Spinal cord injuries without radiologic abnormality in children: a systematic review.

STUDY DESIGN: Systematic review. OBJECTIVES: The objective of this study is to systematically review the literature for pediatric cases of spinal cord injuries without radiologic abnormality (SCIWORA) to investigate any possible relationship between initial neurologic impairment and eventual neurologic status. SETTING: A university department of orthopedics. METHODS: Following the preferred reporting items for systemic reviews and meta-analysis (PRISMA) guidelines for systematic review, the databases of PubMed and OvidSP were electronically searched for articles that use individuals under 18 years old, have trauma resulting in spinal cord injury and have no fractures or dislocations on radiographs. When available, the patients' age, sex, mechanism of injury and spinal cord level were recorded. Individuals with cervical injury, who had specific information on cervical level and mechanism of injury, were recorded as well. Patients who reported specific magnetic resonance imaging findings and the time from the injury were also reported. When possible, the American Spinal Injury Association Impairment Scale (AIS) was determined initially after the injury and then at last follow-up. RESULTS: A total of 433 pediatric patients were identified with SCIWORA. The most prevalent mechanism of injury was sports-related injury cases (39.83%) followed by fall (24.18%) and motor vehicle-related (23.18%) injuries. The mean improvement recorded for all patients was 0.89 AIS grades. CONCLUSION: The most common mechanism of injury was sports-related and cervical injury, which occurred more frequently than other levels. Initial AIS grade A showed poorer outcomes in the pediatric population compared with the adult population. Initial presentation of D showed the highest likelihood of no permanent neurologic impairment (AIS of E).

Compartment Syndrome of the Flexor Compartment of the Arm Secondary to Pectoralis Major Tendon Rupture.

Case. Compartment syndrome following muscle rupture is a rare entity with few mentions in the literature. We present a case of pectoralis major rupture in a 38-year-old male that evolved into compartment syndrome of the anterior compartment of the arm. Rupture of the pectoralis is uncommon and most often occurs during weight lifting. Compartment syndrome secondary to this injury is extremely uncommon, with only one reported case in the pectoralis major itself and several cases of biceps compartment syndrome. Due to the potentially devastating consequences of a missed compartment syndrome, it is imperative that physicians maintain a high level of suspicion in patients with these unusual injuries presenting with severe swelling and pain.

Role of mechanical factors in the evaluation of pedicle screw type spinal fixation devices.

Prior to implantation, spinal implants are subjected to rigorous testing to ensure safety and efficacy. A full battery of tests for the devices may include many steps ranging from biocompatibility tests to in vivo animal studies. This paper describes some of the essential tests from a mechanical engineering perspective (e.g., motion, load sharing, bench type tests, and finite element model analyses). These protocols reflect the research experience of the past decade or so.

"Interventional angiography." A possible role in intraoperative balloon occlusion catheterization of lacerated pelvic arteries.

The use of interventional angiography has been limited in the past to the angiography suite. Significant technical difficulties have been associated with transfer of the unstable patient from the operating room for this procedure. However, current radiographic sophistication now exists to allow rapid intraoperative digital subtraction angiography of uncompromised quality to be performed. An animal model using these techniques is presented.

Compartment syndrome in open tibial fractures.

A retrospective review of the cases of 180 patients who had 198 acute open fractures of the tibial shaft and were admitted to a multiple-trauma referral center over a three-year period revealed an incidence of accompanying compartment syndrome of 9.1 per cent (eighteen fractures in sixteen patients). Each of the eighteen compartment syndromes was documented by measurements of intracompartmental pressure that were obtained by the saline-injection technique, and all were treated by four-compartment fasciotomy. The incidence of compartment syndrome was found to be directly proportional to the degree of injury to soft tissue and bone; this complication occurred most often in association with a comminuted, grade-III open injury to a pedestrian. The physician must maintain a high index of suspicion to detect a compartment syndrome in the patient who has multiple trauma, as its clinical signs and symptoms may be masked by a closed injury of the head or the need for ventilatory support or prolonged anesthesia for other surgical procedures.

Scapulothoracic dissociation.

