasing stride length without changing cadence. STN stimulation almost exclusively affects mechanisms involved in the control of spatial gait measures rather than rhythmicity. The gait measures obtained with STN stimulation alone are in the range of control subjects.

The role of tumor resection in the treatment of glioblastoma multiforme in adults

BACKGROUND

The therapeutic impact of tumor resection is poorly defined. Therefore the current study was conducted.

METHODS

A retrospective, 2-institutional study was conducted (1991-1994) to compare the treatment results of stereotactic biopsy plus radiation therapy (99 patients; tumor dose: 60 gray [Gy]) with those of surgical resection plus radiation therapy (126 patients; tumor dose: 60 Gy). Only adult patients with supratentorial, lobar located, de novo glioblastoma were included. Survival time was analyzed with the Kaplan-Meier method. Prognostic factors were obtained from the multivariate Cox proportional hazards model.

RESULTS

Patients were categorized in the Radiation Therapy Oncology Group (RTOG) Classes IV (46 patients), V (157 patients), and VI (22 patients). The resection group and the biopsy group did not differ in terms of age, pretreatment Karnofsky performance status KPS), gender, duration of symptoms, presenting symptoms, tumor location, tumor size, and the frequency of midline shift. Patients in the biopsy group more often were found to have left-sided tumors (P < 0.001). Transient perioperative morbidity and mortality rates were 1% and 1%, respectively, in the biopsy group and 5% and 1.6%, respectively, in the resection group (P > 0.05). The median survival time was 37 weeks for the resection group and 33 weeks for the biopsy group. The difference was not statistically significant (P = 0.09). The most favorable pretreatment prognostic factor was patient age < 60 years (P < 0.01). Tumor resection was highly effective in patients with midline shift (P < 0.01). In patients without midline shift radiation therapy alone was found to be as effective as tumor resection plus radiation therapy (P = 0.5). Patients with midline shift were more likely to have a worse KPS during the course of primary radiation therapy (P < 0.05).

CONCLUSIONS

For RTOG Classes IV-VI patients with moderate mass effect of the tumor, radiation therapy alone is a rational treatment strategy. Tumor resection should be performed in patients with pretreatment midline shift whenever possible.

Modulation of the biceps femoris tendon jerk reflex during human locomotion

During gait it is generally accepted that there is a reduction in amplitude of H-reflexes as compared to standing. For short-latency stretch reflexes, however, it is less clear whether a similar reduction in reflex gain is present during locomotion. Stretches of constant amplitude are hard to produce under these circumstances and for this reason some previous studies on the biceps femoris (BF) have used "reduced gait" in which the stimulated leg is stepping on the spot while the contralateral leg is walking on a treadmill. With this method it was possible to show that BF tendon jerk reflexes are larger at end swing and therefore are likely to contribute to the EMG burst normally occurring in that part of the step cycle when the BF is rapidly stretched. In the present study two questions were addressed: first, whether the reflex is different in size during gait compared to standing and, second, whether it is modulated in size during the gait cycle not only during reduced but also during normal gait. It was found that during both types of gait there was a general reflex depression with regard to the respective control values obtained during standing at similar EMG activity levels. In previous studies on soleus and quadriceps, discrepancies between EMG activity and reflex amplitude have been ascribed to changes in presynaptic inhibition of Ia terminals mediating the afferent volley of the reflex. Based on the data presented, this may also be true for the BF. In both normal and reduced gait the reflex was similarly modulated in size, showing a maximum at the end of swing. This similarity implies that reduced gait may be useful as an acceptable alternative for normal gait in studies on phase-dependent reflex modulation during locomotion.

