Twenty-Year Radiographic Outcomes Following Single-Level Cervical Disc Arthroplasty: Results From a Prospective Randomized Controlled Trial.

STUDY DESIGN: Prospective randomized controlled trial. OBJECTIVE: Compare range of motion (ROM) and adjacent segment degeneration (ASD) following cervical disc arthroplasty (CDA) versus anterior cervical discectomy and fusion (ACDF) at 20-year follow-up. SUMMARY OF BACKGROUND DATA: Anterior cervical discectomy and fusion is the standard of treatment for single-level cervical disc degeneration causing radiculopathy. CDA is claimed to reduce shear strain, and adjacent-level ROM changes are hypothesized to hasten ASD with ACDF. MATERIALS AND METHODS: This study collected data on 47 patients randomized to ACDF or CDA. Lateral cervical spine radiographs were evaluated preoperatively, postoperatively, and at 20 years for alignment, ROM, ASD, and heterotopic ossification. RESULTS: Eighty-two percent (18/22) of CDA patients and 84% (21/25) of ACDF patients followed up at 20 years. At 20 years, total cervical (C2-C7) ROM was statistically different between the CDA and fusion groups (47.8° vs . 33.4°, P =0.005). Total cervical ROM was not significantly different between preoperative and 20-year periods following CDA (45.6° vs . 47.4°, P =0.772) or ACDF (40.6° vs . 33.0°, P =0.192). Differences in postoperative and 20-year index-level ROM following CDA were not significant (10.1° vs . 10.2°, P =0.952). Final ASD grading was statistically lower following CDA versus ACDF at both adjacent levels ( P <0.005). Twenty-year adjacent-level ossification development was increased following ACDF versus CDA ( P <0.001). Polyethylene mean thickness decreased from 9.4 mm immediately postoperatively to 9.1 mm at 20-year follow up ( P =0.013). Differences in adjacent-level ROM from preoperative to 20-year follow-up in both the ACDF and CDA groups did not meet statistical significance ( P >0.05). CONCLUSIONS: Cervical disc arthroplasty maintains index-level and total cervical ROM with very long-term follow-up. Total cervical ROM was higher at 20 years in CDA relative to ACDF. CDA results in lower rates of ASD and adjacent-level ossification development than ACDF.

Far Lateral/Extraforaminal Approaches for Microdiscectomy and Foraminal Decompression in the Lumbar Spine.

Far lateral approaches to the lumbar spine are uncommon procedures but are essential techniques for spine surgeons to understand and master for the treatment of extraforaminal disk herniations and foraminal stenosis. We present our preferred approaches for open and minimally invasive techniques to perform extraforaminal decompressions and/or discectomies in the lumbar spine.

Long-Term Radiographic and Functional Outcomes of Patients With Absence of Radiographic Union at 2 Years After Single-Level Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Retrospective radiographic investigation. OBJECTIVE: To evaluate the long-term radiographic and functional outcomes of patients in whom there is absence of radiographic union at 2 years after single-level anterior cervical discectomy and fusion (ACDF). METHODS: Thirty-one patients were evaluated at standard postoperative time intervals per index trial protocol. Plain film radiographic fusion criteria at the arthrodesis level was defined as interspinous motion (ISM) <1 mm with corresponding motion at a non-arthrodesed superjacent level ISM ≥4 mm. Radiographs and functional outcome measures were acquired at each follow-up visit. Delayed union was defined as lack of radiographic union by 24 months. RESULTS: Nine patients demonstrated radiographic evidence of delayed radiographic union at 24 months. Of those 9 patients, 5 patients demonstrated evidence of union during the follow-up period to 72 months. Despite the absence of radiographic union based on our criteria, 3 of the 4 remaining patients reported remarkable improvements in pain scores and functional outcomes. CONCLUSIONS: The natural history of delayed union at 24 months after ACDF was still favorable despite the prolonged delay in union. The majority of patients (5 of 9) without radiographic union at 24 months did proceed to radiographic union by final follow-up. In addition, patients that did not meet our criteria for fusion maintained postoperative improvements in patient-reported outcome scores. In summary, our study patients undergoing a single-level ACDF with asymptomatic radiographic delayed union at 24 months can expect maintained improvements in postoperative patient-reported outcomes scores and can still progress to successful radiographic fusion.

