[Left-right asymmetries and other common anatomical variants of temporomandibular articular surfaces]. / Links-rechts asymmetriën en andere anatomische varianten van de temporomandibulaire gewrichtsvlakken.

The purpose of the study was to investigate left-right asymmetries and other anatomical variants of temporomandibular articular surfaces. Digital photography and macroscopic observation were used to gather information about the shape, size, orientation and degeneration of temporomandibular articular surfaces of 100 skull bases and 100 mandibles. Left-right asymmetries in shape, size, orientation and degeneration were found in 39.5, 26, 16 and 31.5% of the mandibular surfaces respectively. The glenoid fossae showed left-right asymmetries in size, orientation and degeneration in 4.1 and 22.5% of cases respectively. Left-right asymmetries in orientation were found in 24% of the articular eminences. Anatomical variants of the mandibular articular surfaces were found as differences in shape: the majority had horizontal oblong outlines and rounded frontal outlines; one fifth showed pear-shaped horizontal outlines and flat or ridge-shaped frontal outlines. The important incidence of left-right asymmetries and anatomical variants of temporomandibular articular surfaces must be considered when observing and treating temporomandibular dysfunction. It can be expected that these asymmetries and anatomical variants may have arthrokinematic consequences for treatment of temporomandibular dysfunction.

Effect of individually chosen bed-height adjustments on the low-back stress of nurses.

OBJECTIVES: The effects of height-adjustable beds in hospitals on the subsequent prevalence of low-back problems among nurses depend on the capacity to reduce low-back stress by bed-height adjustment. This capacity was investigated in the present study. METHODS: Professional nurses performed patient-handling tasks at a standard and an individually chosen bed height. Peak values and time integrals of spinal compression and shear forces were estimated with dynamic biomechanical modeling. RESULTS: The bed-height adjustment led to lower values of time-integrated compression (average 8.8% lower), peak shear force (average 9.3% lower), and time-integrated shear force (average 18.1% lower). No significance was found for the effect on peak compression, nor for the results for each individual task. This finding can be explained by the minor adjustments made in comparison with the standard height or by the application of different criteria for bed-height adjustment. CONCLUSIONS: The decreasing time-integrated forces and peak shear force, without a concomitant rise of peak compression, speak in favor of the use of height-adjustable beds in nursing.

Anterior sacrodural attachments - Trolard's ligaments revisited.

In contrast to the attention paid to the structures surrounding spinal nerve roots in the intervertebral foramina, the anterior dural attachments are largely ignored, although they have been described since the last decades of the 19th century. These anterior attachments were systematically studied in a series of 30 cadaver dissections and were found to be present in almost 94% of cases. Four types of anterior attachments were observed. The most frequent form (84%) being a system of filaments that present as a double cross vault between the dura mater and the posterior longitudinal ligament extending from L3 to S3 levels. Less frequent were sagittal filaments (30%), short strong ligaments (17%) and a median septum from L3 to the end of the dural sac (7%). No attachments were found in two cadavers. Further studies are needed to clarify the possible role of these structures in transmitting movement to the dural sac and periradicular sleeves when mobilising the last three lumbar vertebrae or the sacrum.

The sternoclavicular joint: variants of the discus articularis.

OBJECTIVE: To study the anatomy of the sternoclavicular joint, its discus and its variations.Design. Anatomical study (macroscopic dissection). BACKGROUND: Textbooks on manual therapy give different descriptions of the movements of this joint. These apparent contradictions could be due to poor understanding of the anatomy of this joint resulting in ignoring specific movement patterns under particular conditions. METHODS: Macroscopic dissection of 22 embalmed sternoclavicular joints. RESULTS: The sternoclavicular and the costoclavicular parts of the discus always were quite distinct in orientation, thickness, surface and consistency. The sternoclavicular part was attached to the dorso-cranial part of the extremitas sternalis claviculae by a broad insertion in which several small blood vessels are visible. This part is grossly vertical, thicker than the lateral part and has a fibrous aspect. The costoclavicular part of the discus is always thinner than the sternoclavicular part. Sometimes it is reduced to a fine translucent pellet or is perforated. Subsynovial vascular arcades run along the insertion of the discus on the joint capsule, both on sternal and on clavicular sides. The costosternal articular surface can be divided into a sternal and a costal segment, separated by a vascular zone. CONCLUSIONS: Findings suggest different functions of the distinct parts of the joint. The smooth aspect of the lateral segment of the costosternal articular surface and of the costoclavicular part of the discus could be an argument to consider a functionally distinct costoclavicular compartment. The insertion of the discus on the clavicula strongly suggests that small movements take place between clavicula and discus and that the discus itself is moved only when the increasing amplitude stretches this insertion. We hypothesise that all midrange movements take place between the convex inferior edge of the clavicula and the costoclavicular part of he discus and that larger elevation depression and pro- and retraction movement take place, respectively, between clavicula and discus or discus and sternum. In three specimens we observed a previously not described arterial ramus articularis originating from the left thyrocervical trunk.RelevanceThese findings might explain differences of the arthrokinematic behaviour of this joint between midrange and full range motions.

