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Study Design: A sex- and age-matched case-control study and a cross-sectional study. Objective: In our previous study, patients with early-onset (Methods: In Study 1, the simple brief-type self-administered diet history questionnaire (BDHQ) was used to compare nutrient intake levels of early-onset OPLL patients (n = 13) with those of sex- and age-matched non-OPLL controls (n = 39) or with those of common OPLL (onset age ≥ 50 years, n = 62). In Study 2, serological validation was conducted for thoracic OPLL patients (n = 77) and non-OPLL controls (n = 101) in a nationwide multicenter study in Japan. Results: The BDHQ showed that the early-onset OPLL patients had significantly lower intakes of vitamins A and B6 than non-OPLL controls. These results were validated by lower serum vitamins A and B6 levels in the early-onset thoracic OPLL patients. The severity of OPLL negatively correlated with serum vitamin A levels in male early-onset OPLL patients. The multiple regression analysis revealed that the severity of thoracic OPLL had an association with onset age and serum vitamin A level. Conclusions: Vitamin A deficiency resulting from unbalanced dietary habits is associated with exacerbation of male early-onset OPLL.

To investigate the efficacy of application of VCM powder to surgical wounds. A total of 314 patients who underwent posterior spinal instrumentation with local application of VCM (VCM group) were compared to 354 patients without VCM (control). The wound drainage tube was submitted for bacterial culture. The number of positive cultures, types of bacteria, and incidence of surgical site infections (SSI) were investigated. Drainage tube culture was positive in 1.6% (5/314 cases) and 7.3% (26/354 cases) of the VCM and control groups, respectively (P = 0.004). Among the five positive cases in the VCM group, one had an SSI, compared to three of 26 in the control group. Among the culture-negative cases, 0 and six, respectively, had an SSI. Finally, the incidence of SSI was 0.3% (1/314 cases) and 2.5% (9/354 cases), respectively. SSI occurred significantly less often in the VCM than in the control group (P = 0.01). The pathogenic bacterium was P. aeruginosa in the VCM group and MSSE, S. marcescens, methicillin-resistant S. aureus (MRSA), etc., in the control group. This study indicates that the amount of bacteria in the operative field was decreased by local application of VCM. However, the incidence of positive culture of VCM-resistant bacteria was not decreased by VCM. Importantly, pathogenic bacteria in the VCM group were only VCM-resistant, supporting the efficacy of VCM. In conclusion, local application of VCM decreases the amount of bacteria in the operative field and leads to fewer SSIs.

STUDY DESIGN A retrospective observational study. OBJECTIVE To clarify the exceptional conditions for a favorable neurological recovery after laminoplasty (LMP) for cervical myelopathy caused by K-line (-) ossification of the posterior longitudinal ligament (OPLL). SUMMARY OF BACKGROUND DATA The K-line-based classification of cervical OPLL was developed to predict insufficient neurological recovery after LMP. For patients with K-line (-) OPLL, LMP generally yields the least improvement because of inadequate decompression of the spinal cord; however, there are some exceptional cases wherein LMP promotes favorable neurological recoveries. METHODS We retrospectively reviewed the medical records of 106 consecutive patients who underwent LMP for cervical OPLL to determine the demographic data, radiographic findings, and neurological recoveries of the patients as assessed preoperatively and 2 years postoperatively by their Japanese Orthopedic Association (JOA) scores. The factors associated with favorable outcomes after LMP in patients with K-line (-) were then investigated. RESULTS Of 106 total patients, 31 were classified as K-line (-), of whom 21 achieved the least neurological recovery after LMP (JOA recovery rate

Background Despite repeated efforts for accurate cervical pedicle screw insertion, malpositioning of the inserted screw is commonly noted. To avoid neurovascular complications during cervical pedicle screw insertion, we have developed a new patient-specific screw guide system. This study aimed to evaluate the accuracy of cervical PS placement using the new patient-specific screw guide system. Methods This study is a retrospective clinical evaluation of prospectively enrolled patients. Seventeen consecutively enrolled patients who underwent posterior cervical fusion using the guide system were included. Firstly, three-dimensional planning of pedicle screw placement was done using simulation software. A screw guide for each vertebra was constructed preoperatively. A total of 77 screws were inserted with the guides. Postoperative computed tomography was used to evaluate pedicle perforation, and screw deviations, between the planned and actual screw positions, were measured. Results A total of 76 screws (98.7%) were completely inside the pedicle (C3-7), without neurovascular injuries. The mean screw deviations from the planned trajectory at the narrowest point of the pedicle and at the entry point in the axial and sagittal planes were 0.56 ± 0.43 mm and 0.43 ± 0.35 mm and 0.43 ± 0.30 mm and 0.63 ± 0.50 mm, respectively. There were no significant differences in any parameter at different spinal levels. Angular deviations in the sagittal and axial planes were 2.94 ± 2.04° and 2.53 ± 1.85°, respectively. Sagittal angular deviations tended to increase in the cranial vertebra (C3 and C4) compared to the middle cervical spine. Conclusions We demonstrated that our patient-specific screw guide is vital for guiding precise screw insertion in the cervical pedicle. This technique may be an effective solution for achieving precise screw insertion and reducing the incidence of complications.

