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Harris ring

A Harris ring is a ring-like shadow observed at the base of the odontoid process on a lateral radiograph of the cervical spine. It is formed by the superimposition of the lateral masses of the C2 vertebra (axis) on its body. Disruption of the Harris ring is seen in type III, and less commonly, ...

Brain and Spinal Cord Injury Center score

The Brain and Spinal Injury Center (BASIC) score is a classification system for grading acute traumatic spinal cord injury based on the axial extent of intramedullary signal abnormality on T2 weighted MRI. Classification The BASIC score is an ordinal scale that is graded 0 to 4 1: BASIC 0 (no...

Collar sign in spondylolysis

The Collar sign in spondylolysis refers to a break in the pars interarticularis of the vertebra on oblique radiographs that can have the appearance of a collar around the Scotty dog's neck. unilateral or bilateral 90% seen at the L5 level and less than10% noted at the L4 level1,2 65% of patie...

Superior hypogastric nerve block

Superior hypogastric nerve block is a valuable tool for pain relief in the setting of uterine fibroid embolization. This procedure results in significant ischemic pain, peaking at 6-8 hours and lasting approximately 24 hours, then followed by a lesser degree of post-embolization pain which can l...

Supraodontoid space

The supraodontoid space, also known as the supradental space or apical cave, is an extradural space at the anterior craniocervical junction superior to the odontoid process of C2 (dens axis). Gross anatomy Boundaries The space is a cave-shaped region facing posteriorly with the following boun...

Tuli classification of occipital condyle fractures

The Tuli classification of occipital condyle fractures is a clinically-oriented system for describing these injuries based on fracture displacement and ligamentous injury. It is newer than the more well-known Anderson and Montesano classification of occipital condyle fractures and allows the inc...

Bow-tie sign

"Bow-tie sign" refers to the appearance of rotated facets in unilateral facet joint dislocation. Facet joint displacement coupled with a rotational deformity gives a bow-like like appearance on a lateral view radiograph of spine 1.

Autonomic nervous system

The autonomic nervous system (ANS) is a subdivision of the peripheral nervous system. The autonomic system provides innervation of the involuntary muscles, i.e. myocardium and smooth muscle, and glands, through which fine control of homeostasis is maintained. The afferent innervation of the aut...

Pincer/split fracture

Pincer or split fractures are coronally oriented vertebral body fractures that involve the superior and inferior vertebral body endplates but do not involve the anterior or posterior cortices. Clinical Presentation Pincer fractures may present in the setting of trauma, with an axial loading m...

Kemp test

The Kemp test (also known as the quadrant test and extension-rotation test) is a provocative test on clinical examination that has been described as being useful for diagnosing pain related to facet joint pathology, e.g. arthropathy but is of limited diagnostic accuracy 1. The patient performs c...

Elsberg syndrome

Elsberg syndrome is an established but rarely recognized cause of cauda equina syndrome and lower thoracic myelitis, associated with a presumed infectious etiology. Epidemiology Elsberg syndrome is likely responsible for 10% of combined cauda equina syndrome and myelitis 1. Clinical presenta...

Axial spondyloarthritis

Axial spondyloarthrititis (SpA) is a clinical subset of the seronegative spondyloarthritides that present primarily with back pain and morning stiffness. There is a long delay, on average 14 years, between symptoms onset and diagnosis 1. Epidemiology The prevalence of axial SpA is ~1% 1. Age o...

Hip spine syndrome

Hip spine syndrome is one term used to describe the clinical association between hip osteoarthritis and degenerative lumbar spinal canal stenosis due to overlapping pain distribution. Clinical presentation Patients with hip spine syndrome have hip and lumbar spine degeneration and present wit...

Trefoil appearance of spinal canal

A trefoil appearance of spinal canal (sometimes termed as a cloverleaf spinal canal appearance) is a particular appearance that is of congenital or acquired etiology. This is mainly described in the lumber region and can result in narrowing of the lateral recesess as well as at times involvement...

Lumbar spinal stenosis (grading)

Lumbar spinal stenosis grading refers to systems for classifying the severity of central spinal canal narrowing around the cauda equina nerve roots. Usage The two most popular systems, both applied to visual assessment of MRI, are the Lee grading system, and the Schizas grading system. Both t...

