Ground reaction forces and EMG activity with ankle bracing during inversion stress.

PURPOSE: The purpose of this investigation was to evaluate the effects of external ankle support on ground reaction forces and myoelectrical activity of selected lower extremity muscles during dynamic inversion stress. METHODS: Twenty-four healthy males performed five trials of a lateral dynamic movement at a rate between 80-90% of their maximal speed under three ankle brace conditions (no brace--control, Aircast Sport-Stirrup, Active Ankle). Ground reaction forces along the mediolateral axis and EMG activity of the peroneus longus, tibialis anterior, and medial gastrocnemius were simultaneously recorded during force plate contact. RESULTS: Ankle bracing did not affect peak impact force (P > 0.05), maximum loading force (P > 0.05), or peak propulsion force (P > 0.05) in the lateral direction compared with the control condition. Ankle bracing reduced the EMG activity of the peroneus longus during peak impact force compared with the control condition (P < 0.05), although no differences were noted between the two braces. Furthermore, peroneous longus activity during maximum loading force and peak propulsion remained unaffected (P < 0.05). Ankle bracing did not affect the EMG activity of the tibialis anterior and medial gastrocnemius at the point of peak impact force, maximum loading force (P > 0.05), and peak propulsion force (P > 0.05). CONCLUSIONS: These data suggest that ankle bracing may not affect the forces experienced at the foot and ankle, but helps reduce the strain placed on the peroneus longus during peak impact force. Furthermore, ankle bracing does not alter the function of the tibialis anterior and medial gastrocnemius during dynamic inversion stress.

The location of the vertebral artery foramen and its relation to posterior lateral mass screw fixation.

STUDY DESIGN: This study evaluated the anatomic relationship between the vertebral artery foramen and the posterior midpoint of the cervical lateral mass using cervical spine specimens. OBJECTIVES: To determine quantitatively the location of the vertebral artery foramens from C3 to C6 and their relationship to the posterior midpoints of the lateral masses. SUMMARY OF BACKGROUND DATA: Anatomic studies of the cervical nerve root and facet relative to lateral mass screw placement have been addressed. It is necessary to know the correct location of the vertebral artery foramen during lateral mass screw placement to minimize the risk of injury to the vertebral artery. METHODS: Forty-three cervical spines from C3 to C6 were directly evaluated for this study. Anatomic evaluation included the dimension of the vertebral artery foramen and its projection on the posterior aspect of the lateral mass. The vertical distance from the posterior midpoint of the lateral mass to the posterior border of the vertebral artery foramen, and the angle between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, were also measured. RESULTS: The vertical distances from the posterior midpoint of the lateral mass to the vertebral artery foramens at C3-C6 averaged from 9.3 to 12.2 mm for male and female specimens. The average angles medial to the sagittal plane, between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, from C3 to C5, were found to range from 6.0 degrees to 6.3 degrees for male specimens and from 5.3 degrees to 5.5 degrees for female specimens. At C6, the average angles lateral to the sagittal plane, between the parasagittal plane and the line connecting the posterior midpoint of the lateral mass with the lateral limit of the vertebral artery foramen, were 6.4 degrees for male specimens and 5.4 degrees for female specimens. CONCLUSIONS: The present study indicated that there is no risk of damaging the vertebral artery if a screw is directed perpendicular to the posterior aspect of the lateral mass at C3-C5 and 10 degrees lateral to the sagittal plane at C6 starting at the midpoint of the lateral mass.

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.

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.

Morphology of the second cervical vertebra and the posterior projection of the C2 pedicle axis.

STUDY DESIGN: This study assessed numerous structural features of the second cervical vertebra (C2), describing the projection point of the pedicle on its posterior aspect. OBJECTIVES: Evaluation of the specimens included quantitative description of 18 linear and four angular parameters, which then were correlated between male and female specimens. The point of projection of the C2 pedicle axis was described with an emphasis on a perspective relevant to a posterior approach. SUMMARY OF BACKGROUND DATA: The literature regarding the anatomy of the axis focuses mainly on the dens. Very little research regarding the quantitative study of the C2 pedicle has been reported. METHODS: Fifty dry C2 cervical vertebrae (30 male, 20 female) were obtained for anatomic measurements. Anatomic evaluation focused on the pedicle, vertebral body, dens, superior facet, and vertebral canal. All measurements were made using calipers and a standard rule linear measurements and a goniometer for angular measures. Based on the measurement of 50 specimens, including 18 linear and four angular parameters, the mean, range, and standard deviation were calculated for all of the specimens and for male and female separately. RESULTS: A significant difference was found to exist for 11 of 18 linear measurements and one of four angular parameters. The projection point of the pedicle axis on the posterior aspect of the lateral mass was described with an emphasis on a perspective relevant to a posterior surgical approach. The location of the projection point of the pedicle axis was found to be 5.4 +/- 1.2 mm inferior to the horizontal line, and 7.2 +/- 1.3 mm lateral to the vertical line. The pedicle axis was found to lie at 33 degrees in the medial direction and 20 degrees in the superior direction form the point of pedicle axis projection. CONCLUSIONS: When the techniques described here are used, the findings may be helpful in cases involving C2 when surgical intervention and instrumentation are desired.

