Biomechanical study on effect of upper cervical spine structural injury on stability of C1-C2 and C2-C3 segments

Abstract

Objective To evaluate the effect of type Ⅱ odontoid fracture, type Ι Hangman fracture, C2-C3 disc injury on stability of C1-C2 and C2-C3 segments and investigate the clinical significance. Methods Ten fresh-frozen cadaveric cervical specimens (5 men and 5 women; 25-45 years of age, mean 35.7 years) were selected to test the stability of C1-C2 and C2-C3 segments in the settings of intact condition (control group), type I Hangman fracture, type Ⅱ odontoid fracture, type I Hangman fracture+ type Ⅱ odontoid fracture, type I Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury. Range of motion (ROM) and neutral zone (NZ) of those segments were measured. Results Compared with the intact condition, type I Hangman fracture produced no significant variations in C1-C2 ROM in all loading modes and C2-C3 ROM during left and right lateral bending; type Ⅱ odontoid fracture produced no significant variations in C2-C3 ROM in all loading modes and C1-C2 ROM during left and right rotation; type I Hangman fracture + type Ⅱ odontoid fracture revealed no significant variations in C1-C2 ROM during left and right rotation and C2-C3 ROM during extention; type I Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury produced no significant variations in C1-C2 ROM during left and right lateral bending and extension-flextion and C2-C3 ROM in all loading modes (P<0.05). Conclusions Type I Hangman fracture can reserve C1-C2 segmental left and right rotation and extension-flextion; type Ⅱ odontoid fracture can reserve C1-C2 segmental left and right lateral bending and extension-flextion; type I Hangman fracture + type Ⅱ odontoid fracture + C2-C3 disc injury can reverse atlantoaxial rotationary stability and C1-C3 segmental stability in all directions. This study provides the biomechanical basis for clinical treatments and the related researches of internal fixation. Key words: Cervical vertebrae; Spinal fractures; Intervertebral disk; Biomechanical