Improved response of osteoprogenitor cells to titanium plasma-sprayed PEEK surfaces.

Orthopedic implants benefit from a surface that encourages direct bony ongrowth (contact osteogenesis). This process is initiated as osteoprogenitor cells attach to the implant surface and deposit a calcium-enriched, collagen-deficient interfacial layer known as the cement line, which provides an anchoring foundation for the subsequent production of collagenous bone matrix from differentiated osteoblasts. Despite the importance of the cement line, the conditions affecting its deposition are incompletely understood. The current study aimed to examine cement line formation from human osteoprogenitor cells (hFOB 1.19) on a titanium plasma-sprayed PEEK (termed Ti-PEEK) surface exhibiting hierarchical roughness, compared to two relatively flat implant materials, PEEK and Ti-6Al-4 V (Ti). The hierarchical roughness of Ti-PEEK surfaces created more surface area (40% increase at the microscale) for greater cellular proliferation and stimulated significantly increased calcium deposition, which was produced by osteoprogenitor cells in their undifferentiated state. The absence of increases in alkaline phosphatase confirmed that cells remained undifferentiated, and the lack of variation in collagen measurements supported the non-collagenous composition of the cement line. Impressively, after just 24 h, the calcium deposition measured on Ti-PEEK surfaces was 305% and 470% higher than on Ti and PEEK, respectively, providing evidence that Ti-PEEK surfaces may enhance contact osteogenesis by stimulating accelerated cement line formation from undifferentiated osteoprogenitor cells.

100 consecutive cases of degenerative lumbar conditions using a non-threaded locking screw system with a 90-degree locking cap.

BACKGROUND: This prospective study analyzes the perioperative outcomes and long-term fusion success of 100 consecutive lumbar degenerative cases. The cases were managed using a non-threaded locking screw system, in conjunction with polyetheretherketone (PEEK) cages, for posterior lumbar interbody fusion (PLIF) procedures. These 100 cases were compared to another prospective study treating patients with the same inclusion and exclusion criteria using conventional plate-based pedicle screw spinal instrumentation augmented with carbon fiber interbody cages. METHODS: A total of 167 operative levels were treated in 100 patients (51 single-level, 39 two-level and 10 three-level cases). Eleven cases were revisions and 67 patients received interbody fusion cages. Patients had an average of 22.8 ± 4.0 months followup. RESULTS: There was one instrumentation failure but no significant subsidence at the interbody fusion level. The disc space height was restored as part of the surgical procedure at the interbody cage levels: from 7.5 ± 2.3 mm preoperative to 9.0 ± 2.1 mm postoperative. There were 2 cases of pseudarthrosis (2 / 100 = 2%). The average operative time for 1-level cases was 111 ± 25 minutes; for 2-level cases it was 132.4 ± 21.8 minutes; and for 3-level cases it was 162.6 ± 33 minutes. Blood loss averaged 800 ± 473 cc for 1-level cases, 1055 ± 408 cc for 2 levels, and 1155 ± 714 cc for 3 levels. The length of stay was similar between the 3 groups (4.4 ± 1.2 days for single-level cases, 4.7 ± 1.1 for 2 levels, and 5.0 ± 1.1 for 3 levels; P > .05). There were 3 incidental durotomies, and 4 other patients developed infections postoperatively that required reoperation. CONCLUSION: The disc and foraminal heights can be restored and maintained with a unilateral cage and pedicle screw construct. Unilateral transforaminal lumbar interbody fusion using a PEEK cage combined with a non-threaded locking pedicle screw and rod system results in similar fusion rates to those achieved using the bilateral Brantigan interbody fusion cage or a single BAK Vista implant. When compared to the bilateral Brantigan cages, decreased operative time (P < .001), decreased blood loss (P < .001) and reduced incidence of dural tears (P < .001) are advantages of using a non-threaded locking screw system and single PEEK interbody cage for lumbar degenerative conditions without compromising subsequent fusion rates.

Distribution of in vivo and in vitro range of motion following 1-level arthroplasty with the CHARITE artificial disc compared with fusion.

