Biomedical subjects

R A Yeasting

Publications and source records attributed to R A Yeasting.

At least 37 records · Page 2Linked to original sources

PubMed1999

The anatomic relation of lateral mass screws to the spinal nerves. A comparison of the Magerl, Anderson, and An techniques.

STUDY DESIGN: Analysis of the anatomic relation of the Magerl, Anderson, and An screws to the spinal nerve. OBJECTIVES: To compare the potential incidence of nerve root (ventral and dorsal ramus) injury caused by the Magerl, Anderson, and An techniques. SUMMARY OF BACKGROUND DATA: Posterior plating with lateral mass screw fixation is a common procedure for managing an unstable cervical spine. Comparative study of the Roy-Camille and Magerl techniques has been reported. However, the risk of nerve root injury for the Anderson and An techniques is not known. METHODS: Three lateral mass screw insertion techniques were performed in this study: Magerl, Anderson, and An. Each technique involved two specimens and 20 screws inserted from C3 through C7. A 20-mm-long screw was used to overpenetrate the ventral cortex. The anterolateral aspect of the cervical spine was carefully dissected to allow observation of the screw-ramus relationship. RESULTS: The overall percentage of nerve violation was significantly higher with the Magerl (95%) and Anderson (90%) techniques than with the An (60%) technique (P < 0.05). The largest percentages of nerve violation for the Magerl, Anderson, and An screws were found at the dorsal ramus (50%), the bifurcation of the ventral dorsal ramus (45%), and the ventral ramus (55%), respectively. CONCLUSIONS: The results of this study indicate that the potential risk of nerve root violation is higher with the Magerl and Anderson techniques than with the An technique.

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PubMed1999

Anatomic relation between the cervical pedicle and the adjacent neural structures.

STUDY DESIGN: An evaluation of the anatomic relation between the cervical pedicles and the adjacent neural structures. OBJECTIVES: To determine quantitatively the antomic relation of the cervical pedicles to the adjacent nerve roots and dural sac. SUMMARY OF BACKGROUND DATA: Transpedicular screw fixation in the cervical spine has been reported, but little quantitative data regarding the anatomic relation between the cervical pedicles and the surrounding neural structures are known. METHODS: Twenty cadavers were used for dissection to observe the relations of the cervical pedicles to the adjacent dural sac and nerve roots. After removal of whole posterior bony elements including the spinous processes, laminas, and lateral masses, the isthmus of the pedicles, the dural sac, and the nerve roots of C3-C7 were exposed. Direct measurements included the distance from the pedicle to the superior and inferior nerve roots and the dura. Also, the pedicle height and width were measured at its isthmus. RESULTS: No distance was found between the pedicle and the superior nerve root, nor between the pedicle and the dural sac at C3-C7 for all specimens. The mean distances between the pedicle and the inferior nerve roots for all specimens ranged from 1.4 to 1.6 mm. The mean pedicle heights and widths for all specimens at C3-C7 ranged from 6.0 to 6.5 mm and 4.7 to 5.3 mm, respectively. A significant difference between male and female specimens was noted in the pedicle heights for all levels measured (P = 0.001), and in the pedicle widths for the levels of C4 and C6 (P = 0.05). CONCLUSIONS: This study suggests that the incidence of neurologic injuries may be higher in screw penetration of the medial or superior cortex of the pedicle than in screw penetration of the inferior cortex of the pedicle.

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PubMed1999

The quantitative anatomy of the laminas of the spine.

