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Eduardo Martinez-del-Campo, Jay D. Turner, Hector Soriano-Baron, Anna G. U. S. Newcomb, Samuel Kalb and Nicholas Theodore

OBJECTIVE

The authors assessed the rate of vertebral growth, curvature, and alignment for multilevel constructs in the cervical spine after occipitocervical fixation (OCF) in pediatric patients and compared these results with those in published reports of growth in normal children.

METHODS

The authors assessed cervical spine radiographs and CT images of 18 patients who underwent occipitocervical arthrodesis. Measurements were made using postoperative and follow-up images available for 16 patients to determine cervical alignment (cervical spine alignment [CSA], C1–7 sagittal vertical axis [SVA], and C2–7 SVA) and curvature (cervical spine curvature [CSC] and C2–7 lordosis angle). Seventeen patients had postoperative and follow-up images available with which to measure vertebral body height (VBH), vertebral body width (VBW), and vertical growth percentage (VG%—that is, percentage change from postoperative to follow-up). Results for cervical spine growth were compared with normal parameters of 456 patients previously reported on in 2 studies.

RESULTS

Ten patients were girls and 8 were boys; their mean age was 6.7 ± 3.2 years. Constructs spanned occiput (Oc)–C2 (n = 2), Oc–C3 (n = 7), and Oc–C4 (n = 9). The mean duration of follow-up was 44.4 months (range 24–101 months). Comparison of postoperative to follow-up measures showed that the mean CSA increased by 1.8 ± 2.9 mm (p < 0.01); the mean C2–7 SVA and C1–7 SVA increased by 2.3 mm and 2.7 mm, respectively (p = 0.3); the mean CSC changed by −8.7° (p < 0.01) and the mean C2–7 lordosis angle changed by 2.6° (p = 0.5); and the cumulative mean VG% of the instrumented levels (C2–4) provided 51.5% of the total cervical growth (C2–7). The annual vertical growth rate was 4.4 mm/year. The VBW growth from C2–4 ranged from 13.9% to 16.6% (p < 0.001). The VBW of C-2 in instrumented patients appeared to be of a smaller diameter than that of normal patients, especially among those aged 5 to < 10 years and 10–15 years, with an increased diameter at the immediately inferior vertebral bodies compensating for the decreased width. No cervical deformation, malalignment, or detrimental clinical status was evident in any patient.

CONCLUSIONS

The craniovertebral junction and the upper cervical spine continue to present normal growth, curvature, and alignment parameters in children with OCF constructs spanning a distance as long as Oc–C4.

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Nestor G. Rodriguez-Martinez, Amey Savardekar, Eric W. Nottmeier, Stephen Pirris, Phillip M. Reyes, Anna G. U. S. Newcomb, George A. C. Mendes, Samuel Kalb, Nicholas Theodore and Neil R. Crawford

OBJECTIVE

Transvertebral screws provide stability in thoracic spinal fixation surgeries, with their use mainly limited to patients who require a pedicle screw salvage technique. However, the biomechanical impact of transvertebral screws alone, when they are inserted across 2 vertebral bodies, has not been studied. In this study, the authors assessed the stability offered by a transvertebral screw construct for posterior instrumentation and compared its biomechanical performance to that of standard bilateral pedicle screw and rod (PSR) fixation.

METHODS

Fourteen fresh human cadaveric thoracic spine segments from T-6 to T-11 were divided into 2 groups with similar ages and bone quality. Group 1 received transvertebral screws across 2 levels without rods and subsequently with interconnecting bilateral rods at 3 levels (T8–10). Group 2 received bilateral PSR fixation and were sequentially tested with interconnecting rods at T7–8 and T9–10, at T8–9, and at T8–10. Flexibility tests were performed on intact and instrumented specimens in both groups. Presurgical and postsurgical O-arm 3D images were obtained to verify screw placement.

RESULTS

The mean range of motion (ROM) per motion segment with transvertebral screws spanning 2 levels compared with the intact condition was 66% of the mean intact ROM during flexion-extension (p = 0.013), 69% during lateral bending (p = 0.015), and 47% during axial rotation (p < 0.001). The mean ROM per motion segment with PSR spanning 2 levels compared with the intact condition was 38% of the mean intact ROM during flexion-extension (p < 0.001), 57% during lateral bending (p = 0.007), and 27% during axial rotation (p < 0.001). Adding bilateral rods to the 3 levels with transvertebral screws decreased the mean ROM per motion segment to 28% of intact ROM during flexion-extension (p < 0.001), 37% during lateral bending (p < 0.001), and 30% during axial rotation (p < 0.001). The mean ROM per motion segment for PSR spanning 3 levels was 21% of intact ROM during flexion-extension (p < 0.001), 33% during lateral bending (p < 0.001), and 22% during axial rotation (p < 0.001).