Evaluation of DIAM™ Spinal Stabilization System for lower lumbar disc degenerative disease: A randomized, prospective, single-site study.

OBJECTIVE: To determine the efficacy of DIAM Spinal Stabilization System compared with nonoperative treatment for patients with low back pain and lower lumbar disc degenerative disease. METHODS: A single center collected prospective outcomes data on 38 patients randomized to an interspinous device or non-operative treatment for symptomatic lumbar degenerative disc disease with treatment crossover allowed at 6 months. RESULTS: At all postoperative timepoints out to 2-years, statistically significant improvements in ODI and back pain scores were observed with the interspinous device. Clinically significant improvements (ODI >15-point improvement) were seen in 87.5% of DIAM patients at 2-years postoperatively. A high cross-over rate was noted from the non-operative cohort to the operative group (12 of 15) due to continued pain with nonoperative care. Additionally, 80% of patients receiving the DIAM implant reported a >15-point ODI reduction from pre-surgical scores at 2-year follow-up. CONCLUSION: The DIAM device demonstrates improvement in ODI and Back Pain scores maintained out to a 2-year follow-up timepoint and performed superior to conventional nonoperative treatment regimens commonly used in low back pain.

Functional Outcomes Associated With Adjacent-level Ossification Disease 10 Years After Cervical Disc Arthroplasty or ACDF.

STUDY DESIGN: A retrospective review of a prospective, randomized control Food and Drug Administration (FDA) investigational device exemption trial comparing anterior cervical discectomy and fusion (ACDF) with Bryan cervical disc arthroplasty. OBJECTIVE: Determine the clinical significance of adjacent-level ossification disease (ALOD) on long-term functional outcomes after ACDF or arthroplasty. SUMMARY OF BACKGROUND DATA: ALOD occurs when the anterior longitudinal ligament and annulus adjacent to the index surgical level calcifies. As previously reported, ALOD happens more commonly after an arthrodesis than an arthroplasty. No investigation has previously examined 10-year clinical outcomes associated with ALOD. MATERIALS AND METHODS: Forty patients were included in the 10-year follow-up. The index level was radiographically blinded and the cephalad-adjacent level was evaluated for ALOD. These scores underwent statistical analysis to compare the 2 surgical groups (ACDF and arthroplasty) for differences in the development of ALOD at a decade follow-up. Two investigational groups, on the basis of a high or low ALOD score, then proceeded through statistical analysis to compare the functional outcomes of patients in each group. RESULTS: Statistical evaluation of ALOD findings in patients from each surgical group found a significantly higher rate of high-grade ALOD in patients who underwent cervical arthrodesis with plate fixation compared with cervical arthroplasty (68.2% vs. 11.1%, P=0.0003). Functional outcomes of patients were also assessed at the 10-year mark and outcomes in patients with either high-grade or low-grade ALOD were compared. When stratified by high versus low-grade ALOD, no significant difference was found for Neck Disability Index (NDI) (P=0.6431), VAS-arm (P=0.4497), or VAS-neck (P=0.8700) scores between groups. CONCLUSIONS: The present study suggests that there are no significant long-term functional outcome differences between patients with and without significant ALOD. Our findings suggest ALOD may be a radiographic finding that does not alter patient-reported outcomes. LEVEL OF EVIDENCE: Level III-therapeutic.

Does index level sagittal alignment determine adjacent level disc height loss?