STUDY DESIGN: This study evaluated the dimensions of the laminas from C2 to L5 using adult spine specimens. OBJECTIVES: To provide a set of quantitative data for the laminas from C2 to L5. SUMMARY OF BACKGROUND DATA: Anatomic evaluation of the pedicle and facet joint in the spine has been extensively reported. No detailed studies of the laminas from the cervical to the lumbar spines exist. METHODS: Thirty-seven spines from C2 to L5 were directly evaluated for this study. Anatomic evaluation of the laminas included the laminar height, width, thickness, and angulation. RESULTS: In general, the measurements were greater in male specimens than in female specimens, although significant differences (P < 0.05) between male and female specimens were noted in only three measurements. The greatest laminar height was at T11 (25.1 +/- 2.5 mm), and the least was at C4 (10.4 +/- 1.1 mm). The greatest laminar width was at L5 (15.7 +/- 2.0 mm), and the least was at T4 (5.8 +/- 0.8 mm). Laminar widths in the cervical region were slightly more than those in the thoracic region. The greatest laminar thickness was at T2 (5.0 +/- 0.2 mm), whereas the least was at C5 (1.9 +/- 0.6 mm). Laminar thickness tended to increase in the upper thoracic region and to decrease slightly in the lower thoracic region. The mean laminar thickness of the lower cervical region was least in the whole spine. The widest angle was at C3 (116.1 +/- 8.8 degrees) and T7 (112.3 +/- 8.0 degrees) and the narrowest was at C2 (99.1 +/- 8.0 degrees) and L3 (99.9 +/- 6.3 degrees). The slope angles of the laminas varied from 97.8 +/- 3.0 degrees at T9 to 129.0 +/- 7.5 degrees at L3. CONCLUSIONS: Surgical placement of sublaminar instruments may benefit from this quantitative study through the use of the provided anatomic parameters of the laminas.

Adult↗

PubMed1999

A posterior approach for inspection of reduction of sacroiliac joint disruption.

This anatomic study was undertaken to describe a new posterior approach enabling direct inspection of reduction of sacroiliac joint disruption (SIJD), and guidance of iliosacral screw placement. The reduction of SIJD is usually monitored by inspection of the opposing sacrum and ilium at the posterior margin of the greater sciatic notch and there is a relative lack of information concerning inspection of reduction of SIJD from the posterosuperior aspect of the sacroiliac joint surface. Ten cadavers were dissected to determine the possibility of inspecting reduction of SIJD from the posterosuperior aspect of the sacroiliac joint by means of a posterior approach which passed immediately lateral to the deep back muscles and the fifth lumbar transverse process. The results indicated that the posterosuperior aspect of the sacroiliac joint surface and sacral ala can be directly palpated or visualised. This approach facilitates improved access for inspection of reduction of SIJD and guidance of iliosacral screw placement.

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PubMed1999

Anatomic bases for anterior spinal surgery: surgical anatomy of the cervical vertebral body and disc space.

Twenty adult cadaveric cervical spines were sectioned longitudinally through the midline to display longitudinal sections of the vertebral bodies and disc spaces from C3 to T1. Computer-assisted anatomic images were obtained for measurements of the disc spaces and vertebral bodies. Anteroposterior (AP) depth gradually increased from 16.56 +/- 2.21 mm at C3 to 19.32 +/- 2.30 mm at C7. Greater values of AP depth at the inferior endplate were found at C5 (20.75 +/- 2.87 mm) and C6 (20.56 +/- 2.31 mm) compared with the values at C3 (18.26 +/- 1.82 mm), C4 (19.27 +/- 2.88 mm) and C7 (19.21 +/- 3.22 mm). The AP depth at the superior endplate was greater than that at the inferior endplate. The height of the disc space was found to be lowest at the posterior disc space from C2-3 to C7-T1 (2.95 +/- 0.86 mm at C2-3, 2.78 +/- 0.93 mm at C3-4, 2.45 +/- 0.79 mm at C4-5, 2.92 +/- 0.64 mm at C5-6, 2.46 +/- 0.59 mm at C6-7, 2.93 +/- 1.05 mm at C7-T1), when compared to the height of the disc space at the anterior disc space from C2-3 to C7-T1 (4.07 +/- 0.85 mm at C2-3, 4.34 +/- 1.18 mm at C3-4, 3.95 +/- 1.37 mm at C4-5, 3.55 +/- 1.37 mm at C5-6, 3.55 +/- 0.76 mm at C6-7, 3.67 +/- 1.17 mm at C7-T1). The mid-axis of the disc space was situated at approximately 3 mm above the anterior midpoint of the annulus fibrosus at the level of the lower cervical spine. To reach the posterior portion of the disc space from the anterior midpoint of the annulus fibrosus, a 5 degrees cephalad angulation of the drill relative to the mid-axis of the disc space is necessary. All these original data from cadavers may be helpful during anterior approach for discectomy, vertebrectomy and anterior screw-plate placement.

