Anatomical Study of the Innervation of the Masseter Muscle and Its Correlation with Myofascial Trigger Points.

BACKGROUND AND PURPOSE: Myofascial pain syndrome (MPS) is widely prevalent in the general population; some reports estimate its prevalence ranges from 9 to 85%. Among the different locations where MPS may arise, pain related to the masseter muscle is referred as masticatory myofascial pain. MPS is characterized by myofascial trigger points (MTPs), which represent tender anatomical areas of a muscle where painful symptoms are elicited whenever stimulated. Previous publications have found MTPs to coincide with neuromuscular junctions at the motor end plate, at the innervation zone (IZ). Our study aimed to describe the innervation of the masseter muscle and relate it to clinically described myofascial trigger points (MTPs). MATERIALS AND METHODS: We mapped the nerve fiber distribution into the masseter muscles from 16 cadavers by anatomical dissection. We divided the muscle into six regions, three superior (I-III) and three inferior (IV-VI), and classified the nerve's branches distribution according to these predetermined areas. Statistical analyses was made by Poisson distribution and logarithm link function followed by Bonferroni multiple comparisons (P<0.05). RESULTS: All six areas received branches from the masseteric nerve. Areas I and II (upper posterior and upper intermediate, respectively) had a significant higher number of nerve entries as compared to the remaining areas. CONCLUSION: The penetration areas of the masseteric nerve have been established and MTPs are found in the innervation zones, clinicians should focus initially on the regions of the penetration points, for diagnostics and therapeutic measures, such as injections, dry needling and soft tissue interventions. Anatomical study of nerve supply to the masseter muscle can provide useful additional knowledge to further understanding masticatory myofascial pain and to direct therapeutic interventions and diagnostic studies of temporomandibular junction dysfunction.

Concordance of the location of the innervation zone of the tibialis anterior muscle using voluntary and imposed contractions by electrostimulation.

BACKGROUND: The innervation zone (IZ) corresponds to the location of the neuromuscular junctions. Its location can be determined by using arranged surface linear electrode arrays. Typically, voluntary muscle contractions (VC) are used in this method. However, it also may be necessary to locate the IZ under clinical conditions such as spasticity, in which this type of contraction is difficult to perform. Therefore, contractions imposed by electrostimulation (ES) can be an alternative. There is little background comparing the locations of IZ obtained by two different types of contractions. OBJECTIVE: Evaluate the concordance between using voluntary and imposed contractions from electrostimulation in order to determine the location of the innervation zone of the tibialis anterior muscle in healthy volunteers. METHODS: The tibialis anterior (TA) muscle of sixteen volunteers (men: 8; women: 8; age: 22.1±1.4years, weight: 61.6±7.5kg, height: 167.1±7.5cm) were evaluated using a linear electrode array. The IZ of the TA muscle was located using two types of muscle contractions, voluntary (10% MVC) and imposed contractions by ES. The concordance between both conditions was evaluated using the Bland-Altman method and the concordance correlation coefficient (CCC). The analyses were applied to the absolute and relative positions to the length of an anatomical landmark frame. RESULTS: CCC for absolute position was 0.98 (p<0.0001, 95% CI [0.98-1.00], and CCC for relative positions also was 0.98 (p<0.0001, 95% CI [0.97-1.00]). The Bland-Altman analysis for absolute data showed an average difference of -0.63mm (SD: 4.1). Whereas, for adjusted data, the average difference was -0.20% (SD: 1.2). The power of the results, based on absolute data, was 98%, whereas for relative data, 82%. CONCLUSION: In healthy volunteers, there was a substantially concordance between the location of the IZ of the TA muscle derived from using contractions imposed by ES and the location derived from using VC.

Differences between motor point and innervation zone locations in the biceps brachii. An exploratory consideration for the treatment of spasticity with botulinum toxin.

BACKGROUND: Botulinum toxin (BTX) acts on the neuromuscular junction which can be located by the innervation zone (IZ). Clinically, the motor point (MP) is homologous to the IZ and it is used as the injection site of BTX. Differences in the effectiveness of the application of BTX between MP and IZ locations have been determined. OBJECTIVE: Compare the location of the MP obtained using electrical stimulation and the location of the IZ using a linear surface electrodes array on the biceps brachii muscle. METHODS: The biceps brachii muscle of twenty men was assessed. The MP was located using the torque measurement generated by electrical stimulation. The IZ was detected using a linear surface electrodes array. RESULTS: A difference between the MP and the IZ positions (75.8 vs. 86.5mm, delta 10.7 mm; p=0.003, post-hoc power 0.89) was observed. DISCUSSION: The magnitude of the difference between the MP and the IZ may be clinically relevant. The IZ location using surface electromyography as a guide to optimize BTX injection is proposed.

