Delayed Failure of M6-C Cervical Disc Arthroplasty After Conversion of Adjacent Cervical Disc Arthroplasty to Fusion: A Case Report.

CASE: We present a delayed failure of an M6-C cervical disc arthroplasty after conversion of a subjacent failed cervical disc arthroplasty to fusion. The annular component had failed, and the core had been ejected. Histology demonstrated a giant cell reaction to polyethylene debris, and tissue cultures were positive for Cutibacterium acnes. CONCLUSION: This is the first report of M6-C failure after conversion of an adjacent arthroplasty to fusion. A growing number of reports surrounding the M6-C failure rate and mechanisms raise concern about the device's durability and underscore the importance of routine clinical and radiographic surveillance for these patients.

Robotic-navigated assistance in spine surgery.

The aim of this study was to assess the accuracy of pedicle screw placement, as well as intraoperative factors, radiation exposure, and complication rates in adult patients with degenerative disorders of the thoracic and lumbar spines who have undergone robotic-navigated spinal surgery using a contemporary system. The authors reviewed the prospectively collected data on 196 adult patients who had pedicle screws implanted with robot-navigated assistance (RNA) using the Mazor X Stealth system between June 2019 and March 2022. Pedicle screws were implanted by one experienced spinal surgeon after completion of a learning period. The accuracy of pedicle screw placement was determined using intraoperative 3D fluoroscopy. A total of 1,123 pedicle screws were implanted: 1,001 screws (89%) were placed robotically, 63 (6%) were converted from robotic placement to a freehand technique, and 59 (5%) were planned to be implanted freehand. Of the robotically placed screws, 942 screws (94%) were determined to be Gertzbein and Robbins grade A with median deviation of 0.8 mm (interquartile range 0.4 to 1.6). Skive events were noted with 20 pedicle screws (1.8%). No adverse clinical sequelae were noted in the 90-day follow-up. The mean fluoroscopic exposure per screw was 4.9 seconds (SD 3.8). RNA is highly accurate and reliable, with a low rate of abandonment once mastered. No adverse clinical sequelae occurred after implanting a large series of pedicle screws using the latest generation of RNA. Understanding of patient-specific anatomical features and the real-time intraoperative identification of risk factors for suboptimal screw placement have the potential to improve accuracy further.

Is Diastasis Recti Abdominis Associated With Low Back Pain? A Systematic Review.

BACKGROUND: Low back pain (LBP) is a common cause of disability worldwide; multiple causes and risk factors have been proposed in the genesis of back pain. Some studies reported an association between diastasis recti abdominis (DRA), a surrogate for decreased core strength muscle, and low back pain. We aimed to investigate the relationship between DRA and LBP through a systematic review. METHODS: A systematic review of the literature of clinical studies in English literature was conducted. PubMed, Cochrane, and Embase databases were used to conduct the search up to January 2022. The strategy included the following keywords: "Lower Back Pain" AND "Diastasis Recti" OR "Rectus abdominis" OR "abdominal wall" OR "paraspinal musculature". RESULTS: From 207 records initially found, 34 were suitable for full review. Thirteen studies were finally included in this review, with a total of 2,820 patients. Five studies found a positive association between DRA and LBP (5 of 13 = 38.5%) whereas 8 studies did not find any association between DRA and LBP (8 of 13 = 61.5%). CONCLUSIONS: Of the studies included in this systematic review, 61.5% did not find an association between DRA and LBP whereas a positive correlation was observed in 38.5% of studies included. Based on the quality of the studies included in our review, better studies are warranted to understand the association between DRA and LBP.

Comparing the Efficacy of Radiation Free Machine-Vision Image-Guided Surgery With Traditional 2-Dimensional Fluoroscopy: A Randomized, Single-Center Study.

Background: Three-dimensional (3D) computer-assisted navigation (CAN) has emerged as a potential alternative to 2-dimensional (2D) fluoroscopy in the surgical placement of spinal instrumentation. Recently, 3D-CAN systems have improved significantly in their ability to provide real-time anatomical referencing while shortening the registration and set-up time. A novel system in navigation, Machine-Vision Image-Guided Surgery (MvIGS; 7D Surgical, Toronto, Canada) was cleared by the US Food and Drug Administration, but its potential benefits in reducing intra-operative radiation exposure to patients and enhancing surgical accuracy of pedicle screw placement are not fully known. Purpose: We sought to conduct a prospective, randomized, clinical study comparing the 3D-MvIGS spinal navigation system and 2D-fluoroscopy for pedicle screw insertion up to 3 levels (T10-S1) and for various measures of surgical efficacy. Methods: Sixty-two eligible patients were randomized to receive spine surgery using either the 3D-MvIGS group or the conventional 2D-fluoroscopy for pedicle screw fixation for the treatment of spinal stenosis and degenerative spondylolisthesis. Intra-operative parameters and procedure-related unintended protocol violations were recorded. Results: Operative time and estimated blood loss were not significantly different between groups. Radiation time and exposure to patients were significantly reduced in the 3D-MvIGS group. There was no difference between groups in pedicle screw placement accuracy (2D-fluoroscopy group, 96.6%; 3D-MvIGS group, 94.2%). There were no major complications or cases that required revision surgery. Conclusion: The 3D-MvIGS navigation system performed comparably with 2D-fluoroscopy in terms of pedicle screw placement accuracy and operative time. The 3D-MvIGS showed a significant reduction in radiation exposure to patients. In more complex cases or larger cohorts, the true value of greater anatomical visualization can be elucidated.

