Responses of ankle extensor and flexor motoneurons to transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) of the motor cortex excites limb muscles of the contralateral side of the body. Reports of poorly defined, or a complete lack of systematic excitatory responses of soleus motoneurons compared with those of tibialis anterior (TA) motoneurons has led to the proposal that while all ankle flexor motoneurons receive strong corticomotoneuronal connections, very few soleus motoneurons do. In addition, the connections to these few motoneurons are weak. The nature of corticomotoneuronal connections onto these two motoneuron pools was re-evaluated in the following experiments. The leg area of the left motor cortex was stimulated with a large double-cone coil using Magstim 200, while surface electromyographic (EMG) and single motor unit (SMU) responses were recorded from soleus and TA muscles of healthy adult subjects. Under resting conditions, the onset (25-30 ms) and duration of concomitantly recorded short latency motor evoked potentials (MEPs) in surface EMG from both muscles were similar. The input-output relationships of the simultaneously recorded soleus and TA EMG responses showed much greater increases in TA MEPs compared with soleus MEPs with identical increases in stimulus intensity. Under resting and nonisometric conditions, a later peak with onset latency of approximately 100 ms was observed in soleus. During isometric conditions or with vibration of the TA tendon, the second soleus peak was abolished indicating reflex origin of this peak. Recordings from 42 soleus and 39 TA motor units showed clear response peaks in the peristimulus time histograms (PSTHs) of every unit. Two statistical tests were done to determine the onset and duration of response peaks in the PSTHs. With chi(2) test, the duration was 6.9 +/- 4.2 ms (mean +/- SD) for soleus and 5.1 +/- 2.1 ms for TA. Using the criterion of discerning a peak by bin counts being three SDs above background, the duration was 10.0 +/- 4.4 ms for soleus and 7.8 +/- 2.6 ms for TA. Results of these experiments do not suggest a lack of systematic corticomotoneuronal connections on soleus motoneurons when compared with those on TA, though some differences in the strengths of corticomotoneuronal connections onto the two pools do exist.

Afferent feedback in the control of human gait

Sensory activity contributes to motor control in two fundamentally different ways. It may mediate 'error signals' following sudden external perturbations and it may contribute to the pre-programmed motoneuronal drive. Here we review data, which illustrate these two functions of sensory feedback in relation to human walking. When ankle plantarflexors are unloaded in the stance phase there is a sudden decrease in the sensory activity in muscle and tendon afferents from the active muscles. This decrease in sensory activity results in a drop in EMG activity recorded from the soleus muscle, which demonstrates that the sensory activity contributes importantly to the activation of the muscles. Data suggests that a spinal pathway from gr. II muscle afferents is responsible for this positive feedback contribution to the motoneuronal drive during walking. When cutaneous nerves from the foot are stimulated in the early swing phase of walking a late reflex response may be observed in the tibialis anterior muscle. This reflex may help to ensure that the foot is lifted effectively over an obstacle. Data suggest that this reflex response is at least partly mediated by a transcortical reflex pathway. It seems to be important that reactions to external perturbations are integrated at a supraspinal level during human walking.

The effects of human ankle muscle vibration on posture and balance during adaptive locomotion

