The location of the spinal nerve root on plain radiographs of the cervical spine

Twelve cervical spines from C2 to T1 were harvested from embalmed cadavers to study the location of the nerve root on plain radiographs. After removal of the soft tissue, the spinal nerves just lateral to the transverse processes were exposed and injected with lead oxide. Plain radiographs including anteroposterior (AP) and left and right oblique views were taken. Angular and linear measurements were performed directly on the radiographs. Results showed that the average frontal angle of the nerve root for all levels was 155 degrees on the AP view, 108 degrees on the foraminal side of the oblique view, and 153 degrees on the opposite side of the oblique view. The nerve root height for all levels averaged 4.7 +/- 0.5 mm. The interpedicular space height increased consistently from 7.8 +/- 0.7 mm at C3-C4 to 9.0 +/- 1.3 mm at C6-C7 except at C2-C3. The nerve root height with respect to the interpedicular space height was 56.2% at C2-C3, 57.8% at C4-C5, and 53.7% at C6-C7. A knowledge of the location of the cervical nerve root related to plain radiographs may enhance the value of plain radiographs in the diagnosis and treatment of cervical spinal disorders.

Anatomic considerations of the second sacral vertebra and dorsal screw placement

Direct measurements and measurements from images of axial cross-sections on 20 cadaveric sacra that had been scanned on computer were used in this study. The measurements, including parameters from the vertebral body, lateral mass and spinal canal of the second sacral vertebra (S2) were performed. The length of the screw path and the optimal angulation of the screw placement for dorsal sacral internal fixation were also included. The mean values of height, anteroposterior diameter, width and breadth of the S2 were 25.0 mm, 13.5 mm, 29.4 mm and 83.0 mm, respectively. The mean values of the mid-sagittal diameter, maximum transverse diameter and area of the S2 spinal canal were 10.3 mm, 23.1 mm and 162.4 mm2, respectively. The mean transpedicular screw length of the S2 and optimal medial angle were 25.2 mm and 30.0 degrees, respectively. The mean lateral mass screw length of the S2 and optimal lateral angle were 32.8 mm and 22.0 degrees, respectively. The present study provides quantitative anatomic data of the second sacral vertebra. All parameters indicate that, compared with our previous study, S2 is smaller than S1. When S2 lateral mass screw fixation is intended, anchoring the anterior cortex may violate the iliac vessels or lumbosacral trunk; therefore, understanding the unique anatomy of the S2 is imperative.

Lateral radiologic evaluation of lateral mass screw placement in the cervical spine

STUDY DESIGN

Assessment of the value of lateral radiographs in evaluation of lateral mass screw placement in the cervical spine.

OBJECTIVES

To assess the value of lateral radiographs in determining the safe or hazardous locations of the tips of screws used in lateral mass screw fixation.

SUMMARY OF BACKGROUND DATA

Posterior plating with lateral mass screw fixation is frequently used to stabilize the cervical spine and improve fusion. Injury to the spinal nerves caused by screws that are too long must be identified quickly to minimize neurologic complication. No previous radiologic study in which lateral mass screw placement was evaluated using lateral radiographs has been reported.

METHODS

Six cervical spines were removed from embalmed cadavers. Three screws using the Roy-Camille technique and another three using Magerl technique were placed into the lateral mass at C3-C5 in each specimen. Four screw placements under direct visualization, including placement of the screw tip staying the ventral cortex and 2-mm, 4-mm, and 6-mm overpenetration of the ventral cortex, were performed separately on each specimen for each of the two techniques. After each placement, a lateral radiograph was taken. Each vertebral body was divided vertically into four equal zones with Zone I the most posterior. Another equal zone, posterior to the posterior border of the vertebral body was defined as pre-Zone I. The number of screw tips seen in each zone were quantified for each placement.

RESULTS

In the screws placed using the Roy-Camille technique, 77.8% of screws placed without perforating the ventral cortex were found in Zone I; 72.2% placed with 2-mm overpenetration of the ventral cortex were noted in Zone II; and 61.1% of the screws with 4-mm overpenetration of ventral cortex and 77.8% with 6-mm overpenetration were located in Zone III. For the use of the Magerl technique, 44.4% of the screws placed without perforating the ventral cortex were found in pre-Zone I; 72.2% of the screws placed with 2-mm overpenetration were located in Zone I; and 66.6% with 4-mm overpenetration and 89.7% with 6-mm overpenetration were noted in Zones I and II, respectively.

CONCLUSIONS

Lateral radiographs may be valuable in evaluating lateral mass screw placement. Ideal screw tip positions on lateral radiograph for the Roy-Camille technique may be in Zone I, and for the Magerl technique may be in pre-Zone I.