Cervical Spine Navigation and Enabled Robotics: A New Frontier in Minimally Invasive Surgery.

Background: Robotic-assisted and computer-assisted navigation (CAN) systems utilization has been rapidly increasing in recent years. Most existing data using these systems are performed in the thoracic, lumbar, and sacral spine. The unique anatomy of the cervical spine maybe where these technologies have the greatest potential. To date, the role of navigation-enabled robotics in the cervical spine remains in its early stages of development and study. Purpose: This review article describes the early experience, case descriptions and technical considerations with cervical spine screw fixation and decompression using CAN and robotic-assisted surgery. Methods: Representative cervical cases with early surgical experience with cervical and robotic assisted surgery with CAN. Surgical set up, technique considerations, instrumentation, screw accuracy and screw placement were elevated and recorded for each representative cervical case. Results: Existing robotic assisted spine surgical systems are reviewed as they pertain to the cervical spine. Method for cervical reference and positioning on radiolucent Mayfield tongs are presented. C1 lateral mass, odontoid fracture fixation, C2 pedicle, translaminar, subaxial lateral mass, mid cervical pedicle, navigated decompression and ACDF cases and techniques are presented. Conclusion: In conclusion, within the last several years, the use of CANs in spinal surgery has grown and the cervical spine shows the greatest potential. Several robotic systems have had FDA clearance for use in the spine, but such use requires simultaneous intraoperative fluoroscopic confirmation. In the coming years, this recommendation will likely be dropped as accuracy improves.

Prevalence of Occult Infections in Posterior Instrumented Spinal Fusion.

STUDY DESIGN: This is a prospective observational study. OBJECTIVE: The aim of this study is to determine the rate of occult infection after instrumented spine surgery in presumed aseptic patients. SUMMARY OF BACKGROUND DATA: The reported incidence rate of delayed/occult infection determined by positive culture swabs after instrumented spine surgery in prospective studies is 0.2%-6.9%. However, this rate may be higher as delayed infections are challenging to diagnose. Fever can be absent and inflammatory markers are often normal. If indolent organisms exist in low concentrations surrounding the instrumentation, these organisms can possibly avoid detection and disrupt bone formation leading to instrumentation loosening, pain generation, and/or failure of a solid fusion. MATERIALS AND METHODS: This study included 50 consecutive presumed aseptic patients undergoing a posterior revision requiring removal of instrumentation at least 6 months following their index procedure. Common markers of infection were examined preoperatively. Multiple culture swabs were taken directly from the removed instrumentation and cultured for 14 days. RESULTS: Of the 50 patients, 19 (38%) were culture-positive (CP) for bacteria upon removal of their instrumentation, with 14 patients (28%) having ≥2 positive specimens of the same organism. The average length of time between the index procedure and the revision surgery was 4.55 years (range: 0.53-21 y). Polymicrobial infections were found in 26% (5/19) of CP patients. The most prevalent microorganism found was Propionibacterium acnes, in 63% (12/19) of CP patients. There was no significant difference between CP and culture-negative patients regarding preoperative markers for infection, age, or length between index and revision procedures. CONCLUSIONS: The results of this study indicate a positive culture rate of 38% in presumed aseptic patients who had previously undergone instrumented spine surgery. These results are consistent with other retrospective studies and are >6 times greater than any previous prospective study utilizing culture swabs. LEVEL OF EVIDENCE: Level-III.

Interlaminar stabilization for spinal stenosis in the Medicare population.