Glenohumeral joint kinematics related to minor anterior instability of the shoulder at the end of the late preparatory phase of throwing.

OBJECTIVE: The first aim of this study was an approach to quantify the 3D kinematics of the glenohumeral joint referred to the joint surfaces. The method was used to study the glenohumeral patho-arthrokinematics related to minor anterior instability at the end of the late preparatory phase of throwing. STUDY DESIGN: Using a finite helical axis approach, arthrokinematics focused on: (i) the rotations and shift of the humeral head on the glenoid cavity, and (ii) the migration of contact of the articular surfaces. BACKGROUND: Controversy still exists whether the clinical syndrome called 'minor anterior glenohumeral instability' can be validly termed as an instability. METHODS: Helical CT-data of discrete shoulder positions were three-dimensionally reconstructed. Based on humeral and scapular sets of skeletal landmarks, rotation matrices and translation vectors were estimated and processed in glenohumeral finite helical axes. The finite helical axis parameters of rotation, shift and direction were related to a co-ordinate system embedded on the glenoid, whereas the position of the finite helical axis was related to the articulating surface of the humeral head. RESULTS: From 90 degrees abduction and 90 degrees external rotation to full cocking (90 degrees abduction with full external rotation and horizontal extension), the humeral head in the normal shoulders did not externally/internally rotate on the glenoid. In contrast, a large external rotation component was found in the minor unstable shoulders. The geometrical centre of the humeral head of the normal shoulders translated into a posteriorized position on the glenoid, whereas in minor anterior instability it translated centrally on the glenoid. CONCLUSIONS: Compared with in vitro biomechanical research which states that towards full cocking the anterior part of the inferior glenohumeral ligament limits anterior translation and external rotation of the humeral head on the glenoid, the results suggest in minor anterior instability a dysfunction of the anterior part of the inferior glenohumeral ligament. RELEVANCE: The results indicate that the so-called 'minor anterior glenohumeral instability syndrome' can validly be stated as an instability problem. The results also indicate that the glenohumeral joint does not move consistently as a ball-and-socket joint, meaning that the concave-convex rules for glenohumeral joint mobilization need 'evidence-based' adjustments.

[Simultaneous observation of multiple variants of muscles of the neck and the shoulder girdle, one of which is a M. levator claviculae]. / Observation de multiples variantes simultanées des muscles de la nuque et de la ceinture scapulaire, dont un M. levator claviculae.

We report on the simultaneous occurrence in a male cadaver of bilateral clavicular slips to the M. latissimus dorsi, a bilateral variant of M. sterno-cleido-mastoïdeus known as M. cleido-occipitalis (Wood) and an exceptional form of M. levator claviculae posterior on the left side.

Observation of a supernumerary hamstring muscle: a state of the art on its incidence and clinical relevance.

During routine anatomic dissection of the lower extremities of a 67-year-old male body, a supernumerary ishiocrural muscle was observed. This supernumerary muscle had similarities to a rare variant of the semimembranous muscle. On the left side it arose from the lateral dorsal side of the femur between the short head of the biceps femoris muscle and the origin of the adductor magnus muscle. It inserted on the medial condyle deep to the normal insertion of the semimembranous at the posterior aspect of the articular capsule. This muscle can be regarded either as a short deep semimembranous muscle (M. semimembranosus profondus) or as a short belly of a semitendinous biceps as known in birds. The muscle was situated closely to the vessels and nerves of the popliteal region. On the right side a similar but somewhat fainter muscle was observed whose origin emanated from the fascia of the adductor magnus muscle. The muscle probably has no major clinical importance but might be important to the surgeon who has to intervene in the popliteal region.

Arthro-kinematics of the elbow: study of the carrying angle.