Study Design Retrospective case-control study. Objective This study aimed to identify the underlying pathologies of non-rheumatic retro-odontoid pseudotumors (NRPs), which would help establish an appropriate surgical strategy for myelopathy caused by NRP. Methods We identified 35 patients with myelopathy caused by NRP who underwent surgery between 2006 and 2017. An age- and sex-matched control group of 70 subjects was selected from patients with degenerative cervical myelopathy. Radiographic risk factors for NRP were compared between cases and controls. We also assessed surgical outcomes following occipital-cervical (O-C) fusion, atlantoaxial (C1-2) fusion, or C1 laminectomy. Results Patients with NRP had significantly lower C1 sagittal inner diameter, C2-7 range of motion (ROM), C2-7 Cobb angle, and C7 tilt, as well as significantly higher C1-2 ROM, atlantodental interval (ADI), and C1-2 to O-C7 ROM ratio. Multivariate regression analysis revealed that ADI, C2-7 ROM, and C7 tilt were independent risk factors for NRP. Neurological recovery and pseudotumor size reduction were comparable among surgical procedures, whereas post-operative cervical spine function was significantly lower in the O-C fusion group than in the other groups. Conclusion Non-rheumatic retro-odontoid pseudotumor was associated with an increase in ADI, suggesting that spinal arthrodesis surgery is a reasonable strategy for NRP. C1-2 fusion is preferable over O-C fusion because of the high prevalence of ankylosis in the subaxial cervical spine. Given that 29% of patients with NRP have C1 hypoplasia, such cases can be treated by posterior decompression alone. Our study highlights the need to select appropriate surgical procedures based on the underlying pathology in each case.

OBJECTIVEThe number of spine surgeries performed in elderly patients is consistently increasing. However, to date the prevalence of and risk factors for perioperative complications remain unclear, especially in patients 80 years of age or older. This study had two goals: 1) determine the perioperative complications of spine surgery associated with patients 80 years of age or older; and 2) investigate the risk factors for perioperative systemic complications.METHODSIn this paper, the authors describe a multicenter prospective cohort study. Seven spine centers with board-certified spine surgeons participated in this all-case investigation. A total of 270 consecutively enrolled patients (109 males and 161 females), 80 years of age or older, underwent spine surgery between January and December 2017. Patients with trauma, infection, or tumor were excluded in this cohort. Perioperative complications were defined as adverse events that occurred intraoperatively or within 30 days postoperatively. The patients’ preoperative health status was determined using the following means of assessment: 1) the Charlson Comorbidity Index, 2) the American Society of Anesthesiologists Physical Status Classification System, 3) the Eastern Cooperative Oncology Group Performance Status (ECOG-PS), 4) the presence of sarcopenia, and 5) the Geriatric Nutritional Risk Index. Associations among patient age, preoperative health status, surgical factors (instrumentation surgery, operation time, number of spinal levels treated, and estimated blood loss), and perioperative systemic complications were analyzed.RESULTSOverall perioperative, surgical site, and minor systemic complications were observed in 20.0%, 8.1%, and 14.8% of patients, respectively. Major systemic complications, on the other hand, were not observed. The reoperation rate was low—only 4.1%. Multivariate analysis revealed that the ECOG-PS (p = 0.013), instrumentation surgery (p = 0.024), and an operation time longer than 180 minutes (p = 0.016) were associated with minor systemic complications.CONCLUSIONSTo the best of the authors’ knowledge, this is the first multicenter prospective all-case investigation of perioperative complications of spine surgery in elderly patients. Although decreased daily activity (ECOG-PS), instrumentation surgery, and longer operation time were associated with minor systemic complications, no major systemic complications were observed in these elderly patients. Thus, spine surgery can be safely performed in elderly patients 80 years of age or older.

