Kinematics of the ankle/foot complex--Part 2: Pronation and supination

The influence of pronation and supination of the foot on the joints of the ankle/foot complex was analyzed three dimensionally by roetgen stereophotogrammetry in eight healthy volunteers. Radiopaque markers were introduced into the tibia, talus, calcaneus, navicular, medial cuneiform, and first metatarsal bones. The subjects stood on a platform that was tilted in 10 degree-steps from 20 degrees of pronation to 20 degrees of supination. Pairs of x-ray exposure were made in each position. Calculation of resulting joint deviations from the neutral position showed that the largest amounts of motion occurred in the talonavicular joint followed by the talocalcaneal joint, in the latter case mainly in supination. The joints proximal and distal to the medial cunriform also participated substantially in the total motion registered. The tibia showed an average of 0.2 degrees of external rotation for each degree of supination of the foot.

Kinematics of the ankle/foot complex: plantarflexion and dorsiflexion

In an in vivo investigation of eight healthy volunteers, three dimensional ankle/foot kinematics were analyzed by roentgen stereophotogrammetry in 10 degrees steps of motion from 30 degrees of plantar flexion to 30 degrees of dorsiflexion of the foot. The study included all of the joints between the tibia and the first metatarsal, as well as the talocalcaneal joint, and was performed under full body load. Although the talocrural joint was found to account for most of the rotation around the transverse axis occurring from 30 degrees of plantar flexion to 30 degrees of dorsiflexion, there was a substantial contribution from the joints of the arch. This was seen particularly in the input arc from 30 degrees of plantar flexion to the neutral position, where the dorsiflexion motion of these joints amounted to 10% to 41% of the total transverse axis rotation.

The axis of rotation of the ankle joint

The axis of the talo-crural joint was analysed by roentgen stereophotogrammetry in eight healthy volunteers. Examinations were performed at 10 degrees increments of flexion and pronation/supination of the foot as well as medial and lateral rotation of the leg. Results indicate that the talo-crural joint axis changes continuously throughout the range of movement. In dorsiflexion it tended to be oblique downward and laterally. In rotation of the leg, the axis took varying inclinations between horizontal and vertical. All axes in each subject lay close to the midpoint of a line between the tips of the malleoli. Our study indicates that the talo-crural joint axis may alter considerably during the arc of motion and differ significantly between individuals. This prompts caution in the use of hinge axes in orthoses and prostheses for the ankle.

Effect of different spinal cord lesions on visually guided switching of target-reaching in cats

It has previously been shown that when a target is moved, cats can change the direction of ongoing target-reaching with brief latency suggesting a tectal relay. Switching of target-reaching has now been investigated after spinal lesions: (1) dorsally in C5 interrupting cortico- (CS) and rubrospinal (RS) fibres to forelimb segments; (2) more ventrally in C5 interrupting axons of the C3-C4 propriospinal neurones (PNs) to forelimb motoneurones; and (3) ventrally in C2 interrupting tectospinal and tecto-reticulospinal fibres. Short-latency switching of target-reaching remained after lesions 1 and 2. A subsequent lesion 3 after lesion 1 or 2 prolonged the switching latency. The results show that fast switching, presumably relayed in tectum, can be made when the cat utilizes C3-C4 PNs or interneurones in the forelimb segments for target-reaching. For both neuronal systems, the longer-latency switching after ventral C2 lesion is assumed to be cortically relayed and mediated by the CS and RS tracts.

Motor recovery after serial spinal cord lesions of defined descending pathways in cats

The food-taking movement by which a cat uses its forepaw to take a piece of food and bring it to its mouth normally depends on the cortico- (CS) and rubrospinal (RS) tracts and disappears when they are transected in C5; a slow reappearance over months is due to bulbospinal (BS) take-over. After complete CS transection but minimal RS transection, food-taking remains. If, one month later, the RS tract is completely transected, food-taking is not abolished as it is when transection is made in one session. It is permanently abolished after a third transection of the ventral quadrant in C2. It is suggested that the food-taking remaining after the first lesion is due to combined RS and BS activity and that the RS tract induces the BS neurones to contribute to the extent that they can take over when the RS tract is completely transected.

