Intervertebral disc human nucleus pulposus cells associated with back pain trigger neurite outgrowth in vitro and pain behaviors in rats.

Low back pain (LBP) is often associated with the degeneration of human intervertebral discs (IVDs). However, the pain-inducing mechanism in degenerating discs remains to be elucidated. Here, we identified a subtype of locally residing human nucleus pulposus cells (NPCs), generated by certain conditions in degenerating discs, that was associated with the onset of discogenic back pain. Single-cell transcriptomic analysis of human tissues showed a strong correlation between a specific cell subtype and the pain condition associated with the human degenerated disc, suggesting that they are pain-triggering. The application of IVD degeneration-associated exogenous stimuli to healthy NPCs in vitro recreated a pain-associated phenotype. These stimulated NPCs activated functional human iPSC-derived sensory neuron responses in an in vitro organ-chip model. Injection of stimulated NPCs into the healthy rat IVD induced local inflammatory responses and increased cold sensitivity and mechanical hypersensitivity. Our findings reveal a previously uncharacterized pain-inducing mechanism mediated by NPCs in degenerating IVDs. These findings could aid in the development of NPC-targeted therapeutic strategies for the clinically unmet need to attenuate discogenic LBP.

Racial and Sex Disparities in Resident Attrition in Orthopaedic Surgery.

Studies have suggested that female individuals and individuals from backgrounds under-represented in medicine (URiM) are at increased risk of attrition during residency. This likely exacerbates the lack of diversity in our field. The aims of this study were to (1) characterize demographic composition in orthopaedic residency from 2001 to 2018 and (2) determine the race/ethnicity and identify any disparities. Methods: Demographic and attrition data from 2001 to 2018 were obtained from the Association of American Medical Colleges. Attrition data comprised the following categories: withdrawals, dismissals, and transfers to another specialty. Analysis compared demographic composition and determined attrition rates with subgroup analysis by race/ethnicity and sex. Results: From 2001 to 2018, female orthopaedic residents increased from 8.77% to 15.54% and URiM residents from 9.49% to 11.32%. The overall and unintended attrition rates in orthopaedic surgery were 3.20% and 1.15%, respectively. Among female residents, the overall and unintended attrition rates were 5.96% and 2.09% compared with 2.79% and 1.01%, respectively, in male residents. URiM residents had overall and unintended attrition rates of 6.16% and 3.11% compared with 2.71% and 0.83%, respectively, for their White counterparts. Black/African American residents had an attrition rate of nearly 10%. Female residents averaged 12.9% of all residents but 24% of those leaving orthopaedics. URiM residents were 10.14% of all residents but 19.51% of those experiencing attrition. In logistic regression models, female residents had a relative risk (RR) of 2.20 (p < 0.001) for experiencing all-cause attrition and 2.09 (p < 0.001) for unintended attrition compared with male residents. Compared with their White male counterparts, URiM residents had a RR for overall and unintended attrition of 2.36 and 3.84 (p < 0.001), respectively; Black/African American residents had a RR for the same of 3.80 and 7.20 (p < 0.001), respectively. Conclusion: Although female resident percentage has increased, orthopaedics continues to train fewer female surgeons than all other fields. Female and URiM residents in orthopaedic surgery are disproportionately affected by attrition. While recruitment has been the primary focus of diversity, equity, and inclusion efforts, this study suggests that resident retention through appropriately supporting residents during training is equally critical.

Racial and Sex Disparities in Resident Attrition Among Surgical Subspecialties.

Importance: Racial and sex disparities are prevalent in surgical trainees. Although retrospective studies on resident attrition have been conducted for individual specialties, this study analyzes racial and sex differences in resident attrition among all surgical subspecialties over an 18-year period. Objective: To evaluate the racial and sex differences in resident attrition among surgical specialties over an 18-year period. Design, Setting, and Participants: This was a large, cross-sectional, database study that analyzed program-reported resident censuses (program information, resident demographics, and attrition status) obtained by the Association of American Medical Colleges from 2001 to 2018 for trainees in surgical residency programs. Data were analyzed from March 20, 2021, to June 8, 2022. Main Outcomes and Measures: Demographic trends (including race and ethnicity and sex) for all surgical subspecialty training programs over an 18-year period. Resident attrition includes all-cause withdrawals, dismissals, and transfers to another specialty. Unintended attrition encompasses all withdrawals, dismissals, and transfers except for changing career plans. Results: This study included 407 461 program-reported resident years collected from 112 205 individual surgical residents (67 351 male individuals [60.0%]). The mean percentage of female trainees was 40.0% (44 835) and increased over the study period. Sex disparity remained greatest in orthopedic surgery. Residents who were underrepresented in medicine (URiM) comprised 14.9% (16 695) of all surgical trainees but demonstrated a 2.1% decrease over the study period. Overall attrition rate among all specialties was 6.9% (7759), with an unintended attrition rate of 2.3% (2556). Female residents had a significantly higher relative risk (RR) of attrition (RR, 1.16; 95% CI, 1.11-1.22; P < .001) and unintended attrition (RR, 1.17; 95% CI, 1.08-1.26; P < .001) compared with their male counterparts. URiM residents were at significantly higher RR for attrition (RR, 1.40; 95% CI, 1.32-1.48; P < .001) and unintended attrition (RR, 1.92; 95% CI, 1.75-2.11; P < .001) compared with non-URiM residents. The highest attrition (10.6% [746 of 7043]) and unintended attrition (5.2% [367 of 7043]) rates were in Black/African American residents. The lowest attrition and unintended attrition rates were seen in White residents at 6.2% (4300 of 69 323) and 1.8% (1234 of 69 323), respectively. Black/African American residents were at disproportionate risk for attrition (RR, 1.66; 95% CI, 1.53-1.80; P < .001) and unintended attrition (RR, 2.59; 95% CI, 2.31-2.90; P < .001) compared with all other residents. Orthopedic surgery had the highest attrition (RR, 3.80; 95% CI, 2.84-5.09; P < .001) and unintended attrition (RR, 7.20; 95% CI, 4.84-10.71; P < .001) for Black/African American residents. Conclusions and Relevance: Results of this cross-sectional study suggest that the percentage of female residents in surgical specialties has improved over the last 18 years, and the percentage of URiM residents has remained relatively unchanged. Risk for attrition and unintended attrition was significantly elevated for female and URiM residents, specifically Black/African Americans. These results highlight current racial and sex disparities in resident attrition and demonstrate the importance of developing strategies to recruit, retain, and support residents.

