Identification of the anterior and posterior portions of the lateral pedicle cortex by roentgenograms in pedicle screw fixation.

Forty lumbar pedicles and pedicle screws in four cadavers were used to identify the anterior and posterior portions of the lumbar pedicle cortex by roentgenograms in order to evaluate the penetration of the pedicle cortex by pedicle screws intraoperatively. Firstly, the transverse pedicle angles were measured on roentgenograms. Three roentgenograms were taken on each pedicle in three different directions: (1). medial to the pedicle axis; (2). pedicle axis; (3). lateral to the pedicle axis. They revealed that the anterior portion of the lateral pedicle cortex was demonstrated by the pedicle lateral outline on the roentgenogram medial to the pedicle axis, and the posterior portion by the pedicle lateral outline on the roentgenogram lateral to the pedicle axis. Wire markers were used to confirm these data. Finally, anterior and/or posterior penetrations on the lateral pedicle cortex in pedicle screw fixation were studied by roentgenograms in these cadavers and showed that anterior penetration of lateral cortex was demonstrated by the view medial to the pedicle axis, and posterior penetration by the view lateral to the pedicle axis. It is concluded that projections medical and lateral to the pedicle axis are necessary to identify lateral screw penetration intraoperatively when X-ray checking is used.

Anatomic considerations of the posterolateral lumbar disk region.

Sixteen embalmed cadavers were dissected to determine the location of the lumbar nerve root and sympathetic trunk with reference to the superior border of transverse process. In the posterolateral lumbar disk region, a safe zone was found between the anterior limit of the lumbar nerve and the posterior limit of the sympathetic trunk. It has a transverse dimension of 22 mm at the T12-L1 disk region and 25 mm at the L4-L5 disk region. The only exception to this was the genitofemoral nerve running close to the lateral margin of the L2-L3 disk. The study provides an understanding of the posterolateral orientation of the lumbar nerves and sympathetic trunk.

The location of the pedicle and pars interarticularis in the axis.

STUDY DESIGN: This is an anatomic and radiologic study on the lateral mass of the C2 vertebra. OBJECTIVES: To define the location of the pedicle and pars interarticularis in the C2 vertebra. SUMMARY OF BACKGROUND DATA: Transpedicular screw fixation of the C2 has been addressed in the literature. However, the use of the anatomic terminology of the pedicle or pars interarticularis (isthmus) in C2 is confusing in most of orthopaedic and neurosurgical literature since C2 is considered a transitional vertebra. METHODS: Twenty dry C2 vertebrae were obtained for observation of the external anatomy of the C2 from superior, lateral, and inferior views. Six C2 vertebrae were harvested from cadavers and sectioned in the sagittal, horizontal, and coronal planes to observe the internal structures of the lateral mass using high resolution radiographs. RESULTS: Based on observation, the pedicle of the C2 vertebra is defined as the portion beneath the superior facet and anteromedial to the transverse foramen. The pars interarticularis or isthmus is defined as the narrower portion between the superior and inferior facets. No remarkable difference in bone density and trabecular bone orientation between the pedicle and pars interarticularis was noted. CONCLUSIONS: It is still more appropriate to call this procedure "transpedicular screw fixation" in the C2 to avoid confusion, although this technique requires placing a screw from the posterior aspect of the inferior articular process through the isthmus and pedicle into the vertebral body.

Location of the first and second sacral nerve roots in relation to pedicle screw placement.

Dissection and measurements of the first 2 sacral nerve roots with regard to the commonly used entrance points for S1 and S2 pedicle screw placement were performed to determine the location of the first 2 sacral nerve roots in relation to the pedicle screw entrance points in the upper 2 sacral vertebrae. The sacral nerve roots, dural sac, and pedicles were exposed after laminectomy. The mean distance from the reference point to the adjacent nerve roots superiorly and inferiorly at the S2 pedicle level was smaller than those at the S1 pedicle level. The medial angle of the sacral nerve roots progressively decreased from L5 to S3. The nerve root passing through the next foramen formed an immediate medial relation to the sacral pedicle rather than the dural sac. Pedicle screw placement in the first 2 sacral vertebral pedicles has been recommended for lumbosacral fusion and internal fixation of sacral fractures. No anatomic study is available regarding the location of the sacral nerve roots relative to the entrance points of sacral pedicle screw placement. Violation of the sacral canal and foramina by a sacral pedicle screw may injure the sacral nerve roots, especially at the level of the S2 pedicle.