This study investigated the contribution of ankle muscle proprioception to the control of dynamic stability and lower limb kinematics during adaptive locomotion, by using mechanical vibration to alter the muscle spindle output of individuals' stance limbs. It was hypothesised that muscle length information from the ankle of the stance limb provides information describing location as well as acceleration of the centre of mass (COM) with respect to the support foot during the swing phase of locomotion. Our prediction, based on this hypothesis was that ankle muscle vibration would cause changes to the position and acceleration of the COM and/or compensatory postural responses. Vibrators were attached to both the stance limb ankle plantarflexors (at the Achilles tendon) and the opposing dorsiflexor muscle group (over tibialis anterior). Participants were required to walk along a 9-m travel path and step over any obstacles placed in their way. There were three task conditions: (1) an obstacle (15 cm in height) was positioned at the midpoint of the walkway prior to the start of the trial, (2) the same obstacle was triggered to appear unexpectedly one step in front of the participant at the walkway midpoint and (3) the subjects' walking path remained clear. The participants' starting position was manipulated so that the first step over the obstacle (when present) was always performed with their right leg. For each obstacle condition participants experienced the following vibration conditions: no vibration, vibration of the left leg calf muscles or vibration of the anterior compartment muscles of the lower left leg. Vibration began one step before the obstacle at left leg heel contact and continued for 1 s. Vibrating the ankle muscles of the stance limb during the step over an obstacle resulted in significant changes to COM behaviour [measured as displacement, acceleration and position with respect to the centre of pressure (COP)] in both the medial/lateral (M/L) and anterior/posterior planes. There were also significant task-specific changes in stepping behaviour associated with COM control (measured as peak M/L acceleration, M/L foot displacement and COP position under the stance foot during the step over the obstacle). The results provide strong evidence that the primary endings of ankle muscle spindles play a significant role in the control of posture and balance during the swing phase of locomotion by providing information describing the movement of the body's COM with respect to the support foot. Our results also provide supporting evidence for the proposal that there are context-dependent changes in muscle spindle sensitivity during human locomotion.

Modulation of non-monosynaptic excitation from ankle dorsiflexor afferents to quadriceps motoneurones during human walking

Modulation of non-monosynaptic excitation from ankle dorsiflexors to quadriceps (Q) motoneurones during human treadmill walking was investigated in 25 healthy human subjects. Stimulation of the common peroneal nerve (CPN) evoked a biphasic facilitation in the rectified and averaged (n = 50) Q electromyographic (EMG) activity between 0 and 100 ms after heel strike. Prior to heel strike, the stimulation had no effect on the Q EMG. The latency of both peaks in the response was too long to be explained by a monosynaptic pathway to Q motoneurones. During voluntary tonic co-contraction of Q and tibialis anterior (TA) while standing, only the first of the two peaks was evoked by the CPN stimulation despite a background EMG activity level in the Q and TA muscles corresponding to that observed 30-60 ms after heel strike during walking. Stimulation of cutaneous nerves did not evoke a similar biphasic facilitation in the Q motoneurones, which suggests that muscular afferents mediate the response. The second peak had a higher threshold than the earlier peak. During cooling of the CPN, the latency of the second peak was more prolonged than the latency of the earlier peak. This suggests that afferents of different diameters contributed to the two peaks. It is proposed that afferents from TA assist the contraction of Q during walking via spinal interneurones to stabilize the knee joint and maintain upright posture during walking.

Triggering of balance corrections and compensatory strategies in a patient with total leg proprioceptive loss

