MS2 Spine Test Questions

Describe the osteokinematics at the craniocervical region during cranial protraction (from a fully retracted position). Which tissues, if normal, would become relatively slackened in a position of full protraction?

Protraction of the craniocervical region involves flexion of the lower-to-midcervical spine and simultaneous extension of the upper craniocervical region. In the upper craniocervical region, tissues that are normally slackened in full protraction are those that are posterior to the dens or occipital condyles (such as the upper ligamentum nuchae or posterior atlanto-occipital membrane). In the mid-to-lower craniocervical region, tissues that are normally slackened in full protraction are those that are anterior to the vertebral bodies (such as the anterior longitudinal ligament).

Based on Figure 10-16, which muscle has the greatest moment arm for (a) flexion and (b) lateral flexion at L3?

Rectus abdominis for flexion and obliquus externus abdominis for lateral flexion

How could the natural elasticity of the ligamentum flavum protect the interbody joint against excessive and potentially damaging compression forces?

The elastic nature of the ligamentum flavum gradually resists flexion across the vertebral column. Gradually resisting or braking flexion can protect the interbody joints (intervertebral discs) from excessive compression.

List the bones that make up the temporal fossa of the cranium

The temporal fossa of the cranium consists of the temporal, parietal, frontal, and sphenoid bones.

Compare the distal attachments of the medial and lateral pterygoid muscles. Which attachments form a "functional sling" with the masseter muscle?

The superior head of the lateral pterygoid attaches distally to the pterygoid fossa, medial aspect of the joint capsule, and medial part of the articular disc. The inferior head of the lateral pterygoid attaches distally to the pterygoid fossa and proximal part of the neck of the mandible. Both heads of the medial pterygoid parallel the masseter muscle, attaching distally to the internal surface of the ramus and angle of the mandible. The distal attachments of the medial pterygoid course parallel to and share similar attachments with the masseter, at the angle of the mandible. The muscles form a functional sling around the angle of the mandible, assisting in the effective transfer of biting forces through the molars.

With the aid of a plastic skeleton model or other visual resource, describe the rotational (horizontal plane) action of the right scalenus anterior muscle from (A) the anatomic position, (B) a position of full rotation to the right, and (C) a position of full rotation to the left.

(A) From the anatomic position, contraction of the right scalenus anterior would rotate C3-6 vertebrae a short angular distance to the right, likely only about 5-10 degrees. At about this position, the line of force of the muscle would pass directly through the vertical axis of rotation of the cervical region, thereby losing effective leverage for continued rotation. (B) From a position of full rotation to the right, contraction of the right anterior scalane would rotate C3-6 vertebrae to the left, back toward the anatomic position. (C) From a position of full rotation to the left, contraction of the right anterior scalane would rotate C3-6 vertebrae to the right, back toward the anatomic position. Answers B and C reinforce an important global kinesiologic point. When the cervical spine is rotated well outside the anatomic position, the scalenus anterior has the ability to return the cervical spine back toward the anatomic position. Restricting an analysis of the axial rotation potential of this muscle (and other scalenes) strictly from the anatomic position limits one's appreciation of the muscle's full potential actions within this plane. This point also applies to other muscles in the body.

What is the primary difference between a dorsal ramus of a spinal nerve root and a dorsal nerve root?

A dorsal ramus of a spinal nerve is a mixed nerve (containing both sensory and motor fibers) that innervates tissues associated with the back. A dorsal nerve root is set of sensory fibers that enter the spinal cord at a specific spinal nerve root level.

Explain how a severely degenerated disc can lead to osteophyte formation in the midcervical spine.

A severely degenerated disc can reduce the intervertebral space and cause increased compression on the apophyseal and uncovertebral joints. In the midcervical region, increased compression within the uncovertebral joints may stimulate osteophyte formation in the area of the exiting spinal nerve roots. The osteophytes may compress the nerve root, causing neurologic symptoms throughout the ipsilateral upper extremity.

Explain, in theory, how an overly depressed scapulothoracic joint could predispose derangement of the articular disc of the TMJ.

