Reoperation and Perioperative Complications After Surgical Treatment of Cervical Radiculopathy: A Comparison Between Three Procedures.

STUDY DESIGN: A retrospective database study. OBJECTIVE: The purpose of our study was to compare the perioperative complications and reoperation rates after anterior cervical discectomy and fusion (ACDF), cervical disk arthroplasty (CDA), and posterior cervical foraminotomy (PCF) in patients treated for cervical radiculopathy. SUMMARY OF BACKGROUND DATA: Cervical radiculopathy results from compression or irritation of nerve roots in the cervical spine. While most cervical radiculopathy is treated nonoperatively, ACDF, CDA, and PCF are the techniques most commonly used if operative intervention is indicated. There is limited research evaluating the perioperative complications of these surgical techniques. MATERIALS AND METHODS: A retrospective review was performed using the PearlDiver Patient Record Database to identify cases of cervical radiculopathy that underwent ACDF, CDA, or PCF at one or two levels from 2007 to 2016. Perioperative complications and reoperations following each of the procedures were assessed. RESULTS: During the study period, 25,051 patients underwent ACDF, 522 underwent CDA, and 3986 underwent PCF. After propensity score matching, each of the three groups consisted of 507 patients. Surgical site infection rates were highest after PCF (2.17%) compared with ACDF (0.20%) and CDA (0.59%) at 30 days and three months ( P =0.003, P <0.001), respectively. New-onset cervicalgia was highest following ACDF (34.32%) and lowest after PCF (22.88%) at three and six months ( P <0.001 and P =0.003), respectively. Revision surgeries were highest among those who underwent CDA (6.90%) versus ACDF (3.16%) and PCF (3.55%) at six months ( P =0.007). Limb paralysis was significantly higher after PCF compared with CDA and ACDF at six months ( P <0.017). CONCLUSIONS: The rate of surgical site infection was higher in PCF compared with ACDF and CDA. New-onset cervicalgia was higher after ACDF compared with PCF and CDA at short-term follow-up. Revision surgeries were highest among those undergoing CDA and lowest in those undergoing ACDF. LEVEL OF EVIDENCE: 3.

Opportunistic assessment of bone density in patients with adolescent idiopathic scoliosis using MRI-based vertebral bone quality.

Patients with Adolescent Idiopathic Scoliosis (AIS) have increased prevalence of lower bone mineral density (BMD) compared to healthy adolescents. Our goal was to compare bone density in patients with AIS and a nonaffected control group using an MRI-based vertebral bone quality (VBQ) score. We reviewed 50 consecutive lumbar MRIs of patients with AIS and of 50 nonaffected controls that were matched for age and sex. The VBQ score was calculated and compared between the groups. The VBQ score for the AIS group was 2.5 (SD 0.4) and for the control group 2.1 (SD 0.3) (p < 0.001). Multiple linear regression analyses were performed for control of confounding from body weight, body height, corrected BMI, and Cobb angle. Besides the diagnosis of AIS, there was no variable that was independently associated with the VBQ score. This is the first study to evaluate bone density in pediatric patients with AIS. We found a significant difference in the VBQ-score between patients with AIS and nonaffected controls matched for sex, age, and race. MRI can be used to assess the bone quality in patients with adolescent idiopathic scoliosis.

Intra- and inter-observer reliability of the novel vertebral bone quality score.

PURPOSE: To assess the intra- and inter-observer reliability of the novel vertebral bone quality (VBQ) scoring system. METHODS: Four orthopedic surgery residents at various levels of training (PGY1-4) evaluated 100 noncontrast, T1-weighted MRIs of the lumbar spine. VBQ was calculated as quotient of the median of L1-L4 average signal intensity (SI) and the L3 cerebral spinal fluid (CSF) SI, as described by Ehresman et al. All measurements were repeated 2 weeks later. We performed a stratified analysis based on patient history of instrumentation, pathology, and MRI manufacturer/magnet strength to determine their effect on VBQ reliability. Spinal pathologies included compression fracture, burst fracture, vertebral osteomyelitis, epidural abscess, or neoplasm. The interclass correlation coefficient (ICC) two-way mixed model on absolute agreement was used to analyze inter-rater and intra-rater reliability. ICC less than 0.40 was considered poor, 0.40-0.59 as fair, 0.60-0.74 as good, and greater than 0.75 as excellent. RESULTS: Intra-observer reliability was excellent (≥ 0.75) for all four observers. When stratified by history of spinal instrumentation or spinal pathology, all raters showed excellent intra-observer reliability except one (0.71 and 0.69, respectively). When stratified by MRI manufacturer, intra-observer reliability was ≥ 0.75 for all raters. Inter-observer reliability was excellent (0.91) and remained excellent (≥ 0.75) when stratified by history of spinal instrumentation, spinal pathology, or MRI-manufacturer. CONCLUSIONS: VBQ scores from spine lumbar MRIs demonstrate excellent intra-observer and inter-observer reliability. These scores are reliably reproduced in patients regardless of previous instrumentation, spinal pathology, or MRI manufacturer/magnetic field strength.