Triggering of balance corrections may depend on both leg and trunk proprioceptive inputs. To study this issue and to determine how a total proprioceptive loss in the legs (ToLPL) would affect postural reactions in different directions, we investigated the postural control of a patient with a long-standing dorsal root ganglionopathy. This patient had absent stretch reflexes at the ankle and knee joints, delayed reflexes at the hips, but normal muscle strength. Postural control was probed with support-surface movements driven by two different experimental protocols. The first protocol concentrated on leg muscle responses by varying ankle inputs during pitch plane perturbations. The second protocol focussed on the directional sensitivity of upper body responses using combined roll and pitch tilt perturbations. For both protocols, identical techniques were used to record ankle torques, angular velocities of the upper legs and trunk, and surface EMG from leg, hip and trunk muscles. For the first protocol, pitch plane stance perturbations with three different ankle inputs were imposed by a movable support surface. A simultaneous 4-cm rearward translation and 4-deg toe-up rotation produced an 80-deg/s "enhanced ankle input", a simple toe-up rotation gave a 40-deg/s "normal" ankle input and a simultaneous 4-cm rearward translation and 4-deg "toe-down" rotation yielding a 0-deg/s "nulled ankle input". Responses in the ToLPL patient were compared to those of healthy controls and those of patients with lower-leg proprioceptive loss (LLPL). Following normal and enhanced ankle input perturbations, stretch reflexes were absent in ankle and knee joint muscles of the ToLPL patient. Balance correcting responses in the lower legs were diminished and delayed by some 45 ms. In quadriceps, balance-correcting responses were larger than normal, peaked earlier and were not delayed. During the nulled ankle input condition, the ankle muscle responses in the ToLPL patient were again diminished and delayed by 40 ms with respect to both normal subjects and LLPL patients. However, the ToLPL patient again generated an earlier, larger, balance correcting response in quadriceps. For the second protocol, combinations of roll and pitch perturbations were also delivered by a moving support surface. The amplitude was 7.5 deg at 50 deg/s. Eight different directions were applied randomly (pure "toes down", pure "toes up" and directions at 45-deg intervals of roll). As with the first protocol pre-stimulus background muscle activity was excessive in all trunk and most leg muscles. Responses to roll tilt produced several striking changes from normal in the ToLPL patient. First reflexes in gluteus medius were delayed. Second, the trunk roll which commences around 30 ms in normals was in the opposite direction. This roll was accompanied by oppositely directed stretch reflexes in paraspinal muscles. Third, directional sensitivity of balance corrections was far more roll oriented in leg and trunk muscles. Fourth, some tilt directions caused a deactivation response of background activity. This "deactivation strategy" strongly contrasted with the strategy of controls who had low pre-stimulus background activity and activated responses around 100 ms to correct postural instability. These findings provide new insights into the generation of pitch and roll plane directed balance corrections based on the interaction of proprioceptive trigger signals from the ankles, knees and hips. Without proprioceptive input from the ankle and knee, ankle muscle responses are delayed but not absent. Upper leg and trunk responses are not delayed. This suggests that most, if not all, lower leg balance correcting responses are triggered by hip and, possibly, trunk proprioceptive inputs. When leg proprioceptive input is absent, balance correcting responses lose pitch plane sensitivity. The solution used by the patient to overcome these deficits was to markedly raise background muscle activity levels, presumably to provide a stiffer body structure. The lack of trunk flexibility and lateral instability this produced for roll tilts was offset by the ability to compensate by using a hitherto not described "deactivation response" strategy. The patient had a clinical picture usually described as "deafferented"; yet our roll tilt perturbations revealed delayed reflex responses in hip muscles. With vestibulospinal and neck-proprioceptive inputs, these responses may have helped with the development of compensation processes for the total leg proprioceptive deficit.

Transitions in a postural task: do the recruitment and suppression of degrees of freedom stabilize posture?

In this study, we examined flexibility in postural coordination by inducing transitions between postural patterns. Previous work demonstrated that the postural control system produces two task-specific postural patterns as a function of the frequency of support surface translation. For slow translation frequencies (<0.5 Hz), subjects ride on the platform reminiscent of upright stance (ride pattern), and for fast frequencies (> or =0.75 Hz) subjects actively fixed the head and trunk in space (head fixed pattern) during anterior-posterior platform motion. To study the adaptation of the postural control system, we had subjects stand on a support surface undergoing increases (from 0.2 to 1.0 Hz in 0.1-Hz steps) and decreases (from 1.0 to 0.2 Hz in 0.1-Hz steps) in translation frequency with the eyes open and closed. Kinematic measures of sagittal plane body motion revealed a gradual transition between these two postural patterns as a function of frequency scaling. In both the increasing and decreasing frequency conditions with visual input, center of mass displacements gradually decreased and increased, respectively, whereas upper-trunk (and head) displacement decreased gradually within the ride pattern until a head fixed pattern was observed without any significant changes in displacement for translation frequencies at and above 0.6 Hz. Without visual input, the scaling of the ride pattern was similar except the transition to the head fixed pattern never emerged with increasing frequency; instead, a less stable pattern exhibiting slow drift in head-trunk anterior-posterior motion (drift pattern) was observed at and above 0.5 Hz oscillations. The stability of the head fixed pattern at fast frequencies was clearly dependent on visual input suggesting that vision was more critical for trunk and head control in space at high than low translation frequencies. Head velocity was kept constant, and lower with vision, as translation frequency (and velocity) changed suggesting a head velocity threshold constraint across postural patterns. The gradual transition from the ride to the head fixed pattern was made possible by the recruitment of available degrees of freedom in the form of ankle, then knee, and then hip joint motion. In turn, the transition from the head fixed or drift pattern was made possible by the gradual suppression of available degrees of freedom in the form of reducing hip, then knee, and then ankle motion. The gradual change in postural kinematics without instabilities and hysteresis suggests that the ability to recruit and suppress biomechanical degrees of freedom allows the postural control system to gradually change postural strategies without suffering a loss of stability. The results are discussed in light of possible self-organizing mechanisms in the multisensory control of posture.