Perioperative Complications Following Spine Surgery in Adult Patients with Achondroplasia.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: To describe the common types of complications and their risk factors during spine surgery in patients with achondroplasia. METHODS: A retrospective review was performed of medical records of adult achondroplasia patients who underwent spine surgery at our institution between 2007 and 2021. Inclusion criteria were achondroplasia and age >16 years. Surgical encounters were evaluated for durotomy, postoperative neurologic deficit, wound compromise, medical complications, and return to the operating room. Statistical analysis included evaluation of relationships across complications and fisher exact test applied to bivariate/categorical variables and t-test/ANOVA for continuous variables. Multivariable analysis using logistic regression was performed to account for patient characteristics. RESULTS: Fifty-five patients with achondroplasia underwent 95 surgeries. Forty-nine percent of the surgeries involved a complication. These included durotomy (33.7%), neurologic deficit (11.6%), wound compromise (6.3%), and other medical complications (6.3%). Thirteen percent of surgeries required return to the operating room. The greatest number of complications occurred in thoracolumbar region (60.0%) compared to cervicothoracic (18.2%) and craniocervical junction (33.3%). Chronologically later surgical encounters had decreased complications and durotomies only occurred in thoracolumbar surgeries (45.7%). CONCLUSIONS: Adult patients with achondroplasia undergoing surgery chronologically later in this set of consecutive patients were at a decreased risk for complications. Thoracolumbar surgeries were at the greatest risk for durotomies. Male sex was a risk factor for durotomy, while age was a risk factor for neurologic deficit. The potential for adverse surgical events should be considered when evaluating patients with achondroplasia for spine surgery. .

Advanced Glycation End Product Inhibitor Pyridoxamine Attenuates IVD Degeneration in Type 2 Diabetic Rats.

Type 2 diabetes mellitus (T2DM) is associated with advanced glycation end product (AGE) enrichment and considered a risk factor for intervertebral disc (IVD) degeneration. We hypothesized that systemic AGE inhibition, achieved using pyridoxamine (PM), attenuates IVD degeneration in T2DM rats. To induce IVD degeneration, lumbar disc injury or sham surgery was performed on Zucker Diabetic Sprague Dawley (ZDSD) or control Sprague Dawley (SD) rats. Post-surgery, IVD-injured ZDSD rats received daily PM dissolved in drinking water or water only. The resulting groups were SD uninjured, SD injured, ZDSD uninjured, ZDSD injured, and ZDSD injured + PM. Levels of blood glycation and disc degeneration were investigated. At week 8 post-surgery, glycated serum protein (GSP) levels were increased in ZDSDs compared to SDs. PM treatment attenuated this increase. Micro-MRI analysis demonstrated IVD dehydration in injured versus uninjured SDs and ZDSDs. In the ZDSD injured + PM group, IVD dehydration was diminished compared to ZDSD injured. AGE levels were decreased and aggrecan levels increased in ZDSD injured + PM versus ZDSD injured rats. Histological and immunohistochemical analyses further supported the beneficial effect of PM. In summary, PM attenuated GSP levels and IVD degeneration processes in ZDSD rats, demonstrating its potential to attenuate IVD degeneration in addition to managing glycemia in T2DM.

NF-κB inhibitor, NEMO-binding domain peptide attenuates intervertebral disc degeneration.