To conduct a retrospective multicenter study to investigate the accuracy of pedicle screw (PS) placement in the cervical spine by freehand technique and the related complications in various pathological conditions including trauma, rheumatoid arthritis, degenerative conditions and others. 283 patients with 1,065 PSs in the cervical spine who were treated at eight spine centers and finished postoperative CT scan were enrolled. The numbers of placed PSs were 608 for trauma, 180 for rheumatoid arthritis (RA), 199 for spondylosis, and 78 for others. Malposition grades on CT image in the axial plane were defined as grade 0 (G-0) correct placement, grade 1 (G-1): malposition by less than half screw diameter, grade 2 (G-2): malposition by more than half screw diameter. The direction of malposition was classified into four categories: medial, lateral, superior and inferior. Overall malposition rate was 14.8 % (9.6 % in G-1 and 5.3 % in G-2). The highest malposition rate was 26.7 % for RA, followed by 16.6 % for spondylosis, and 11.2 % for trauma. The malposition rate for RA was significantly higher than those for other pathologies. 79.7 % of the malpositioned screws were placed laterally. Though intraoperative vertebral artery injury was observed in two patients with RA, there were no serious complications during a minimal 2-year follow-up. Malposition rate of PS placement in the cervical spine by freehand technique was high in rheumatoid patients even when being performed by experienced spine surgeons. Any guidance tools including navigation systems are recommended for placement of cervical PSs in patients with RA.

Study Design. A retrospective study. Objectives. To evaluate clinical outcomes of palliative spinal reconstruction using cervical pedicle screws in metastatic spine tumors. Summary of Background Data. No study to date has investigated the effectiveness of cervical pedicle screw fixation in metastatic lesions of the spine. Methods. A total of 32 patients with metastatic spine tumors who underwent reconstructive surgery using cervical pedicle screws were reviewed. Four patients presented upper cervical lesions and 28 patients had subaxial lesions. All patients had intractable pain, 29 presented myelopathy, and 18 patients were nonambulatory. Combined anterior column reconstruction was considered in cases of life expectancy more than 2 years and anterior spinal cord compression that could not be solved by posterior decompression and kyphosis correction. Posterior fixation alone was performed in 25 patients, and posterior fixation combined with anterior column reconstruction was performed in 7 patients. Results. The average postoperative survival period was 12.2 months. Neck pain was improved in all cases. Twenty-four (83%) of the 29 patients with spinal cord lesions presented neurologic improvement. Of 18 patients who were not ambulatory, 16 patients (89%) became ambulatory. Pain relief, neurologic function, and spinal stability were maintained throughout the survival period in 30 of 32 patients (94%). Conclusion. Spinal reconstruction using cervical pedicle screws improved spinal stability, pain, and neurologic function. These improvements were maintained throughout the survival period in 94% of the patients. Anterior column reconstruction could be avoided in 78% of the patients in spite of damaged anterior column.

STUDY DESIGN Pedicle screw fixation alone for sequential spinal instabilities was biomechanically compared with pedicle screw fixation using interbody cages. OBJECTIVE To evaluate biomechanical effects of interbody cages on construct stiffness, pedicle-screw strain, and the adjacent level in posterior lumbar reconstruction using pedicle screw fixation. SUMMARY OF BACKGROUND DATA It remains undetermined what types of spinal instability require interbody support in posterior lumbar reconstruction. METHODS For this study, 10 calf spines (L3-L6) were used. Sequential destabilization was performed at L4-L5 followed by posterior reconstruction using pedicle screw fixation (PS) and interbody cages as follows: intact + PS (I-PS), medial facetectomy + PS (MF-PS), total facetectomy + PS (TF-PS), partial discectomy + PS (D-PS), and D-PS + interbody cages (PLIF). Biomechanical testing was performed under flexion and extension loading modes. Construct stiffness (L4-L5), rod-screw bending strain, and range of motion (ROM) at the upper adjacent level (L3-L4) were analyzed. RESULTS In terms of construct stiffness (L4-L5), all the reconstructions except D-PS demonstrated higher construct stiffness than the intact spine (P < 0.05). The PLIF showed the highest stiffness among all the reconstructions (P < 0.05). In terms of ROM (L3-L4), all the reconstructions increased the ROM, as compared with the intact state (P < 0.05). Importantly, PLIF showed significantly greater ROM than all the other reconstructions except I-PS (P < 0.05). In terms of rod-screw strain, the D-PS resulted in higher strain than the other groups (P < 0.05). The PLIF presented less strain than the other reconstructions (P < 0.05). CONCLUSIONS For spinal instability with preserved anterior load sharing, pedicle screw fixation alone is biomechanically adequate, and interbody cages should not be used because they further increase segmental motion at the adjacent segment. However, PS alone provides insufficient stability and high implant strain in case of damaged anterior column. In such cases, additional interbody cages significantly increase construct stiffness and decrease hardware strain. However, they increase ROM at the adjacent segment as well.

Background context: Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate. Purpose: To optimize construct design and enhance implant survival until a successful spinal arthro- desis is achieved. Study design: This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction. Methods: Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis. Results: The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p .05). In flexion, similar results were obtained for the 4-mm construct (p Conclusions: Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.

