Bobby Tay

Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease.

BACKGROUND CONTEXT Cervical total disc replacement (TDR) is intended to address radicular pain and preserve functional motion between two vertebral bodies in patients with symptomatic cervical disc disease (SCDD). PURPOSE The purpose of this trial is to compare the safety and efficacy of cervical TDR, ProDisc-C (Synthes Spine Company, L.P., West Chester, PA), to anterior cervical discectomy and fusion (ACDF) surgery for the treatment of one-level SCDD between C3 and C7. STUDY DESIGN/SETTING The study was conducted at 13 sites. A noninferiority design with a 1:1 randomization was used. PATIENT SAMPLE Two hundred nine patients were randomized and treated (106 ACDF; 103 ProDisc-C). OUTCOME MEASURES Visual analog scale (VAS) pain and intensity (neck and arm), VAS satisfaction, neck disability index (NDI), neurological exam, device success, adverse event occurrence, and short form-36 (SF-36) standardized questionnaires. METHODS A prospective, randomized, controlled clinical trial was performed. Patients were enrolled and treated in accordance with the US Food and Drug Administration (FDA)-approved protocol. Patients were assessed pre- and postoperatively at six weeks, 3, 6, 12, 18, and 24 months. RESULTS Demographics were similar between the two patient groups (ProDisc-C: 42.1+/-8.4 years, 44.7% males; Fusion: 43.5 +/- 7.1 years, 46.2% males). The most commonly treated level was C5-C6 (ProDisc-C: 56.3%; Fusion=57.5%). NDI and SF-36 scores were significantly less compared with presurgery scores at all follow-up visits for both the treatment groups (p<.0001). VAS neck pain intensity and frequency as well as VAS arm pain intensity and frequency were statistically lower at all follow-up timepoints compared with preoperative levels (p<.0001) but were not different between treatments. Neurologic success (improvement or maintenance) was achieved at 24 months in 90.9% of ProDisc-C and 88.0% of Fusion patients (p=.638). Results show that at 24 months postoperatively, 84.4% of ProDisc-C patients achieved a more than or equal to 4 degrees of motion or maintained motion relative to preoperative baseline at the operated level. There was a statistically significant difference in the number of secondary surgeries with 8.5% of Fusion patients needing a re-operation, revision, or supplemental fixation within the 24 month postoperative period compared with 1.8% of ProDisc-C patients (p=.033). At 24 months, there was a statistically significant difference in medication usage with 89.9% of ProDisc-C patients not on strong narcotics or muscle relaxants, compared with 81.5% of Fusion patients. CONCLUSIONS The results of this clinical trial demonstrate that ProDisc-C is a safe and effective surgical treatment for patients with disabling cervical radiculopathy because of single-level disease. By all primary and secondary measures evaluated, clinical outcomes after ProDisc-C implantation were either equivalent or superior to those same clinical outcomes after Fusion.

CALCIUM SULFATE– AND CALCIUM PHOSPHATE–BASED BONE SUBSTITUTES: Mimicry of the Mineral Phase of Bone

Calcium sulfate and calcium phosphate have provided the orthopedic surgeon a viable alternative to autogenous bone grafting as either an osteoconductive bone void filler or a bone graft extender. These materials mimic the mineral phase of bone and are resorbed at a rate similar to the rate of bone formation. Thus, they are able to provide some structural support and prevent ingrowth of fibrous tissue while facilitating creeping substitution by the host bone.

Intervertebral disc replacement maintains cervical spine kinetics.

Study Design. An in vitro biomechanical study of C4–C5 intervertebral disc replacement using a cadaveric model. Objectives. To investigate the degree of motion afforded by a ball-and-socket cervical intervertebral disc prosthesis design. Summary of Background Data. Intervertebral disc prostheses designs attempt to restore or maintain cervical disc motion after anterior cervical discectomy and reduce the likelihood of accelerated degeneration in adjacent discs by maintaining normal motion at the affected disc level. Surprisingly, the actual kinetic and biomechanical effects that cervical disc arthroplasty imparts on the spine have not been widely reported. Accordingly, we investigated what effect implanting a cervical disc prosthesis has on the range of motion at the affected level as well as how it changes the coupled motion patterns at the level of implantation. Methods. Six fresh-frozen human cadaveric cervical spines (C2–C7) were used in this study. We evaluated two different spinal conditions: intact and after disc replacement at C4–C5. Compression (using the follower load concept) and pure moment loading were applied to the specimen. Range of motion was measured using an optical tracking system. Statistical differences between the intact and replaced condition range of motion was determined using analysis of variance with post hoc comparisons (&agr; = 0.05). Results. The data indicate that the intervertebral disc prosthesis approximated the intact motion in all three rotation planes at the affected level. Finally, changes in cervical coupled rotations, specifically lateral bending during axial rotation loading and axial rotation during lateral bending loading, were not statistically significant between the two tested conditions. Conclusions. Our data demonstrate that a ball-and-socket design can replicate physiologic motion at the affected and adjacent levels. More importantly, the data indicate that motion coupling, which is most dramatic in the cervical spine and plays an important biomechanical role, is maintained.