OBJECTIVE: The authors sought to compare the effect of index level sagittal alignment on cephalad radiographic adjacent segment pathology (RASP) in patients undergoing cervical total disc arthroplasty (TDA) or anterior cervical discectomy and fusion (ACDF). METHODS: This was a retrospective study of prospectively collected radiographic data from 79 patients who underwent TDA or ACDF and were enrolled and followed prospectively at two centers in a multicenter FDA investigational device exemption trial of the Bryan cervical disc prosthesis used for arthroplasty. Neutral lateral radiographs were obtained pre- and postoperatively and at 1, 2, 4, and up to 7 years following surgery. The index level Cobb angle was measured both pre- and postoperatively. Cephalad disc degeneration was determined by a previously described measurement of the disc height/anteroposterior (AP) distance ratio. RESULTS: Sixty-eight patients (n = 33 ACDF; n = 35 TDA) had complete radiographs and were included for analysis. Preoperatively, there was no difference in the index level Cobb angle between the ACDF and TDA patients. Postoperatively, the ACDF patients had a larger segment lordosis compared to the TDA patients (p = 0.002). Patients who had a postoperative kyphotic Cobb angle were more likely to have undergone TDA (p = 0.01). A significant decrease in the disc height/AP distance ratio occurred over time (p = 0.035), by an average of 0.01818 at 84 months. However, this decrease was not influenced by preoperative alignment, postoperative alignment, or type of surgery. CONCLUSIONS: In this cohort of patients undergoing TDA and ACDF, the authors found that preoperative and postoperative sagittal alignment have no effect on RASP at follow-up of at least 7 years. They identified time as the only significant factor affecting RASP.

Biomechanical Analysis of the Cervical Spine Following Disc Degeneration, Disc Fusion, and Disc Replacement: A Finite Element Study.

BACKGROUND: Discectomy and fusion is considered the "gold standard" treatment for clinical manifestations of degenerative disc disease in the cervical spine. However, clinical and biomechanical studies suggest that fusion may lead to adjacent-segment disease. Cervical disc arthroplasty preserves the motion at the operated level and may potentially decrease the occurrence of adjacent segment degeneration. The purpose of this study was to investigate the effect of disc generation, fusion, and disc replacement on the motion, disc stresses, and facet forces on the cervical spine by using the finite element method. METHODS: A validated, intact, 3-dimensional finite element model of the cervical spine (C2-T1) was modified to simulate single-level (C5-C6) and 2-level (C5-C7) degeneration. The single-level degenerative model was modified to simulate both single-level fusion and arthroplasty (total disc replacement [TDR]) using the Bryan and Prestige LP discs. The 2-level degenerative model was modified to simulate a 2-level fusion, 2-level arthroplasty, and single-level disc replacement adjacent to single-level fusion (hybrid). The intact models were loaded by applying a moment of ±2 Nm in flexion-extension, lateral bending, and axial rotation. The motion in each direction was noted and the other modified models were loaded by increasing the moment until the primary C2-T1 motion matched that of the intact (healthy) C2-T1 motion. RESULTS: Both Bryan and Prestige discs preserved motion at the implanted level and maintained normal motions at the adjacent nonoperative levels. A fusion resulted in a decrease in motion at the fused level and an increase in motion at the unfused levels. In the hybrid construct, the TDR (both) preserved motion adjacent to the fusion, thus reducing the demand on the other levels. The disc stresses followed the same trends as motion. Facet forces increased considerably at the index level following a TDR. CONCLUSION: The Bryan and Prestige LP TDRs both preserved motion at the implanted level and maintained normal motion and disc stresses at the adjacent levels. The motion patterns of the spine with a TDR more closely resembled that of the intact spine than those of the degenerative or fused models.

Long-term Clinical Outcomes of Cervical Disc Arthroplasty: A Prospective, Randomized, Controlled Trial.

STUDY DESIGN: Prospective, randomized, single-center, clinical trial. OBJECTIVE: To prospectively examine the 7- and 10-year outcomes of cervical arthroplasty to anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA: Degeneration of the cervical discs causing radiculopathy is a frequent source of surgical intervention, commonly treated with ACDF. Positive clinical outcomes are associated with arthrodesis techniques, yet there remains a long-term concern for adjacent segment change. Cervical disc arthroplasty has been designed to mitigate some of the challenges associated with arthrodesis whereas providing for a similar positive neurological outcome. As data has been collected from numerous prospective US FDA IDE trials, longer term outcomes regarding adjacent segment change may be examined. METHODS: As part of an FDA IDE trial, a single center collected prospective outcomes data on 47 patients randomized in a 1:1 ratio to ACDF or arthroplasty. RESULTS: Success of both surgical interventions remained high at the 10-year interval. Both arthrodesis and arthroplasty demonstrated statistically significant improvements in neck disability index, visual analog scale neck and arm pain scores at all intervals including 7- and 10-year periods. Arthroplasty demonstrated an advantage in comparison to arthrodesis as measured by final 10-year NDI score (8 vs. 16, P = 0.0485). Patients requiring reoperation were higher in number in the arthrodesis cohort (32%) in comparison with arthroplasty (9%) (P = 0.055). CONCLUSION: At 7 and 10 years, cervical arthroplasty compares favorably with ACDF as defined by standard outcomes scores in a highly selected population with radiculopathy. LEVEL OF EVIDENCE: 1.

