RESUMO
INTRODUCTION: This case report details the application of a treatment regimen using a serial elastic tension digital neoprene orthosis (ETDNO) protocol for a patient with an eight-month-old finger crush injury who experienced recurrence of a 45º proximal interphalangeal joint (PIPJ) flexion contracture two months after arthrolysis. PURPOSE OF THE STUDY: To illustrate how the application strategy of ETDNO can increase the daily total end range time (TERT) and modify finger stiffness. RESULTS: The patient reached full extension following 15 weeks of ETDNO treatment. The six-month follow-up evaluation revealed that the PIPJ was stable with full flexion and extension. The joint did not require continued orthosis use. DISCUSSION: The literature describes orthosis application as the treatment of choice for PIPJ flexion contracture, but no study has described an ideal program for use nor the full and stable resolution of the flexion contracture. The current literature describes a maximum daily total end range time (TERT) of 12 hours a per day. The serial ETDNO protocol that this study described increased the daily TERT to nearly 24 hour per day and demonstrated an excellent result in the treatment of PIPJ flexion contracture CONCLUSION: This outcome suggests that clinicians will want to consider this new orthosis design and management protocol as a novel option for the treatment of PIPJ flexion contracture. We need future research to better define the optimum number of hours of daily TERT for the effective treatment of PIPJ flexion contracture. In addition, we will also benefit from the exploration of the optimum orthosis design to enable the highest amount of TERT.
RESUMO
In the deltoid muscles of Pan troglodytes and Homo sapiens, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms. Our aim was to identify differences between the two species that could be related to their different uses of the upper limb. The deltoid muscle of six adult Pan troglodytes and six adult Homo sapiens were dissected. The muscle fascicle length (MFL) and the physiological cross-sectional area (PCSA) of each muscle were calculated in absolute and normalized values. The expression pattern of the MHC-I, MHC-IIa and MHC-IIx isoforms was analyzed in the same muscles by real-time polymerase chain reaction. Only the acromial deltoid (AD) presented significant architectural differences between the two species, with higher MFL values in humans and higher PCSA values in chimpanzees. No significant differences in the expression pattern of the MHC isoforms were identified. The higher PCSA values in the AD of Pan troglodytes indicate a greater capacity of force generation in chimpanzees than in humans, which may be related to a greater use of the upper limb in locomotion, specifically in arboreal locomotion like vertical climbing. The functional differences between chimpanzees and humans in the deltoid muscle are more related to muscle architecture than to a differential expression of MHC isoforms.
Assuntos
Músculo Deltoide , Pan troglodytes , Animais , Músculo Deltoide/anatomia & histologia , Humanos , Cadeias Pesadas de Miosina/genética , Pan troglodytes/genética , Isoformas de Proteínas , Extremidade SuperiorRESUMO
OBJECTIVES: To identify anatomic differences in the insertion sites of the palmar radiocarpal ligaments in different species of hominoid primates that may be related to their different types of locomotion. MATERIALS AND METHODS: We have used three-dimensional geometric morphometrics (3D GM) to analyze the distal radius ligament insertion sites in 31 Homo sapiens, 25 Pan troglodytes, 31 Gorilla gorilla, and 15 Pongo pygmaeus. We have also dissected the radioscaphocapitate (RSC), long radiolunate (LRL) and short radiolunate (SRL) ligaments in six H. sapiens and five P. troglodytes to obtain quantitative values that were then compared with the results of the 3D GM analysis. RESULTS: H. sapiens had a relatively larger insertion site of the RSC + LRL ligament than the other hominoid primates. P. pygmaeus and P. troglodytes had a relatively large SRL ligament insertion site with a palmar orientation. In G. gorilla, the two ligament insertion sites were relatively smaller and the SRL insertion site had an ulnopalmar orientation. DISCUSSION: The morphological differences observed can be related to the types of locomotion used by the different species and to quantitative data obtained from the dissection of ligaments in H. sapiens and P. troglodytes. 3D GM analysis of ligament insertion sites can help in interpreting the types of locomotion used by extinct hominoid primates through the analysis of preserved fossilized fragments of the distal radius.
