Mario J. Cardoso

810 nm Wavelength light: An effective therapy for transected or contused rat spinal cord

Light therapy has biomodulatory effects on central and peripheral nervous tissue. Spinal cord injury (SCI) is a severe central nervous system trauma with no effective restorative therapies. The effectiveness of light therapy on SCI caused by different types of trauma was determined.

Does superior-segment facet violation or laminectomy destabilize the adjacent level in lumbar transpedicular fixation? An in vitro human cadaveric assessment.

Study Design. This is an in vitro biomechanical study. Objective. The current investigation was performed to evaluate adjacent level kinematic change following unilateral and bilateral facet violation and laminectomy following 1-, 2-, and 3-level reconstruction. Summary of Background Data. The incidence of superior-segment facet violation with lumbar transpedicular fixation has been reported as high as 35%; however, its contribution to biomechanical instability at the supradjacent level is unknown. In addition, superior-segment laminectomy has been implicated as a risk factor for the development of adjacent level disease. The authors assess the acute biomechanical effects of proximal facet violation and subsequent laminectomy in an instrumented posterior fusion model in 10 cadaveric specimens. Methods. Biomechanical testing was performed on 10 human cadaveric spines under axial rotation (AR), flexion-extension (FE), and lateral bending (LB) loading. After intact analysis, pedicle screws were inserted from L5-S1 and testing repeated with: (1) preserved L4–L5 facets, (2) unilateral facet breach, (3) bilateral breach, and (4) L5 laminectomy. Following biomechanical analysis, instrumentation was extended to L4, then L3 and biomechanical testing repeated. Full range of motion (ROM) at the proximal adjacent levels were recorded and normalized to intact (100%). Results. Supradjacent level ROM was increased for all groups under all loading methods relative to intact (P < 0.05). However, AR testing revealed progressive instability at the adjacent level in groups 3 and 4, relative to group 1, following 1-, 2- and 3-level fixation (P < 0.05). During FE, supradjacent level ROM was significantly increased for group 4 specimens compared with group 1 after L5-S1 fixation (P < 0.05), and was greater than all other groups for L3-S1 constructs (P < 0.05). Interestingly, under lateral bending, facet joint destabilization did not change adjacent segment ROM. Conclusion. There were significant changes in proximal level ROM immediately after posterior stabilization. However, an additional increase in supradjacent segment ROM was recorded during AR after bilateral facet breach. Subsequent complete laminectomy at the uppermostfixation level further destabilized the supradjacent segment in FE and AR. Therefore, meticulous preservation of the cephalad–most segment facet joints–is paramount to ensure stability.

Effect of Teriparatide [rhPTH(1,34)] and Calcitonin on Intertransverse Process Fusion in a Rabbit Model

Study Design. Randomized, double-blinded, placebo controlled animal study. Objective. To evaluate the effect of teriparatide and calcitonin after an intertransverse process spinal fusion in a rabbit model. Summary of Background Data. It is widely recognized that some osteoporosis medications, including bisphosphonates, can interfere with bone healing. Although prescribed frequently in the treatment of osteoporosis, the effect of teriparatide and calcitonin on spinal fusion has not been fully elucidated. We hypothesized that teriparatide, being the only anabolic medication for osteoporosis treatment, would have a beneficial effect on spine fusion. Methods. Fifty-one New Zealand white rabbits underwent a posterolateral L5–L6 intertransverse process arthrodesis using autogenous iliac crest bone graft. The rabbits were randomly divided into 3 groups. All animals received daily subcutaneous injections of group I (n = 17) 1 mL of saline placebo; group II (n = 17) 10 &mgr;g/kg/day of teriparatide; group III (n = 17) 14 IU/animal of calcitonin during the 8-week postoperative period. Postmortem analyses included manual palpation, radiographic, biomechanical, and histologic assessment. Three random 10× fields were examined/graded within the cephalad, middle, and caudal regions of each section (810 fields). Fusion quality was graded using the Emery histologic scale (0–7 based on fibrous/bone content of the fusion mass). Results. Histologic fusion rates for teriparatide averaged 86.7% and was significantly greater than the autograft control group (50%) (P = 0.033). Radiographically, there was a strong trend towards teriparatide being superior to the calcitonin group (85.7% vs. 56.3%, respectively; P = 0.07). The average Emery grading score was 5.99 ± 1.46 SD for the autologous group and 6.26 ± 0.93 SD for the teriparatide group (P = 0.031). Although not significant, the teriparatide group showed less motion in flexion/extension, lateral bending, and axial rotation. Conclusion. Our results suggest that teriparatide enhances spinal fusion while calcitonin has a neutral effect. The teriparatide group had the best histologic fusion rate and Emery scores, while the calcitonin group was similar to the saline controls. Although not significant, the teriparatide group had a strong trend towards superior radiographic fusion over the calcitonin group.