Computed tomographic considerations of dorsal sacral screw placement

Axial computed tomographic scans were obtained from 40 sacrum specimens. The best scans close to the inferior portion of S1 superior facet and the middle of S2 pedicle were chosen to evaluate various screw paths. Measurements of screw paths included the screw path lengths and angulations as well as the distances between the screw and the sacral canal. The results showed that no significant differences between male and female specimens were found in any parameters, although the linear measurements were greater for male specimens than for female specimens. In S1, the greatest value of the screw path lengths was noted in screw path IV (anterolaterally directed) with an average of 36.9 +/- 7.3 mm. The mean value for screw path 1 (30 degrees anteromedially directed) was 32.5 +/- 7.2 mm, and the mean distance between screw path I and the lateral cortex of the sacral canal was 6.0 +/- 3.1 mm. For S2, the mean value (31.9 +/- 7.6 mm) of screw path II (anterolaterally directed) was significantly greater than that (24.2 +/- 4.9 mm) of screw path I (30 degrees anteromedially directed) (p < or = 0.001). The mean distance between screw path I and the lateral cortex of the sacral canal was 4.8 +/- 3.2 mm. This study showed that computed tomography (CT) scans provide more accurate information of screw path lengths. Preoperative CT evaluation of the sacral screw path angle and length is recommended.

Lumbosacral plexus: a histological study

Two hundred and forty histological paraffin sections were obtained from the midportion of the spinal nerve roots of 20 lumbosacral plexus (from L4 to S3) bilaterally. All microscopic images were digitized using the NIH image software with a Nikon microscope and Sony videocamera. The total, fascicular as well as epineurial cross-sectional areas of the nerve roots in the lumbosacral plexus were determined. The total cross-sectional area of the lumbosacral trunk (LST) was the largest (28.56 +/- 12.28 mm2) followed by the S1 (21.97 +/- 11.22 mm2) and L5 (21.00 +/- 8.79 mm2) nerve roots. The total cross-sectional areas of the L4 (6.93 +/- 3.32 mm2), S2 (13.93 +/- 5.86 mm2) and S3 (6.03 +/- 3.74 mm2) were significantly lower. Statistical differences were found among all absolute values at different levels (p < 0.0001) with the exception of the levels between L4 and S3, L5 and S1, and LST and S1 (p > 0.05). The total areas occupied by the fascicles in L5 (7.78 +/- 3.26 mm2), LST (9.97 +/- 4.01 mm2) and S1 (8.55 +/- 3.27 mm2) nerve roots were greater than those in L4 (2.96 +/- 1.50 mm2), S2 (5.56 +/- 2.34 mm2) and S3 (2.28 +/- 1.14 mm2). However, the percentages of the total cross-sectional areas occupied by the fascicles in the L5 nerve root (38%) and LST (36.4%) were smaller compared to other nerve roots (44.9% at L4, 40.5% at S1, 40.8% at S2 and 41.6% at S3). The cross-sectional areas and percentages of the epineurium were greater in L5 (13.22 +/- 6.48 mm2, 62.0%), LST (18.58 +/- 9.31 mm2, 63.6%) and S1 (13.42 +/- 8.88 mm2, 59.5%) roots. The L5 (12.1 +/- 5.0), LST (27.5 +/- 11.4) and S1 (15.0 +/- 7.3) roots contained more fascicles than L4 (6.3 +/- 3.3), S2 (9.5 +/- 4.1) and S3 (7.1 +/- 2.7). Statistical differences were found among all absolute values at different levels (p < 0.0001) with the exception of the levels between L4 and S3, L5 and S1 and LST and S1 (p > 0.05). No statistical differences were found for percentages among different levels (p > 0.05) with the exception of the levels between L4 and L5, L4 and LST, LST and S1, LST and S2, and LST and S3 (p < or = 0.05). The histological structure of nerve roots of the lumbosacral plexus is identical to that of the peripheral nerve. The midportions of L5 and S1 roots and the LST have a relatively higher epineurial content. These nerve roots also have a greater number of the fasicles, but the total cross-sectional area occupied by the fascicles is less than in L4, S2 and S3 nerve roots.

Vulnerability of the recurrent laryngeal nerve in the anterior approach to the lower cervical spine

STUDY DESIGN

To perform anatomic dissections and measurements of the recurrent laryngeal nerve between the inferior thyroid artery and superior border of the clavicle (mid-portion) on both sides.

OBJECTIVES

To determine quantitatively the differences in course and location between the recurrent laryngeal nerves on both sides and to relate this to the vulnerability of the recurrent laryngeal nerve during an anterior approach to the lower cervical spine.

SUMMARY OF BACKGROUND DATA

The midportion of the recurrent laryngeal nerve is usually encountered in the anterior approach to the lower cervical spine, especially on the right side. No quantitative regional anatomy describing the course and location of the mid-portion of the recurrent laryngeal nerve is available in the literature.

