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Operative treatment of spondylolisthesis in children and adolescents with tight hamstrings syndrome.

Of 10 patients with spondylolisthesis of the fifth lumbar vertebra, 8 had characteristic tight hamstrings syndrome, and 4 showed a Grade IV slip. Sciatic pain was present in all cases. In 5 there were also signs of compression of the first sacral root. In 4 cases impaired pattern of walking was the first symptom. Extraperitoneal anterior interbody fusion was performed in 9 cases. Laminectomy was combined with posterior fusion in one. Posterior fusion alone was performed in another. The follow-up period ranged from 2 to 14 years. All patients were free from symptoms at the last follow-up examination and they had normal living patterns and physical activities. Fusion was obtained in every case. There were no complications in this series, except for one fatigue fracture of the neural arch of the vertebra one level above fusion, discovered at 6 months after the operation; this patient has had no symptoms in a period of time of 14 years since the operation. The above described excellent results of anterior fusion without reduction raises questions as to the necessity of extensive major surgical interventions to obtain operative reduction of the displacement in patients, even with Grade IV spondylolisthesis.

Adolescent↗

Effects of resistance exercise and cycling on recovery blood pressure.

The purpose of this investigation was to examine blood pressure responses during recovery from resistance exercise and cycling. Seven normotensive volunteers (5 males, 2 females) were studied. Resistance exercise consisted of three sets of five exercises (arm curl, hamstring curl, squat, 'lat pull' and bench press) on four occasions: (1) twice using 40% one-repetition maximum (1RM) for 20-25 repetitions, and (2) twice using 70% 1RM for 8-10 repetitions. The subjects also cycled for 25 min at 70% of heart rate reserve on two occasions. Measurements of recovery systolic and diastolic blood pressure were made at 2, 5, 10, 15, 30 and 60 min post-exercise with subjects in the seated position. Analysis of variance with repeated measures revealed that there were no significant differences between recovery blood pressures after the cycling or resistance exercise treatments. Average systolic blood pressure after 2 min of recovery was elevated (115 +/- 2 mmHg, P < 0.0001) and diastolic blood pressure was depressed (48 +/- 3 mmHg, P < 0.0001) in comparison to previously determined baseline values. Systolic blood pressure at 5 min and diastolic blood pressure at 15 min post-exercise were not significantly lower than resting baseline values, and remained so after 60 min of recovery. It was concluded that different intensities of resistance exercise produce the same blood pressure response in recovery and that these changes were approximately equal to those produced by cycling.

Adult↗

Comparison of tibiofemoral joint forces during open-kinetic-chain and closed-kinetic-chain exercises.

The purpose of this study was to analyze forces at the tibiofemoral joint during open and closed-kinetic-chain exercises. Five healthy subjects performed maximum isometric contractions at 30, 60, and 90 degrees of knee flexion during open-kinetic-chain extension, open-kinetic-chain flexion, and closed-kinetic-chain exercises. Electromyographic activity of the quadriceps and hamstrings, as well as load and torque-cell data, were recorded. Tibiofemoral shear and compression forces were calculated with use of a two-dimensional biomechanical model. The results showed that, during the open-kinetic-chain extension exercise, maximum posterior shear forces (the resisting forces to anterior drawer) of 285 +/- 120 newtons (mean and standard deviation) occurred at 30 degrees of knee flexion and maximum anterior shear forces (the resisting forces to posterior drawer) of 1780 +/- 699 newtons occurred at 90 degrees of knee flexion. The closed-kinetic-chain exercise produced significantly less posterior shear force at all angles when compared with the open-kinetic-chain extension exercise. In addition, the closed-kinetic-chain exercise produced significantly less anterior shear force at all angles except 30 degrees when compared with the open-kinetic-chain flexion exercise (p < 0.05). Analysis of tibiofemoral compression forces and electromyographic recruitment patterns revealed that the closed-kinetic-chain exercise produced significantly greater compression forces and increased muscular co-contraction at the same angles at which the open-kinetic-chain exercises produced maximum shear forces and minimum muscular co-contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

[Causes of development of genu recurvatum after surgical treatment in spastic forms of childhood cerebral palsy].