OBJECT: One of the goals of lumbar arthroplasty is to restore and maintain range of motion (ROM) and to protect adjacent levels from abnormal motion, which may be a factor in transition syndrome following arthrodesis. In this study, in vitro ROM results were compared with in vivo, 2-year postoperative radiographic ROM evaluations. METHODS: Radiographs of patients enrolled in the CHARITE investigational device exemption study were analyzed at baseline and at 2 years postoperatively. The ROM in flexion/extension at the implanted and adjacent levels was measured, normalized, and compared with ROM results obtained using cadaver (in vitro) evaluations. RESULTS: Preoperative ROM distributions in patients enrolled for arthroplasty or fusion at the L4-5 level was as follows: 28% motion was observed at L3-4, 35% at L4-5 and 37% at L5-S1. Following a one-level arthroplasty at L4-5, the in vivo ROM distribution from L-3 to S-1 at the 2-year time point was 36% at L3-4, 30% at L4-5 and 35% at L5-S1. Following a one-level fusion with BAK and pedicle screws at L4-5, the in vivo ROM distribution from L-3 to S-1 at the 2-year time point was 45% at L3-4, 9% at L4-5 and 46% at L5-S1. CONCLUSIONS: The baseline as well as the 2-year in vivo data confirmed previously published in vitro data. One-level arthroplasty was shown herein to replicate the normal distribution of motion of the intact spine.

Revisability of the CHARITE artificial disc replacement: analysis of 688 patients enrolled in the U.S. IDE study of the CHARITE Artificial Disc.

STUDY DESIGN: A prospective, randomized, multicenter, FDA-regulated Investigational Device Exemption clinical trial. OBJECTIVES: To analyze the incidence of, and reasons for, reoperation in all patients (treatment and control) enrolled in the IDE study. SUMMARY OF BACKGROUND DATA: This is the first report of the incidence and nature of reoperations following lumbar TDR as part of a controlled, prospective, multicenter trial. METHODS: A total of 688 patients meeting the inclusion and exclusion criteria were enrolled in one of three arms of the study at 14 centers across the United States. This cohort includes 71 nonrandomized cases, 205 randomized cases, and 313 continued access cases, all receiving the CHARITE Artificial Disc, as well as 99 randomized cases in the control group (ALIF with threaded fusion cages and autograft). A detailed analysis was performed of clinical chart notes, operative notes, and adverse event reports for all patients requiring reoperation following their index surgery. RESULTS: Of the 589 patients with TDR, 52 (8.8%) required reoperation. Of the 99 patients with lumbar fusion, 10 (10.1%) required reoperation, and an additional 2 required surgery for adjacent level disease (P = 0.7401). There were 24 TDR patients who underwent a repeated anterior retroperitoneal approach, with 22 (91.7%) having had a successful removal of the prosthesis. Seven of the 24 TDR prostheses requiring removal were revised to another CHARITE Artificial Disc. The mean time to reoperation in all patients was 9.7 months. A total of 29 patients (4.9%) in the TDR group required posterior instrumentation and fusion as did 10 (10.1%) in the control group (P = 0.0562). At 2 years or more follow-up, 93.9%(553/589 = 93.9%) of patients receiving TDR with the CHARITE Artificial Disc had a successfully functioning prosthesis with a mean of over 7 degrees of flexion-extension mobility. CONCLUSIONS: Lumbar TDR with the CHARITE Artificial Disc did not preclude any further procedures at the index level during primary insertion, with nearly one third being revisable to a new motion-preserving prosthesis and just over two thirds being successfully converted to ALIF and/ or posterior pedicle screw arthrodesis, the original alternative procedure.

The indications for interbody fusion cages in the treatment of spondylolisthesis: analysis of 120 cases.