Study design An in vitro human cadaveric study comparing the effects of anterior and posterior sequential destabilization conditions on thoracic functional unit mechanics was studied. Objectives To investigate the biomechanical properties of the human thoracic spine. Summary of background data Few studies have addressed the mechanical role of the costovertebral joints under torsion in the stability of the human thoracic spine. Methods Sixteen functional spinal units with intact costovertebral joints were obtained from six human cadavers and randomized into two groups based on destabilization procedures: Group 1, anterior to posterior sequential resection; and Group 2, posterior to anterior sequential destabilization. Biomechanical testing was performed after each destabilization procedure, and the range of motion under maximum load was calculated. Results Group 1: Under flexion-extension, lateral bending, and axial rotation loading, discectomy increased the range of motion by 193%, 74%, and 111%, respectively. Moreover, subsequent right rib head resection further increased the range of motion by 81%, 84%, and 72%, respectively. Group 2: Under all loading conditions laminectomy + medial facetectomy resulted in a 22-30% increase in range of motion. Subsequent total facetectomy led to an additional 15-28% increase in range of motion. Conclusion The rib head joints serve as stabilizing structures to the human thoracic spine in the sagittal, coronal, and transverse planes. In anterior scoliosis surgery additional rib head resection after discectomy may achieve greater curve and rib hump correction. The lateral portion of the facet joints plays an important role in providing spinal stability and should be preserved to minimize postoperative kyphotic deformity and segmental instability when performing decompressive wide laminectomy.

Study design This in vitro biomechanical study examines segmental anterior vertebral screw strain and solid rod construct stiffness with and without the addition of multilevel, threaded cortical bone dowels in a bovine model. Objective To determine whether strain at the bone-screw interface is higher at the end levels during physiologic range loading, and whether solid interspace support decreases segmental strain on the implant. Summary of background data Anterior instrumentation provides greater correction and preserves distal motion segments. However, nonunion and implant failure are observed more frequently than with posterior segmental instrumentation, and when observed, loss of fixation occurs at the end levels. Methods Eight calf spines underwent mechanical testing in the following sequence: 1) intact condition, 2) anterior release with anterior solid rod and bicortical rib grafts, and 3) anterior release with anterior solid rod and threaded cortical bone dowels (L2-L5). Instrumented vertebral screws were used to assess strain within the vertebral body by the near cortex, whereas an anterior extensometer spanning the instrumented segments was used to measure segmental displacements to calculate construct stiffness. The protocol included axial compression (-400 N), right lateral bending (4 Nm (Newton-meter), away from the implant), and left lateral bending (4 Nm, toward the implant). Statistical analysis included a one-way analysis of variance and a Student-Newman-Keuls post hoc test. A pilot study was performed using four additional specimens loaded for 4000 cycles to investigate macroscopic loosening after fatigue loading. Results In lateral bending toward the implant, the strain was higher at both end levels, with no differences between the rib and dowel reconstructions. The stiffness values were greater than the intact values for both groups. In lateral bending away from the implant, the strain also was higher at both end screws, and the dowel group had less strain at these levels than the rib group. Both groups were stiffer than the intact condition, and the dowel group was stiffer than the rib group. Axial compressive strain also was higher at the end levels, but this difference did not reach statistical significance. The rib group did not reach intact stiffness values, whereas the dowel group was stiffer than the intact condition. The fatigue study showed gross loosening at one or both end levels in all cases. Conclusions Higher strain was observed at the bone-screw interface in both end screws of an anterior solid rod construct during lateral bending, which correlates with the clinically observed failure location. This suggests that physiologic range loading may predispose to failure at the end levels. Disc space augmentation with solid implants increased construct stiffness in all three load paths and decreased strain at the end levels in lateral bending away from the implant. Future implant modifications should achieve better fixation at the end screws, and the current model provides a means to compare different strategies to decrease strain at these levels.

STUDY DESIGN Three types of anterior thoracolumbar multisegmental fixation were biomechanically compared in construct stiffness and rod-screw strain. OBJECTIVES To investigate the effects of rod diameter and rod number on construct stiffness and rod-screw strain in anterior thoracolumbar multisegmental instrumentation. SUMMARY OF BACKGROUND DATA No studies have been undertaken to investigate the biomechanical effects of rod diameter and rod number in thoracolumbar anterior instrumentation. METHODS Ten fresh-frozen calf spines (T13-L5) were used. After intact analysis, a total discectomy and transection of the ALL and PLL were performed at L1-L2, L2-L3, and L3-L4 with intervertebral reconstruction using carbon fiber cages. Three types of anterior fixation were then performed at L1-L4: 1) 4.75-mm diameter single-rod, 2) 4.75-mm dual-rod, and 3) 6.35-mm single-rod systems. Single screws at each vertebra were used for single-rod and two screws for dual-rod fixation. These systems share the same basic design except rod diameter. Nondestructive biomechanical testing was performed and included compression, torsion, flexion-extension, and lateral bending. Construct stiffness and rod-screw strain of the three reconstructions were compared. RESULTS The 6.35-mm single-rod fixation significantly improved construct stiffness compared with the 4.75-mm single rod fixation only under torsion (P < 0.05). The 4. 75-mm dual rod construct resulted in significantly higher stiffness than did both single-rod fixations (P < 0.05), except under compression. No statistical differences were observed in rod-screw strain between the two types of single rods, whereas dual-rod reconstruction exhibited less rod-screw strain (P < 0.05). CONCLUSIONS For single-rod fixation, increased rod diameter neither markedly improved construct stiffness nor affected rod-screw strain, indicating the limitations of a single-rod system. In thoracolumbar anterior multisegmental instrumentation, the dual-rod fixation provides higher construct stiffness and less rod-screw strain compared with single-rod fixation.