PURPOSE OF THE STUDY: To evaluate the contribution of different surgical techniques of lengthening of distal hamstrings on the development of hyperextension deformity of the knee in spastics. MATERIAL: Totally 51 patients of age 7.6 + 3.7 years at operation. Follow-up after surgical release for 4-10 years. Basically two surgical techniques were used: 1. Simple division of gracilis and semitendinosus, fractional lengthening of semimembranosus and biceps femoris. 2. Gracilis and semitendinosus were anchored after its transverse division to fractionally lengthened semimembranosus. METHODS: Pre-operative and post-operative Bleck popliteal angles were estimated. Hyperextension was tested in lying and standing positions. RESULTS: Type of surgery (1 or 2) did not influence the development of hyperextension deformity of the knee (tested by Fisher exact test). Nevertheless the relation between type of surgery (1 or 2) and the stratified value of Bleck popliteal angle was statistically significant. In the subgroup 2, in which the superficial tendons were anchored to semimebraneous, the occurrence of values of Bleck angle less than 20 degrees, was lower than in the subgroup 1. DISCUSSION: It seems, that the type of described two different surgical techniques is not so much decisive for development of hyperextension deformity. CONCLUSION: Authors surmise, that principal role play stronger deep knee flexors (semimembranosus and biceps femoris). Its fractional lengthening must be very careful.

Cerebral Palsy↗

Effectiveness of serial stretch casting for resistant or recurrent knee flexion contractures following hamstring lengthening in children with cerebral palsy.

A retrospective review of all cerebral palsy (CP) patients with resistant or recurrent knee flexion contractures treated with serial stretch casting was performed. The protocol consisted of sequential wedging (5 degrees per week) of fiberglass casts until maximum knee extension had been achieved. Measurements were made prior to the initiation of casting, at completion of the casting, and at 1 year after the casting. Forty-six subjects, with 75 involved extremities, met the study inclusion criteria. Mean age at the time of initiation of casting was 12.7 years. Using radiographic measurements, the mean initial degree of knee flexion contracture was -17.6 degrees. At the completion of casting, the mean knee flexion angle was -8.1 degrees. The mean duration of casting was 30 days. At 1 year after completion of the casting, the mean knee flexion angle was -12.2 degrees. Initial correction to within 10 degrees of full extension was achieved in 76% of extremities. Age less than 12 years and initial flexion contracture of less than -15 degrees were statistically significant factors related to maintenance of correction at 1 year. Complications included soft tissue compromise in 13 extremities (17%), transient neurapraxia in 9 extremities (12%), and tibial subluxation in 1 extremity (1%). Serial stretch casting was successful in correcting resistant knee flexion contractures in the majority of cases. Casting was less effective in teenagers and those with larger contractures. Complications were minimized by proper casting technique and controlled rate of correction.

Adolescent↗

The relationship between isometric contraction durations during hold-relax stretching and improvement of hamstring flexibility.

AIM: Previous research suggests proprioceptive neuromuscular facilitation (PNF) stretching techniques produce greater increases in range of motion than static or ballistic. The purpose of this study was to determine the isometric contraction hold time that best produces gains in hip range of motion after a 3-s (3-HR), 6-second (6-HR), and 10-s (10-HR) hold-relax PNF stretch. METHODS: The experimental design was a within subjects repeated measures 2 factor (baseline and treatment) by 3 factor (3-HR, 6-HR, 10-HR) ANOVA. The dependent variable was hamstring flexibility as measured in degrees of passive hip flexion with the knee extended. Measurements were taken in a university athletic therapy clinic. Sixty active individuals without history of knee or hip injury volunteered for this study. Each subject was randomly assigned to a 3-HR, 6-HR, or 10-HR group for the hold-relax PNF stretch. All subjects were passively taken to the end range of motion 3 times and a goniometric measurement was taken. Each subject then performed the hold-relax PNF stretch 3 times with either a 3-HR, 6-HR, or 10-HR isometric contraction hold time and another goniometric measurement was taken. An average of each of these 3 trials was then calculated. RESULTS: The data analysis revealed a significant main effect difference (F(1,5 7)+/-633.97, p<.001, eta2=0.918) between the baseline and treatment measurements. There were no significant differences for the between groups (3-HR, 6-HR, 10-HR) main effect or for the interaction term. CONCLUSIONS: All 3 hold-time conditions produced significant gains in range of motion compared to baseline measurements. The application of the findings suggest that clinicians could choose any of the hold-times and produce the same result to patient hip joint flexibility.

Adolescent↗

Evaluation of tibial bone tunnel enlargement using MRI scan cross-sectional area measurement after autologous hamstring tendon ACL replacement.

