Bruce E. Heck

The quantitative anatomy of the vertebral artery groove of the atlas and its relation to the posterior atlantoaxial approach

Study Design. An evaluation of the vertebral artery groove of the atlas vertebra using dry bony vertebrae. Objectives. To measure the dimension of the vertebral artery groove of the atlas and to define its relation to the posterior midline. Summary of Background Data. Anatomic descriptions of the vertebral artery groove of the atlas exist, but very little quantitative data focused on this groove have been reported. Methods. Fifty dry atlas vertebrae were obtained for this study. Anatomic evaluation focused on the vertebral artery groove and its relation to the midline. A total of eight linear and two angular measurements were made bilaterally. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately. Results. Differences in dimensions of male and female specimens were found to be statistically significant in one linear and two angular parameters. The average depths of the medial and lateral entrances, lengths of the axis, and thicknesses of the vertebral artery groove for male and female specimens were 9 mm, 6 mm, 14 mm, and 4 mm, respectively. The average angle of the vertebral artery groove axis for both genders was 64° lateral to the sagittal plane. The distances from the midline to the medial‐most edge of the vertebral artery groove on the inner and outer cortexes for male and female specimens averaged 10 mm, with a minimum of 8 mm, and 18 mm, with a minimum of 12 mm, respectively. Conclusions. The results of this study suggest that dissection on the posterior aspect of the posterior ring should remain within 12 mm lateral to the midline, and dissection on the superior aspect of the posterior ring should remain within 8 mm of the midline.

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° ± 4.7° relative to sagittal plane, compared with 4.7° ± 3.7° 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.

Vulnerability of the Sympathetic Trunk During the Anterior Approach to the Lower Cervical Spine

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

Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability

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

Anatomic considerations of superior cluneal nerve at posterior iliac crest region.

No previous studies describe the anatomic relationship of the superior cluneal nerve to the posterior iliac crest and thoracolumbar fascia. In the current study, 15 cadavers were dissected to determine the relationship of the superior cluneal nerve to the posterior iliac crest and thoracolumbar fascia. The distances from the medial branch of the superior cluneal nerve to the posterior superior iliac crest and the midline were 64.7 ± 5.3 mm and 81.0 ± 9.2 mm, respectively. The distances between the level of the iliac crest and perforating points of the superior cluneal nerve on the thoracolumbar fascia were 5.8 ± 1.8 mm inferiorly for the medial branch, 2.2 ± 1.8 mm superiorly for the intermediate branch, and 12.0 ± 4.4 mm superiorly for the lateral branch, respectively. The proximal dissection above the perforating point of the nerve showed that the medial branch of the superior cluneal nerve is confined within a tunnel consisting of the thoracolumbar fascia and the superior rim of the iliac crest as it passes over the iliac crest. The intermediate and lateral branches of the superior cluneal nerve either pierce the thoracolumbar fascia or pass through an orifice or fissure in the thoracolumbar fascia. In two specimens, the medial branches of the superior cluneal nerve were constricted within the osteofibrous tunnel. The nerve was entrapped between the rigid fibers of the thoracolumbar fascia and the iliac crest.

Technique for removal of intramedullary nails when there is failure of the proximal extraction device : A report of three cases

When attempting to remove an intramedullary nail, the extraction device can fail. This can occur due to stripping of the proximal threads or, more rarely, due to entrapped broken metal devices (impacted cap screws; broken introducers, extractors, or taps). This latter situation is particularly problematic if access to the intramedullary portion of the nail and proximal threads is not possible. A technique for implant removal utilizing a high-speed drill is described in this report.

Anatomic considerations for safe placement of calcaneal pins.

Placement of a Steinmann pin in the calcaneus is indicated in various orthopaedic conditions. Planning the point of entry and the direction of transcalcaneal pin insertion is crucial for avoidance of neurovascular injury, tendon injury, and subtalar joint violation. Fifteen cadaveric feet were studied in which transfixing calcaneal pins were inserted in posteromedial and anteromedial sites. The posteromedial site was at a point ¾ the distance between the palpable tip of the medial malleolus and the heel, with the pin inserted transversely. The anteromedial site was at the sustentaculum tali with the pin inserted transversely angled 25 ° to 30 ° inferolaterally. Radiographs were then taken and the specimens were dissected to determine the path of each pin and the safe and danger zones for transcalcaneal pin placement. It was concluded that the posteromedial calcaneal pin site is safer and easier to determine.

Location of the sacral pedicle, foramina, and ala on the lateral aspect of the sacrum : A radiographic study

Twenty-one adult dry-bone sacral specimens were used to quantitatively determine the location of the sacral pedicle, foramina, and ala on the lateral radiographic view of the sacrum. The anterior and posterior sacral foramina from S1 to S3, the midlines of the anterior sacrum and cephalad border of the S1 vertebral body, and the lateral limit of the lateral sacral mass were outlined with wires. A lateral radiograph was taken, and measurements were made directly from the radiograph. The average sacral pedicle height for both male and female specimens was approximately 20 mm for S1, 12 mm for S2, and 7 mm for S3. The sacral foramina height averaged approximately 13 mm for S1 and S2, and 10 mm for S3. The average ala and S1 body-ala angles were 88 degrees and 35 degrees. The distance from the ala tip to the anterior aspect of the sacrum averaged 12 mm, and the average anterior height of the S1 vertebral body above the ala was 11 mm. These measurements, in conjunction with inlet and outlet radiographs, may aid in the recognition of the vital structures of the sacrum on the lateral radiographic view and enhance the safety of dorsal sacral screw placement.

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.