BACKGROUND CONTEXT: The number of complex fusions performed on Medicare beneficiaries, defined as ≥age 65, with lumbar spinal stenosis with or without spondylolisthesis has been increasing. Typically, these procedures are longer, more invasive and pose a greater risk for complications. Interlaminar stabilization (ILS) serves as an intermediary between decompression alone and decompression with fusion. PURPOSE: The purpose of this study was to prospectively examine the efficacy of ILS in patients ≥age 65 through comparison to fusion in the same age group and ILS in younger patients. STUDY DESIGN/SETTING: A prospective, multicentered, randomized controlled trial comparing decompression with ILS to decompression with posterolateral fusion with bilateral pedicle screw instrumentation. PATIENT SAMPLE: Patients from 21 sites in the United States underwent surgery for moderate stenosis with up to a grade 1 degenerative spondylolisthesis and failure of conservative treatment with low back pain at 1 or 2 contiguous levels from L1-L5. Preoperatively, patient-reported assessment had to meet the criteria of significant pain and disability (Visual Analog Scale [VAS back pain] ≥50 mm on a 100 mm scale; Oswestry Disability Index [ODI] of ≥20/50). OUTCOME MEASURES: The primary outcome was overall Composite Clinical Success (CCS) as determined by ODI scores, incidence of postoperative epidural injections and/or reoperations, incidence of device-related complications, and persistent or progressive neurological deficit. Secondary outcomes included patient satisfaction as measured by VAS for back and worse leg pain and Zurich Claudication Questionnaire scores. Narcotic usage data and radiographic assessment of changes in postoperative posterior disc height and foraminal height were also evaluated. METHODS: At 1- or 2-levels, 84 patients ≥age 65 underwent decompression with ILS, 57 patients ≥age 65 underwent decompression with fusion, and 131 patients

Single-center, consecutive series study of the use of a novel platelet-rich fibrin matrix (PRFM) and beta-tricalcium phosphate in posterolateral lumbar fusion.

PURPOSE: To evaluate the radiographic and clinical outcomes of the combination of platelet-rich fibrin matrix (PRFM) with beta-tricalcium phosphate (ß-TCP) and bone marrow aspirate (BMA) as a graft alternative in posterolateral lumbar fusion procedures. METHODS: Researchers evaluated 50 consecutive patients undergoing one-level to three-level posterolateral lumbar fusion procedures, resulting in a total of 66 operated levels. The primary outcome was evidence of radiographic fusion at 1-year follow-up, assessed by three independent evaluators using the Lenke scoring system. Secondary outcomes included back and leg VAS scores, incidence of reoperations and complications, return-to-work status, and opioid use. RESULTS: At 1-year follow-up, radiographic fusion was observed in 92.4% (61/66) of operated levels. There was significant improvement in VAS scores for both back and leg pain (p < 0.05). Compared to baseline figures, the number of patients using opioid analgesics at 12-months decreased by 38%. The majority (31/50) of patients were retired, yet 68% of employed patients (n = 19) were able to return to work. No surgical site infections were noted, and no revision surgery at the operated level was required. CONCLUSIONS: This is the first report to analyze the combination of PRFM with ß-TCP and BMA for PLF procedures. Our results indicate a rate of fusion similar to those reported using iliac crest bone graft (ICBG), while avoiding donor site morbidity related to ICBG harvesting such as hematoma, pain, and infection. These slides can be retrieved under Electronic Supplementary Material.

The 2-Level Experience of Interlaminar Stabilization: 5-Year Follow-Up of a Prospective, Randomized Clinical Experience Compared to Fusion for the Sustainable Management of Spinal Stenosis.

BACKGROUND: To alleviate the symptoms of lumbar spinal stenosis, widely accepted methods of surgical treatment include decompression alone and decompression with fusion. As an alternative to these methods, interlaminar stabilization (ILS) devices with decompression were introduced. There is a large amount of research dedicated to examining the efficacy of ILS devices in single-level procedures, but fewer studies focus on their efficacy in 2-level procedures. The purpose of this study was to compare decompression with instrumented posterolateral fusion to decompression with interlaminar stabilization in patients who require surgical treatment at 2 levels for lumbar spinal stenosis at 5 years postoperation. METHODS: Of the 322 patients enrolled in the Investigational Device Exemption clinical trial, 116 required surgical treatment at 2 levels. The ILS group consisted of 77 patients, and the fusion group consisted of 39 patients. Efficacy was measured using composite clinical success (CCS). Patients achieve CCS if they achieve all 4 of the following outcomes: ≥15-point improvement from baseline Oswestry Disability Index (ODI); no reoperation or epidural injections; no persistent, new, or increasing neurological deficits; and no major device-related complications. RESULTS: There was a 91% rate of follow-up within the participant population in the 5-year data. There was a difference trending toward significance between groups for the absence of reoperation or epidural injection, with 68.8% of ILS patients and only 51.3% of fusion patients meeting this criteria (P = .065); 13.0% of ILS patients and 25.7% of fusion patients required secondary surgery. The percentage of patients achieving overall CCS was much greater in the ILS group than the fusion group, with 55.1% (38/69) of ILS patients and only 36.4% (12/33) of fusion patients achieving CCS at month 60 (P = .077). With regard to the ODI, the visual analog scale back and worse leg pain, the Short Form-12, and the Zurich Claudication Questionnaire, both groups had significantly better results at every follow-up time point when compared to their respective baseline scores. CONCLUSIONS: The 2-level ILS patient group performed as well as, if not better than, the 2-level fusion group across almost all outcome measures, demonstrating both clinical outcome success and favorably low reoperation rates in patients who received ILS surgery. CLINICAL RELEVANCE: This is the first 5-year analysis of the 2-level ILS experience, which supplements previous studies that describe the advantages of ILS by extending such advantages to 2-level cases.