Clinical and functional outcome after alcohol neurolysis of the tibial nerve for ankle-foot spasticity

PURPOSE

To report one's experience of using 50-100% alcohol for neurolysis of the tibial nerve in chronic ankle-foot spasticity.

METHODS

The records of patients who received alcohol neurolysis of the tibial nerve were retrospectively reviewed. Repetitive monopolar nerve stimulation was used to localize the tibial nerve. Outcome measures included muscle tone as measured by the Modified Ashworth Score (MAS), passive ankle range of motion (PROM), effect on clonus, plantar flexor motor strength, visual gait analysis and use of orthoses.

RESULTS

A total of 21 tibial nerves were neurolysed in 18 patients (mean age 38.9 +/- 15.8 years, 12 males, six females). Mean duration post-event was 14.8 +/- 3.9 months. The mean pre-neurolysis MAS was 2.50 +/- 0.77 and this improved to 0.97 +/- 0.88 (p < 0.001) and 0.93 +/- 0.85 (p < 0.001) at 1 and 6 months post-procedure, respectively. Average duration of effect was 10.5 +/- 8.9 months. Eleven out of 12 patients (91.7%) with sustained ankle clonus had complete abolishment lasting 6 months. Mean gain in PROM was 24.6 +/- 16.1 degrees and 32.6 +/- 19.0 degrees at 1 and 3 months post-neurolysis, respectively (p < 0.001, < 0.02). No decrease in motor strength was seen post-neurolysis. All 13 ambulant patients had visible improvements in gait. Complications were transient and included dysesthetic pain (4), sensory loss (1) and distal limb oedema (1).

CONCLUSION

Alcohol neurolysis (50-100%) of the tibial nerves is an effective and safe method of managing ankle-foot spasticity.

Isolated sural neuropathy presenting as lateral ankle pain

A case of job-related, unilateral traumatic sural neuropathy causing severe lateral ankle pain and impaired work performance for a 26-yr-old female grocery clerk is reported. This diagnosis is made both clinically and electrophysiologically. We review the pertinent electrophysiologic features, anatomy, and clinical findings in our patient with an isolated sural neuropathy. A review of the literature demonstrates that trauma is the most common cause of this unusual isolated neuropathy. Despite its rare occurrence, it should be considered in patients who present with lateral ankle pain and concomitant loss of sensation in the sural nerve distribution. The establishment of a neuropathic origin assists with management strategies that will differ from the more common musculoskeletal causes of lateral ankle pain. After an appropriate diagnosis and treatment, an excellent outcome resulted for our patient.

Soleus neurotomy for treatment of the spastic equinus foot. Groupe d'Evaluation et de Traitement de la Spasticité et de la Dystonie

OBJECTIVE

This prospective, nonrandomized, noncontrolled study was performed to evaluate the results of a new type of neurotomy, namely the soleus neurotomy, for treatment of the spastic equinus foot.

METHODS

Between May 1996 and March 1998, 46 patients were treated for a spastic equinus foot. Clinical status, spasticity (Ashworth Scale score), and kinematic parameters of the gait were determined before and after surgery. The neurotomy was performed on the upper nerve of the soleus in all cases and was associated with other neurotomies (lower nerve of the soleus, 21 patients; gastrocnemius, 9 patients, tibialis posterior, 18 patients; flexor hallucis longus, 16 patients; and flexor digitorum longus, 17 patients).