Anterior instrumentation and fusion (scoliosis)

Anterior instrumentation and fusion is a surgical procedure used in patients with adolescent idiopathic scoliosis to correct vertebral curvature. This technique is preferred to posterior instrumentation and fusion in skeletally immature patients with a Lenke 5C thoracolumbar or lumbar adolescent...

Scoliosis surgery (overview)

Scoliosis surgery is indicated when conservative management has failed. Indications Cobb angle ≥45º (skeletally immature) or ≥40-50º (skeletally mature) 1,2 progressive scoliosis deformity spinal functional compromise pain not responsive to non-operative treatment pulmonary function compro...

Degenerative spinal instability

Degenerative spinal instability is frequent although somewhat controversial clinical entity with evolving theories on its clinical relevance, in particular, its role as a causative factor of low back pain (LBP). While radiographic instability may be evident, this does not always correlate with t...

Spinal instability (overview)

Spinal instability is a broad term with no generally agreed-upon definition but can be thought of the potential for or actual abnormal segmental spinal motion. Terminology Spinal microinstability refers to abnormal segmental movement without bony changes 1. Pathology Spinal instability is ...

Discectomy

Discectomy is the most common surgery for lower back pain performed for the treatment of disk herniations. It is often combined with other spinal procedures as laminotomy or foraminotomy or artificial disk replacement and other forms of spinal fusion. Discectomy techniques can be generally subdi...

Anterior vertebral body tether (AVBT)

Anterior vertebral body tethering (AVBT) is a fusionless technique for treating and managing idiopathic scoliosis in skeletally immature patients to reduce the typical side effects of rigid posterior fusion (such as loss of spinal motion and risks adjacent segment degeneration later in life) 1,3...

Vertical expandable prosthetic titanium rib (VEPTR) procedure

Vertical expandable prosthetic titanium rib (VEPTR) procedure is a surgical technique that was initially developed to treat thoracic insufficiency syndrome and then it was used in congenital scoliosis with rib abnormalities, and has since been successfully used to treat early-onset scoliosis wit...

In situ contouring

In situ contouring is a surgical technique used in thoracolumbar scoliosis surgery and thoracolumbar fracture reduction and fixation. Procedure Thoracolumbar scoliosis surgery The key of this technique is to " make the rod take the shape of the spine and then to make the spine take the shape...

In situ spinal fusion

In situ spinal fusion is, as the name suggests, where fusion is performed without a change in alignment. It is a technique used to treat: isthmic spondylolisthesis 1 osteogenesis imperfecta 2

Posterior dynamic lumbar stabilization

Posterior dynamic lumbar stabilization is an alternative instrumented method to rigid spinal fusion aiming to improve segmental stability. Purported advantages of this technique include reduced posterior element and intervertebral disc loading reducing symptoms and potentially allowing for disc ...

Stork test

The Stork test (also known as the Gillet test) is a clinical test used to assess the movement (intrapelvic motion) of the sacroiliac joint between the innominate bone and sacrum. It can be useful in evaluating suspected sacroiliac joint pathology / dysfunction. It involves placing the examiner'...

Lumbar disc arthroplasty

Lumbar disc arthroplasty is a procedure involving the replacement of lumbar intervertebral discs with artificial discs to manage lower back pain. Similar to its cervical counterpart (cervical disc arthroplasty), it is an alternative to fusion procedures as a means of maintaining an increased ra...

Implant migration

Implant migration or hardware migration refers to the displacement of an implant or component away from its designated position and is associated with hardware failure and loosening. Examples of implant migration include screw break out or screw back out, cage extrusion, inlay extrusion, choledo...

Osseous surgical spinal fusion

Osseous surgical spinal fusion refers to spinal fusion surgery with bone grafts, bone graft supplements or bone graft substitutes. Osseous spinal fusion eventually supplies the best stability for the respective spinal segment and most types of spinal fusion surgeries are directed to establish a...

Posterior instrumentation and fusion (scoliosis)

Posterior instrumentation and fusion is a surgical technique to improve spinal curvature in scoliosis patients. Procedure The vertebral column is manipulated into the desired position and held in place with metalwork namely pedicle screws and/or hooks transfixed with rods with or without in si...

Spinal instrumentation hardware

Spinal instrumentation hardware refers to various types of implants used for fixation in spinal surgery. They can be used in various combinations and include wires, clamps, screws, different plate-screw and rod-screw interfaces, intervertebral prostheses and disk replacements. Cervical spine in...

