The human temporo-mandibular joint: current anatomic and physiologic status

Summary The aim of this study was to take stock of current anatomic and physiologic knowledge of the human temporo-mandibular joint. Though the lateral pterygoid m. plays an essential role in joint movements, we believe that the small deep portion of the masseter and temporalis have a supplementary action in guiding the articular disc forward. The embryologists have demonstrated joint movements in the two-month embryo and at this stage there already exists a triple attachment of the temporalis, pterygoid and masseter to the disc.

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L'articulation temporo-mandibulaire humaine: données actuelles anatomiques et physiologiques

Résumé Ce travail a pour objectif de faire le point sur les connaissances anatomiques et physiologiques actuelles de l'articulation temporo-mandibulaire humaine. Si le m. ptérygoïdien latéral joue un rôle essentiel dans la dynamique articulaire, nous pensons que les petits chefs profonds du m. masséter et du m. temporal ont une action complémentaire dans le guidage antérieur du ménisque. Les embryologistes ont mis en évidence des mouvements articulaires chez l'embryon de 2 mois et à ce stade il existe déjà une triple insertion temporo-ptérygo-massétérine sur le ménisque articulaire.

     

Interrelation of temporal fascia,temporalis and masseter muscles

Introduction

In the study; interrelation in between the distal part of deep layer of temporal fascia, temporalis muscle and the muscle fibers of deep layer of masseter were examined in order to detect the possible different relationships in between them.

Positional relationships between the masticatory muscles and their innervating nerves with special reference to the lateral pterygoid and the midmedial and discotemporal muscle bundles of temporalis

For an accurate assessment of jaw movement, it is crucial to understand the comprehensive formation of the masticatory muscles with special reference to the relationship to the disc of the temporomandibular joint. Detailed dissection was performed on 26 head halves of 14 Japanese cadavers in order to obtain precise anatomical information of the positional relationships between the masticatory muscles and the branches of the mandibular nerve. After complete removal of the bony elements, the midmedial muscle bundle in all specimens and the discotemporal muscle bundle in 6 specimens, derivatives of the temporalis, which insert into the disc were observed. On the anterior area of the articular capsule and the disc of the temporomandibular joint, the upper head of the lateral pterygoid, the midmedial muscle bundle of temporalis and the discotemporal bundle of temporalis were attached mediolaterally, and in 3 specimens the posterosuperior margin of the zygomaticomandibularis was attached to the anterolateral area of the disc. It is suggested that these muscles and muscle bundles contribute to various mandibular movements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observed in the present study, relative positional relationships of the muscles and muscle bundles and of nerves of the mandibular nerve are consistent. A possible scheme of the developmental formation of the masticatory muscles based on the findings of the positional relationships between the muscles and the nerves is presented.     

不同牙 合 位时翼外肌对颞下颌关节盘的生物力学影响

目的　研究在牙尖交错位和最大张口位时可复性关节盘前移位中翼外肌对关节盘的生物力学影响及两牙合 位之间的差异。 方法　对已经建立的可复性关节盘前移位的颞下颌关节数字化仿真模型,在不同牙合 位时进行翼外肌加载,通过三维有限元的方法进行生物力学分析。 结果　最大张口位时,关节盘应力集中区较牙尖交错位时向前外侧移动,集中于关节盘中间带偏外侧区;关节盘中间带与关节盘后带之间存在明显位移差,形成位移撕裂带,而在牙尖交错位时则无类似位移差现象。 结论　在可复性关节盘前移位中,最大张口位时翼外肌可导致关节盘中间带偏外侧区的应力集中,在关节盘中间带形成位移撕裂带,导致此区域变薄、穿孔甚至撕裂。     

A possible etiology of the internal derangement of the temporomandibular joint based on the MRI observations of the lateral pterygoid muscle

The purpose of this study was to evaluate the relationship of the temporomandibular joint (TMJ) internal derangement and lateral pterygoid muscle (LPM) by magnetic resonance imaging (MRI). In this study, 115 subjects with TMJ internal derangement (total 230 TMJs) and 21 subjects without clinical symptoms (total 42 TMJs) were included. TMJ disc position and LPM were evaluated using MRI. LPM attachments were categorized into two different types: type 1, where fibers of the superior head of the LPM (SLPM) were attached to the disc and fibers of the inferior head of the LPM (ILPM) were attached to condyle, and type 2, where fibers of the SLPM were attached to the disc and condyle, and fibers of the ILPM were attached to condyle. The presence of muscle atrophy and degeneration were also evaluated. LPM attachments were observed in two different parts. Disc displacements were common in the muscle attachments of both types. Type 1 muscle attachments were seen in 85.9% of all the anterior disc displacement without reduction (ADD) TMJs (total 64 TMJs). Atrophy was seen in a higher proportion (43.7%) in TMJs with ADD (28/64) than in TMJs with normal and anterior disc displacement with reduction (ADDR). Out of 74 TMJs with atrophy, 68 had type 1 muscle attachment. Four TMJs had atrophy in both superior and inferior heads of the lateral pterygoid. However, atrophy was not present only in the ILPM. It has been concluded that since the SLPM only attached to the disc in type 1, the disc may displace anteriorly very easily. Therefore, this situation will reduce the function of the SLPM. Reduced muscle function may cause muscle atrophy. The activity of the SLPM may be more reduced since the disc permanently dislocated in TMJs with ADD. Finally, spasm of the LPM causes disc displacement and atrophy and then the degeneration of the LPM may follow disc displacement.     