STUDY DESIGN: This study retrospectively examines outcomes of unilateral transforaminal lumbar interbody fusion (TLIF) with posterior fixation using anterior carbon fiber cages and 360 degrees fusion in spondylolisthesis. OBJECTIVES: The goals were to examine the outcomes and perioperative complications of using anterior column support in the treatment of various types of spondylolisthesis. SUMMARY OF BACKGROUND DATA: In 2000, Brantigan et al reported the Brantigan interbody fusion cage used as a posterior lumbar interbody fusion in the US IDE clinical trial. This is the largest series to date of TLIF cages specifically used in the treatment of spondylolisthesis. METHODS: A comprehensive long-term follow-up study was conducted to evaluate the fusion success and morbidity following implantation with an anterior column support and posterior pedicle screw fixation. The 120 patients with spondylolisthesis were comprised by 11 cases, dysplastic; 58 cases, degenerative; and 51 cases, isthmic-acquired spondylolisthesis. Anterior column support was either a rectangular carbon fiber/PEEK device or a cylindrical carbon fiber/PEEK device. Twenty-eight cases (23%) were revisions. RESULTS: There were no pseudarthrosis, instrumentation failures, or significant subsidence at the TLIF level. The disc space height and foraminal height were restored as part of the surgical procedure. Disc height, as measured from the posterior edge of the superior vertebral body, increased from a mean of 5.6 mm before surgery to a mean of 9.3 mm after surgery. Although reduction of the slip was not the primary goal during the surgical procedure for the 120 cases with spondylolisthesis (isthmic-acquired = 51, degenerative = 58, and dysplastic = 11), the 23% slip reduction achieved at surgery was maintained at follow-up. Mean operative time was 143 +/- 33 minutes (range, 70-255 minutes) for all cases. Mean blood loss was 724 +/- 431 mL (range, 300-2,500 mL). There were seven incidental durotomies and three infections. One patient with Grade I degenerative spondylolisthesis required revision of the carbon fiber cage for posterior migration secondary to a traumatic event 3 months after surgery. Fusion success was 98% using the criteriaof Lenke for the posterior fusion and Brantigan and Steffee for the TLIF graft incorporation. CONCLUSIONS: Interbody cages in spondylolisthesis are useful to increase neuroforaminal height, to facilitate reduction, and to improve the chances of achieving a successful 360 degrees fusion.

Prospective randomized study of the Charite artificial disc: data from two investigational centers.

BACKGROUND CONTEXT: For decades there has been a desire to restore motion of a painful degenerated spinal segment. Artificial discs have been used in Europe for almost 20 years. In the few reports available in the literature, the results have been promising. However, there have been no prospective randomized studies comparing artificial discs with spinal fusion. PURPOSE: The purpose of this study was to determine if patients with symptomatic degenerative disc disease treated with Charite artificial disc (DePuy Spine, Raynham, MA) arthroplasty would show significant improvement in functional outcome measures and to compare these results to fusion. STUDY DESIGN/SETTING: This was a prospective randomized clinical trial comparing total disc replacement with anterior lumbar interbody fusion using cages. The data reported were collected from two spine specialty centers participating in a Food and Drug Administration regulated trial. METHODS: A consecutive series of 144 patients were randomized using a 2:1 ratio of Charite versus BAK (Zimmer Spine, Minneapolis, MN). All patients were being treated for single-level discogenic pain confirmed by plain radiography, magnetic resonance imaging and provocative discography. Data were collected at designated follow-up periods for up to 24 months. RESULTS: The mean age was 40.1 years (range, 21 to 56 years). Forty-four cases had BAK anterior interbody fusion, and 100 cases were randomized to Charite disc replacement. The mean operating time was 76.2 minutes (range, 54 to 137 minutes) for the Charite cases. The mean estimated blood loss was 196.2 cc (range, 50 to 1,800 cc). Most patients were discharged in 1 to 2 days with a soft corset and returned to normal activities within 3 weeks if they underwent the disc replacement. The mean Oswestry Disability Index score for the BAK group was 69.6+/-12.8 preoperatively and 27.5+/-26.4 at 24-month follow-up (p<.001) The corresponding mean Oswestry score for the Charite disc patients was 70.9 preoperatively and 30.0 at 24-month follow-up (p<.001). CONCLUSIONS: In this prospective randomized study, both surgical groups improved significantly. Complications of total disc replacement were similar to those encountered with anterior lumbar interbody fusion. Total disc replacement appears to be a viable alternative to fusion for the treatment of single-level symptomatic disc degeneration unresponsive to nonoperative management.

Experimental design of total disk replacement-experience with a prospective randomized study of the SB Charitè.

