Palmar Nerve Research Articles

Anatomical Features of the Carpal Flexor Retinaculum of the Horse

This study aims to elucidate the topographical anatomy of the carpal flexor retinaculum or palmar anular carpal ligament (PACL) in the horse. Ten specimen of the carpus of five healthy horses were studied by dissection in layers. Slices of 5 mm in thickness facilitated observation of the soft tissues. The superficial layer of the PACL subdivides into five compartments: one for the palmar nerve and the arterial and venous branches, one for only the radial artery, one for the radial vein, and one for the tendon of the radial carpal flexor muscle, and finally for the deep layer that supports all tendinous structures located palmar to the carpus, as well as the median artery and palmar medial nerve. The sections of the segmented PACL that are affected by carpal canal syndrome may vary with the aetiology of the space-occupying process. Precise anatomical knowledge of the structures may help in understanding the pathological processes and determining the most appropriate therapy.

Development of a technique for continuous perineural blockade of the palmar nerves in the distal equine thoracic limb

ObjectiveTo develop a technique for placing continuous peripheral nerve block (CPNB) catheters adjacent to palmar nerves in horses and to evaluate the effect of low-volume local anesthetic (LA) infusion on nociception in the distal equine thoracic limb. Study designIn vitro and in vivo laboratory investigation.Study material and animals Forty-two thoracic limbs from 22 equine cadavers and five horses. MethodsThoracic limb specimens were dissected to find landmarks for catheter insertion adjacent to medial and lateral palmar nerves. Based on the anatomy of the proximal metacarpus, a technique for placing palmar CPNB catheters was developed and the potential for catheter dislodgement studied in vitro by fluoroscopic visualization during passive carpal flexion and dye injection following simulated limb motion. The feasibility of CPNB catheter instrumentation in standing, sedated horses was tested in five animals, with ultrasound control. Electrical and mechanical stimulation thresholds and response latencies for hoof withdrawal responses (HWR) were determined following saline or LA infusion. ResultsMedial and lateral CPNB catheters were inserted percutaneously 2 and 4–5 cm, respectively, distal to the accessory carpal bone and advanced for ∼7 and 10 cm, respectively, to place the tip just proximal to the communicating branch of the nerves. Catheters were placed correctly in 88% and 85% of cadaver limbs. In the standing horses, LA infusion not only increased HWR thresholds and latencies to noxious mechanical or electrical stimulation but also caused vasodilation and limb swelling over time. ConclusionThe technique, developed in vitro, for placing and maintaining palmar CPNB catheters in the equine thoracic limb was successfully applied in vivo. Catheters were well tolerated but LA infusion may cause limb swelling, suggesting a need for further exploration of drug and infusion regimens. Clinical relevanceContinuous perineural LA infusion along palmar nerves may develop into an effective analgesic technique in horses suffering from lower limb pain.

Indirect Decompression of the Carpal Tunnel During Basal Joint Arthroplasty of the Thumb

In patients having basal joint arthroplasty, rates of concomitant carpal tunnel syndrome may exceed 43%. Excision of the trapezium during basal joint arthroplasty partially releases the transverse carpal ligament. The objective of this study was to determine whether indirect release of the remaining fibers of the ligament at its insertion on the scaphoid tubercle through the same incision would adequately decompress the carpal canal. This would avoid the morbidity of a second incision. We retrospectively reviewed 10 consecutive patients treated over a 2-year period who had concurrent ligament reconstruction, tendon interposition basal joint arthroplasty of the thumb with complete trapezial resection, and indirect carpal tunnel release through a single incision. Self-reported postoperative pain relief was documented. Preoperative and postoperative evaluations of light touch sensibility, Tinel's sign, Phalen's test, median nerve compression test, and Weinstein Enhanced Sensory Test monofilament testing were analyzed. All patients had preoperative electrodiagnostic testing. At mean 12 month follow-up (range, 5-35 months), numbness and paresthesias resolved in all cases: 9 patients had good or excellent pain relief and 1 reported fair pain relief despite transient postoperative reflex sympathetic dystrophy. Tinel's, Phalen's, and median nerve compression tests were each positive in 9 patients preoperatively and 0 patients postoperatively. Diminished light touch sensibility was present in 7 preoperatively and 1 postoperatively. WEST monofilament thresholds improved postoperatively in 8 patients. These improvements were statistically significant. One patient had postoperative nerve conduction studies performed to evaluate an ulnar nerve lesion at the elbow; the preoperative median nerve abnormalities had normalized. Carpal tunnel syndrome can be successfully managed with indirect release of the transverse carpal ligament during basal joint arthroplasty, thus avoiding a second incision, reducing operating time, and potentially reducing the possibility of perineural adhesions, recurrent motor branch injury, palmar cutaneous nerve damage, weakness, stiffness, and pillar pain. Therapeutic IV.