Impaired modulation of quadriceps tendon jerk reflex during spastic gait: differences between spinal and cerebral lesions

In healthy subjects, functionally appropriate modulation of short latency leg muscle reflexes occurs during gait. This modulation has been ascribed, in part, to changes in presynaptic inhibition of Ia afferents. The changes in modulation of quadriceps tendon jerk reflexes during gait of healthy subjects were compared with those of hemi- or paraparetic spastic patients. The spasticity was due to unilateral cerebral infarction or traumatic spinal cord injury, respectively. The modulation of the quadriceps femoris tendon jerk reflex at 16 phases of the step cycle was studied. The reflex responses obtained during treadmill walking were compared with control values obtained during gait-mimicking standing postures with corresponding levels of voluntary muscle contraction and knee angles. In healthy subjects the size of the reflexes was profoundly modulated and was generally depressed throughout the step cycle. In patients with spinal lesion the reflex depression during gait was almost removed and was associated with weak or no modulation during the step cycle. In patients with cerebral lesion there was less depression of the reflex size associated with a reduced reflex modulation on the affected side compared with healthy subjects. On the 'unaffected' side of these patients reflex modulation was similar to that of healthy subjects, but the reflex size during gait was not significantly different from standing control values. These observations suggest that the mechanisms responsible for the depression of reflex size and the modulation normally seen during gait in healthy subjects are impaired to different extents in spasticity of spinal or cerebral origin, possibly due to the unilateral preservation of fibre tracts in hemiparesis.

The role of afferent feedback in the control of hamstrings activity during human gait

In vertebrates, possibly also in man, the pattern of activation of muscles during locomotion can be generated by the spinal cord (locomotor CPG, central pattern generator). However, sensory feedback is crucial to adapt the functioning of the CPG to the external requirements during gait. It is postulated that afferent input from skin and muscles can contribute to the EMG activation patterns as observed in various limb muscles during gait. The activity of the hamstrings at end swing may be partially due to stretch reflexes of these muscles. At end stance the hamstring activity may be assisted by reflexes from natural skin activation from the dorsum of the foot. In addition, more specific actions are also incorporated. For example, sural nerve stimulation induces an activation of biceps femoris (BF) whereas a suppression is usually obtained for semitendinosus (ST), indicating that the induced activation is aimed at exorotation of the lower leg. Similarly, the preferential activation of medial versus lateral gastrocnemius (GM versus GL) in sural nerve induced reflexes could favor such exorotation. It is concluded that the present evidence points towards a possible contribution of various reflexes to the motor output seen during gait for movements both inside and outside the sagittal plane.

The risk of interstitial radiotherapy of low-grade gliomas

BACKGROUND AND PURPOSE

The risk of side effects of low activity (i.e. <20 mCi) Iodine-125I (125I) interstitial radiotherapy was analyzed in patients with low-grade gliomas.

MATERIALS AND METHODS

Permanent (247 patients) or temporary 125I-implants (268 patients) were used with a median reference dose of 60 Gy and 100 Gy, respectively, which was calculated to the outer rim of the tumour. The mean dose rate for temporary implants was low (median, 10 cGy/h). Risk factors were obtained from the multivariate proportional-hazards model.

RESULTS

Radiogenic complications occurred in 39/515 patients (28 patients with transient symptoms and 11 patients with progressive symptoms). The most important risk factor was the volume of the intratumoural 200 Gy isodose. Available experimental data have associated a high dose zone in this range with the size of the treatment induced radionecrosis. Rapid tumour shrinkage (decrease of the tumour volume > or =50%) within the first 6 months with subsequent centripetal movement of non-pathologic tissue into the high dose zone and a reimplantation were additional risk factors. Radiation injury after rapid tumour shrinkage could be better avoided with temporary implants. A 200 Gy isodose volume <4.5 ml corresponded to an estimated risk of radiogenic complications <3%. There was a steep increase of the risk beyond this limit. Translation of the 200 Gy isodose volume in terms of the treatment volume and the reference dose allows rational treatment planning. The estimated risk of a temporary implant with an applied reference dose of 60 Gy and a treatment volume <23 ml was <3%.

CONCLUSIONS

The intratumoural necrotizing effect of a low activity 125I implant limits its application to small treatment volumes. Radiation injury outside the treatment volume can be better avoided with temporary implants in the case of rapid tumour shrinkage.

Supratentorial World Health Organization Grade 2 astrocytomas and oligoastrocytomas. A new pattern of prognostic factors

BACKGROUND

Prognostic factors for adult patients with supratentorial World Health Organization (WHO) Grade 2 astrocytomas and poorly defined.