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PubMed1999

The projection of the cervical disc and uncinate process on the posterior aspect of the cervical spine.

BACKGROUND: Surgical techniques of foraminotomy for decompression of the cervical nerve have been well described in the literature. Excessive resection of the facet joint and laminae may decrease segmental stability and increase scar formation. How much bony resection is adequate to remove a soft or hard disc herniation is not known. No studies regarding this subject are available. METHODS: Thirty-nine adult dry bone spines from C3 to C7 were used and four measurements on each vertebra were taken in this study. The first three measurements included the vertical distances between the superior borders of the lamina and the vertebral body measured at the midline of the laminae, the middle of the lamina, and the lamina-facet junction, respectively. The fourth was the horizontal distance between the medial most border of the superior facet and the tip of the uncinate process. RESULTS: No significant differences between male and female specimens were found in any measurements in this study. The mean vertical distances from the superior border of the lamina inferior to the superior border of the vertebral body measured at the three points for all levels were approximately 1-3 mm, although the standard deviations for those were relatively high. The tip of the uncinate process was located from 2 mm at C3 to 1 mm at C6 medial to the medial most border of the superior facet, and then changed to be located 1 mm lateral to the medial most border of the superior facet. CONCLUSIONS: This study suggests that a semicircular laminotomy placed on the inferior aspect of the lamina above may be adequate for a lateral soft disc herniation because the inferior border of the disc is higher than the superior border of the inferior lamina, whereas a traditional foraminotomy is needed for a hard disc pathology.

Adult↗

PubMed1999

The quantitative study of the lateral region to the lumbar pedicle.

BACKGROUND: An anatomic study of the lumbar nerve lateral to the pedicle was performed on 12 cadavers. Three courses of the lumbar nerve were noted around the pedicle. The direct measurements, including the angle of the lumbar rami with the spinal cord, the axis of the pedicle with the cord in the coronal plane, and the distance between the lateral border of the pedicle to the rami, were made bilaterally. RESULTS: The results showed that both angles increased as the lumbar spine descended. The spaces between the lumbar rami and the pedicle were found to be less than 5 mm. CONCLUSION: The region latero-superior to the pedicle had a similar relationship with the region medial inferior to the pedicle. Nerve entrapment was observed around the lumbar pedicle.

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PubMed1999

Cartilage and synovium of the peroneocuboid joint: an anatomic and histological study.

The surface area, thickness, and composition of the articular cartilage of the peroneocuboid articulation and the location of the synovium were investigated in 15 cadaver foot specimens. The articulations of the medial side of the peroneus longus tendon and lateral side of the cuboid were covered with fibrous and hyaline cartilages, respectively. On the lateral tuberosity of the cuboid, there is a facet that has 79.37+/-20.24 mm2 articular cartilage area with an oval shape to conform to that of the articular surface of the peroneus longus tendon (articular cartilage area, 67.35+/-28.53 mm2) with which it articulates. The mean thickness of the articular cartilage of the peroneus longus tendon and cuboid was 0.34+/-0.08 and 0.52+/-0.07 mm, respectively. The peroneocuboid joint has its own joint capsule. The synovial cavity does not communicate with the sheath of the peroneus longus tendon. Synovial membranes were attached to the margins of the articular surfaces of the cuboid immediately peripheral to the cartilage region.

Adult↗

PubMed1999

Anatomic considerations for anterior instrumentation of the lumbar spine.