Stereological Characteristics of the Equine Accessory Nerve

Stereological techniques have been increasingly employed for assessment and characterization of neuromuscular diseases in humans and animals. As an adjunct to histopathology, morphometrical algorithms provide quantitative evidence of the peripheral nerve composition, thereby shedding light on its fibre characteristics and basic electrophysiological properties. In the horse, stereological investigations already have focussed on the recurrent laryngeal, deep peroneal and lateral palmar nerves (LPN). Of these, only the latter is suitable for taking biopsies in clinical settings, however, it does not contain any motor fibres and Ia-afferents. On account of its virtually mixed fibre qualities, most researchers today recommend the cervical branch of the equine accessory nerve (AN) for harvesting diagnostic samples. Thus, the present study was carried out to gain morphometrical proof of the AN composition and to obtain stereological base values in healthy individuals using state-of-the-art technology. All parameters were compared to the common peroneal nerve (CPN), known to harbour all myelinated fibre classes. As this second biopsy site is located farther distally to the neuro-axis, attention was paid to possible length-dependent features. Taken together, digital image analysis could be accurately applied on all AN samples. Stereology supported the histological and clinical evidence that the AN contains all myelinated fibre types. The huge range and scatter of fibre counts and density (3351-17,812/mm(2)) per fascicle were comparable to that measured in the equine common peroneal, deep peroneal, lateral palmar and recurrent laryngeal nerves. Similar to those, fibre diameter distribution was bimodal with slow Abeta- and Agamma-mechanoceptor afferents outnumbering large myelinated Aalpha-fibres by a factor of about 1.5. With a g-ratio at 0.55 +/- 0.001, the overall degree of myelination in the AN is highly consistent and insignificantly ranges between that of the equine common peroneal and LPNs. Apart from this subtle deviation, a statistically relevant difference between the more proximal AN and the distal CPN could not be documented. By obtaining morphometrical standard parameters and even more sophisticated distribution indices, stereology is a valuable tool for detection of subtle changes that are likely to escape from the investigators' eyes. The AN serves as a reliable source for advanced peripheral nerve research and should be accompanied by farther distal nerve probes for assessment of neuropathies that present with a proximodistal gradient.

Neuropathy of the palmar cutaneous nerve in association with palpable swellings at the wrist: A report of two cases

We report 2 cases of neuropathy of the palmar cutaneous branch of the median nerve presenting with sensory disturbance in the hands in addition to a tender, palpable lesion in the palmar aspect of the wrist. The cause of the swelling resulting in the neuropathy was found to be a non-traumatic neuroma of the palmar cutaneous nerve in one case, and palmar cutaneous nerve entrapment from a volar wrist ganglion in the other. We have found no previous case reports of neuropathy caused by non traumatic neuroma of the palmar cutaneous nerve.