This experimental study used synthetic spine models to compare the effect of the angle of kyphosis, rod diameter, and hook number on the biomechanical stiffness of a long-segment posterior spinal construct.To examine the biomechanical effects of incremental kyphosis on variously instrumented long-segment posterior spinal constructs.Euler's formula for loading of curved long columns would suggest that kyphosis has a profound impact on the biomechanical behavior of long-segment posterior spinal constructs. The effects of sagittal contour on the mechanical properties of long-segment posterior spinal constructs have not been well documented.Kyphotic and straight synthetic spine models were used to test long-segment posterior instrumentation constructs biomechanically while varying rod diameter and the number of hook sites. The synthetic spines, composed of polypropylene vertebral blocks and isoprene elastomer intervertebral spacers, were fabricated with either 0 degrees, 27 degrees, or 53 degrees of sagittal contour. The models were instrumented with 5.5- or 6.35-mm titanium rods, and with either 8 or 12 hooks. The models were loaded from 0 to 300 N in a cyclical ramp fashion using an MTS 858 Bionix testing device testing device. Construct stiffness (force and displacement) during axial compression was determined.Straight model: Changing the hook number from 8 to 12 caused a 32% increase in construct stiffness with the 5.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 36% increase in construct stiffness with the 8-hook pattern. Changing both the rods and hooks caused the stiffness to increase 44%. 27 degreesChanging the hook number from 8 to 12 caused a 20% increase in construct stiffness with the 6.5-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 29% increase in construct stiffness with the 12-hook pattern. Changing both the rods and hooks caused the construct stiffness to increase 26%. 53 degreesChanging the hook number from 8 to 12 caused a 14% increase in construct stiffness with the 6.35-mm rod. Changing the rod diameter from 5.5 to 6.35 mm caused a 17% (P0.0005) increase in construct stiffness with the 12-hookpattern. Changing both rods and hooks caused the stiffness to increase 21%. Summary data on angular kyphosis: Using the same rod diameter and the same number of hooks, and progressing from a straight alignment to 27 degrees of sagittal contour decreased construct stiffness 32%. Going from straight alignment to 53 degrees decreased the stiffness 59.6%. All reported values were statistically significant (P0.0005).The biomechanical stiffness of the straight spine was sensitive to both an increase in hook fixation sites and an increase in rod diameter. The kyphotic spines, however, were more sensitive to variations in rod diameter. Although with increasing kyphosis, the optimum instrumentation strategy will maximize both rod diameter and the number of hook sites, instrumented kyphotic spines remain biomechanically "disadvantaged" as compared with nonkyphotic instrumented spines.

This study examines the biomechanical effects of interbody cages and variations in posterior rod diameter in a simulated single-level spinal fusion. A single-level spinal fusion model composed of polyethylene cylinders, posterior pedicular instrumentation, and variously positioned single or dual interbody cages was used for biomechanical testing. Constructs were tested under compressive flexural load, with measurement of stiffness, rod strain, cage strain, and intracage pressure. A strong linear correlation emerged between the mean construct stiffness and cage positioning within the sagittal plane that was inversely related to posterior rod strain. Two small titanium mesh cages were equivalent to one large cage. In a single-level spine model, the presence of and sagittal position of interbody cages significantly influences overall construct stiffness. Cage strain increased with more anterior positions and was inversely related to rod strain.

Epidural hematoma associated with osteoporotic vertebral collapse has not been reported yet in the literature. We report a case of myelopathy caused by chronic epidural hematoma associated with L1 osteoporotic vertebral collapse and review the relevant literature.