One hundred seventy lumbar vertebrae from L1-L4 were used to quantitatively evaluate the lumbar vertebral body and examine the relationship of the maximum posterior angles of screw placement to the spinal canal. Anatomic evaluation included dimensions of the vertebral body. Three entrance points on the lateral aspect of the vertebral body for screw insertion and an additional point 3 mm from the posterolateral corner of the spinal canal were defined and marked. The maximum posterior screw angles were determined as the angles between the line connecting the entrance point with the additional point and the coronal plane. Results showed that vertebral body dimensions increased from L1-L4. The average vertebral body depth, width, and height were approximately 26 mm, 36 mm, and 22 mm at L1, and 30 mm, 44 mm, and 23 mm at L4, respectively. The spinal canal may be penetrated if the screws are directed posteriorly 2 degrees-5 degrees at L1 - L2 and 9 degrees - 14 degrees at L3-L4 starting at the junction between the pedicle and vertebral body, 22 degrees - 32 degrees at L1-L4 from the level of 10 mm anterior to the junction, and 43 degrees -50 degrees from the level of 20 mm anterior to the junction. Therefore, mid-body screws should be directed perpendicular to the lateral plane of the vertebral body. For a more anteriorly placed screw, slightly posterior angulation is recommended.

Adult↗

PubMed1999

Computed tomographic evaluation of the internal structure of the lateral sacral mass in the upper sacra.

Because dimensions of the upper sacral cortexes vary greatly among individuals, preoperative computed tomographic (CT) evaluation of individual sacrum may help surgeons choose sacral screw insertion techniques. Axial CT scans were performed on 40 dry sacrum specimens to quantitatively evaluate the internal structure of the lateral sacral mass in the first and second segments. The results showed that the greatest cortical thickness in the S1 vertebra was found in the anterior cortex (3.4+/-0.9 mm), followed by the anterolateral (3.2+/-1.2 mm), and anteromedial (2.9+/-1 mm). The greatest cortical thickness in the S2 region was noted in the anteromedial cortex (2.4+/-0.5 mm), followed by the anterior and anterolateral (2.2+/-0.9 mm). The mean percentage of the anterior cortex thickness versus the lateral sacral mass depth was 12.8+/-3.7 for S1 and 11.1+/-2.8 for S2. Bicortical screw placement is recommended to achieve stronger fixation, but care should be taken not to violate the vital structures anterior to the sacrum.

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PubMed1999

Anatomic relationship of the cervical nerves to the lateral masses.

Eight cervical specimens were transversely sectioned with slices approximately 2 mm to 3 mm in thickness to evaluate the anatomic relationship of the spinal nerves to the lateral masses. Results showed that the spinal nerve either does not appear or, when it does, is situated anteromedially to the superior facet on the cross sections through the upper portion of the superior facet. The anterolateral aspect of the superior facet is free from the spinal nerve. Cross sections through the lower pedicle of the vertebra showed that the spinal nerve rested on the transverse process anterolateral to the lateral mass. The mean distances between the posterior midline of the lateral mass and the posterior border of the spinal nerve measured 15 degrees in the lateral direction were 16.1+/-1.7 mm for C3, 16.5+/-1.8 mm for CA, 16.8+/-1.2 mm for C5, 16.3+/-2.0 mm for C6, and 8.5+/-0.9 mm for C7. This study suggests that the anterolateral corner of the superior facet and the anterior aspect of the lateral mass lateral to the origin of the transverse process would be safer zones for screw exit. Attention should therefore be paid to the screw orientation for the Magerl technique and to the screw length for the Roy-Camille technique. Care should be taken to insert the screw into the C7 lateral mass.

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PubMed1999

Thoracic pedicle screw placement guided by computed tomographic measurements.