Anatomic study of the cervicothoracic spinal nerves and their relation to the pedicles.

Twelve cadavers were dissected for the study of the cervicothoracic junction. The results showed that the mean heights and widths of the ganglia tend to decrease from the C-6 to T-4 nerve. The mean distances between the dura and the ganglion and the mean spinal nerve angles increased consistently from C-5 to T-4. The mean distances from the spinal nerves to the superior and inferior pedicles ranged 0.8-2.3 mm. It was noted that the mean value was significantly greater for the distance from the spinal nerve to the superior pedicle than that to the inferior pedicle for the spinal nerves C5-7 (P< or =.05). This information, in conjunction with imaging studies, may minimize spinal nerve injury during posterior pedicle screw fixation in the cervicothoracic spine.

The anatomy of the posterior interosseous nerve as a graft.

Thirty upper limbs from skeletally mature embalmed cadavers were studied to determine the anatomic reliability of the posterior interosseous nerve as a donor nerve graft. The posterior interosseous nerve branches 0.43 +/- 0.52 cm from the distal edge of the superficial head of the supinator and 8 +/- 1.6 cm from the lateral epicondyle form a common leash. There are 6 branches, which are arranged from the ulnar to the radial side at their origin from this leash. The first and second branches supply the extensor digitorum communis, the third branch supplies the extensor carpi ulnaris, the fourth branch supplies the extensor digiti minimi, and the fifth branch arises from the undersurface of the common leash and divides into 2 sub-branches (medial and lateral) 10.1 +/- 3.2 cm distal to the lateral epicondyle and 12.8 +/- 2.2 cm proximal to Lister's tubercle. These 2 sub-branches make an inverted V shape around the extensor pollicis longus. The medial branch supplies the extensor pollicis longus and extensor indicis proprius. The lateral branch supplies the extensor pollicis longus and extensor pollicis brevis and ends at the wrist capsule. At a mean distance of 8.1 +/- 1.2 cm proximal to Lister's tubercle the lateral sub-branch gives off its last muscular branch to the extensor pollicis longus and becomes a pure sensory terminus. As the terminal part of the lateral sub-branch approaches the wrist capsule it expands at a mean distance of 1.9 +/- 0.5 cm proximal to Lister's tubercle. The sixth branch arises from the radial side of the common leash and divides into 3 sub-branches. The first sub-branch supplies the abductor pollicis longus and extensor pollicis brevis, the second supplies the abductor pollicis longus, and the third supplies the superficial head of the supinator. This study showed that the mean length obtainable for harvesting the lateral sub-branch of the fifth branch of the posterior interosseous nerve is 6.2 +/- 0.7 cm, which represents the length of the nerve between the last muscular branch to the extensor pollicis longus to the point at which the nerve expands.

Quantitative anatomical study of the posterior interosseous nerve.

An anatomic study of the posterior interosseous nerve (PIN) in 20 cadaver upper limbs was performed to measure different segments of the PIN and its relationship with radius and ulna (results given as mean +/- SD). The length of the PIN from radial head to the arcade of Frohse (AF) was 26.5 +/- 1.6 mm and 25.3 +/- 1.1 mm in male and female cadavers, respectively. The length of the PIN from radial head to the PIN exit point from the supinator was 66.7 +/- 4.7 mm and 64.0 +/- 2.5 mm in male and female cadavers, respectively. The overall length of the PIN underlying the supinator muscle was 44.0 +/- 0.5 mm and 37.0 +/- 0.5 mm in male and female cadavers, respectively. The distance between the PIN exit point from the supinator and the radial margin of the radius was 15.0 +/- 0.9 mm and 14.5 +/- 0.9 mm in male and female cadavers, respectively. The distance between the PIN exit point from the supinator and ulnar margin of ulna was 18.2 +/- 0.6 mm and 17.9 +/- 0.7 mm in male and female cadavers, respectively. In 70% (n = 14) of the cadavers, the AF was tendinous and in 30% (n = 6), it was membranous. The length, width, and thickness of AF in males and females, respectively, were 18.6 +/- 1.2 mm / 18.5 +/- 1.3 mm; 2.8 +/- 0.4 mm / 2.5 +/- 0.4 mm; and, 0.8 +/- 0.08 mm / 0.7 +/- 0.07 mm. In all specimens, the PIN exited through the distal supinator muscle by penetrating the muscle. The PIN exit point from the supinator belly was about 11-19 mm from distal border of the latter. The mean distances between PIN exit point from the supinator and the origin of the extensor digitorum communis, abductor pollicis longus, and extensor pollicis longus branches were 7.5 mm, 31 mm, and 58 mm, respectively.