CONCLUSIONS

Biomechanically, fixation with a novel technique in the thoracic spine involving transvertebral screws showed restoration of stability to well within the stability provided by PSR fixation.

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Luis Perez-Orribo, Laura A. Snyder, Samuel Kalb, Ali M. Elhadi, Forrest Hsu, Anna G. U. S. Newcomb, Devika Malhotra, Neil R. Crawford and Nicholas Theodore

OBJECTIVE

Craniovertebral junction (CVJ) injuries complicated by transverse atlantal ligament (TAL) disruption often require surgical stabilization. Measurements based on the atlantodental interval (ADI), atlas lateral diameter (ALD1), and axis lateral diameter (ALD2) may help clinicians identify TAL disruption. This study used CT scanning to evaluate the reliability of these measurements and other variants in the clinical setting.

METHODS

Patients with CVJ injuries treated at the authors' institution between 2004 and 2011 were evaluated retrospectively for demographics, mechanism and location of CVJ injury, classification of injury, treatment, and modified Japanese Orthopaedic Association score at the time of injury and follow-up. The integrity of the TAL was evaluated using MRI. The ADI, ALD1, and ALD2 were measured on CT to identify TAL disruption indirectly.

RESULTS

Among the 125 patients identified, 40 (32%) had atlas fractures, 59 (47.2%) odontoid fractures, 31 (24.8%) axis fractures, and 4 (3.2%) occipital condyle fractures. TAL disruption was documented on MRI in 11 cases (8.8%). The average ADI for TAL injury was 1.8 mm (range 0.9–3.9 mm). Nine (81.8%) of the 11 patients with TAL injury had an ADI of less than 3 mm. In 10 patients (90.9%) with TAL injury, overhang of the C-1 lateral masses on C-2 was less than 7 mm. ADI, ALD1, ALD2, ALD1 – ALD2, and ALD1/ALD2 did not correlate with the integrity of the TAL.

CONCLUSIONS

No current measurement method using CT, including the ADI, ALD1, and ALD2 or their differences or ratios, consistently indicates the integrity of the TAL. A more reliable CT-based criterion is needed to diagnose TAL disruption when MRI is unavailable.

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Luis Perez-Orribo, Samuel Kalb, Laura A. Snyder, Forrest Hsu, Devika Malhotra, Richard D. Lefevre, Ali M. Elhadi, Anna G. U. S. Newcomb, Nicholas Theodore and Neil R. Crawford

OBJECTIVE

The rule of Spence is inaccurate for assessing integrity of the transverse atlantal ligament (TAL). Because CT is quick and easy to perform at most trauma centers, the authors propose a novel sequence of obtaining 2 CT scans to improve the diagnosis of TAL impairment. The sensitivity of a new CT-based method for diagnosing a TAL injury in a cadaveric model was assessed.

METHODS

Ten human cadaveric occipitocervical specimens were mounted horizontally in a supine posture with wooden inserts attached to the back of the skull to maintain a neutral or flexed (10°) posture. Specimens were scanned in neutral and flexed postures in a total of 4 conditions (3 conditions in each specimen): 1) intact (n = 10); either 2A) after a simulated Jefferson fracture with an intact TAL (n = 5) or 2B) after a TAL disruption with no Jefferson fracture (n = 5); and 3) after TAL disruption and a simulated Jefferson fracture (n = 10). The atlantodental interval (ADI) and cross-sectional canal area were measured.

RESULTS

From the neutral to the flexed posture, ADI increased an average of 2.5% in intact spines, 6.25% after a Jefferson fracture without TAL disruption, 34% after a TAL disruption without fracture, and 25% after TAL disruption with fracture. The increase in ADI was significant with both TAL disruption and TAL disruption and fracture (p < 0.005) but not in the other 2 conditions (p > 0.6). Changes in spinal canal area were not significant (p > 0.70).

CONCLUSIONS

This novel method was more sensitive than the rule of Spence for evaluating the integrity of the TAL on CT and does not increase the risk of further neurological damage.

