Richard C. Hallgren

Anatomic Relation between the Rectus Capitis Posterior Minor Muscle and the Dura Mater

Study Design Anatomic study of the suboccipital region, specifically the deep muscles of the suboccipital triangle, was performed in cadaveric specimens. Objective To observe and describe the relationship between the deep subocipitel musculature and the spinal dura. Summary of Background Data A review of the literature revealed no reports describing a physical connection between suboccipital musculature and the spinal dura. Methods Dissections of the suboccipital region were performed in 10 embalmed and one fresh sagittally hemisected head and neck specimens. Results Aconnective tissue bridge between the rectuss capitis posterior minor muscle and the dorsal spinal sura at the atlanto-occipital junction was observed in every specimen. the fibers of the connective tissue bridge were oriented primarily parpondicular to the dura. This arrangement of fibers appears to resist movement of the dura toward the spinal cord. Conclusions Awareness of the physical relation between the rectus capitis posterior minor muscle and spinal dura via this connective tissue bridge should lesson the potential risk of durel damage during surgery. This connective tissue bridge may help resist dural infolding during head and meck extension.

Neurogenic atrophy of suboccipital muscles after a cervical injury: a case study.

This case report describes abnormalities in bilateral rectus capitis posterior minor muscles in one individual with persistent head and neck pain. These findings are muscle atrophy, fatty infiltration on magnetic resonance imaging, and electromyographic abnormalities compatible with denervated muscle. The objective of the study contained herein was to determine if fatty infiltration on magnetic resonance imaging of the rectus capitis posterior minor muscle is the result of disuse or denervation. Electromyography and magnetic resonance imaging data were collected from normal and atrophied muscles. Electromyography and magnetic resonance imaging abnormalities compatible with denervation atrophy were detected. Although we cannot rule out aging or other unknown causes, we suspect that denervation is caused by nerve damage from trauma to the C1 dorsal ramus as a consequence of entrapment within the rectus capitis posterior major muscle.

Chronic Headache Relief After Section of Suboccipital Muscle Dural Connections: A Case Report

The presence of a connective tissue bridge, attaching suboccipital muscles to the dura mater, is now recognized as a feature of normal human anatomy. The role that this myodural bridge may play in headache production is uncertain; however, a new conceptual model is emerging. Postsurgical myodural adhesions have been reported as a complication resulting from excision of acoustic tumors. Extensive research now exists implicating these myodural adhesions as a possible source of postoperative headache. Integrating these 2 types of myodural unions (anatomic and pathologic) into a unified theory of headache production, we report a single patient who experienced relief from chronic headache after surgical separation of the myodural bridge from the suboccipital musculature.

UNDERSHOOTING OF A NEUTRAL REFERENCE POSITION BY ASYMPTOMATIC SUBJECTS AFTER CERVICAL MOTION IN THE SAGITTAL PLANE

OBJECTIVE The objective of this study was to determine if blindfolded, asymptomatic subjects undershoot or overshoot a self-selected neutral reference position (NRP) when performing a full-cycle, head repositioning accuracy test in the sagittal plane. METHODS An asymptomatic group of subjects, consisting of 7 men and 5 women with no history of head and neck pain, were recruited for the study. Subjects, performing a full-cycle series of head/neck movements in the sagittal plane, attempted to return to a self-selected NRP, defined at the beginning of the movement sequence, without benefit of visual clues. Data were collected for each subject, and repositioning errors were calculated. The sign of the error was used to determine if undershooting or overshooting of the NRP had occurred. RESULTS Subjects undershot a self-selected NRP at statistically significant levels (P < .01) when performing the head repositioning accuracy test while blindfolded. Subjects undershot the NRP 83% of the time when moving from flexion to the NRP and undershot the NRP 92% of the time when moving from extension to the NRP. A Fisher exact test showed no significant difference between the number of times subjects undershot the NRP when moving from either flexion to the NRP or from extension to the NRP. To our knowledge, neither undershooting nor overshooting of an NRP has previously been reported for asymptomatic subjects at statistically significant levels. CONCLUSION Knowing that asymptomatic subjects undershoot an NRP may help to direct treatment and rehabilitation of patients who have experienced whiplash-type injuries and are shown to overshoot the NRP when performing the same test.