Mobility of the ankle mortise. A roentgen stereophotogrammetric analysis

In 7 adult volunteers, a roentgen stereophotogrammetric technique was used to analyze the tibiofibular relationship during active unloaded movements of the ankle. The greatest movements were observed during plantar to dorsiflexion with an average widening of the ankle mortise of 1.0 mm and an average dorsal translation of the fibula of 0.9 mm. No significant rotation of the fibula could be revealed.

Long C3-C5 propriospinal neurones in the cat

Intracellular recording was made in the C3-C5 segments of cats from cells identified as long propriospinal neurones (PNs) by antidromic activation from the lower thoracic segments. The cell bodies were in laminae VII and VIII and their ventrally located axons were either uncrossed or crossed. Stimulation of higher motor centres revealed monosynaptic excitatory postsynaptic potentials (EPSPs) from cortico-, rubro-, tecto-, reticulo-, interstitio-, fastigio- and trigeminospinal fibres. Monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked from reticulospinal fibres. These PSPs were in addition to the separately described effects from the vestibular nuclei. Monosynaptic EPSPs were also evoked in some cells from neck or forelimb afferents and disynaptic EPSPs or IPSPs from forelimb afferents.

Vestibular effects in long C3-C5 propriospinal neurones

The effects of stimulation of the vestibular nerve and of regions in and around the vestibular nuclei on long C3-C5 propriospinal neurones (PNs) were investigated with intracellular recording. Disynaptic excitatory postsynaptic potentials were evoked from the contralateral (co) or ipsilateral (i) vestibular nerve in many long PNs but mainly in crossed PNs from the co and in uncrossed from the i nerve. Disynaptic inhibitory postsynaptic potentials were evoked more rarely, mainly from the i vestibular nerve. Threshold mapping revealed an excitatory relay from the co nerve in the medial vestibular nucleus (MVN) and also that the excitatory MVN neurones projecting to the long PNs send collaterals to the abducens and interstitial nucleus of Cajal. Excitation from the i vestibular nerve was relayed in the lateral vestibular nucleus (LVN) and in the MVN. Also, non-second order LVN neurones project to the long PNs. Monosynaptic IPSPs were evoked from the i MVN and i LVN.

Subpopulations and functions of long C3-C5 propriospinal neurones

Long C3-C5 propriospinal neurones (PNs) are classified in 3 types depending on their pyramidal and vestibular input. The first type of PNs received pyramidal excitation but lacked vestibular effects. The second type of PNs was excited from the medial vestibular nucleus but not from the pyramid. The third type of PNs was excited from the lateral vestibular nucleus either from second order neurones or from non-second order neurones. Monosynaptic excitatory postsynaptic potentials from neck afferents and/or oligosynaptic postsynaptic potentials from forelimb afferents were found in some of the PNs of the second and third type but not in those of the first type. Collision experiments revealed that cortico- and rubrospinal fibres to the long C3-C5 PNs terminate in the rostral spinal cord, presumably in the forelimb segments. Vestibular and reticular effects on the PNs are partly from fibres terminating in the rostral spinal cord and partly from fibres projecting to the lumbar cord. It is postulated that the different types of PNs contribute to the adjustment of hindlimb posture which is required during different movements of the forebody. It is suggested that the basic tonus is maintained mainly by the direct projection to the hindlimb segments from lateral vestibulospinal and reticulospinal neurones which excite antigravity muscles via lumbar interneurones and that the long C3-C5 PNs converge onto the same interneurones so that they act by modulation of the basic tonus.