Spinal Stenosis in the Absence of Spondylolisthesis: Can Interlaminar Stabilization at Single and Multi-levels Provide Sustainable Relief?

BACKGROUND: In the absence of spondylolisthesis, fusion procedures are generally not recommended. However, decompression alone often does not provide long-term clinical success of intractable leg and back pain. Decompression with interlaminar stabilization (ILS) offers a new option within the clinical continuum of care by providing a nonfusion surgical alternative. The objective of this study is to examine the sustainability of decompression with ILS and to understand the clinical success at either 1 or 2 levels as a surgical treatment for nonspondylolisthesis patients with spinal stenosis. METHODS: Under an FDA-regulated investigational device exemption (IDE) study, a total of 322 patients were enrolled in the prospective, randomized trial. This investigation focuses only on the subset of patients (116 total) from this overall cohort who were treated with decompression plus ILS at 1 or 2 levels and who did not present with spondylolisthesis preoperatively. The patients were assessed before and after surgery up to 60 months. RESULTS: At 60-month follow up, there was no statistically significant difference in ODI ≥ 15 point improvement between patient populations (81.6% of 1 level, 90.3% of 2 level). At 60 months, 83.1% of 1 level and 86.3% of 2 level patients did not require a secondary surgical procedure. At 60 months, 94.7% of 1 level and 100% of 2 level reported ≥20 mm improvement in Visual Analogue Scale leg pain. Patients reported improvement in their physical state according to Short Form-12 scores (89.3% of 1 level, 88.9% of 2 level). Patient satisfaction at 60 months was 97.4% for 1 level and 93.3% for 2 level. CONCLUSIONS: The therapeutic sustainability for the treatment of spinal stenosis without spondylolisthesis with ILS at 1 or 2 levels in the lumbar region has been shown to be safe and efficacious for patients who have failed conservative treatment. CLINICAL RELEVANCE: Decompression with ILS offers a nonterminal surgical option for the treatment of the symptomology of spinal stenosis, a progressive degenerative condition, that potentially can provide longer durability and stability than decompression alone.

Biomechanical and histologic assessment of a novel screw retention technology in an ovine lumbar fusion model.

BACKGROUND CONTEXT: Screw loosening is a prevalent failure mode in orthopedic hardware, particularly in osteoporotic bone or revision procedures where the screw-bone engagement is limited. PURPOSE: The objective of this study was to evaluate the efficacy of a novel screw retention technology (SRT) in an ovine lumbar fusion model. STUDY DESIGN/SETTING: This was a biomechanical, radiographic, and histologic study utilizing an ovine lumbar spine model. METHODS: In total, 54 (n=54) sheep lumbar spines (L2-L3) underwent posterior lumbar fusion (PLF) via pedicle screw fixation, connecting rod, and bone graft. Following three experimental variants were investigated: positive control (ideal clinical scenario), negative control (simulation of compromised screw holes), and SRT treatments. Biomechanical and histologic analyses of the functional spinal unit (FSU) were determined as a function of healing time (0, 3, and 12 months postoperative). RESULTS: Screw pull-out, screw break-out, and FSU stability of the SRT treatments were generally equivalent to the positive control group and considerably better than the negative control group. Histomorphology of the SRT treatment screw region of interest (ROI) observed an increase in bone percentage and decrease in void space during healing, consistent with ingrowth at the implant interface. The PLF ROI observed similar bone percentage throughout healing between the SRT treatment and positive control. Less bone formation was observed for the negative control. CONCLUSIONS: The results of this study demonstrate that the SRT improved screw retention and afforded effective FSU stabilization to achieve solid fusion in an otherwise compromised fixation scenario in a large animal model.

ISASS Recommendations and Coverage Criteria for Bone Graft Substitutes used in Spinal Surgery.

Autologous bone graft remains the gold standard by which bone graft substitutes are compared in spine fusion surgery. The utilization of bone graft substitutes, either as (1) an extender for spinal fusion constructs or (2) an alternative to minimize morbidity while maximizing outcomes, is changing. Moreover, current procedures technology (CPT) code 20939 became effective in 2018 defining bone marrow aspirate for bone grafting, spine surgery only. Changes in the complex landscape of grafting materials have prompted ISASS to provide category guidance for bone graft substitutes by comparing and contrasting US regulatory pathways, mechanisms of action, and supportive clinical evidence for these bone grafting materials.

Efficacy comparison of Accell Evo3 and Grafton demineralized bone matrix putties against autologous bone in a rat posterolateral spine fusion model.