An overly depressed scapulothoracic joint can stretch and thereby increase the resting tension in the omohyoid. In theory, this tension can be transferred upward and forward to the hyoid bone and the suprahyoid muscles, and ultimately to the mandible. The force may pull the mandible inferiorly and posteriorly slightly, creating abnormal alignment of the mandibular condyle and disc relative to the mandibular fossa. Over time, the increased stress on the disc may trigger spasm in the lateral pterygoid muscle, potentially perpetuating the abnormal alignment of the disc and leading to its chronic derangement.

From an anterior to posterior direction, list, in order, the connective tissues that exist at the atlanto-axial joint. Start anteriorly with the anterior arch of the atlas, and finish posteriorly at the tips of the spinous processes. Be sure to include the dens and transverse ligament of the atlas in your answer.

Anterior arch of the atlas, dens, transverse ligament of the atlas, tectorial membrane, meninges surrounding the spinal cord, posterior atlanto-occipital membrane, ligamentum nuchae.

Assume a person has a complete spinal cord injury at the level of T8. Based on your knowledge of muscle innervation, predict which muscles of the trunk would be unaffected and which would be partially or completely paralyzed. Consider only the abdominal muscles, multifidi, and erector spinae in your response.

Assuming no innervation below the T8 vertebral level, you would generally expect the following: (a) The multifidi would show essentially normal strength above T8 and complete paralysis below T8. (b) The erector spinae would show normal to near normal strength above T8 and complete paralysis below T8. (Weakness may persist in some muscle fibers above T8 because of the reduced stabilization of the more [paralyzed] inferior parts of the muscle.) (c) Only the most superior fibers of selected abdominal muscles would remain innervated. Paralysis of the muscle group would be nearly complete. From a practical perspective, however, as a group, the abdominal muscles would likely be considered nonfunctional. Clinical scenarios often vary due to partial or asymmetric trauma to the spinal cord, a combined injury to the exiting spinal nerve roots, and the natural variability in muscle innervation.

Describe the functional role of the oblique fibers of the lateral ligament of the TMJ during opening the mouth.

At the end of the early phase of opening the mouth, the rotated condyle of the mandible stretches the oblique fibers of the lateral ligament of the TMJ. The increased tension in the ligament helps initiate the forward translation of the mandible—the primary arthrokinematics of the late phase of opening the mouth.

As indicated in Figure 10-29, why is the axial rotation function of the rectus capitis posterior major muscle limited to the atlanto-axial joint only?

Axial rotation is not considered a degree of freedom at the atlanto-occipital joint

. Justify why an isolated strong contraction of the semispinalis thoracis would likely produce contralateral axial rotation, whereas a strong isolated contraction of the longissimus cervicis or capitis would likely produce ipsilateral axial rotation. Use Figures 10-7 and 10-9 as a reference for answering this question.

Based on fiber direction, the resultant force produced by each muscle in question could be trigonometrically resolved into horizontal and vertical components. Although considerably less than the muscle's vertical force component, the horizontal force component would produce some magnitude of axial rotation torque. Assuming a strong contraction directed from a cranial-to-caudal direction, each muscle would produce either a contralateral or an ipsilateral rotation. A contraction of the left semispinalis thoracis, for example, would pull the spinous processes to the left, causing the body (front) of the vertebrae to rotate to the right. Furthermore, contraction of the left longissimus capitis, for example, would pull the left mastoid process of the temporal bone to the right (toward the midline), causing the front of the cranium to rotate to the left. From the anatomic position, the line of force of these muscles for horizontal plane rotation is slight to moderate. By observing Figures 10-7 and 10-9, appreciate that the line of force of each muscle is more favorable for axial rotation if the contraction starts from a position that is opposite to the muscles' rotation action.

Explain the function of the temporalis muscles in closing the mouth.

By attaching to and near the coronoid process, contraction of the temporalis pulls the mandible upward, thereby closing the mouth and opposing the teeth. The posterior oblique fibers of the muscle elevate and retrude the mandible, effectively reseating the condyle and disc within the mandibular fossa.