Estudo comparativo experimental da injeção perineural do álcool benzílico 0,75% e do álcool etílico absoluto nos nervos palmares de eqüinos

Foi estudada a neurólise química dos nervos Palmares em 10 eqüinos. Usando-se uma ferradura especial para induzir claudicação, a locomoção avaliada ao passo e trote e os graus foram registrados antes e após a injeção perineural do álcool benzílico 0,75% (Grupo A) e o álcool etílico absoluto (Grupo B). Os testes mostraram que ambos os neurolíticos dessensibilizaram completamente a sola dos animais a partir de 30 dias, assim permanecendo até o 150º dia nos animais do Grupo A, quando ocorreu retorno progressivo da sensibilidade. Já no Grupo B, aos 180 dias, a sensibilidade permanecia ausente. A análise histopatológica revelou que nos nervos infiltrados com álcool benzílico 0,75% prevaleceram lesões próprias de axonotemese, sugerindo tendência de regeneração e restabelecimento da condução nervosa, enquanto que nos nervos infiltrados com álcool etílico absoluto, prevaleceram lesões simuladoras de neurotemese, com degeneração nervosa permanente. Concluiu-se que os álcoois utilizados foram eficientes bloqueadores temporários ou permanentes dos nervos Palmares em eqüinos.

Continuous Perineural Block of the Palmar Nerves: A New Technique for Pain Relief in the Distal Equine Forelimb

Pain therapy is an important aspect of equine orthopedic and trauma surgery. Although long-term epidural analgesia has become an almost routine method of treatment for painful conditions in the horse’s hind limb, a similarly effective technique for management of pain originating in the horse’s front limb has not yet been developed. Continuous perineural nerve block (CPNB) is a method that entails continuous low-volume infusion of local anesthetics via catheters placed along peripheral nerves. This technique has gained much popularity in human medicine and is currently applied with great success for treatment of perioperative pain in upper and lower extremities. Recently, both in vitro and in vivo experiments were conducted to adopt this treatment method to the horse by developing a simple and reproducible technique for placing in standing, sedated horses CPNB catheters along peripheral nerves in the forelimb. Simultaneously, the analgesic efficacy of CPNB with low-volume local anesthetic infusion without significantly affecting systemic health was evaluated. The present report outlines a continuous palmar nerve block technique suitable for pain therapy in the horse. Anatomic landmarks and a technique for safe placement of catheters along the lateral and medial palmar nerves including sedation and local anesthetic protocols are described in detail, as are local anesthetic drug regimens for effective CPNB. Furthermore, special precautions and potential complications are addressed, followed by a brief clinical case report that demonstrates the potential of the described CPNB technique to provide sustained pain relief in the lower forelimb of horses suffering from severely painful conditions.

Scintigraphic examination of the cartilages of the foot

Radiographic examination of the cartilages of the foot is well documented; however, there is limited information about their scintigraphic assessment. To evaluate the scintigraphic appearance of the cartilages of the foot using subjective and quantitative image analysis and to correlate radiographic and scintigraphic findings. An ossified cartilage would have similar radiopharmaceutical uptake (RU) to the ipsilateral aspect of the distal phalanx; RU would extend throughout the length of the ossified cartilage; a separate centre of ossification (SCO) would be identified on a scintigraphic image; and fracture or trauma to an ossified cartilage would manifest as increased RU (IRU). Front feet (n = 223) of horses (n = 186) that had dorsopalmar radiographic views and dorsal scintigraphic images were included in the study. The cartilages of the foot were graded radiographically and scintigraphically. Quantitative evaluation of the scintigraphic images was carried out using region of interest (ROI) analysis. For statistical analysis RU ratios were used. Correlations between a radiographically detected SCO and focal RU and between IRU and radiographic abnormalities were assessed. There was a good correlation and an excellent agreement between radiographic and scintigraphic grades. ROI analysis showed a proximal to distal increase in RU ratios within each cartilage of the foot. A radiographically identified SCO could be detected scintigraphically in 12/17 feet (70.6%). Thirty-eight feet had IRU in the region of a cartilage, 25 of which (65.8%) had corresponding radiographic abnormalities. Fracture of an ossified cartilage was associated with IRU in all horses. Scintigraphy may give information about the potential clinical significance of ossification of the cartilages of the foot and associated lesions, therefore prompting further investigation by use of a uniaxial ipsilateral palmar nerve block and imaging, using either magnetic resonance imaging and/or computed tomography.