Object The objectives of this study were to compare the biomechanical effects of five lumbar reconstruction models on the adjacent segment and to analyze the effects of three factors: construct stiffness, sagittal alignment, and the number of fused segments. Methods Nondestructive flexion–extension tests were performed by applying pure moments to 10 calf spinal (L3–S1) specimens. One-segment (L5–6) or two-segment (L5–S1) posterior fusion methods were simulated: 1) one-segment posterolateral fusion (PLF); 2) one-segment PLF with interbody fusion cages (one-segment PLIF/PLF); 3) two-segment PLF; 4) two-segment PLIF/PLF; and 5) two-segment PLF in kyphosis (two-segment kyphotic PLF). The range of motion (ROM) of the reconstructed segments, intradiscal pressure (IDP), and lamina strain in the upper (L4–5) adjacent segment were analyzed. The ROM was significantly decreased in the PLIF/PLF models compared with that in the PLF alone models after both the one- and two-segment fusions. If the number of fused segments was increased, the pressure and strains were also increased in specimens subjected to the PLIF/PLF procedure, more so than the PLF-alone procedure. In the one-segment PLIF/PLF model the authors observed a reduced IDP and lamina strain compared with those in the kyphotic two-segment PLF model despite the latter’s higher levels of initial stiffness. Conclusions If the number of fused levels can be reduced by using PLIF to correct local kyphosis, then this procedure may be valuable for reducing adjacent-segment degenerative changes.

Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate.To optimize construct design and enhance implant survival until a successful spinal arthrodesis is achieved.This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction.Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis.The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p.001). The remaining constructs were not significantly different from each other (p.05). In flexion, similar results were obtained for the 4-mm construct (p.001) but not the 5-mm construct, because the reconstruction-alone, one-, two- and three-cage constructs were all significantly stiffer than the intact specimen (p.05). Multisegmental construct stiffness under extension loading, as well as right and left lateral bending, also exhibited significant differences between the seven-level interbody cage reconstructions and the remaining constructs. Apical rod strain for both the 4-mm-rod and 5-mm-rod groups were significantly higher for the two cage constructs (a cage at either end but not the apex where the strain gauges were located) as compared with the other constructs (p.05). These differences were more pronounced in the 4-mm-rod group. Similar results were obtained in anterior flexion, extension and lateral bending.Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.

Object. Posterior lumbar interbody fusion (PLIF) was developed to overcome the limitations of posterolateral fusion in correcting spinal deformity and maintaining lumbar lordosis. In this study the authors compare the biomechanical effects of three different posterior reconstructions on the adjacent motion segment. Methods. Ten calf spinal (L2—S1) specimens underwent nondestructive flexion—extension testing (± 6 Nm). The specimens were destabilized at the L5—S1 levels after intact testing. This was followed by pedicle screw fixation with and without interbody cages as follows: 1) with straight rods (“aligned” posterolateral fusion); 2) with kyphotically prebent rods (“kyphotic” posterolateral fusion); and 3) with interbody cages combined with straight rods (“aligned” PLIF/posterolateral fusion). The range of motion (ROM) of the operative segments, the intradiscal pressure (IDP), and longitudinal lamina strain in the superior adjacent segment (L4–5) were analyzed. The ROM associated with aligned PLIF/posterolateral fusion-treated specimens was significantly less than both the aligned and kyphotic posterolateral fusion-treated procedures in both flexion and extension loading (p < 0.05). The aligned PLIF/posterolateral fusion was associated with greater IDP and the lamina strain compared with the aligned and kyphotic posterolateral fusion groups in flexion loading. Under extension loading, greater IDP and lamina strain were present in the kyphotic posterolateral fusion group than in the aligned posterolateral fusion group. The highest IDP and lamina strain were shown in the aligned PLIF/posterolateral fusion group. Conclusions. Compared with kyphotic posterolateral fusion, PLIF may lead to even higher load at the superior adjacent level because of the increased stiffness of the fixed segments even if local kyphosis is corrected by PLIF.

STUDY DESIGN: After total spondylectomy, five types of spinal reconstruction techniques were compared biomechanically. OBJECTIVES: To evaluate the stability provided by five reconstruction methods after total spondylectomy. SUMMARY OF BACKGROUND DATA: Total spondylectomy presents a worst-case scenario for spinal reconstruction. However, few investigators have biomechanically investigated spinal reconstruction stability after total spondylectomy. METHODS: Eight human cadaveric spines (T11-L5) were used. After intact analysis, a total spondylectomy was performed at L2 and reconstructed using Harms titanium mesh (Depuy-Motech, Warsaw, IN) as an anterior strut. Anterior, posterior, or circumferential instrumentation techniques were then performed using the Kaneda SR and ISOLA pedicle screw systems (AcroMed Corp., Cleveland, OH) as follows: 1) anterior instrumentation at L1-L3 with multisegmental posterior instrumentation at T12-L4 (AMP), 2) anterior instrumentation at L1-L3 with short posterior instrumentation at L1-L3 (ASP), 3) anterior instrumentation at L1-L3 (A), 4) multilevel posterior instrumentation at T12-L4 (MP), and 5) short posterior instrumentation at L1-L3 (SP). Nondestructive biomechanical testing was performed under axial compression, flexion-extension, and lateral bending loading modes. RESULTS: Only circumferential instrumentation techniques (AMP, ASP) exhibited higher stiffness than the intact spine in all loading modes (P < 0.05). Short circumferential fixation provided more stability than did multilevel posterior instrumentation (P < 0.05). Multilevel posterior fixation provided more stiffness than did short posterior and anterior instrumentation alone (P < 0.05). CONCLUSIONS: Only circumferential fixation techniques provide more stability than the intact spine in all testing modes. Short circumferential instrumentation provides more stability than multilevel posterior instrumentation alone and requires fewer levels of spinal fusion.