At the level of the third lumbar vertebra, which connective tissues form the anterior rectus sheath (of the abdominal wall)?

Connective tissues that are associated with the obliquus externus abdominis and the obliquus internus abdominis.

Describe how the inferior head of the lateral pterygoid muscle and the suprahyoid muscles act synergistically during a rapid opening of the mouth.

During a rapid opening of the mouth, the inferior head of the lateral pterygoid pulls the mandible forward as the suprahyoid muscles pull the mandible posterior and superior. As shown in Figure 11-22A, these muscles act as a force couple for opening the mouth, each pulling on either side of the axis of rotation.

Describe arthrokinematics at the apophyseal joints between C4 and C5 during full extension.

During full extension, the inferior articular facets of the C4 apophyseal joints slide generally inferiorly and posteriorly across the full extent of the surface of the superior articular facets of the C5 apophyseal joints.

Using Figure 11-22 as a guide, describe the specific function of the lateral pterygoid muscle during opening and closing of the mouth.

During opening of the mouth the inferior head of the lateral pterygoid pulls the neck of the mandible forward. Because this pull is superior to the axis of rotation, the muscle contraction "swings" the mandible open. During closing of the mouth, the superior head of the lateral pterygoid acts eccentrically to help guide the posterior migration of the disc back to its resting position. The activation of the superior head of the lateral pterygoid also limits (or balances) the retrusion pull on the condyle by the posterior oblique fibers of the temporalis muscle.

Explain the mechanism by which the intermediate region of the articular disc within the temporomandibular joints protects the joint throughout the late phase of opening the mouth.

During the late phase of opening the mouth the articular disc translates forward along with the forward translating mandibular condyle. These mechanics maintain the position of the intermediate region of the disc between the superior aspect of the mandibular condyle and the dense articular eminence. This position of the disc increases the surface area for dispersing joint forces, thereby reducing potentially damaging joint stress.

As a group, the trunk extensor muscles produce greater maximal-effort torque than the trunk flexor muscles (abdominals). Cite two factors that can account for this difference in strength.

First, the cross-sectional area of the trunk extensor exceeds that of the abdominal muscles. Second, as a group, the average fiber direction of the trunk extensor is more vertically oriented than the abdominal muscles.

Why are the superficial and intermediate muscles of the posterior back classified as "extrinsic" muscles? Describe how the specific innervation of these muscles is associated with this classification.

From an embryologic perspective, the deep muscles of the posterior back have retained their original location near the neuraxis. For this reason these muscles are classified as "intrinsic" muscles of the back. In contrast, the superficial and intermediate muscles of the back have migrated from their original location within the limb buds to their final location in the back region. These muscles are embryologically associated with the extremities and therefore classified as "extrinsic" muscles of the back. Extrinsic muscles of the back are innervated by nerves that branch for the ventral ramus of spinal nerves.

Describe the similarities and differences in the structure of the multifidi and the semispinales muscles.

In general, the multifidi and most of the semispinales muscles attach between transverse and spinous processes. The specific attachments of these muscles differ, however, in at least two ways: (a) the semispinales cross 6-8 intervertebral junctions, whereas the multifidi span only 2-4; (b) the multifidi are most developed in the lumbar region, the semispinales in the cranial region.

Describe the mechanical role of the annulus fibrosis in distributing compression forces across the interbody joint.

Increasing the intervertebral joint compression increases hydrostatic pressure within the nucleus pulposus. The increased nuclear pressure pushes radially (outward), as it is resisted and partially absorbed by tension in the stretched annulus fibrosis. The combined nuclear pressure and taut annular rings help support and evenly distribute intervertebral compression. Tears or weakness within the annulus fibrosis reduce the effectiveness of this load absorption system.

Which of the major trunk muscles would experience the most significant stretch (elongation) after a motion of full trunk extension, right lateral flexion, and right axial rotation?

Left internal oblique muscle.

Persons with a history of a posterior herniated disc are usually advised against lifting a large load held in front the body, especially with a flexed lumbar spine. How would you justify this advice?