Multilevel cervical arthroplasty with artificial disc replacement

OBJECT In this study, the authors review the technique for inserting the Prestige ST in a contiguous multilevel cervical disc arthroplasty in patients with radiculopathy and myelopathy. They describe the preoperative planning, surgical technique, and their experience with 10 patients receiving a contiguous Prestige ST implant. They present contiguous multilevel cervical arthroplasty as an alternative to multilevel arthrodesis. METHODS After institutional board review approval was obtained, the authors performed a retrospective review of all contiguous multilevel cervical disc arthroplasties with the Prestige ST artificial disc between August 2007 and November 2009 at a single institution by a single surgeon. Clinical criteria included patients who had undergone a multilevel cervical disc arthroplasty performed for radiculopathy and myelopathy without the presence of a previous cervical fusion. Between August 2007 and November 2009, 119 patients underwent cervical arthroplasty. Of the 119 patients, 31 received a Hybrid construct (total disc resection [TDR]-anterior cervical decompression and fusion [ACDF] or TDR-ACDF-TDR) and 24 received a multilevel cervical arthroplasty. The multilevel cervical arthroplasty group consisted of 14 noncontiguous and 10 contiguous implants. This paper examines patients who received contiguous Prestige ST implants. RESULTS Ten men with an average age of 45 years (range 25-61 years) were treated. Five patients presented with myelopathy, 3 presented with radiculopathy, and 2 presented with myeloradiculopathy. Twenty-two 6 x 16-mm Prestige ST TDRs were implanted. Six patients received 2-level Prestige ST implants. Five patients received TDRs at C5-6 and C6-7, and 1 patient received TDRs at C3-4 and C4-5. One patient received a TDR at C3-4, C5-6, and C6-7 where C4-5 was a congenital block vertebra. Three patients (2 with 3-level disease and 1 with 4-level disease) received contiguous Prestige ST implants as well as a Prevail ACDF as part of their constructs. The mean clinical and radiographic follow-up was 12 months. There has been no case of screw backout, implant dislodgment, progressive kyphosis, formation of heterotopic bone, evidence of pseudarthrosis at the Prevail levels, or development of symptomatic adjacent level disease. CONCLUSIONS Multilevel cervical arthroplasty with the Prestige ST is a safe and effective alternative to fusion for the management of cervical radiculopathy and myelopathy.