STUDY DESIGN: Prospective randomized clinical trial. OBJECTIVES: To determine if a prospective randomized study of patients with symptomatic degenerative disc disease treated with disc arthroplasty could be safely completed. METHODS: Sixty patients with one-level discogenic pain confirmed by plain radiography, magnetic resonance imaging, and provocative discography for degenerative disc disease were randomized comparing 1/3 BAK anterior interbody fusion and 2/3 anterior SB Charitè artificial disc replacement. RESULTS: The mean age was 40.3 years (range 21-56 years). Nineteen cases were at L4-L5 and 41 cases were at L5-S1. Nineteen cases had BAK anterior interbody fusion and 41 cases were randomized as SB Charitè disc replacement. The length of surgery was mean 88.4 minutes (range 54-137 minutes) for both groups. The estimated blood loss was mean 289.5 cc (range 50-1800 cc). The length of hospital stay was a mean of 3.03 days (range 2 to 6 days). Oswestry Disability Index for the BAK control group was 45.9 +/- 10.4 before surgery and 23.5 +/- 17.2 at follow-up (P < 0.001). The corresponding ODI scores for the SB Charitè disc were 50.0 +/- 14.3 before surgery and 25.0 +/- 20.1 at a mean of 2 years' follow-up (P < 0.001). CONCLUSIONS: This is the first study that shows improvement of functional outcome measures in a prospective randomized design treating primarily mechanical back pain and achieving comparable successful results to lumbar spinal stenosis decompression.

SB Charité disc replacement: report of 60 prospective randomized cases in a US center.

Sixty patients with one-level discogenic pain confirmed by plain radiography, magnetic resonance imaging, and provocative discography for degenerative disc disease were randomized: one-third BAK anterior interbody fusion and two-thirds anterior SB Charité artificial disc replacement. The mean age was 40.3 years (range 21-56 years). Nineteen cases were at L4-L5 and 41 cases were at L5-S1. Nineteen cases had BAK anterior interbody fusion and 41 cases were randomized as SB Charité disc replacement. The length of surgery was mean 88.4 minutes (range 54-137 minutes) for both groups. The estimated blood loss was mean 289.5 mL (range 50-1800 mL). The length of hospital stay was a mean of 3.03 days (range 2-6 days). Oswestry Disability Index scores for the SB Charité disc (aggregate study group) were 50.0 +/- 14.3 preoperatively and 25.0 +/- 20.1 at 1-3 years' follow-up (P < 0.001). This is the first study that shows improvement of functional outcome measures in a prospective randomized design with disc arthroplasty treating primarily mechanical back pain and achieving comparable successful results to lumbar fusion-interbody fusion cage and BMP or interbody autograft and pedicle screw instrumentation.

Analysis of porous ingrowth in intervertebral disc prostheses: a nonhuman primate model.

STUDY DESIGN: A study was conducted to investigate the biomechanical, histochemical, and biologic ingrowth characteristics of the most widely used total disc prosthesis, the hydroxyapatite-coated SB Charité prosthesis. OBJECTIVE: To compare the porous ingrowth, linear apposition, or bony ingrowth in total disc replacement with published reports of porous ingrowth prostheses in the appendicular skeleton. METHODS: Seven mature baboons (Papio cynocephalus) underwent L5-L6 total disc replacement through an anterior transperitoneal approach. The SB Charité prosthetic vertebral endplates (n = 14) were cobalt-chrome covered by two layers of thin titanium with a hydroxyapatite coating, which was electrochemically bonded to the implant surface. RESULTS: At 6 months after surgery, the range of motion exhibited by the SB Charité and the nonoperative control subjects under axial compression, flexion-extension, and lateral bending showed no statistical difference (P > 0.05). Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Gross histopathologic analysis of the hydroxyapatite-coated SB Charité prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. Histochemical assays showed no accumulation of particulate wear debris (no titanium, ultrahigh molecular weight polyethylene, or cobalt-chrome) nor cytokines (tumor necrosis factor-alpha, prostaglandin E2, interleukin-1, -2, or -6). Total endplate area showed a mean ingrowth (volume fraction) of 47.9% +/- 9.12% and a total ingrowth range of 35.5% to 58.8%. CONCLUSIONS: The porous ingrowth (percentage of pore ingrowth coverage at the bone-metal interface) was more favorable for total disc replacement than for cementless total joint components in the appendicular skeleton (range, 10-30%). The reason for the improved degree of porous ingrowth in total disc replacement prostheses probably is that ligamentotaxis causes sustained compression across the metal-bone interface.

Anterior BAK instrumentation and fusion: complete versus partial discectomy.

