CONTINUOUS LEARNING LIBRARY Anatomy Occipitocervical Anatomy Author: Dr Juan Emmerich Editor In Chief: Dr Néstor Fiore Senior Editor: Dr Luiz Gustavo Dal Oglio da Rocha OBJECTIVES CONTINUOUS LEARNING LIBRARY Anatomy Occipitocervical Anatomy ■■ To describe the anatomical areas corresponding to the occipital region and the cervical spine. ■■ To define the important points in the relationship between the spine and the neural axis. ■■ To identify relevant data to be taken into account when considering surgical approaches. ■■ To understand the region’s anatomy in terms of practical data prepared for spine surgeons, important for everyday procedures. Occipitocervical Anatomy. Author: Dr Juan Emmerich 2 CONTENTS 1. Introduction ..........................................................................................................04 Overview ........................................................................................................................................04 2. Bone structure The overall spine .........................................................................................................................06 The occipital ..................................................................................................................................07 Cervical spine ...............................................................................................................................11 3. Articulations The atlanto-occipital joint .........................................................................................................17 The atlanto-axial joint ................................................................................................................18 C2 to C7 joints.............................................................................................................................19 4. Ligaments C0, C1 and C2 ligaments ........................................................................................................22 Ligaments in the C2 to C7 region ........................................................................................24 Anterior longitudinal ligament ................................................................................................26 Posterior longitudinal ligament ..............................................................................................26 Supraspinous ligament .............................................................................................................26 Interspinous ligament ................................................................................................................26 Ligamentum flavum ...................................................................................................................27 5. Basic anatomy Posterior region ...........................................................................................................................28 Anterior and lateral regions .....................................................................................................32 Anatomical projections .............................................................................................................40 6. The spinal cord and spinal nerves Overview ........................................................................................................................................41 Cord characteristics at the occipitocervical level..............................................................43 Spinal nerve characteristics at the occipitocervical level ..............................................43 References ......................................................................................................................45 Occipitocervical Anatomy. Author: Dr Juan Emmerich 3 1. INTRODUCTION Overview These functions define the properties of the spine. ■■ A long extension that runs along the body’s entire axis. The spinal column consists of a chain of overlapping vertebrae with interconnecting ■■ 1 articulations. The spine considered as a complete unit presents the following It has a dual function. characteristics: ■■ ■■ On one hand, it forms the body’s main axis, serving as a link between the an internal channel – the spinal canal – housing the cord and its skull, thorax, abdomen and pelvis, transferring the weight in a standing protective casings; and position from the head, upper limbs and trunk, through the sacroiliac joints, to ■■ intervertebral foramina - lateral openings to allow the passage of spinal the lower limbs. nerves. ■■ On the other hand, it protects the spinal cord, the most caudal segment of Overall, the spine has the capacity for flexo-extensional, rotational and lateral the central nervous system. movements, as well as the capacity to bear axial loads. These capacities increase at more caudal points of the spine, demonstrated by the regional characteristics of the vertebrae. Atlas (C1) Atlas (C1) Atlas (C1) Axis (C2) Axis (C2) Axis (C2) Cervical curve Cervical vertebrae C7 C7 C7 T1 T1 T1 Thoracic vertebrae Thoracic curve T12 T12 T12 L1 L1 L1 Lumbar vertebrae Lumbar curve L5 L5 L5 Sacrum (S1-S5) Sacrum (S1-S5) Sacrum (S1-S5) Sacral curve Coccyx Coccyx Coccyx Anterior view Left lateral view Posterior view Complete view of the spinal column (Sobotta, 1985) Occipitocervical Anatomy. Author: Dr Juan Emmerich 4 2. BONE STRUCTURE The number of vertebrae is usually quite constant, from 33 to 35: This distribution, which is considered typical, is only present in 65% of individuals. ■■ 7 cervical; While the number of cervical and thoracic vertebrae is almost always constant, 2 ■■ 12 thoracic; any variations that do occur are usually in the number of lumbar and sacral vertebrae. In the general population, there is a high incidence of L5 assimilation ■■ 5 lumbar; by the sacrum (sacralization), and often a lack of S1 fusion with the rest of the ■■ 5 sacral vertebrae; and sacral vertebrae, resulting in an additional mobile segment (lumbarization). ■■ 3 to 5 coccygeal vertebrae This topic covers the occipital and cervical vertebrae, while the next topic shall deal with the remaining bone structures which make up the spinal axis. zygomatic arch mastoid process 1. mandibular angle transverse process of atlas 2. 3. 4. hyoid bone 5. anterior tubercle laryngeal prominence posterior tubercle 6. spinous process 7. I. I. I. II. II. III. IV. Collective view of the cranium, cervical spine and thorax (Pernkopf, 1963) IV. V. III. V. IV. Occipitocervical Anatomy. Author: Dr Juan Emmerich 5 Occipital The occipital is an unpaired, medial bone with the following articulations: Two surfaces can be differentiated: the posteroinferior, or exocranial, and the ■■ laterally with the temporal bone; anterosuperior, or endocranial. ■■ posteriorly and superiorly with the parietals bones; The foramen magnum (FM), or occipital hole, is an ample, oval-shaped orifice ■■ anteriorly and superiorly with the sphenoid bone; and with average dimensions of 35 mm in the anteroposterior direction and 30 mm 2 laterally. It has a rounded posterior margin while the anterior border is angular. ■■ inferiorly with the atlas. The posterior section of the FM is neurovascular and the following elements pass through it: frontal crest foramen caecum ■■ meninges; groove for superior sagittal sinus ala cristae galli fronto-ethmoidal suture cristae galli ■■ medulla oblongata transition; pituitary tubercle cribriform plate of ethmoid sphenoid bone dorsum sellae frontal eminences ■■ vertebral arteries; and digital impressions anterior cranial fossa ■■ anterior cranial fossa sphenofrontal suture spinal root of the accessory or spinal nerve. posterior clinoid process frontal bone optic canal superior orbital fissure arterial groove lesser wing of sphenoid bone anterior clinoid process round foramen hypophyseal fossa lingula sphenoidalis carotid groove foramen lacerum sphenosquamous suture arterial groove oval foramen petro-occipital fissure foramen spinosum medial cranial fossa medial body of the sphenoid bone cranial fossa groove for inferior temporal bone, petrosal sinus squamous part petrosquamous suture internal acoustic meatus superior margin of petrous part of temporal bone jugular foramen petrosal lesser parietal bone nerve grooves groove for greater sigmoid sinus jugular process of temporal bone, occipital bone petrous part posterior groove for superior condylar canal petrosal sinus occipitomastoid suture mastoid foramen jugular tubercle hypoglossal anterior surface of petrous canal part of temporal bone spheno-occipital synchondrosis subarcuate fossa groove for transverse sinus superior margin of petrous clivus, basilar portion of the occipital bone part of temporal bone jugular foramen foramen magnum posterior cranial fossa hypoglossal canal occipital bone internal occipital ridge posterior cranial fossa internal occipital protuberance groove for superior sagittal sinus Superior view of the cranium’s base after removing the cranial vault (Sobotta, 1985) Occipitocervical Anatomy. Author: Dr Juan Emmerich 6 Exocranial surface occipital plane external occipital protuberance occipital squama The exocranial surface has its own characteristics. highest nuchal line external occipital crest superior nuchal line lambdoid margin 2 inferior nuchal line nuchal plane lateral portion condylar fossa posterior condylar canal foramen magnum jugular process occipital condyle hypoglossal canal basilar portion Exocranial surface of the occipital bone (Sobotta, 1985) ■■ There is a rectangular lamina