Anatomic considerations for posterior approach to the sacroiliac joint.

STUDY DESIGN: This anatomic study describes a new intraosseous, posterior approach to the sacroiliac joint. OBJECTIVES: To define a transosseous approach to the sacroiliac joint in which a triangular bony window is raised on the posterosuperior aspect of the ilium that provides improved access to the sacroiliac joint for posterior fusion. SUMMARY OF BACKGROUND DATA: A posterior approach to the sacroiliac joint has been widely used for debridement of infectious diseases and for fusion. Most conventional approaches to the sacroiliac joint are interosseous, and there is a relative lack of information on transiliac approaches. METHODS: The projection of the sacroiliac joint on the outer table of the ilium and the thickness of the posterior ilium forming part of the sacroiliac joint were determined in 15 cadaveric pelves. A right angle, triangular bony window was raised from the posterior ilium to investigate the suitability of a transiliac approach in performing sacroiliac debridement and arthrodesis. A horizontal reference line 3-3.5 cm in length was drawn between a point 1 cm anterosuperior to the posteroinferior iliac spine and a point 1.5 cm superior to the superior border of the greater sciatic notch. A vertical reference line was extended superiorly for 2-2.5 cm perpendicular to and beginning at the anterior end of the horizontal reference line. The oblique arm of the right triangle was created by joining the superior end of the vertical reference line to the posterior end of the horizontal line. RESULTS: Thirty percent to fifty percent of the articular surface of the iliac bone was removed with this triangular segment of bone, and a corresponding area of the sacral articular surface was visualized directly. It was possible to remove the rest of the articular cartilage with angled curettes in all specimens. CONCLUSIONS: This approach facilities improved access to the sacroiliac joint for debridement and arthrodesis with minimal soft tissue dissection and iliac bone resection.

Anatomic considerations for posterior iliac bone harvesting.

STUDY DESIGN: This study analyzed bony features of the posterior ilium and relevant vital structures using cadavers and dry ilium specimens. OBJECTIVES: To determine quantitatively the safely zone of the posterior ilium and relevant vital structures with regard to bone graft harvesting. SUMMARY OF BACKGROUND DATA: The most frequently used site for bone graft harvesting is the posterior ilium. However, complications related to posterior iliac bone harvesting, such as donor site pain, neurovascular injury, instability of the sacroiliac joint, and herniation of abdominal contents, are still major concerns. Very little research with regard to the quantitative study of the posterior ilium has been reported. METHODS: Six cadavers (four male, two female) were used for the first part of this study. The posterior superior iliac spine was determined as a reference landmark. The distances from the posterior superior iliac spine to the superior cluneal nerves, the gluteal line, and the superior gluteal vessels were measured. The second part of the study involved 30 adult, dry iliac bony specimens. The posterior iliac region (extra-articular portion) was divided into three zones, and the corresponding dimensions of these zones were measured. RESULTS: The average distances from the posterior superior iliac spine to the superior cluneal nerves, gluteal line, and superior gluteal vessels were 68.8, 26.6, and 62.4 mm, respectively. The average width, height, and maximum thickness for Zone 1 were 34, 27.8, and 17.1 mm, respectively; the measurements for Zone 2 were 16.5, 31.8, and 14.2 mm, respectively. The average height for Zone 3 was 20.4 mm, and the average maximum thickness was 16.8mm. CONCLUSION: The ideal area of the posterior ilium for bone graft harvesting was found in Zone 1. Zones 2 or 3 may be considered it a greater quantity of cancellous bone graft is required; however, the risk of injury to the sacroiliac joint and superior gluteal vessels in these zones is increased.

