| Objective 1. To measure and obtain the anatomic parameters of atlantoaxial ventral structures as well as the imageologic parameters of atlanto-odontoid joint in Chinese people so as to provide morphological data references for designing and improving relative instruments. 2. To design cervical anterior atlantoaxial reduction instrument(AARI) and introduce its constructions and procedure principles while observe its clinical effect.3. To discuss the advantages and disadvantages, indications and contraindications as well as complications while evaluate its effect of release, decompression and instant reduction during the operation and application prospect about AARI.Methods 1. Vernier caliper and a goniometer were used to measure relative anatomic parameters of atlantoaxial ventral structures of 20 sets of complete dry Chinese adults' atlanto-odontoid specimens including length of atlas arcus anterior(AtAL),height of atlas arcus anterior(AtAH),thickness of atlas arcus anterior(AtAT),height of atlas tuberculum anterior(AtTH),thickness of atlas tuberculum anterior(AtTT),width of axis corpus vertebrae(AxW),height of axis corpus vertebrae(AxL),height of axis corpus anterior(AxAH),height of odontoid process(DH),coronal diameter of odontoid process(DCD),sagittal diameter of odontoid process(DSD),posterior angulation of odontoid process(a),posterior angulation of the screw placement(P);The goniometer of Photoshop9.0 software in computer was used to measure atlanto-odontoid interval(ADI) and space available for the spinal cord(SAC) on 50 lateral X-ray films(neutral position) in normal occipit-atlantoaxial region. The data were statistically analyzed in order to provide the morphological parameter range for designing AARI.2.A new type of cervical anterior atlantoaxial reduction instrument will be designed and used to clinically treat a case of old irreducible atlantoaxial dislocation with odontoid dysplasia(by release and depression technique through cervical anterior approach and internal fixation and arthrodesis technique using plate and screws in the lateral masses of the atlas and axis through cervical posterior approach).Result 1 .Measurement results showed that AtAL was for (20.4±0.632)mm, AtAH for (left 10.2±1.06,right 10.1±1.08)mm, AtAT for (left 8.87±1.37,right 8.80±1.24)mm, AtTH for (10.4±0.867)mm, AtTT for (8.16±1.50)mm, AxW for (18.5±1.29)mm, AxL for (37.3±3.56)mm, AxAH for (22.1±1.90)mm, DH for (15.2±1.82)mm, DCD for (8.74±0.810)mm, DSD for (10.1±1.15)mm,αfor (10.3±2.94)°,βfor (16.1±2.87)°, ADI for (1.38±0.340)mm, SAC for (19.7±0.790)mm.2.The AARI is made up of 3 components:atlas part(a stretch plate for atlas arcus anterior and another for atlas lateral masses),axis part(screw sticks with thread in both sides,screw nut,packing block) and accessories(a spanner,2 bent rectangular clamps and a mandubular hook). Its clinical application to 1 case proved that AARI could achieve satisfactory release and depression as well as instant reduction during the operation. 3. The follow-up results after operation showed that both patients had good wound healing without infections or complications.The symptoms of neck pain and limb asthenia were alleviated at different degrees. For example,the muscle strength recoverd and the pathological reflexs disappered. In rephotograghed X-ray films we could watch that the atlas and axis had already achieved complete anatomical reduction with satisfactory position and stable internal fixation about plate and screws.Conclusions 1.The designation of AARI is feasible in as morphology.2.During the operation AARI is made good use of releasing atlanto-odontoid interval, reducing tissue adhesion formation,relieving spinal compression and achieving instant reduction which will be helpful to further fixation.2.AARI design is a novel strategy. Its operative procedure is simple and feasible. Compared with transoropharyngeal approach the operation risk of transanterior approach is much lower. Above all,AARI is creative and has excellent prospect.
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