Assuntos
Ligamentos Articulares/anatomia & histologia , Primatas/anatomia & histologia , Rádio (Anatomia)/anatomia & histologia , Animais , Antropologia Física , Feminino , Humanos , Imageamento Tridimensional , Ligamentos Articulares/diagnóstico por imagem , Ligamentos Articulares/fisiologia , Masculino , Rádio (Anatomia)/diagnóstico por imagem , Rádio (Anatomia)/fisiologia , Articulação do Punho/anatomia & histologia , Articulação do Punho/diagnóstico por imagem , Articulação do Punho/fisiologiaRESUMO
Lumbrical muscles originate on the flexor digitorum profundus (FDP) tendons and, during fist making, they move in the same direction when FDP muscle produces maximal proximal tendon gliding. Injuries of the bipennate lumbricals have been described when a shear force acts between the origins on adjacent tendons of the FDP, as they glide in opposite directions in asymmetric hand postures. Other structures of the deep flexors complex can be affected during this injury mechanism, due to the so-called quadriga effect, which can commonly occur during sport climbing practise. Biomechanical studies are needed to better understand the pathomechanism. A cadaveric study was designed to analyse the effects of load during the fourth lumbrical muscle injury mechanism. The amount of FDP tendon gliding and metacarpophalangeal (MCP) joint flexion of the 5th finger were calculated. Ten fresh-frozen cadaveric specimens (ten non-paired forearms and hands) were used. The specimens were placed on a custom-made loading apparatus. The FDP of the 5th finger was loaded, inducing isolated flexion of the 5th finger, until rupture. The rupture occurred in all specimens, under a load of 11 kg (SD 4.94), at 9.23 mm of proximal tendon gliding (SD 3.55) and at 21.4° (SD 28.91) of MCP joint flexion. Lumbrical muscle detachment from the 4th FDP was observed, from distal to proximal, and changes in FDP tendons at the distal forearm level too. The quadriga effect can lead to injury of the bipennate lumbrical muscles and the deep flexors complex in the hand and forearm.
Assuntos
Cadáver , Músculo Esquelético , Tendões , Humanos , Músculo Esquelético/fisiopatologia , Músculo Esquelético/fisiologia , Tendões/fisiopatologia , Tendões/fisiologia , Fenômenos Biomecânicos , Masculino , Montanhismo/fisiologia , Pessoa de Meia-Idade , Idoso , Traumatismos dos Tendões/fisiopatologia , Feminino , Antebraço/fisiopatologia , Antebraço/fisiologia , Ruptura/fisiopatologia , Articulação Metacarpofalângica/fisiopatologia , Articulação Metacarpofalângica/lesões , Modelos BiológicosRESUMO
Turner Syndrome (TS) is a rare genetic disorder that affects females when one of the X chromosomes is partially or completely missing. Due to high genetic and phenotypic variability, TS diagnosis is challenging and is often delayed until adolescence, resulting in poor clinical management. Numerous oral, dental and craniofacial anomalies have been associated with TS, yet a comprehensive description is still lacking. This study addresses this gap through a detailed analysis of oral health and craniofacial characteristics in a cohort of 15 females with TS and their first-degree relatives. Subjects with TS ranged from 3 to 48 years old, none showed evidence of periodontal disease and only the youngest was in mixed dentition. Using the Multifunction System, we identified an aggregation of multiple signs and symptoms in each TS subject, including tooth anomalies (supernumerary molars, agenesis, microdontia, enamel defects, alterations in eruption patterns -advanced and delayed for chronological age-, crowding, rotations and transpositions), malocclusion (class II/1 and II/2) and Class II facial profile, while relatives exhibited fewer manifestations. The early detection of these signs and symptoms is crucial for appropriate referral and the optimal clinical management of TS, especially during the critical period of 9 to 10 years when congenital dental anomalies appear. The use of an established taxonomy to describe these phenotypic features is essential for early detection. Multidisciplinary teams are required to ensure holistic care management in rare diseases like TS.
