| Part I "Pedicle Exposure Technique" for Atlas Screw Fixation:A Radiological ResearchObjective:To investigate the meaning of "pedicle exposure technique" for screw fixation on Atlas with the vertebral artery groove height less than 4mm by using reconstructive computed tomography.Methods:From April 2015 to June 2015,84 pedicles of 51 cases with groove heights less than 4mm were studied by digital reconstruction CT respectively. Parameters of atlas pedicle screw fixation were measured.Results:Among the cases, the vertebral artery groove height was (3.28±0.51)mm. Lateral mass heights, lateral mass widths and the transition area heights between lateral mass and posterior arch were all fit for 3.5mm screws implanting. Ideal pedicle screw trajectory lengths from 0° to 15° were (27.36±1.81)mm, (27.01±1.68)mm, (27.07±1.75)mm, (27.48±1.72)mm, exposure technique trajectory lengths from 0° to 15° were (23.48±1.79)mm, (23.87±1.84)mm, (24.58±1.89)mm, (25.56±2.01)mm, the lateral mass screw trajectory length was (20.78±2.05)mm. The mean values of CT values on 5 sections through the pedicle screw trajectory/the lateral mass screw trajectory were (701.89±141.48)HU and (599.11±137.33)HU. There were no significant differences among ideal pedicle screw trajectory lengths from 0° to 15° (P>0.05). Exposure technique trajectory lengths increased with medial angles from 0° to 15° significantly (P <0.05), and longer than the lateral mass screw trajectory length (P<0.05). The mean CT value of pedicle screw sections was higher than the mean CT value of lateral mass screw sections significantly (P<0.01).Conclusion:Screws can be implanted in Atlas with vertebral artery groove heights less than 4mm by using "pedicle exposure technique". Few trajectory lengths would be sacrificed with favorable pull-out strength due to adequate bone mass purchased.Part Ⅱ The Strategy of Using Posterior Screw Fixations in Treating Atlantoaxial Dislocation:A Retrospective StudyObjective:To investigate the strategy and the efficacy of using posterior screw fixations in treating atlantoaxial dislocation.Methods:From September 2010 to October 2015,84 cases (39 males,45 females, mean age 32.6, age range 4 to 68) diagnosed with atlantoaxial dislocation underwent posterior C1-C2 screw fixation and fusion were analyzed retrospectively. All cases were divided into 3 types according to the vertebral artery groove height (VGH) and the transition area height(TAH) of the posterior arch and the lateral mass by preoperative radiological evaluations. Type I, which has the VGH and the TAH both beyond 4mm, was treated with C1 pedicle screw fixation. Type II, which has the VGH less than 4mm and TAH beyond 4mm, was treated with C1 pedicle exposure technique screw fixation. Type III, which has the VGH and the TAH both less than 4mm, was treated with C1 lateral mass screw fixation. Visual analogue scale (VAS), Japanese Orthopaedic Association (JOA) score and neck disability index (NDI) were used preoperatively and during follow-up to evaluate the clinical efficacy.Results:168 screws of 84 cases were inserted successfully with 51 cases in type I,28 cases in type II and 5 cases in type III. All the cases were followed from 6 to 58 months. Bony fusion was observed 3 to 6 months after surgery by CT scan in all cases. No vertebral artery or spinal cord injury was found during follow-up. Venous bleeding was engaged in 7 cases during dissecting; no occipital neuralgia was found after surgery among the 5 cases underwent lateral mass screw fixations. The preoperative VAS of pain, JOA score and NDI were (6.2±1.8), (9.5±1.3) and (38.4±8.4). The VAS of pain, JOA score and NDI at the last follow-up were (2.3±0.6), (14.8±2.6) and (18.5±7.7). Significant improvement was confirmed in the statistical analysis.Conclusion:The strategy of choosing appropriate screw technique among pedicle screw fixation, pedicle exposure technique screw fixation and lateral mass screw fixation according to VGH and TAH is reliable and effective. |
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