The median palmar cutaneous nerve in normal subjects and CTS

Objective The neurophysiological confirmation of carpal tunnel syndrome (CTS) relies on detecting abnormal median nerve transcarpal conduction in the presence of unaffected comparator nerves. We compare the palmar cutaneous median branch (PCBm) with the ulnar sensory nerve conduction to digit 5 (US 5) as comparator nerves for diagnosing CTS. Methods In a prospective case control study of patients with clinically defined carpal tunnel syndrome and normal subjects, we determined and compared the PCBm and US 5 conduction velocity. Results We examined 57 hands with clinically defined CTS and 59 control hands. Comparison showed highly significantly slowed PCBm conduction ( p < 0.0001) but not for US 5 conduction ( p = 0.488). Using a 3 percentile cut-off for abnormality derived from controls, PCBm conduction velocity was abnormal in 46% of CTS hands. Conclusions The high frequency of PCBm nerve conduction abnormality in CTS suggests that this nerve should not be used as a comparator nerve for the neurophysiological diagnosis of CTS. This finding may help explain some of the extension of sensory symptoms outside the median nerve distribution in CTS. Significance In CTS frequent abnormality of PCBm conduction makes this a poor comparator nerve and may explain extension of sensory symptoms beyond the median nerve.

Überbrückung peripherer Nervendefekte durch den Einsatz von Nervenröhrchen

The nerve autograft is the gold standard for the reconstruction of peripheral nerve defects. In short gaps, nerve repair by means of tubulization has become an alternative. This technique is discussed based on the current literature and our own experience. Nerve reconstruction by means of tubulization was performed in 11 patients. Nerve gaps in the hand of up to 18 mm were reconstructed. Sensibility was assessed using static and dynamic two point discrimination (s-, d2PD) and monofilament testing 3, 6 and 12 months postoperatively. Three out of 11 patients complained of a temporary foreign body sensation in the area of the implant; this was persistent in one case. Four out of six patients showed excellent results with s2PD of <or=7 mm (Highet S4) assessed 12 months postoperatively. One patient regained no (s2PD>15 mm, S0), another poor sensibility (s2PD 15 mm, S3). D2PD and monofilament testing confirmed these results. Nerve reconstruction by means of tubulization seems to be a suitable method for certain indications in the reconstruction of short defects of digital and palmar nerves. Donor site morbidity can be avoided. Similarly to nerve transplantation, the operation requires microsurgical skills.

The role of sensory nerve conduction study of the palmar cutaneous nerve in the diagnosis of carpal tunnel syndrome in patients with polyneuropathy

Conventional methods in the diagnosis of carpal tunnel syndrome (CTS) in patients with polyneuropathy (PNP) are insufficient. We suggest that the comparison of the conduction of the median nerve with that of the neighboring peripheral nerves may be more beneficial in the diagnosis of entrapment neuropathy. The median nerve sensory conduction in healthy volunteers, in cases of CTS, PNP cases without CTS and in cases of PNP in whom clinical findings point to CTS, were compared by palmar cutaneous nerve (PCN) sensory conduction. Comparative parameters were difference of PCN-1st digits' nerve conduction velocities (NCV), PCN/1st digit NCVs ratio, difference of 5th-2nd digits' NCVs and 5th/2nd digits' NCVs ratio. The statistical analysis was performed by the SPSS package for statistics. Student t test and receiver operating characteristic were used. Although the ratio of PCN-1st digit did not differ significantly between the control group and the polyneuropathy group, there was a significant difference between CTS and PNP+CTS groups and the control group ( P < 0.001 and P < 0.001, respectively). The ratio of PCN-1st digit nerve conduction velocity was also significantly different between polyneuropathy and PNP+CTS groups ( P < 0.001). To diagnose CTS on a background of polyneuropathy in mild cases in which sensory conduction is preserved, the ratio of sensory nerve conduction velocities of the palmar cutaneous nerve and the median nerve 1st digit-wrist segment may be a criterion.