BACKGROUND CONTEXT: Nonphysiological mechanical loading and inflammation are both critically involved in intervertebral disc (IVD) degeneration, which is characterized by an increase in cytokines and matrix metalloproteases (MMPs) in the nucleus pulposus (NP). This process is known to be mediated by the NF-κB pathway. CLINICAL SIGNIFICANCE: Current clinical treatments for IVD degeneration focus on the alleviation of symptoms rather than targeting the underlying mechanism. Injection of an NF-κB inhibitor may attenuate the progression of IVD degeneration. PURPOSE: To investigate the ability of the NF-κB inhibitor, NEMO binding domain peptide (NBD), to alter IVD degeneration processes by reducing IL-1ß- and mechanically-induced cytokine and MMP levels in human nucleus pulposus cells in vitro, and by attenuating IVD degeneration in an in vivo rat model for disc degeneration. STUDY DESIGN: Experimental in vitro and animal model. PATIENT SAMPLE: Discarded specimens of lumbar disc from 21 patients, and 12 Sprague Dawley rats. OUTCOME MEASURES: Gene and protein expression, cell viability, µMRI and histology. METHODS: IL-1ß-prestimulated human nucleus pulposus cells embedded into fibrin constructs were loaded in the Flexcell FX-5000 compression system at 5 kPa and 1 Hz for 48 hours in the presence and absence of NBD. Unloaded hNPC/fibrin constructs served as controls. Cell viability in loaded and unloaded constructs was quantified, and gene and protein expression levels determined. For in vivo testing, a rat needle disc puncture model was employed. Experimental groups included injured discs with and without NBD injection and uninjured controls. Levels of disc degeneration were determined via µMRI, qPCR and histology. Funding sources include $48,874 NASS Young Investigator Research Grant and $119,174 NIH 5K01AR071512-02. There were no applicable financial relationships or conflicts of interest. RESULTS: Mechanical compression of hNPC/fibrin constructs resulted in upregulation of MMP-3 and IL-8. Supplementation of media with 10 µM NBD during loading increased cell viability, and decreased MMP-3 gene and protein levels. IVD injury in rat resulted in an increase in MMP-3, IL-1ß and IL-6 gene expression. Injections of 250 µg of NBD during disc injury resulted in decreased IL-6 gene expression. µMRI analysis demonstrated a reduction of disc hydration in response to disc needle injury, which was attenuated in NBD-treated IVDs. Histological evaluation showed NP and AF lesion in injured discs, which was attenuated by NBD injection. CONCLUSIONS: The results of this study show NBD peptide's capacity to reduce IL-1ß- and loading-induced MMP-3 levels in hNPC/fibrin constructs while increasing the cells' viability, and to attenuate IVD degeneration in rat, involving downregulation of IL-6. Therefore, NBD may be a potential therapeutic agent to treat IVD degeneration.

The effect of insulin dependent diabetes on bone metabolism and growth after spinal fusion.

STUDY DESIGN: Experimental animal model. OBJECTIVE: The purpose of this study was to evaluate the hypothesis that insulin dependent diabetes mellitus (IDDM) will inhibit the formation of a solid bony union after spinal fusion surgery via an alteration of the microenvironment at the fusion site in a rat model. SUMMARY OF BACKGROUND DATA: Previous studies report diabetes mellitus (DM) and specifically IDDM as a risk factor for complications and poor surgical outcomes following spinal fusion. METHODS: Twenty control and 22 diabetic rats were obtained at 5 weeks of age. At 20 weeks of age, all animals underwent posterolateral lumbar fusion surgery using a tailbone autograft with diabetic rats receiving an implantable time release insulin pellet. A subset of rats was sacrificed 1-week postsurgery for growth factor (PDGF, IGF-I, TGF-ß, and VEGF) and proinflammatory cytokine ELISA analysis. All other rats were sacrificed 3-months postsurgery for fusion evaluation via manual palpation and micro CT. Glycated hemoglobin (HbA1c) was measured at surgery and sacrifice on all animals. RESULTS: Compared with healthy rats undergoing spinal fusion, rats with IDDM demonstrated a significant reduction in manual palpation fusion rates (16.7% vs. 43%, p<.05). Average bone mineral density, bone volume, and bone volume fraction were also significantly reduced and negatively correlated to blood glucose levels. IL-1B, IL-5, IL-10, TNF-α, and KC/GRO were significantly elevated in fusion beds of IDDM rats. CONCLUSIONS: This study demonstrates that rats with IDDM demonstrate a reduced rate and quality of spinal fusion with increased local levels of inflammatory cytokines. Targeted modalities are required to improve bone healing in this growing, high-risk population. CLINICAL SIGNIFICANCE: This is the first translational animal model of IDDM to evaluate the rate and quality of spinal fusion while controlling for other surgical and patient-related risk factors. Our findings demonstrate the complex nature by which IDDM impairs bone healing and highlight the need for additional basic science research to further elucidate this mechanism in order to develop more effective therapeutic interventions.

Omega-3 Fatty Acid Supplementation Reduces Intervertebral Disc Degeneration.

BACKGROUND Intervertebral disc (IVD) degeneration is a common cause of lower back pain, which carries substantial morbidity and economic cost. Omega-3 fatty acids (n-3 FA) are known to reduce inflammatory processes with a relatively benign side effect profile. This study aimed to investigate the effect of n-3 FA supplementation on IVD degeneration. MATERIAL AND METHODS Two non-contiguous lumbar discs of 12 Sprague Dawley rats were needle-punctured to induce disc degeneration. Post-surgery, rats were randomly assigned to either a daily n-3 FA diet (530 mg/kg/day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in a 2: 1 ratio, administered in sucrose solution) or control diet (sucrose solution only), which was given for the duration of the study. After 1 month, blood serum arachidonic acid/eicosapentaenoic acid (AA/EPA) ratios were analyzed. After 2 months, micro-MRI (magnetic resonance imaging) analysis and histological staining of disc explants were performed to analyze the IVD. RESULTS A reduction of blood AA/EPA ratios from 40 to 20 was demonstrated after 1 month of daily supplementation with n-3 FA. Micro-MRI analysis showed an injury-induced reduction of IVD hydration, which was attenuated in rats receiving n-3 FA. Histological evaluation demonstrated the destruction of nucleus pulposus tissue in response to needle puncture injury, which was less severe in the n-3 FA diet group. CONCLUSIONS The results of this study suggest that n-3 FA dietary supplementation reduces systemic inflammation by lowering AA/EPA ratios in blood serum and has potential protective effects on the progression of spinal disc degeneration, as demonstrated by reduced needle injury-induced dehydration of intervertebral discs and reduced histological signs of IVD degeneration.