Cervical hybrid arthroplasty with 2 unique fusion techniques

OBJECTIVE Multilevel cervical arthroplasty achieved using the Prestige ST disc can be challenging and often unworkable. An alternative to this system is a hybrid technique composed of alternating total disc replacements (TDRs) and fusions. In the present study, the authors review the safety and radiological outcomes of cervical hybrid arthroplasty in which the Prestige ST disc is used in conjunction with 2 unique fusion techniques. METHODS After obtaining institutional review board approval, the authors completed a retrospective review of all hybrid cervical constructs in which the Prestige ST disc was used between August 2007 and November 2009 at the Walter Reed Army Medical Center. A Prestige ST total disc replacement was performed in 119 patients. Thirty-one patients received a hybrid construct defined as a TDR and fusion (TDR-anterior cervical decompression and fusion [ACDF]) or as 2 TDRs separated by a fusion (TDR-ACDF-TDR). A resorbable plate and graft system (Mystique) or stand-alone interbody spacer (Prevail) was implanted at the fusion levels. Plain radiographs were compared and evaluated for cervical lordosis, range of motion, implant complications, development of adjacent-level disease, and pseudarthrosis. In addition, charts were reviewed for clinical complications related to the index surgery. RESULTS Thirty-one patients (18 men and 13 women; mean age 50 years, range 32-74 years) received a hybrid construct. All patients were diagnosed with radiculopathy and/or myelopathy. Twenty-four patients received a 2-level and 7 a 3-level hybrid construct. In 2 patients in whom a 2-level hybrid construct was implanted, a noncontiguous TDR was also performed. The mean clinical and radiological follow-up duration was 18 months. There was no significant difference in preoperative (19.3° ± 13.3°) and postoperative (19.7° ± 10.5°) cervical lordosis (p = 0.48), but there was a significant decrease in range in motion (from 50.0° ± 11.8° to 38.9° ± 12.7°) (p = 0.003). There were no instances of screw backout, implant dislodgement, progressive kyphosis, formation of heterotopic bone, pseudarthrosis, or symptomatic adjacent-level disease. Seven patients had dysphasia and 1 patient had vocal cord paralysis at 6 weeks. By 3 months, both the dysphasia and the vocal cord paralysis were resolved in all patients. CONCLUSIONS Hybrid cervical arthroplasty involving the placement of a Prestige ST disc and either the Mystique resorbable plate or Prevail stand-alone interbody device is a safe and effective alternative to multilevel fusion for the management of cervical radiculopathy and myelopathy.

Neurosurgical management of spinal dysraphism and neurogenic scoliosis.

Study Design. To review diagnosis and treatment of neurogenic factors implicated in the development of progressive scoliosis. Objective. Increased awareness of neurogenic causes as a contributing component of spinal cord tethering has led to enhanced radiographic surveillance for etiologic factors contributing to the genesis of scoliosis. Review of various manifestations of spinal dysraphism offers better definition of clinical indications for surveillance MRI scans and thus may contribute to improving outcomes for affected individuals. Summary of Background Data. Increasing utilization of surveillance MRI has led to a greater awareness of neurogenic causes as contributing factors in the setting of scoliosis. It is imperative for clinicians treating individuals with scoliosis to be aware of the most common etiologies of neurogenic factors as well as be cognizant of the neurosurgical approaches to treating these conditions in a pre-emptive fashion. This will serve to minimize potential neurological complications and offer improved surgical outcomes after instrumentation. Methods. Current therapeutic approaches were outlined for various etiologies of neurogenic scoliosis as well as neurosurgical management of the tethered cord, spinal cord tumors in addition to current challenges surrounding Chiari malformations and syringomyelia. Results. Timely recognition of these frequently progressive conditions may not only prevent irreversible neurologic compromise but may also help to ameliorate or stabilize concurrent scoliosis. Tethered cords are best treated by releasing the affected cord and offers the best opportunity to stabilize or improve the scoliosis. Syringomyelia, often associated with a Chiari malformation, is a well-known progenitor of scoliosis, and addressing the underlying cause with a Chiari decompression frequently leads to a reduction or resolution of the syrinx and may result in a concomitant improvement in scoliosis. Conclusion. Surveillance MRI should be undertaken for scoliosis when there are clinical indications consistent for a tethered cord, spinal cord tumor, or Chiari malformation and associated syringomyelia.

Biomechanical contribution of transverse connectors to segmental stability following long segment instrumentation with thoracic pedicle screws.

