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Pathophysiology of Cervical Spondylosis, Radiculopathy, and Myelopathy

Summary of Key Points Cervical spondylosis is present radiographically in nearly 95% of the population by age 65 years. Intervertebral disc desiccation initiates the cascade of cervical spondylosis. Cervical spine ligaments and joints undergo hypertrophy and osteophyte formation to increase weightbearing surface area. Cervical spondylosis can result in axial neck pain, radiculopathy, or myelopathy. Location of the offending compression, longitudinal extent of compression, and preexisting spinal…

Chiari Malformations and Syringomyelia

Summary of Key Points The Chiari malformations are a spectrum of developmental conditions involving bone and parenchymal abnormalities of the hindbrain and craniovertebral junction. The Chiari I malformation is defined by the anatomic anomaly of cerebellar tonsil descent below the foramen magnum, causing at least one of these physiological consequences: traction or compression of adjacent neural structures and aberration of cerebrospinal fluid (CSF) flow in the…

Dural and Meningeal Pathologies

Summary of Key Points Small dural defects can lead to devastating neurological disease. Superficial siderosis, spinal cord herniation, spontaneous intracranial hypotension, and segmental amyotrophy represent a continuum of disease secondary to dural deficiencies and can present as distinct pathological entities or in combination. Superficial siderosis is characterized by hemosiderin deposition in the subpial layers of the brain and spinal cord and presents with sensorineural hearing loss…

Tarlov Cysts

Summary of Key Points Tarlov cysts are common, occurring in 1% to 2% of persons undergoing spinal magnetic resonance imaging (MRI), particularly in the sacrum. Some 10% to 30% are potentially symptomatic. Sacral nerve root compression by the cyst/s can result in lower back and sacral symptoms, including S1, S2, and S3 radiculopathy, perineal and pelvic pain, and bowel, bladder, or sexual dysfunction that can be…

Developmental Deformity in the Cervical Spine

Summary of Key Points Congenital and developmental deformities in the cervical spine are rare but clinically relevant; failure to recognize a deformity can result in otherwise preventable neurological injury. As a pediatric patient grows, the movement of the cervical spine changes with progressive caudal movement of the fulcrum of movement. As a result, the pattern of traumatic injury changes as children age. Although basilar impression is…

Craniovertebral Junction Deformities

Summary of Key Points The atlantoaxial joint is the most mobile and the most unstable joint of the body. The round and flat articular surface of the joint allows circumferential movements but makes it susceptible to instability. Apart from the more commonly identified anteroposterior type, atlantoaxial instability can also be rotatory, lateral, vertical, or translatory. Atlantoaxial instability can be diagnosed on the basis of an abnormal…

Developmental Spondylolisthesis

Summary of Key Points The etiology of development spondylolisthesis is multifactorial, and involves hereditary, traumatic, biomechanical, growth, and morphological factors. Assessment of global sagittal balance in spondylolisthesis should include a thorough assessment of the alignment of the spine, pelvis, and lower extremities. Unbalanced pelvis refers to a retroversion of the pelvis (increasing pelvic tilt) and a verticalization of the sacrum (increasing sacral slope) in an attempt…

Scheuermann Disease

Summary of Key Points Other names include Scheuermann kyphosis (Scheuermann thoracic kyphosis), Calve disease, idiopathic juvenile kyphosis of the spine, and juvenile discogenic disease. Scheuermann kyphosis is the most common cause of hyperkyphosis in adolescents aged 12 to 17 years. Although the proximate etiology remains largely obscure, there is evidence for a substantial genetic contribution. The natural history of Scheuermann kyphosis is still controversial and not…

Late-Onset Idiopathic Scoliosis

Summary of Key Points Late-onset scoliosis, or adolescent idiopathic scoliosis (AIS), as it has previously been described, is a coronal and rotational deformity that usually presents near puberty. AIS curves with greater Cobb angles are at higher risk of progression after skeletal maturity, whereas curves with lower Cobb angles tend to stabilize following skeletal maturity. Curves frequently follow very characteristic patterns, and if an unexpected pattern…