The aim of this study was to evaluate tibial bone tunnel enlargement following four-strand hamstring tendon anterior cruciate ligament (ACL) reconstruction, using a new method of magnetic resonance imaging (MRI) assessment. Correlation with clinical outcome was also examined. In a prospective study following ACL reconstruction, 24 patients underwent MRI and clinical assessment, at a mean follow-up of 6.5 months. A four-strand semitendinosus and gracilis (STG) tendon graft with the polyester Soffix (Surgicraft Ltd) fixation device was placed via an instrument guided tibial tunnel and an over-the-top femoral route. Cross-sectional area (CSA) perpendicular to the long axis of the tibial tunnel was calculated digitally at three levels, using MRI. Clinical assessment included physical examination, Lysholm subjective self-evaluation score and KT 2000 arthrometric measurement. A mean CSA tibial tunnel enlargement of 33% was found. The mean side-to-side KT-2000 arthrometric difference was 1.66 mm and the mean Lysholm score was 92. We concluded that this previously unused MRI evaluation using digital direct CSA measurements provides a highly accurate method of tunnel assessment. We found no correlation between tibial tunnel enlargement, knee stability, joint function and patient satisfaction scores in the short term.

Adult↗

Patellar tendon or semitendinosus tendon autografts for anterior cruciate ligament reconstruction? A prospective randomized study with a two-year follow-up.

BACKGROUND: There are well-known problems with the use of bone-patellar tendon-bone autografts for anterior cruciate ligament reconstruction, especially in terms of donor site morbidity. Hamstring tendon grafts have been increasingly used as an alternative, but there are very few controlled studies comparing the methods. HYPOTHESIS: Use of semitendinosus tendon grafts will cause less donor site morbidity and result in better knee-walking ability. STUDY DESIGN: Prospective randomized clinical trial. METHODS: Seventy-one patients who had a unilateral anterior cruciate ligament rupture underwent arthroscopic reconstruction with interference screw fixation and use of either bone-patellar tendon-bone or semitendinosus tendon graft. Outcome assessment was performed by physiotherapists not involved in the patients' care. RESULTS: At the 2-year follow-up, no differences were found in terms of the Lysholm score, Tegner activity level, KT-1000 arthrometer side-to-side laxity measurement, single-legged hop test, or International Knee Documentation Committee classification results. The knee-walking test was rated difficult or impossible to perform by 53% of the bone-patellar tendon-bone group and by only 23% of the semitendinosus graft patients, a significant difference. CONCLUSIONS: The semitendinosus tendon graft is at least an equivalent option to the bone-patellar tendon-bone graft for anterior cruciate ligament reconstruction, and we recommend its use.

Adolescent↗

Effects of intrathecal orphanin FQ on a flexor reflex in the rat after inflammation or peripheral nerve section.

We examined the effects of intrathecal orphanin FQ, the endogenous ligand for the orphan opioid-like receptor, on the hamstring nociceptive flexor reflex in decerebrate, spinalized, unanesthetized rats after carrageenan-induced inflammation or unilateral sciatic nerve transection. As described previously [Xu, X.-J., Hao, J.-X., Wiesenfeld-Hallin, Z., 1996. Orphanin FQ or antiorphanin FQ: potent spinal antinociceptive effect of orphanin FQ/orphanin FQ in the rat. NeuroReport 7, 2092-2094.], intrathecal orphanin FQ induced a dose-dependent depression of the flexor reflex with a ED50 of 965 ng. Initial reflex facilitation was noted in some experiments at lower doses (10 or 100 ng). A similar bi-phasic response pattern to intrathecal orphanin FQ was observed in experiments conducted in inflamed or axotomized rats. However, the magnitude of the initial reflex facilitation was significantly increased in inflamed rats compared to normals whereas the duration of reflex depression was significantly shortened. The ED50 for reflex depression was 2.4 jig for inflamed rats. In contrast, axotomy did not significantly alter the facilitatory and depressive effect of orphanin FQ with ED50 for reflex depression being 374 ng. These results confirmed an inhibitory action of orphanin FQ on spinal nociception in rats. It is suggested that the effect of orphanin FQ may be modulated by inflammation and nerve injury. In particular, unlike morphine, there seems to be no reduction in the effect of spinal orphanin FQ in inducing antinociception after peripheral nerve axotomy.

Animals↗

Quantitative clinical measure of spasticity in children with cerebral palsy.