Study Design. An in vitro biomechanical cadaver study of long segment thoracic pedicle screw constructs with transverse connectors (TC). Objective. To determine the resultant degree of motion of the instrumented thoracic spine after segmental pedicle screw instrumentation with and without TC. Summary of Background Data. TC are generally not thought to be necessary with thoracic pedicle screw constructs, yet to date no study has reported the effect of TCs after all pedicle screw long thoracic fusions. Methods. Eight human cadaveric spines were potted and then instrumented from T4-T10 with bilateral 5.5 mm multiaxial titanium (Ti) pedicle screws and 5.5 mm contoured Ti rods. Specimens were tested with a six-degree-of-freedom spine stimulator in the intact condition, after instrumentation, after placement of 1 TC (3 different locations) and after placement of both TCs. Data were analyzed by loading modality (axial rotation, flexion-extension, and lateral bending) using one-way analysis of variance with an alpha of 0.05. Paired t tests were used for post hoc analysis with correction for multiple comparisons. Results. There was no difference with the addition of 1 or 2 TCs in terms of flexion-extension or lateral bending when compared to the instrumented condition (P > 0.05). Biomechanical testing of the long-segment thoracic constructs in axial rotation (torsion) loading modes generated the most significant findings of this study. After instrumentation with thoracic pedicle screws, T4-T10 full ROM was significantly reduced from the intact condition (P < 0.05). On average, TPS alone resulted in a 65% decrease in ROM. However, the addition of a transverse connector at 1 of the 3 positions tested yielded another 20% improvement in axial segmental stability as represented by further ROM reduction. These differences were significant from the TPS only group (no TCs), regardless of the TC position (P < 0.05). Furthermore, 2 TCs placed at the proximal and distal ends of the construct provided the greatest biomechanical axial stability to the instrumented specimens (P < 0.05). This was highlighted by an average of 35% ROM reduction from the stability level achieved with the TPS only constructs (P < 0.05), or an additional 15% improvement in axial stability over a single TC. Conclusion. For long thoracic pedicle screw constructs, the addition of 1 or 2 TCs significantly decreases construct axial rotation, which is the primary plane of motion for the thoracic spinal region. A single TC contributed to a significant reduction of T4-T10 ROM (an additional 20%) relative to TPS fixation alone (P < 0.05), while the location of the TC within the construct was irrelevant. A second TC had an additive effect (an additional 15% reduction) on axial stability. (P < 0.05) Flexion-extension and lateral bending are not affected. Single TC significantly improves axial rotation stability in long thoracic pedicle screw constructs. Two crosslinks, however, are better than one.

Using lamina screws as a salvage technique at C-7: computed tomography and biomechanical analysis using cadaveric vertebrae. Laboratory investigation.

OBJECT Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique. METHODS Nine fresh-frozen C-7 cadaveric specimens were scanned for bone mineral density using dual energy x-ray absorptiometry. Prior to testing, all specimens were imaged using CT to obtain 1-mm axial sections. Caliper measurements of both pedicle width and laminar thickness were obtained. On the right side, pedicle screws were first inserted and then pulled out. Salvage intralaminar screws were inserted into the left lamina from the right spinous process/lamina junction and then pulled out. All screws were placed by experienced cervical spine surgeons under direct fluoroscopic visualization. Pedicle and lamina screws were 4.35- and 3.5-mm in diameter, respectively. Screws sizes were chosen based on direct and radiographic measurements of the respective anatomical regions. Insertional torque (IT) was measured in pounds per inch. Tensile loading to failure was performed in-line with the screw axis at a rate of 0.25 mm/sec using a MiniBionix II system with data recorded in Newtons. RESULTS Using lamina screws as a salvage technique generated mean pullout forces (778.9 +/- 161.4 N) similar to that of the index pedicle screws (805.3 +/- 261.7 N; p = 0.796). However, mean lamina screw peak IT (5.2 +/- 2.0 lbs/in) was significantly lower than mean index pedicle screw peak IT (9.1 +/- 3.6 lbs/in; p = 0.012). Bone mineral density was strongly correlated with pedicle screw pullout strength (r = 0.95) but less with lamina screw pullout strength (r = 0.04). The mean lamina width measured using calipers (5.7 +/- 1.0 mm) was significantly different from the CT-measured mean lamina width (5.1 +/- 0.8 mm; p = 0.003). Similarly, the mean pedicle width recorded with calipers (6.6 +/- 1.1 mm) was significantly different from the CT-measured mean pedicle width (6.2 +/- 1.3 mm; p = 0.014). The mean laminar width measured on CT at the thinnest point ranged from 3.8 to 6.8 mm, allowing a 3.5-mm screw to be placed without difficulty. CONCLUSIONS These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.