RESULTS

The mean follow-up period was 15 months (range, 8-28 mo). The equinus deformity disappeared clinically in all patients. Before the operation, all patients had an Ashworth Scale score of 2, with an inexhaustible clonus present on knee extension and persisting with knee flexion (Tardieu Scale score, 4), which was abolished in 95% of the patients after surgery. Two patients still had some clonus on knee extension; this did not interfere with their clinical improvement. Knee recurvatum disappeared in eight patients. Analysis of kinematic parameters demonstrated a statistically significant increase in joint motion of the second rocker (P = 0.0026) of the ankle during stance. The duration of the stance or swing phase, length of the walking cycle, and velocity or rate of spontaneous walking were not significantly modified.

CONCLUSION

The study demonstrated that soleus neurotomy is effective for the treatment of spastic equinus foot, leading to abolition of spasticity and improvement in the range of ankle motion during the stance phase of gait.

Excitability properties of median and peroneal motor axons

Threshold tracking was used to compare excitability properties (stimulus-response curves, strength-duration properties, recovery cycle, and threshold electrotonus) of median motor axons at the wrist and peroneal motor axons at the ankle in 12 healthy subjects. Stimulus-response curves and strength-duration properties were similar, though higher stimulus intensities were required for peroneal axons. However, there were significant differences in the recovery cycle of excitability following a conditioning stimulus and in threshold electrotonus. In the recovery cycle, median axons had significantly greater supernormality and late subnormality. In threshold electrotonus, the initial slow threshold changes in response to subthreshold depolarizing and hyperpolarizing currents (S1) were significantly greater in median axons, and there was also greater accommodation to depolarizing currents (S2) and greater threshold undershoot after depolarization. Similar differences in supernormality and the S1 phase of threshold electrotonus were found between peroneal axons at ankle and knee, suggesting that these properties may be dependent on nerve length. When median motor axons at the wrist were compared with peroneal motor axons at the knee, there were no differences in refractoriness and supernormality and only small differences in S1, but the late subnormality and undershoot were significantly greater in the median axons. These findings suggest that, in addition to any length-dependent differences, peroneal axons have a less prominent slow K(+) conductance. We conclude that the properties of different motor axons are not identical and their responses to injury or disease may therefore differ.

Normal values of F wave in lower extremities of 73 healthy individuals in Iran

F wave latency has been shown to be a simple and valuable method in evaluation of proximal part of peripheral nerves. According to our previous study of F wave of upper extremity nerves (1), maximum normal F wave latency for the median nerve was 28 ms with stimulation at wrist and 25 ms with stimulation at elbow. These values for the ulnar nerve were 29 ms and 25 ms respectively. Maximum normal difference between right and left F wave latency with wrist stimulation was 2 ms for median nerve and 2.5 ms for ulnar nerve. Maximum normal difference between median and ulnar nerve F latency was 3.5 ms with stimulation at wrist. In this study we measured F wave of lower extremity nerves in 73 healthy individuals in Shiraz. Maximum normal F wave latency for tibial nerve was 55 ms with stimulation at ankle and 46 ms with stimulation at popliteal area. Maximum normal F wave latency for the peroneal nerve was 54 ms with stimulation at ankle and 47 ms with stimulation at fibular head. Mean F ratio for both nerves was 1.29 with stimulation at knee. Maximum normal difference in F wave latency between right and left lower extremities was 3.5 ms with stimulation at ankle and 3 ms with stimulation at knee for the peroneal nerve. These values were 3 ms and 2.5 ms for the tibial nerve respectively. Maximum normal difference in F wave latency between tibial and peroneal nerve was 4 ms with stimulation at ankle and 3 ms with stimulation at knee.

