Neuroscience Clerkship

Neurosurgery Lecture

Anatomy of the Spine

Cervical spine

• 7 vertebrae

• Unique anatomy of C1 and C2 allows majority of flexion/extension (occiput to C1) and rotation (C1 to C2) of the head

• 8 paired nerve roots – the most rostral is numbered “1”. It emerges between the occiput and C1, and is purely motor. The remaining 7 are motor-sensory roots that emerge rostral to the corresponding numbered pedicle. That is, the C5 nerve root emerges rostral to C5 pedicle. The 8th cervical root emerges rostral to the T1 pedicle and is called C8

• C5 through C8 roots form the brachial plexus.
 

Thoracic spine

• 12 vertebrae

• 12 paired motor-sensory nerve roots that emerge caudal to the corresponding numbered pedicle. That is, the T8 nerve root emerges caudal to T8. These roots become intercostal nerves and supply the thoracic wall.
 

Lumbar spine

• 5 vertebrae

• 5 paired motor-sensory nerve roots that emerge caudal to the corresponding numbered pedicle. That is, the L3 nerve root emerges caudal to the L3 pedicle.

• The spinal cord terminates as the conus medullaris at the vertebral level of L1

• The cauda equina (latin for horse’s tail) is the bundle of spinal nerve roots within the spinal canal that arise from the lumbar enlargement and conus medullaris. It comprises all the roots from L1 and below.

• The lumbosacral plexus is the network of nerves that emerge from the spinal canal. These nerves go on to innervate the lower extremities and pelvis (i.e., femoral nerve, sciatic nerve, etc.)
 

Sacral spine

• 5 paired motor-sensory nerve roots emerge via neural foramina in the sacrum. Primary control of bowel, bladder and sexual function travels via these nerves.

SURGICAL TREATMENT  OF SPINAL DISORDERS

• Degenerative Disease

Spine problems are the 2nd most common reason why people see physicians, after viral URI. Commonly results in nerve root dysfunction (radiculopathy) or spinal cord dysfunction (myelopathy) due to disc herniations, bone spur (osteophyte) formation, stenosis (narrowing of neural foramen or spinal canal, usually seen with simultaneous disc and facet joint pathology) or deformity (kyphosis, scoliosis).

Evaluation includes plain X-rays, MRI, and occasionally CT or CT-myelogram; EMG/NCV frequently helpful; Psychosocial evaluation is essential, as many patients with depression, chronic pain, seconday gain etc. will not improve with surgery; Discography or facet injections are controversial.

Indications for surgery include: Medically unmanageable pain, sensory or motor loss, spinal cord compression, instability. Almost everyone has some degree of degenerative spine disease! Concordance of symptoms with pathology is crucial to determining who needs surgery. Acute instability is rare; glacial instability is common.

• Trauma

Causes radiculopathy and/or myelopathy in addition to local pain. Fractures and/or ligamentous injury can cause compression of neural elements by direct compression, stretching, or rarely can cause ischemic injury via hypotension or vascular trauma. Evaluation includes plain X-rays, CT, and MRI; sometimes flexion/extension films are needed.

Indications for surgery: Neural element compression, instability, deformity. Many types of fracture will heal with immobilization or no intervention. Few, if any, unstable ligamentous injuries will heal.

• Tumor

Spinal neoplasms are either intra- or extradural (almost never both). Intradural lesions require resection to prevent / stop progression of neurologic deficits, but rarely require stabilization unless extensive bony removal is required to get access to resect the tumor. Extradural tumors frequently destroy much spinal architecture, making stabilization necessary after resection. Involvement of surrounding structures (chest wall, mediastinum, retroperitoneum, pelvis, etc) frequently complicates surgery. Evaluation includes MRI and CT, sometimes biopsy to establish diagnosis.

Indications for surgery: Neural element compression causing new or progressive deficit, instability, need for tissue diagnosis. Must develop treatment plan with oncology / radiation oncology.

• Infection

Must differentiate epidural abscess from vertebral osteomyelitis / discitis. Epidural abscess is usually a surgical emergency. Complete paralysis often arises not from spinal cord compression alone, but from spinal cord ischemia due to local inflammatory thrombophlebitis. Osteo / discitis can usually be treated with antibiotics unless local tissue destruction is severe enough to cause instability. Evaluation includes MRI, also plain X-ray and/or CT to assess extent of bony destruction.

Indications for surgery: Epidural abscess, neural element compression, instability.

• Congenital

Scoliosis is most common. Typical juvenile scoliosis treated with either observation, bracing, and/or surgery depending on degree of curvature and skeletal maturity.

Techniques

• Decompression

Laminectomy, laminotomy, discectomy, corpectomy, vertebrectomy, laminoplasty, foraminotomy

• Fusion

Instrumented vs. in situ. Autograft, allograft, “extras”. Posterior onlay vs. posterior interbody vs. anterior interbody. Molecular biology: BMP, marrow cells

• Instrumentation

Pedicle screw – rod. Sacral screws. Laminar hooks – rod. Lateral mass screws with rod or plate. Anterior plates. Anterior screw-rod constructs. Interbody devices, e.g. cages (stackable, expandable, standard). Direct screw fixation of odontoid fractures. Transarticular screws.

• Minimally invasive surgery

Dilator systems, percutaneous techniques, thoracoscopic

• New stuff

Constantly evolving. Artifical discs. Bioresorbable implants. What next???

Final Thoughts

• Spine surgery is truly multidisciplinary: Requires good, knowledgeable care from PT, OT, orthotics, PM&R, Pain Management, Neurology, Radiology, etc. Often involves general or thoracic surgery.

• Absolute knowledge of spinal anatomy, physiology, biomechanics, osteobiology, and the patient are mandatory to have successful outcomes!

SURGICAL TREATMENT  OF PERIPHERAL NERVES
 

Major mixed (motor + sensory) nerves

• median
• ulnar
• radial
• musculocutaneous
• femoral
• obturator
• sciatic

Major entrapment sites

• carpal tunnel
• cubital tunnel
• tarsal tunnel

Major causes of acute injury

• bullets
• knives
• tourniquets
• fractures (Colles’, mid-humerus)

Surgical work-up

• History and physical examination are paramount!
- What are the dermatomal and myotomal deficits, do they correspond to a given peripheral nerve? To a spinal root level? To a CNS problem? To nothing?
- Physical signs: Tinel’s or Phalen’s, atrophy, fasiculations

• EMG/NCV required for all but hyperacute injuries (will not help the patient with a knife in their shoulder). Many processes do not demonstrate EMG changes for up to 6 weeks. MRI is frequently helpful for brachial plexus, nerve tumors, etc.

• Indications include a visibly divided nerve within an open wound, loss of neurological function that has been localized by EMG/NCV, and the presence of a tumor that requires a tissue diagnosis.

Surgery

• Techniques include release of entrapment, transposition, debridement/neurolysis, perineurial suture (with or without fresh autogenous nerve graft), epineurial suture, limb shortening, tendon transfer, and tumor resection.

• Postoperative care includes physical and/or occupational therapy

• Must prepare patient for what to expect: Nerves regrow at ~1mm per day, or roughly one inch per month (i.e.,. one foot per year). Thus an injury to the brachial plexus, in order to reinnervate a muscle in the hand (roughly two feet away), may take up to two years to improve.