Spine and Cervical Region — Surgical Anatomy and Approaches

Introduction

The spine, traversing from the base of the skull to the sacrum, presents the orthopedic surgeon with the most varied set of surgical approaches in the skeleton, reflecting both the regional anatomical complexity and the diverse pathologies encountered (degenerative disease, deformity, trauma, tumor, infection). Each region — craniocervical junction, subaxial cervical, thoracic, thoracolumbar, lumbar, sacral — has its own approach considerations, with the central principle being safe access to the bony and neural elements while protecting the adjacent neurovascular and visceral structures. The orthopedic surgeon must understand both the anterior and posterior options at each spinal level, the regional variations in anatomy (including the substantial vertebral artery considerations in the cervical spine and the thoracic outlet considerations at the cervicothoracic junction), and the principles of patient positioning that facilitate safe and effective surgery. This chapter, drawing on Orthopaedic Surgical Approaches, Rothman-Simeone The Spine, Netter’s Concise Orthopaedic Anatomy, and Gray’s Anatomy, addresses the surgical anatomy and approaches of the spine and cervical region, with emphasis on the practical considerations of each approach.

Vertebral Anatomy — Regional Variations

The general vertebral pattern includes the vertebral body anteriorly, the vertebral arch posteriorly (with pedicles, lamina, transverse processes, spinous process, and articular processes), and the vertebral foramen between, transmitting the spinal cord and its coverings. The regional variations along the spine reflect functional adaptation: Cervical vertebrae (C1-C7): The bodies are small and shallow; the spinous processes (except C1) are typically short and bifid; the transverse processes contain the foramen transversarium transmitting the vertebral artery (typically C1 through C6, with the artery typically entering at C6); the uncinate processes on the superior surface of C3-C7 form the uncovertebral (Luschka) joints; C1 (atlas) is a ring without a body, articulating superiorly with the occipital condyles; C2 (axis) has the dens (odontoid process) projecting superiorly to articulate with the anterior arch of C1; C7 has a particularly long spinous process (vertebra prominens). Thoracic vertebrae (T1-T12): The bodies are intermediate in size with costal facets (demifacets on the superior and inferior aspects for the heads of the ribs, and a single facet on the transverse process for the tubercle of the rib); the spinous processes are long and angled inferiorly (T5-T8 are the most caudally angled, projecting roughly one vertebral body below their level); the orientation of the facet joints permits limited rotation but restricts flexion-extension. Lumbar vertebrae (L1-L5): The bodies are large; the spinous processes are stout and project posteriorly; mammillary and accessory processes are useful surgical landmarks; the facets are oriented sagittally (permitting flexion-extension) but with progressively

more coronal orientation toward L5-S1; L5 has the most caudal position with significant transitional anomalies (lumbarization, sacralization) in approximately 5 percent of the population. Sacrum (S1-S5): Fused vertebrae forming the posterior pelvic ring; the ala (lateral mass), sacral foramina (anterior and posterior), and sacral hiatus are key landmarks; the medial sacral crest is the fusion of the spinous processes.

Anterior Cervical Approach (Smith-Robinson Approach)

The anterior cervical approach — developed by Smith and Robinson (1958) and refined by Cloward and others — is the workhorse approach to the anterior cervical spine for anterior cervical discectomy and fusion (ACDF), corpectomy, anterior cervical plating, and tumor or infection access.

Patient Positioning The patient is supine with the head extended (often supported by a roll under the shoulders), with the head taped or pinned in a stable position. The arms are tucked at the sides, with shoulders depressed by traction tape (allowing fluoroscopic visualization of the lower cervical levels). The neck is generally turned slightly away from the side of approach (typically the right side is the surgeon’s preference because of the more predictable course of the right recurrent laryngeal nerve, with the left-sided approach advocated by some because of the more vertical and consistent course of the left recurrent laryngeal nerve — the choice is largely surgeon preference). Surgical Anatomy The key structures encountered include: Skin and platysma muscle: The transverse skin incision is centered on the desired level (using surface landmarks: hyoid bone at C3, thyroid cartilage at C4-C5, cricoid cartilage at C6). Sternocleidomastoid muscle (SCM) retracted laterally. Carotid sheath (containing common carotid artery, internal jugular vein, vagus nerve) retracted laterally with the SCM. Strap muscles (sternohyoid, sternothyroid, omohyoid) retracted medially with the trachea and esophagus. Pretracheal fascia is opened, and the prevertebral fascia is exposed. Esophagus lies posterior to the trachea and must be protected during retraction. Recurrent laryngeal nerve (RLN): The right RLN ascends from the right vagus around the subclavian artery and is more variable in course; the left RLN ascends from the left vagus around the aortic arch and is more consistent. The RLN runs in the tracheoesophageal groove and supplies the intrinsic muscles of the larynx (except the cricothyroid, supplied