Comparative Efficacy of Commonly Available Human Bone Graft Substitutes as Tested for Posterolateral Fusion in an Athymic Rat Model.

BACKGROUND: Insufficient data exist on bone graft substitute materials efficacy; two thirds lack any clinical data.1,2 This prospective animal study identified efficacy differences among commercially available materials of several classes. METHODS: Historically validated muscle pouch osteoinduction study (OIS) and posterolateral fusion (PLF) were performed in an athymic rat model. Grafting material products implanted were demineralized bone matrix (DBM)-based allografts (Accell EVO3, DBX Mix, DBX Strip, Grafton Crunch, Grafton Flex, Grafton Matrix, Grafton Putty, Magnifuse, and Progenix Plus), allografts (OsteoSponge, MinerOss), cellular allograft (Osteocel Plus), ceramics (Mozaik Strip), or activated ceramics (Actifuse ABX Putty, Vitoss BA). After 4 weeks, OIS specimens were evaluated ex vivo by histologic osteoinductivity. After 8 weeks, PLF ex vivo specimens were evaluated for fusion by manual palpation (FMP), radiography (FXR), and histology (FHISTO). RESULTS: OIS: No materials exhibited a rejection reaction on histology. All DBM-based materials exhibited osteoinductive potential as new bone formation at > 88% of implanted sites. One plain allograft (OsteoSponge) formed bone at 25% of sites. No bone formed for one ceramic (Mozaik Strip), three activated ceramics (Actifuse ABX Putty), or one cellular allograft, regardless of human bone marrow aspirate (hBMA) when added. PLF: Among the 10 DBMs, 6 had FMP of 100% (Accell EVO3, DBX Mix, DBX Strip, Grafton Flex, Grafton Putty, Magnifuse), 2 had FMP of 94% (Grafton Crunch, Grafton Matrix), and 2 conditions had FMP of 0% (Progenix Plus, Progenix Plus + athymic rat iliac crest bone graft [arICBG]). Ceramics (Mozaik Strip), activated ceramics (Actifuse ABX Putty, Vitoss BA), plain allograft (OsteoSponge, MinerOss (PLF study), and cellular allograft (Osteocel Plus) demonstrated 0% FMP. ArICBG demonstrated 13% FMP. CONCLUSIONS: Eight DBM-based materials (Accell EVO3, DBX Mix, DBX Strip, Grafton Crunch, Grafton Flex, Grafton Matrix, Grafton Putty, Magnifuse) demonstrated excellent (> 90% FMP) efficacy in promoting fusion via bone healing. Two DBM conditions (Progenix Plus, Progenix Plus + arICBG) showed no manual palpation fusion (FMP). Systematically, over the 2 studies (OIS and PLF), cellular (Osteocel Plus), plain allografts (OsteoSponge, MinerOss; PLF study), ceramic (Mozaik Strip), and activated ceramics (Actifuse ABX Putty, Vitoss BA) demonstrated poor FMP efficacy (< 10%). CLINICAL RELEVANCE: When selecting DBMs, clinicians must be cognizant of variability in DBM efficacy by product and lot. While theoretically osteoinductive, cellular allograft and activated ceramics yielded poor in vivo efficacy. Whole allograft and ceramics may provide osteoconductive scaffolding for mixed-material grafting; however, surgeons should be cautious in using them alone. Direct clinical data are needed to establish efficacy for any bone graft substitute.

The impact of type 2 diabetes on bone metabolism and growth after spinal fusion.

BACKGROUND CONTEXT: Some clinical reports suggest diabetes may have a negative effect on spinal fusion outcomes, although no conclusive experimental research has been conducted to investigate the causality, impact, and inherent risks of this growing patient population. PURPOSE: To analyze the hypothesis that type 2 diabetes (T2DM) inhibits the formation of a solid bony union after spinal fusion surgery by altering the local microenvironment at the fusion site through a reduction in growth factors critical for bone formation. STUDY DESIGN/SETTING: In vivo rodent model of type 2 diabetes. METHODS: Twenty control (Sprague Dawley, SD) and 30 diabetic (Zucker Diabetic Sprague Dawley, ZDSD) rats underwent posterolateral and laminar fusion surgery using a tailbone autograft implanted onto the L4/L5 transverse processes. A subset of animals was sacrificed 1-week postsurgery for growth factor analysis. Remaining rats were sacrificed 3-month postsurgery for fusion evaluation via manual palpation, micro-CT, and histology. RESULTS: There was no significant difference in the manual palpation fusion rate between ZDSD rats and SD control rats. Growth factor assay of fusion site explants at early sacrifice demonstrated PDGF was upregulated in the ZDSD rats. TGFB, IGF, and VEGF were not statistically different between groups. Bone mineral density as determined by micro-CT was significantly lower in ZDSD rats compared to SD controls and was a significant function of HbA1c. CONCLUSIONS: Data generated in this in vivo rat model of T2DM demonstrate that the metabolic dysregulation associated with the diabetic condition negatively impacts the quality and density of the formed fusion mass. Increased measures of diabetic status, as determined by blood glucose and HbA1c, were correlated with decreased quality of formed fusion, highlighting the importance of diabetic status monitoring and regulation to bone health, particularly during bone healing. CLINICAL RELEVANCE: T2DM rats demonstrated increased rates of infection, metabolic dysregulation, and a reduction in spinal fusion consolidation. Clinicians should consider these negative effects during preoperative care and treatment of this growing patient population.