The carrying angle of the elbow is usually assessed in full elbow extension, with a protractor goniometer, or derived from X-ray images. Substantial differences in carrying angle values have been reported, possibly explained by methodological differences. Carrying angles tend to show higher values in women than in men. The aim of this study was to confirm the previously described progressive decrease of the carrying angle as a function of increasing elbow flexion. After assessment of the carrying angle with a protractor goniometer and an electromagnetic tracking system (Flock of Birds) in extension, flexion-extension movements with the forearm held in supination were recorded by means of the latter system. Three recordings were averaged in both the left and the right elbows of 20 volunteers without a history of elbow pathology (10 males and 10 females; mean age 25 years). In extension, a mean (+/- SD) carrying angle of 11.6 +/- 3.2 degrees was found in the male and 16.7 +/- 2.6 degrees in the female subjects. The carrying angles progressively decreased with flexion, at the end changing into a mean (+/- SD) varus angle of 1.8 +/- 2.9 degrees in men and 1.6 +/- 2.3 degrees in women. Significant differences in carrying angles between the sexes were recorded in moving from 0 to 30 degrees of flexion (p < 0.03 for the left and p < 0.01 for the right elbows), but disappeared beyond 30 degrees . No statistically significant differences were found between the results of left and right elbows. Although statistically significant differences (p < 0.05 to p < 0.001) were found along the course of flexion and extension, these differences were small (<0.6 degrees ). The mean carrying angles at 0, 30, 60, 90 and 120 degrees of flexion revealed larger standard deviations in the male group than in the female group.

[Anatomical background of low back pain: variability and degeneration of the lumbar spinal canal and intervertebral disc]. / Der anatomische Hintergrund von Rückenschmerz - Formvariabilität und Degeneration des lumbalen Spinalkanals und der Zwischenwirbelscheibe.

The central and lateral lumbar canals constitute complex osteofibrous neurovascular tunnels, allowing movement and deformation of the spine without loss of their main configuration. Intervertebral discs play an important role in determining their configuration. Disc degeneration may alter or even threat the functional anatomical relationships between successive adjacent "juncturae" of the vertebral column. Shape and morphometric aspects of the bony neural canals reveal level dependency [39], inter-individual variation [11], and are particularly susceptible for changes with aging [49]. Articular tropism and other left-right differences may influence their morphology. In the epidural compartments behind the vertebral bodies, a sagittal membrane may totally or partly connect the deeper layer of the posterior longitudinal ligament (PLL) with the posterior midline of the vertebral body. This membrane is considered clinically significant in the prevention of movement of disc material from one side to the other at the level of the vertebral bodies [44]. Meningovertebral ligaments represent a heterogenous group of membranous formations, connecting the dura with the PPL and other elements of the spinal canal. They prevent the dura from moving away from the bony container. These ligaments may vary from loose areolar tissue to clearly individualised ligaments and from pure midsagittal septa to more laterally oriented attachments. A double cross vault structure between the PPL and the dura mater often extends from L3 to the end of the dural envelope [3]. A retrospective study of medial and paramedial attachments in CT- and MRT-scans confirmed the presence of a mediosagittal structure below L3 in 35% of the cases 7). It was hypothesized that meningovertebral ligaments may play a [7] role as a barrier to transverse displacement of extruded disc material [43]. The surrounding morphology renders the lateral neural canal its typical inverted teardrop shape [39]. The subpedicular notch of the upper vertebra provides the widest part and represents the neural foramen strictu sensu. The posterolateral aspect of two articulating vertebrae and the interposed intervertebral disc constitute the anterior wall. The morphology of the anteroinferior aspect of the intervertebral foramen strongly depends on the condition of the apophyseal rings and the intervertebral disc. The latter may show a slight physiological posterior bulging at lower lumbar levels. The posterior wall of the nerve root canal is represented by the ligamentum flavum, the pars interarticularis of the upper vertebra, and the superior articular facet of the vertebra below. Thickening of the ligamentum flavum must be considered in relationship to alterations of anterior components: trabecular reorganization and spreading of vertebrae in aging [49], and disc degeneration [38, 49]. Nerve root sleeves display a level dependent, variable oblique course from their emanation from the thecal sac towards the outer third of the neural canal [39]. The presence of anamalous lumbosacral nerve roots may result in considerable course alterations, originating from an abnormal high or low level emanation, conjoined nerve roots, a double set of nerve roots or anastomosis between nerve roots of adjacent levels [20]. Variation exists in the position of the dorsal root ganglia (DRG) relative to the intervertebral foramen. An intraforaminal position seems to be more common at L4 and L5 levels; an intraspinal position has to be expected for the S1 DRG. Intraspinal position of L4 and L5 DRG renders them more susceptible to compression from a superior articular facet or a bulging disc. Cases of extraforaminal positions of dorsal root ganglia have been reported at L4 and L5 levels [22]. On its recurrent course through the lateral canal, the sinuvertebral nerve(s) supplies the laterodorsal outer annulus of the intervertebral disc, the PLL, the anterior 2/3 of the dural sac and the anterior vascular plexus [4, 14]. Many blood vessels pass through the lateral neural canal: the anterior and posterior spinal canal branches, anterior and posterior radicular branches, and veins of the anterior and posterior internal vertebral venous plexus [9]. Per segment, one ore two thick and one to four thin sinuvertebral nerves (SVN) originate from rami communicantes close to the connection of the latter to the spinal nerve [14]. The extensive ramifications of the thin SVNs complete a thorough network at the floor of the central lumbar canal. A large part of it supplies the PLL. The PLL is assumed to play an important role in proprio- and nociception [34, 39]. It is probably one of the first structures to mediate nociceptive information from disc tissue [14]. After injection of neuronal tracers into the sympathetic trunk at L3-L4 in rats, labeled cells were found in higher DRGs as well as labeled nerve fibers in the dura mater at lower levels. These findings indicate both a segmental and a non segmental pathway of sensory innervation of the dura mater and a role of higher DRGs in mediating LBP [25]. In the neighborhood of the SVN, other small branches emanate from the rami communicantes and join the dorsal ramus and the segmental artery that enters the neural canal. The sympathetic nerve plexus inside the anterior longitudinal ligament and the SNVs provide a network of nerve fibers around the vertebral bodies and intervertebral discs. These pathways explain the sympathetic component of the innervation of a number of spinal structures. The dorsal ramus innervates the facet joints at the corresponding level and one below, before it gives off muscular and cutaneous branches.