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Nestor G. Rodriguez-Martinez, Luis Perez-Orribo, Samuel Kalb, Phillip M. Reyes, Anna G. U. S. Newcomb, Jeremy Hughes, Nicholas Theodore and Neil R. Crawford

OBJECT

The effects of obesity on lumbar biomechanics are not fully understood. The aims of this study were to analyze the biomechanical differences between cadaveric L4–5 lumbar spine segments from a large group of nonobese (body mass index [BMI] < 30 kg/m2) and obese (BMI ≥ 30 kg/m2) donors and to determine if there were any radiological differences between spines from nonobese and obese donors using MR imaging.

METHODS

A total of 168 intact L4–5 spinal segments (87 males and 81 females) were tested using pure-moment loading, simulating flexion-extension, lateral bending, and axial rotation. Axial compression tests were performed on 38 of the specimens. Sex, age, and BMI were analyzed with biomechanical parameters using 1-way ANOVA, Pearson correlation, and multiple regression analyses. MR images were obtained in 12 specimens (8 from obese and 4 from nonobese donors) using a 3-T MR scanner.

RESULTS

The segments from the obese male group allowed significantly greater range of motion (ROM) than those from the nonobese male group during axial rotation (p = 0.018), while there was no difference between segments from obese and nonobese females (p = 0.687). There were no differences in ROM between spines from obese and nonobese donors during flexion-extension or lateral bending for either sex. In the nonobese population, the ROM during axial rotation was significantly greater for females than for males (p = 0.009). There was no significant difference between sexes in the obese population (p = 0.892). Axial compressive stiffness was significantly greater for the obese than the nonobese population for both the female-only group and the entire study group (p < 0.01); however, the difference was nonsignificant in the male population (p = 0.304). Correlation analysis confirmed a significant negative correlation between BMI and resistance to deformation during axial compression in the female group (R = −0.65, p = 0.004), with no relationship in the male group (R = 0.03, p = 0.9). There was also a significant negative correlation between ROM during flexion-extension and BMI for the female group (R = −0.38, p = 0.001), with no relationship for the male group (R = 0.06, p = 0.58). Qualitative analysis using MR imaging indicated greater facet degeneration and a greater incidence of disc herniations in the obese group than in the control group.

CONCLUSIONS

Based on flexibility and compression tests, lumbar spinal segments from obese versus nonobese donors seem to behave differently, biomechanically, during axial rotation and compression. The differences are more pronounced in women. MR imaging suggests that these differences may be due to greater facet degeneration and an increased amount of disc herniation in the spines from obese individuals.

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Nestor G. Rodriguez-Martinez, Sam Safavi-Abbasi, Luis Perez-Orribo, Anna G. U. S. Newcomb, Phillip M. Reyes, Galyna Loughran, Nicholas Theodore and Neil R. Crawford

OBJECT

The Universal Clamp Spinal Fixation System (UC) is a novel sublaminar connection for the spine that is currently used in conjunction with pedicle screws at the thoracic levels for the correction of scoliosis. This device allows the surgeon to attach rods and incorporate a pedicle screw construction. The flexible composition of the UC should provide flexibility intermediate to the uninstrumented spine and an all-screw construct. This hypothesis was tested in vitro using nondestructive flexibility testing of human cadaveric spine segments.

METHODS

Six unembalmed human cadaveric thoracic spine segments from T-3 to T-11 were used. The specimens were tested under the following conditions: 1) intact; 2) after bilateral screws were placed at T4-T10 and interconnected with longitudinal rods; 3) after placement of a hybrid construction with screws at T-4, T-7, and T-10 with an interconnecting rod on one side and screws at T-4 and T-10 with the UC at T5–9 on the contralateral side; (4) after bilateral screws were placed at T-4 and T-10 and interconnected with rods and bilateral UC were placed at T5–9; and 5) after bilateral screws at T-4 and T-10 were placed and interconnected with rods and bilateral sublaminar cables were placed at T5–9. Pure moments of 6.0 Nm were applied while optoelectronically recording 3D angular motion.

RESULTS

Bilateral UC placement and bilateral sublaminar cables both resulted in a significantly greater range of motion than bilateral pedicle screws during lateral bending and axial rotation, but not during flexion or extension. There were no differences in stability between bilateral UC and bilateral cables. The construct with limited screws on one side and UC contralaterally showed comparable stability to bilateral UC and bilateral cables.

CONCLUSIONS

These results support using the UC as a therapeutic option for spinal stabilization because it allows comparable stability to the sublaminar cables and provides flexibility intermediate to that of the uninstrumented spine and an all-screw construct. Equivalent stability of the hybrid, bilateral UC, and bilateral cable constructs indicates that 6-level UC provides stability comparable to that of a limited (3-point) pedicle screw-rod construct.