BACKGROUND CONTEXT: Spinal fusion procedures are intended to stabilize the spinal column for a multitude of disorders including abnormal curvature, traumatic instability, degenerative instability, and damage from infections or tumors. As an aid in the bone healing response, bone graft materials are used to bridge joints for arthrodesis and promote unions in pseudoarthrosis. Currently, the gold standard for stabilizing fusion masses in spinal procedures involves using the osteogenic, osteoinductive, and osteoconductive properties of autologous iliac crest corticocancellous bone. However, considerable morbidity is associated with harvesting the autologous graft. Donor site complications including infection, large hematomas, and pain have been reported at rates as high as 50% (Boden and Jeffrey, 1995). Biologically, the rate of bone repair dictates the rate at which the fusion mass will unite under autologous graft conditions. PURPOSE: The purpose of this study is to compare the quality and rate of fusion between Accell Evo3 and Grafton demineralized bone matrix (DBM), with the gold standard iliac crest bone graft (ICBG) as the control, in athymic rat posterolateral fusion. STUDY DESIGN: This study was a randomized, controlled study in a laboratory setting at the Hospital for Special Surgery in New York City. Blinded observations were made, which created an assessment of outcomes for successful fusions between each method. PATIENT SAMPLE: Forty-eight (48) athymic rats were used in this study and underwent posterolateral lumbar fusion. They were assessed at either 3 weeks or 9 weeks to see the rate and efficacy of fusion. OUTCOME MEASURES: Outcome measures will be the efficacy of the different bone grafts and their success rates of fusion in the rats. METHODS: A comparison of the quality and rate of fusion between Accell Evo3® (DBM A) and Grafton (DBM B), with the gold standard iliac crest bone graft (ICBG) as the control, was performed using the established posterolateral intertransverse process on an athymic rat model. Materials were evaluated for fusion by several criteria, including manual palpation, standard and high-resolution radiographic imaging, micro-computed topography, and histologic analysis. Forty-eight (48) athymic rats received a bilateral intertransverse process fusion, using either bone from the iliac crest (control group), Accell Evo3, or Grafton. Twelve (12) rats (four from each group) were sacrificed at 3 weeks postoperatively, whereas the remaining thirty-six (36) were sacrificed at 9 weeks postoperatively. Three blinded observers examined the spines after the rats were euthanized, and they blindly assessed each rat for fusion success. RESULTS: Manual palpation of the three different groups at 3 weeks postoperatively found successful fusion in 1 of 4 (25%) of the autologous bone graft (ABG) group and 4 of 4 (100%) of both DBM A and B groups. Manual palpation of the remaining animals that were sacrificed at 9 weeks postoperatively showed successful fusion in 4 of 12 (33%) of the ABG group, 8 of 12 (66%) of the DBM A group, and 12 of 12 (100%) of the DBM B group. Radiography found that 9 of 16 (56%) of the ABG group and 16 of 16 (100%) of both DBM Putty A and B groups had fused. Histologic analysis of the ABG group demonstrated less mature and less organized osteoid at both 3 and 9 weeks than the DBM Putty A and B groups. Nondestructive mechanical testing demonstrated increased stiffness in 4-point bending of both DBM A and B compared with ABG. CONCLUSIONS: Both DBM-treated groups achieved a significantly higher rate of fusion than the ABG-treated group at 9 weeks in this model. Successful fusion was also demonstrated in the DBM-treated groups at 3 weeks.

Optimizing surface characteristics for cell adhesion and proliferation on titanium plasma spray coatings on polyetheretherketone.