Anti-Inflammatory Peptide Attenuates Edema and Promotes BMP-2-Induced Bone Formation in Spine Fusion.

Recombinant human bone morphogenic protein-2 (BMP-2)-loaded absorbable collagen sponges (ACS) have been successfully used to enhance bone formation and to induce spinal fusion in humans. However, side effects, such as soft tissue edema and inflammation, have been reported. NEMO binding domain peptide (NBD) inhibits activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), a central regulator of immune response. In this study, we investigated NBD's potential to reduce BMP-2-induced soft tissue inflammation without affecting BMP-2-mediated spinal fusion in rat. For evaluation of soft tissue inflammation, ACS containing BMP-2, BMP-2+NBD, NBD, or ACS only were implanted into intramuscular paraspinal sites of 32 rats. At day 2 postsurgery, edema formation at the implant sites was assessed using magnetic resonance imaging. T2-weighted relaxation time (T2-RT) values were increased in the BMP-2 group compared with BMP-2+NBD, NBD, and ACS groups. No difference in T2-RT values was detected between BMP-2+NBD versus NBD and ACS controls. Postsacrifice, histological analysis of the implant-surrounding zones showed increased mononuclear cell infiltration in the BMP-2 group compared with BMP-2+NBD and controls. The presence of BMP-2 increased relative NF-κB binding and gene expression of inflammatory markers, interleukin (IL)1ß, IL6, IL18, and chemokine ligand (CCL)2 and CCL3 compared with controls. In the BMP-2+NBD group, cytokine expression was blocked. No differences were found between BMP-2+NBD and control groups. For evaluation of spinal fusion, posterolateral intertransverse lumbar fusion procedures were performed on 16 rats. ACS were loaded with BMP-2 or BMP-2+NBD. After sacrifice at week 12, microcomputed tomographic assessment of the fusion site detected a higher bone volume and reduced trabecular spacing in the BMP-2+NBD group compared with BMP-2. Histological analysis did not show any differences in newly formed bone microarchitecture. In summary, addition of NBD to BMP-2-loaded ACS reduces BMP-2-induced soft tissue edema formation and mononuclear cell infiltration, diminishes NF-κB binding, and thus blocks transcription of NF-κB-regulated cytokines in rat. Furthermore, NBD stimulates bone formation in BMP-2-mediated spinal fusion, possibly through crosstalk of the NF-κB pathway with other pathways. The results of this study might provide the basis to develop new therapeutic bone grafting approaches with combinatory administration of BMP-2 and NBD for spinal fusion.

The relationship between serum vitamin D levels and spinal fusion success: a quantitative analysis.

STUDY DESIGN: An in vivo dosing study of vitamin D in a rat posterolateral spinal fusion model with autogenous bone grafting. Rats randomized to 4 levels of vitamin D-adjusted rat chow, longitudinal serum validation, surgeons/observers blinded to dietary conditions, and rats followed prospectively for fusion endpoint. OBJECTIVE: To assess the impact of dietary and serum levels of vitamin D on fusion success, consolidation of fusion mass, and biomechanical stiffness after posterolateral spinal fusion procedure. SUMMARY OF BACKGROUND DATA: Metabolic risk factors, including vitamin D insufficiency, are often overlooked by spine surgeons. Currently, there are no published data on the causal effect of insufficient or deficient vitamin D levels on the success of establishing solid bony union after a spinal fusion procedure. METHODS: Fifty rats were randomized to 4 experimentally controlled rat chow diets: normal control, vitamin D-deficient, vitamin D-insufficient, and a nontoxic high dose of vitamin D, 4 weeks prior to surgery and maintained postsurgery until sacrifice. Serum levels of 25(OH)D were determined at surgery and sacrifice using radioimmunoassay. Posterolateral fusion surgery with tail autograft was performed. Rats were sacrificed 12 weeks postoperatively, and fusion was evaluated via manual palpation, high-resolution radiographs, micro-computed tomographic scans, and biomechanical testing. RESULTS: Serum 25(OH)D and calcium levels were significantly correlated with vitamin D-adjusted chow (P < 0.001). There was a dose-dependent relationship between vitamin D-adjusted chow and manual palpation fusion, with greatest differences found in measures of radiographical density between high and deficient vitamin D (P < 0.05). Adequate levels of vitamin D (high and normal control) yielded stiffer fusion than inadequate levels (insufficient and deficient) (P < 0.05). CONCLUSION: Manual palpation fusion rates increased with supplementation of dietary vitamin D. Biomechanical stiffness, bone volume, and density were also positively related to vitamin D and calcium. LEVEL OF EVIDENCE: N/A.