Pedicle subtraction osteotomy in adult spinal deformity correction: Clinical and radiographic risk factors for early instrumentation failure.

BACKGROUND: Early instrumentation failure (EIF) after pedicle subtraction osteotomy (PSO) is a known complication of adult spine deformity (ASD) correction. In contrast to the more common failure that occurs secondary to pseudarthrosis, early instrumentation failure (<6 months after surgery) and its risk factors are not as well understood. OBJECTIVE: To identify risk factors for EIF in patients undergoing PSO for ASD correction. METHODS: Patients with ASD who underwent correction with PSO from 2013 to 2018 were retrospectively reviewed. Demographic characteristics, number of rods, spinopelvic parameters, bone density derived from computed tomography (CT) attenuation in Hounsfield units (HU), Global Alignment and Proportion (GAP) score, and type of instrumentation failure were evaluated. Potential risk factors for EIF were analyzed. RESULTS: 9 out of 46 (19.5%) patients who underwent PSO had EIF. All 9 patients with EIF had 2-rod constructs and failed secondary to rod fracture. The number of rods used in the EIF group was significantly lower than the non-EIF group (2.00 ± 0.00 vs 2.81 ± 0.995, p = .000. The EIF group demonstrated a significantly higher pre-op PI (77.33 ± 13.23), p = .022, pre-op PT (37.22 ± 6.46),p = .012, and post-op SVA (89.96 ± 23.85), p = .028 compared to the non-EIF group. CONCLUSION: High pre-op PI, pre-op PT, and post-op SVA were significant risk factors associated with EIF after PSO. Use of multiple rod constructs are protective and may help mitigate risk of EIF in these patients.

Sacral Endplate Penetrating Screw for Lumbosacral Fixation: A Cadaveric Biomechanical Study.

BACKGROUND: Cortical bone trajectory is a relatively new alternative for instrumentation of the lumbar spine. When performing lumbosacral instrumentation, a novel S1 endplate penetrating screw (EPS) has been recently shown to have higher insertional torque than the traditional trajectory screw, but the biomechanical properties of this new trajectory are yet to be verified with the cadaveric studies. OBJECTIVE: To evaluate 2 screw trajectories in sacra using cyclic loading and pullout tests, and to determine whether bone quality had different effects on the 2 trajectories. METHODS: Nine cadaveric sacra were used, 5 of which had normal bone mineral density (BMD) and 4 were osteoporotic. Each side of the sacra was randomly assigned to either EPS trajectory or S1-alar screw (S1AS) trajectory. Each screw then underwent cyclic loading followed by pullout force measurement. A mixed-design 2 way ANOVA test was used to detect differences between the groups. RESULTS: The EPS group had less relative rotation at the bone-screw interface during cyclic loading than the S1AS group (P = .016) regardless of bone quality. The pullout force following the cyclic loading was significantly higher in the EPS group (2349 ± 838 N) than the S1AS group (917 ± 909 N) in normal bone (P < .0001). The difference was more pronounced in osteoporotic bone with the EPS (1075 ± 216 N) compared to the S1AS (365 ± 422 N; P < .0001). CONCLUSION: The S1 EPS trajectory is significantly more stable against loosening and has a higher pullout force compared to the S1AS trajectory. The difference between the 2 trajectories is more pronounced in osteoporotic bone.

Measurement Techniques and Utility of Hounsfield Unit Values for Assessment of Bone Quality Prior to Spinal Instrumentation: A Review of Current Literature.

