Summary Occipital condyle fractures are traumatic injuries that involve articulation between the base of the skull and the cervical spine. Diagnosis of the fracture is best made with a CT scan. An MRI and/or flexion-extension radiographs are used to evaluate for associated occipitocervical instability. Most fractures are treated with immobilization with a cervical orthosis. Occipitocervical fusion is indicated in the rare cases where occipitocervical instability is present. Epidemiology Incidence relatively uncommon. approximately 1-3% of population with blunt craniocervical trauma. often missed due to low diagnosis sensitivity of plain radiographs. reported incidence is increasing due to increased utilization of CT scans. ETIOLOGY Pathophysiology terminology occipital condyle fractures represent a subset of basilar skull fractures. mechanism high energy trauma to the head/neck motor vehicle accident fall from height. low energy trauma to head and neck occasionally seen in ground level falls in elderly due to direct blow to the skull. pathoanatomy fracture patterns are dependent on the directional forces applied to the craniocervical junction at the time of the injury including axial compression horizontal sheer due to a direct blow on the skull rotation lateral bending Associated injuries orthopaedic manifestations cervical spinal cord injuries (31%) neurological deficits may be acute (63% of cases) or delayed (37% of cases) cervical fractures vertebral artery injury polytrauma medical manifestations intracranial bleeding brainstem and vascular lesions elevated ICP Anatomy Osteology occipital condyle morphology occipital condyles are paired oval prominences of the occipital bone. form the lateral aspects of the foramen magnum. occipitoatlantal joint (occiput/C1) articulation each occiput articulates with a shallow dish-like joint on the superior aspect of the lateral mass of C1. joint morphology allows for large range of flexion and extension of craniocervical junction. ligamentous stability provide by a combination of occipitoatlantal joint joint capsule alar ligaments (dens to each occipital condyle) Ligaments intrinsic ligaments are located within the spinal canal, provide most of the ligamentous stability. They include transverse ligament connects the posterior odontoid to the anterior atlas arch, inserting laterally on bony tubercles. primary stabilizer of atlantoaxial junction. paired alar ligaments connect the odontoid to the occipital condyles. relatively strong and contributes to occipitocervical stability. apical ligament runs vertically between the odontoid and foramen magnum. relatively weak midline structure. tectorial membrane connects the posterior body of the axis to the anterior foramen magnum and is the cephalad continuation of the PLL. Vascular system vertebral artery occipital condyles are in proximity to vertebral arteries. Nervous system occipital condyles in close proximity to medulla oblongata spinal cord lower cranial nerves (CN IX - CN XII) C2 nerve root Biomechanics occipitoatlantoaxial complex (craniocervical junction) function an anatomic complex that provides stability and function of craniocervical junction (occiput to C2). includes 6 articulations 2 occipitoatlantal joints 2 paired lateral C1-C2 facets/joints 1 dens-anterior arch of C1 articulation 1 posterior midline atlantoaxial joints three ligamentous structure connect C2 directly to base of skull (thereby skipping C1) apical ligament alar ligament tectorial membrane Classification Anderson and Montesano Classification of Occipital Condyle Fractures Type I 3% of OC fracture IImpaction-type fracture with comminution of the occipital condyle Due to compression between the occipitoatlantal joint Stable injury due to minimal fragment displacement into the foramen magnum Type II 22% of OC fractures Basilar skull fracture that extends into one- or both occipital condyles Due to a direct blow to skull and a sheer force to theoccipitoatlantaljoint Stable injury as the alar ligament and tectorial membrane are usually preserved Type III 75% Avulsion fracture of condyle in region of the alar ligament attachment (suspect underlying occipitocervical dissociation) Due to forced rotation with combined lateral bending. Has the potential to be unstable due to craniocervical disruption Presentation History clinical presentation is highly variable often a history of high energy trauma with associated head injury (head injury, vertebral artery injury, spinal cord injury) Symptoms high cervical pain neck stiffness double vision upper and lower extremity weakness Physical examination inspection look for trauma to skull (e.g, skull laceration) ROM remove collar and