Reflex pathways from group II muscle afferents. 2. Functional characteristics of reflex pathways to alpha-motoneurones

The convergence of group II muscle afferents on interneurones in reflex pathways has been elucidated by investigating interaction in transmission to motoneurones. Recording was also made from interneurones activated from group II afferents. Maximal group II EPSPs evoked in motoneurones from different muscles (extensors or flexors and extensors) did not summate linearly but with a deficit of 35-40%. The corresponding deficit in summation with Ia EPSPs was 7%. It is suggested that the difference in deficit is caused largely by occlusion due to shared interneuronal discharge zones and that it gives an approximate minimal measure of the convergence of group II afferents from different muscles on the interneurones. Tests with weak group II volleys from different muscles gave no or little evidence for spatial facilitation in the disynaptic excitatory pathway to flexor motoneurones, and there was no or little temporal facilitation of transmission in this pathway. It is suggested that group II excitation of the interneurones in this pathway depends on few afferents giving large unitary EPSPs. Convergence of cutaneous afferents and joint afferents on the interneurones was evidenced by spatial facilitation from these afferents of group II transmission to motoneurones. Convergence on interneurones in the trisynaptic inhibitory pathway from group II afferents to extensor motoneurones was also investigated with the spatial facilitation technique. There was convergence on common interneurones of group II afferents from different muscles (extensors or flexors and extensors) and from cutaneous afferents as well as joint afferents. Trisynaptic group II IPSPs, including those depending on spatial facilitation from different muscles were resistant to recurrent depression from motor axon collaterals and are therefore not mediated by the reciprocal Ia inhibitory pathway. Interneurones with monosynaptic group II EPSPs were recorded from in the dorsal horn and intermediate region. Graded stimulation revealed large unitary EPSPs from few group II afferents. The EPSP evoked by a single group II afferent may produce firing (extracellular recording). Convergence of monosynaptic group II EPSPs from different muscles was rather limited but could be from flexors and extensors. Extensive multisensory convergence onto some of these interneurones was indicated by di- or polysynaptic EPSPs from group II and III muscle afferents, from joint afferents and from cutaneous afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Reflex pathways from group II muscle afferents. 3. Secondary spindle afferents and the FRA: a new hypothesis

A hypothesis is forwarded regarding the role of secondary spindle afferents and the FRA (flexor reflex afferents) in motor control. The hypothesis is based on evidence (cf. Lundberg et al. 1987a, b) summarized in 9 introductory paragraphs. Group II excitation. It is postulated that subsets of excitatory group II interneurones (transmitting disynaptic group II excitation to motoneurones) may be used by the brain to mediate motor commands. It is assumed that the brain selects subsets of interneurones with convergence of secondary afferents from muscles whose activity is required for the movement. During movements depending on coactivation of static gamma-motoneurones impulses in secondary afferents may servo-control transmission to alpha-motoneurones at an interneuronal level. The large group II unitary EPSPs in interneurones are taken to indicate that, given an adequate interneuronal excitability, impulses in single secondary afferents may fire the interneurone and produce EPSPs in motoneurones; interneuronal transmission would then be equivalent to that in a monosynaptic pathway but with impulses from different muscles combining into one line. It is postulated that impulses in the FRA are evoked by the active movements and that the role of the multisensory convergence from the FRA onto the group II interneurones is to provide the high background excitability which allows the secondary spindle afferents to operate as outlined above. The working hypothesis is put forward that a movement governed by the excitatory group II interneurones is initiated by descending activation of these interneurones, but is maintained in a later phase by the combined effect of FRA activity evoked by the movement and by spindle secondaries activated by descending activation of static gamma-motoneurones. As in the original "follow up length servo" hypothesis (Rossi 1927; Merton 1953), we assume that a movement at least in a certain phase can be governed from the brain solely or mainly via static gamma-motoneurones. However, our hypothesis implies that the excitatory group II reflex connexions have a strength which does not allow transmission to motoneurones at rest and that the increase in the gain of transmission during an active movement is supplied by the movement itself. Group II inhibition. It is suggested that the inhibitory reflex pathways like the excitatory ones have subsets of interneurones with limited group II convergence. When higher centres utilize a subset of excitatory group II interneurones to evoke a given movement, there may mobilize inhibitory subsets to inhibit muscles not required in the movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Reflex pathways from group II muscle afferents. 1. Distribution and linkage of reflex actions to alpha-motoneurones