METHODS

Fifteen adult cadavers were used for dissections of the recurrent laryngeal nerve. The length of the recurrent laryngeal nerve between the superior border of the clavicle and the inferior thyroid artery, and the angle of the recurrent laryngeal nerve with respect to sagittal plane, were measured bilaterally. In addition, six cross-sections at C7 were obtained to determine the linear distances between esophagotracheal groove and the recurrent laryngeal nerve.

RESULTS

The recurrent laryngeal nerve on the right runs in a superior and medial direction, with an angle of 25.0 degrees +/- 4.7 degrees relative to sagittal plane, compared with 4.7 degrees +/- 3.7 degrees on the left. The length of the recurrent laryngeal nerve between the superior border of the clavicle and the inferior thyroid artery is 23.0 +/- 4.4 mm on the left, and 22.8 +/- 4.3 mm on the right. The recurrent laryngeal nerve lies deep within the esophagotracheal groove on the left, but 6.5 +/- 1.2 mm anterior and 7.3 +/- 0.8 mm lateral to the esophagotracheal groove on the right.

CONCLUSIONS

The recurrent laryngeal nerve on the right side is highly vulnerable to injury if ligature of the inferior thyroid vessels is not performed as laterally as possible or if retraction of the midline structures along with the recurrent laryngeal nerve is not performed intermittently. Avoiding injury to the recurrent laryngeal nerve, especially on the right side, is a major consideration during an anterior approach to lower cervical spine.

Radiographic and CT evaluation of tibiofibular syndesmotic diastasis: a cadaver study

Twelve cadaver lower limbs were used for radiographic and CT assessment of the tibiofibular syndesmosis. Plastic spacers were placed in the distal tibiofibular intervals of each specimen in successive 1-mm increments until diastasis could be appreciated on the plain radiographs. All 2- and 3-mm diastases could be noted and clearly identified on CT scans, while the 1-, 2-mm, and half of the 3-mm syndesmotic diastases could not be appreciated with routine radiographs. CT scanning is more sensitive than radiography for detecting the minor degrees of syndesmotic injuries. Therefore, a CT scan can be performed in cases of syndesmotic instability after ankle injuries and for preoperative or postoperative evaluation of the integrity of the distal tibiofibular syndesmosis in cases of doubtful condition of the syndesmosis.

Anatomic relations between the lumbar pedicle and the adjacent neural structures

STUDY DESIGN

The authors analyzed anatomic parameters between the lumbar pedicles and the dural sac as well as the spinal nerve roots.

OBJECTIVES

To determine quantitatively the anatomic relations between the lumbar pedicle and adjacent dural sac and nerve roots.

SUMMARY OF BACKGROUND DATA

Posterior transpedicular screw fixation is the most commonly used method of instrumentation for stabilization of the unstable lumbar spine. A thorough knowledge of the unique anatomy of the lumbar pedicle and adjacent neural structures may avoid or minimize neurologic complications with pedicular screw placement.

METHODS

Fifteen adult cadavers were obtained to evaluate quantitatively the anatomic relations of the lumbar pedicle to the adjacent neural structures. After removal of the laminas and facets, the lumbar pedicles, dural sac, and nerve roots were exposed. Direct measurements were taken from the pedicle to the dural sac medially, to the nerve roots superiorly and inferiorly, and between the pedicles. Also, the superoinferior diameter of the nerve root and the frontal angle of the nerve root were measured. Symmetric structures were measured bilaterally.

RESULTS

No consistent changes from L1 to L5 were found in all parameters. The mean distances from the lumbar pedicle to the dural sac medially and to the adjacent nerve roots superiorly and inferiorly for all levels were 1.5 mm, 5.3 mm, and 1.5 mm, respectively. The mean interpedicular distance ranged from 23.2 to 24.4 mm. The mean superoinferior diameter of the nerve root ranged from 3.8 to 4.6 mm. The mean nerve root angle ranged from 33.7 degrees to 39.2 degrees.

CONCLUSIONS

On the basis of this study, improper placement of the pedicle screw medially or caudally in the lumbar spine should be avoided.

The location of the intervertebral lumbar disc on the posterior aspect of the spine

BACKGROUND

Epidural fibrosis or scar formation is considered one cause of failed lumbar discectomy. Avoidance of unnecessary bony resection of the lamina may prevent or decrease postoperative scar formation. The knowledge of the precise location of the projection of the lumbar disc may also facilitate surgery and decrease patient morbidity. No studies exist regarding the projection of the lumbar disc on the posterior aspect of the lumbar spine.

METHODS

Thirty-six whole lumbar spine specimens from L1 to L5 (180 lumbar vertebrae) and sacra were used for this study. Anatomic evaluation included the distance between the superior border of the vertebral body (inferior border of the intervertebral disc) and the superiormost margin of the lumbar lamina, and the distance between the inferior border of the vertebral body (superior border of the intervertebral disc) and the inferiormost margin of the lumbar lamina. The width of the interlaminar space was also measured.