Scapulothoracic dissociation is a rare entity that consists of disruption of the scapulothoracic articulation. The mechanism of injury is probably traction caused by a blunt force to the shoulder girdle. This lesion is characterized by massive soft-tissue swelling of the shoulder; lateral displacement of the scapula, measured radiographically; an injury to bone (an acromioclavicular separation, a displaced fracture of the clavicle, or a sternoclavicular disruption); a severe neurovascular injury; and a variety of upper and lower-extremity fractures. We treated fifteen patients who had this lesion, most of whom had several associated injuries. Three patients died: two from exsanguination and one from a cardiac arrest. In most patients, the damaged artery was repaired and the brachial plexus was explored. All of the twelve patients who had a complete brachial-plexus injury were left with a flail upper extremity. Most patients refused amputation.

Anatomic considerations of C2 nerve root ganglion.

STUDY DESIGN: Dissection and observation of the dorsal root ganglion of the second cervical spinal nerve bilaterally. OBJECTIVES: To determine the position of the C2 dorsal root ganglion and the heights of the C2 ganglion and its corresponding foramen. SUMMARY OF BACKGROUND DATA: The dorsal root ganglion has been well studied in the middle and lower cervical spine and in the lumbar spine. In no previous study are the position and height of the C2 dorsal root ganglion and its corresponding foramen described. METHODS: Fifteen cadaveric cervical spines were exposed posteriorly. The C2 nerve roots and ganglia were dissected between the arch of the atlas and the lamina of the axis. The heights of the C2 ganglion and foramen were measured. The location of the C2 ganglion was also macroscopically observed. RESULTS: The heights of the C2 ganglion and foramen are 5.7 +/- 0.8 mm and 7.7 +/- 1.2 mm, respectively. The C2 ganglion occupies 76% of the foramen height. All C2 dorsal root ganglia are confined within foramens between the arch of the atlas and the lamina of the axis. CONCLUSIONS: The C2 dorsal dorsal root ganglia are all proximally placed and occupy most of the foramen height, which may render the C2 ganglion vulnerable to entrapment.

Assessment of lumbosacral fusion mass by angled radiography. Technical notes.

STUDY DESIGN: Lumbosacral fusion masses were assessed by angled radiography. OBJECTIVES: To introduce the use of the angled anteroposterior radiograph in the evaluation of the fusion mass at the lumbosacral region. SUMMARY OF BACKGROUND DATA: Determination of the presence and progress of the fusion mass at the lumbosacral junction may be difficult clinically and radiologically. Few studies regarding the use of the angled anteroposterior view of plain radiographs in evaluating L5-S1 fusion are available. METHODS: The patient was placed in the supine position, and an angled view of the lumbosacral junction was obtained. Radiography of the angled anteroposterior view was performed with the x-ray beam oriented toward the cranial portion at 50 degrees to 55 degrees relative to the x-ray table. RESULTS: The use of the angled view of the lumbosacral junction eliminates the superimposition of the L5 transverse process on the posterior part of the superior ala of the sacrum, widens the L5-S1 intertransverse space, and enhances direct visualization. CONCLUSIONS: The use of the angled anteroposterior view on plain radiographs is recommended in the evaluation of the fusion status at L5-S1.

Zone III fractures of the sacrum. A case report.

STUDY DESIGN: Case reports. OBJECTIVES: To define the radiologic characteristics, management, and results of Zone III fractures of the sacrum. SUMMARY OF BACKGROUND DATA: Zone III fractures of the sacrum are rare. There are few case reports of longitudinal fractures of the sacrum involving Zone III. METHOD: The authors report eight (four transverse, four longitudinal) Zone III fractures of the sacrum. Seven patients were treated surgically by posterior sacral decompression with or without transiliac bar fixation, and one neurologically intact patient with undisplaced longitudinal fracture was treated conservatively. RESULTS: Two neurologically compromised patients had return of normal bladder and rectal function, and another had bladder recovery only. The rest continued to show neurogenic bladder and required intermittent self-catheterization. The patient with bilateral foot drop had partial motor recovery and did not require an ankle-foot orthosis. CONCLUSIONS: These fractures may be difficult to diagnose in polytraumatized patients and require a high index of suspicion. The longitudinal fractures may not be apparent on anteroposterior radiographs, and computed tomography scan may be necessary for establishing the diagnosis. The transverse fractures may show a characteristic step ladder sign on anteroposterior radiographs when the fracture is displaced severely. Proper lateral radiographs often are difficult to obtain, particularly in obese polytraumatized patients. Routine computed tomography scan may overlook the diagnosis. Therefore 2- to 3-mm computed tomography cuts are recommended, which may show double neural foramina in presence of significant anteroposterior displacement and overriding of the fracture fragments. Sagittal computed tomography reconstructions are useful in evaluating the transverse fractures. Posterior sacral decompression is safe and probably promotes nerve root recovery. Longitudinal fractures may be stabilized satisfactorily by transiliac rod fixation.