evaluate limited motion limited cervical ROM may elicit pain neurologic extremity exam rectal exam lower cranial nerve exam deficits most commonly affect CN IX, X, and XI Imaging Radiographs recommended views AP, lateral, open-mouth AP view alternative views flexion and extension views findings diagnosis rarely made on plain radiographs due to superimposition of structures (maxilla, occiput) blocking view of occipital condyles open-mouth AP view may depict occipital condyle injuries measurements Powers ratio used to diagnosis occipitocervical dislocation technique Powers ratio = C-D/A-B C-D: distance from basion to posterior arch A-B: distance from anterior arch to opisthion significance ratio of ~ 1 is normal if > 1.0 concern for anterior dislocation if ratio < 1.0 raises concern for posterior dislocation, odontoid fractures, or ring of atlas fractures O-C2 angle technique angle between McGregor line and C2 significance needs to be established prior to OC fusion to prevent postoperative dysphagia by causing a significant change relative to the preoperative O-C2 angle C2 to T1 lordotic alignment CT indications diagnostic method of choice usually obtained as routine CT imaging in high-energy trauma patients clinical criteria altered consciousness occipital pain and tenderness impaired CCJ motion lower cranial nerve paresis motor paresis views must include cranial-cervical junction with thin-section technique findings occiput fracture may see migration of fragment into spinal canal joint diastasis (2mm or less is considered normal) CT angiogram indications concern for vertebral artery injury surgical planning to identify location of vertebral artery MRI indications evaluation of soft-tissue craniocervical trauma spinal cord or brain stem ischemia findings edema or fluid collection in the occipitoatlantal joint representing rupture of the occipitoatlantal joint capsule edema or fluid collection consistent with avulsion injury of alar ligament from dens or occiput MRA (Magnetic Resonance Angiogram) indications considered with suspected vascular injury Differential Key differential occipitocervical instability atlas fractures odontoid fracture Treatment Nonoperative immobilization with cervical orthosis indications indicated in vast majority of low energy fractures Type 1 and 2 Type 3 without overt instability modalities semi-rigid or rigid cervical collar usually worn for 6 weeks Operative occipitocervical fusion indications very rarely indicated Type 3 with overt instability neural compression from displaced fracture fragment associated occipital-atlantal or atlanto-axial injuries Techniques Occipitocervical fusion approach posterior midline incision with patient in prone position Mayfield retractor used to obtain proper craniocervical alignment establish preoperative O-C2 angle with lateral fluoroscopy prior to draping deep dissection if performing C1 lateral mass screw fixation work within safe zone and do not dissect above the posterior arch of C1 more than 1 cm lateral to midline to avoid injury to vertebral artery instrumentation length posterior segmental instrumented fusion is usually performed from the occiput to C3 occipital occipital plates usually allow for 3 or 4 total screws with adjustable rod holders occipital screws usually unicortical to avoid injury to venous sinus major dural venous sinuses are located just below the external occipital protuberance and are at risk of penetrative injury some institutions prefer bicortical screws but they come at increase risk occipital screw safe zone the safe zone for occipital screws is located within an area measuring 2 cm lateral and 1 cm inferior to the external occipital protuberance along the superior nuchal line C1 lateral mass screws often skipped due to angle at base of skull making it more difficult to place a rod may choose a unilateral screw to provide some rotational stability to C1 ring C2 fixation pars, pedicle screws, transarticular, or translaminar screws all options C3 fixation standard lateral mass screws aimed cephalad and lateral to avoid vertebral artery arthrodesis perform decortication of occiput, posterior arch of C1, and lamina of C2 may require autogeneous bone grafting or bone allograft postoperative immobilization patients frequently immobilized in halo or hard cervical orthosis for 6-12 weeks to obtain fusion Complications Nonoperative neck pain & stiffness Operative intracranial venous sinus injury (occipital screws) vertebral artery injury (C1 lateral mass screws) adjacent segment disease neck pain & stiffness Prognosis high mortality rate (11%) due to associated injuries. rate has decreased due to improvement in first responder cervical spine precautions.