METHODS

The prognostic importance of pretreatment patient- and tumor-related factors was analyzed retrospectively in 197 adult patients with supratentorial astrocytomas (n = 153) or oligoastrocytomas (n = 44) using the multivariate Cox proportional hazards model. Endpoints were death and date of malignant transformation. All patients were treated similarly between 1979 and 1992 with iodine-125 implants as the primary treatment.

RESULTS

A new prognostic pattern was detected. Unfavorable prognostic factors with regard to survival were 1) a tumor volume > or = 20 mL; 2) a performance status < or = 80; and 3) age > or = 40 years for the female subpopulation. Midline shift (another important tumor-related factor after univariate analysis) was highly correlated with tumor volume and therefore not included in the multivariate model. Risk factors of malignant transformation were 1) a tumor volume > or = 20 mL; 2) an enhancement in the computed tomography scan; and 3) age > or = 40 years for the female subpopulation. Prognostic factors created subsets of patients with 5-year survival rates ranging from as low as 5% to as high as 79%.

CONCLUSIONS

Any treatment decision or evaluation of treatment efficacy should take into account the strong influence of both patient- and tumor-related factors. Any further study design should consider the detected interaction between gender and age and the importance of tumor volume.

Biceps femoris tendon jerk reflexes are enhanced at the end of the swing phase in humans

The phase-dependent modulation of the biceps femoris (BF) tendon jerk reflexes was investigated in a reduced form of walking. All subjects (12) investigated showed tendon reflexes throughout the whole step cycle but the amplitude was largest in the middle and late swing phase of the ipsilateral leg. It is concluded that the normally occurring BF burst at end swing could be due to stretch-induced activity.

Stereotactic management of lesions of the pineal region

OBJECTIVE

The relevance of the computed tomography-guided stereotactic approach for the management of lesions of the pineal region is analyzed.

METHODS

In a retrospective analysis conducted between 1985 and 1993, the risk profile, the diagnostic accuracy, and the therapeutic relevance of the stereotactic approach in 106 patients was studied. Survival analysis was used to assess the reliability of the stereotactically obtained diagnosis in terms of follow-up observation.

RESULTS

A histological diagnosis was obtained in 103 of the 106 patients. In three patients, a conclusive diagnosis could not be established because of intraoperative complications. One lesion was misdiagnosed as a pineocytoma instead of a pineoblastoma. Two of the 106 patients died; 9 patients experienced perioperative morbidity. In 38 patients, the stereotactic approach was also useful for therapy. Cyst aspiration and/or internal drainage was performed in 18 patients with symptomatic cystic lesions, and radiosurgical treatment with use of interstitial 125iodine was performed in 16 patients with low-grade tumors and in 4 patients with solitary metastases. In 12 patients, the obtained tissue diagnosis was the basis for deferring additional therapy. In 43 patients with germ-cell tumors, pineoblastomas, or malignant gliomas, a stereotactic biopsy was the starting point for additional radiotherapy/chemotherapy. Open tumor resection played a minor role (five patients).

CONCLUSION

The stereotactic approach to the pineal region is a relatively safe procedure in experienced hands. The diagnosis obtained by computed tomography-guided stereotactic biopsy is a valid basis for treatment decisions. Long-term follow-up observation of the benign lesions is necessary for a definite confirmation of diagnostic accuracy.

Modulation, probably presynaptic in origin, of monosynaptic Ia excitation during human gait

Modulation of presynaptic inhibition of Ia afferents projecting monosynaptically to soleus motoneurones was investigated during human gait. Changes in presynaptic inhibition of Ia afferents were deduced from alterations in the amount of heteronymous soleus H-reflex facilitation evoked by a constant femoral nerve stimulation. It has been shown that this facilitation is mediated through a monosynaptic Ia pathway and that during its first 0.5 ms it is still uncontaminated by any polysynaptic effect and can be used to assess ongoing presynaptic inhibition of Ia terminals to soleus motoneurones. During gait, heteronymous facilitation was reduced with respect to its control value (rest during sitting) and modulated during the step cycle: it reached its maximum at mid-stance and decreased to near zero by the end of stance. At the same time the H-reflex amplitude was to some extent similarly modulated. It is argued that this decrease in heteronymous Ia facilitation and in H-reflex amplitude reflects an increased, ongoing presynaptic inhibition of Ia terminals projecting onto soleus motoneurones, which could be from central and/or peripheral origin. D1 inhibition, i.e. the late and long-lasting inhibition of the soleus H-reflex evoked by a train of stimuli to the common peroneal nerve, was used as another method to assess presynaptic inhibition. This D1 inhibition was decreased during gait, and it is argued that this decrease might reflect an occlusion in presynaptic pathways or increased presynaptic inhibition of pathways mediating the conditioning volley.