Bone marrow enhances the performance of rhBMP-2 in spinal fusion: a rodent model.

BACKGROUND: Reliable and rapid bone formation is the goal of biologics and cell-based spinal fusion technologies. While no cell-based therapy alone has been successful, recombinant human bone morphogenetic protein-2 (rhBMP-2) has been successfully used in a wide spectrum of patients undergoing a variety of spinal fusion procedures since its approval by the United States Food and Drug Administration (FDA) in 2002. However, the question remains how to improve the biologic efficiency, or osteoinductivity, of rhBMP-2 for successful application in the most challenging patients undergoing spinal fusion or to reduce the doses currently required. The present study investigated how varying the cellular environments through the addition of freshly harvested bone marrow aspirate (BMA) modulates rhBMP-2 efficiency. METHODS: An L4-L5 posterolateral intertransverse process spinal fusion procedure was performed in Lewis rats. The implants were a subeffective concentration of 0.006 mg/mL of rhBMP-2/two absorbable collagen sponges (ACS) plus directly applied fresh syngeneic BMA transplants (n = 18), 0.006-mg/mL rhBMP-2/two ACS/side (n = 12), 0.006-mg/mL rhBMP-2/one ACS/side (n = 12), or BMA/one ACS/side (n = 6). Rats were killed at eight weeks and were evaluated with use of manual palpation, radiographs, and biomechanical testing. RESULTS: BMA plus 0.006-mg/mL rhBMP-2/ACS significantly increased the L4-L5 fusion rate to 89% (sixteen of eighteen) compared with a base fusion rate of 33% (four of twelve) to 50% (six of twelve) for rats implanted with rhBMP-2/ACS (p < 0.05), with no difference in strength or stiffness between conditions. No fusion or bone formation was observed in the six rats that received BMA/ACS alone. CONCLUSIONS: Less rhBMP-2 was needed for effect when mixed with BMA. A nearly twofold increase in the fusion rate was found when BMA was mixed with a deliberate subeffective concentration of rhBMP-2. There was no improvement in terms of fusion strength or stiffness.

Spinal fusion in the United States: analysis of trends from 1998 to 2008.

STUDY DESIGN: Epidemiological study using national administrative data. OBJECTIVE: To provide a complete analysis of national trends in spinal fusion from 1998 to 2008 and compare with trends in laminectomy, hip replacement, knee arthroplasty, percutaneous transluminal coronary angioplasty, and coronary artery bypass graft. SUMMARY OF BACKGROUND DATA: Previous studies have reported a rapid increase in volume of spinal fusions in the United States prior to 2001, but limited reports exist beyond this point, analyzing all spinal fusion procedures collectively. METHODS: Data were obtained from the Healthcare Cost and Utilization Project Nationwide Inpatient Sample for the years 1998 to 2008. Discharges were identified using International Classification of Diseases, Ninth Revision, Clinical Modification procedure codes for the following procedures: spinal fusion, laminectomy, hip replacement, knee arthroplasty, percutaneous transluminal coronary angioplasty, and coronary artery bypass graft. Population-based utilization rates were calculated from the US census data. RESULTS: Between 1998 and 2008, the annual number of spinal fusion discharges increased 2.4-fold (137%) from 174,223 to 413,171 (P < 0.001). In contrast, during the same time period, laminectomy, hip replacement, knee arthroplasty, and percutaneous coronary angioplasty yielded relative increases of only 11.3%, 49.1%, 126.8%, and 38.8% in discharges, while coronary artery bypass graft experienced a decrease of 40.1%. Between 1998 and 2008, mean age for spinal fusion increased from 48.8 to 54.2 years (P < 0.001), in-hospital mortality rate decreased from 0.29% to 0.25% (P < 0.01), and mean total hospital charges associated with spinal fusion increased 3.3-fold (P < 0.001). The national bill for spinal fusion increased 7.9-fold (P < 0.001). CONCLUSION: Frequency, utilization, and hospital charges of spinal fusion have increased at a higher rate than other notable inpatient procedures, as seen in this study from 1998 to 2008. In addition, patient demographics and hospital characteristics changed significantly; in particular, whereas the average age for spinal fusion increased, the in-hospital mortality rate decreased.

Genetically modified mesenchymal stem cells induce mechanically stable posterior spine fusion.