Study design The biomechanical effects of chondroitinase ABC and chymopapain related to spinal segmental instability were investigated using a canine model, as well by as radiologic and histologic analyses. Objectives To evaluate the biomechanical, radiologic, and histologic affects on the lumber intervertebral disc of chondroitinase ABC compared with chymopapain. Summary of background data No study on the biomechanical effects of chondroitinase ABC has been reported. Methods Forty-eight lumbar intervertebral discs in eight beagles were randomly assigned to three groups and received one of three materials: chondroitinase ABC, chymopapain, or buffered saline, using a lateral percutaneous procedure. One week after injection, the animals were killed and the lumbar spinal motion segments were removed. Spinal segmental instability after chemonucleolysis was evaluated in spinal motion segments without posterior elements. Radiologic and histologic changes were also investigated. Results Spinal segmental instability and disc space narrowing were more greater in the chymopapain group than in the chondroitinase ABC group. Destruction of nucleus and anulus proteoglycans, indicated by loss of safranin-O staining, was less intense in chondroitinase ABC-injected discs. Conclusions Chondroitinase ABC results in less spinal segmental instability, disc space narrowing, and destruction of proteoglycans in intervertebral disc matrix than chymopapain.

Study design This is a biomechanical study of the thoracic spine. Various ligaments and joints were resected sequentially and nondestructive cyclic loading tests were performed. Effects of each resection were analyzed biomechanically. Objectives To investigate the role of the posterior elements, costovertebral joints, and rib cage in the stability of the thoracic spine. Summary of background data There have been no experimental studies concerning the mechanical interaction between the thoracic spine and rib cage. Methods Eight canine rib cage-thoracic spine complexes, consisting of the sixth to eighth ribs, sternum, and T5-T9 vertebrae, were used. Six pure moments along three axes were applied to the specimens, and angular deformation of T6-T7 was recorded. After testing the intact specimen, resection of the stabilizers was conducted incrementally in the following manner: 1) removal of the posterior elements at T6-T7, 2) resection of the bilateral seventh costovertebral joints, and finally, 3) destruction of the rib cage. The same loading tests were repeated at each stage. The ranges of motion and neutral zones were calculated by digitization. Results A large increase in the range of motion in flexion-extension was observed after resection of the posterior elements and in lateral bending and axial rotation after resection of the costovertebral joints. A significant increase in the neutral zone in lateral bending and axial rotation was observed after bilateral resection of the costovertebral joints and destruction of the rib cage. Conclusions The costovertebral joints and rib cage play an important role in providing stability to the thoracic spine. The state of the costovertebral joints and rib cage should be assessed to evaluate the stability of the thoracic spine.

The stabilizing effects of five different occipitocervical fixations were compared.To evaluate the construct stability provided by five different occipito-atlanto-axial fixation techniques.Few studies have addressed occipitocervical reconstruction stability and no studies to data have investigated anterior-posterior translational stiffness.A total of 21 human cadaveric spines were used. After testing intact spines (CO-C2), a type II dens fracture was created and five different reconstructions were performed: 1) occipital and sublaminar wiring/rectangular rod, 2) occipital screws and C2 lamina claw hooks/rod, 3) occipital screws, foramen magnum screws, and C1-C2 transarticular screws/rod, 4) occipital screws and C1-C2 transarticular screws/Y-plate, and 5) occipital screws and C2 pedicle screws/rod. Biomechanical testing parameters included axial rotation, flexion/extension, lateral bending, and anterior-posterior translation.Pedicle screw fixation demonstrated the highest stiffness among the five reconstructions (P0.05). The two types of transarticular screw methods provided greater stability than hook or wiring reconstructions (P0.05). The C2 claw hook technique resulted in greater stability than sublaminar wiring fixation in anterior-posterior translation (P0.05). However, the wiring procedure did not significantly increase the stiffness levels beyond the intact condition under anterior-posterior translation and lateral bending (P0.05).C2 transpedicular and C1-C2 transarticular screws significantly increased the stabilizing effect compared to sublaminar wiring and lamina hooks. The improved stability afforded by C2 pedicular and C1-C2 transarticular screws offer many potential advantages including a high rate of bony union, early ambulation, and easy nursing care.Occipitocervical reconstruction techniques using C1-C2 transarticular screws or C2 pedicle screws offer biomechanical advantages compared to sublaminar wiring or lamina hooks. Pedicle screw fixation exhibited the highest construct stiffness among the five reconstructions.