RESUMO
OBJECTIVES: A morphocline of the glenoid cavity has been used to infer differences in locomotor behaviors; however, the glenoid cavity is surrounded by the glenoid labrum, a fibrocartilaginous structure that could influence the functionality of the glenoid. The objectives of this study are to explore the effects of the glenoid labrum on the area, depth, and morphology of the glenoid cavity in primates. MATERIALS AND METHODS: Photogrammetry was used to build 3D models of the glenoid, with and without the labrum, and three- (3D) and two-dimensional (2D) geometric morphometrics (GM) was applied. 2D areas were collected from zenithal images for glenoids with and without labrum to evaluate the availability of articular surface area. RESULTS: In the 2D GM the morphocline is present in the dry-bone sample but not with the presence of the glenoid labrum. In the 3D GM there are differences between species mainly concerning the depth of the glenoid cavity. 2D areas reveal that the amount of articular area of the glenoid cavity increases with the presence of the labrum, particularly in humans. DISCUSSION: The glenoid labrum changes the shape, increases the depth and the surface area of the glenoid cavity, particularly in humans. Therefore, the glenoid labrum might hold a functional role, increasing the stability of the glenohumeral joint of primates in general, and especially in humans.
Assuntos
Cavidade Glenoide , Articulação do Ombro , Humanos , Articulação do Ombro/anatomia & histologia , Cavidade Glenoide/diagnóstico por imagem , Escápula/anatomia & histologiaRESUMO
Proximal interphalangeal joint flexion contracture is a frequent condition in hand therapy. Clinicians most frequently apply orthosis management for conservative treatment. Orthoses should apply forces for long periods of time following the total end range time (TERT) concept. These forces necessarily transmit through the skin; however, skin has physiological limitations determined by blood flow. Using three fresh frozen human cadavers, this study quantified and compared forces, skin contact surfaces and pressure of two finger orthoses, an elastic tension digital neoprene orthosis (ETDNO) and an LMB 501 orthosis. The study also investigated the effects of a new method of orthosis construction (serial ETDNO orthoses) that customizes forces to a specific finger position. We evaluated forces and contact surfaces for multiple ETDNO models tailored to the cadaver fingers in multiple PIP flexion positions. The results showed that the LMB 501 orthosis applied pressures beyond the recommended limits if applied for more than eight hours a day. This fact was the cause of time limited LMB orthosis application. This results also show that, at 30° of PIPJ flexion, straight ETDNOs created a mean pressure approaching the end of the recommended pressure limits. If the therapist modified the ETDNO design, the skin pressure decreased and reduced the risk of skin damage. With the results of this study, we concluded that for PIPJ flexion contracture, the upper limit of force application is 200 g (1.96 N). Forces beyond this amount would likely cause skin irritation and possibly skin injuries. This would cause a reduction in the daily TERT and limit outcomes.
RESUMO
Focusing on fingers with proximal interphalangeal joint flexion contractures, this study seeks to determine whether significant differences exist between the joint passive range of motion PROM improvement when receiving higher doses of daily total end range time (TERT) compared to those that receive lower doses. The study randomized a parallel group of fifty-seven fingers in fifty patients with concealed allocation and assessor blinding. Divided into two groups receiving different doses of daily total end range time with an elastic tension digital neoprene orthosis, they also participated in an identical exercise program. Patients reported orthosis wear time, and the researchers performed goniometric measurements at every session during the three-week period. The primary outcome related the time patients wore the orthosis to the degrees of improvement in PROM extension. Compared to group B (daily TERT of twelve hours), group A (TERT, twenty+ hours) showed a statistically significant greater improvement in PROM after three weeks of treatment. Group A improved by a mean of 29° compared to group B's mean of 19° improvement. This study provides evidence that a higher dose of daily TERT can generate better results in the treatment of the proximal interphalangeal joint flexion contractures.