Major role for sensory feedback in soleus EMG activity in the stance phase of walking in man

1. Sensory feedback plays a major role in the regulation of the spinal neural locomotor circuitry in cats. The present study investigated whether sensory feedback also plays an important role during walking in 20 healthy human subjects, by arresting or unloading the ankle extensors 6 deg for 210 ms in the stance phase of gait. 2. During the stance phase of walking, unloading of the ankle extensors significantly (P < 0.05) reduced the soleus activity by 50 % in early and mid-stance at an average onset latency of 64 ms. 3. The onset and amplitude of the decrease in soleus activity produced by the unloading were unchanged when the common peroneal nerve, which innervates the ankle dorsiflexors, was reversibly blocked by local injection of lidocaine (n = 3). This demonstrated that the effect could not be caused by a peripherally mediated reciprocal inhibition from afferents in the antagonist nerves. 4. The onset and amplitude of the decrease in soleus activity produced by the unloading were also unchanged when ischaemia was induced in the leg by inflating a cuff placed around the thigh. At the same time, the group Ia-mediated short latency stretch reflex was completely abolished. This demonstrated that group Ia afferents were probably not responsible for the decrease of soleus activity produced by the unloading. 5. The findings demonstrate that afferent feedback from ankle extensors is of significant importance for the activation of these muscles in the stance phase of human walking. Group II and/or group Ib afferents are suggested to constitute an important part of this sensory feedback.

Foot and ankle sensory neuropathy, proprioception, and postural stability

Foot and ankle sensory neuropathy may result from a variety of pathologic conditions, especially diabetes mellitus. Decreased sensation, particularly on the plantar surface of the feet, leads to obvious risks of cutaneous injury. Less obvious are the risks of fall-related injury associated with changes in other sensory systems of the foot and ankle, such as the receptors involved in joint movement and position perception. The results of a number of studies demonstrate that the neuropathic process affects these receptors in individuals with diabetes mellitus. Associated with the decreased sensory function of the foot and ankle is decreased performance on tests of static and dynamic postural stability. Subjective feelings of instability and an increased incidence of fall-related injuries have also been reported. The reduced postural stability in persons with diabetic neuropathy cannot be attributed exclusively to loss of plantar cutaneous sensation; it appears to be the result of a general loss of peripheral sensory receptor function in the lower legs, including that of the muscle spindles. During the evaluation of an individual with foot and ankle sensory neuropathy, the possibility of balance deficits should be given proper attention. Assessment of balance deficits could be particularly important when planning the course of rehabilitation for individuals with foot and ankle neuropathy who use modified footwear or have an amputation of a section of the foot or lower extremity.

Regional anesthesia. Nerve blocks of the extremities and face

Regional nerve blocks are useful for anesthetizing the hand and fingers, the foot and toes, and the face and mouth. These simple procedures may be performed prior to wound repair or surgery of the affected area. The authors discuss the indications, techniques, dosages, and potential complications of regional anesthesia.

The medial and inferior calcaneal nerves: an anatomic study

The existence of chronic heel pain induced by the compression of nerves prompted us to conduct an anatomic study of the innervation of the heel. Fifteen cadaver feet were dissected to investigate the origin, course and branches of the medial calcaneal nerve (MCN) and the inferior calcaneal nerve (ICN). Despite a variable origin (tibial n. (TN) or lateral plantar n. (LPN)), the medial calcaneal nerve branches which lay superficial to the abductor hallucis muscle (AH) were quite constant. The medial calcaneal nerve gave branches to the abductor hallucis muscle and innervated the posterior part of the medial face of the heel. It terminated in the superficial heel pad at the inferior part of the heel. In our study, the inferior calcaneal nerve always originated from the lateral plantar nerve. Its relationship to the deep fascia of the abductor hallucis muscle and anterior tubercle of calcaneus may explain the entrapment syndrome of the inferior calcaneal nerve.

Neurophysiological evaluation of areflexia in Holmes-Adie syndrome

PURPOSE

To evaluate ankle areflexia in Holmes-Adie syndrome (HAS).

PATIENTS AND METHODS

Hoffmann (H) and Tendon (T) soleus reflexes, tonic vibration reflex (TVR), and polysynaptic extension reflex of soleus muscle (PERS) were evaluated in eight patients with idiopathic HAS. Motor (MNCV) and sensory (SNCV) nerve conduction velocities, compound motor-action potential (CMAP), and sensory action potential (SAP) were also determined in upper and lower limbs.

