Rectus Capitis Anterior Research Articles

Congenital occipitoatlantoaxial malformation in a Warmblood mare

SummaryA 3‐year‐old Warmblood mare was presented with spinal ataxia of 3 months’ duration. Clinically, reduced mobility of the neck and a prominent atlas were identified. Neurological evaluation revealed hypermetria, circumduction and reduced proprioception, predominantly in the hindlimbs. Occipitoatlantoaxial malformation (OAAM) was diagnosed based on radiography and computed tomography, and confirmed on post‐mortem magnetic resonance imaging and pathological examination. Both the atlas and axis were hypoplastic and dysplastic, and a fusion of the atlanto‐occipital joint was found. A dynamic compression of the spinal cord was present at the first and second cervical vertebrae. Histologically, the spinal cord was degenerated due to compression. Furthermore, there were muscular malformations including a fibrotic obliquus capitis cranialis muscle, aplasia of parts of the rectus capitis muscles and presence of additional abnormal muscle. Such muscular abnormalities associated with OAAM have not been reported yet and this is the first report of a case of OAAM in a Warmblood horse.

Injury Threshold of Rectus Capitis Muscles at the Atlanto-occipital Joint

ObjectiveThe objective of this study was to collect muscle stiffness data from the 4 rectus capitis (RC) muscles to better understand their role in stabilizing the atlanto-occipital joint. The passive load displacement properties of these muscles have not been previously reported. MethodsRectus capitis muscles were removed from 3 unembalmed head and neck specimens. Passive length-force (stiffness) data were collected by using a servo-controlled hydraulic test machine. Multivariate analysis of variance with Bonferroni correction was used to assess the significance of the differences among passive stiffness within the elastic region of each muscle and the load and strain at the yield points. ResultsRectus capitis lateralis (RCL) muscles failed at significantly higher levels of load and strain compared with the other 3 pairs of muscles. Passive stiffness of both RCL and RC anterior muscles was significantly higher than the other 2 pairs of muscles. ConclusionThe anatomic location of the RCL muscles, along with their high levels of passive stiffness, would be expected to facilitate the maintenance of atlanto-occipital joint congruence during normal daily activities. The level at which the RC posterior minor muscles failed could put them at risk of a strain injury during a rear end motor vehicle accident. Diagnostic and treatment protocols that apply forces to the upper cervical spine should be tailored to consider the patient’s age, gender, and history of previous injuries to avoid overstretching RC muscles.

Craniovertebral junction 360°: A combined microscopic and endoscopic anatomical study.

Objectives:Craniovertebral junction (CVJ) can be approached from various corridors depending on the location and extent of disease. A three-dimensional understanding of anatomy of CVJ is paramount for safe surgery in this region. Aim of this cadaveric study is to elucidate combined microscopic and endoscopic anatomy of critical neurovascular structures in this area in relation to bony and muscular landmarks.Materials and Methods:Eight fresh-frozen cadaveric heads injected with color silicon were used for this study. A stepwise dissection was done from anterior, posterior, and lateral sides with reference to bony and muscular landmarks. Anterior approach was done endonasal endoscopically. Posterior and lateral approaches were done with a microscope. In two specimens, both anterior and posterior approaches were done to delineate the course of vertebral artery and lower cranial nerves from ventral and dorsal aspects.Results:CVJ can be accessed through three corridors, namely, anterior, posterior, and lateral. Access to clivus, foreman magnum, occipital cervical joint, odontoid, and atlantoaxial joint was studied anteriorly with an endoscope. Superior and inferior clival lines, supracondylar groove, hypoglossal canal, arch of atlas and body of axis, and occipitocervical joint act as useful bony landmarks whereas longus capitis and rectus capitis anterior are related muscles to this approach. In posterior approach, spinous process of axis, arch of atlas, C2 ganglion, and transverse process of atlas and axis are bony landmarks. Rectus capitis posterior major, superior oblique, inferior oblique, and rectus capitis lateralis (RCLa) are muscles related to this approach. Occipital condyles, transverse process of atlas, and jugular tubercle are main bony landmarks in lateral corridor whereas RCLa and posterior belly of digastric muscle are the main muscular landmarks.Conclusion:With advances in endoscopic and microscopic techniques, access to lesions and bony anomalies around CVJ is becoming easier and straightforward. A combination of microscopic and endoscopic techniques is more useful to understand this anatomy and may aid in the development of future combined approaches.

