EDITOR'S NOTE: The following is a small sample of the Interactive Spine CD in the ground breaking Primal Pictures 3-D Anatomy CD ROM series.
|Atlas (First Cervical Vertebra):
|Axis (Second Cervical Vertebra):
Articular Facet for Anterior Arch of Atlas
Slightly convex anteriorly, the short flattened anterior arch of C1 (atlas) has an anterior tubercle in the midline, giving attachment to the anterior longitudinal ligament, either side of which is the attachment of the superior oblique part of longus colli. Posteriorly, a concave circular facet articulates with the dens (odontoid process) of C2 (axis). The superior and inferior borders give attachment to the anterior atlanto-occipital membrane and anterior longitudinal ligament respectively.
On the anterior aspect of the dens (odontoid process) lies an ovoid, vertically orientated facet. It is covered with hyaline cartilage and articulates with the facet on the posterior aspect of the anterior arch of C1 (atlas) at the median atlanto-axial joint.
The clavicle is a curved subcutaneous bone extending almost horizontally from the manubrium of the sternum to the acromion and acts as a strut to hold the scapula laterally. The flat lateral end articulates with the medial aspect of the acromion and the enlarged medial, sternal end with the manubrium and first costal cartilage. The medial two-thirds of the shaft is convex anteriorly and approximately circular in cross-section. The lateral third is concave anteriorly and flattened from above downwards. With the scapula it forms the pectoral (shoulder) girdle transmitting the weight of the upper limb to the axial skeleton and facilitating the wide range of movement of the upper limb. A direct blow or indirect force may fracture the clavicle at the junction of the two curvatures. In females, the clavicle is shorter, thinner, less curved and smoother.
The lateral third has superior and inferior surfaces and anterior and posterior borders. The palpable superior border is smooth except at its margins. Posteriorly on the inferior surface at the junction of the two curvatures is the rounded conoid tubercle for the conoid part of the coracoclavicular ligament. The rough trapezoid line runs antero-laterally. The anterior border is thin, rough and concave and has a small deltoid tubercle; the posterior border is convex. A small oval articular facet for articulation with the medial aspect of the acromion faces laterally. The lateral third provides attachment for the deltoid anteriorly and trapezius posteriorly.
The medial two-thirds has anterior, superior, posterior and inferior surfaces. The posterior surface is smooth but has a roughened depression (rhomboideus fossa) medially for the costoclavicular ligament. The inferior surface is grooved laterally for the attachment of the subclavius muscle. The medial end faces medially and slightly antero-inferiorly. The inferior three-quarters is beveled, sometimes extending onto the inferior surface, for articulation with the manubrium above, which it projects.
The clavicle undergoes intramembranous ossification and is the first bone in the body to begin ossification. Medial and lateral centers appear in the shaft in the fifth and sixth weeks in-utero, and fuse with each other one week later. The medial end contributes more to growth than the lateral end. An ossification center appears in the sternal end of the clavicle between the ages of 14 and 18 years, usually two years earlier in females, fusing with the shaft between the ages of 18 and 23 years. A small inconstant lateral center appears between 18 and 20 years, this soon fuses with the shaft.
The sternoclavicular joint is a shallow, saddle-shaped joint between the manubrium and the first costal cartilage medially and the medial end of the clavicle laterally. The sternal articular surface of the clavicle is larger than that of the sternum, and is convex vertically and slightly concave in the sagittal plane. The clavicular notch of the sternum is reciprocally curved, although the surfaces are not completely congruent. The joint is lined with fibrocartilage and a fibrocartilaginous disc divides it into two synovial cavities, each lined with its own synovial membrane. The fibrous capsule surrounds the articular surfaces, thickened in front and behind but thin above and below.
The brachiocephalic vein is formed posterior to the sternoclavicular joint.
The acromioclavicular (AC) joint is a planar synovial joint between the small oval facet on the lateral end of the clavicle and the facet at the medial aspect of the acromion. The articular surfaces are lined with fibrocartilage.
A wedge-shaped articular disc is often found in the AC joint, partially separating the joint surfaces. The capsule is attached to the articular margins and reinforced by superior and inferior acromioclavicular (AC) ligaments. The coracoclavicular ligament, with its conoid and trapezoid components provides major stability to the joint.
The coccyx is formed by the fusion of three to five (usually four) coccygeal vertebrae to form a small triangular bone. The coccygeal vertebrae are usually fused and consist of rudimentary vertebral bodies, possibly with traces of transverse processes and pedicles to the level of the second vertebra. The second, third and fourth coccygeal vertebrae decrease in size as they descend.
The coccyx descends antero-inferiorly, its upper end articulating with the sacral apex at the sacro-coccygeal joint. Its orientation varies with its mobility, but generally the pelvic surface faces supero-anteriorly and the dorsal surface postero-inferiorly. It gives attachment to the sacrotuberous and sacrospinous ligaments and coccygeus, levator ani and gluteus maximus muscles.