Interstitial radiosurgery of low-grade gliomas

The treatment of patients with low-grade gliomas remains a subject of controversy, especially with respect to new treatment modalities such as interstitial radiosurgery (brachytherapy), radiosurgery, and stereotactic radiotherapy. In a retrospective analysis conducted between 1979 and 1991, the authors studied the results of interstitial radiosurgery in 455 patients with low-grade gliomas (World Health Organization (WHO) Grade I+WHO Grade II) with regard to survival time, quality of life, the risk of malignant transformation, and the risk profile of the treatment concept. Interstitial radiosurgery with iodine-125 was performed using permanent (1979-1985) or temporary implants (after 1985) with low-dose rates (< or = 10 cGy/hr) and a reference dose of 60 to 100 Gy calculated to the outer rim of the tumor. The 5- and 10-year survival rates in patients with pilocytic astrocytomas (97 patients) were 84.9% and 83%, and in patients with WHO Grade II astrocytomas (250 patients) 61% and 51%, respectively. Five-year survival rates for patients with oligoastrocytomas (60 patients), oligodendrogliomas (27 patients), and gemistocytic astrocytomas (21 patients) were 49%, 50%, and 32%, respectively. In the group with WHO Grade II gliomas, young age and a good performance status were associated with a better prognosis. Unfavorable factors were midline shift, enhancement on computerized tomography (CT) scan, and tumor recurrence after previous radiotherapy or surgery. Tumor location had no influence on the prognosis (247 patients in this series had deep-seated tumors). Malignant transformation was the major cause of death. Important risk factors for malignancy were the patient's age, tumor enhancement in CT scan, and tumor recurrence after previous surgery or radiotherapy. Perioperative mortality was 0.9% and perioperative morbidity was 1.7%. Radiogenic complications were observed in 2.7% of all patients, most often in larger tumors and after using permanent implants. The authors conclude that interstitial radiosurgery represents a specific treatment modality for selected patients with unifocal circumscribed low-grade gliomas with a diameter of less than 4 cm in any location. The efficacy of this treatment lies in the same range as the best results after surgery and radiotherapy.

A quantitative assessment of presynaptic inhibition of Ia afferents in spastics. Differences in hemiplegics and paraplegics

Soleus H-reflex facilitation evoked by a supramaximal conditioning stimulation to the femoral nerve was investigated in 28 healthy control subjects and 35 spastic patients of whom 17 were paraplegics with bilateral spinal cord lesion and 18 were hemiplegics with unilateral cerebral lesion. Heteronymous facilitation from quadriceps to soleus was measured 0.4 ms after onset, while the monosynaptic Ia excitation is still uncontaminated by any non-monosynaptic effect and can be used to assess ongoing presynaptic inhibition on Ia terminals to soleus motor neurons. In paralegics, this heteronymous Ia facilitation was significantly larger than in control subjects (all individual results in these patients being above the mean observed in controls). This must reflect a decrease in presynaptic inhibition of Ia terminals in the paraplegics explored here. There was no correlation between this decreased presynaptic inhibition of Ia terminals and the degree of spasticity measured by Ashworth's scale. Surprisingly, the amount of heteronymous Ia facilitation in hemiplegics was the same as in normal subjects. This indicates that presynaptic inhibition of Ia terminals is unchanged in these patients and disagrees with the usual interpretation of reduced vibratory inhibition of the soleus H-reflex in hemiplegics. It is argued that this disagreement is due to the fact that vibratory inhibition of the reflex also depends on post-activation depression following repetitive synaptic transmission.