by the superior laryngeal nerve). RLN injury produces hoarseness and dysphagia; preservation of the RLN is the principal nerve concern in the approach. Sympathetic chain: Lateral to the longus colli muscles, vulnerable to injury during over- lateral dissection. Injury produces Horner’s syndrome (miosis, ptosis, anhidrosis). Longus colli muscles: Bilateral muscles overlying the anterior cervical vertebral bodies; subperiosteal elevation provides access to the bone. Approach Technique The incision is transverse along a skin crease at the appropriate level (or longitudinal along the medial border of the SCM for multilevel approaches). The platysma is divided in line with the skin incision. The deep cervical fascia is opened along the medial border of the SCM. The avascular plane between the carotid sheath (lateral) and the strap muscles (medial) is developed bluntly. The prevertebral fascia is opened in the midline (or just to one side), and the longus colli muscles are elevated subperiosteally laterally to provide bony exposure. Caspar pins or similar distraction devices are inserted into the vertebral bodies above and below the desired level. The disc or vertebral body is then approached as the procedure requires. The levels accessible through the standard Smith-Robinson approach are typically C3 to T1, with the lower levels (C6-T1) requiring careful retraction and the upper levels (C2-C3) requiring extension of the dissection upward. The C1-C2 region typically requires a different approach (transoral, retropharyngeal, or posterior).

Complications The complications of the anterior cervical approach include recurrent laryngeal nerve injury (1 to 3 percent in most series), esophageal perforation (rare but serious), vascular injury (carotid artery or vertebral artery — the latter at risk in lateral dissection), Horner’s syndrome (from sympathetic chain injury), dysphagia (very common in the postoperative period, generally transient), and adjacent segment degeneration (the long-term concern related to the biomechanical changes of arthrodesis).

Posterior Cervical Approach

The posterior cervical approach provides access to the posterior elements of the cervical spine for laminectomy, laminoplasty, posterior cervical fusion, foraminotomy, and tumor or infection access. Patient Positioning The patient is prone, with the head supported in a Mayfield head holder or horseshoe; pin fixation provides the most stable positioning for complex procedures. The neck is flexed slightly to open the posterior elements (“military tuck” position), with attention to avoiding excessive flexion that could compromise spinal cord perfusion. The shoulders are

pulled caudally with tape to allow fluoroscopic imaging of the lower cervical levels. Reverse Trendelenburg position reduces venous engorgement and bleeding. Surgical Anatomy The midline structures encountered include: Skin and subcutaneous tissue in the midline. Ligamentum nuchae: The fibrous septum in the midline that should be split rather than crossed; staying within this avascular plane minimizes muscular bleeding. Paraspinal muscles: Trapezius, splenius capitis, splenius cervicis, semispinalis capitis, semispinalis cervicis, and the deeper short muscles. These are elevated subperiosteally from the spinous processes and laminae. Spinous processes: Variable in size; the bifid spinous processes of C3-C6 should be respected during muscle elevation. Laminae: The lateral extent of dissection should be limited to avoid injury to the vertebral artery as it passes through the foramen transversarium and the dorsal exit of the cervical nerve roots. Facet joints: Lateral to the laminae; specific identification is important for fusion procedures.

Approach Technique A midline longitudinal incision is made over the spinous processes at the desired levels. The ligamentum nuchae is split in the midline, and subperiosteal elevation of the paraspinal muscles from the spinous processes and laminae is performed bilaterally. The dissection is carried laterally to the lateral border of the facet joints when needed (for facet joint fusion or screw placement). Self-retaining retractors maintain the exposure. Specific Procedures Cervical laminectomy: Removal of the lamina to decompress the spinal cord. Modern technique uses bilateral troughs (at the junction of the lamina and facet) created with high- speed burr, with the lamina removed as a unit. Laminoplasty preserves the lamina by creating a hinge on one side and an opening on the other, allowing the lamina to remain attached and to act as a posterior wall after expansion. Posterior cervical fusion: Lateral mass screw fixation (Magerl technique) is the standard, with screws placed into the lateral mass (Roy-Camille or Magerl trajectory). Pedicle screws in the subaxial cervical spine are more demanding because of the small pedicle size and the proximity of the vertebral artery; their use is selective. C1 lateral mass screws and C2 pars or pedicle screws form the basis of C1-C2 fusion constructs.