Use of a collagen-hydroxyapatite matrix in spinal fusion. A rabbit model.

Study Design. The efficacy of a specially designed mineralized bovine collagen matrix as a carrier for bone marrow stem cells was studied in a rabbit posterolateral spinal fusion model. Objectives. To determine if bone marrow cells added to Healos matrix will lead to fusion rates, biomechanical properties, and histologic properties comparable with those of fusions using autologous iliac crest bone graft; and to determine if the addition of preservative‐free heparin to anticoagulate the bone marrow during harvest will adversely affect the fusion rate. Summary of Background Data. Although the development of new preparations of osteoinductive agents has advanced rapidly in recent years, the carrier systems that have been used in their application have received less attention. The composition and structure of the matrix used are key components affecting the ability of the matrix to function as a scaffold on which cells can migrate, adhere, proliferate, and form bone. The composition and design of matrix components also determine the ability of osteoinductive agents to influence local and hematogenously derived osteogenic precursor cells, which migrate to or are brought into the fusion site. Thus, the properties of the carrier can affect the behavior and efficacy of the osteoinductive agent that is used. The authors studied the properties of a new mineralized collagen matrix called Healos, which has been engineered specifically for spinal fusion application. Methods. Forty‐four adult female New Zealand white rabbits were divided into five groups. Groups 1‐4 underwent bilateral intertransverse fusion between L5 and L6. The fusions were augmented with either autologous iliac crest bone graft, Healos matrix alone, Healos matrix mixed with autologous bone marrow, or Healos matrix combined with heparinized autologous bone marrow. At 8 weeks after surgery, the fusions were characterized radiographically, histologically, and biomechanically. The rate of fusion was determined by radiographic analysis. The fifth group consisted of two animals whose bone marrow was aspirated from their tibias and femurs and then sent for determination of total nucleated cell count. Results. At 8 weeks, the radiographically determined fusion rate for autologous bone graft was 75% (9/12 animals), compared with 100% (10/10 and 9/9 animals) for groups in which fusions were done by using Healos matrix augmented with bone marrow (P ≤ 0.1). Matrix used alone yielded a fusion rate of 18% (2/11 animals, P ≤ 0.006). Histologically, the most mature bone was seen in the group augmented with autologous iliac crest graft, followed in decreasing order by the groups augmented with Healos with heparinized bone marrow, Healos with unheparinized bone marrow, and Healos alone. Biomechanically, the group augmented with autologous graft had the highest mean stiffness, followed by the groups augmented with Healos with heparinized bone marrow, Healos with untreated bone marrow, and finally Healos matrix alone. However, the differences in stiffness between groups were not statistically significant with the number of spines tested. Conclusions. These results show that Healos is an osteoconductive matrix that can be a useful carrier in the biologic and mechanical environment of a posterolateral intertransverse fusion site. In combination with bone marrow, it produces fusion rates that are comparable with those of autologous bone graft. However, it must be combined with an osteoinductive or osteogenic agent to ensure reliable fusion rates and alone cannot produce reliable osteogenesis. The Healos matrix was not compared with other commercially available matrices currently in use. Therefore, the efficacy of Healos relative to these other materials could not be determined.

Reoperation after primary fusion for adult spinal deformity: rate, reason, and timing.