RESUMO
PURPOSE: The main objective of this study was to identify anatomical differences between men and women in the absolute and relative size of the carpal tunnel (CT), its inner structures, and related external anatomical structures in order to shed light on the higher prevalence of CT syndrome (CTS) in women. BASIC PROCEDURES: We have dissected the forearms and hands of ten men and ten women and compared the cross-sectional area (CSA) of the CT between the two sexes. The size of the CT relative to the tendons passing through it, the median nerve (MN), and to hand and wrist size was also compared between men and women. MAIN FINDINGS: The absolute CSAs of the CT and other parameters were larger in men than in women. The CSA of the CT relative to the length of the capitate bone was also larger in men. However, no significant differences were observed between men and women in the size of the CT relative to its inner structures. PRINCIPAL CONCLUSIONS: The size of the inner structures of the CT are in proportion to that of the CT itself in both sexes. These findings suggest that the etiology of CTS seems to be primarily related to workload and personal traits.
Assuntos
Síndrome do Túnel Carpal , Punho , Síndrome do Túnel Carpal/diagnóstico por imagem , Feminino , Mãos , Humanos , Masculino , Nervo Mediano/diagnóstico por imagem , Ultrassonografia , Punho/diagnóstico por imagemRESUMO
OBJECTIVES: The objective of this study is to explore the anatomical differences in the insertion sites of the palmar radiocarpal ligaments between hylobatids and other hominoids that may be related to their different locomotor behaviors. MATERIALS AND METHODS: The morphology of the insertion sites of the palmar radiocarpal ligaments was analyzed with three-dimensional geometric morphometrics (3D GM) in the distal radial epiphysis of 44 hylobatids, 25 Pan, 31 Gorilla and 15 Pongo. RESULTS: Relative to other hominoids, hylobatid insertion sites of the palmar radiocarpal ligaments were relatively larger and the insertion site of the short radiolunate ligament had a palmar orientation. DISCUSSION: Larger palmar radiocarpal ligaments in hylobatids can help stabilize the wrist during the radial and ulnar displacement that occurs in ricochetal brachiation, the characteristic locomotor behavior of hylobatids, and compensate for the large traction loads on the wrist during extended-elbow vertical climbing.
Assuntos
Hominidae , Punho , Animais , Rádio (Anatomia)/diagnóstico por imagem , Articulação do Punho/anatomia & histologia , Hominidae/anatomia & histologia , Ligamentos Articulares/anatomia & histologiaRESUMO
The anatomical and functional characteristics of the elbow extensor muscles (triceps brachii and anconeus) have not been widely studied in non-human hominoid primates, despite their great functional importance. In the present study, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms in the elbow extensors in humans and chimpanzees. Our main objective was to identify differences in these muscles that could be related to the different uses of the upper extremity in the two species. In five humans and five chimpanzees, we have analyzed muscle mass (MM), muscle fascicle length (MFL), and the physiological cross-sectional area (PCSA). In addition, we have assessed the expression of the MHC isoforms by RT-PCR. We have found high MM and PCSA values and higher expression of the MHC-IIx isoform in the triceps brachii of chimpanzees, while in humans, the triceps brachii has high MFL values and a higher expression of the MHC-I and MHC-IIa isoforms. In contrast, there were no significant differences between humans and chimpanzees in any of the values for the anconeus. These findings could be related to the participation of the triceps brachii in the locomotion of chimpanzees and to the use of the upper extremity in manipulative functions in humans. The results obtained in the anconeus support its primary function as a stabilizer of the elbow joint in the two species.