BACKGROUND: Titanium plasma spray coating on polyetheretherketone (PEEK) is a recent innovation to interbody spacer technology. The inherent hydrophobic properties of standard, uncoated PEEK implants can hamper cell attachment and bone healing during fusion. The addition of titanium coating not only offers initial stability due to increased surface roughness but also long-term stability due to bony ongrowth created from osteoconductive microenvironment on the device surface. The previously established hydrophilic and osteophilic properties of commercially pure titanium (CPTi) can potentially provide an ideal environment promoting cell attachment and bony ongrowth when applied at the end plate level of the fusion site. Because the surface material composition and topography is what seems to directly affect cell adhesion, it is important to determine the ideal titanium coating for the highest effectiveness. PURPOSE: The purpose of the study is to determine whether there is an optimal surface roughness for the titanium coatings and whether different polishing methods have a greater effect than roughness or topography in mediating cell adhesion to the surface. STUDY DESIGN/SETTING: The study was divided into two phases. In Phase 1, the effects of varying surface roughnesses on identical polishing method were compared. In Phase 2, the effect of varying polishing methods was compared on identical surface roughnesses. METHODS: Coating thickness, porosity, and surface roughness were characterized using an optical microscope as per ASTM F 1854 standards. For both phases, PEEK coupons with plasma-sprayed CPTi were used, and human mesenchymal stem cells (hMSCs) at an initial density of 25,000 cells/cm2 were seeded and cultured for 24 hours before fixation in 10% formalin. The cultured hMSCs were visualized by 4',6-diamidino-2-phenylindole (DAPI) staining, a fluorescent stain that binds to the DNA of living cells. Samples were imaged using an environmental scanning electron microscope (eSEM) (Carl Zeiss Microscopy, Thornwood, NY, USA) using a backscattered detector. RESULTS: Image analysis of the CPTi coatings showed uniform and rough surfaces. For Phase 1, roughness was evaluated as fine, medium, and coarse. The eSEM image analysis and cell counting by DAPI demonstrated that hMSCs have a tendency to form stronger adhesion and greater pseudopodia extensions on fine roughness surfaces. Individual hMSCs were seen forming cytoplasmic processes extending across the width of a pore. There was a 4- and 20-fold reduction in adhered hMSCs with an increase to medium and coarse roughnesses, respectively. For Phase 2, studied groups are (1) medium CPTi coating with zirconia polishing, (2) medium CPTi coating with CPTi polishing, and (3) fine CPTi coating with CPTi polishing. The eSEM image analysis and cell counting by DAPI demonstrated that hMSCs have a tendency to form stronger adhesion and greater pseudopodia extensions on Group 3 over the other two groups. There was a twofold reduction in adhered hMSCs on medium roughness relative to fine. No difference in cell adhesion was found between Groups 1 and 2. Individual hMSCs were seen forming cytoplasmic processes extending across the width of a pore. CONCLUSIONS: Previously, it was accepted without much scrutiny that surface coatings were beneficial. This study begins to discover that surface topography directly affects the potential for cells to adhere and proliferate and lead to greater surgical efficacy.

Feasibility and Biomechanics of Multilevel Arthroplasty and Combined Cervical Arthrodesis and Arthroplasty.

STUDY DESIGN: A new experimental protocol was applied utilizing a simplified postural control model. Multiple constructs were tested nondestructively by interconnecting segmental rods to screws. OBJECTIVE: To investigate how posture and distribution of segmental angles under physiological loads are affected by combined cervical arthroplasty and fusion. SUMMARY OF BACKGROUND DATA: Previous studies of biomechanics of multilevel arthroplasty have focused on range of motion and intradiscal pressure. No previous study has investigated postural changes and segmental angle distribution. METHODS: In 7 human cadaveric C3-T1 specimens, C4-C5, C5-C6, and C6-C7 disks were replaced with ProDisc-C (Synthes). Combinations of fusion (f) adjacent to arthroplasty (A) were simulated at C4-C5, C5-C6, and C6-C7, respectively: fAA, AfA, AAf, ffA, fAf, Aff, fff. C3-C4 and C7-T1 remained intact. A compressive belt apparatus simulated normal muscle cocontraction and gravitational preload; C3-C4, C4-C5, C5-C6, C6-C7, and C7-T1 motions were tracked independently. Parameters studied were segmental postural compensation, neutral buckling, and shift in sagittal plane instantaneous axis of rotation (IAR). RESULTS: With one or more levels unfused, the arthroplasty levels preferentially moved toward upright posture before the intact levels. Neutral buckling was greatest for 3-level arthroplasty, less for 2-level arthroplasty, and least for 1-level arthroplasty. Among the three 1-level arthroplasty groups (ffA, fAf, Aff), arthroplasty at the caudalmost level resulted in significantly greater buckling than with arthroplasty rostralmost or at mid-segment (P<0.04, analysis of variance/Holm-Sidak). Although IAR location was related to buckling, this correlation did not reach significance (P=0.112). CONCLUSIONS: Arthroplasty levels provide the "path of least resistance," through which the initial motion is more likely to occur. The tendency for specimens to buckle under vertical compression became greater with more arthroplasty levels. Buckling appeared more severe with arthroplasty more caudal. Buckling only moderately correlated to shifts in IAR, meaning slight malpositioning of the devices would not necessarily cause buckling.

Assessment of the injection behavior of commercially available bone BSMs for Subchondroplasty® procedures.

