Steve P. Haman

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.

Cervical intervertebral disc space narrowing and size of intervertebral foramina

Computer-assisted simulation of C4-C5, C5-C6, and C6-C7 intervertebral disc space narrowing was performed on 16 anatomic specimen cervical spines to determine the relationship of the cross sectional foraminal areas with the degree of narrowing of the cervical intervertebral disc space. Compared with normal foraminal area values, reduction of 20% to 30% of the foraminal area was found after 1 mm narrowing of the intervertebral disc spaces; reduction of 30% to 40% of the foraminal area was found after 2 mm narrowing of the intervertebral disc space; and reduction of 35% to 45% of the foraminal area was found after 3 mm narrowing of the intervertebral disc space. Statistically significant differences were found among the remaining cross sectional foraminal areas after different degrees of intervertebral disc space narrowing. Compression of the nerve root within the intervertebral foramina after the collapse of the intervertebral disc space cannot be ignored, and an appropriate surgical procedure to maintain the normal height of the disc space is essential. The size of the intervertebral foramen is related directly to the height of the intervertebral disc space. A 3-mm vertical reduction of the intervertebral disc space is associated more frequently with severe narrowing of the neuroforamen.

External Rotation-Lateral View of the Ankle in the Assessment of the Posterior Malleolus

Demonstration of a posterior malleolar fragment on a radiograph of an ankle fracture is important in the diagnosis and evaluation of posterior malleolus fractures. The size and extent of displacement of a posterior malleolar fragment can be evaluated. The diagnosis of nonunion of the posterior malleolus is also important because it can lead to failure of reduction of ankle fractures. The authors present a case in which nonunion of the posterior malleolus was diagnosed by an external-rotation lateral view of the ankle. This could not be demonstrated on the AP or the lateral views. Thirteen cadaver feet were then used to study the external-rotation lateral view. A posterior malleolar fracture was created, and the borders of the fracture line were marked with solder wire. The average external rotation angle required to best demonstrate the posterior malleolar fracture was 50° (range, 43°–55°). The actual size of the posterior malleolus fragment was measured and compared to the x-ray measurement. There was a 0.10 correction for the determination of the actual size of the fragment. The unmarked fragment could not be demonstrated on AP and lateral views.

Vulnerability of the spinal accessory nerve in the posterior triangle of the neck: A cadaveric study

Injury to the accessory nerve results in an obvious shoulder droop, loss of shoulder elevation, and pain. Prevention of inadvertent injury to the accessory nerve is critical in neck dissection. No previous study, however, anatomically demonstrates the mechanism of the spinal accessory nerve traction injury. Anatomic determination of the location and course of the spinal accessory nerve may be helpful for a better understanding of the mechanism of the nerve injury. The accessory nerve courses obliquely across the posterior triangle on the surface of the levator scapula muscle and reaches the trapezius. The length of the spinal accessory nerve in the posterior triangle is 34.7+/- 6.3 mm. The nerve passes through the posterior border of the sternocleidomastoid muscle 50.7+/- 12.9 mm below the tip of the mastoid process and reaches the anterior border of the trapezius 49.8 +/- 5.9 mm above the clavicle. It makes a posterior angle of 73.1 degrees +/- 19.4 degrees, on average, relative to the posterior border of the sternocleidomastoid. When the shoulder is pulled down and the head is turned to the opposite direction, the spinal accessory nerve is stretched in the posterior triangle. In the posterior triangle, the nerve is vulnerable, since it is superficial and covered only by skin and subcutaneous fascia. Therefore, extreme caution should be taken with any surgical procedures in the posterior triangle. Traction injury of the spinal accessory nerve in the posterior triangle cannot be ignored.

Quantitative anatomy of the transverse foramen and pedicle of the axis.

Forty dry C2 cervical vertebrae were obtained to evaluate quantitatively the anatomy of the C2 transverse foramen and pedicle. Computed tomography (CT) scans and plain radiographs were also obtained of 20 specimens to evaluate the internal structure of the transverse foramen and pedicle. The results of the measurements showed that differences between male and female specimens were found to be significant for four of seven linear parameters and for one of the two angular parameters. With regard to the sides, differences were found to be significant for two of the seven linear parameters and both of the angular parameters between right and left measurements. The variation of the foramen size between sexes was more significant than that between sides, and a remarkable variation between sides and between sexes was found in the transverse foramen horizontal angle and the pedicle width. The inferior pedicle width was approximately 3 mm less than the superior pedicle width. CT scans revealed that the lateral wall of the pedicle is very thin compared with the medial wall. Considering the greater variation of the C2 foramen orientation, smaller inferior pedicle dimension, and thinner lateral pedicle wall, a screw placement as close as possible to the mediosuperior cortex is recommended to avoid violation of the transverse foramen if transpedicular screw fixation in C2 is intended.

