title: Teardrop fracture following head-first impact in an ice hockey player: Case report and analysis of injury mechanisms.
abstract: BACKGROUND
  We report a case of a young male athlete who sustained a three column displaced teardrop fracture of the C5 vertebra due to a head-first impact in hockey, suffered neurapraxia, yet made full neurological recovery. This full recovery was in sharp contrast to multiple case series which reported permanent quadriplegia in the vast majority of teardrop fracture patients. We investigate the etiology and biomechanical mechanisms of injury.
  
  
  METHODS
  Admission imaging revealed the teardrop fracture which consisted of: a frontal plane fracture which separated an anterior quadrilateral-shaped fragment from the posterior vertebral body; a vertical fracture of the posterior vertebral body in the sagittal plane; and incomplete fractures of the neural arch that initiated superiorly at the anterior aspect of the spinous process and left lamina adjacent to the superior facet. Epidural hematoma in the region of the C5 vertebra was observed in addition to disc and ligamentous disruptions at C4-5 and C5-6. Our patient was ultimately treated surgically with anterior fusion from C4 through C6 and subsequently with bilateral posterior fusion at C5-6.
  
  
  RESULTS
  The injuries were caused by high-energy axial compression with the neck in a pre-flexed posture. The first fracture event consisted of the anterior vertebral body fragment being sheared off of the posterior fragment under the compression load due in part to the sagittal plane concavity of the C5 inferior endplate. The etiology of the vertical fracture of the posterior vertebral body fragment in the sagittal plane was consistent with a previously described hypothesis of the mechanistic injury events. First, the C4-5 disc height decreased under load which increased its hoop stress. Next, this increased hoop stress transferred lateral forces to the C5 uncinate processes which caused their outward expansion. Finally, the outward expansion of the uncinate processes caused the left and right sides of the vertebral body to split and spread. Evidence in support of this mechanistic event sequence was provided by the neural arch fractures which initiated superiorly, average angulation of the C5 uncinate processes, and similar well-established mechanisms causing vertical fractures at other spinal regions.
  
  
  CONCLUSIONS
  Our case study and analyses provide insight into the etiology of the specific teardrop fracture patterns observed clinically.
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Yue
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Ivancic
authors.affiliation: Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Scott
keywords: Cervical Spine; hockey; impact biomechanics; injury mechanism; teardrop fracture