Lifting a large load held in front of the body can generate large muscular-based compression forces across the lumbar intervertebral discs. Lifting with a flexed lumbar spine converts the large compression force to a large disc pressure. Lumbar flexion tends to direct the flow of the nucleus pulposus in a posterior direction. If degenerative clefts exist in the annulus, the nucleus may flow posteriorly in the direction of the sensitive neural elements.

Define nutation and counternutation at the sacroiliac joint

Nutation is a sacroiliac joint tilt (rotation) consisting of an anterior sacral-on-iliac tilt and/or a posterior iliac-on-sacral tilt. Counternutation, a reverse movement, consists of a posterior sacral-on-iliac tilt and/or an anterior iliac-on-sacral tilt.

Assume the subject depicted in Fig. 9-10C has increased lumbar lordosis caused primarily by tightened (shortened) hip flexor muscles. Describe the possible negative kinesiologic or biomechanical consequences that may result within the lumbar and lumbosacral regions.

Significantly increased lumbar lordosis may be associated with the following negative kinesiologic consequences: 1. Increased stress on fully extended lumbar apophyseal joints 2. Increased sacrohorizontal angle and resultant increased anterior shear forces at the L5-S1 junction 3. Reduced size of the intervertebral foramina and possible compression of the exiting lumbar spinal nerve roots

Describe the synergistic relationship between the masseter and contralateral medial pterygoid muscle during the production of shearing (grinding) force between the molars.

Strong contraction of the left masseter and the right medial pterygoid muscles, for example, elevates the mandible, generating a biting force. In addition, the left masseter draws the mandible to the left as the right medial pterygoid also draws the mandible to the left. (This lateral excursion action is enhanced if the muscles are activated from a position of right lateral excursion.) The biting force in conjunction with the left lateral excursion of the mandible can generate very effective shearing forces between the molars.

Based on moment arm length alone, which connective tissue most effectively limits flexion torque within the thoracolumbar region?

Supraspinous ligaments are located farthest posterior to the medial-lateral axis of rotation through the body of each vertebra. This position maximizes the tissue's moment arm for resisting a flexion torque.

Compare the different functional demands placed on the dome of the mandibular fossa and the articular eminence of the temporal bone while chewing

The demands placed on the dome of the mandibular fossa during chewing are typically small. In contrast, the demands placed on the articular eminence of the temporal bone are large. This large demand (stress) placed on the articular eminence is normally reduced by the coordinated action of the articular disc.

Describe the general transition in spatial orientation of the articular surfaces of the apophyseal joints, starting with the atlanto-axial joint and finishing with the lumbosacral junction. Explain how this transition influences the predominant kinematics across the various regions. Include in your answer the kinematics associated with the most often expressed spinal coupling pattern within the mid and lower craniocervical region.

The facet surfaces within the apophyseal joints throughout the vertebral column have a specific spatial orientation, which affects the predominant osteokinematics within each region (see Table). Region Kinematics Predominant Spatial Orientation Primary Effect of the Apophyseal Joints Atlanto-axial joint Near horizontal plane Favors axial (horizontal plane) rotation Intracervical (and upper thoracic) region Between horizontal and frontal planes Favors the combination of axial rotation and lateral flexion kinematics* Midthoracic region Near frontal plane Favors lateral flexion, although not fully expressed because of the splinting action of the ribs Lumbar (and lower thoracic region) Near sagittal plane Favors flexion and extension (and limits axial rotation) Lumbosacral junction Near frontal plane Limits excessive anterior translation of L5 on S1 *Partially responsible for the lateral flexion/axial rotation ipsilateral coupling pattern of the mid-to-lower cervical spine.

Are the intertransverse ligaments between L3 and L4 positioned to limit sagittal plane rotation? If so, which motion?

The intertransverse ligaments limit flexion based on their location posterior to the medial-lateral axis of rotation through the body of the corresponding lumbar vertebrae.

Describe the arthrokinematics at the apophyseal joints between L2 and L3 during full axial rotation to the right.