STUDY DESIGN In an in vivo sheep model, the effects of spinal fusion and kyphotic deformity on the neighboring motion segments were analyzed. OBJECTIVES To investigate the effects of spinal fusion and kyphotic deformity on the adjacent motion segment. SUMMARY OF BACKGROUND DATA The in vivo effects of kyphotic deformity on the neighboring motion segments have not been investigated in any studies. METHODS Eighteen sheep were equally randomized into three groups based on surgical procedure: L3-L5 in situ posterolateral fusion (n = 6) L3-L5 kyphotic posterolateral fusion (n = 6), and surgical exposure alone (n = 6). After a 16-week survival period, the adjacent motion segment changes were analyzed radiographically, biomechanically, and histologically. RESULTS The kyphosis group showed 5.0 degrees +/- 2.6 degrees and 1.7 degrees +/- 1.8 degrees compensatory hyperlordosis at L2-L3 and L5-L6, respectively, compared with surgical exposure and in situ posterolateral fusion, the kyphotic posterolateral fusion significantly influenced cranial adjacent motion segment biomechanics by inducing more stiffness in the posterior ligamentous complex (P < 0.05) and increasing lamina strain under flexion-extension loading (P < 0.05). Results of histologic analysis showed significant degenerative changes of the L2-L3 facet joints in the kyphosis group. CONCLUSIONS It is inferred that in the kyphosis group, compensatory hyperlordosis at the cranial adjacent level leads to lordotic contracture of the posterior ligamentous complex. The increased lamina strain, exhibited by the in situ group under flexion-extension, was further increased in the kyphosis group, indicating higher load transmission through the posterior column. Significant degenerative changes of the cephalad adjacent facet joints observed in the kyphosis group served to corroborate the biomechanical data. These results indicate that a kyphotic deformity may lead to facet joint contracture and facet arthritis and may serve as the origin of low back pain at the cranial adjacent level.

Study Design. Biomechanical evaluation was performed to investigate the stability of the thoracic spine. Unilateral resection of the intervertebral disc, the rib head joint, and the costotransverse joint were sequentially performed, and nondestructive cyclic loading tests were conducted at each injury stage to examine the roles of the intervertebral disc and the costovertebral joint of the thoracic spine. The effects of each resection were three-dimensionally analyzed as the main motion and the associated coupled motions. Objective. To examine the role of the intervertebral disc and the costovertebral joint in stability of the thoracic spine. Summary of Background Data. The effects of unilateral resection of the intervertebral disc and the costovertebral joints in the thoracic spine with the rib cage have not been documented three-dimensionally in a biomechanical study. Materials and Methods. Ten canine rib cage-thoracic spine complexes, consisting of the sixth to eighth ribs, the sternum and T5-T8 vertebrae, were used. Six pure moments along three axes, flexion-extension, lateral bending, and axial rotation, were applied to the specimen, and the angular deformation between T6-T7 was recorded by a stereophotogrammetric method. After the intact specimens were tested, staged resections were conducted in the following manner: partial resection of the T6-T7 intervertebral disc, performed as a resection of the anterior longitudinal ligament, the nucleus pulposus, and the annulus fibrosus on the approach side, leaving the posterior longitudinal ligament intact; resection of the right seventh rib head with the joint capsule: and resection of the right seventh costotransverse joint. At each stage, the main motion and associated coupled motions were determined three dimensionally. Results. The ranges of motion (ROM) in flexion-extension, lateral bending, and axial rotation were significantly increased after partial discectomy (P < 0.01). Moreover, along with large increases in the ROM of the main motions in left axial rotation and right lateral bending, coupled motions, expressed by right lateral bending and left axial rotation, showed marked increases after resection of the rib head joint (P < 0.05). The neutral zones also increased in lateral bending, axial rotation, and flexion-extension after partial discectomy (P < 0.01). A further increase in the neutral zone was observed in lateral bending after resection of the right seventh rib head (P < 0.01). Conclusions. in this canine spine model, the intervertebral disc regulates the stability of the thoracic spine in flexion-extension, lateral bending, and axial rotation. Moreover, the articulation of the rib head with the vertebral bodies provides stability to the thoracic spine in lateral bending and axial rotation. Unilateral resection of the rib head joint after partial discectomy on the same side produces significant coupled motions in lateral bending and axial rotation, resulting in a significant decrease in thoracic spinal stability, and integrity.