Beginning in January 1994, a prospective, clinical study was done comparing the effectiveness of complete anterior (Group 1) versus partial reamed channel discectomies (Group 2) in 100 consecutive patients who had anterior BAK instrumentation and fusion using autogenous iliac crest bone graft. At 2 or more years of followup, all patients in Group 1 who had complete operative disc removal achieved solid arthrodesis. There were no revision surgeries. However, in Group 2, there were seven patients who had a pseudarthrosis and an additional patient with early postoperative cage displacement, which resulted in eight patients in Group 2 requiring revision surgery. The differences in operative preparation of the disc space for BAK instrumentation surgery resulting in complications proved to be significant. The use of interbody titanium cages dramatically increases the biomechanical efficacy of anterior fusions. Original proponents of cages advocated removing a cylindrical channel of disc material using a drill. A prospective review of 100 patients who had complete versus partial discectomy revealed 14% of patients in Group 2 eventually had a pseudarthrosis develop.

Osseointegration of autograft versus osteogenic protein-1 in posterolateral spinal arthrodesis: emphasis on the comparative mechanisms of bone induction.

BACKGROUND CONTEXT: Recent studies have documented increased fusion success afforded by bone morphogenetic proteins versus autogenous graft for posterolateral spinal arthrodesis. PURPOSE: The current study was designed to investigate the time-course maturation processes of lumbar posterolateral arthrodeses performed with Osteogenic Protein-1 (Stryker Biotech, Inc., Hopkinton, MA, USA) (rhOP-1) versus "gold standard" autograft. STUDY DESIGN: The primary focus of this study was to compare the histologic mechanisms of posterolateral osseointegration produced by "hot topic" growth factors. METHODS: A total of 36 coonhounds were equally divided into one of four postoperative time periods of 4, 8, 12 and 24 weeks (nine animals per period). Posterolateral arthrodesis treatments included 1) autograft alone, 2) autograft plus rhOP-1, or 3) rhOP-1 alone. The treatments and animals were divided such that a value of n=6 was obtained for each treatment group per time period and no one animal received the same treatment at both operative sites. Functional spinal unit (FSU) fusion status was assessed using radiographic analysis, biomechanical testing and undecalcified histopathologic and histomorphometric analyses. RESULTS: Radiographic differences in fusion maturation between the treatment groups were evident as early as the 4-week time interval and continued through the 24-week time period. The Osteogenic Protein-1 treatments demonstrated an accelerated rate of radiographic fusion by 4 weeks, which plateaued after the 8-week time period (22% autograft, 88% autograft/rhOP-1 and 66% rhOP-1). In contradistinction, the so-called "gold standard" autograft alone treatments reached a maximum of 50% fusion by the 6-month interval. Biomechanical testing of the FSUs indicated lower flexion-extension and axial rotation range of motion levels for both rhOP-1 treatments versus autograft alone at the 8- and 12-week time periods, respectively (p<.05). Histomorphometric analysis yielded no difference in the posterolateral trabecular bone area (mm(2)) between the three treatments (p>.05), and histopathology indicated no significant histopathologic changes. The most distinctive finding in this study deals with the mechanisms of posterolateral ossification. Based on plain and polarized light microscopy, bone induction and development for the rhOP-1 treatments, with and without autograft, was the result of intramembranous ossification, whereas the process of osseointegration for autograft alone was endochondral bone formation. By the 24-week interval, no discernable differences in trabecular histomorphology were evident based on the different mechanisms of ossification. CONCLUSIONS: This serves as the first study to document the mechanisms of bone induction and fusion maturation between posterolateral arthrodeses treated with autograft versus rhOP-1. The histological data served to corroborate the radiographic and biomechanical findings, because the rhOP-1 treatments consistently demonstrated increased fusion rates and lower range of motion levels compared with the autograft group, particularly at the 8-week postoperative time period. The improvements in these fusion criteria for Osteogenic Protein-1 versus autograft were considered secondary to the differing mechanisms of bone induction. When implanted for posterolateral arthrodesis, rhOP-1 induces an intramembranous healing response, obviating the need for the cartilage intermediate phases found in endochondral bone development. The mechanism of increased speed and incidence of fusion using growth factors (rhOP-1) is delineated by this comprehensive study of preferential intramembranous ossification.