Congenital scoliosis

Congenital scoliosis refers to scoliosis resulting from a congenital abnormality of the vertebra, e.g. a segmentation or fusion defect. Terminology There are several definitions of congenital scoliosis. Some authors include neurological congenital causes. In this article, our focus will only ...

Neuromuscular scoliosis

Neuromuscular scoliosis is a term that can be used to describe scoliosis that is caused by underlying brain, spine or muscular conditions. While the underlying conditions can be a very broad group of disparate conditions, they tend to result in similar spinal curves. Radiographic features Neur...

Interspinous device

Implantation of interspinous devices is one option for treating lumbar canal stenosis and other causes of low back pain. These devices attempt to produce lumbar flexion by distracting the lumbar spinous processes restoring height and resulting in tightening of the thickened ligamentum flavum, an...

Hardware failure

Orthopedic implant or hardware failure refers to the failure of the implant to live up to its expected requirements with respect to the manufacturer's or the surgeon's allegations. This includes any complication directly related to the implant such as wear, fractures, dissociations and dislocati...

Craniocervical fixation

Craniocervical fixation, instrumentation or occipitocervical fusion refer to surgical fixation techniques with the goal to stabilize the craniocervical junction. History and etymology An occipitocervical fusion with fibular only bone graft was already described by Forrester in 1927 1,2. Severa...

Atlantoaxial fixation

Atlantoaxial fixation refers to various surgical techniques to stabilize the atlantoaxial complex. History and etymology The first effort of an atlantoaxial stabilization was made by Mixter and Osgood in 1910 by fixation of the spinous processes with a heavy silk thread 1,2. Posterior cervic...

Odontoid process fixation

Odontoid process fixation or odontoid process repair refers to the surgical fixation of an odontoid fracture. Anterior odontoid screw fixation is performed with single and double screw techniques, non-cannulated and cannulated screws, and uni- or bicortical fixation techniques. Odontoid plate ...

Osteoporotic vs pathological vertebral fractures

Discriminating between acute osteoporotic and pathological vertebral fractures is sometimes challenging. This may be especially true in the elderly population, in which both osteoporosis and malignant disease often co-occur, and vertebral fractures of both kinds are common and indeed may coexist...

Oblique lumbar interbody fusion (OLIF)

Oblique lumbar interbody fusion (OLIF) is one of several techniques used in lumbar interbody fusion. It provides minimally invasive access to the disc space, passing between the peritoneum and the psoas muscles. Indications Indications for the procedure generally overlap with those of LLIF and...

Posterior cervical fusion

Posterior cervical fusion refers to a surgical spinal fusion technique of the cervical spine for conditions requiring posterior stabilization. It might be done for the management of cervical spine fractures or combined with spinal decompression techniques such as laminectomy or laminotomy. Hist...

Posterior sacroiliac ligament

The posterior (a.k.a. dorsal) sacroiliac ligament (TA: ligamentum sacroiliacum posterius) is a very strong ligament important in stabilizing the sacroiliac joint. Gross anatomy Some texts state that the posterior sacroiliac ligaments have two components; a more superior part, the short posteri...

Complications of spinal surgery

Complications of spinal surgery are common and can occur at different time intervals after the surgery. Some of them are related to instrumentation, the procedure and/or the approach others are not. Anyhow, it is essential for the radiologist to be aware of them in the assessment of radiographs,...

Paraspinal muscles

The paraspinal muscles (PSM) , also known as paravertebral muscles, is a descriptive term given to those muscles that closely surround the spine, primarily the thoracolumbar spine. There has been great research interest in using the cross-sectional area of these muscles as a measure of overall m...

Laminotomy

A laminotomy is a spinal decompression procedure with partial removal of the vertebral arch usually at its base. Laminotomies might be combined with other spinal procedures such as discectomy or spinal fusion procedures. If a laminotomy is combined with a foraminotomy, then the procedure is call...

Cervical disc arthroplasty

Cervical disc arthroplasty is a procedure involving the replacement of degenerative cervical intervertebral discs with artificial discs to enable decompression of the cervical spinal cord. This procedure is an alternative to anterior cervical discectomy and fusion (ACDF) and avoids the loss o...