Electromyographic activity of rectus capitis posterior minor muscles associated with voluntary retraction of the head.

BACKGROUND CONTEXT The functional role of rectus capitis posterior minor (RCPm) muscles is not well defined. To the best of our knowledge, electromyographic (EMG) data from RCPm muscles in humans have never been collected and analyzed. PURPOSE To test the null hypothesis that there will be no difference in normalized levels of EMG activity measured from RCPm muscles with the head in a neutral position and with the head in a retracted position. STUDY DESIGN A repeated measures design intended to quantify normalized levels of EMG activity measured from RCPm muscles. METHODS Disposable 25-gauge, bipolar fine wire hooked electrodes were used to collect EMG data from both right and left RCPm muscles from 17 asymptomatic subjects. Data were collected while subjects performed five trials with the head maintained in a neutral position; performed three maximal voluntary isometric contraction efforts; performed four trials with the head maintained in a retracted position. Mixed effects beta regression models were used to analyze the data. RESULTS Normalized EMG activity of RCPm muscles collected with the subjects head held in a retracted position was significantly higher (p<.0001) than normalized EMG activity collected with the subjects head held in a self-selected, neutral position. CONCLUSIONS Rectus capitis posterior minor muscles are active when the head is held in a neutral position and show a significant increase in activity when the head is held in a retracted position.

In vitro characterization of the anterior to posterior curvature of the superior articular facets of the atlas as a function of age

BACKGROUND CONTEXT Reference is made in the literature to the inherent instability of the atlantooccipital joint in infants and young children because of pliant ligaments, undeveloped musculature, smaller condyles, and the relative lack of anteroposterior curvature of the superior articular facet surfaces of the atlas. The combination of these morphologic factors is purported to make this population particularly vulnerable to whiplash-type injuries. Although a significant difference in the magnitude of the anteroposterior curvature of the superior articular facet surfaces of the atlas between young children and adults has been observed, quantitative analysis of the curvature of these surfaces has not been documented. PURPOSE To quantify the anterior to posterior curvature of the superior articular facet surfaces of the atlas as a function of age. STUDY DESIGN This study is a retrospective analysis of the anterior to posterior curvature of the superior articular facet surfaces of the atlas as a function of age in 15 pediatric cadaver specimens from the Hamann-Todd Osteology Collection in Cleveland, Ohio, and 18 adult cadaver specimens from the Department of Experimental Anatomy in Brussels, Belgium. METHODS A stylus, connected to a three-dimensional digitizer, was used to manually define a series of points on the perimeter of the superior articular facet surfaces of the atlas of each specimen. The digitized data points were then used to generate two planes that approximated the anterior and posterior aspects of the articular surfaces in three-dimensional space. A line through a point on each plane and perpendicular to that plane was defined for each of the two planes. The angle between the two perpendicular lines was calculated and used to quantify the curvature of the facet surface. RESULTS The anteroposterior curvature of the superior articular facet surfaces of the atlas increases from an average angle of 11.5 (±4.7) degrees at 1 year of age and asymptotically approaches an average angle of 43.5 (±13.4) degrees at 80 years of age. There is a direct relationship between age and the anterior to posterior curvature of the superior articular surfaces of the atlas that can be approximated (r(2)=0.94) with a sigmoid function. Ninety percent of the final curvature is achieved at approximately 8 years of age.

A standardized protocol for needle placement in suboccipital muscles.