Most spine fusion procedures involve the use of prosthetic fixation devices combined with autologous bone grafts rather than biological treatment. We had shown that spine fusion could be achieved by injection of bone morphogenetic protein-2 (BMP-2)-expressing mesenchymal stem cells (MSCs) into the paraspinal muscle. In this study, we hypothesized that posterior spinal fusion achieved using genetically modified MSCs would be mechanically comparable to that realized using a mechanical fixation. BMP-2-expressing MSCs were injected bilaterally into paravertebral muscles of the mouse lumbar spine. In one control group BMP-2 expression was inhibited. Microcomputed tomography and histological analyses were used to evaluate bone formation. For comparison, a group of mouse spines were bilaterally fused with stainless steel pins. The harvested spines were later tested using a custom four-point bending apparatus and structural bending stiffness was estimated. To assess the degree to which MSC vertebral fusion was targeted and to quantify the effects of fusion on adjacent spinal segments, images of the loaded spine curvature were analyzed to extract rigidity of the individual spinal segments. Bone bridging of the targeted vertebrae was observed in the BMP-2-expressing MSC group, whereas no bone formation was noted in any control group. The biomechanical tests showed that MSC-mediated spinal fusion was as effective as stainless steel pin-based fusion and significantly more rigid than the control groups. Local analysis showed that the distribution of stiffness in the MSC-based fusion group was similar to that in the steel pin fusion group, with the majority of spinal stiffness contributed by the targeted fusion at L3-L5. Our findings demonstrate that MSC-induced spinal fusion can convey biomechanical rigidity to a targeted segment that is comparable to that achieved using an instrumental fixation.

Cost comparison of patients with 3-level artificial total lumbar disc replacements versus 360° fusion at 3 contiguous lumbar vertebral levels: an analysis of compassionate use at 1 site of the US investigational device exemption clinical trial.

BACKGROUND: We sought to evaluate the difference between hospital service costs of 2 treatment options for patients diagnosed with 3-level degenerative disc disease (DDD) in the lumbar spine. In this retrospective analysis, itemized billing records of hospital stay for patients with 3-level DDD treated with artificial disc replacement (ADR) were compared with those treated with circumferential fusion (standard of care). METHODS: Sequential 3-level DDD patients treated with either ADR (ProDisc-L; Synthes, West Chester, Pennsylvania) or circumferential fusion during the period from January 2004 to October 2005 were included. Surgeries were performed at the same hospital for all patients. The ADR-treated patients were participating in the investigational device exemption clinical trial as part of the compassionate-use arm. Patients treated with fusion at the same institution during this same time interval were evaluated. Itemized billing records were collected at least 1 year after the index surgery. Costs according to hospital service categories were compared between ADR-treated and fusion-treated patients by use of analysis of variance and multivariate statistical techniques. RESULTS: There were 43 consecutive patients treated for 3-level DDD between January 2004 and October 2005. Of these, 21 underwent 3-level ADR and 22 had a 3-level fusion procedure. There was a mean of 3 fewer hospital days for patients treated with ADR (4.77 ± 1.11 days) than for those treated with fusion (8.00 ± 1.82 days) (P < .0001). The cost of hospital services for ADR-treated patients was 49% less excluding instrumentation costs and 54% less when accounting for instrumentation. The pattern of cost was similar when workers' compensation patients were analyzed separately. CONCLUSIONS: ADR-treated 3-level patients benefited from significantly lower costs from their in-hospital stay compared with those treated by fusion. Hospital service costs were 49% (54% when instrumentation was included in the costs) less for ADR patients than for fusion patients.

A comparison of commercially available demineralized bone matrix for spinal fusion.

In an effort to augment the available grafting material as well as to increase spinal fusion rates, the utilization of a demineralized bone matrix (DBM) as a graft extender or replacement is common. There are several commercially available DBM substances available for use in spinal surgery, each with different amounts of DBM containing osteoinductive proteins. Each product may have different osteoinductivity potential due to different methods of preparation, storage, and donor specifications. The purpose of this study is to prospectively compare the osteoinductive potential of three different commercially available DBM substances in an athymic rodent spinal fusion model and to discuss the reasons of the variability in osteoinductivity. A posterolateral fusion was performed in 72 mature athymic nude female rats. Three groups of 18 rats were implanted with 1 of 3 DBMs (Osteofil, Grafton, and Dynagraft). A fourth group was implanted with rodent autogenous iliac crest bone graft. The rats were sacrificed at 2, 4, 6, and 8 weeks. A dose of 0.3 cm(3) per side (0.6 cm(3)per animal) was used for each substance. Radiographs were taken at 2 weeks intervals until sacrifice. Fusion was determined by radiographs, manual palpation, and histological analysis. The Osteofil substance had the highest overall fusion rate (14/18), and the highest early 4 weeks fusion rate of (4/5). Grafton produced slightly lower fusion rates of (11/17) overall, and lower early 4 weeks fusion rate of (2/5). There was no statistically significant difference between the rate of fusion after implantation of Osteofil and Grafton. None of the sites implanted with Dynagraft fused at any time point (0/17), and there was a significantly lower fusion rate between the Dynagraft and the other two substances at the six-week-time point and for final fusion rate (P = 0.0001, Fischer's exact test). None of the autogenous iliac crest animals fused at any time point. Non-decalcified histology confirmed the presence of a pseudarthrosis or the presence of a solid fusion, and the results were highly correlated with the manual testing. Although all products claim to have significant osteoinductive capabilities, this study demonstrates that there are significant differences between some of the tested products.

Intervariability and intravariability of bone morphogenetic proteins in commercially available demineralized bone matrix products.