STUDY DESIGN: A systematic review. OBJECTIVE: The aim of this study was to evaluate the clinical utility of assessing bone quality using computed tomography (CT) attenuation in Hounsfield units (HU). SUMMARY OF BACKGROUND DATA: Assessing bone quality before spine instrumentation is an essential step of preoperative planning. Dual energy x-ray absorptiometry (DEXA) has been the gold standard for assessing bone mineral density (BMD); however, DEXA can result in spuriously elevated BMD measurements in patients with degenerative disease, compression fractures, and/or vascular calcifications. Measuring vertebral HU values has been proposed as an alternate method of assessing BMD and bone quality. METHODS: We searched MEDLINE, Cochrane Library, and EMBASE for studies correlating HU to BMD and to spine surgery outcomes. RESULTS: HU measurements correlate with success of lumbar interbody fusion (133.7 vs. 107.3 HU) and posterolateral fusion (167 vs. 139.8 HU), cage subsidence (112.4 vs. 140.2 HU), adjacent segment fractures (145.6 vs. 199.4 HU), pedicle screw loosening (116.4 vs. 132.7 HU) and (99.1 vs. 141.2 HU), and risk of incidental durotomy (149.2 vs. 177.0 HU). Intra and inter-rater reliability coefficients are 0.964 and 0.975. The correlation between HU values and BMD in nondegenerative patients is r = 0.52 compared with HU versus BMD in degenerative patients r = 0.18. CONCLUSION: HU value measurement is a simple and rapid technique to assess bone quality that should be performed in all patients with pre-existing CT scans. HU measurement has excellent inter and intra-rater reliability and can be performed on axial or sagittal images. L1 HU threshold values of 110 HU for detecting osteoporosis, and 135 HU for detecting osteopenia are 90% specific. In patients with significant degenerative disease, HU values should be given more credence. Additional high-quality prospective studies comparing HU and DEXA values to patient outcomes are necessary to validate the role of CT measurements in preoperative evaluation. LEVEL OF EVIDENCE: 4.

Pedicle screws with modular head vs. preassembled head used in cortical bone trajectory: Can pars and pedicle fractures be prevented in osteoporotic bone?

Pars and pedicle fractures as a result of CBT (cortical bone trajectory) during pedicle screw placement have been reported. The primary aim of the study is to compare the fracture rate between screws with modular heads to screws with standard pre-assembled tulip heads. The secondary aim of the study is to determine the potential variables that can be identified prior to instrumentation in order to predict risk of fractures. Twenty-four fresh frozen lumbar vertebrae were obtained from five different cadavers. Anatomical landmark measurements were obtained. Right and left pedicles of each vertebra were randomly instrumented with the preassembled head screws (n=24) and modular head screws (n=24) under video recording. X-ray images were obtained for measuring relative angle deviations between tapped and final screw trajectories. Finally, pullout tests were performed. Seventeen out of twenty-four (70.8%) of the spinous processes had to be excised in order to obtain proper trajectories. Six fractures occurred with pre-assembled head screws versus one in the modular head screws (p=0.04). Distances from the midline to the medial wall of the pedicle were marginally significant as a predictor for fracture (p=0.08). The pullout loads between both types of screws were not statistically different (p=0.38). Age was better correlated with pullout load than absolute bone density value (p<0.001). In conclusion, modular head screws had a significantly lower fracture rate than pre-assembled head screws for cortical bone trajectory in osteoporotic bone. There was no clear anatomic variable that could be measured pre-operatively to predict potential fracture risk in CBT.

A comparison of Staphylococcus aureus biofilm formation on cobalt-chrome and titanium-alloy spinal implants.

The use of cobalt chrome (CoCr) implants in spinal surgery has become increasingly popular. However, there have been no studies specifically comparing biofilm formation on CoCr with that of titanium-alloy spinal implants. The objective of this study was to compare the difference in propensity for biofilm formation between these two materials, as it specifically relates to spinal rods. Staphylococcus aureus subsp. Aureus (ATCC 6538) were incubated with two different types of spinal rods composed of either CoCr or titanium-alloy. The spinal rods were then subject to a trypsin wash to allow for isolation of the colonized organism and associated biofilms. The associated optical density values (OD) from the bacterial isolates were obtained and the bacterial solutions were plated on brain-heart infusion agar plates and the resultant colony-forming units (CFU) were counted. The OD values for the titanium-alloy rods were 1.105±0.096nm (mean±SD) and 1.040±0.026nm at 48hours and 96hours, respectively. In contrast, the OD values for the CoCr rods were 1.332±0.161nm and 1.115±0.207nm at 48 and 96hours, respectively (p<0.05). The CFU values were 1481±417/100mm(2) and 745±159/100mm(2) at 48 and 96hours, respectively for the titanium-alloy group. These values were significantly lower than the CFU values obtained from the CoCr group which were 2721±605/100mm(2) and 928±88/100mm(2) (p<0.001) at both 48 and 96hours respectively. Our findings, evaluating both the OD and CFU values, indicate that implants composed of CoCr had a higher proclivity towards biofilm formation compared to titanium-alloy implants.