RESULTS

The data showed that the level of the superior margin of the lamina was consistently inferior to the superior border of the corresponding vertebral body from L1 to S1. This distance for both sexes ranged from 10 to 11 mm for L1-L5 and 14 mm for S1. The level of the inferior margin of the lamina varied from 3 mm inferior to 9 mm superior to the inferior border of the corresponding vertebral body for L1-L5. The width of the interlaminar space averaged from 16.8 mm for L1 to 31.0 mm for L5.

CONCLUSIONS

This study suggests that the superior margin of the lamina represents a consistent, useful landmark in determining the location of the lumbar disc on the posterior aspect of the spine. The relationship between the inferior margins of the lamina and the vertebral body is not consistent.

The quantitative anatomy of the thoracic facet and the posterior projection of its inferior facet

STUDY DESIGN

This study evaluated the dimensions of the thoracic facet from T1 to T12 and determined the posterior projection of the inferior facet using thoracic spine specimens.

OBJECTIVES

To evaluate quantitatively the thoracic facet and determine the projection of the inferior facet on the posterior aspect of the lamina relative to facet hook placement in the thoracic spine.

SUMMARY OF BACKGROUND DATA

Anatomic evaluation of the thoracic facet has not been extensively addressed. No detailed studies of the thoracic facet relative to posterior facet hook fixation exist.

METHODS

Forty-three thoracic spines from T1 to T12 were directly evaluated for this study. Anatomic evaluation of the thoracic superior and inferior facets included the facet width, height, and angulation relative to sagittal plane. The projection of the inferior facet on the posterior aspect of the lamina was constructed and measured.

RESULTS

In general, the male linear and angular parameters were larger than the female ones. The average transverse angle of the facets at T1-T12 for both men and women ranged approximately from 74 degrees to 88 degrees for the superior facet and 74 degrees to 108 degrees for the inferior facet. The average inferior thickness from T1 to T12 for both sexes ranged from 3 to 5 mm. The posterior projection height of the inferior facet was found to be 9 to 12 mm from T1 to T12 for both men and women. The distance between the posterior midline and the inferior facet projection ranged from 7 to 11 mm at T1-T12 for both sexes.

CONCLUSIONS

This study may aid in the understanding of the location, angulation, and dimensions of the facet and proper placement of hooks into the thoracic facet joint.

Quantitative anatomy of the cervical facet and the posterior projection of its inferior facet

For this study, 41 cervical spines from C3 to C7 were directly evaluated. Anatomic evaluation of the cervical superior and inferior facets included the facet height, width, and angulation relative to the coronal plane. The projection of the inferior facet on the posterior aspect of the lateral mass was constructed and measured, and the dimensions of the lateral mass were evaluated. In general, the male linear parameters were larger than the female parameters, but the male angular dimensions were smaller than those of females. The posterior projection height of the inferior facet was found to be 7.4-9.0 mm from C3 to C7 for both sexes and was approximately 2 mm larger than half the height of the lateral mass. C6 and C7 had relative larger superior and inferior facet angles. The lateral mass was thinner at the level of C6-7. This study indicated that there may be a risk of violating the inferior articular facet and the related superior articular facet of the most caudal facet joint if a screw starting at the midpoint or below the midpoint of the lateral mass is directed perpendicular to the posterior aspect of the lateral mass at the level of C3-7.

Placement of screws in the uncemented acetabulum: anatomic analysis of the danger zone

Six cadavers were used to define the projection of the external iliac artery on the inner table of the acetabulum, and to quantitatively determine bony dimensions of the danger zone with regard to screw placement. The results showed that the majority of projections of the external iliac arteries were located on the superior portion of the posterosuperior quadrant and extended to the mid-superior portion of the anterosuperior quadrant (danger zone). The inferior portion of the danger zone was relatively far from the external iliac artery. The greatest depths of bone were found in the inferior portion of the danger zone, and the depths of bone in the middle and superior portion of the danger zone were relatively thinner. This anatomic study showed that the real danger zone was found in the middle and superior portions of the anterosuperior quadrant of the acetabulum. The inferior portion of the anterosuperior quadrant was relatively safer. This area may be considered if transacetabular screw replacement in the anterosuperior quadrant is required.