Cadaveric pedicle screw placement guided by the measurements from axial computed tomography (CT) scans in the thoracic spine was assessed in this study. Axial CT scans were performed on four cadaveric thoracic spines, and the measurements included the pedicle transverse angle, inner pedicle width, and distance between the midline of the vertebra and the pedicle axis on the dorsal aspect of the lamina. With utilization of the data from CT scans, screws were directly placed into the thoracic pedicle from T1 to T10. Screw penetration of the pedicle was determined by gross examination. The results showed that the largest pedicle transverse angle was found at the levels of T1-2, and the smallest occurred at the T3 through T8 levels. The value of the pedicle inner width was quite different between specimens with a minimum of 3.0 mm at T4 and a maximum of 9.2 mm at T10. Gross examination of the pedicle showed that 13 (16.3%) of 80 screws penetrated the pedicle wall, with a Grade I penetration in 11 pedicles and a Grade II penetration in 2 pedicles. Screw penetration of the medial wall was found in four pedicles and penetration of the lateral wall was noted in nine pedicles. No screw penetration of the superior and inferior walls of the pedicle was identified in any of the four specimens. Thoracic pedicle screw placement guided by the measurements from axial CT scans significantly reduced the incidence of pedicle penetration. Axial CT measurements of the pedicle inner diameter and transverse angle as well as the starting point for screw insertion are recommended if pedicle screw fixation is intended in the thoracic spine.

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PubMed1999

Evaluation of the upper sacrum by three-dimensional computed tomography.

Axial and sagittal computed tomographic (CT) scans of 40 sacrum specimens were obtained. The measurements of the upper sacral canal and S1-2 and S2-3 anterior sacral foramina were performed on axial scans, and the evaluation of the upper sacral pedicle was based on sagittal scans. The results showed that there were statistically significant differences between male and female specimens in 3 of 29 measurements. In general, the measurements of male specimens were slightly larger than those of the female specimens, and the linear dimensions of the sacral canal, anterior foramina, and pedicle decreased from the S1 to S3. This study indicated that the critical area of the sacral pedicle for screw insertion lies in the junction between the pedicle and vertebral body. CT scans provide more accurate information about the essential sacral anatomy.

Female↗

PubMed1998

The vertebral body depths of the cervical spine and its relation to anterior plate-screw fixation.

STUDY DESIGN: A study was performed to measure the vertebral body depths in different locations from C2 to C7. OBJECTIVES: To measure the vertebral body depths in 10 linear dimension from C2 to C7. SUMMARY OF BACKGROUND DATA: Anterior plate-screw fixation of the cervical spine has been the common surgical procedure for management of multilevel degenerative disc disease and fracture dislocation. However, injury to the spinal cord during drill or screw placement is the most feared complication of this procedure. It is beneficial for one to have a knowledge of the vertebral body depths in different locations of the vertebral body before anterior cervical plating. METHODS: Twenty-seven cervical spines from C2 to C7 were evaluated directly for this study. Anatomic evaluation of the vertebral body included the anteroposterior midline sagittal depth and the anteroposterior parasagittal depth 5 mm lateral to midline on the superior and inferior endplates, as well as on the middle body. Measurements also were made of anteroposterior parasagittal vertebral depth with both medial and lateral inclination of 10 degrees, with respect to the parasagittal plane of the vertebral body. RESULTS: In general, the measurements of male specimens were larger than those of female specimens. Significant differences were noted at 21 measurements over C3 through C7. The mean depths of the superior endplate for all male and female specimens increased consistently from C3 to C7. The mean depths of the inferior endplate varied but generally increased from C2 to C6, then decreased to C7. The mean sagittal and parasagittal middle vertebral body depths were both 14 mm. CONCLUSIONS: This information, in conjunction with preoperative computed tomographic evaluation, may be helpful in determining proper screw length during anterior plating of the cervical spine.

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PubMed1998

The reliability of the lateral radiograph in determination of the optimal transarticular C1-C2 screw length.