Pars and pedicle fracture and screw loosening associated with cortical bone trajectory: a case series and proposed mechanism through a cadaveric study.

BACKGROUND CONTEXT: Cortical bone trajectory (CBT) technique for pedicle screw placement in the lumbar spine has become more popular since its introduction in 2009. The distinct advantages of using the CBT technique involve increased screw purchase within the cortical bone and reduced surgical dissection. However, contrary to several favorable biomechanical results, there were anecdotal reports of clinical complications associated with CBT. PURPOSE: This study aimed (1) to report on two unique pars and pedicle fracture cases involving the use of the CBT technique and (2) to perform a cadaveric pilot study to determine the possible mechanism for this fracture pattern. STUDY DESIGN/SETTING: A case report and cadaveric study were carried out. METHODS: After presenting two clinical cases, 19 fresh-frozen lumbar vertebrae were obtained from 8 cadavers. Pedicle screws were instrumented on each level using CBT under video recording. After the instrumentation, X-ray images were obtained, and anatomical dissections were performed. RESULTS: To be able to reach a necessary angle for medial to lateral CBT trajectory, 13 out of 19 (68%) spinous processes had to be removed. There were a total of seven complications. One pars and pedicle fracture out of 37 trajectories (2.7%) and 6 out of 37 trajectory deviations (16.2%), which resulted in gross loosening, were observed. CONCLUSIONS: The head of the pedicle screw impinging on the base of spinous process and lamina was observed in our cadaveric model. This mechanism could potentially explain both screw loosening and fractures associated with the CBT technique.

Early complications after instrumentation of the lumbar spine using cortical bone trajectory technique.

This retrospective chart review aimed to identify and report on a series of early complications that resulted from instrumentation of the lumbar spine using the cortical bone trajectory (CBT) technique. CBT technique is a novel method for fixation of the lumbar spine. Since it was first described in 2009 this technique has gained significant popularity. Here we report a series of early complications that have developed in patients who had lumbar spine fusion using the CBT technique. A retrospective chart review was performed in which all cases utilizing the CBT technique for instrumentation of the lumbar spine by two fellowship trained spine surgeons at our institution between July 2012 and May 2014 were reviewed. Medical records were reviewed to determine the number of patients who went on to develop an early complication after instrumentation with this technique. An early complication was defined as any of the following occurring within 3 months of surgery: (1) early screw loosening confirmed by post-operative CT scan, (2) evidence of fracture development confirmed by post-operative CT scan, (3) intra-operatively identified durotomy, (4) superficial or deep post-operative infection and (5) neurological injury. A total of 22 cases using the CBT technique were performed in our department. Of these cases two patients went onto develop early screw loosening, one developed an intra-operative pars fracture, one developed a dural tear and lastly, one patient developed both a pedicle fracture and early screw loosening. At our institution a total of five patients thus far have developed early complications after undergoing instrumentation of the lumbar spine using the CBT technique between 2012-2014.

Independent assessment of a new pedicle probe and its ability to detect pedicle breach: a cadaveric study.

OBJECT: The authors undertook an independent, non-industry funded cadaveric study to evaluate the efficacy of a pedicle-probing device, which uses impedance measurement to warn of impending and actual pedicle screw breach. METHODS: A previously validated fresh-frozen cadaver model (saline-soaked spine) was used. Individuals at 3 levels of training (attending spine surgeon, orthopedic surgery resident, and medical student) used a cannulated pedicle-probing device to cannulate each of the levels between T-2 and S-1. Each pedicle was cannulated freehand using 2 approaches: 1) a standard trajectory through the middle of the pedicle, and 2) a medial trajectory aimed to breach the medial wall of the pedicle. A 16-slice helical CT scanner was used. The images were interpreted and analyzed by 2 orthopedic spine surgeons and a neuroradiologist. RESULTS: The sensitivity of the pedicle probe to detect impending breach or breach of 4 mm or less was 90.06%. The sensitivity in detecting medial wall breach was 95.8%. The positive predictive value was 87.1%. The device detected medial breach more often than lateral breach. CONCLUSIONS: This study showed that this pedicle-probing device could reasonably be used to detect impending breach and actual breach of 4 mm or less. Medial breach was detected better than lateral breach. Use of the pedicle probe may improve patient safety.