Are anatomic landmarks reliable in determination of fusion level in posterolateral lumbar fusion?

STUDY DESIGN: Determination of the fusion level by direct observation and palpation of anatomic landmarks is compared with the finding obtained from a lateral intraoperative radiograph. OBJECTIVES: To assess the reliability of the use of intraoperative anatomic landmarks in determination of the fusion level. SUMMARY OF BACKGROUND DATA: Accurate determination of the level to be fused in noninstrumented posterolateral fusion is crucial. No studies are available in which the value of direct observation and palpation of the anatomic landmarks in determination of the fusion level has been assessed. METHODS: Eighty patients who underwent posterolateral fusion without instrumentation in the lumbosacral spine were included in this study. During surgery, first, the cephalad transverse process at the desired level to be fused was determined by direct observation and palpation of the anatomic landmarks; second, a metal mark was placed beneath the cephalad transverse process at the level determined by anatomic landmarks. This was followed by a lateral radiograph. The consistency and discrepancy between the use of the anatomic landmarks and lateral radiography in determining the desired fusion level were recorded. RESULTS: The fusion level determined by direct observation and palpation of the anatomic landmarks was accurate in 76 (95%) cases. In the remaining four cases, intraoperative x-rays determined that the selection of the cephalad transverse process for fusion was one level too high in three cases and one level too low in the other case. All errors in determination of the level to be fused occurred in patients who had extensive laminectomy at L4-S1. CONCLUSIONS: Determination of fusion level by direct observation and palpation of the anatomic landmarks is not reliable in patients who have had or require decompressive procedures. A lateral radiograph should be routinely obtained for accurate identification of the level to be fused.

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.

Computed tomographic findings in patients with persistent sacroiliac pain after posterior iliac graft harvesting.

STUDY DESIGN: A retrospective study of 24 sacroiliac joint computed tomographic (CT) scans of patients with persistent donor site pain. OBJECTIVE: To illustrate the computed tomographic findings of sacroiliac joints in patients who underwent posterior iliac bone graft harvesting with subsequent persistent donor site pain. SUMMARY OF BACKGROUND DATA: In a previous study the posterior iliac bone harvesting site was divided into three zones. Zone 1 carried no risk of violation of the synovial part of the sacroiliac joint. In Zones 2 and 3 there was a potential risk of violation to the synovial part of the sacroiliac joint. There is no study in the literature on the effect of violating the different parts of the sacroiliac joint during posterior iliac bone graft harvesting. METHODS: Computed tomographic scans of the sacroiliac joints of 22 patients with persistent pain in 24 sacroiliac joints after posterior iliac bone graft harvesting were retrospectively reviewed. RESULTS: Of the 16 sacroiliac joints with evidence of disruption of the inner table at the ligamentous part, 10 showed mild degenerative changes, and 6 showed moderate changes. Three joints with evidence of disruption of the inner table at the synovial part showed severe degenerative changes. Five joints with no evidence of inner table disruption did not show degenerative changes. CONCLUSION: There is a high prevalence of inner table disruption in patients with persistent sacroiliac joint pain after posterior iliac bone graft harvesting. The computed tomographic scan showed that involvement of the synovial part caused more severe degenerative changes than involvement of the ligamentous part.

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.

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.

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 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 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 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.

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.