STUDY DESIGN: This study assessed the value of using lateral radiographs in evaluating the optimal screw length in transarticular C1-C2 screw fixation. OBJECTIVES: To assess the reliability of the lateral radiograph in determining the optimal transarticular C1-C2 screw length. SUMMARY OF BACKGROUND DATA: Transarticular C1-C2 screw placement is usually performed using anatomic landmarks and fluoroscopy. A lateral fluoroscopic image is valuable when directing screws in the sagittal plane, but its exact role in determining screw length has not been investigated. METHODS: Eight cervical spine specimens were used in this study. Screw placements were performed in each specimen, fixed in the exact lateral position and under direct visualization. After each placement, a lateral radiograph was taken. The odontoid process was divided into three equal portions. Another portion anterior to the odontoid process was called the anterior tubercle region. The number of screw tips appearing in each portion on the radiograph was then recorded for each placement. In addition, 30 C1 specimens were measured to evaluate the anterior part of C1. RESULTS: The results showed that 12.5% of the screws placed 2 mm short of reaching the ventral cortex and 0 mm overpenetrating the ventral cortex of the lateral mass of C1 projected in the radiograph on the anterior tubercle region, 37.5% on the anterior region of the odontoid process, and 50% on the middle region of the odontoid process. Twenty-five percent of the screws that were placed to overpenetrate, by 2 or 4 mm, the ventral cortex of the lateral mass of C1 were projected on the anterior tubercle region in the radiograph, and 50% and 62.5% were projected on the anterior region of the odontoid process, respectively. The mean vertical distance between the anteriormost point of the anterior tubercle of the anterior ring and the middle of the ventral cortex of the lateral in all specimens was 5.6 +/- 1 mm, and the mean transverse angle of the anterior ring relative to the frontal plane was 21.1 +/- 3.5 degrees. CONCLUSIONS: This results in this study indicate that a lateral radiograph may not be reliable in determining the optimal screw length, although it is valuable in directing accurate screw angle in the sagittal plane. Preoperative computed tomographic evaluation of the C1-C2 region may be helpful in estimating the location of the screw tip on the lateral radiograph during surgery.

Adult↗

PubMed1998

The anatomic location of the dorsal ramus of the cervical nerve and its relation to the superior articular process of the lateral mass.

STUDY DESIGN: This study analyzed the anatomic relation of the dorsal ramus of the cervical spinal nerve to the lateral mass. OBJECTIVES: To determine the location of the dorsal rami of the cervical spinal nerves from C3 to C7 in relation to the superior articular processes of the lateral masses. SUMMARY OF BACKGROUND DATA: The anatomic study of the cervical spinal nerve and its relations to adjacent bony structures have been addressed. No previous anatomic study with regard to the location of its dorsal ramus relative to the lateral mass has been reported. METHODS: Twelve specimens were obtained for study of the dorsal rami of the cervical spinal nerves. All soft tissues surrounding the cervical spinal nerves from C3 to C7 were dissected from the intervertebral foramens until the dorsal rami were clearly exposed. The facet joints in the corresponding levels were then opened by removal of the capsules. Three measurements, including the height of the dorsal ramus, the distance between the dorsal ramus and the tip of the superior articular facet, and the angle of the dorsal ramus relative to the superior articular surface, were taken for each ramus. RESULTS: The results showed that the mean height of the dorsal ramus for both sides decreased progressively from C3 (2.2 +/- 0.6 mm) to C7 (1.2 +/- 0.2 mm). The mean distance between the dorsal ramus and the tip of the superior facet showed an inconsistent change, with the maximum value seen at C5 (7.4 +/- 1.6 mm) and the minimum at C7 (5.5 +/- 2.9 mm). The mean angle of the dorsal ramus relative to the superior articular facet ranged from 23.3 degrees +/- 14.3 degrees to 29.8 degrees +/- 11.2 degrees. CONCLUSIONS: The dorsal ramus of the cervical spinal nerve is closer to the anterolateral corner of the base of the superior articular processes. Lateral mass screws directed to the anterolateral corner of the base of the superior articular process should be avoided.

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PubMed1998

Safe lateral-mass screw lengths in the Roy-Camille and Magerl techniques. An anatomic study.