Foraminotomy: Decompression of the cervical nerve root by opening the medial wall of the facet joint and the lateral aspect of the disc space, with attention to preserving at least 50 percent of the facet to maintain stability. Complications The complications of the posterior cervical approach include vertebral artery injury (catastrophic if it occurs; prevention by precise screw placement is essential), nerve root injury (particularly C5 palsy after multilevel decompression, occurring in 5 to 10 percent of patients and typically transient), dural tear with CSF leak, infection (1 to 3 percent), and postlaminectomy kyphosis (delayed development of kyphotic deformity after laminectomy without fusion).

Anterior Approaches to the Cervicothoracic Junction

The cervicothoracic junction (C7-T2) is a challenging region for surgical access because of the transition from the cervical to thoracic anatomy and the presence of the thoracic outlet with its vascular and neural structures. Low Anterior Cervical Approach For C7-T1, the standard Smith-Robinson approach can often be extended caudally with careful retraction. The shoulders pulled caudally with traction tape allows fluoroscopic visualization; the right-sided approach may be preferred to avoid the thoracic duct (which empties into the left subclavian vein at this level). Manubriotomy or Sternotomy Approach For more caudal access (T1-T3), a manubriotomy (partial division of the manubrium) or sternotomy (full sternal split) provides extended access. The manubriotomy preserves the sternal body and allows access to the cervicothoracic junction without entry into the chest. The brachiocephalic vein, brachiocephalic artery, and left common carotid and left subclavian arteries must be carefully retracted. Trans-clavicular Approach The trans-clavicular approach (with mobilization or resection of a portion of the clavicle) provides extended lateral access to the cervicothoracic junction; it is used less commonly than the manubriotomy approach.

Anterior Thoracic Approaches

The anterior thoracic spine is accessed primarily for vertebral body pathology (fractures with anterior column involvement, tumors, infection, severe deformity). Thoracotomy The classical thoracotomy approach to the thoracic spine uses a lateral position with the convex side of the deformity (or the side of pathology) up. The skin incision parallels a rib

(typically two ribs above the desired level, since the ribs angle caudally). The latissimus dorsi, trapezius, and rhomboid muscles are divided or retracted; the serratus anterior is divided to expose the chest wall. A subperiosteal rib resection (or rib spreader without resection for some procedures) provides chest entry. The lung is deflated (using a double- lumen endotracheal tube for selective ventilation). The parietal pleura is opened over the vertebral body, with the segmental vessels identified and ligated, and the vertebral body is exposed. The right-sided approach is generally preferred for the upper and middle thoracic spine because the heart is away from the operative field; the left-sided approach is preferred for the thoracolumbar junction (T11-L2) because the diaphragm is more accessible on the left and the aorta provides a more pulsatile and identifiable landmark than the inferior vena cava on the right. The complications of the thoracotomy approach include chest wall pain (a substantial concern with the muscle-splitting approach; muscle-sparing thoracotomy has been developed to reduce this), pleural effusion (managed with chest drain), pneumonia and atelectasis, chylothorax (with thoracic duct injury at the upper levels), and intercostal nerve injury (with persistent pain). Thoracoabdominal Approach For the thoracolumbar junction (T11-L2), a combined thoracoabdominal approach with takedown of the diaphragm provides access. The diaphragm is divided around its periphery (preserving as much functional muscle as possible) to allow continuous exposure from the chest to the retroperitoneum. Video-Assisted Thoracoscopic Surgery (VATS) Video-assisted thoracoscopic surgery (VATS) uses small thoracoscopic ports rather than thoracotomy for selected indications, with reduced postoperative pain and recovery time. Applications include anterior release for scoliosis, disc removal, and selected anterior vertebrectomies; the technique is less commonly used than open thoracotomy because of its technical demands and limited reach for fusion procedures.

Anterior Lumbar Approaches

The anterior lumbar spine is accessed for anterior lumbar interbody fusion (ALIF), corpectomy, tumor or infection, and motion preservation procedures (artificial disc).

Anterior Retroperitoneal Approach The standard approach to the L4-L5 and L5-S1 levels uses a transverse or oblique flank incision with retraction of the abdominal contents anteriorly and entry into the retroperitoneum without traversing the peritoneal cavity. The left-sided approach is preferred because the great vessels (aorta and inferior vena cava) bifurcate on the right of the spine, and approaching from the left allows the aorta to be retracted with less risk of venous injury (the aorta is more easily mobilized than the inferior vena cava).