Posterolateral lumbar fusion

Posterolateral lumbar fusion is an alternative technique to lumbar interbody fusion and can be a primary procedure or performed after lumbar laminectomy for spinal decompression to aid in stability after disruption of the posterior tension band. Posterior instrumentation via pedicle screws and r...

Lumbar interbody fusion (overview)

Lumbar interbody fusion is a common technique that aims for osseous fusion after discectomy. There are anterior and posterior approaches (relative to the transverse process), some of which require additional instrumentation, and none of which have been demonstrated to be clinically superior wi...

Rule of Spence

The Rule of Spence is a radiologic method to evaluate the likelihood of injury to the transverse atlantal ligament (TAL) on an open mouth AP (“peg”) radiograph. As originally framed, if the combined projection of the lateral masses of the atlas is more than 6.9 mm beyond the lateral masses of th...

Facet joint tropism

Facet joint tropism refers to a situation where there is a difference in the orientation/angle of facet joints (i.e. between the left and right sides) with respect to each other in the sagittal plane. This can lead to unequal biomechanical forces on the facet joints and intervertebral disc durin...

Dedifferentiated chordoma

Dedifferentiated chordomas are biphasic malignant tumors composed of notochordal and high-grade sacomatous components. Epidemiology Dedifferentiated chordomas are very rare tumors that might be seen in recurrences or after radiotherapy 1-3. Diagnosis The diagnosis is based on typical imaging...

Idiopathic scoliosis

Idiopathic scoliosis describes scoliosis that has no clinically or radiologically identifiable underlying cause. It is the dominant type of scoliosis with ~80% of all scolioses being idiopathic. Pathology Idiopathic scoliosis can be classified by age into: adolescent idiopathic scoliosis (>11...

CT thoracic spine (protocol)

The CT thoracic spine or T-spine protocol serves as an examination for the assessment of the thoracic spine. As a separate examination, it is often performed as a non-contrast study. It might be combined or simultaneously acquired with a CT chest or CT chest-abdomen-pelvis as part of a trauma or...

Backfill

Backfill refers to intra-articular high signal intensity on T1 weighted images seen in axial spondylarthritis within the sacroiliac joint filling up excavated bone erosions 1. It has been characterized as a complete loss of the cortical bone within the sacroiliac joint at the anticipated locatio...

Rigid spine

A rigid spine is a condition that is characterized by the ossification and/or fusion of spinal segments thus leading to a change in biomechanics. The shock absorption capabilities of normal intervertebral discs, as well as the elasticity of ligaments, is eliminated thus making the rigid spine mo...

Discoligamentous injury

Discoligamentous injuries are severe spinal injuries in which the intervertebral disc and the intervertebral ligamentous structures are involved. They include cervical, thoracic or lumbar anterior tension band injuries as well as translational injuries. Terminology The term transdiscal fractur...

Segmental endplate angles in spine injuries

Segmental endplate or segmental kyphosis angles include the monosegmental and bisegmental endplate angle as well as the vertebral compression angle and play a role in the stability assessment after spinal injuries. The following angles might be used 1-3: monosegmental endplate angle or Gardner...

Braid-like sign (spinal sarcoidosis)

The braid-like sign is an imaging pattern of sarcoidosis spinal cord involvement. It is characterized by a ventral subpial enhancement in the spinal cord.

Subarticular zone stenosis

Subarticular zone stenosis is a form of spinal stenosis where there is narrowing of the subarticular zone, including the lateral recess. This may occur with or without other forms of spinal stenosis. Pathology Root compression at the lateral recess can occur in two morphological forms: trefoi...

Dialysis-related spondyloarthropathy

Dialysis-related spondyloarthropathy is a relatively uncommon complication of renal dialysis. It is part of the spectrum of dialysis-related amyloidosis. Pathology Thought to be mainly due to extensive deposition of beta-2 microglobulin (amyloid-like substance) within the spine (especially in...

Lateral atlantodental instability

Lateral atlantoaxial instability is a subtype of atlantoaxial subluxation, and is a poorly understood entity that may be encountered in post-traumatic and rheumatic patients with equal frequency to established sagittal plane atlantoaxial subluxation 1. There is limited information regarding cl...

Odontoid process agenesis

Odontoid process agenesis is rare, occuring due to a lack of failure of ossification of the odontoid process. It is seen in patients with spondyloepiphyseal and spondylometaphyseal dysplasia 1,2. Radiographic features Plain radiograph On plain film, odontoid process agenesis appears small, as...