RESUMO
The environmental conditions of captive hominoid primates can lead to modifications in several aspects of their behavior, including locomotion, which can then alter the morphological characteristics of certain anatomical regions, such as the knee or wrist. We have performed tridimensional geometric morphometrics (3D GM) analyses of the distal radial epiphysis in wild and captive gorillas, chimpanzees, and orangutans. Our objective was to study the morphology of the insertion sites of the palmar radiocarpal ligaments, since the anatomical characteristics of these insertion sites are closely related to the different types of locomotion of these hominoid primates. We have identified significant differences between the wild and captive specimens that are likely related to their different types of locomotion. Our results indicate that the habitat conditions of captive hominoid primates may cause them to modify their locomotor behavior, leading to a greater use of certain movements in captivity than in the wild and resulting in the anatomical changes we have observed. We suggest that creating more natural environments in zoological facilities could reduce the impact of these differences and also increase the well-being of primates raised in captive environments.
RESUMO
The mobility of the primate tongue allows for the manipulation of food, but, in addition, houses both general sensory afferents and special sensory end organs. Taste buds can be found across the tongue, but the ones found within the fungiform papillae on the anterior two thirds of the tongue are the first gustatory structures to come into contact with food, and are critical in making food ingestion decisions. Comparative studies of both the macro and micro anatomy in primates are sparse and incomplete, yet there is evidence that gustatory adaptation exists in several primate taxa. One is the distally feathered tongues observed in non-destructive nectar feeders, such as Eulemur rubriventer. We compare both the macro and micro anatomy of three lemurid species who died of natural causes in captivity. We included the following two non-destructive nectar feeders: Varecia variegata and Eulemur macaco, and the following destructive flower feeder: Lemur catta. Strepsirrhines and tarsiers are unique among primates, because they possess a sublingua, which is an anatomical structure that is located below the tongue. We include a microanatomical description of both the tongue and sublingua, which were accomplished using hematoxylin-eosin and Masson trichrome stains, and scanning electron microscopy. We found differences in the size, shape, and distribution of fungiform papillae, and differences in the morphology of conical papillae surrounding the circumvallate ones in all three species. Most notably, large distinct papillae were present at the tip of the tongue in nectar-feeding species. In addition, histological images of the ventro-apical portion of the tongue displayed that it houses an encapsulated structure, but only in Lemur catta case such structure presents cartilage inside. The presence of an encapsulated structure, coupled with the shared morphological traits associated with the sublingua and the tongue tip in Varecia variegata and Eulemur macaco, point to possible feeding adaptations that facilitate non-destructive flower feeding in these two lemurids.
RESUMO
PURPOSE: To identify anatomical differences in the deltoid tuberosity of Homo sapiens and Pan troglodytes, potentially relating to the different uses of the forelimb in these two phylogenetically related species. BASIC PROCEDURES: We have used three-dimensional geometric morphometrics (3D GM) to analyze the deltoid tuberosity of scanned humeri from 30 H. sapiens and 27 P. troglodytes. We also used the 3D scans of the humeri to calculate the surface area of the deltoid tuberosity. Finally, we dissected the deltoid muscles of three H. sapiens and three P. troglodytes to determine the relative mass and the physiological cross-sectional area (PCSA) of each part of the muscle. MAIN FINDINGS: The 3D GM analysis of the deltoid tuberosity identified an anteroposterior enlargement of the P. troglodytes tuberosity, with a lateral displacement of the middle segment, whereas in H. sapiens, there was a distal displacement of the middle segment. Muscle architecture analysis indicated higher normalized values ââof the PCSA of the clavicular and acromial deltoid in P. troglodytes. PRINCIPAL CONCLUSIONS: The anatomical features observed in our P. troglodytes specimens serve to strengthen the three parts of the deltoid muscle. This fact can be related to the use of the forelimb in locomotion, both arboreal and knuckle-walking, in this species. Humans use the forelimb mainly in manipulative tasks, so they do not develop - as do chimpanzees - the anatomical features that increase the deltoid force. Our findings have shown that the different uses of the forelimb in modern humans and common chimpanzees can affect both muscle architecture and bone morphology, either jointly or separately.