BACKGROUND: Bone substitute materials (BSMs) have been commercially available for over 30 years and have been used extensively in orthopedic procedures. Some BSMs are described as "injectable." With rising focus on minimally invasive surgical procedures, the range of applications in which these materials are injectable is of clinical interest. Specifically, their performance in closed, pressurized environments in the trabecular bone with microdamage or abnormal bone remodeling have not been well characterized. This issue arises often in the presence of bone marrow lesions of the subchondral bone in early onset osteoarthritis. The objective was to evaluate the in vitro injectability of several common commercially available BSMs. It was hypothesized that some materials self-described as "injectable" would fail to function in a small microarchitecture in comparison to the large void areas. METHODS: Mechanical testing was performed and force data was collected. Each sample was additionally radiographed and then imaged under micro-computed tomography (CT). RESULTS: Most of the BSM materials failed to be successfully injected into a simulated trabecular model. Simplex™, AccuFill® and StrucSure™ materials were the only ones that were injected successfully. Many of the materials underwent phase separation at higher pressures and were not able to be deployed from the injection syringe. In addition, a clinically relevant difference was seen between the manners in which the materials interdigitated into the existing structure. CONCLUSION: The AccuFill® was the only material able to inject in a closed model and demonstrate adequate implantation of BSM into the simulated trabecular bone. CLINICAL RELEVANCE: Injectability of BSMs is clinically relevant as the interest in minimally invasive surgical procedures is rising rapidly.

Biomechanical evaluation of a low-profile, anchored cervical interbody spacer device at the index level or adjacent to plated fusion.

STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: To test the hypotheses: (1) an anchored spacer device would decrease motion similarly to a plate-spacer construct, and (2) the anchored spacer would achieve a similar reduction in motion when placed adjacent to a previously fused segment. SUMMARY OF BACKGROUND DATA: An anchored spacer device has been shown to perform similar to the plate-spacer construct in previous biomechanical evaluation. The prevalence of adjacent segment disease after fusion is well established in the literature.There is currently no evidence supporting the use of an anchored interbody spacer device adjacent to a previous fusion. METHODS: Eight human cervical spines (age: 45.1 ± 13.1 yr) were tested in moment control (±1.5 Nm) in flexion-extension, lateral bending, and axial rotation without preload. Flexion-extension was then retested under 150-N preload. Spines were tested intact and after anterior cervical discectomy and fusion (ACDF) at C4-C5 and C6-C7 with either a plate-spacer or anchored spacer construct (randomized). The specimens were tested finally with an ACDF at the floating C5-C6 segment using the anchored spacer device adjacent to the previous fusions. RESULTS: Both the plate-spacer and anchored spacer significantly reduced motion from the intact spine in flexion-extension, lateral bending, and axial rotation (P < 0.005). There was no statistically significant difference between the 2 fusion constructs in their abilities to reduce motions (P = 1.0). ACDF using the anchored spacer at the floating C5-C6 level (in between the plate-spacer and anchored spacer constructs) resulted in significant motion reductions in all modes of testing (P < 0.05). These motion reductions did not significantly differ from those of a single-level anchored-spacer construct or a single-level plated ACDF. CONCLUSION: The anchored spacer provided significant motion reductions, similar to a plated ACDF, when used as a single-level fusion construct or placed adjacent to a previously plated segment. LEVEL OF EVIDENCE: N/A.

Evaluation of a new formulation of demineralized bone matrix putty in a rabbit posterolateral spinal fusion model.

BACKGROUND CONTEXT: Alternatives to autologous bone graft (ABG) with osteoconductive, osteoinductive, and osteogenic potential continue to prove elusive. Demineralized bone matrix (DBM) however, with its osteoconductive and osteoinductive potential remains a viable option to ABG in posterolateral spine fusion. PURPOSE: To compare the efficacy of a new formulation of DBM putty with that of ABG in a rabbit posterolateral spinal fusion model. STUDY DESIGN: Efficacy of a new formulation of DBM was studied in an experimental animal posterolateral spinal fusion model. METHODS: Twenty-four male New Zealand White rabbits underwent bilateral posterolateral spine arthrodesis of the L5-L6 intertransverse processes, using either ABG (control group, n=12) or DBM (DBM made from rabbit bone) putty (test group, n=12). The animals were killed 12 weeks after surgery and the lumbar spines were excised. Fusion success was evaluated by manual palpation, high resolution X-rays, microcomputed tomography imaging, biomechanical four-point bending tests, and histology. RESULTS: Two animals were lost because of anesthetic related issues. Manual palpation to assess fusion success in the explanted lumbar spines showed no statistical significant difference in successful fusion in 81.8% (9/11) of DBM group and 72.7% (8/11) of ABG group (p=.99). Reliability of these assessments was measured between three independent observers and found near perfect agreement (intraclass correlation cofficient: 0.92 and 0.94, respectively). Fusion using high resolution X-rays was solid in 10 of the DBM group and 9 of the ABG group (p=.59). Biomechanical testing showed no significant difference in stiffness between the control and test groups on flexion, extension, and left lateral and right lateral bends, with p values accounting for .79, .42, .75, and .52, respectively. The bone volume/total volume was greater than 85% in the DBM treated fusion masses. Histologic evaluation revealed endochondral ossification in both groups, but the fusion masses were more mature in the DBM group. CONCLUSIONS: The DBM putty achieved comparable fusion rates to ABG in the rabbit posterolateral spinal fusion model.