The influence of triazolam and flunitrazepam on isokinetic and isometric muscle performance.

The influences of two benzodiazepines (triazolam 0.25 mg and flunitrazepam 2 mg) on isokinetic and isometric muscle performance and on cardiovascular parameters were examined after a standard period of sleep. A randomized and double-blind test procedure was used (n = 15). Triazolam had no significant (p < 0.05) influence on either of the test conditions. Administration of flunitrazepam significantly lowered values for maximal isometric force and for the cardiovascular parameters. It was concluded that triazolam does not influence performance. On the other hand, flunitrazepam does influence a number of strength characteristics and cardiovascular parameters in effort situations.

Muscle strength, task performance and low back load in nurses.

Poor muscle strength, relative to the physical demands of specific jobs, is considered a risk factor for low back pain. To gain an understanding of the underlying mechanisms, this study questioned whether muscle strength was related to task performance and low back load in nursing tasks. Trunk extension, elbow flexion and knee extension strength were therefore measured in 17 nurses. The independent effects of muscle strength on task duration, jerkiness of effort and L5-S1 torque were investigated as the nurses performed several patient handling tasks. Despite a large variation in muscle strength within the subject population, no effect of strength on task duration, jerkiness or L5-S1 torques was observed. In conclusion, poor muscle strength was found not to be related to increased low back load. If 'weaker' nurses were to be at a higher risk, it would be due to a reduced capability to withstand the mechanical load, rather than to an increased mechanical load.

Moments of force, power, and muscle coordination in speed-skating.

Two well-trained speed-skaters were subjected to a biomechanical analysis incorporating push-off forces, cinematographic data, and link segment modeling. To gain knowledge on the backgrounds on technique and performance in speed-skating, the muscle coordination was studied by EMG and muscle contraction velocities. In speed-skating during the push-off, the body center of gravity (cg) is accelerated with respect to the point of application of the push-off force, with a forward gliding skate. The velocity of cg is a result of rotation of segments. Due to the absence of plantar flexion of the foot, the knee extension range is limited. The short and explosive push-off can be considered as a catapult-like action. The knee extensor muscles vastus medialis and rectus femoris are prestretched in the gliding phase by the antagonistic action of gastrocnemius and biceps femoris. In this phase the skater rotates his cg from the lateral to the medial side of the skate to reach an optimal push-off angle. The power output in the push-off phase is mainly generated by the monoarticular extensor muscles gluteus maximus and vastus medialis.