STUDY DESIGN: Investigation of the mean safe lateral-mass screw lengths in the Roy-Camille and Magerl screw techniques in cadaveric cervical specimens. OBJECTIVES: To report the mean screw path length and to evaluate the relation of the screw trajectory to the nerve root in the Roy-Camille and Magerl screw techniques. SUMMARY OF BACKGROUND DATA: Potential injury to the cervical nerve root caused by too long a screw remains a major concern. Few studies regarding proper screw length and its relation to the adjacent nerve root are available. METHODS: Fourteen cervical spines were used for this study. Each lateral mass from C3 to C7 was drilled according to the techniques described by Roy-Camille (right side) and Magerl (left side). The cervical spines were harvested from the cadavers, and the anterior aspect of the lateral mass and spinal nerve were exposed. The screw path length between the dorsal and ventral cortices of the lateral mass were measured. An additional measurement was taken from the ventral aspect of the lateral mass to the nerve root along the screw path. RESULTS: The mean screw path length in the Roy-Camille technique decreased consistently from C3 (15.7 +/- 1.7 mm) to C7 (11.3 +/- 0.8 mm). The mean distance from the ventral cortex to the nerve root ranged from 1.2 to 2.3 mm, and the smallest value was at C7. The mean screw path length in the Magerl technique also decreased from cephelad to caudal, with a range of 15-16 mm at C3-C6 and a mean value of 13.8 mm at C7. CONCLUSIONS: A safe screw length is 14-15 mm in the Roy-Camille technique and 15-16 mm in the Magerl technique at C3-C6. A short screw may be used at C7 if desired.

Bone Plates↗

PubMed1998

Anatomic considerations of anterior transarticular screw fixation for atlantoaxial instability.

STUDY DESIGN: Anatomic parameters of C1 and C2 were measured in 30 dried human cervical spines. Anterior transarticular C1-C2 screws were placed in 15 cadaveric spines. OBJECTIVE: To provide anatomic data for anterior transarticular atlantoaxial screw or C1-C2 screw and plate fixation. SUMMARY OF BACKGROUND DATA: A posterior approach to fixation in the atlantoaxial joint has been well described. Damage to the vertebral artery is documented as a rare complication of posterior atlantoaxial transarticular screw fixation. An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. No anatomic information regarding the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 is available in the literature. METHODS: Direct measurements using digital calipers and a goniometer were taken from 30 pairs of dried human C1 and C2 vertebrae. The anterior transarticular C1-C2 screw insertion point is at the junction of the lateral edge of the C2 vertebral body to 4 mm above the inferior edge of the C2 anterior arch. The parameters related to anterior transarticular atlantoaxial screw fixation or screw and plate fixation between the C1 lateral mass and the C2 vertebral body were measured. Fifteen embalmed cadavers were used for anterior C1-C2 transarticular screw placement. Longer screws (30-40 mm) were used to detect whether the screw tips violated the upper cervical canal or vertebral arteries. RESULTS: In the anterior transarticular atlantoaxial screw placement, lateral angulation of the screw placement relative to sagittal plane ranged from 4.8 +/- 1.8 degrees to 25.3 +/- 2.6 degrees. The posterior angulation of the screw placement relative to the coronal plane ranged from 12.8 +/- 3.1 degrees to 22.6 +/- 3.2 degrees. The length of the medial screw path ranged from 14.7 +/- 1.5 mm to 25.4 +/- 2.8 mm. In the anterior screw and plate fixation, the anteroposterior diameter of the inferior facet articular surface ranged from 16.2 +/- 1.6 mm to 17.1 +/- 1.8 mm. The anteroposterior diameter of the C2 vertebral body ranged from 9.3 +/- 1 mm to 16.2 +/- 1.8 mm. The anterior prevascular retropharyngeal approach appropriately exposed the atlantoaxial joint for anterior transarticular C1-C2 screw placement. No screws violated the vertebral artery and cervical canal. CONCLUSIONS: An anterior transarticular atlantoaxial screw 15-25 mm long can be inserted with a lateral angulation of 5-25 degrees relative to the sagittal plane and a posterior angulation of 10-25 degrees relative to the coronal plane. Additionally, in C1-C2 anterior plate fixation screws 15 mm long could be anchored in the inferior facet of the C1, and screws 9-15 mm long could be anchored in the C2 vertebral body.

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