OBJECTIVE: This investigation developed an objective measure to quantify the degree of spasticity. DESIGN: Specifications included a single variable that integrated key elements characterizing spasticity: velocity, range of motion, and resistance to passive motion. A dynamometer at a children's hospital quantified the passive resistance of the hamstrings to knee extension for a range of motion at 4 different speeds for the prospective descriptive investigation. PATIENTS: A convenience sample of six children with able bodies and 17 children with spastic diplegic cerebral palsy volunteered. DATA PROCESSING: Torque-angle data were processed to calculate the work done by the machine on the children for each speed and then determine the slope of the work-velocity curves. This slope was considered to be the measure of spasticity and it was hypothesized that children with cerebral palsy would have a greater slope than children with able bodies. An independent test determined whether a significant difference existed between groups (p < .05). RESULTS: Torque-angle data for children with able bodies indicated little change in passive resistance as a function of speed. Similar data for children with cerebral palsy indicated larger resistive torques with increasing speed. Slope from the work-velocity data was close to zero for children with able bodies [.003 J/(degrees/sec)], while the corresponding slope for children with cerebral palsy was approximately 10 times greater [.031 J/(degrees/sec)] and significantly different (p < .05). CONCLUSION: The slope of the work-velocity data integrates three major components characterizing spasticity, it is a single number that can easily be evaluated and interpreted in a clinical setting, and it utilizes a machine that is available at many centers.

Adolescent↗

Concurrent surgeries are a factor in predicting success of rectus transfer outcomes.

Cerebral palsy (CP) patients exhibit a wide range of functional responses to specific surgical interventions. The variability associated with surgical outcomes within this patient population precipitates the need to determine the functional effects in advance of the surgery. Pilot studies have indicated that the application of statistical models towards predicting functional outcomes of surgery produces clinically meaningful results. The purpose of this study was to evaluate the influence of pre-operative kinematic parameters in conjunction with concurrent surgeries on rectus transfer (RT) outcomes. Gait analysis data were collected from 68 patients (94 legs) pre- and post-operatively within a year of surgery. Patients were divided into four groups. Group 1 (N=14) contained only legs experiencing a rectus transfer. Group 2 (N=30) contained legs experiencing RT and hamstring lengthening (HL). Group 3 (N=7) contained legs experiencing RT and lower leg surgeries: either Achilles lengthening (AL), or gastrocnemius lengthening (GL). Finally, Group 4 (N=43) contained legs which experienced all four surgeries (RT+HL+AL+GL) concurrently. Multivariate jackknifed linear regression was used to predict the change in knee range of motion, DeltaROM, due to surgery on a group-by-group basis. In each case, the sole significant pre-surgical variable was the range of motion. Group 1 legs had the best correlation (R=0.846) between pre-surgical ROM and DeltaROM whereas Group 4 legs had the worst correlation (R=0.661). Group 3 results were not significant. Group 1 DeltaROM were also significantly lower as a whole, than all other groups, due to a larger percentage of patients needing the surgery to change timing of flexion in swing phase. When compared to modeling without consideration of surgery, modeling by surgical group produced results with fewer outliers and better correlation coefficients. Regardless of surgical group, patients with a lower pre-surgical ROM (<40 degrees ) were more likely to experience an increase in ROM as a result of surgical intervention compared to their peers with an elevated pre-surgical ROM who were likely to see a decrease in ROM. Pre-surgical ROM therefore serves as a useful predictor of outcome in rectus transfer surgery.

Achilles Tendon↗

Coordination of two-joint rectus femoris and hamstrings during the swing phase of human walking and running.

It has been hypothesized previously that because a strong correlation was found between the difference in electromyographic activity (EMG) of rectus femoris (RF) and hamstrings (HA; EMG(RF)-EMG(HA)) and the difference in the resultant moments at the knee and hip (Mk-Mh) during exertion of external forces on the ground by the leg, input from skin receptors of the foot may play an important role in the control of the distribution of the resultant moments between the knee and hip by modulating activation of the two-joint RF and HA. In the present study, we examined the coordination of RF and HA during the swing phase of walking and running at different speeds, where activity of foot mechanoreceptors is not modulated by an external force. Four subjects walked at speeds of 1.8 m/s and 2.7 m/s and ran at speeds of 2.7 m/s and 3.6 m/s on a motor-driven treadmill. Surface EMG of RF, semimembranosus (SM), and long head of biceps femoris (BF) and coordinates of the four leg joints were recorded. An inverse dynamics analysis was used to calculate the resultant moments at the ankle, knee, and hip during the swing phase. EMG signals were rectified and low-pass filtered to obtain linear envelopes and then shifted in time to account for electromechanical delay between EMG and joint moments. During walking and running at all studied speeds, mean EMG envelope values of RF were statistically (P<0.05) higher in the first half of the swing (or at hip flexion/knee extension combinations of joint moments) than in the second half (or at hip extension/knee flexion combinations of joint moments). Mean EMG values of BF and SM were higher (P<0.05) in the second half of the swing than in the first half. EMG and joint moment peaks were substantially higher (P<0.05) in the swing phase of walking at 2.7 m/s than during the swing phase of running at the same speed. Correlation coefficients calculated between the differences (EMG(RF)-EMG(HA)) and (Mk-Mh), taken every 1% of the swing phase, were higher than 0.90 for all speeds of walking and running. Since the close relationship between EMG and joint moments was obtained in the absence of an external force applied to the foot, it was suggested that the observed coordination of RF and HA can be regulated without a stance-specific modulation of cutaneous afferent input from the foot. The functional role of the observed coordination of RF and HA was suggested to reduce muscle fatigue.