Interstitial 125-iodine radiosurgery of low-grade gliomas of the insula of Reil

Between 1979 and 1991 67 patients with low-grade gliomas of the insula (of Reil) were treated with 125-iodine interstitial radiosurgery. Retrospective analysis with a median follow-up of 55 months demonstrated a 5- and 10-year survival rate of 54% and 47%, respectively, for all low-grade gliomas treated and a 5- and 10-year survival rate of 57% for 49 patients with astrocytomas WHO grade II analysed separately. The median Karnofsky performance status of survivors was 90%. Malignant change was the cause of death in 85%, failure to control tumour growth in the remaining cases. Multivariate analysis with a Cox proportional hazard model identified solely the pre-operative Karnofsky performance score of 70-80 vs. 90% as a prognostic factor for outcome (p = 0.001, risk ratio 3.62), but not age, gender, tumour volume, length of disease before treatment, mode of implantation, or major vs. moderate or no shrinkage of tumour volume after interstitial radiosurgery. Thus, 125-iodine radiosurgery yielded survival rates in these deep-seated insular gliomas comparable to those reported after surgery and radiation therapy of lobar tumours. This was achieved with a low peri-operative mortality and morbidity and at low costs.

Distribution of heteronymous Ia facilitation and recurrent inhibition in the human deltoid motor nucleus

Distribution of heteronymous Ia facilitation and of heteronymous recurrent inhibition in motoneurones innervating the anterior part of the deltoid muscle were investigated in normal human subjects following electrical stimulation of the nerves innervating the main muscles of the upper limb. Activation of group I afferents originating from deltoid, biceps, triceps and extensor carpi radialis (ECR) muscles resulted in an early increase in firing probability of voluntarily activated motor units belonging to the anterior part of the deltoid muscle whereas activation of motor axons supplying deltoid, triceps, ECR and flexor carpi radialis (FCR) muscles resulted in an early and long-lasting decrease in firing probability. No effect was seen following activation of group I afferents and motor axons contained in the ulnar nerve. The characteristics of the early facilitation suggest that it is at least partly due to heteronymous Ia monosynaptic connections while these of the long-lasting inhibition suggest that it is at least partly due to heteronymous recurrent inhibition. Their patterns of distribution are discussed with regards to the functional role of the human deltoid.

Amplitude modulation of the human quadriceps tendon jerk reflex during gait

Amplitude modulation of the quadriceps tendon jerk reflex was investigated during the step cycle in normal human subjects. Reflex amplitude was compared with that obtained during a control stance condition, with "equivalent" levels of EMG activity and limb position. During gait there was a progressive decrease in the reflex amplitude early in the stance phase, i.e. during yielding of the knee, and it remained reduced throughout the step cycle. This pattern of changes in reflex amplitude correlated with neither the quadriceps EMG activity nor with the knee joint movements. The behavior of the tendon reflex was similar to that described for the modulation of the quadriceps H-reflex during the early stages of the stance phase of gait. In the latter study it was argued that changes in presynaptic inhibition of quadriceps la terminals could account for the amplitude modulation. We conclude that there is no dramatic change in the gamma drive to quadriceps muscle spindles: tendon reflexes are modulated during the step cycle in much the same way as H-reflexes, in spite of the peripheral and central differences between them. Similar behavior has been described for the soleus H-reflex and Achilles tendon reflex during gait although the modulation of these reflexes followed a different pattern than that seen in the quadriceps.

Amplitude modulation of the quadriceps H-reflex in the human during the early stance phase of gait

Amplitude modulation of the quadriceps H reflex was investigated during the early part of the stance phase of gait in normal human subjects. Stability of the M wave was used to ensure constancy of the effective stimulus strength. In all subjects there was a progressive decrease in the reflex amplitude throughout the early knee flexion (yield of the knee), whereas the quadriceps EMG activity remained constant or even increased. At an equal stimulus strength and EMG level, the reflex was often larger at the onset of the stance phase of gait than during voluntary contraction, whereas it was always smaller during the knee extension following the yield of the knee. It is argued that changes in presynaptic inhibition of quadriceps Ia terminals could account for this amplitude modulation of the monosynaptic reflex during gait. The possible role of changes in the gain of the quadriceps stretch reflex during bipedal gait is discussed.