A study of the lateral pterygoid muscle: anatomic sections and CT appearances

Summary The authors have studied the relationship between anatomic and CT sections of the lateral pterygoid muscle in 39 anatomic specimens. Good superimposition of the images was found, which seems important in neoplastic invasion of the infratemporal fossa and which may lead to a pathogenic interpretation of the algo-dysfunctional syndrome of the masticatory apparatus.

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Etude anatomo-radiologique (TDM) du muscle ptérygoïdien latéral

Résumé Les auteurs ont étudié, sur 39 pièces anatomiques, la corrélation entre coupes anatomiques et tomodensitométriques (TDM) du muscle ptérygoïdien latéral. Il apparaît une bonne superposition des images ce qui semble intéressant dans les envahissements de la fosse infratemporale en carcinologie et qui pourrait déboucher sur une interprétation pathogénique du syndrome algo dysfonctionnel de l'appareil manducateur.

     

Functional anatomy of the human lateral pterygoid muscle

The authors studied the lateral pterygoid muscle of 179 fresh cadavers by both anatomical dissection and magnetic resonance imaging. The aim was to define the general morphology and the architectural organisation of the lateral pterygoid muscle. Dissection plane by plane, anatomical sections in different planes of space and dissections via multiple approaches on harvested blocks allowed the demonstration that the lateral pterygoid shows an architectural arrangement different from that which is usually described but similar to that, from its typically penniform structure of the masseter and the medial pterygoid. The anatomical situation of this muscle gives rise to numerous differences in opinion much to its morphology as to its functional examination. This study has shown that one part of the muscle has a typical penniform structure made up of alternating musculo-aponeurotic layers and by the absence of individual muscle bellies. In addition the particular shape of this muscle makes it useless to insert intramuscular electrodes in its only accessible portion, which makes the results of electromyographic studies debatable.     

Innervation of the human lateral pterygoid muscle

The one- or two-headed arrangement of the lateral pterygoid m. (LPM) was analysed by studying the motor nerve distribution within the muscular tissue. In all subjects, the main innervation of the lateral pterygoid m. came from the anterior trunk of the mandibular n. by one to three nerves. These nerves divided into five or six vertical branches which ramified into parallel horizontal tiny fibers. Consequently, the lateral pterygoid m. appeared to be divided into oblique sagittal planes and horizontal layers by the nerve branches, reflecting the multipennate organisation of the muscle. These layers can be selectively recruited during mandibular movements, ensuing a fine medial-lateral control. According to its nerve supply, the LPM has to be considered as a single unit made of independent functional musulo-aponeurotic layers even though its morphologic conformation is in one, two or three heads.     

The anatomical basis for ultrasonography of the lateral pterygoid muscle and the infratemporal fossa

Summary The infratemporal fossa and its contents (particularly the pterygoid muscles) is a region difficult to explore, in spite of its importance in odontostomatological pathology. In order to reduce the indications that justify examination by computed tomography and magnetic resonance imaging, for reasons of economy of health, the authors describe by application of orientated anatomical slices the way in which ultrasonography can be performed. Only the posterior approach between the mandible laterally and the mastoid process medially provided consistently adequate exploration of the infratemporal fossa and the pterygoid muscles.Communication presented at the French Section of the European Association of Clinical Anatomy meeting, Bobigny, France, June 20, 1992     

Reflex inhibition in single motor units of the human lateral pterygoid muscle

Summary Reflex electromyographic (EMG) responses to electrical stimulation in the human lateral pterygoid muscle are ambiguous, possibly due to previous methods of EMG analysis. In a rigorous paradigm, single motor unit (SMU) activity in 30 units was recorded in the inferior head of the lateral pterygoid muscle in 5 subjects. Single pulses of 1 ms duration at 6T intensity were delivered via bipolar electrodes attached to the gingiva near the maxillary canine. The firing frequency of each SMU was constrained to 10 or 15 Hz by biofeedback techniques. Stimuli were delivered at known positions relative to a series of preselected spikes. Successive stimuli were delivered sequentially by increasing increments of 1 ms. SMUs were activated consistently by incisal clenching and jaw opening against resistance applied to the chin. When the SMU prestimulus firing frequency was constrained at 10 Hz, each unit displayed an inhibitory effect which was highly dependent on the stimulus position. In units with a constrained firing frequency of 15 Hz, no effect was observed. These findings qualitatively resemble responses observed in the human masseter muscle.     