The interneuronally mediated reflex actions evoked by electrical stimulation of group II muscle afferents in low spinal cats have been reinvestigated with intracellular recording with motoneurones to knee flexors and ankle extensors. The results of Eccles and Lundberg (1959) have been confirmed and extended. There was wide convergence from flexors and extensors of group II excitation to flexor and group II inhibition to extensor motoneurones. Some quantitative differences in the effect from the different nerves are described. Latency measurements suggest that the minimal linkage is disynaptic in the excitatory interneuronal pathways and trisynaptic in the inhibitory pathways. Disynaptic group II EPSPs were found in 14% of the ankle extensor motoneurones but were much more common in unanaesthetized high spinal cats (Wilson and Kato 1965). From these results and corresponding ones on flexors (Holmqvist and Lundberg 1961) it is postulated that secondary afferents in addition to the weak monosynaptic connexions (Kirkwood and Sears 1975) have disynaptic excitatory pathways and trisynaptic inhibitory pathways to both flexor and extensor motoneurones. It is proposed that the group II actions of the flexor reflex pattern characterizing the anaesthetized low spinal cat are due to suppression of the inhibitory pathway to flexor motoneurones and the excitatory pathway to extensor motoneurones. In some ankle extensor motoneurones the disynaptic group II EPSPs occurred in combination with IPSPs from the FRA (including group II and III muscle afferents). The possibility is considered that these group II EPSPs are mediated by an interneuronal group II pathway with little or no input from group III muscle afferents but probably from extramuscular receptors. In other ankle extensor motoneurones group II EPSPs were combined with EPSPs from group III muscle afferents, cutaneous afferents and joint afferents. It is postulated that these group II EPSPs are mediated by an interneuronal pathway from the FRA which also supply interneuronal pathways giving inhibition to extensor or/and flexor motoneurones and excitation to flexors as postulated by Eccles and Lundberg (1959) and Holmqvist and Lundberg (1961).

Hypermetria in forelimb target-reaching after interruption of the inhibitory pathway from forelimb afferents to C3-C4 propriospinal neurones

Forelimb target-reaching in cats with a transection at C5/6 of the cortico- and rubrospinal tracts is known to depend on C3-C4 propriospinal neurones (PNs). An additional lesion transecting the dorsal column (DC) in C5/6, caudal to the C3-C4 PNs, gave pronounced hypermetria in lifting and protraction during target-reaching. If the additional DC lesion instead was made in C2, rostral to the C3-C4 PNs, there was only small hypermetria in lifting and none in protraction. It is postulated that the hypermetria after the C5/6 DC lesion is due to interruption of the inhibitory pathway from the forelimb to the C3-C4 PNs. It is suggested that feedback control from the forelimb of the premotoneurones is an integral part of the control of normal target-reaching.

Effects of dorsal column transection in the upper cervical segments on visually guided forelimb movements

Complete transection of the dorsal column in C2 in cat gave severe defects in forelimb target-reaching and food-taking tested with retrieval of food from a cylinder. Among the symptoms were marked dysmetria in all directions and dyscoordination of movements in different joints, with only slow recovery over weeks and months. It is postulated that normal visual guidance of forelimb movements to a stationary target depends on somatosensory information to the brain via the dorsal column.

The inhibitory feedback pathway from the forelimb to C3-C4 propriospinal neurones investigated with natural stimulation

Light mechanical stimulation of the skin and passive joint movements in the forelimb gave effective activation of interneurones located medially in the C3-C4 segments. Such interneurones may be inhibitory to C3-C4 propriospinal neurones (PNs) and recording from PNs revealed that the stimuli which activated the interneurones evoked inhibition in the PNs. It is postulated that a movement commanded via the C3-C4 PNs evoke impulses in forelimb afferents which by negative feedback control transmission in the C3-C4 PNs and thus govern the execution of the movements.