STUDY DESIGN: Enzyme-linked immunosorbent assay was used to detect bone morphogenetic proteins (BMPs) 2, 4, and 7 in 9 commercially available ("off the shelf") demineralized bone matrix (DBM) product formulations using 3 different manufacturer's production lots of each DBM formulation. OBJECTIVES: To evaluate and compare the quantity of BMPs among several different DBM formulations (inter-product variability), as well as examine the variability of these proteins in different production lots within the same DBM formulation (intra-product variability). SUMMARY OF BACKGROUND DATA: DBMs are commonly used to augment available bone graft in spinal fusion procedures. Surgeons are presented with an ever-increasing variety of commercially available human DBMs from which to choose. Yet, there is limited information on a specific DBM product's osteoinductive efficacy, potency, and constancy. METHODS: There were protein extracts from each DBM sample separately dialyzed 4 times against distilled water at 4 degrees C for 48 hours. The amount of BMP-2, BMP-4, and BMP-7 was determined using enzyme-linked immunosorbent assay. RESULTS.: The concentrations of detected BMP-2 and BMP-7 were low for all DBM formulations, only nanograms of BMP were extracted from each gram of DBM (20.2-120.6 ng BMP-2/g DBM product; 54.2-226.8 ng BMP-7/g DBM). The variability of BMP concentrations among different lots of the same DBM formulation, intra-product variability, was higher than the variability of concentrations among different DBM formulations, inter-product variability (coefficient of variation range BMP-2 [16.34% to 76.01%], P < 0.01; BMP-7 [3.71% to 82.08%], P < 0.001). BMP-4 was undetectable. CONCLUSIONS: The relative quantities of BMPs in DBMs are low, in the order of 1 x 10(-9) g of BMP/g of DBM. There is higher variability in concentration of BMPs among 3 different lots of the same DBM formulation than among different DBM formulations. This variability questions DBM products' reliability and, possibly, efficacy in providing consistent osteoinduction.

Computed tomography assessment of the accuracy of in vivo placement of artificial discs in the lumbar spine including radiographic and clinical consequences.

STUDY DESIGN: Prospective cohort study of 52 patients who had undergone artificial lumbar disc replacement. OBJECTIVES: To evaluate the implantation accuracy of prosthesis positioning, subsequent facet joint changes and prosthesis migration, and the clinical consequences of implant position. SUMMARY OF BACKGROUND DATA: Accuracy of spinal prosthesis implantation has not been evaluated rigorously, especially with a mini-incision approach. It is unknown if the inexact placement of a mobile device in the spine has any biomechanical, radiographic, or clinical repercussions. METHODS: A total of 52 consecutive patients were treated using standard methods of disc implantation with an intervertebral prosthesis. Computed tomography scans were performed within 3 days and again at 6 to 24 months. An independent radiologist analyzed the images for prosthesis position, rotation, migration, and facet changes. Results were compared with clinical outcome, measured by the Visual Analog Scale and Oswestry Disability Index. RESULTS: Deviation of the prosthesis from the center position was under 1.2 mm, and rotation off of midline was under 12 degrees. Follow-up CT scans showed no migration or facet changes. Regression analysis showed no correlation of prosthesis position with clinical outcome. CONCLUSIONS: Current prosthetic disc implantation methods, with minimally invasive access techniques, are relatively accurate. Although there can be deviation of the prosthesis from ideal placement, no repercussions were attributable.

ProDisc artificial total lumbar disc replacement: introduction and early results from the United States clinical trial.

STUDY DESIGN: Multicenter prospective randomized study of artificial disc replacement (ProDisc) versus circumferential fusion (standard of care) for one- and two-level degenerative disc disease. This is an interim analysis on patients seen at the Spine Institute Saint John's Health Center, Santa Monica, California. OBJECTIVES: To evaluate early pain and functional outcomes of patients treated with disc replacement or fusion and to assess the capacity of this intervertebral disc replacement for preserving motion in the lumbar spine. SUMMARY OF BACKGROUND DATA: Disc replacement is intended to reduce pain via removal of the diseased disc while restoring physiologic motion and height at the affected level. The long-term physiologic advantage of disc replacement to fusion is that preservation of motion may prevent additional degeneration at adjacent levels. METHODS: Patients meeting inclusion criteria were consented for study. Randomization was performed using a 2 to 1 ratio of disc replacement procedure to a fusion procedure. Patients rated their pain on the Visual Analogue Scale and completed the Oswestry Disability Index questionnaire. Radiographs were taken. Assessments were made before surgery and after surgery at 6 weeks, 3 months, 6 months, and 1 year (ongoing). Changes from preoperative pain, disability, or motion were separately evaluated as a function of treatment using repeated measures mixed design analysis of variance. RESULTS: This analysis includes data up to 6 months from the first 53 randomized patients. There were 35 patients who underwent disc replacements, and 18 patients had fusion procedures. Disc replacement patients had a significant reduction in pain and disability at earlier evaluations. By 6 months, the relative improvement on both the Visual Analogue Scale and Oswestry (both, P < 0.05) were similar for disc replacement and fusion patients. Greater motion was found at L4-L5 for disc replacement patients (P < 0.05) than fusion patients. A similar trend was noted at L5-S1 (P was not significant). CONCLUSIONS: Disc replacement patients reported significantly less pain (Visual Analogue Scale) and disability (Oswestry) in the early period following surgery compared to fusion patients. This difference disappeared by 6 months. When compared to fusion, the disc replacement allowed preservation of motion at L4-L5 with a similar trend at L5-S1.