An anatomic study of the divisions of the lateral pterygoid muscle based on the findings of the origins and insertions

The lateral pterygoid muscle has been generally described as a muscle composed of two separate heads, however, the border between these heads has not clearly identified. In the present study, we investigated the positional relationships between the muscle and the surrounding nerves, and examined the muscle bundle arrangements to determine the detailed information of the origins and insertions. We used 94 specimens of 52 Japanese cadavers (29 males and 25 females) for the investigations of the nerve courses, and randomly chose and used 10 specimens of 5 (2 males and 3 females) cadavers from above-mentioned 52 cadavers for the detailed examinations of the muscle fiber constructions. In some specimens, the buccal nerve passed through the gap in the muscle, however, in many cases the nerve pierced the muscle. The muscle inserted into the medial half of the anterior surface and the medial surface of the condylar process. Only a thin superficial layer of the muscle fibers was attached to the inferior surface of the articular disc. According to the positions of the origins and insertions of the muscle and the positional relationships to the nerves, the muscle was not clearly divided into heads. The detailed findings of the origins and insertions of the present study suggest that the muscle is a single muscle with no clear border, containing fibers of various directions. A two-head muscle pattern would be indicated by the differences of the convergences of the muscle fibers.     

Anatomical study of the arrangement and attachments of the human medial pterygoid muscle

The authors have studied the medial pterygoid muscle on 179 fresh cadavers using anatomical dissection and magnetic resonance imaging (MRI). The aim of this study was to define the general morphology and architectural organisation of the human medial pterygoid. Plane by plane dissection, anatomical sections in different spatial planes on half heads and isolated blocks demonstrated that the medial pterygoid has different architectural disposition and insertional zones from those which are normally described. The study has shown that the muscle has a typical penniform structure made up of seven alternating muscular/aponeurotic layers and that the tendinous intramuscular sheets were particularly well developed. This allows supporting a future functional study.     

Aberrant muscle between the temporalis and the lateral pterygoid muscles: M. pterygoideus proprius (Henle).

During examination of the positional relationships between the lateral pterygoid and the temporalis muscles and the innervating nerves, an aberrant muscle was observed in three of 66 head halves. The aberrant muscle originated from the medial surface of the anteromedial muscle bundle of the temporalis (Shimokawa et al. 1998, Surg. Radiol. Anat. 20:329-334) and inserted into the inferolateral surface of the lower head of the lateral pterygoid. Due to its location, origin and insertion this aberrant muscle slip is considered to correspond to the pterygoideus proprius described by Henle (1858, Handbuch der Anatomie des Menschen). Based on the innervation findings, the present aberrant muscle might be considered as a remnant muscle bundle between the anteromedial muscle bundle of the temporalis and the lateral pterygoid during differentiation of the lateral masticatory muscle anlage.     

Functional organization of the human masseter muscle

The authors carried out an anatomic and magnetic resonance imaging study of the architecture of the elevator muscles of the mandible in 169 cadavers. The aim of this study was to define the architectural organization of the human masseter muscle, temporalis and pterygoid muscles. Layered dissections and anatomic sections in different spatial planes showed that the masseter muscle exhibited a typical pennate structure consisting of a succession of alternating musculoaponeurotic layers. The muscle had three well-differentiated parts the superficial, intermediate and deep masseter muscles. The same pattern was constantly found 1) for the superficial masseter, two alternate musculoaponeurotic layers oriented at 60∘ in relation to the plane of occlusion, 2) for the intermediate masseter, a single musculo-aponeurotic layer oriented at 90∘ in relation to the occlusal plane, 3) for the deep masseter, three musculoaponeurotic layers whose general orientation was at 90∘ for the bounding layers and 110∘ for the intermediate layer. The MRI study confirmed the reality of this architectural arrangement.     

足底内侧和外侧群肌的肌内神经整体分布模式及临床意义

目的 揭示足底内侧和外侧群肌的肌内神经整体分布模式,探讨其临床意义.方法 24具成年尸体,完整取下足底内侧和外侧群肌,采用改良Sihler染色显示肌内神经分布模式.结果 (足母)收肌的神经支从肌止端的深面入肌,而(足母)展肌、(足母)短屈肌、小趾展肌和小趾短屈肌的神经支常从肌起端的深面入肌.(足母)展肌中有1个半月形和...     