Location of the vertebral artery foramen on the anterior aspect of the lower cervical spine by computed tomography

Axial computed tomography scans were performed on 14 cadaveric cervical spines to determine the location of the vertebral artery foramen on the anterior aspect of the lower cervical spine. The best scan through the vertebral artery foramen from each level at C3-C6 was selected. Measurements of the vertebral artery foramen included the foramen depth, foramen width, interforaminal distance, the distance from the anterior border of the transverse foramen to the anterior border of the transverse process, the distance from the posterior border of the transverse foramen to the posterior border of the lateral mass, and the distance from the medial border of the vertebral artery foramen to the lateral border of the vertebral body. The results show that the average transverse foramen width was 5.5 +/- 0.4 mm at C3, 5.7 +/- 1.0 mm at C4, 5.9 +/- 0.7 mm at C5, and 5.7 +/- 0.7 mm at C6. The average transverse foramen depth and average interforaminal distance gradually increased from C3 to C6. The distance from the anterior border of the vertebral artery foramen to the anterior border of the transverse process gradually increased from C3 (1.2 +/- 0.4 mm) to C6 (2.7 +/- 0.8 mm) as well. The average distance between the medial border of the transverse foramina and the lateral border of the vertebral body for C3-C6 ranged from 1.8 to 2.2 mm. The average distance between the anterior borders of the vertebral artery foramina and the anterior border of the vertebral body gradually decreased from C3 (8.4 +/- 1.4 mm) to C6 (7.0 +/- 1.6 mm). This study suggested that the lateral border of the vertebral body may be a reliable landmark during anterior cervical decompression. The vertebral artery foramen should be free of violation if vertebrectomy or subtotal vertebrectomy is performed medial to the lateral border of the vertebral body.

Anatomic relations of the thoracic pedicle to the adjacent neural structures

STUDY DESIGN

This study analyzed anatomic parameters between the thoracic pedicles and the spinal nerve roots.

OBJECTIVES

To quantitatively determine the anatomic relations of the thoracic pedicle to the adjacent neural structures.

SUMMARY OF BACKGROUND DATA

Pedicular screw placement carries with it potential hazard to the surrounding neural structures, especially in the thoracic spine. No studies exist regarding the anatomic relations of the thoracic pedicle to the adjacent nerve roots.

METHODS

Fifteen cadavers were obtained for study of the thoracic spine. All soft tissue was dissected off the thoracic spine. Laminectomy and total removal of the superior and inferior articular facets was then performed on C7-T1 through T12-L1 to expose the pedicles, nerve roots, and dura. Measurements were taken from the pedicle to the nerve root superiorly and inferiorly as well as between the pedicles. Also, the superoinferior diameter of the nerve root and the frontal angle of the nerve root were measured. Symmetrical structures were measured bilaterally.

RESULTS

The results showed that no epidural space could be found between the dural sac and the pedicle in all 15 cadavers. The average distances from the thoracic pedicle to the adjacent nerve roots superiorly or inferiorly at all levels ranged from 1.9 to 3.9 mm and from 1.7 to 2.8 mm, with a minimum of 1.3 mm, respectively. The interpedicular distance increased from T1 (13.8 mm) to T3, slightly decreased in T4-T5, then gradually increased to T12 (16.6 mm). The superoinferior diameter of the nerve root increased consistently from 2.9 mm at T1 to 4.6 mm at T11. The frontal nerve root angle decreased consistently from T1 (120.1 degrees) to T12 (57.1 degrees), except at T4-T5.

CONCLUSIONS

This study suggested that more care be taken into consideration in placing a transpedicular screw in the transverse plane than in placing a screw in the sagittal plane in the thoracic spine.

Location of the extraforaminal lumbar nerve roots. An anatomic study

Twelve cadavers were used to determine the anatomic location of the extraforaminal lumbar nerve root in the intertransverse space. After exposure of the transverse processes of the lumbar spine and the extraforaminal lumbar nerve roots, direct measurements, including the nerve root angle, nerve root diameter, distance to the superior facet, and the intertransverse space, were made bilaterally. The results showed that the extraforaminal nerve root angle and diameter and the distance between the superior facet and lateral limit of the nerve root consistently increased from cephalad to caudal. The largest dimension for height and width of the intertransverse space was found at the level of L3-4, and the smallest was found at the level of L5-S1. This information may be helpful in minimizing the incidence of injury to the lumbar nerve root during a posterolateral approach to lumbar disc.

Anatomic considerations of anterior instrumentation of the thoracic spine

Forty-seven dry thoracic specimens from T-3 to T-12 (470 thoracic vertebrae) were used to measure the dimensions of the vertebral body of the thoracic spine and to determine the relationship of the posterior angulation of screw placement to the spinal canal from different entrance points. Statistically significant differences in dimensions of male and female specimens were found in the anterior vertebral body height and all of the angular measurements. The average maximum posterior angle relative to the frontal plane from T-3 to T-12 for both sexes ranged from 11 degrees to 14 degrees at the initial point (the level of the most anterior edge of the upper costal facet), from 20 degrees to 23 degrees at the point of 5 mm anterior to the initial point, and from 30 degrees to 34 degrees at the point of 10 mm anterior to the initial point. This study suggests that there is considerable risk of violating the spinal canal if the screws are inadvertently angled posteriorly. The authors recommend insertion of screws in the anterior or middle part of the lateral aspect of the vertebral body. The screws should be directed perpendicular to the lateral plane of the vertebral body. A posteriorly placed screw should be directed anteriorly.