Single-Level Cervical Disc Arthroplasty with a Bryan Device.

INTRODUCTION: The anterior cervical approach for discectomy with modified distraction and milling tools (Video 1) provides an ideal method for surgical treatment of symptomatic discogenic disease and subsequent placement of an arthroplasty device. STEP 1 PATIENT POSITIONING: Position the patient supine on a radiolucent table that allows for anteroposterior and lateral fluoroscopic imaging. STEP 2 SURGICAL APPROACH: Use a standard Smith-Robinson approach to the anterior cervical spine at the index level of pathological involvement. STEP 3 DISCECTOMY DISTRACTION AND INITIAL END-PLATE PREPARATION: Perform the initial discectomy with a modified distraction technique; then perform the index neurological decompression followed by bilateral neuroforaminal decompression. STEP 4 END-PLATE PREPARATION: Size the end plates and eventual arthroplasty device, and mill the end plates. STEP 5 INSERTION OF ARTHROPLASTY DEVICE: Prepare the arthroplasty device and insert it. STEP 6 IMAGING AND WOUND CLOSURE: Close the wound and incision in a fashion typical for a Smith-Robinson-type approach. RESULTS: Pain, neurological, and functional outcomes in the immediate perioperative period are at least similar, if not superior, to those achieved with arthrodesis, as are the outcomes over the ensuing months and years.

Comparison of Long-term Differences in Dysphagia: Cervical Arthroplasty and Anterior Cervical Fusion.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: This study investigates the incidence of long-term dysphagia in cervical disc arthroplasty, and anterior cervical discectomy and fusion (ACDF) patients. SUMMARY OF BACKGROUND DATA: No long-term comparison of dysphagia between cervical arthroplasty and fusion patients has been published. Widely variable short-term postsurgical dysphagia rates have been reported. MATERIALS AND METHODS: Cohorts for this study are patients with single-level cervical degenerative disc disease previously enrolled in a randomized clinical trial comparing cervical arthroplasty and ACDF. Subjective modified Bazaz Dysphagia Severity questionnaires were distributed to each patient at a minimum of 5 years postoperative for the long-term assessment. Dysphagia severity data were pooled to compare the rate of patients with dysphagia (grade>1) to asymptomatic (grade=1). RESULTS: In the arthroplasty cohort, 15 of 22 (68%) patients completed long-term swallowing questionnaires with no reports of dysphagia. Eighteen of 25 (72%) ACDF patients completed questionnaires, with 5 of 18 (28%) reporting dysphagia. This is a statistically significant difference (P=0.042) favoring lower rates of long-term dysphagia after cervical arthroplasty at an average interval of 7 years postoperative (range, 5.5-8.5 y). No significant difference between rates of self-reported short-term dysphagia was noted with 12% (3/25) and 9% (2/22) in the ACDF and arthroplasty groups, respectively (P=0.56). All short-term dysphagia cases in the arthroplasty cohort reported complete resolution of symptoms within 12 months postoperative. In the ACDF cohort, persistent symptoms at 7 years were noted in all responding patients. Three ACDF patients reported new late-onset, which was not noted in the arthroplasty cohort. CONCLUSIONS: To date, these findings represent the longest reported follow-up interval comparing rates of dysphagia between randomized cohorts of cervical arthroplasty and fusion patients. Our study suggests that cervical arthroplasty is less likely than ACDF to cause sustained long-term or late-presenting dysphagia.

Efficacy of i-Factor Bone Graft versus Autograft in Anterior Cervical Discectomy and Fusion: Results of the Prospective, Randomized, Single-blinded Food and Drug Administration Investigational Device Exemption Study.