Computed tomography and biomechanical evaluation of screw fixation options at the cervicothoracic junction: intralamina versus intrapedicular techniques.

Study Design. In vitro cadaveric biomechanical analysis. Objective. Define the T1 and T2 anatomic lamina size and evaluate the bone-screw interface strength of various pedicle screw options and intralamina techniques. Summary of Background Data. Transpedicular instrumentation is well accepted, but salvage techniques in the proximal thoracic spine are limited. Intralamina fixation has been described at C2 with favorable biomechanical characteristics. In addition, this technique has been introduced clinically in the proximal thoracic spine. However, the biomechanical potential has not been evaluated. Methods. Fourteen fresh-frozen cervicothoracic cadaveric specimens were scanned using dual-energy radiograph absorptiometry for bone mineral density, imaged under computed tomography, and then instrumented in the following configuration: (1) Right-sided pedicle screws in a straight-forward trajectory, (2) “salvage anatomic trajectory pedicle screws, and (3) “salvage” intralamina screws into the contralateral lamina. Insertional torque (IT) was recorded with each revolution and screws were pulled out in-line (POS) with the screw axis to simulate intraoperative failure of fixation. Results. Lamina screws as a salvage technique generated statistically greater peak IT (P = 0.002) and relative POS (P < 0.05) in comparison with straight-forward transpedicular screws as the initial fixation type. Furthermore, lamina screws, when compared to the salvage anatomic trajectory pedicle screws, had a significantly greater peak IT (P = 0.011). The peak IT showed a stronger correlation with POS in lamina screws than straight-forward or anatomic pedicle screws with a similar trend noted in mean IT. Bone mineral density correlated with POS in all methods of fixation. The mean lamina width measured on computed tomography at the thinnest point was 5.9 ± 0.7 mm (range, 4.9–7.9). Conclusion. Our results suggest that lamina screws, used as a salvage technique in the proximal thoracic spine, provide stronger fixation than transpedicular screws when using standard 4.5-mm cervical screws. In-tralamina screws appear to be a biomechanically sound salvage technique in the region, and appear to be a safe, effective technique for instrumenting the proximal thoracic spine.

Structures at risk from pedicle screws in the proximal thoracic spine: computed tomography evaluation

BACKGROUND CONTEXT Pedicle screw placement in the proximal thoracic spine may result in unwanted bicortical breach. An understanding of the potential structures at risk is paramount to safe screw placement. PURPOSE To assess the anatomic location of structures at risk with the placement of bicortical pedicle screw fixation in the proximal thoracic spine. STUDY DESIGN Retrospective radiographic review. PATIENT SAMPLE Twenty patients with dedicated computed tomography (CT) scans of the thoracic spine. OUTCOME MEASURES Radiographic parameters on CT. METHODS AND MATERIALS Computed tomography was performed on 20 patients and analyzed from T1 to T4 for proximity of major structures at risk with breach of the anterior vertebral body cortex from pedicle screw placement. Descriptive statistics, analyses of variance and post hoc paired t tests were used to analyze screw position relative to the esophagus, trachea, aortic arch, carotid, and vertebral arteries. RESULTS One hundred sixty potential anterior cortical violation positions were analyzed. Left-sided pedicle screws posed a significantly higher risk (p<.05) to the esophagus at T1-T3; in particular, the left T2 screw was significantly closer (p<.05). Right-sided pedicle screws posed a significantly higher risk to the trachea at T2-T4 (p<.05). The right T3 and T4 screws posed the greatest risk to the trachea and right main bronchus, respectively (p<.05). The carotid and vertebral arteries were not at risk for injury. The aortic arch was present at T4 in 70% of patients and was not at risk. CONCLUSIONS Careful preoperative evaluation with CT is warranted to determine anatomic structures at risk when placing proximal thoracic pedicle screws. Left-sided screws pose the greatest risk to the esophagus; right-sided screws pose the greatest risk to the trachea. The carotid and vertebral arteries, along with the aortic arch are at minimal risk for injury.