In order to provide anatomical basis for transoral approach (TOA) in dealing with the ventro lesions of craniocervical junction, and the design and application of artificial atlanto-odontoid joint, microsurgical dissecting was performed on 8 fresh craniocervical specimens layer by layer through transoropharyngeal approach. The stratification of posterior pharyngeal wall, course of vertebral artery, adjacent relationship of atlas and axis and correlative anatomical parameters of replacement of artificial atlanto-odontoid joint were observed. Besides, 32 sets of atlanto-axial joint in adults' fresh bony specimens were measured with a digital caliper and a goniometer, including the width of bony window of anterior arch of atlas, the width of bony window of axis vertebra, the distance between superior and inferior two atlas screw inserting points, the distance between two axis screw inserting points etc. It was found that the width of atlas and axis which could be exposed were 40.2+/-3.5 mm and 39.3+/-3.7 mm respectively. The width and height of posterior pharyngeal wall which could be exposed were 40.1+/-5.2 mm and 50.2+/-4.6 mm respectively. The distance between superior and inferior two atlas screw inserting points was 28.0+/-2.9 mm and 24.0+/-3.5 mm respectively, and the distance of bilateral axis screw inserting points was 18.0+/-1.2 mm. The operative exposure position through TOA ranged from inferior part of the clivus to the superior part of the C3 vertebral body. Posterior pharyngeal wall consisted of 5 layers and two interspaces: mucosa, submucosa, superficial muscular layer, anterior fascia of vertebrae, anterior muscular layer of vertebrae and posterior interspace of pharynx, anterior interspace of vertebrae. This study revealed that it had the advantages of short operative distance, good exposure and sufficient decompression in dealing with the ventro lesions from the upper cervical to the lower clivus through the TOA. The replacement of artificial atlanto-odontoid joint is suitable and feasible. The design of artificial atlanto-odontoid joint should be based on the above data.
Atlanto-Axial Joint/*anatomy & histology ; Atlanto-Axial Joint/*surgery ; Bone Plates ; Bone Screws ; Cadaver ; Cervical Vertebrae/*anatomy & histology ; Cervical Vertebrae/surgery ; Equipment Design ; Internal Fixators ; Joint Prosthesis ; Models, Anatomic ; Odontoid Process/*surgery ; Prosthesis Design

OBJECTIVETo observe and measure morphological parameters of the Chinese atlanto-odontoid joint anatomically in order to provide an anatomic data for designing artificial atlanto-odontoid joint used for substituting the destroyed atlanto-odontoid joint in the orthopedic clinic.

METHODSThe relative anatomic parameters of 32 sets of fresh Chinese adults'atlanto-odontoid joint specimens were measured with a digital caliper and a goniometer, including the width of anterior arch of atlas (AW), the thickness of atlas at the junction of anterior arch and lateral mass (AD), the thickness and height of anterior tubercle of atlas (AT and AH), the middle height, length and width of the lateral mass (MHL, L and LW), the height, transverse and anteroposterior distance of odontoid process (DH, DW and DD), the retroversion angle of odontoid process (beta degree),the facial angle of odontoid process (theta degree) and so on. The data were statistically analyzed in order to ascertain the morphological parameter ranges of artificial atlanto-odontoid joint. An artificial atlanto-odontoid joint was designed according to these data. The operations of anlanto-odontoid joint arthroplasty were conducted in 3 cases of adult cadaver specimens.

RESULTSThe width of AW was (20.45+/-1.53) mm, AD (3.91+/-1.32) mm, AT and AH (9.43+/-1.93)mm and (10.23+/-1.32) mm, respectively, MHL and LW (13.68+/-1.38) mm and (12.98+/-1.52) mm, respectively, DH (15.25+/-2.11) mm, DW and DD (9.69+/-1.38) mm and (11.26+/-1.02) mm, respectively, beta degree (12.23+/-4.27) degree, theta degree (65.48+/-2.17) degree. The prosthesis was composed of atlas part, axis part and accessories. Neither the vertebral artery nor the medulla oblongata was injured.