Radiographic and computed tomographic evaluation of Lisfranc dislocation: a cadaver study

Six cadaver feet were used for radiological and computed tomographic (CT) evaluation. The tarsometatarsal joints of each specimen were displaced dorsolaterally in successive 1-mm increments. None of the 1-mm and two thirds of the 2-mm dorsolateral Lisfranc dislocations could be visualized on routine radiographs; they could all be noted on CT scans. There was good assessment on CT scan for the extent of the minor lesions that are normally obscured by overlapping projection in routine radiographs. A Lisfranc injury that appears undisplaced on radiographs or acceptable after closed reduction may still have an unpredictable outcome because of the presence of an occult joint subluxation. CT scanning is more sensitive than radiography for detecting the minor amounts of Lisfranc displacement. If there is any doubt on the radiographs, a CT scan should be performed. The early diagnosis and treatment of Lisfranc injuries may minimize development of post-traumatic degenerative arthritis.

Anatomic considerations of the lumbar isthmus

STUDY DESIGN

A morphometric study of lumbar isthmus from L1 to L5 on 30 dried lumbar spines was conducted.

OBJECTIVE

To provide anatomic data about the lumbar isthmus and to quantitatively evaluate structural features of the lumbar isthmus and its relationship to adjacent anatomic structures.

SUMMARY OF BACKGROUND DATA

There are very few anatomic studies about the lumbar isthmus, and no study describes the relationship of the lumbar isthmus to its adjacent structures.

METHODS

Direct measurements using digital calipers and a goniometer were taken from 30 dried lumbar spines. Anatomic evaluation focused on the lumbar isthmus and its related structures, the isthmus pedicle, and superior and inferior facets. Seven linear and four angular parameters of the lumbar isthmus were determined.

RESULTS

The length of the superior edge of the isthmus gradually increased from L2 to L5 (from 8.22 +/- 1.43 mm at L2 to 10.44 +/- 1.90 mm at L5), and that of its inferior edge progressively decreased from L2 to L5 (from 8.67 +/- 1.76 mm at L2 to 6.34 +/- 1.74 mm at L5). The superoinferior diameter of the isthmus decreased from L3 to L5 (from 13.87 +/- 1.77 mm at L3 to 13.26 +/- 2.49 mm at L5). The superior edge of the isthmus was the thinnest at L4 (1.62 +/- 0.58 mm), and its thickness inferiorly increased from L1 to L5 (from 6.71 +/- 1.47 mm at L1 to 7.76 +/- 1.08 mm at L5). The medial and caudal inclination of the isthmus with respect to the pedicle gradually increased from L1 to L5 (from 112.3 degrees +/- 13.8 degrees at L1 to 119.2 degrees +/- 11.2 degrees at L5 medial inclination and from 132.5 degrees +/- 8.8 degrees at L2 to 139.0 degrees +/- 12.1 degrees at L5 caudal inclination, respectively). The dimensions of the lumbar isthmus were positively correlated to dimensions of the pedicle and orientations of the facets.

CONCLUSIONS

This study provides detailed anatomic data of the lumbar isthmus. Anatomic parameters of the lumbar isthmus are related to the vertebral levels and have a significant correlation with the angles of the facets and the dimensions of the pedicles. The vulnerability of the pars interarticularis of the fifth lumbar vertebra has been anatomically confirmed.

Radiology of the sacroiliac joint

STUDY DESIGN

Radiology of the sacroiliac joint was investigated by obtaining different and multiple radiographs of cadaveric pelves marked with solder metal wire and radiopaque paint.

OBJECTIVES

To demonstrate the orientation of the sacroiliac joint on various, radiographic views.

SUMMARY OF BACKGROUND DATA

Interpretation of the sacroiliac joint projection on plain radiography is difficult. It requires an understanding and appreciation of its components and their orientation. Emphasizing the definition of the orientation of the plane of the joint on the different projection views of the sacroiliac joints can aid the orthopaedic surgeon in obtaining the proper radiographs and in the proper interpretation of the different radiographic views.

METHODS

Nineteen sacroiliac joints from 10 cadaveric pelves, 5 male and 5 females were studied. Each joint was found to be composed of three portions: anterosuperior, middle, and posteroinferior portions, each lying in a different plane. Each sacroiliac joint was marked with solder wires and radiopaque paint to define the orientation of each of the three portions of the joint on radiographs. The following radiographic projection views were taken for each joint anteroposterior, lateral, inlet, craniocaudal axial, outlet, lithotomy and oblique views. For the oblique views, the angulation of the x-ray tube needed to view each portion of the joint tangentially was recorded.