A comparison of patients who have undergone 1-Level versus 2-Level ProDisc arthroplasty: a prospective study with minimum of 5-year follow-up.

STUDY DESIGN: Analysis of data collected prospectively from the United States Food and Drug Administration Investigational Device Exemption (U.S. FDA IDE) clinical trial for patients who underwent ProDisc-L arthroplasty at 1- and 2- levels performed at 2 study centers. OBJECTIVE: To determine if there is any clinical or radiographical differences between patients who received 1-level ProDisc-L and patients who received 2-level ProDisc-L with a minimum follow-up of 5 years. SUMMARY OF BACKGROUND DATA: Recent prospective U.S. FDA clinical trial results have been published showing efficacy of the ProDisc (DePuy Synthes, West Chester, PA) prosthesis in both single and 2 level surgical procedures. Results of these prospective randomized multicenter FDA IDE clinical trials showed safety, efficacy, and superiority over circumferential fusion. METHODS: Patients were part of the FDA clinical trial for the ProDisc-L versus circumferential fusion study at 2 institutions. We identified 20 patients who received ProDisc-L at 1 level and 21 who received it at 2 levels for a total of 41 patients. Pre- and postoperative pain, clinical function, and range of motion were measured. An unpaired t test was done to compare the 2- versus 1-level disc replacement patients. RESULTS: All patients had more than 60 months of clinical follow-up. The mean scores on the visual analogue scale were 37.1 and 28.7, respectively (P = 0.33) for 1- and 2-level patients. Oswestry Disability Index scores were 33 and 29.1, respectively for 1- and 2-level patients (P = 0.60); and SF-36 health survey physical scores were 43 and 43.9, respectively for 1- and 2-level patients (P = 0.81); SF-36 health survey mental scores were 46.2 and 46.6, respectively for 1- and 2-level patients (P = 0.923). The average final follow-up postoperative range of motion for 1- and 2-level total disc replacement was 6.0º and 5.4º, respectively (P = 0.632). CONCLUSION: This study was unable to identify statistical differences in all clinical and radiographical outcomes for patients who underwent 1- and 2-level ProDisc arthroplasty in a cohort from 2 centers. Future studies with longer-term follow-up are needed to confirm these results. LEVEL OF EVIDENCE: 4.

The mechanical performance of cervical total disc replacements in vivo: prospective retrieval analysis of prodisc-C devices.

STUDY DESIGN: Prospective retrieval analysis of Prodisc-C cervical total disc replacements (CTDRs) from 24 explanting surgeons during a 6-year period. OBJECTIVE: To determine the in vivo mechanical performance and fixation to bone of explanted Prodisc-C CTDRs. SUMMARY OF BACKGROUND DATA: The nature and quantity of damage sustained by an implanted device has proven to be important in the prediction of clinical longevity. We hypothesized that retrieval analysis of the Prodisc-C will display characteristic modes of wear consistent with increased posterior angulation and translation of the functional spinal unit after resection of the discoligamentous anatomy. METHODS: Thirty CTDRs from 29 patients (mean age, 45.1 ± 1.9; range, 31-57 yr) after a mean length of implantation of 1.0 ± 0.2 years (range, 2 d-3.5 yr) were studied. Operative level was C4-C5 in 20% (6 of 30), C5-C6 in 47% (14 of 30), C6-C7 in 20% (6 of 30), and unknown in 13% (4 of 30). Polyethylene and metallic (cobalt chrome molybdenum [CoCrMo]) components were examined using light stereo-microscopy (6X-31X), scanning electron microscopy, and energy dispersive x-ray analysis. RESULTS: CTDRs were explanted for indications of axial pain (n = 9), radicular symptoms (n = 6), atraumatic loosening (n = 6), trauma (n = 5), metal allergy (n = 1), myelopathy (n = 1), hypermobility (n = 1), and unknown (n = 1). Surface area of ongrowth (mean = 7.2 ± 1.4%) was not associated with operative level (P = 0.37), surgeon-reported axial pain (P = 0.56), or atraumatic loosening (P = 0.93). Burnishing consistent with metallic endplate impingement was present in 80% (24 of 30) of retrieved CTDRs, most commonly in the posterior quadrant (P < 0.001). There was no association between implant height (P = 0.19) or depth (P = 0.17) and posterior impingement. Backside wear was not observed on any of the disassembled implants (0 of 16). Third-body wear occurred in 23% (7 of 30) and the donor site was confirmed by scanning electron microscope/energy dispersive x-ray analysis to be the porous-coated surface of the CTDR. CONCLUSION: Early clinical failures of Prodisc-C CTDRs display surface damage evidence of metal endplate-endplate impingement, most commonly posteriorly. Backside wear was not evident; however, third-body wear was found. Future studies will determine the clinical impact of these predominant modes of wear on long-term metal-on-polyethylene semiconstrained CTDR performance.