The base is formed by the upper surface of the first coccygeal vertebral body and exhibits an oval articular facet for the sacrococcygeal disc. Postero-lateral to this facet are two processes referred to as the coccygeal cornua. The coccygeal cornua project upwards to articulate with the sacral cornua. Rudimentary transverse processes project supero-laterally from each side of the body. They may articulate or fuse with the infero-lateral sacral angle to complete the fifth sacral foramina. The interval between the body of the fifth sacral vertebra and the sacral and coccygeal cornua on each side forms an intervertebral foramen, transmitting the fifth sacral spinal nerve.
Coccygeal segments each ossify from a single primary center with that of the first ossifying at birth and the others at various intervals until the age of 20 years. The coccygeal cornua may ossify from separate centers soon after birth. The segments gradually fuse; however, fusion between the first and second segments is commonly delayed until the 30th year. In females, the coccyx often fuses with the sacrum later in life.
Eighth Thoracic Vertebra
The eighth thoracic vertebra (T8) is a typical thoracic vertebra with a heart-shaped body and a small, circular vertebral foramen; it has a larger body than that of the thoracic vertebrae above. On each side of the body are two costal demifacets for articulation with the heads of the eighth (superior facet) and ninth (inferior facet) ribs.
From the vertebral body pedicles project posteriorly and the short, thick laminae project postero-medially, overlapping the laminae of the vertebra below. A spinous process projects inferiorly from the junction of the laminae, overlapping that of T9. Anteriorly and infero-medially facing inferior articular facets are located on the inferior articular processes that project from the laminae. The pediculo-laminar junctions give rise to thin, flat superior articular processes, which face posteriorly and supero-laterally and support the oval superior articular facets. Also projecting postero-laterally from the pediculo-laminar junctions are the transverse processes, which display concave oval facets on their anterior surfaces for articulation with the tubercle of the eighth ribs.
The centrum and each half of the vertebral arch ossify from single centers that appear in-utero in the seventh week and fourth month, respectively. The arches unite during the first year and then join with the vertebral body by the fourth year. The ring apophyses (or epiphyseal rings) form secondary ossification centers at approximately 12 years and fuse with the vertebral body between the ages of 14 and 25 years. At 16 years centers also appear at the tips of the transverse and spinous processes and fuse with the rest of the vertebra by 25 years.
Secondary ossification centers may remain unfused at these sites and are known as accessory ossification centers. They must be differentiated from fracture on plain-film radiographs.
The normal vertebral column is made up of 29 vertebrae (7 cervical, 12 thoracic, 5 lumbar and 5 sacral) and the coccyx. Anteriorly, the vertebrae are connected via secondary cartilaginous joints, which form the intervertebral discs. Posteriorly, the neural arch has paired synovial joints, known as facets or zygapophyseal joints.
Contours of the Spine
The overall contour of the spine in the coronal plane is straight. However, in the sagittal plane the contour changes with development. At birth, there is a kyphotic posture to the whole spine (primary curves). With development of the erect posture, lordotic (secondary) curves develop in the cervical and lumbar spines.
Overall, spine alignment is altered in many conditions. Scoliosis, which is a descriptive term for lateral curvature, is usually accompanied by rotational abnormality as well. This can be due to congenital deformity, degeneration or associated with numerous neuro-muscular conditions. The most common type, however, is idiopathic.
One way to quantify the degree of curvature is to use the Cobb Measurement Method. The curvature is measured by drawing a line along the upper and lower end plates of the respective upper and lower vertebrae that are most tilted. The angle between these lines is then measured, usually by drawing additional lines at perpendicular angles to the end-plates.
Sagittal plane alignment can also be altered by disease and injury. This is manifested clinically with abnormal kyphosis or lordosis.
Primary spinal tumors may result from primary tumors of bone, spinal cord and nerve roots, or the meninges. The vertebral column may also be involved with secondary disease via local spread from paraspinous soft tissues, or distant spread via metastatic disease.
The majority of malignant tumors, both primary and metastatic, will originate anteriorly and involve the vertebral body and possibly one or both pedicles. Strictly posterior localization, even when more than one level is involved, is far more typical of benign lesions.
Tumors have a tendency to be located in certain parts of the vertebrae:
- Vertebral body: chordoma, giant cell tumor, hemangioma, eosinophilic granuloma, metastatic disease and multiple myeloma
- Posterior elements: aneurysmal bone cyst , osteoblastoma, osteoid osteoma and osteochondroma
- Adjacent vertebrae: aneurysmal bone cyst, chondrosarcoma and chordoma
- Multiple vertebrae: eosinophilic granuloma, metastases and myeloma