STUDY DESIGN: A prospective, randomized, controlled, parallel, single-blinded noninferiority multicenter pivotal FDA IDE trial. OBJECTIVE: The objective of this study was to investigate efficacy and safety of i-Factor Bone Graft (i-Factor) compared with local autograft in single-level anterior cervical discectomy and fusion (ACDF) for cervical radiculopathy. SUMMARY OF BACKGROUND DATA: i-Factor is a composite bone substitute material consisting of the P-15 synthetic collagen fragment adsorbed onto anorganic bone mineral and suspended in an inert biocompatible hydrogel carrier. P-15 has demonstrated bone healing efficacy in dental, orthopedic, and nonhuman applications. METHODS: Patients randomly received either autograft (N = 154) or i-Factor (N = 165) in a cortical ring allograft. Study success was defined as noninferiority in fusion, Neck Disability Index (NDI), and Neurological Success endpoints, and similar adverse events profile at 12 months. RESULTS: At 12 months (follow-up rate 87%), both i-Factor and autograft subjects demonstrated a high fusion rate (88.97% and 85.82%, respectively, noninferiority P = 0.0004), significant improvements in NDI (28.75 and 27.40, respectively, noninferiority P < 0.0001), and high Neurological Success rate (93.71% and 93.01%, respectively, noninferiority P < 0.0001). There was no difference in the rate of adverse events (83.64% and 82.47% in the i-Factor and autograft groups, respectively, P = 0.8814). Overall success rate consisting of fusion, NDI, Neurological Success and Safety Success was higher in i-Factor subjects than in autograft subjects (68.75% and 56.94%, respectively, P = 0.0382). Improvements in VAS pain and SF-36v2 scores were clinically relevant and similar between the groups. A high proportion of patients reported good or excellent Odom outcomes (81.4% in both groups). CONCLUSION: i-Factor has met all four FDA mandated noninferiority success criteria and has demonstrated safety and efficacy in single-level ACDF for cervical radiculopathy. i-Factor and autograft groups demonstrated significant postsurgical improvement and high fusion rates. LEVEL OF EVIDENCE: 1.

Assessment of SiCaP-30 in a Rabbit Posterolateral Fusion Model with Concurrent Chemotherapy.

Chemotherapy derivatives of the rabbit posterolateral fusion model are considered a challenging environment in which to test bone graft materials. The purpose of this study was to determine the performance characteristics of SiCaP-30 as a bone graft substitute relative to autograft (iliac crest bone graft [ICBG]), Actifuse ABX and ß-Tricalcium Phosphate-Bioactive Glass-Type I Collagen (ßTCP-BG) in a rabbit posterolateral spine fusion model with concurrent chemotherapy treatment This was a randomized, controlled study in a laboratory setting with blinded assessment of fusion by manual palpation and flexibility testing. Sixty rabbits were entered into the study with 45 used for analysis. Chemotherapeutic agents, doxorubicin and cis-platin (2.5 mg/kg), were administered one week prior to surgery, and one, two and three weeks post surgery. Bilateral posterolateral lumbar intertransverse process fusions were performed at L5-L6. The lateral two thirds of the transverse processes were decorticated and covered with 3cc/side of one of the following graft materials: autologous ICBG, Actifuse ABX (ApaTech Ltd, UK), Vitoss BA (Orthovita, USA) or SiCaP-30 (ApaTech Ltd., UK). Animals were euthanized 12 weeks post surgery. The ICBG group had a 45% (5/11) manual palpation fusion rate and correlated with motion analysis fusion results of 36% (4/11). The Actifuse ABX group had a 33% (4/12) manual palpation fusion rate and a motion analysis fusion rate of 25% (3/12). No motion segments in the Vitoss BA group (0/11) showed any signs of fusion. The SiCaP-30 group demonstrated a statistically higher manual palpation and motion analysis fusion rate of 82% (9/11; p<0.05) and produced superior bone formation compared with Actifuse ABX and ßTCP-BG.

Biomechanical Analysis of Cervical Disc Replacement and Fusion Using Single Level, Two Level, and Hybrid Constructs.