Posterior interosseous nerve terminal branches.

Thirty upper limbs from skeletally mature embalmed cadavers were studied to define the most common pattern of the terminal branches of the posterior interosseous nerve. At 0.43 +/- 0.52 cm from the distal edge of the superficial head of the supinator and 8 +/- 1.6 cm from the lateral epicondyle, the posterior interosseous nerve branches, forming a common leash. There were six branches, which were arranged from the ulnar to the radial side at their origin from the common leash. The first and second branches supplied the extensor digitorum communis, the third branch supplied the extensor carpi ulnaris, the fourth branch supplied the extensor digiti minimi, and the fifth branch arose from the undersurface of the common leash and divided into two branches (medial and lateral) at 10.1 +/- 3.2 cm distal to the lateral epicondyle and 12.8 +/- 2.2 cm proximal to Lister's tubercle. The medial branch supplied the extensor pollicis longus and extensor indicis proprius. The lateral branch supplied the extensor pollicis longus and extensor pollicis brevis and ended at the wrist capsule. The sixth branch arose from the radial side of the common leash and divided into three branches. The first branch supplied the abductor pollicis longus and extensor pollicis brevis. The second branch supplied the abductor pollicis longus. The third branch supplied the superficial head of the supinator. The authors of this study describe the most efficient way to identify the six branches and how to avoid the risk of damaging them during surgical exposure.

Vulnerability of the sympathetic trunk during the anterior approach to the lower cervical spine.

STUDY DESIGN: Anatomic dissection and measurements of the cervical sympathetic trunk relative to the medial border of the longus colli muscle and lateral angulation of the sympathetic trunk relative to the midline on both sides were performed. OBJECTIVE: To determine the course and location of the sympathetic trunk quantitatively and relate this to the vulnerability of the sympathetic trunk during the anterior approach to the lower cervical spine. SUMMARY OF BACKGROUND DATA: The sympathetic trunk is sometimes damaged during the anterior approach to lower cervical spine, resulting in Horner's syndrome with its associated ptosis, meiosis, and anhydrosis. No quantitative regional anatomy describing the course and location of the sympathetic trunk and its relation to the longus colli muscle is available in the literature. METHODS: In this study, 28 adult cadavers were used for dissection and measurements of the sympathetic trunk. The distance between the sympathetic trunk and the medial borders of the longus colli muscle at C6 and the angle of the sympathetic trunk with respect to the midline were determined bilaterally. The distance between the medial borders of the longus colli muscle from C3 to C6 and the angle between the medial borders of the longus colli muscle also were measured. RESULTS: The sympathetic trunk runs in a superior and lateral direction, with an average angle of 10.4 +/- 3.8 degrees relative to the midline. The average distance between the sympathetic trunk and the medial border of the longus colli muscle is 10.6 +/- 2.6 mm. The average diameter of the sympathetic trunk at C6 is 2.7 +/- 0.6 mm. The length and width of the middle cervical ganglion were 9.7 +/- 2.1 mm and 5.2 +/- 1.3 mm, respectively. The distance between the medial borders of the longus colli muscle was 7.9 +/- 2.2 mm at C3, 10.1 +/- 3.1 mm at C4, 12.3 +/- 3.1 mm at C5, and 13.8 +/- 2.2 mm at C6, and the angle between the medial borders of the longus colli muscle was 12.5 +/- 4. 7 degrees. CONCLUSIONS: The sympathetic trunk may be more vulnerable to damage during anterior lower cervical spine procedures because it is situated closer to the medial border of the the longus colli muscle at C6 than at C3. The longus colli muscles diverge laterally, whereas the sympathetic trunks converge medially at C6. As the transverse foramen or uncovertebral joint is exposed with dissection or transverse severance of the longus colli muscle at the lower cervical levels, the sympathetic trunk should be identified and protected.