Integration in descending motor pathways controlling the forelimb in the cat. 11. Inhibitory pathways from higher motor centres and forelimb afferents to C3-C4 propriospinal neurones

Intracellular recording was made in the C3-C4 segments from cell bodies of a previously described system of propriospinal neurones (PNs), which receive convergent monosynaptic excitation from different higher motor centres and mediate disynaptic excitation and inhibition from them to forelimb motoneurones. Inhibitory effects in these PNs have now been investigated with electrical stimulation of higher motor centres and forelimb nerves. Short-latency IPSPs were evoked by volleys in the cortico-, rubro- and tectospinal tracts and from the reticular formation. Latency measurements showed that those IPSPs which required temporal summation were disynaptically mediated. After transection of the corticospinal tract in C2, only small and infrequent disynaptic IPSPs were evoked from the pyramid. It is postulated that disynaptic pyramidal IPSPs only to a small extent are evoked by monosynaptic excitation of reticulospinal inhibitory neurones known to project directly to the PNs, and that they are mainly mediated by inhibitory interneurones in the C3-C4 segments. Tests with spatial facilitation revealed monosynaptic excitatory convergence from tecto-, rubro- and probably also from reticulospinal fibres on inhibitory interneurones monosynaptically excited from corticospinal fibres (interneuronal system I). Disynaptic IPSPs were also evoked in the great majority of the PNs by volleys in forelimb muscle and skin nerves. A short train of volleys was usually required to evoke these IPSPs from group I muscle afferents. In the case of cutaneous nerves and mixed nerves single volleys were often effective, and the lack of temporal facilitation of IPSPs produced by a train of volleys showed strong linkage from these nerves. The results obtained after transection of the dorsal column at different levels show that the relay is almost entirely rostral to the forelimb segments. Test with spatial facilitation revealed that interneurones monosynaptically activated from forelimb afferents receive convergent excitation from corticospinal but not or only weakly so from tecto- or rubrospinal fibres. There was also convergence from group I muscle afferents and low threshold cutaneous afferents on common interneurones. It is postulated that the disynaptic IPSPs from forelimb afferents are mediated by inhibitory interneurones (interneuronal system II) other than those receiving convergent descending excitation. Volleys in corticospinal fibres, in addition to the disynaptic IPSPs, evoke late IPSPs in the PNs. Similar late IPSPs were evoked from the ipsilateral forelimb by stimulation of the FRA.(ABSTRACT TRUNCATED AT 400 WORDS)

Integration in descending motor pathways controlling the forelimb in the cat. 10. Inhibitory pathways to forelimb motoneurones via C3-C4 propriospinal neurones

A further analysis has been made of inhibitory pathways to motoneurones via C3-C4 propriospinal neurones (PNs). Intracellular recording was made from triceps brachi motoneurones and effects from higher centres and forelimb afferents on corticospinal IPSPs were investigated after transection of the corticospinal tract at the C5/C6 border. The shortest latencies of the IPSPs evoked by stimulation of the pyramid were as brief as those of the pyramidal EPSPs (Illert et al. 1977). It is postulated that the minimal linkage of the pyramidal IPSPs is disynaptic via inhibitory C3-C4 PNs projecting directly to motoneurones. It was confirmed that pyramidal IPSPs usually are depressed by volleys in forelimb motor axon collaterals (Illert and Tanaka 1978). A quantitative comparison was made of the recurrent depression of pyramidal IPSPs and of IPSPs caused by activation of the Ia inhibitory interneurones. The result support the hypothesis of two parallel inhibitory cortico-motoneuronal pathways via C3-C4 PNs, one disynaptic via the inhibitory PNs and the other trisynaptic via excitatory PNs and Ia inhibitory interneurones. Pyramidal volleys also evoked late IPSPs which in some cases were not depressed from forelimb motor axon collaterals. It is postulated that the late IPSPs are partly due to activation of inhibitory C3-C4 PNs. Disynaptic pyramidal IPSPs were effectively facilitated by volleys in rubro-, tecto- and reticulospinal fibres - but not from vestibulospinal fibres - showing a convergence from the former descending tracts on common inhibitory C3-C4 PNs. Projection from forelimb afferents and corticospinal fibres on common inhibitory C3-C4 PNs was revealed by strong facilitation of disynaptic pyramidal IPSPs from cutaneous forelimb afferents. No corresponding effect was evoked from C2 neck afferents. Stimulation in the lateral reticular nucleus (LRN) evoked monosynaptic IPSPs in some motoneurones. The results of threshold mapping in and around the LRN suggest that the IPSPs are caused by antidromic stimulation of ascending collaterals of inhibitory neurones also projecting to motoneurones, possibly the inhibitory C3-C4 PNs.