RESULTS

Soleus T reflex was obtained in one out of eight patients, and H-reflex was found in none of the patients. TVR was recorded in four out of eight patients, and PERS in all of the patients. MNCV, SNCV, CMAP and SAP showed normal values in all patients. In six out of the eight patients a late response following the tibial nerve stimulation showed constant latency, amplitude and morphology, with no recovery cycle or vibration inhibition.

CONCLUSION

In this study, the neurophysiological spinal reflex circuitry evaluations support the view that HAS ankles areflexia is due to a selective impairement of monosynaptic connections of Ia afferents. A normal nuclear excitability is suggested by polysynaptic activation of the soleus motor nucleus.

Cutaneous innervation of the medial ankle: an anatomic study of the saphenous, sural, and tibial nerves and their clinical significance

The distribution and variability of the nerves innervating the skin overlying the medial ankle were determined in 22 human anatomic specimens using x3.5 loupe magnification for dissection. Five different types could be identified: (1) Type A received contributions from the saphenous (SP), sural (SR), and the tibial (TB) nerves (54%); (2) Type B received contributions from the SR and SP nerves (14%); (3) Type C received contributions from the TB and SP nerves (9%); (4) Type D was singularly innervated by the SP (14%); and (5) Type E received contributions only from the TB nerve (9%). In two specimens, an unusual connection between the SP and the medial plantar nerves was found. Based on these findings, an incision line for tarsal tunnel release is suggested to avoid injury to the small cutaneous branches of the SP, SR, and TB nerves.

Anatomic relations between ankle arthroscopic portal sites and the superficial peroneal and saphenous nerves

Ankles from 100 cadavers were dissected to evaluate the risk of nerve injury from an arthroscopic procedure. A total of 65 cadavers (104 ankles) were examined to assess the course of the peroneal nerve, and 35 cadavers (77 ankles) were examined for the saphenous nerve (SN). In 82% of specimens, the superficial peroneal nerve ran between the lateral border of the talocrural joint and the peroneus tertius tendon at the talocrural joint level, where the anterolateral portal was placed. Therefore, the superficial peroneal nerve was at high risk for injury with anterolateral portal placement. At the anteromedial portal site, between the medial border of the talocrural joint and the tibialis anterior tendon, the SN coursed an average of 6 +/- 5 mm medial to the medial border of the talocrural joint. SNs in this area were all terminal branches; therefore, anteromedial portal placement avoids nerve injury.

Lumbar foot innervation of the medial foot and ankle region

BACKGROUND

Differences in the dermatomal maps appearing in standard anatomic texts which are in common use may lead to diagnostic confusion in the assessment of patients who suffer from nerve root deficiency. This is particularly evident in the variable depiction of the L4 nerve root dermatome which is carried distally in the saphenous nerve. The purpose of this study is to establish the distal limit of L4 nerve root innervation in the foot by performing cadaveric dissection of the saphenous nerve.

METHODS

Dissection of the dorsum of the medial foot and ankle was performed on 20 cadaveric specimens.

RESULTS

The saphenous nerve was found to enter the dermis of the medial ankle region (mean = 14.75 mm) distal to the tip of the medial malleolus in the direction of the hallux. In three cases the nerve terminated proximal to the medical malleolus. In all cases the medial forefoot and hallux were supplied by the most medial branch of the superficial peroneal nerve.

CONCLUSIONS

These findings suggest that the sensory component of the L4 nerve root terminates in most cases near the medical malleolus, well proximal to the bunion area of the forefoot.

Extensor digitorum brevis muscle flap: new refinements

Two original operative techniques of raising the extensor digitorum brevis muscle flap are presented. These methods allow for covering distal foot defects that are difficult to cover by other reconstructive means. In the first technique, the flap is based on an extended distal pedicle supplied by the dorsal interosseous artery of the first intermetatarsal space. In the second technique, the flap receives its vascular supply from the medial tarsal artery; this procedure may be valuable when the vascular supply of the dorsalis pedis pedicle has been disrupted. To confirm the availability of these vascular pedicles, cadaver dissections were performed and proved that the extended pedicle dissection enhances the rotation arc of the flap. Four selective clinical cases, in which the flap was successfully used, are discussed. Advantages of these techniques, in reconstructing large defects in the distal foot, are delineated.