Anatomic considerations of costotransverse screw placement in the thoracic spine.

BACKGROUND: Numerous techniques have been reported to restore spinal stability and to correct spinal deformities, including rods with wires/hooks, and rods or plates with pedicular screws. It was thought that posterior fixation of the thoracic spine through the costotransverse joint may be another alternative. METHODS: Nine cadavers were obtained for study of screw fixation of the costotransverse joint for posterior thoracic instrumentation. The entrance point for screw insertion was designed to be at the posterior center of the clubbed extremity of the transverse process. From this point, a 3-mm drill bit was used to create the screw path penetrating the costotransverse joint and the ventral cortex of the rib. Under direct visualization of the costotransverse joint, the drill bit was directed parallel to the sagittal plane and toward the upper portion of the rib. Measurements included the screw path length and sagittal angulation. Also, the distance between the superior borders of the transverse process and the tubercle of the rib and the anatomic relationship of the drill bit exit to the intercostal vessels and nerves were evaluated. RESULTS: The maximum length of the screw path was found at T1 (19.7 mm), whereas the minimum length was noted at T4-T5 (13.9 mm). This value decreased gradually from T1 to T4-T5, and slightly increased to T10. The larger sagittal angles of the screw path were found at the levels of T1-T4 (78-86 degrees ), whereas the smaller were noted at the levels below T5 (53-61 degrees ). The mean distance between the superior borders of the transverse process and the tubercle of the rib was smaller at T1-T5 (0.2-0.4 mm), and significantly increased to T8 (5. 1 mm), and then slightly decreased to T10. The variation of this parameter was remarkable. All of the exit points for the drill bit were located in the upper half of the rib, and away from the intercostal vessels. CONCLUSIONS: The ideal screw orientation is parallel to the sagittal plane, and angled 80-90 degrees relative to the frontal plane for T1-T4 and 50-70 degrees for T5-T10 superiorly, starting at the posterior center of the transverse process. Costotransverse screw fixation in the thoracic spine may be an alternative to pre-existing methods.

Extensile posterior approach to the radius.

An extensile posterior approach to the radius was studied on 20 forearm anatomic specimen upper limbs. The skin incision followed a line from the lateral epicondyle of the humerus to a point corresponding to the middle of the posterior aspect of the wrist. Dissection was done between the extensor digitorum communis and the extensor carpi radialis brevis. The posterior interosseous nerve was identified, and the muscle fibers of the superficial head of the supinator were divided from distal to proximal to the posterior interosseous nerve, which was dissected and carefully retracted laterally. The muscle fibers of the deep head of the supinator were divided to the bone. An incision was made along the superior and inferior margins of the abductor pollicis longus and extensor pollicis brevis. A nerve tape was placed around the two muscles, and they were retracted proximally and medially or distally and laterally, as necessary. To expose the distal third of the radius, the obliquely placed muscles, abductor pollicis longus, and extensor pollicis brevis were retracted proximally and medially. Dissection was done between the extensor carpi radialis brevis and extensor pollicis longus. Anatomic study of the posterior interosseous nerve branches was done to understand the vulnerability of such branches seen in this approach.

Quantitative anatomy of the scapula.

Thirty adult bony scapulae were used to report detailed bony dimensions of the scapula. The measurements of bony dimensions of the scapula included the glenoid, coracoid, spine, and body. The results of the measurements showed that the thickest bony stock (posteroanterior diameter), with a mean value of 13 mm to 23 mm in the glenoid process, was found in the middle third of the area within 1 cm medial to the glenoid rim. In the scapular spine region, the greatest superoinferior diameter of the bone was noted in the lateral portion of the spine, followed by the medial portion. It was also found that smallest superoinferior diameter (2 mm to 7 mm) of the spine was located at the middle portion between the base and ridge along the whole spine. On the lateral border of the scapula, the posteroanterior diameter of bone was relatively greater for the upper portion (8 mm) than for the lower portion, including the inferior angle (6 mm). This information may be helpful in open reduction and internal fixation of significantly displaced scapular fractures.