Projection of the lumbar pedicle and its morphometric analysis.

STUDY DESIGN: This study defined the projection point of the lumbar pedicle on its posterior aspect and its relation to a reliable landmark and reported pedicle dimensions based on 50 lumbar spines. OBJECTIVES: To establish the best starting point for a pedicle screw for passing the screw down the center (axis) of the pedicle; to describe quantitatively the relations of the pedicle projection point to a reliable landmark; and to evaluate the linear and angular dimensions of the lumbar pedicle. SUMMARY OF BACKGROUND DATA: Posterior transpedicular screw fixation has been most widely used for management of the unstable lumbar spine. Several studies of pedicular anatomy exist, but little quantitative data regarding the location of the lumbar pedicle axis for each level have been reported. METHODS: Fifty dry lumbar specimens (250 lumbar vertebrae) were obtained for study of the lumbar pedicle. Anatomic evaluation focused on determination of the projection point of the lumbar pedicle axis on the junction of the superior facet and the transverse process and measured the distance from the projection point to the midline of the transverse process for each level of the lumbar vertebrae. Pedicle dimensions, including linear and angular, also were measured. RESULTS: Differences in dimensions between men and women were not found to be statistically significant. The average distance from the projection point to the midline of the transverse process consistently changed from L1 to L5. Above L4, the projection point for men and women averaged 3.9 mm for L1, 2.8 mm for L2, and 1.4 mm for L3 superior to the midline of the transverse process, respectively. At L4, the projection point was close to the midline of the transverse process (0.5 mm inferior). At L5, the projection point was an average of 1.5 mm inferior to the midline of the transverse process. CONCLUSIONS: The average distance from the projection point of the lumbar pedicle axis to the midline of the transverse process consistently varied at different levels. This information may prove helpful in the placement of screws into the lumbar pedicle.

Anatomic consideration of transpedicular screw placement in the cervical spine. An analysis of two approaches.

STUDY DESIGN: This study compared the effectiveness of two transpedicular screw placement techniques: blind screw placement versus screw placement after direct determination of the superior, medial, and inferior borders of the pedicle through the opening of a "window" by the partial laminectomy and tapping technique. OBJECTIVES: To determine if the incidence and severity of pedicle violations resulting from transpedicular screw placement could be reduced by direct determination of the superior, medial, and inferior borders of the pedicle through the opening of a "window" by partial laminectomy. SUMMARY OF BACKGROUND DATA: Several studies regarding transpedicular screw fixation for unstable cervical spine injuries have been reported, but none has addressed the effectiveness in lowering the incidence of pedicle violation by opening a "window" by partial laminectomy for direct determination of the superior, medial, and inferior borders of the pedicle and using the tapping technique before and in planning for screw placement. METHODS: Eight adult cadaveric cervical spines (40 vertebrae from C3 to C7) were used for this study. Two groups were formed according to screw placement techniques. The first group was composed of 38 blinded transpedicular screw placements. The second group was composed of 40 screw placements using the partial laminectomy and tapping technique. After transpedicular screw placement, all specimens were evaluated radiographically and visually for violation of the pedicle. RESULTS: A decrease in the incidence and severity of pedicle violation was seen in the second group with opening of the lamina and tapping technique compared with the blind screw placement group. However, the percentage of screws found to violate the pedicle with the opening of the lamina and tapping technique still was relatively high. CONCLUSIONS: Transpedicular screw placement in the cervical spine is difficult, and a high percentage of violations of the pedicle wall occur. This technique should not be used routinely.

Anatomic considerations of pedicle screw placement in the thoracic spine. Roy-Camille technique versus open-lamina technique.