The objective of this study was to assess the safety and accuracy of using common anatomic landmarks to guide the placement of needle electrodes into suboccipital muscles. Atrophic changes in suboccipital muscles have been reported in some patients who have tension‐type headaches, and in some patients who have headaches resulting from whiplash‐type injuries. These atrophic changes most likely result from disuse or denervation. Needle electromyography is a definitive technique for determining the cause of muscle atrophy, but requires that needle electrodes be inserted into the muscle. Suboccipital muscles present a challenge to the electromyographer in that they are physically small and are located in close proximity to one another. Atrophied muscles with fatty replacement and the presence of critical structures such as the vertebral artery further complicate the procedure. Using a standardized protocol, three investigators attempted blind needle insertions into each of the suboccipital muscles of eight embalmed cadavers. A dissector then assessed targeted muscle penetrations, final resting positions of the wires, and their proximity to critical structures. Eighty‐one percent of 181 attempted insertions penetrated the targeted muscles: 83% for the rectus capitis posterior minor, 83% for the rectus capitis posterior major, 94% for the obliquus capitis superior, and 63% for the obliquus capitis inferior muscles, respectively. It was concluded that readily palpable external landmarks can be used to safely and reliably guide the insertion of needle electrodes into three of the four pairs of suboccipital muscles. Clin. Anat. 21:501–508, 2008.

Improved solid surface rendering with the simulated fluorescence process (SFP) algorithm

The simulated fluorescence process (SFP) algorithm (van der Voort et al., 1987) is a versatile tool for rendering realistic images obtained from a confocal scanning laser microscope. It is a simplified ray tracing algorithm that consists of two independent steps corresponding to the excitation and emission phases in a fluorescence process. Based upon rectilinear data scanning, this algorithm traces the path of a ray of light through a volume of data generating realistic shadows on succeeding voxels and ultimately upon a background plane. While the SFP algorithm excels in exploiting the inherent transparency of a confocal data set, it is sub-optimal when topographical information related to surface structure is desired. Rendering such an image can be accomplished quite easily by filtering the raw data through a depth coding function. First an adjustable threshold is set to remove background noise by separating the raw data into two regions: pixel values below the threshold are set equal to zero (totally transparent), pixel values above the threshold are added to a scaling factor that is inversely related to the distance between each visible point and the display screen. Since the intensity of raw data is directly related to the amount of fluorescence, this adjustable threshold allows one to selectively choose data points that are above a specified level of fluorescent staining. The modified data set is then passed to the standard SFP algorithm. A 70 slice set of confocal data (Z step size = 0.5pm, XY step size = 0.5pm) was obtained from a plant pollen stained with acridine orange using an ACAS 570 Interactive Laser Cytometer (Meridan Instruments Inc., Okemos, MI 48864, U.S.A.). Figure 1 shows a reconstruction of these data using the standard SFP algorithm. Figure 2 shows a reconstruction of these same data using the depth-weighted SFP algorithm. As can be seen, depth-weighting of raw data provides an effective means of enhancing visibility of surface structure.

Computer display of multidimensional biomedical data

By combining the abstract qualities of a mathematical model with the realism of an iconic model, a computer-based image rendering tool has been developed that permits accurate visualization and quantification of three-dimensional serial slice data from anatomical structures located within the human body. Such a tool also enables an investigator to model a physical system, and then to visualize the effects that manipulation of system parameters has upon the performance of the model. Three examples of the application of computer visualization techniques to medically related projects are presented in this paper: (1) visualization of three-dimensional structure and motion in the lumbar spine; (2) visualization of three-dimensional structures in the brain and the cervical spine; and (3) visualization of the effect of changes in system parameters upon the training characteristics of an artificial neural network. These applications range in complexity from the simplicity of displaying orthogonal data, to the complexity of a ray tracing algorithm. They are presented to stimulate the imagination of readers who might find applications for such a tool in their clinical practice or research program.

Activation of rectus capitis posterior major muscles during voluntary retraction of the head in asymptomatic subjects

OBJECTIVE The purpose of this study was to assess levels of electromyographic activity measured from rectus capitis posterior major (RCPM) muscles of asymptomatic subjects as their heads moved from a self-defined neutral position to a retracted position. METHODS A 2 × 2 within-subjects factorial research design was used. Disposable, intramuscular electrodes were used to collect electromyographic data from asymptomatic subjects between the ages of 20 and 40 years old. Data analysis was performed using mixed effects β regression models. RESULTS Activation of RCPM muscles was found to significantly increase (P < .0001) as the head moved from a self-defined neutral position to a retracted position. Rectus capitis posterior major muscle activation levels, measured as a function of head position, have not been previously reported. CONCLUSIONS The findings from this study showed that RCPM muscle activation significantly increases during voluntary retraction of the head.