Early-Onset Scoliosis

Summary of Key Points Management of early-onset scoliosis (EOS) requires an understanding of not only spinal deformity but also of the natural history and growth of the spine, thorax, and lungs. Idiopathic EOS is a diagnosis of exclusion and should not be presumed. Magnetic resonance imaging is recommended in EOS because 13% to 25% of presumed idiopathic EOS cases will have an underlying anomaly identified on…

Congenital Spinal Deformity

Summary of Key Points Congenital spine deformity originates in early gestation, with multiple combinations of failure of formation, segmentation, and other anomalies possible. Associated vertebral, intraspinal, and visceral anomalies are common and may be clinically hidden. Screening for renal, cardiac, and intraspinal anomalies by ultrasound or magnetic resonance imaging is indicated. Congenital spinal deformities are an “early-onset spine deformity” with risk of thoracic insufficiency syndrome from…

Spinal Cord Dysraphism and Myelodysplasia

Summary of Key Points Spinal dysraphisms result from errors in neural tube development; the types and severities of spinal dysraphism can be traced back to specific events in embryogenesis. Open neural tube defects, or spina bifida aperta, include myeloschisis, meningocele, and myelomeningocele. Early closure of myelomeningoceles is vital to decrease the risk of infection and worsening neurological deficits. Closed neural tube defects, or spina bifida occulta,…

Complications in Spine Surgery: Expected Rates and Classification

Summary of Key Points Complications are common in spine surgery, with reported rates ranging from 8% to 40%. In addition to typical complications of surgery, spinal surgery presents unique complication risks, including neurological deficits, implant failure, and adjacent-segment disease, among others. Spine surgery complications can have significant impacts on surgical outcomes, health-related quality of life, costs, and value of care. Multiple attempts have been made to…

Biomechanics of Motion Preservation Techniques

Summary of Key Points Motion-preserving surgery has been developed in an attempt to reduce the likelihood of intervertebral disc degeneration at segments adjacent to a fusion. The functional spinal unit (FSU) is defined as the smallest motion segment of the spine that exhibits biomechanical characteristics representative of the physiological motion of the whole spine. As the disc degenerates, a cascade of events ensues that eventually may…

Biomechanics and Implant Materials: The Anterior Column

Summary of Key Points Interbody cages are commonly used to supplement fusion procedures and function to stabilize the anterior spine, increase the area for fusion, provide indirect decompression of nerve roots, and restore lumbar lordosis. Cages may be inserted via anterior, lateral, or posterior approaches. Cage designs incorporate features to provide immediate stability and resistance to migration, allow ingrowth of fusion, and localize the implant on…

Implant Attributes: Cantilever Beam Fixation

Summary of Key Points Cantilever beam fixation, widely used in spinal instrumentation, is described as a beam that is rigidly fixed at one end and supports a load. Each screw and rod in a segmental/nonsegmental construct is a potential cantilever. Shear stress and rotational moment are resisted at the bone–screw interface. Increasing the contact area between the bone and the screw increases yield strength. The resistive…

Spine Fusion: Biology and Biomechanics

Summary of Key Points Successful integration and mechanical performance of a bone graft in spinal fusion is a function of graft properties and the graft–host interface. The principles of osteoinduction, osteoconduction, and osteogenesis dictate bone graft incorporation, the process of graft tissue resorption and replacement with new host bone. Autograft, allograft, demineralized bone matrix, xenograft, ceramics, bone morphogenetic proteins, cellular bone matrices, mesenchymal stem cells, and…

Applied Anatomy of the Spinal Cord

Summary of Key Points The spinal cord is essential in the relay, modulation, and control of neurological information to and from the periphery. An understanding of the structural anatomy of the cord will allow for the study of its function. A spinal cord lesion can be localized, based on clinical examination and an understanding of the cord’s functional anatomy. There are three main classifications of the…

Fundamentals of Spinal Alignment and Balance

Summary of Key Points The pelvis is the foundation of the spinal column and has a primary role in determining the alignment of the spinal column. Pelvic version is important as a compensatory mechanism between mobile lower extremities and the mobile spine. Alignment is a static radiographic measurement. Balance is distinct from alignment and captures the dynamic interplay between alignment and the functional harmony of the…