Assuntos
Músculo Deltoide/anatomia & histologia , Úmero/anatomia & histologia , Locomoção/fisiologia , Pan troglodytes/anatomia & histologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Animais , Cadáver , Feminino , Humanos , Imageamento Tridimensional , Masculino , Pessoa de Meia-Idade , Pan troglodytes/fisiologiaRESUMO
SUMMARY: The main objective of this study was to analyze by real-time quantitative polymerase chain reaction (RT-qPCR) the expression patterns of the myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIa, MHC-IIx) in the sphenomandibularis portion of the temporalis muscle. We expected to find differences between the sphenomandibularis and the other portions of the temporalis that could be related to the functional characteristics of the sphenomandibularis identified by electromyography. We dissected the right temporalis muscle of ten adult human individuals (five men and five women). Samples of the anterior and posterior temporalis and of the sphenomandibularis portion were obtained from each dissected muscle. These samples were analyzed by RT-qPCR to determine the percentages of expression of the MHC-I, MHC-IIa and MHC-IIx isoforms. No significant differences were identified between the anterior and the posterior temporalis in the expression patterns of the MHC-I, MHC-IIa and MHC-IIx isoforms. However, there were significant differences between the sphenomandibularis and the anterior temporalis. Specifically, the sphenomandibularis portion had a higher percentage of expression of the MHC-I isoform (P=0.04) and a lower percentage of expression of the MHC-IIx isoform (P=0.003). The pattern of expression that we observed in the sphenomandibularis reflects a greater resistance to fatigue, a lower contraction speed, and a lower capacity of force generation in the sphenomandibularis compared to the anterior temporalis. These characteristics are consistent with electromyographic findings on the functional differences between these two portions.
RESUMEN: El principal objetivo de este estudio fue analizar mediante real-time quantitative polymerase chain reaction (RT-qPCR) los patrones de expresión de las isoformas de la cadena pesada de la miosina (MHC-I, MHC-IIa y MHC-IIx) en la porción esfenomandibular del músculo temporal. Se esperó encontrar diferencias entre el esfenomandibular y las otras porciones del músculo temporal que se pudieran relacionar con las características funcionales del esfenomandibular, identificadas mediante electromiografía. Para obtener estos resultados, se diseccionó el músculo temporal derecho en diez humanos adultos (cinco hombres y cinco mujeres) y se obtuvieron muestras de la porción anterior y posterior del músculo temporal y de su porción esfenomandibular. Estas muestras fueron analizadas mediante RT-qPCR para determinar los porcentajes de expresión de las isoformas MHC-I, MHC- IIa y MHC-IIx. No se identificaron diferencias significativas de los patrones de expresión entre la porción anterior y la porción posterior del músculo temporal, pero sí que se observaron diferencias significativas entre la porción anterior del músculo temporal y su porción esfenomandibular. Concretamente, la porción esfenomandibular presentó un mayor porcentaje de expresión de la isoforma MHC-I (P=0.04) y un menor porcentaje de expresión de la isoforma MHC-IIx (P=0.003). El patrón de expresión que hemos observado en la porción esfenomandibular del músculo temporal refleja una mayor resistencia a la fatiga, una velocidad de contracción más lenta y una menor capacidad de generar fuerza si se compara esta porción con la porción anterior del músclo temporal. Estas características son consistentes con las diferencias funcionales que presentan estas dos porciones, que han sido descritas mediante electromiografía.