STUDY DESIGN: A biomechanical study comparing arthroplasty with fusion using human cadaveric C2-T1 spines. OBJECTIVE: To compare the kinematics of the cervical spine after arthroplasty and fusion using single level, 2 level and hybrid constructs. SUMMARY OF BACKGROUND DATA: Previous studies have shown that spinal levels adjacent to a fusion experience increased motion and higher stress which may lead to adjacent segment disc degeneration. Cervical arthroplasty achieves similar decompression but preserves the motion at the operated level, potentially decreasing the occurrence of adjacent segment disc degeneration. METHODS: 11 specimens (C2-T1) were divided into 2 groups (BRYAN and PRESTIGE LP). The specimens were tested in the following order; intact, single level total disc replacement (TDR) at C5-C6, 2-level TDR at C5-C6-C7, fusion at C5-C6 and TDR at C6-C7 (Hybrid construct), and lastly a 2-level fusion. The intact specimens were tested up to a moment of 2.0 Nm. After each surgical intervention, the specimens were loaded until the primary motion (C2-T1) matched the motion of the respective intact state (hybrid control). RESULTS: An arthroplasty preserved motion at the implanted level and maintained normal motion at the nonoperative levels. Arthrodesis resulted in a significant decrease in motion at the fused level and an increase in motion at the unfused levels. In the hybrid construct, the TDR adjacent to fusion preserved motion at the arthroplasty level, thereby reducing the demand on the other levels. CONCLUSION: Cervical disc arthroplasty with both the BRYAN and PRESTIGE LP discs not only preserved the motion at the operated level, but also maintained the normal motion at the adjacent levels. Under simulated physiologic loading, the motion patterns of the spine with the BRYAN or PRESTIGE LP disc were very similar and were closer than fusion to the intact motion pattern. An adjacent segment disc replacement is biomechanically favorable to a fusion in the presence of a pre-existing fusion.

The effect of multi-level laminoplasty and laminectomy on the biomechanics of the cervical spine: a finite element study.

Laminectomy has been regarded as a standard treatment for multi-level cervical stenosis. Concern for complications such as kyphosis has limited the indication of multi-level laminectomy; hence it is often augmented with an instrumented fusion. Laminoplasty has emerged as a motion preserving alternative. The purpose of this study was to compare the multidirectional flexibility of the cervical spine in response to a plate-only open door laminoplasty, double door laminoplasty, and laminectomy using a computational model. A validated three-dimensional finite element model of a specimen-specific intact cervical spine (C2-T1) was modified to simulate each surgical procedure at levels C3-C6. An additional goal of this work was to compare the instrumented computational model to our multi-specimen experimental findings to ensure similar trends in response to the surgical procedures. Model predictions indicate that mobility was retained following open and double door laminoplasty with a 5.4% and 20% increase in flexion, respectively, compared to the intact state. Laminectomy resulted in 57% increase in flexion as compared to the intact state, creating a concern for eventual kyphosis--a known risk/complication of multi-level laminectomy in the absence of fusion. Increased disc stresses were observed at the altered and adjacent segments post-laminectomy in flexion.

Sheep cervical spine biomechanics: a finite element study.

INTRODUCTION: Animal models are often used to make the transition from scientific concepts to clinical applications. The sheep model has emerged as an important model in spine biomechanics. Although there are several experimental biomechanical studies of the sheep cervical spine, only a limited number of computational models have been developed. Therefore, the objective of this study was to develop and validate a C2-C7 sheep cervical spine finite element (FE) model to study the biomechanics of the normal sheep cervical spine. METHODS: The model was based on anatomy defined using medical images and included nonlinear material properties to capture the high flexibility and large neutral zone of the sheep cervical spine. The model was validated using comprehensive experimental flexibility testing. Ten adult sheep cervical spines, from C2-C7, were used to experimentally ascertain overall and segmental flexibility to ±2 Nm in flexion-extension, lateral bending, and axial rotation. RESULTS: The ranges of motion predicted by the computational model were within one standard deviation of the respective experimental motions throughout the load cycle, with the exception of extension and lateral bending. The model over- and under predicted the peak motions in extension and lateral bending, respectively. Nevertheless, the model closely represents the range of motion and flexibility of the sheep cervical spine. DISCUSSION: This is the first multilevel model of the sheep cervical spine. The validated model affords additional biomechanical insight into the intact sheep cervical spine that cannot be easily determined experimentally. The model can be used to study various surgical techniques, instrumentation, and device placement, providing researchers and clinicians insight that is difficult, if not impossible, to gain experimentally.