How to optimize the evaluation of carpal tunnel syndrome in patients with polyneuropathy?

Carpal tunnel syndrome (CTS) is the most frequent consequences of the neuropathy and the CTS on nerve peripheral nerve entrapment. Treatment decision conduction. Development or expertise of new tools is depends on a combination of clinical criteria including always interesting. In this issue, Tokcaer et al propose to tolerance of pain and presence of sensory or motor deficits study the palmar cutaneous nerve, a branch of the median and intensity of electrophysiological abnormalities. nerve which does not pass through the carpal tunnel. Existence of an underlying polyneuropathy in a patient The ratio of conduction velocities of this nerve and the with CTS may complicate the matters since standard first digit median nerve branch appears to be both sensitive electrophysiological explorations are often unable to and specific to detect a CTS in patients with an associated differentiate abnormalities due to the polyneuropathy and polyneuropathy and can thus be used in addition to the entrapment. However, in this situation, conventional methods especially. electrophysiological conclusions are especially important because carpal tunnel syndrome is more frequent in case Jean-Philippe Camdessanche of polyneuropathy, particularly in association with Department of Neurology, Bellevue Hospital, CHU Saint-Etienne, Furthermore, an early diagnosis of carpal 42055 Saint-Etienne Cedex 02 France. E-mail: jean.philippe.camdessanche@chu-st-etienne.fr tunnel entrapment may be warranted since the polyneuropathy frequently reduces nerve abilities to regenerate preventing a good outcome after treatment. On References another hand, interpreting electrophysiological abnormalities in patients with polyneuropathy may lead 1. Tokcaer AB, Goðuþ F, Gullap S, Keleþ I, Gokce M. The role of to an over-diagnosis of CTS. sensory nerve conduction study of the palmar cutaneous nerve in In the exploration of CTS, sensory conduction velocities the diagnosis of carpal tunnel syndrome in patients with polyneu­ ropathy. Neurol India 2007;55:17.21. are clearly more sensitive than motor conduction velocities 2. Perkins BA, Olaleye D, Bril V. Carpal tunnel syndrome in patients to detect abnormalities. [3] However, in case of with diabetic polyneuropathy. Diabetes Care 2002;25:565-9. polyneuropathy, sensory nerves are often more severely 3. American Association of Electrodiagnostic Medicine, American Academy of Neurology and American Academy of Physical Medicine involved. Comparison of median and ulnar sensory nerve and Rehabilitation. Practice parameter for electrodiagnostic studies velocities on the fourth digit or on two different digits is in carpal tunnel syndrome: Summary statement. Muscle Nerve the usual method to differentiate the respective 2002;25:918-22. diabetes.

Variability of the palmar cutaneous branch median nerve sensory nerve action potential with carpal tunnel syndrome

Variability of the palmar cutaneous branch median nerve sensory nerve action potential with carpal tunnel syndrome

Does a Real Henle's Nerve Exist? A Detailed Anatomic Study

The purpose of this study was to delineate the detailed distribution of the palmar cutanaeous nerve and its branches in the hand.