Distribution and density of contacts from noradrenergic and serotonergic boutons on the dendrites of neck flexor motoneurons in the adult cat.

Serotonergic (5-HT) and noradrenergic (NA) input to spinal motoneurons is essential for generating plateau potentials and self-sustained discharges. Extensor motoneurons are densely innervated by 5-HT and NA synapses and have robust plateau potentials and self-sustained discharges. Conversely, plateau potentials and self-sustained discharges are very rare in flexor motoneurons. The most likely reasons for this difference are that flexor motoneurons have few 5-HT and NA synapses and/or they are distributed distant to the channels responsible for plateau potentials and self-sustained discharges. However, the distribution of 5-HT and NA synapses on flexor motoneurons is unknown. Here we describe the distribution and density of 5-HT and NA synapses on motoneurons that innervate the flexor neck muscle, rectus capitis anterior (RCA), in the adult cat. Using a combination of intracellular staining, fluorescent immunohistochemistry, and 3D reconstruction techniques, we found that 5-HT and NA synapses are widely distributed throughout the dendritic trees of RCA motoneurons, albeit with a strong bias to small-diameter dendrites and to medial dendrites in the case of NA contacts. The number of 5-HT and NA contacts per motoneuron ranged, respectively, from 381 to 1,430 and from 642 to 1,382, which is 2.3- and 1.4-fold less than neck extensor motoneurons (Montague et al., J Comp Neurol 2013;521:638-656). These results suggest that 5-HT and NA synapses on flexor motoneurons may provide a powerful means of amplifying synaptic currents without incurring plateau potentials or self-sustained discharges. This feature is well suited to meet the biomechanical demands imposed on flexor muscles during different motor tasks.

Malignant Granular Cell Tumor of the Skull Base

Malignant granular cell tumors (MGCTs) are extremely rare, high-grade sarcomas of Schwann cell origin. They often metastasize and are associated with short survival. We describe a patient with a large MGCT arising from the suboccipital nerve that eroded the posterior skull base, invaded the perifocal neck muscles, demonstrated perineural extension, and metastasized to regional lymph nodes. A 60-year-old woman with several years' history of neck pain noticed a right-sided suboccipital swelling 4 months prior to seeking medical attention. Magnetic resonance imaging (MRI) showed a 5-cm bone-eroding suboccipital tumor and a second tumor, anterocaudal to this, 4 cm in diameter. The patient underwent surgery. A 4-cm multinodular tumor was removed, freeing it from the internal jugular vein. A 5-cm suboccipital tumor infiltrated the trapezius, semispinalis capitis, and longissimus capitis muscles. The major and minor rectus capitis muscles were completely engulfed by tumor and their attachments to the occipital bone completely eroded. The oblique capitis muscle was infiltrated at its attachment to the C1 transverse process. These muscles were resected with a free margin to remove all tumor tissue. We then removed tumor encasing the right vertebral artery, the medial mastoid process up to the transverse sinus and anteriorly to the stylomastoid foramen, and lastly, the posterior third of the occipital condyle, achieving a gross total removal and no visible residual on postoperative contrast-enhanced MRI. This case represents the first report of resected primary MGCT involving the posterior fossa and arising from the suboccipital nerve.

Age-related changes in the anatomical landmarks of the osseous epipharynx

We investigated age-related spatial relations of the osseous epipharynx--the region between the vomer and the anterior border of the great occipital foramen (basion) on 60 skulls of both sexes: 16 adult (age range 21-59 years), 19 aged (age range 60-86 years), and macerated occipital bones, sphenoid bones, and vomers in 25 specimens of children disarticulated skulls aged 1-15 years. We measured the distances basion-tuberculum pharyngeum, tuberculum pharyngeum-ala vomeris, tuberculum pharyngeum-crista choanalis vomeris, basion-crista choanalis vomeris, width of the pars basilaris at the level of the tuberculum pharyngeum, narrowest width of the pars basilaris, width at the level of pyramidal apexes; and width at the level of laminae mediates processus pterygoidei of the sphenoid bone. We found a statistically significant increase in the frontal and sagittal measurements of the osseous epipharynx increasing from childhood to adulthood, without further significant changes into old age. In the aged adult and skulls, the distance from the tuberculum pharyngeum to the basion was half the distance to the vomer, whereas in children the ratio of these distances was 1:3. The major difference in the bony landmarks of the osseous epipharynx between children and adults were the attachments of muscles, m. longus capitis and m. rectus capitis anterior. Whereas the most common morphological feature of the m. longus capitis attachment was a bony fossa lateral to the tuberculum pharyngeum, the muscle attached to a prominent crest in children. These previously unreported findings illustrate the role of muscle activity in the formation of osseous landmarks of the epipharynx.