Assuntos
Humanos , Masculino , Feminino , Adulto , Pessoa de Meia-Idade , Idoso , Idoso de 80 Anos ou mais , Músculo Temporal/metabolismo , Cadeias Pesadas de Miosina/metabolismo , Osso Esfenoide , RNA Mensageiro/metabolismo , Imuno-Histoquímica , Isoformas de Proteínas , Eletromiografia , Reação em Cadeia da Polimerase em Tempo RealRESUMO
PURPOSE: The common chimpanzee (Pan troglodytes) is the primate that is phylogenetically most closely related to humans (Homo sapiens). In order to shed light on the anatomy and function of the temporalis muscle in the chimpanzee, we have analyzed the expression patterns of the mRNA transcripts of the myosin heavy chain (MyHC) isoforms in different parts of the muscle. BASIC PROCEDURES: We dissected the superficial, deep and sphenomandibularis portions of the temporalis muscle in five adult P. troglodytes and quantified the expression of the mRNA transcripts of the MyHC isoforms in each portion using real-time quantitative polymerase chain reaction. MAIN FINDINGS: We observed significant differences in the patterns of expression of the mRNA transcripts of the MyHC-IIM isoform between the sphenomandibularis portion and the anterior superficial temporalis (33.6% vs 47.0%; P=0.032) and between the sphenomandibularis portion and the anterior deep temporalis (33.6% vs 43.0; P=0.016). We also observed non-significant differences between the patterns of expression in the anterior and posterior superficial temporalis. PRINCIPAL CONCLUSIONS: The differential expression patterns of the mRNA transcripts of the MyHC isoforms in the temporalis muscle in P. troglodytes may be related to the functional differences that have been observed in electromyographic studies in other species of primates. Our findings can be applicable to the fields of comparative anatomy, evolutionary anatomy, and anthropology.
Assuntos
Cadeias Pesadas de Miosina/metabolismo , RNA Mensageiro/metabolismo , Músculo Temporal/metabolismo , Animais , Feminino , Humanos , Masculino , Cadeias Pesadas de Miosina/genética , Pan troglodytes , Especificidade da Espécie , Distribuição TecidualRESUMO
SUMMARY: Both the masseter and medial pterygoid muscles elevate the mandible, raising the lower jaw by acting simultaneously on the lateral and medial surfaces of the mandibular ramus. Nevertheless, electromyographic studies indicate that these muscles, as well as the superficial and deep heads of the masseter, act in a different way during mastication. We have analyzed by real time quantitative polymerase chain reaction (RT-qPCR) the expression of myosin heavy chain (MHC) isoforms in the masseter and medial pterygoid muscles in humans in order to identify possible differences in the expression patterns that may be related to functional differences identified with electromyography. Our findings indicate that the expression pattern of MHC isoforms in the two muscles is characteristic of fast and powerful phasic muscles. We have also observed a high percentage of expression of the MHC-IIx isoform and the expression of the MHC-M isoform at the mRNA level in both muscles, an isoform that does not translate into protein in the masticatory muscles of humans. The high percentage of expression of the MHC-IIx isoform in humans can be related to a high contractile speed of the masseter and medial pterygoid in humans. On the other hand, the low percentage of expression of the MHC-M isoform at the mRNA level in both muscles can be related to the complex evolutionary process that has reduced the size and force of the masticatory muscles in humans.
RESUMEN: Los músculos masetero y pterigoideo medial elevan la mandíbula actuando de forma simultánea sobre las caras lateral y medial de su rama. Sin embargo, los estudios electromiográficos indican que estos dos músculos actúan de forma diferente durante la masticación, de la misma forma que lo hacen las porciones superficial y profunda del músculo masetero. En el presente estudio hemos analizado mediante PCR en tiempo real la expresión de las isoformas de la cadena pesada de la miosina o myosin heavy chain (MHC) en los músculos masetero y pterigoideo medial en humanos, con la finalidad de identificar diferencias en los patrones de expresión que se puedan relacionar con las diferencias funcionales identificadas con la electromiografía. Nuestros resultados indican que el patrón de expresión de las isoformas de la MHC en los dos músculos es la característica de los músculos rápidos y potentes. También hemos observado un elevado porcentaje de expresión de la isoforma MHC-IIx y la expresión a nivel de ARNm de la isoforma MHC-M en los dos músculos, una isoforma que no se detecta a nivel de proteína en los músculos masticadores humanos. El elevado porcentaje de expresión de la isoforma MHC-IIx que hemos observado se puede relacionar con una elevada velocidad de contracción de los músculos masetero y pterigoideo medial en los humanos. Por otro lado, el bajo porcentaje de expresión de la isoforma MHC-M a nivel de ARNm en ambos músculos se puede relacionar con los procesos evolutivos complejos que han reducido el tamaño y la fuerza de los músculos masticadores en los humanos.