A New Approach for Perineural Injection of the Lateral Palmar Nerve in the Horse

To evaluate the accuracy of a new technique for perineural injection of the lateral palmar nerve and to determine frequency of inadvertent injection into the carpal synovial sheath with this technique. Prospective experimental study. Thirty equine cadaver forelimbs. Each of 3 clinicians injected 0.5 mL of a 1% aqueous solution of new methylene blue as a marker at the medial aspect of the accessory carpal bone of 10 limbs. Immediately after each injection, the lateral palmar nerve was identified by dissection of and inspected for proximity of dye, and the carpal synovial sheath was inspected for the presence of dye. New methylene blue solution was observed to surround the nerve (29 limbs) or to lie within 2 mm of it (1 limb). Dye was not found in the carpal synovial sheath of any specimen. Using this technique, perineural injection of the lateral palmar nerve can be consistently achieved, and the carpal synovial sheath is unlikely to be penetrated by the needle during the procedure. The technique described provides an accurate and simple method for perineural injection of the lateral palmar nerve proximal to the origin of its deep branch. This technique can be used to anesthetize the lateral palmar nerve for diagnosis of pain originating in the palmaroproximal aspect of the metacarpus without risk of inadvertently desensitizing structures within the carpal synovial sheath.

Mini-open carpal tunnel decompression.

Carpal tunnel syndrome is the most common entrapment neuropathy, and it is caused by compression of the median nerve at the wrist. The authors describe the mini-open carpal tunnel technique for surgical release of the transverse carpal ligament. The success of the procedure depends on meticulous technique with attention to certain important anatomic details and careful avoidance of injury to the palmar cutaneous nerve and the recurrent motor branch.

Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging.

The differential diagnosis of foot pain has long proved difficult and the use of magnetic resonance imaging (MRI) offers the opportunity to further the clinical understanding of the subject. To determine the incidence of deep digital flexor tendon (DDFT) injuries in a series of 75 horses with lameness associated with pain localised to the digit, with no significant detectable radiographic or ultrasonographic abnormalities, using MRI; and to describe a variety of lesion types and relate DDF tendonitis with anamnesis, clinical features, response to local analgesic techniques and nuclear scintigraphic and ultrasonographic findings. All horses undergoing MRI of the front feet between January 2001 and October 2002 were reviewed and those with DDFT injuries categorised according to lesion type; horses with primary tendonitis (Group I) and those with concurrent abnormalities of the navicular bone considered to be an important component of the lameness (Group II). The response to perineural analgesia of the palmar digital nerves and palmar (abaxial sesamoid) nerves, intra-articular analgesia of the distal interphalangeal (DIP) joint and analgesia of the navicular bursa were reviewed. The result of ultrasonography of the pastern and foot was recorded. Lateral, dorsal and solar pool and bone phase nuclear scintigraphic images were assessed subjectively and objectively using region of interest (ROI) analysis. Forty-six (61%) of 75 horses examined using MRI had lesions of the DDFT considered to be a major contributor to lameness. Thirty-two horses (43%) had primary DDFT injuries and 14 (19%) a combination of DDF tendonitis and navicular bone pathology. Lesions involved the insertional region of the tendon alone (n = 3), were proximal to the navicular bone (n = 23) or were at a combination of sites (n = 20). Lesion types included core lesions, focal and diffuse dorsal border lesions, sagittal plane splits, insertional injuries and lesions combined with other soft tissue injuries. Many horses had a combination of lesion types. Lameness was abolished by palmar digital analgesia in only 11 of 46 horses (24%). Twenty-one of 31 horses (68%) in Group I showed > 50% improvement in lameness after intra-articular analgesia of the DIP joint, whereas 11 of 12 horses (92%) in Group II had a positive response. Twelve of 18 horses (67%) in Group I had a positive response to analgesia of the navicular bursa. Nineteen horses had lesions of the DDFT extending proximal to the proximal interphalangeal joint seen using MRI, but these were identified ultrasonographically in only 2 horses. Scintigraphic abnormalities suggestive of DDFT injury were seen in 16 of 41 horses (41%), 8 in pool phase images and 8 in bone phase images. DDFT injuries are an important cause of lameness associated with pain arising from the digit in horses without detectable radiographic abnormalities. Lameness is not reliably improved by palmar digital analgesia, but may be improved by intra-articular analgesia of the DIP joint in at least 68% of horses. Ultrasonography is not sensitive in detecting lesions of the DDFT in the distal pastern region, but a combination of pool and bone phase scintigraphic images of the digit is helpful in some horses. Further follow-up information is required to determine the prognosis for horses with lesions of the DDFT in the digit and to establish whether this is related to lesion severity and/or location.