Distribution of motoneurons supplying dorsal and ventral suboccipital muscles in the feline neck.

A combination of retrograde tracers was used to compare the relative distributions of motoneurons supplying the ventral and lateral suboccipital muscles, rectus capitis anterior (RCA), and rectus capitis lateralis (RCL), with those supplying dorsal muscles, including rectus capitis posterior muscles (RCP), complexus (CM), and the medial head of obliquus capitis superior (OCS). Three of the tracers, horseradish peroxidase, fluororuby, and fluorescein-conjugated dextran, were applied to cut nerve ends. Fast blue was applied by intramuscular injection, and fluorogold was delivered both by injection and by cut nerve exposure. Motoneurons supplying RCA and RCL were clustered on the medial wall of the ventral horn in a restricted region defined previously as the commissural nucleus. Labelled cells supplying RCL were confined to the C1 segment, but those supplying RCA were distributed from C1 to rostral C4. Motoneurons supplying RCA tended to lie more dorsomedially than those supplying RCL, but there was substantial overlap between the two populations. Motoneurons supplying dorsal muscles had a separate, more ventral distribution. RCP motoneurons were located primarily in the ventromedial nucleus, but a small proportion of cells was found in the white matter of the ventral funiculus or the gray matter surrounding the central canal. Motoneurons supplying CM and OCS were located dorsomedially to the RCP cell population. These results suggest that neck motoneurons are arranged according to a "musculotopic" pattern in which dorsal muscles have the most ventral locations, and progressively more lateral and then ventral muscles are layered dorsomedially along the medial wall of the ventral horn.

Suboccipital muscles in the cat neck: morphometry and histochemistry of the rectus capitis muscle complex.

The morphometry, histochemistry, and biomechanical relationships of rectus capitis muscles were examined in adult cats. This family of muscles contained six members on the dorsal, ventral, and lateral aspects of the upper cervical vertebral column. Three dorsal muscles (rectus capitis posterior major, medius, and minor) formed a layered complex spanning from C1 and C2 to the skull. Rectus capitis posterior major was composed predominantly of fast fibers, but the other two deeper muscles contained progressively higher proportions of slow fibers. One ventral muscle, rectus capitis anterior major, was architecturally complex. It originated from several cervical vertebrae and appeared to be divided into two different heads. In contrast, rectus capitis anterior minor and rectus capitis lateralis were short, parallel-fibered muscles spanning between the skull and C1. The ventral muscles all had nonuniform distributions of muscle-fiber types in which fast fibers predominated. Dorsal and ventral muscle groupings usually had cross-sectional areas of 0.5 cm2 or more, reflecting a potential capacity to generate maximal tetanic force in excess of 9 N. Biomechanical analyses suggested that one muscle, rectus capitis lateralis, had its largest moment in lateral flexion, whereas the other muscles had large, posturally dependent moment arms appropriate for actions in flexion-extension. The observation that most rectus muscles have relatively large cross-sectional areas and high fast-fiber proportions suggests that the muscles may have important phasic as well as postural roles during head movement.

Neck Injuries: I. Occipitoatlantal Dislocation—A Pathologic Study of Twelve Traffic Fatalities

Twelve of 155 persons killed in traffic crashes had occipitoatlantal dislocations. Nine were vehicular occupants, 2 were cyclists, and one was a pedestrian. The dislocations involved various combinations of lacerations of the alar ligaments, the occipitoatlantal joint capsules, the dura mater, the tectorial membrane, the rectus capitis muscles, and the suboccipital muscles. In 2 instances, an occipital condyle failed instead of the corresponding alar ligament, producing condyle fractures. Atlas ring fractures occurred in 3 instances. Axial and subaxial cervical trauma were uncommon. Facial or mandibular fractures occurred in a majority of cases, vault skull fractures were uncommon, and basilar fractures were absent. Pontomedullary brainstem lacerations occurred in 9 of the 12, and 4 had midbrain lacerations. The majority of the victims succumbed to acute neurogenic shock as the sole or the major mechanism of death. The biomechanical basis for occipitoatlantal dislocation is discussed, and the author suggests that distraction, in concert with variable combinations of extension, rotation, and posterior translation is responsible for occipitoatlantal dislocations.