The optimal transarticular c1-2 screw length and the location of the hypoglossal nerve.

BACKGROUND: Injury to the hypoglossal nerve is a complication associated with transarticular C1-2 screw placement. This complication can be caused by a misdirected or too long screw. Little is known about the optimal screw length and its relationship to the hypoglossal nerve. METHODS: Twenty cervical spine specimens were used to study the optimal length of the transarticular C1-2 screw. Using the Magerl technique, a 3.0 mm drill bit was inserted into the C2 lateral mass, passing through the C1-2 facet joint and penetrating the upper portion of the ventral cortex of the lateral mass of the atlas. After drilling, the hole length was measured between the dorsal cortex of the C2 inferior articular process and the ventral cortex of the C1 lateral mass. In addition, six sagittal-sectioned cadavers were carefully dissected to observe the location of the hypoglossal nerve in the anterior aspect of the atlantoaxial region. RESULTS: The results of the measurements showed that the mean optimal screw path length for all specimens was 38.1 +/- 2.2 mm with a range of 34-43 mm. There was no significant difference between sexes in the screw path length (p 0.05). The hypoglossal nerve lies vertically in front of the lateral portion of the C1 lateral mass and the C1-2 facet joint. The area where the hypoglossal nerve lies is approximately 2-3 mm lateral to the middle of the anterior aspect of the C1 lateral mass. CONCLUSIONS: This study suggests that the mean optimal transarticular C1-2 screw length may be 38 mm; however, the determination of the accurate optimal C1-2 screw length should be made on an individual basis. Risk to the hypoglossal nerve can be eliminated if Magerl's technique is performed exactly.

Cervical venous structure in the inter-transverse and intra-transverse foraminal region: an anatomic study.

Vertebral venous bleeding is frequently encountered during anterolateral cervical decompression. The present study was undertaken to identify the pattern and location of the vertebral vein in relationship to the vertebral artery in the inter-transverse and intra-transverse foraminal regions. Twenty-one cadavers were dissected to determine the anatomic features of the vertebral vein in the inter-transverse and intra-transverse foramina. The vertebral veins in the inter-foraminal and intraforaminal regions from C-3 to C-6 can be classified into three types: single or double veins, venous plexus, and absence of the vein. Of the 21 specimens, vertebral veins were found bilaterally in five specimens (24%) and unilaterally in eight specimens (38%). The veins were situated either anterolateral or anteromedial to the vertebral artery. The venous structures showed in venous plexus in two specimens (9.5%). In six specimens (29%), there were no obvious venous structures related to the vertebral artery in its intra-transverse and inter-transverse foraminal course. The veins are contained in a fibrous and osseous tunnel as they descend through the transverse foramina. Subperiosteal dissection of fibrous tissue from the lateral aspect of the uncinate process after removal of the anterior wall of the transverse foramen may minimize hemorrhages from the vertebral vein in the inter-transverse and intra-transverse foraminal region during resection of the uncovertebraljoint or neural foraminotomy with retraction of the vertebral artery laterally.

Anatomical and radiological considerations of the fifth metatarsal bone.

Twenty cadaver fifth metatarsals were harvested from cadaver feet. They were then sectioned coronally in three locations. The cortical thickness (medial, lateral, dorsal, and plantar) and the intra-medullary canal diameter (dorsoplantar and mediolateral) were measured at the three sectional sites. The intra-medullary canal of six specimens was outlined with radiopaque solder wire. The canal was then examined radiographically with the lateral and dorsoplantar views. A lateral bow on the dorsoplantar view was observed in some specimens, which could contribute to surgical complications. On lateral view the intramedullary canal appeared straight in all specimens. The canal projects at least partially into the fifth metatarsal cuboid joint. When considering intra-medullary fixation a surgeon must take into account quality of bone stock and bowing of the canal. A bowed intra-medullary canal lends to vulnerability of the medial cortex at roughly mid-shaft of the fifth metatarsal. The canal has a narrower diameter in the dorsoplantar dimension than the mediolateral dimension. The cortical thickness was found to be less in the dorsal and plantar areas of the fifth metatarsal when compared to medial and lateral cortex. All of these findings lead to causes for complication in intra-medullary fixation of the fifth metatarsal.