RESULTS

There was a wide variation in the orientation of the planes of the joint portions between the right and the left sides as well as between different pelves. Although the twisting of the plane of the whole joint produced by the successive examination of the portions could be either internal or external, it was the same bilaterally in a given specimen. The outlet and lithotomy views provided the best tangential representation of the two sacroiliac joints on one film.

CONCLUSION

The sacroiliac joint is composed of three portions oriented in different planes. To study the sacroiliac joints, it seems desirable to obtain an anteroposterior view of the pelvis with the patient in a lithotomy position; then, if needed, each joint can be radiographed separately by using oblique views. It is important to not that the plane of the articular portion of the joint can be directed from anterolateral to posteromedial, and therefore, the oblique views should be obtained accordingly.

Anterior iliac crest bone graft. Anatomic considerations

STUDY DESIGN

A morphologic study of the anterior part of the iliac crest was performed.

OBJECTIVE

To define the anatomic characteristics of the anterior part of the ilium and to determine an optimal area to harvest the iliac bone graft from the anterior iliac crest.

SUMMARY OF BACKGROUND DATA

Stress fracture or avulsion fracture of the anterior cut for anterior iliac crest graft have been noted previously. However, there is insufficient published information on the morphology of the anterior part of the ilium relative to the optimal location of harvesting the bone graft.

METHODS

Direct measurements using digital calipers were taken from 30 dried human pelves and 10 cadaveric pelves. The thickness of the anterior part of the ilium was measured, with different starting points on the iliac crest. The length of the bicortical iliac bone graft also was determined.

RESULTS

The thickest portion of the ilium was 18.9 +/- 2.3 mm at the iliac tubercle, which was 45% thicker than at a point 3 cm posterior to the anterior superior iliac spine. The thick region of the anterior iliac crest extended 54.0 +/- 10.2 mm posteriorly from a point 3 cm posterior to the anterior superior iliac spine. The mean length of a 10 mm thick bicortical iliac tubercle bone graft was 36.8 +/- 8.7 mm.

CONCLUSIONS

The region around the iliac tubercle is suitable for harvesting bicortical or tricortical bone graft.

The effect of anterior translation of the vertebra on the canal size in the lower cervical spine: a computer-assisted anatomic study

Eighteen adult dry-bone spine specimens were used in conjunction with computer analysis to determine the average axial spinal canal area at the levels of C6, C7, and T1 after different degrees of anterior translation of the cephalad vertebra. Simulating a distractive flexion injury, the cephalad vertebra was anteriorly displaced on the caudal vertebra at 1-mm intervals. After each displacement, the remaining axial spinal canal area of the caudal vertebra was calculated. The results showed that the average axial spinal canal areas for both male and female specimens were approximately 222 mm2 for C6, 217 mm2 for C7, and 210 mm2 for T1, respectively. After a 6-mm anterior translation of the cephalad vertebra (assuming 50% of anterior translation of the vertebral body), the average axial spinal canal area of the caudal vertebra for both sexes significantly decreased to 59% at C6, 51% at C7, and 56% at T1, respectively. This study suggests that the size of the axial spinal canal directly depends on the degree of anterior vertebral translation.

The relationship of lumbosacral plexus to the sacrum and the sacroiliac joint

The lumbosacral plexus was dissected bilaterally in 20 adult cadavers to define the anatomic relationship of the lumbosacral plexus to the sacrum and the sacroiliac joint. All results are mean values +/- standard deviation. The length of the nerve roots of the lumbosacral plexus gradually decreased from L-4 to S-3 (from 93.8 +/- 6.9 mm in males and 108.7 +/- 7.7 mm in females at L-4 to 43.7 +/- 4.3 mm in males and 49.0 +/- 7.6 mm in females at S-3). The angle projected by the nerve roots of the lumbosacral plexus with respect to the sagittal plane gradually increased from L-4 to S-3 (from 14.3 degrees +/- 3.4 degrees in males and 16.7 degrees +/- 4.8 degrees in females at L-4 to 51.8 degrees +/- 9.0 degrees in males and 57.8 degrees +/- 9.1 degrees in females at S-3). The width of the nerve roots of the lumbosacral plexus was greatest at S-1 (9.8 +/- 1.8 mm in males, 8.6 +/- 1.5 mm in females). The L-5 nerve root was the thickest in males (4.4 +/- 0.5 mm), and the S-1 nerve root was thickest in females (4.3 +/- 0.4 mm). The lumbosacral trunk was 30.0 +/- 9.0 mm in length in males and 32.0 +/- 6.0 mm in females; 11.4 +/- 1.8 mm wide in males and 11.2 +/- 1.5 mm in females; and 4.4 +/- 0.5 mm thick in males and 4.0 +/- 0.6 mm in females. The fifth lumbar nerve root and lumbosacral trunk coursed across the sacroiliac at a level 2.0 +/- 0.2 cm below the pelvic brim and were relatively fixed to the sacral ala with fibrous connective tissue.