Evaluation of a novel silicate substituted hydroxyapatite bone graft substitute in a rabbit posterolateral fusion model.

STUDY DESIGN/SETTING: Randomized, controlled study in a laboratory setting. Blinded observations/assessment of study outcomes. OBJECTIVE: The purpose of this study is to determine the performance characteristics of a novel silicate-substituted hydroxyapatite bone graft substitute (BGS), SiCaP EP (Baxter Healthcare/ ApaTech, Elstree, UK), in a stand-alone mode, a stand-alone with bone marrow aspirate (BMA) mode, and an extender mode with iliac crest autograft (ICBG) in a rabbit posterolateral spine fusion model. The investigational BGS is compared to a standard iliac crest autograft (ICBG) control. SUMMARY OF BACKGROUND DATA: The rabbit posterolateral fusion model is an established environment for testing of fusion efficacy. It offers the opportunity to obtain radiographic, histological, and biomechanical data on novel bone graft substitutes. METHODS: One hundred and twenty rabbits were entered into the study with 116 used for analysis. Bilateral posterolateral lumbar intertransverse fusions were performed at L5-L6. The lateral two thirds of the transverse processes were decorti cated and covered with graft material in the following five groups: ICBG, SiCaP EP stand-alone, SiCaP EP with BMA (1:0.5 by volume), and SiCaP EP with ICBG (1:3 by volume). Rabbits were necropsied at 4, 8, and 12-week time points and fusion rate, quantity, and quality was evaluated based on manual palpation, mechanical stiffness testing, pqCT, and histological assessment. RESULTS: SiCaP EP, ICBG+SiCaP EP (3:1), and SiCaP EP+BMA (1:0.5) compare favorably to iliac crest autologous bone by multiple metrics in this rabbit posterolateral fusion model. Fusion efficacy via manual palpation and mechanical stiffness testing metrics indicate that all SiCaP EP groups had similar group-to-group performance, and were not significantly different than the ICBG control at each time period evaluated. CONCLUSIONS: In this commonly used rabbit posterolateral fusion model, SiCaP EP utilized as a stand-alone, as a stand-alone with BMA, and as an autograft (ICBG) extender produces results that are clinically and radiographically similar to ICBG.

Assessment of BioPlex interbody fusion device in a sheep lumbar fusion model.

OBJECTIVE: The purpose of this study was to evaluate the bioPlex bioresorbable interbody device in a sheep lumbar fusion model and compare it to the concorde, a standard carbon fiber interbody cage. BACKGROUND: Lumbar interbody fusion devices are made from a variety of materials, including titanium alloys, carbon-fiber, and PEEK. The BioPlex Continuous Phase Composite (CPC) is a unique bioresorbable material comprised of Pro Osteon 500R and 70:30 Poly (L/D, L-lactic acid). The BioPlex device is radiolucent, resorbable and due to its bulk nanoporosity of 8%, has a more consistent degradation profile as compared to a polymer alone. METHODS: A total of twenty five male Suffolk sheep were used in this study; nineteen of which were implanted with a bioPlex or concorde device at the L3-L4 and L5-L6 levels using a modified transforaminal/lateral approach. A discectomy was performed and each implant (filled with autologous bone) was placed within the disc space. The sheep were sacrificed at 6, 12, 24 months postimplantation. Fusion was assessed via motion, radiographic and histological data. RESULTS: The BioPlex and Concorde implanted levels had significantly less motion (p<0.05) than the normal controls in flexion/extension and lateral bending at 6, 12, and 24 months. No significant difference in motion was detected between the bioPlex and concorde implants. CT fusion scores correlated with the motion analysis in all the three cases. CONCLUSION: In comparison to the concorde device, the bioPlex implant appears to have equivalent radiographic and biomechanical fusion success.