Integration in descending motor pathways controlling the forelimb in the cat. 12. Interneurones which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb to C3-C4 propriospinal neurones

Extra- and intracellular recording was made from cells in the C3-C4 segments with the aim of finding interneurones of previously described inhibitory pathways to the C3-C4 propriospinal neurones, which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb, respectively. The lateral interneurones were found in the lateral part of lamina VII interspersed among the C3-C4 PNs and like them they receive convergent monosynaptic EPSPs and disynaptic IPSPs from the cortico-, rubro-, tecto- and reticulospinal tracts. Disynaptic IPSPs, but only rarely monosynaptic EPSPs, are evoked in them from forelimb nerves. The lateral interneurones do not project to the lateral reticular nucleus (LRN). The medial interneurones were found medially in laminae V and VI in a region where volleys in forelimb nerves evoke extracellular monosynaptic focal potentials (Rosén 1969). There is somatotopic organization of the projection from the forelimb to this region. Many neurones are strongly monosynaptically excited from group I muscle or/and cutaneous forelimb afferents. In addition, late discharges are evoked in many cells from cutaneous afferents and high threshold muscle afferents. Corticospinal volleys evoked monosynaptic excitation in the great majority of these cells and usually also late EPSPs or IPSPs. Typically, rubrospinal and tectospinal volleys evoked neither monosynaptic excitation nor late effects as those elicited from corticospinal fibres. In some of the interneurones, IPSPs were evoked from forelimb nerves. About 20% of the medial "interneurones" have an ascending projection to the caudal brain stem. Threshold mapping for antidromic stimulation revealed termination in the main cuneate nucleus, the external cuneate nucleus and/or the LRN and also a branch projecting to more rostral levels in the brain. A few of the neurones in the medial region are PNs projecting to the forelimb segments. It is postulated that interneurones both of the lateral and medial type are inhibitory and project to the C3-C4 PNs. It is further postulated that the former are intercalated in the descending feed-forward inhibitory pathway to the C3-C4 PNs and the latter in the feed-back inhibitory pathway from the forelimb to these PNs. The role of feed-forward and feed-back inhibition of transmission from the brain to forelimb motoneurones via the C3-C4 PNs is discussed.

Longitudinal study of physical working capacity of young people with spastic cerebral palsy

Nineteen adolescents with spastic diplegia and 12 able-bodied controls took part in a longitudinal study of aerobic capacity and physical working capacity during their teens. Absolute values for aerobic capacity and physical working capacity increased during the teens for both groups, which appears to contradict earlier descriptions of prematurely decreased physical working capacity among cerebral-palsied adolescents. On the other hand, net mechanical efficiency during submaximal bicycle ergometer tests decreased significantly in the diplegic group during their teens, and especially among those with severe motor handicap. This is of interest because these children are at risk of insufficient physical activity at school, partly because of the unsatisfactory design of physical education programmes for motor-handicapped children.