The left inferior articular facet of L2 approximates (or compresses) against the left superior articular facet of L3, and the right inferior articular facet of L2 gaps (separates) from the right superior articular facet of L3.

Which ligament of the sacroiliac joint is slackened by the motion of nutation? Why?

The long posterior sacroiliac joint ligament is slackened by nutation, a motion that brings the attachment points of this ligament closer together. This is in contrast to the increase in tension (i.e., due to stretch) in the other ligaments by nutation of the sacroiliac joint, a motion that naturally stabilizes the joint.

List structures that receive sensory innervation from the recurrent meningeal nerve. What nerves provide sensory innervation to the capsule of the apophyseal joints?

The recurrent branch of the meningeal nerve is a segmental nerve that is responsible for carrying sensation from the meninges of the spinal cord, posterior longitudinal ligament, and more superficial regions of the annulus fibrosis. Sensory innervation from the capsule of the apophyseal joint is supplied by afferent fibers within dorsal rami of local spinal nerves.

List three muscles that attach to anterior tubercles and three that attach to posterior tubercles of transverse processes of cervical vertebrae. What important structure passes between these muscle attachments?

The scalenus anterior, longus colli, and longus capitis attach to anterior tubercles of cervical transverse processes. The scalenus medius, splenius cervicis, and longissimus cervicis attach to posterior tubercles of cervical transverse processes. The brachial plexus passes between these two sets of muscles.

Describe the articulations between the sixth rib and the midthoracic spine.

The sixth rib attaches to the thoracic spine by costocorporeal and costotransverse joints. At the costocorporeal joint, the head of the sixth rib articulates with the pair of demifacets located at the T5-T6 intervertebral junction. At the costotransverse joint, the articular tubercle of the sixth rib articulates with the costal facet on the transverse process of T6.

With the visual aid of Fig III-1 (in Appendix III, Part A), explain why a severe posterior herniated disc between the bodies of L4 and L5 can compress the L4 spinal nerve root, but possibly L5 and all sacral nerve roots as well.

The spinal cord ends approximately at the L1 vertebral level. The spinal nerve roots that flow caudally from the end of the spinal cord form the cauda equina, which occupies the vertebral canal of most of the lumbar and sacral vertebrae. Disc material that protrudes posteriorly into the vertebral canal adjacent to L4 and L5, for example, could potentially impinge on all remaining fibers within the cauda equina, which includes all sacral nerve roots.

As described in the chapter, the Valsalva maneuver is often used as a way to increase pneumatic-based stability within the lumbopelvic region when lifting or performing other activities. List three muscle groups within the axial skeleton that are directly involved with this activity, and describe the common mechanical principle by which they, acting in concert, increase stability within the region.

Three muscle groups directly involved in the Valsalva maneuver are the diaphragm, deep abdominal muscles, and the pelvic floor muscles. Coordinated contraction of the muscles reduces intra-abdominal volume (abdominal muscles pulling in, diaphragm pulling down, and pelvic floor muscles pulling up), thereby increasing pressure within this sealed cavity.

Describe the most likely craniocervical posture resulting from (a) unilateral and (b) bilateral spasm (or shortening) in the sternocleidomastoid muscle(s).

Unilateral shortening of the sternocleidomastoid typically results in varying amounts of flexion (especially in the lower region), lateral flexion, and contralateral rotation of the craniocervical region. Bilateral shortening of the sternocleidomastoid typically results in a protracted posture of the craniocervical region: slight flexion of the mid- and lower craniocervical region with slight extension of the upper craniocervical region.

Describe how an overshortened (contracted) iliacus muscle can cause an increased lumbar lordosis while a person is standing. What effect could this posture have on the stress at the lumbosacral junction?

While in a standing position, a contracted iliacus muscle rotates the ilium (pelvis) anteriorly toward the femur. Assuming the trunk is maintained upright, this movement is typically described as an excessive anterior tilt of the pelvis. The lumbar spine is forced to rotate into extension, which increases its lordosis. Excessive lumbar lordosis is likely associated with an increased sacrohorizontal angle and an increased anterior shear force at the L5-S1 junction.