The structures encountered include: Skin and subcutaneous fat. External oblique, internal oblique, and transversus abdominis muscles — divided in line with their fibers or in the muscle-splitting plane. Transversalis fascia opened to enter the retroperitoneum. Peritoneum retracted anteromedially (the retroperitoneum is developed posterior to the peritoneal sac, preserving peritoneal integrity). Ureter identified and protected (running over the bifurcation of the iliac vessels in the typical position). Sympathetic chain identified along the lateral side of the vertebral bodies (injury produces a warm leg or altered ejaculation in males — retrograde ejaculation is a recognized complication). Common iliac vessels identified and retracted; the bifurcation typically lies at L4-L5, with the L5-S1 disc lying below the bifurcation. Anterior longitudinal ligament identified over the disc space and incised. L5-S1 Approach For the L5-S1 disc, the anterior approach proceeds below the iliac vessel bifurcation. The median sacral vessels and the superior hypogastric plexus (with its parasympathetic branches important for sexual function) must be carefully preserved. The mid-line approach with division of the anterior longitudinal ligament directly over the L5-S1 disc provides access. Mini-Open and Minimally Invasive Variants Lateral retroperitoneal approaches (XLIF, LLIF, DLIF) provide minimally invasive access to the L1-L5 disc spaces through a transpsoas approach. The patient is positioned in true lateral decubitus, and a small lateral incision is made over the appropriate level. Blunt dissection through the retroperitoneal fat reaches the psoas muscle, which is split with neuromonitoring guidance to avoid the lumbosacral plexus (lying within the psoas). The disc space is accessed laterally, with placement of a large interbody cage. The technique is limited to L1-L4-5 (the iliac crest blocks access to L5-S1), and has substantial advantages of reduced morbidity but the specific concern of lumbar plexus injury (the L4 nerve root in particular is at risk in the lower lumbar levels). Complications of Anterior Lumbar Approaches The complications of anterior lumbar approaches include vascular injury (the most feared complication, with potential for catastrophic bleeding; the left common iliac vein is at greatest risk during L4-L5 exposure), ureteral injury (rare but described), retrograde ejaculation (in 1 to 5 percent of males, from injury to the superior hypogastric plexus),

ileus, incisional hernia, and adjacent segment degeneration (the long-term concern related to fusion biomechanics).

Posterior Lumbar Approach

The posterior lumbar approach is the workhorse approach for lumbar discectomy, laminectomy, lumbar fusion (PLIF, TLIF, posterolateral fusion), pedicle screw instrumentation, tumor or infection access, and most other lumbar procedures. Patient Positioning The patient is prone, with the abdomen free (using a Jackson table or Wilson frame to allow the abdomen to hang free, reducing epidural venous engorgement and intraoperative bleeding). The arms are typically positioned with the shoulders abducted and elbows flexed less than 90 degrees to avoid brachial plexus injury. Surgical Anatomy The midline structures include: Skin and subcutaneous tissue in the midline. Thoracolumbar fascia: The thick fascial layer overlying the paraspinal muscles, opened in the midline. Paraspinal muscles (erector spinae — iliocostalis, longissimus, spinalis; multifidus deeper to these): Subperiosteally elevated from the spinous processes and laminae, with the multifidus being a particularly important muscle for spinal stability that should be preserved when possible (the Wiltse approach through the intermuscular plane between the multifidus and longissimus preserves the multifidus). Spinous processes, laminae, pars interarticularis, facet joints, transverse processes: The bony structures of the posterior lumbar spine. Pedicles: Anterior to the lamina, accessed through the entry points at the junction of the transverse process, lamina, and superior articular facet (the Roy-Camille point, modified by others). Approach Technique A midline longitudinal incision is made over the appropriate spinous processes. The thoracolumbar fascia is opened in the midline. Subperiosteal elevation of the paraspinal muscles from the spinous processes, laminae, and facets is performed bilaterally. The dissection is carried laterally to expose the bone needed for the procedure (often to the lateral margin of the transverse processes for pedicle screw instrumentation and posterolateral fusion). Self-retaining retractors maintain exposure.