Ubicación de la zona de inervación del músculo flexor corto del pulgar en individuos sanos de ambos sexos / Flexor pollicis brevis muscle innervation zone location in healthy individuals of both sexes

El músculo flexor corto del pulgar (FCP) se localiza en la eminencia tenar y tiene un importante rol en las funciones del dedo pulgar. Existen escasos antecedentes acerca de la distribución de las zonas de inervación (ZI) de este músculo y las posibles diferencias entre individuos de diferente sexo. El conocimiento de la localización de las ZI del FCP podría ser de ayuda en el tratamiento de la mano espástica, sirviendo para definir el sitio de inyección de la toxina botulínica. El objetivo de esta investigación fue describir las ubicaciones de las ZI del FCP usando electromiografía de superficie, y hacer una comparación entre individuos de sexo masculino y femenino. Treinta jóvenes voluntarios sanos, participaron en este estudio (15 hombres: 21.5 +/- 2.6 años, 70.7 +/- 7.2 kg y 175.0 +/- 5.5 cm. 15 Mujeres: 19.9 +/- 1.4 años, 57.9 +/- 11.1 kg y 161.9 +/- 6.6 cm). Las ZI fueron identificadas mediante la grabación de los potenciales de acción de las unidades motoras del FCP, usando un arreglo de dieciséis electrodos de superficie. Los potenciales fueron grabados durante contracciones isométricas al 10 por ciento de la contracción voluntaria máxima. Las localizaciones de las ZI fueron expresadas en forma absoluta y relativa en relación a un sistema de referencia construido en la palma de la mano, en base a referencias anatómicas. No existieron diferencias significativas en las ubicaciones de las ZI entre los participantes de sexo masculino y femenino de la muestra evaluada. Para el grupo de participantes en este estudio, las ZI del FCP se encontraron al 41.9 por ciento de la distancia comprendida entre el extremo palpable más distal y medial de la interlínea articular metacarpofalángica del pulgar y la línea que nace en el vértice palpable del extremo proximal de la primera falange del tercer dedo pasado por el pliegue longitudinal radial.

The flexor pollicis brevis (FPB) is a muscle of the thenar eminence that plays an important role in thumb function. There is data about its innervation zone (IZ) distribution and sex differences. Knowing the location of the ZI of FPB could be helpful in treating spastic hand, serving to define the site of injection of the botulinum toxin. The aim of this study was to describe the IZ location in the FPB using surface electromyography (sEMG), and also make a comparison between male and female subjects. Thirty young healthy volunteers participated in this study (15 males: 21.5 +/- 2.6 years, 70.7 +/- 7.2 kg y 175.0 +/- 5.5cm. 15 Females: 19.9 +/- 1.4 years, 57.9 +/- 11.1 kg y 161.9 +/- 6.6 cm). The IZ was identified by recording the action potentials of the FPB motor units, using a sixteen-electrode array. The action potentials were recorded during isometric contractions at 10 percent of maximum voluntary contraction. The location of the IZ was expressed as absolute and relative values in relation to a reference system constructed in the palm of the hand, based on anatomic references. There were not significant differences in the location of the IZ between male and female subjects. Of all the subjects, the IZ of the FPB was found at the 41.9 percent of the distance between the most distal and medial palpable extreme of the metacarpophalangeal joint line of the thumb and the line which rises at the palpable apex of the proximal side of the first phalanx of the third finger passing through the radial longitudinal fold.

Biceps Brachii Muscle Innervation Zone Location in Healthy Subjects Using High-Density Surface Electromyography / Ubicación de la Zona de Inervación del Músculo Bíceps Braquial en Sujetos Sanos Mediante Electromiografía de Superficie de Alta Densidad

Among the sequelae of central nervous system injury is spasticity which is difficult to manage in rehabilitation. Current treatments consider the administration of the botulinum toxin. However, results have proved highly variable in terms of effectiveness, attributable to the distance between the injection site and the innervations-zone (IZ). High Density sEMG (HDsEMG) has been used to gather information about muscle physiology and for location of the IZ. The aim of this study was to characterize the IZ of the biceps brachii muscle in healthy subjects during isometric contraction. We assessed the biceps brachii muscle of twenty healthy subjects (n=20) using a 64 surface electrodes matrix. The average location of the IZ was 34 percent distal to the line between the cubital fossa and the anterior acromion.

Entre las secuelas de lesiones del Sistema Nervioso Central se encuentra la espasticidad, la cual es de difícil manejo terapéutico. Los tratamientos actuales de la espasticidad consideran la administración de la toxina botulínica. Sin embargo, los resultados de su aplicación han sido muy variables en términos de eficacia, atribuible a las distintas distancias entre el lugar de inyección y la zona de inervación (ZI). La EMG de alta densidad se ha utilizado para recolectar información acerca de la fisiología muscular y para localizar la ZI. El objetivo de este estudio fue describir la ubicación de la ZI del músculo bíceps braquial en sujetos jóvenes sanos, durante una contracción isométrica. Evaluamos el músculo bíceps braquial en 20 sujetos sanos usando una matriz de 64 electrodos. El promedio de localización de la ZI fue de 34 por ciento en el sentido distal de la línea trazada entre la fosa cubital y el acromion anterior.