CONCLUSIONSThe design of artificial atlanto-odontoid joint is feasible according to these parameters. The artificial joint can not only rebuild the stability of atlanto-axial joint, but also reserve the rotation function between atlas and axis. Every part of the joint has their own parameter ranges in purpose to firm fixation, convenient operation and good motion without further injury. The prosthesis can be used for patients suffering from compression of medulla oblongata and resection of dens when it is required.

Adult ; Asian Continental Ancestry Group ; Atlanto-Axial Joint ; anatomy & histology ; China ; Female ; Humans ; Joint Prosthesis ; Male ; Middle Aged ; Odontoid Process ; anatomy & histology

OBJECTIVETo study relevant anatomical features of the structures involved in transoral atlanto-axial reduction plate (TARP) internal fixation through transoral approach for treating irreducible atlanto-axial dislocation and providing anatomical basis for the clinical application of TARP.

METHODSTen fresh craniocervical specimens were microsurgically dissected layer by layer through transoral approach. The stratification of the posterior pharyngeal wall, the course of the vertebral artery, anatomical relationships of the adjacent structures of the atlas and axis, and the closely relevant anatomical parameters for TARP internal fixation were measured.

RESULTSThe posterior pharyngeal wall consisted of two layers and two interspaces: the mucosa, prevertebral fascia, retropharyngeal space, and prevertebral space. The range from the anterior edge of the foramen magnum to C(3) could be exposed by this approach. The thickness of the posterior pharyngeal wall was (3.6+/-0.3) mm (ranging 2.9-4.3 mm) at the anterior tubercle of C1, (6.1+/-0.4) mm (ranging 5.2-7.1 mm) at the lateral mass of C(1) and (5.5+/-0.4) mm (ranging 4.3-6.5 mm) at the central part of C(2), respectively. The distance from the incisor tooth to the anterior tubercle of C(1), C(1) screw entry point, and C(2)screw entry point was (82.5+/-7.8) mm (ranging 71.4-96.2 mm), (90.1+/-3.8) mm (ranging 82.2-96.3 mm), and (89.0+/-4.1) mm (ranging 81.3-95.3 mm), respectively. The distance between the vertebral artery at the atlas and the midline was (25.2+/- 2.3) mm (ranging 20.4-29.7 mm) and that between the vertebral artery at the axis and the midline was (18.4+/- 2.6) mm (ranging 13.1-23.0 mm). The allowed width of the atlas and axis for exposure was (39.4+/-2.2) mm (ranging 36.2-42.7 mm) and (39.0+/-2.1) mm (ranging 35.8-42.3 mm), respectively. The distance (a) between the two atlas screw insertion points (center of anterior aspect of C(1) lateral mass) was (31.4+/-3.3) mm (ranging 25.4-36.6 mm). The vertical distance (b) between the line connecting the two C(1) screw entry points and that connecting the two C(2) screw entry points (at the central part of the vertebrae, namely 3-4 mm lateral to the midline of C(2) vertebrae) was (21.3+/-2.7) mm (ranging 19.4-24.3 mm), with an a/b ratio of 1.3-1.5. The screws of TARP had a lateral tilt of 12.2 degrees+/-0.4 degrees(ranging 10.2 degrees-14.6 degrees) at C(1) and a medial tilt of 7.3 degrees+/-0.3 degrees (ranging 5.1 degrees-9.4 degrees) at C(2) relative to the coronal plane.

CONCLUSIONSAn atlanto-axial surgery through transoral approach is safe and feasible. This approach is suitable for an anterior TARP internal fixation, and the design of the internal fixation system should be based on the above anatomical data.

Atlanto-Axial Joint ; anatomy & histology ; surgery ; Bone Plates ; Bone Screws ; Cadaver ; Decompression, Surgical ; methods ; Humans ; Internal Fixators ; Joint Dislocations ; surgery ; Mouth ; surgery ; Spinal Fusion ; methods ; Vertebral Artery ; anatomy & histology