Adult↗

Reciprocal coactivation patterns of the medial and lateral quadriceps and hamstrings during slow, medium and high speed isokinetic movements.

The effect of movement velocity and fatigue on the reciprocal coactivation of the quadriceps and hamstrings was investigated through analysis of the root mean square (RMS) and the median frequency (MDF) of surface electromyography for the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH) and biceps femoris (BF). Fourteen subjects performed six continuous isokinetic knee extension and flexion movements at 60 degrees, 180 degrees and 300 degrees s(-1), and 30 continuous movements at 300 degrees s(-1) to examine muscular fatigue patterns. Statistical analyses revealed that the RMS activity of the VM displayed greater coactivation than the VL (P<0.01) and the BF displayed greater coactivation than the MH (P<0.0001). There was no effect of velocity on the coactivation levels of the VM, the VL, or the MH; however, there was an effect of velocity on the coactivation levels of the BF (P<0.0001). Relative to MDF activity, the MH shifted upward as velocity increased (P<0. 01) while the BF decreased between 180 and 300 degrees s(-1) (P<0. 01). Results of the muscular fatigue test indicated that the RMS activity of the VM showed a higher degree of coactivation than the VL (P<0.01) and the BF showed approximately three times the coactivation level of the MH (P<0.001). The MDF of the VL and MH shifted downward as the repetitions progressed (P<0.01) with no changes for the VM or for the BF. Results of this study suggest that during isokinetic testing, both the VM and BF have significantly greater reciprocal coactivation levels when compared to the VL and MH, respectively. In addition, these results suggest that motor unit recruitment patterns of the VM and VL and the MH and BF differ with regard to the effects of velocity and fatigue.

Adult↗

Interference screw position and hamstring graft location for anterior cruciate ligament reconstruction.

Anterior cruciate ligament reconstruction with hamstring tendon graft and interference screw fixation has recently been considered. Concerns for the use of interference screws with soft tissue grafts include damage to the graft during screw insertion, decreased fixation strength, and a decrease in the bone-tendon contact area for healing within the tunnel when the screw is placed in an eccentric position. This last concern could be addressed by placing the interference screw centrally between the four limbs of the hamstring graft. The purpose of this study was to determine the mode of failure, the pullout force, and graft slippage before graft fixation failure of hamstring tendons fixed with an interference screw positioned eccentrically in relation to the hamstring tendons verses an interference screw positioned centrally between the four graft limbs. The semitendinosus and gracilis tendons were harvested from six, fresh cadaveric specimens. Each tendon was divided into two segments of equal length. Both the semitendinosus and gracilis tendon segments were looped to form four strands. The specimens were then fixed with a bioabsorbable interference screw in the two different positions and pulled from a standardized polyurethane foam. All tendons in both groups failed by pulling out from between the interference screw and tunnel, regardless of the screw position. No tendon was cut by the screw in either group. There was no significant difference between the forces required to produce specific amounts of graft slippage between the two fixation techniques tested. There was no significant difference between the average total slippage at maximum pullout, 11.8 mm for the screw placed in the eccentric position and 13.7 mm for the screw placed in the central position. The maximum pullout force averaged 265.3 N for the screw placed in the eccentric position, and 244.7 N for the screw placed in the central position; these values were not significantly different. Placement of the interference screw in the central position did not compromise strength and it improves graft contact within the bone tunnel. Interference screw fixation, when applied against a bone plug, has been shown to consistently have a pullout force of more than 400 N.