Projection of the thoracic pedicle and its morphometric analysis

STUDY DESIGN

This study defined the projection point of the thoracic pedicles on their posterior aspect and its relation to a reliable landmark. It also reported pedicle dimensions based on 43 thoracic spines.

OBJECTIVES

To determine the projection point of the pedicle axis on the posterior aspect of the thoracic spine, quantitatively describe relations of the projection point to some reliable landmarks, and evaluate linear and angular dimensions of the thoracic pedicle.

SUMMARY OF BACKGROUND DATA

Posterior segmental screw fixation is the current standard of internal fixation at the level of the second lumbar vertebrae or below. However, pedicular screw fixation in the thoracic spine, especially in the middle and upper thoracic region, is not common because the small dimensions of the pedicle in this region make screw insertion difficult. More information about pedicle axis projection (not pedicle zone) and its quantitative relationship to some reliable landmarks is essential.

METHODS

Forty-three dry thoracic specimens (516 vertebrae) were obtained for study of the thoracic pedicle. Anatomic evaluation focused on the determination of the projection point of the thoracic pedicle axis on its posterior aspect and the anatomic relationship of this point to the lateral edge of superior facet and the midline of the transverse process. Also, pedicle dimensions, including linear and angular, were measured. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately.

RESULTS

Sexual difference was found to be significant statistically in more than half of parameters. For T1-T2, the projection point of the pedicle axis was approximately 7-8 mm medial to the lateral edge of the superior facet and 3-4 mm superior to the midline of the transverse process. For T3-T12, this point was 4-5 mm medial to the lateral margin of the facet and 5-8 mm superior to the midline of the transverse process. The transverse angle of the pedicle axis was found to be 30-40 degrees at T1-T2, 20-25 degrees at T3-T11, and 10 degrees at T12.

CONCLUSIONS

This information, in conjunction with preoperative computed tomography evaluation, may enhance our knowledge of transpedicular screw fixation in the thoracic pedicle.

Morphometric evaluation of lower cervical pedicle and its projection

STUDY DESIGN

This study evaluated the lower cervical pedicle from C3 to C6 to provide information for accurate transpedicular screw fixation in this region.

OBJECTIVES

To measure the dimensions of the lower cervical pedicle and to determine the correct location of the pedicle axis on the posterior aspect of the lateral mass.

SUMMARY OF BACKGROUND DATA

Several anatomic studies and clinical applications of transpedicular screw fixation in the cervical spine have been documented, but little quantitative data concerning the lower cervical pedicle and its projection are available.

METHODS

Forty dry cervical specimens from C3 to C6 (160 cervical vertebrae) were used for this study. Anatomic evaluation included pedicle height, width, effective length, and anguli. The distances from the projection point of the pedicle axis to reference lines related to the lateral edge of the lateral mass (vertical) and the inferior edge of the superior facet (horizontal) also were measured. The means, ranges, and standard deviations were calculated for all of the specimens and separately for male and female spines.

RESULTS

Statistically significant differences in dimensions of males and females were found in one linear and one angular measurement, which included the pedicle height of C6 and the pedicle sagittal angle of C4. The greatest variation for males and females was found in the pedicle sagittal angle, with a range of 4.3-9.8 degrees. The distances from the projection point to the horizontal line did not show any real pattern of change from C3 to C6, whereas the distances from the projection point to the vertical line consistently increased from cephalad to caudad.

CONCLUSIONS

Taking into consideration some variations between individuals, this information, combined with evaluation of results of preoperative axial computed tomography and conventional radiography, may enhance the safety of transpedicular screw fixation in the lower cervical spine.

Anatomic considerations for a modified posterior approach to the scapula

A modified posterior approach to the scapula was tested on 20 cadavers. The approach also was used in 2 cases with fractures involving the scapular neck and glenoid fossa. The incision is C shaped, with the convexity directed toward the lateral angle of the scapula. The posterior muscle fibers of the deltoid are reflected laterally after detaching them from their origin. The infraspinatus is mobilized without division to expose the posterior surface of the scapular neck and glenoid. Access to the rest of the posterior and the superior surfaces of the glenoid can be achieved by osteotomizing the acromion. The suprascapular neurovascular bundle is identified and protected at an average of 1.4 +/- 0.1 cm from the glenoid rim, where it is adherent to the spinoglenoid angle of the scapula. The circumflex scapular artery is protected at the lateral border of the scapula at an average of 2.8 +/- 0.5 cm from the inferior glenoid margin. The axillary nerve is protected inferior to the teres minor. However, care should be taken not to excessively retract the teres minor because the nerve lies in close proximity to the shoulder joint capsule.