Jail bar sign (vertebral hemangioma)

The jail bar sign refers to the vertically striated appearance seen in vertebral hemangiomas due to thickening of the bony trabeculae. It is the sagittal and coronal correlate of the polka-dot sign observed on axial imaging. It is caused by replacement of normal cancellous bone by coarse, scler...

Anderson and Montesano classification of occipital condyle fractures

The Anderson and Montesano classification is a widely used system for describing occipital condyle fractures. It divides injuries into three types based on morphology and mechanism of injury 1-5. Classification type I: impacted type occipital condyle fracture morphology: comminution of the co...

V sign (disambiguation)

Signs inspired by the letter V have been described in several different pathologies: inverted V sign (pneumoperitoneum) inverted V sign (spinal cord) Naclerio V sign (pneumomediastinum) V sign (interphalangeal joint subluxation)

Gehweiler classification of atlas fractures

The Gehweiler classification of atlas fractures described 5 types of fractures of the atlas. In addition, Dickman classified injuries of the transverse atlantal ligament (a.k.a. transverse band of the cruciform ligament) which has been incorporated into this classification system. type 1: fract...

Traynelis classification of atlanto-occipital dislocations

The Traynelis classification of atlanto-occipital dislocations describes injuries of the atlanto-occipital joint according to the displacement of the occipital condyles relative to the atlas: type I: anterior displacement type II: longitudinal distraction (superior-inferior displacement) type...

Lumbar puncture

Lumbar puncture is a commonly-performed hospital procedure in which a needle is inserted through the back to the subarachnoid space in the spinal canal often to collect some cerebrospinal fluid or inject a therapeutic agent. The procedure can be performed under imaging-guidance, e.g. fluoroscopy...

Epidural venous congestion

Epidural venous congestion represents the pathological dilatation of the spinal epidural venous plexus, and is typically a complication of other pathologies. Clinical presentation Radiculopathy caused by the dilated epidural veins is not uncommon 1. Pathology Several spinal and pelvic dise...

Surfer's myelopathy

Surfer's myelopathy is a rare, non-traumatic spinal cord injury occurring in novice surfers in whom prolonged hyperextension of the back causes infarction of the artery of Adamkiewicz. Terminology These patients are almost always novice surfers 1,2. However, cases of a similar syndrome have be...

Split atlas

Split or bipartite atlas is the rare congenital anomaly where the atlas is split into two halves by fusion defects in both the anterior and posterior arches. The osseous defects are spanned by fibrous tissue. They are usually asymptomatic and found incidentally on spinal imaging. Patients may h...

Pars interarticularis

The pars interarticularis or simply pars is the part of a vertebra located between the superior and inferior articular processes. In the axial plane the pars is located at the junction of the pedicle and lamina. In the oblique lumbar radiograph, the neck of the Scottie dog represents the pars. ...

Lumbar gravity line

The lumbar gravity line is a measurement made on spinal / chiropractic imaging. It is usually drawn on an erect weight bearing radiograph as plumb line drawn downwards on a sagittal image from the L3 vertebra and usually should pass through the anterior 1/3 of the sacrum. See also cervical gra...

Gertzbein and Robbins classification

The Gertzbein and Robbins classification assesses the position of transpedicular screws. Classification Transpedicular screw position is graded from A to E based on the extent by which the screw breaches the cortex of the pedicle 1-3: A: fully intrapedicular position without breach of the ped...

Cervical gravity line

The cervical gravity line is a measurement made on spinal / chiropractic imaging. It is usually drawn on an erect weight bearing radiograph as plumb line drawn downwards on a sagittal image from the dens. See also lumbar gravity line

Lumbar foraminal stenosis

Lumbar foraminal stenosis or lumbar neuroforaminal stenosis is described as narrowing of the neural exit foramina. It is a common cause of backache and/or radiculopathy and is assessed as part of the routine evaluation of lumbar MRI studies to determine what impact, if any, the surrounding struc...

Cone artery

The cone artery, also known as the artery of Desproges-Gotteron, is a rare anatomical variant which commonly arises from the internal iliac artery. Gross anatomy Origin The cone artery has a variable origin and may arise from the internal iliac artery or its branches, commonly the iliolumbar ...