Internal architecture of the sacrum in the elderly. An anatomic and radiographic study.

STUDY DESIGN: A description of the internal architecture of the sacrum, including its trabecular arrangement, cortical thickness, and overall bone density. OBJECTIVES: To determine the strong and weak areas in the sacrum to understand more clearly the sacral structure and its clinical implications. METHODS: First, seven cadaveric sacral specimens were sectioned in different planes. Horizontal sections were performed at the upper S1, middle S1, S2, S3, and S4. Sagittal sections were made through the median sacral crest, the sacral foramina, and medial to the articular surface. A coronal section through the whole length of a sacral specimen was produced. All sections were studied radiographically, and the trabecular pattern was analyzed. In the second part of the study, axial computed tomography scans of 40 dry sacrum specimens were analyzed by using the National Institutes of Health Image 1.61 program. The cortical thickness and bone density were determined. RESULTS: In the upper sacrum, three distinctive distributions of bony trabeculae were noted, one extending from the center of the sacral body anterolaterally, and the other two extending from the pedicle toward the auricular surface. A condensation zone was observed at the intersection of these trabeculae and was located at the anterior cortex of the foraminal zone. The junction between S2 and S3 represented a weak area with abrupt disappearance of the condensation zone. Analysis of the bone density of the sacrum using the plot analysis demonstrated that, at S1 and S2, the anterior cortex of the foraminal zone (condensation zone) is the most compact part of the sacrum. CONCLUSION: These results suggest that the strongest part of the sacrum is the anterior cortex above the foramina in S1 and S2. The weakest point of the sacrum was found to lie at the level of the junction of S2 and S3.

The lumbosacral nerves in relation to dorsal S1 screw placement and their locations on plain radiographs.

Seven adult cadaver lumbopelvises were harvested to study the anatomic relationship of the L4 and L5 nerves to S1 dorsal screw placement and the location of the L4, L5, and S1 nerves on plain radiographs. The mean lateral angle of S1 screw trajectory toward the L4 nerve was 31+/-8 degrees, and the mean screw trajectory length was 53+/-8 mm. The mean lateral angle of the screw trajectory toward the L5 nerve was 21+/-8 degrees, and the mean screw trajectory length was 38+/-4 mm. On both inlet and outlet radiographs, the lateral angle of the nerves increased from L4 to S1. The L4 nerve coursed over the middle third of the superior ala in the inlet view and the middle third of the lateral mass in the outlet view. The L5 nerve coursed over the inner third of the superior ala and inner third of the lateral mass. On the lateral view, the mean distances from the sacral promontory to the L4, L5, and S1 nerves along the anterior border of the sacrum were 4+/-7 mm, 12+/-5 mm, and 28+/-8 mm, respectively. This study suggests that S1 sacral screws be directed between 30 degrees and 40 degrees lateral to avoid compromising the lumbosacral trunk and sacroiliac joint.

Anatomic considerations of a modified anterior approach to the cervicothoracic junction.

The results of a study on 30 adult human cadavers showed that the anterior aspect of T-3 can be easily exposed through a modified anterior approach to the cervicothoracic spinal junction. Anterior exposure of T-4 caused significant tension on the brachiocephalic vein in 57%; in 7% the vein actually tore. The location of the vital structures is as follows: the left brachiocephalic vein is at T-1 and T-2 in 80%; the aortic arch is at T-2 and T-3 in 90%; the right recurrent laryngeal nerve reaches the tracheoesophageal groove at the level of C-6 in 50%; the thoracic duct empties into the systemic venous system from C-7 to T-2. Adequate exposure of the low cervical to the upper thoracic spine can be obtained with this approach. Preoperative computed tomographic evaluation of the location of the left brachiocephalic vein with respect to the vertebral levels is recommended.

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.

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.