Anatomic study of the tendinous insertion lamina of the temporalis muscle

Lengthening temporalis myoplasty is indicated in long-standing and congenital facial paralysis. Its principle is the transfer of the coronoid tendinous insertions onto the lip and the nasolabial fold. Knowledge of the anatomy of this strong and wide tendon is necessary for successful use of its anatomic advantages. A study on 10 cadavers (20 temporalis muscles) confirmed the surgical anatomy found during lengthening temporalis myoplasty procedures: the strong tendon, when freed from the coronoid process, is 4–6 cm wide.     

Synergy between bifunctional muscles at the ankle joint

Summary The activation of antagonistic muscles is studied during isometric combined contractions of bifunctional muscles. It is established that the co-contraction mechanism observed in such situations limits unwanted movements. Furthermore, when a co-contraction appears between two biantagonistic muscles, the phenomenon underlies a conflicting situation and, consequently, the muscular patterns encountered are in most cases the reverse of those classically described. In these circumstances the inhibition usually present between antagonistic muscles could be masked, due to convergence on the motoneurones of both inhibitory and excitatory discharges coming from homonymous and antagonistic muscles of a given bifunctional muscle.     

人翼外肌肌内神经肌梭的分布及其意义

目的:研究人翼外肌肌内神经和肌梭配布特征,以期深入了解翼外肌上、下头的功能特性。方法:对10具成人尸体的翼外肌肌梭以及肌内神经分支、分布进行了观察。结果:改良Sihler氏神经染色显示翼外肌上、下头有各自独立的神经支。支配翼外肌上头的神经支较短而细小,入肌后分出两个次级分支,与肌纤维排列方向成一定的角度向肌止点处走行;支配下头的神经支较粗,入肌后在肌纤维之间迂曲走行,发出呈树支状的多个次级分支,分支间无吻合。翼外肌肌梭仅分布在上头肌腹中央,下头未发现肌梭。结论:翼外肌具有划分亚部的形态学特征,每一亚部作为一个功能独立体在整肌功能中行使作用。     

General organization of the human intra-masseteric aponeuroses: changes with ageing

A magnetic resonance imaging (MRI) study of the layout of the aponeurotic layers of the masseter muscle was done on a series of 18 patients, aged from 6 to 79 years. The study was undertaken in parallel with a study on 169 cadavers to correlate the anatomical dissection and MRI findings. The aims were as follows. On the cadavers, the results of dissection were compared with the results of MRI: the layer-by-layer dissections and the anatomical dissections of the different spatial planes have shown that the masseter muscle displays a penniform structure typically characterized by the presence of alternating muscular/aponeurotic layers. The anatomical sections and the MRI section in the same plane allowed the appearance of the intra-muscular aponeurotic layers on MRI to be defined. The patients were then divided into four age cohorts, and the arrangement and variations of the human masseter muscle defined as a function of age. This double study has brought new elements to the understanding of the timing of the development of the intra-muscular aponeurotic structures and the modifications which they undergo with ageing. It appears that the aponeurotic structures only become individually identifiable towards the age of 17 years and that ageing is accompanied by a reduction in the transverse muscular mass accompanied by a verticalization of the aponeurotic layers.

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Electronic Supplementary Material The french version ot this article is available in the form of electronic supplementary material and can be obtained by using the Springer Link server located at .

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Organisation générale des lames aponévrotiques du muscle masséter humain: effet de le vieillissement

Résumé Les auteurs ont effectué une étude en imagerie par resonance magnetique (IRM) de la disposition des lames aponévrotiques du muscle masséter sur une série de 18 patients âgés de 6 à 79 ans. Cette étude a été menée parallèlement à une étude sur 169 cadavres associant la dissection anatomique et l'imagerie par résonance magnétique. Les buts de cette étude ont été les suivants: (1) Sur les cadavres, les données des dissections ont été comparées avec les résultats de l'imagerie par résonance magnétique; les dissections plan par plan, les coupes anatomiques dans différents plans de l'espace ont permis de montrer que le muscle masséter présente une structure penniforme typique caractérisée par la présence de couches musculo-aponévrotiques alternées; les coupes anatomiques et les coupes en IRM réalisées dans les mêmes plans ont permis de préciser l'aspect en IRM des lames aponévrotiques intra-musculaires. (2) Sur les patients, répartis en quatre tranches d'âge, nous avons précisé la disposition et les variations concernant les structures aponévrotiques du muscle masséter de l'Homme en fonction de l'âge. Cette double étude, permet d'apporter des éléments nouveaux dans la compréhension de l'époque de la mise en place des structures aponévrotiques intra-musculaires et des modifications qu'elles subissent avec le vieillissement. Il apparaît que les structures aponévrotiques ne sont nettement individualisée que vers l'âge de 17 ans et que le vieillissement se traduit par réduction transversale de la masse musculaire accompagnée d'une verticalisation des lames aponévrotiques.