Aged↗

The effectiveness of reconstruction of the anterior cruciate ligament with hamstrings and patellar tendon . A cadaveric study comparing anterior tibial and rotational loads.

BACKGROUND: The objective of this study was to evaluate the effectiveness of reconstructions of the anterior cruciate ligament to resist anterior tibial and rotational loads. We hypothesized that current reconstruction techniques, which are designed mainly to provide resistance to anterior tibial loads, are less effective in limiting knee instability in response to combined rotational loads. METHODS: Twelve fresh-frozen young human cadaveric knees (from individuals with a mean age [and standard deviation] of 37 +/- 13 years at the time of death) were tested with use of a robotic/universal force-moment sensor testing system. The loading conditions included (1) a 134-N anterior tibial load with the knee at full extension and at 15 degrees, 30 degrees, and 90 degrees of flexion, and (2) a combined rotational load of 10 N-m of valgus torque and 10 N-m of internal tibial torque with the knee at 15 degrees and 30 degrees of flexion. The kinematics of the knees with an intact and a deficient anterior cruciate ligament, as well as the in situ force in the intact anterior cruciate ligament, were determined in response to both loads. Each knee then underwent reconstruction of the anterior cruciate ligament with use of a quadruple semitendinosus-gracilis tendon graft and was tested. A second reconstruction was performed with a bone-patellar tendon-bone graft, and the same knee was tested again. The kinematics of the reconstructed knees and the in situ forces in both grafts were determined. RESULTS: The results demonstrated that both reconstructions were successful in limiting anterior tibial translation under anterior tibial loads. Furthermore, the mean in situ forces in the grafts under a 134-N anterior tibial load were restored to within 78% to 100% of that in the intact knee. However, in response to a combined rotational load, reconstruction with either of the two grafts was not as effective in reducing anterior tibial translation. This insufficiency was further revealed by the lower in situ forces in the grafts, which ranged from 45% to 65% of that in the intact knee. CONCLUSIONS: In current reconstruction procedures, the graft is placed close to the central axis of the tibia and femur, which makes it inadequate for resisting rotational loads. Our findings suggest that improved reconstruction procedures that restore the anatomy of the anterior cruciate ligament may be needed.

Adult↗

Cutaneous receptive field and morphological properties of hamstring flexor alpha-motoneurones in the rat.

Intracellular recordings have been made from twenty antidromically identified posterior biceps femoris/semitendinosus (p.b.s.t.) hamstring flexor alpha-motoneurones in the decerebrate-spinal rat. The hamstring motoneurones had either low or no spontaneous background activity. In nineteen of the twenty cells high-frequency phasic responses could be elicited by stimulation of the ipsilateral hind paw with firm pressure or pinch. There was no response to light touch or brush. Contralateral cutaneous mechanoreceptive fields with higher thresholds and weaker responses were present in 70% of the motoneurones. Noxious heating of the ipsilateral hind paw produced excitatory responses in six of eight cells tested and two of these cells also responded to heating of the contralateral hind paw. Stimulation of the ipsilateral sural nerve at graded strengths that successively activated A beta, A delta and C afferents produced excitatory post-synaptic potentials (e.p.s.p.s) at progressively longer latencies in the motoneurones. The C-fibre induced e.p.s.p. lasted up to 200 ms. Horseradish peroxidase was injected into ten motoneurones and in seven cases full reconstructions of dendritic field, cell body and axon could be made. In agreement with previous reports from studies in the cat, the dendritic fields of rat motoneurones are very extensive in the rostrocaudal, mediolateral and dorsoventral planes. The general pattern of dendritic branching for each motoneurone in this functionally homogeneous population was uniformly organized. Three major spatial orientations were always present: a rostrocaudally restricted series of dendrites emerging from the cell body and directed dorsolaterally towards the dorsolateral funiculus with branches in the lateral dorsal horn, a laterally, and a ventromedially directed series of branches arranged obliquely in the ventral horn, both of which were distributed rostrocaudally for equal distances from the cell body. Many of these dendritic branches terminated within the lateral and ventral white columns. Although the sizes of the rat flexor motoneurones' somas (51 +/- 4.9 micron, S.E., n = 10) were similar to those of cat lumbosacral alpha-motoneurones, the tip-to-tip rostrocaudal extent of their dendritic fields (1130 +/- 34 micron, S.E., n = 7) was half that reported in the cat. These results are discussed in terms of the organization of the cutaneous flexor withdrawal reflex in the rat.

Action Potentials↗