Richard A. Yeasting

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 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.

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°) to T12 (57.1°), 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.

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 verte bra (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 pedicie 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 mesurement 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 seperately. 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 predicle axis was found to lie at 33° in the medial direction and 20° 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.

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.

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

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

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

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

Lateral femoral cutaneous nerve : An anatomic study

The purpose of our study was to determine the location of the lateral femoral cutaneous nerve and its branches at the inguinal ligament and proximal thigh. We think that further defining the location of the nerve and its branches based on certain measurements from known anatomic landmarks would enable us to determine a danger zone that could aid in preventing iatrogenic injury to the lateral femoral cutaneous nerve. The anatomic course of the lateral femoral cutaneous nerve was studied in 29 cadaver specimens and distances from various landmarks were recorded. In addition, the branching pattern of the nerves was recorded. We observed variability in the course and branching patterns of the lateral femoral cutaneous nerve. The lateral femoral cutaneous nerve was found to potentially be at risk as far as 7.3 cm medial to the anterior superior iliac spine along the inguinal ligament and as much as 11.3 cm distal on the sartorius muscle from the anterior superior iliac spine. As many as five branches of the lateral femoral cutaneous nerve were found and in 27.6% of cases the lateral femoral cutaneous nerve branched before traversing the inguinal ligament. We used this information to describe a danger zone, which could be used as a guide to help prevent unnecessary injury during certain procedures.

An Anatomic Study of the Thickness of the Occipital Bone: Implications for Occipitocervical Instrumentation

Study Design The authors measured the thickness and quality of occipital bone regions to determine screw placement during occipitocervical fusion and described the projection of the posterior dural venous sinuses. Objective This study provides anatomic data relevant to areas of screw placement into the occiput during occipitocervical fixation. Summary of Background Data Few reports exist regarding the morphometrics of the occipital bone and intracranial structures relevant to occipitocervical fusion. Method The thickness of the posterior inferior occipital bone was measured relative to a 10 × 5 cm grid. Sections were evaluated grossly and histologically. The projections of the posterior dural venous sinuses were determined by direct measurements. Results The maximum thickness of the occipital bone, which ranged from 11.5 to 15.1 mm in males and from 9.7 to 12.0 mm in females, was at the level of the external occipital protuberance. The occipital bone was thicker than 8 mm in an area extending laterally from the external occipital protuberance for 23 mm and consisted of dense cortical bone with little or no diploic bone. The projection of most of the torcula on the external surface of the occipital bone was located superior to the center of the external occipital protuberance (mean, 12.6 mm superior and 4.7 mm inferior to external occipital protuberance), whereas that of the transverse sinus was distributed more evenly above and below the external occipital protuberance (mean, 7.3 mm superior and 6.5 mm inferior). Conclusions Screws that are 8‐mm long may be inserted in the region of the superior nuchal line (Level 0) extending 2 cm laterally from the center of the external occipital protuberance, 1 cm from the midline at a level 1 cm inferior to the external occipital protuberance (Level 1), and 0.5 cm from the midline at a level 2 cm inferior to the external occipital protuberance (Level 2). The major dural venous sinuses are situated immediately beneath the thickest regions of the occiput and are at risk of penetrative injury during screw placement.