Morphometric analyses of the cervical superior facets and implications for facet dislocation

The articular facets of the cervical spine have been well addressed; however, little information is available on the relationship of the superior facets of the cervical spine to traumatic dislocation in the literature. Morphometric analyses of the superior facets of 30 dried cervical spines from C3 to C7 were performed to determine any morphological differences. The angle of the superior facet with respect to the transverse plane was also measured on computed tomography (CT) scans of 30 patients having neck injury without fracture/dislocation. The vertical and surface lengths of the superior facet were significantly lower (P < 0.01) at C6–C7 levels than at C3–5 levels. The anteroposterior diameter of the superior facet was smaller (P < 0.05) at C6 and C7 levels compared to C3–5 levels. Although the superior facet joint surface is in a more coronal orientation in lower cervical vertebrae, the inclination of the superior facet is more horizontal relative to the transverse plane when measured in vivo. A combination of lower height, smaller anteroposterior diameter of the superior facet, and a more horizontally oriented superior facet at C6 and C7 levels in vivo may explain the predilection of translation relative to one another in the lower cervical spine.RésuméLes facettes articulaires de la colonne cervicale sont bien analysées cependant une meilleure connaissance des relations de l’articulaire supérieure lors des traumatismes avec luxations de la colonne dans la littérature est possible. L’analyse morphométrique de l’articulaire supérieure a été analysée sur 30 colonnes cervicales de cadavres, de C3 à C7, de façon à analyser les différences morphologiques. L’angle supérieur de l’articulaire a été mesuré sur le scanner de 30 patients ayant présenté un traumatisme cervical sans fracture, ni luxation. Les dimensions verticales et les surfaces de l’articulaire supérieure sont, significativement, moins importantes au niveau C6 et C7 qu’au niveau C3 à C5 (p < 0.01). Le diamètre antéropostérieur de l’articulaire supérieure est également plus petit au niveau de C6 C7 qu’au niveau de C3 C5 (p < 0.05). De la même façon, l’articulaire supérieure est dans un plan plus frontal dans la partie basse de la colonne. L’inclinaison de cette articulaire est, de même, plus horizontale par rapport au plan transversal, mesure in vivo. La combinaison de tous ces facteurs : dimensions moins importantes, petits diamètres, antéropostérieur et facettes supérieures de l’articulaire plus horizontale en C6 C7, expliquent la fréquence des translations relatives possibles des vertèbres dans la partie basse de la colonne et donc la fragilité de cette zone.

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

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

The sustentaculum tali: anatomic, radiographic, and surgical considerations.

Three purposes of this study were to: 1) describe the sustentaculum tali in relation to surrounding structures, 2) identify its radiographic projection onto the lateral calcaneus, and 3) determine optimal angles for screw placement. Twelve cadaver specimens were used. The length and width of the sustentaculum was measured. Its midpoint was measured from surrounding anatomic landmarks. A point on the lateral calcaneal wall “point A” was chosen. This marks the intersection of two lines bisecting the midpoint of the posterior facet and the lateral calcaneal height. The angles required to pass a pin from point A into the sustentaculum were determined. The sustentaculum projected as a triangular/elliptical structure on the lateral radiograph. It was superimposed on the anterior portion of the posterior facet.

Congruity of the Subtalar Joint in Tongue Fracture of the Calcaneus: An Anatomical Study

Study Design: An anatomic study. Objectives: To evaluate the effect of displacement of the fractured posterior facet in tongue fracture of the calcaneus on the congruity of the subtalar joint. Methods: Eleven feet were used in this study. Seven females and four males with age range from 59 to 78. The specimens were dissected from both the lateral and the medial aspects of the calcaneus to expose these surfaces. A primary fracture line was created first, then a secondary line was engineered to simulate tongue fracture. Displacement of the superio-lateral fragment was done with 5-mm increment. Radiography was performed and the graphs were scanned and studied on specific computer software to explore the effects of displacement on joint congruity. Results: The anterior end of the fragment of the tongue fracture, when displaced, not only is depressed but also rotated in the sagittal plane in a downward or planterward direction. The articular surface of the posterior facet of the calcaneus and the inferior facet of the talus are maintained in congruence with each other despite the varying degree of displacement and rotation. Conclusion: Congruity of the subtalar joint in tongue fractures is maintained despite different degrees of displacement. This study explains why the non-surgical treatment outcome is comparable to that of the operative treatment in tongue fractures of calcaneus. It also explains why tongue fractures have a good outcome with closed reduction.