Sinuvertebral nerve

The sinuvertebral nerve, also known as the recurrent meningeal nerve, or the recurrent nerve of Luschka, is a branch of the primary ventral ramus and grey ramus communicans in the intervertebral foramen. It enters the spinal canal and supplies the posterior portion of the annulus of the interver...

Cancellous bone

Cancellous, trabecular or spongy bone is one of the two macroscopic forms of bone, the other being cortical bone, and comprises 20% of skeletal mass. Gross anatomy Cancellous bone is located in the medullary cavity of bone, in particular tubular and short bones, and consists of dense trabecul...

Empty vertebral body sign

The empty vertebral body sign is referred to as a radiolucency on a vertebral body seen on the AP radiograph in patients with a flexion-distraction injury mechanism 1-3 caused by the absent superposition of the posterior spinal elements onto the vertebral body. In other words, the sign results ...

Lumbar spine fracture

Lumbar spine fractures are often a result of significant blunt trauma such as motor vehicle accidents or a fall from height. Non-traumatic causes include osteoporotic and pathological fractures. Epidemiology Traumatic fractures are more common in males. The risk of osteoporotic fractures incre...

Thoracolumbar spine fracture

Thoracolumbar spine fractures are often the result of significant blunt trauma such as motor vehicle accidents or falling from a height. Fractures in this region range from non-complex to highly complex and will vary in prognosis. Epidemiology Males are affected more commonly than females wit...

Functional neuroanatomy

Functional neuroanatomy is the study of the functional connections in the brain and spinal cord, distinct but interconnected with the structural or "more conventional" anatomic descriptions of the central nervous system. It focuses on the relationship between structure and function and hence it ...

Vertebral centroid angle

The vertebral centroid angle is considered an alternative to the Cobb angle especially in kyphosis and lordosis measurement. It is considered less susceptible to variations in the vertebral end-plate architecture 2.

Sandwich sign (disambiguation)

The sandwich sign is used for two different imaging appearances: sandwich sign (Marchiafava-Bignami disease) sandwich sign (mesentery) Sandwich sign has also been coined for the appearance of: primary pleural lymphoma 1,2 mediastinal lymphoma 3 marrow edema and hemorrhage on MRI of flexion...

Translation-rotation spine injury

Translation-rotation spine injuries are severe injuries characterized by horizontal displacement or rotation of one vertebral body with respect to another. Pathology These injuries result from torsional and shear forces. This type of injury is usually severe and involves the posterior ligament...

Meniscus sign (myelography)

The meniscus sign refers to the intradural filling defect which is outlined by the sharp meniscus of intrathecal contrast due to blockage of subarachnoid space by an intradural lesion. The CSF above the blocked segment remains unopacified.

Methotrexate-induced myelopathy

Methotrexate-induced myelopathy is an uncommon toxic manifestation of intrathecal methotrexate administration that closely mimics subacute combined degeneration of the cord but with normal vitamin B12 and copper 1,2. It is far less common than methotrexate-related leukoencephalopathy. Epidemiol...

Whiplash syndrome

Whiplash syndrome, also known as whiplash-associated disorders (WAD), are the various symptoms caused by rapid acceleration and/or deceleration injuries, which result in cervical sprain or strain. Epidemiology Whiplash is a common injury, usually associated with motor vehicle collisions 1-5. T...

Scimitar (disambiguation)

The term scimitar, referring to the characteristic shape of the Middle Eastern sword, may refer to the following: scimitar syndrome (lungs) scimitar sign (cystic adventitial disease) scimitar sacrum (bones)

Sacroiliitis

Sacroiliitis (rare plural: sacroiliitides), is an inflammation of one or both sacroiliac (SI) joints, and a common cause of buttocks or lower back pain. Sacroiliitis can be a manifestation of a wide range of disease processes. Clinical presentation Symptoms of sacroiliitis can vary. People wit...

Cyst of the ligamentum flavum

Cysts of the ligamentum flavum, also known as flaval cysts, are classified as a type of degenerative spinal cysts 1, which arise from the ligamentum flavum. Epidemiology Cyst of the ligamentum flavum do not show a gender predilection (M=F) and are most commonly found in the middle aged and eld...

Alar ligament calcification

Alar ligament calcification is rare. The alar ligaments arise bilaterally from the upper portion of the odontoid process and run obliquely cephalad and laterally to insert on the medial surface of the occipital condyles. They stabilize the head during rotatory movements. Epidemiology Focal c...