STUDY DESIGN: In this cadaveric study, the outcomes of two techniques for pedicle screw placement in the thoracic spine were compared. OBJECTIVES: To assess the Roy-Camille technique, and to determine whether pedicle screw placement, aided by partial laminectomy, could decrease the incidence of pedicle violations. SUMMARY OF BACKGROUND DATA: Pedicle screw fixation in the thoracic spine remains technically challenging. The Roy-Camille method may be one of the leading techniques of thoracic pedicle screw placement. However, there are few studies evaluating this technique and determining methods to decrease the incidence of thoracic pedicle penetration with screw insertion. METHODS: Ten cadaveric thoracic spines from T1 to T10 were used for pedicle screw placement. Two techniques of transpedicular screw placement were used, the Roy-Camille technique (screw placed on the right side; used in 95 screw placements) and the open-lamina technique screw placement with combined partial laminectomy (screw placed on the left side; used in 94 screw placements). After screw placement, all specimens were evaluated visually to determine violation of the pedicle. RESULTS: The screw placement with the Roy-Camille technique had a higher percentage of pedicle violation (54.7%) than did that with the open-lamina technique (15.9%). No Grade III violation was seen in the screw placement with the open-lamina technique. CONCLUSIONS: The Roy-Camille technique was associated with a high incidence of pedicle violation, whereas screw placement with a partial laminectomy significantly reduced the incidence of pedicle violation. Pedicle screw fixation in the thoracic spine remains a technical challenge and should not be used routinely. Screw placement with the open-lamina technique is recommended if pedicle screw fixation is strongly indicated in the thoracic spine.

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.

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.

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.

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.

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.

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.

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.

Evaluation of cervical posterior lateral mass screw placement by oblique radiographs.

STUDY DESIGN: The present study analyzed the two-dimensional representation of cervical lateral mass screws by oblique radiographs compared with cadaveric placement. This was accomplished by posterior and lateral cervical dissection of the lateral masses and intervertebral foramina, keeping the emerging nerve roots intact. The intervertebral foramina were divided into two zones for the study. OBJECTIVES: To identify and describe the value of oblique radiographs in evaluating posterior lateral mass screw placement in the cervical spine. SUMMARY OF BACKGROUND DATA: Posterior plate-screw fixation is an effective method of stabilizing the traumatized cervical spine. Because of the surrounding anatomy, precise placement of screws must be attained to avoid iatrogenic injury to the nerve roots, and incorrectly placed screws must be identified quickly to minimize the neurologic complication. No previous radiologic study regarding evaluation of the lateral mass screw placement has been reported. METHODS: Six cervical spines were removed from embalmed cadavers. Posterior and lateral removal of soft tissue ensued until the lateral masses and spinal nerves were clearly and completely exposed. Two specimens and 20 screws were used for each of the following methods: Roy-Camille, zone 1 placement, and zone 2 placement. Zone 1 was defined as the area between pedicles of adjacent vertebrae. Zone 2 was defined as the area between transverse processes of adjacent vertebrae. Forty-five degrees oblique left and right, anteroposterior, and lateral radiographs were taken. RESULTS: All screws placed by the Roy-Camille technique and 19 of 20 screws intentionally placed in zone 1 were represented accurately by oblique radiographs. Nineteen of 20 screws placed in zone 1 were well appreciated in the foramen in oblique view. However, 13 of 20 screws placed in zone 2 and approximating the nerve root were inaccurately represented or ambiguous in oblique radiographs. CONCLUSIONS: Oblique radiographs are valuable to view the relationship between screw placement and foramina. Screws crossing the line connecting the posterior borders of the intervertebral foramina and appearing in the pedicle actually exit the bone and may risk damaging the nerve root.

The projection of the lateral sacral mass on the outer table of the posterior ilium.

STUDY DESIGN: This study was designed to construct the projection of the lateral sacral mass on the posterior ilium using cadaveric pelves and to measure the dimensions of the projection. OBJECTIVES: The present study was undertaken to determine quantitatively the location of the lateral sacral mass on the outer table of the ilium. SUMMARY OF BACKGROUND DATA: Anatomic studies relative to instrumentation of the posterior iliosacral region are few. No previous anatomic studies with regard to the projection of the lateral sacral mass have been reported. METHODS: Twelve cadaveric pelves were used for this study. To determine the projection of the lateral sacral mass on the outer table of the posterior ilium, several Kirschner wires were drilled along the outermost peripheral edge of the lateral sacral mass from the inner table of the ilium through the outer table. A triangle projection on the outer table of the posterior ilium was then constructed according to the placed Kirschner wires. The widths and height of the projection, and the distances from the axis of the projection to posterior superior iliac spine and posterior inferior iliac spine were measured bilaterally. RESULTS: The average height of the projection of the lateral sacral mass was 61.4 mm. The average base width of the projection was 56.8 mm. The average distances from posterior superior iliac spine and posterior interior iliac spine to the longitudinal axis of the projection of the lateral mass were 30 mm and 27.4 mm, respectively. CONCLUSIONS: This study reported the average location of the lateral sacral mass on the outer table of the ilium. The superior area of the projection may be an ideal zone for transiliosacral screw placement.