Axonal degeneration in association with carpal tunnel syndrome.

Median nerve entrapment in the palm to wrist segment is known as carpal tunnel syndrome (CTS). Electromyography is the best evaluation test to confirm the disease, as it shows a median reduced conduction velocity and/or conduction block; however, the usual CTS electrodiagnostic tests do not separate segmental demyelination alone from segmental demyelination plus secondary axonal degeneration. We studied 100 hands from CTS patients (classified as mild, moderate, and severe), and 50 hands from normal subjects. The median palmar sensory nerve action potential (SNAP) amplitude was measured and compared between the two groups. It would be expected that SNAP was normal if no axonal degeneration had occurred. The results showed that in mild CTS group and part of moderate CTS group SNAP amplitude was normal, whereas in severe CTS group, and part of moderate group SNAP amplitude was reduced, proving that axonal degeneration was involved. As it is well stated that axonal lesions have worse prognosis than segmental demyelinating ones, this simple test may help to preditic the CTS outcome and treatment.

Selective deafferentation of hand cutaneous territory is followed by changes in fibre type distribution of a forearm muscle in the horse.

Based on previous observations that capsaicin can selectively damage group III and IV afferents and induce muscle fibre transformation, we hypothesized that eliminating, by means of capsaicin, the group III and IV afferents of a peripheral territory it could lead to a fibre transformation in a muscle involved in the flexor reflexes of the same peripheral territory. Therefore, capsaicin was injected into the palmar nerves of the forelimb of the horse to investigate if eliminating group III and IV afferents from the hand of the horse a muscle fibre transition would occur in the flexor carpi radialis (FCR) muscle, which is involved in the flexor reflexes of the finger itself. 120 days after capsaicin injection, type I slow fibres increased and type IIA fast fibres decreased. We presume that the long lasting deafferentation of the ergo-nociceptive fibres causes a plastic remodelling in the central nervous system and indirectly influences the motoneuron excitability via short or long loop-pathways enhancing their tonic discharge.

Effect of perineural anesthesia on the ultrasonographic appearance of equine palmar metacarpal structures.

The purpose of this study was to describe ultrasonographic changes of the equine palmar metacarpal area attributed to the infiltration of local anesthetic solution and to determine whether these changes were noted immediately or at 24 h. The palmar metacarpal region of one forelimb in each of six horses was examined ultrasonographically with a 10-MHz linear array transducer and a 7.5-MHz curvilinear transducer. Transverse and longitudinal images were recorded at 5-cm intervals distal to the accessory carpal bone. High and low palmar and palmar metacarpal nerve blocks were performed with a 2% mepivacaine hydrochloride solution. Ultrasonographic examinations similar to the initial examination then were performed immediately, 1 h and 24 h postinjection. Cross-sectional area and mean pixel value were determined for the superficial and deep digital flexor tendons, the accessory ligament of the deep digital flexor tendon, the suspensory ligament, and the suspensory branches at each level and time period. Subjective ultrasonographic changes also were noted. No significant difference was noted in the cross-sectional area or mean pixel value of any structure at any level or time period compared to baseline. Subjective changes in the tendons and ligaments were not noted. There was mild hypoechoic swelling of the surrounding soft tissues and gas in the region of the injections. Gas could interfere with the evaluation of the origin of the suspensory ligament and the proximal portion of the accessory ligament of the deep digital flexor tendon within the first hour but was not detectable ultrasonographically at 24 h. Based on these findings, if gas interferes with an ultrasonographic examination performed temporally close to perineural anesthesia, a repeat examination at 24 h is recommended.