Specific Procedures Discectomy and microdiscectomy: A small midline incision and limited laminotomy at the level of the disc herniation provides access for removal of the herniated fragment. The technique can be performed through tubular retractors for minimally invasive discectomy. Laminectomy: Removal of the lamina to decompress the spinal canal, performed bilaterally with attention to preservation of the facets for stability. Lumbar fusion: Includes posterolateral fusion (decorticate the transverse processes and place bone graft), posterior lumbar interbody fusion (PLIF) (bilateral entry into the disc space with placement of interbody cages), transforaminal lumbar interbody fusion (TLIF) (unilateral entry into the disc space through the foramen with cage placement), and pedicle screw instrumentation (screws into the pedicles connected by rods, providing rigid stabilization). Foraminotomy for nerve root decompression by enlarging the neural foramen.

Wiltse Approach The Wiltse paramedian intermuscular approach (Wiltse et al., 1968) develops the natural plane between the multifidus and longissimus muscles, providing direct access to the pars interarticularis, transverse process, and facet joints without midline disruption. The approach is used for pars repair, posterolateral fusion, pedicle screw placement, and lateral foraminotomy. The advantage is preservation of the midline structures and the multifidus muscle, with reduced postoperative pain. Complications The complications of posterior lumbar approaches include dural tear with CSF leak (3 to 10 percent in routine procedures, higher in revision surgery), nerve root injury, infection (1 to 3 percent in primary procedures), epidural hematoma, pseudarthrosis (failure of fusion), adjacent segment degeneration, and iatrogenic instability with progressive deformity after extensive decompression without fusion.

Pediatric Spinal Considerations

The pediatric spine introduces specific approach considerations: Smaller anatomy: The smaller anatomical scale demands precise technique and appropriate instrumentation. Open growth plates: The cartilaginous endplates and ring apophyses must be respected, particularly in young children. The vertebral body growth occurs at the endplate; the posterior elements grow at the synchondroses (between the lamina, pedicles, and body).

Triradiate-like anatomy at the vertebral level: The neurocentral synchondrosis between the body and the posterior elements is the principal growth zone for the spinal canal; iatrogenic injury produces canal stenosis. Scoliosis correction: The pediatric scoliosis correction (Topic Orth-14) uses both anterior and posterior approaches, with posterior pedicle screw constructs being the modern standard. Anterior approaches are reserved for selected indications (rigid deformity requiring anterior release, very young patients requiring extensive growth modulation). Vertebra plana: In children, eosinophilic granuloma (Langerhans cell histiocytosis) produces the classical vertebra plana deformity that usually heals with observation.

Summary and Take-Home Points

The spine offers the orthopedic surgeon the most varied set of surgical approaches in the skeleton. Anterior cervical approach (Smith-Robinson) accesses C3-T1 through a transverse skin incision and the avascular plane between the carotid sheath (lateral) and the strap muscles (medial), with the recurrent laryngeal nerve in the tracheoesophageal groove being the principal nerve concern and the vertebral artery in the foramen transversarium being the principal vascular concern (with lateral dissection limited accordingly). Posterior cervical approach through midline incision and ligamentum nuchae split accesses the posterior elements, with lateral mass screws (Magerl) being the standard fusion construct and C5 palsy being a recognized postoperative complication. Anterior thoracic approaches use thoracotomy (typically right-sided for upper thoracic, left-sided for thoracolumbar junction) with rib resection, or VATS for selected indications. The anterior lumbar approach uses retroperitoneal exposure (typically left-sided to avoid the IVC), with vascular injury (particularly the left common iliac vein) being the principal concern; retrograde ejaculation from superior hypogastric plexus injury is a recognized complication in males. Lateral retroperitoneal approaches (XLIF/LLIF) provide minimally invasive access to L1-L4-5 with the lumbar plexus in the psoas being the principal nerve concern. Posterior lumbar approach through midline incision and subperiosteal paraspinal muscle elevation is the workhorse for the lumbar spine, with pedicle screw fixation and various interbody fusion techniques (PLIF, TLIF) providing rigid stabilization. The Wiltse paramedian intermuscular approach preserves the multifidus and provides access to the lateral structures. The principles of safe spinal approach — appropriate patient positioning, understanding of regional anatomy, attention to neurovascular structures (vertebral artery in cervical, thoracic duct in cervicothoracic, great vessels in lumbar, lumbosacral plexus in lateral lumbar), and selection of approach matched to pathology — apply across all spinal regions. The pediatric spine introduces additional considerations of growing skeleton and smaller anatomical scale. The chapter that follows turns to the shoulder, beginning the systematic regional anatomy section through the upper extremity.