Study Design. Retrospective cohort study of consecutive patients undergoing primary fusion with segmental fixation for adult spinal deformity. Obejctive. We sought to determine the survivorship of primary fusion for adult spinal deformity and identify patient-specific predictors of complications requiring reoperation. Summary of Background Data. Compared with the adolescent population, surgery for adult deformity is often more complex and technically difficult, contributing to a high reported rate of complications that can result in the need for reoperation. Reported complication rates vary widely. Methods. From 1999–2004 all patients who underwent primary instrumented fusion for nonparalytic adult spinal deformity at a single center were included. Inclusion criteria included minimum age at surgery of 20 years and minimum fusion length of 4 motion segments. Surgical, demographic, and comorbidity data were recorded. Reoperation was defined as any additional surgery involving levels of the spine operated on during the index procedure and/or adjacent levels. Comparisons were performed between patients who required reoperation and those who did not. Results. Eighty-nine patients met inclusion criteria. Endpoint (minimum 2 years follow-up or reoperation) was reached for 91%. Mean follow-up was 3.8 years. Cumulative reoperation rate was 25.8%. Survival was 86.4% at 1 year, 77.2% at 2 years, and 75.2% at 3 years. Reasons for reoperation included infection (n = 8), pseudarthrosis (n = 3), adjacent segment problems (n = 5), implant failure (n = 4), and removal of painful implants (n = 3). Multivariate analysis showed smoking was significantly higher in the reoperation group. Conclusion. Using a strict definition of reoperation for a well-defined cohort, in the presence of relevant risk factors, many patients undergoing primary fusion for adult spinal deformity required reoperation. The results indicate that complex medical and surgical factors contribute to the treatment challenges posed by patients with adult spinal deformity. This represents the largest cohort reported to date of patients undergoing primary fusion using third-generation instrumentation techniques.

Use of C-reactive protein after spinal surgery: comparison with erythrocyte sedimentation rate as predictor of early postoperative infectious complications.

Study Design. This is a prospective observational study of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in a cohort of patients undergoing spinal surgery. Objective. We sought to characterize the normal kinetics of ESR and CRP after spinal surgery and compare their usefulness as predictors of infectious complications in the early postoperative period. Summary of Background Data. ESR and CRP are nonspecific markers of inflammation used to evaluate postoperative infection. CRP is a quantitative test that exhibits predictable kinetics consisting of a postoperative rise and a peak followed by a decrease toward the normal value. Deviation from normal kinetics may be an indicator of infection. Methods. ESR and CRP were collected before surgery and daily after surgery in consecutive patients. All infectious complications were recorded. Results. One hundred forty-nine patients met inclusion criteria. Infectious complications occurred in 20 patients. A postoperative peak, which is necessary to apply the test, was observed in 78% of patients for CRP and 48% for ESR. Multiple linear regression analysis revealed preoperative CRP, number of levels, and lumbar region as significant predictors of greater CRP peak value (r2 = 0.435, P = 0.001). After the peak, CRP showed an exponential decrease with a half-life of 2.6 days (r2 = 0.701, P < 0.001). No trend could be determined for ESR. A second rise or failure to decrease as expected had a sensitivity, specificity, positive predictive value, and negative predictive value of 82%, 48%, 41%, and 86% for infectious complications, respectively. Of 8 cases of deep wound infection, 7 exhibited substantial deviations from expected CRP values. Conclusion. CRP is more applicable, predictable, and responsive in the early postoperative period compared with ESR. The postoperative kinetics of CRP derived in this study seems to be conserved regardless of operation, magnitude, or region. Knowledge of the kinetics allows assessment of the degree of difference between actual and expected values. Using a second rise or failure to decrease as expected for CRP is sensitive for infection. A negative test is reassuring that infection is unlikely.

Percutaneous plasma decompression alters cytokine expression in injured porcine intervertebral discs

BACKGROUND CONTEXT Discectomy is a surgical technique commonly used to treat bulging or herniated discs causing nerve root compression. Clinical data suggest discectomy may also help patients with contained discs and no clear neural compromise. However, the mechanisms of clinical efficacy are uncertain, and consequently bases for treatment optimization are limited. PURPOSE To determine the effect of percutaneous plasma decompression on the histologic, morphologic, biochemical and biomechanical features of degenerating intervertebral discs. STUDY DESIGN An adult porcine model of disc degeneration was used to establish a degenerative baseline against which to evaluate discectomy efficacy. OUTCOME MEASURES Cytokines interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor (TNF)-alpha were measured from tissue samples using enzyme-linked immunosorbent assay. Histology and morphology images were rated for degenerative findings (of cells and matrix) in both the nucleus and annulus. Proteoglycan content was determined, and intact specimen stiffness and flexibility were measured biomechanically. Magnetic resonance images were collected for biomechanical specimens. METHODS Using a retroperitoneal surgical approach, stab incisions were made in four or five lumbar discs per spine in 12 minipigs. Animals were allocated into one of three groups: 6-week recovery, 12-week recovery and percutaneous plasma decompression using an electrosurgical device at 6 weeks with recovery for 6 additional weeks. Four additional animals served as controls. RESULTS Discs treated with discectomy had a significant increase in IL-8 and a decrease in IL-1 as compared with the 12-week, nontreated discs. There were no significant differences in morphologic and biomechanical parameters or proteoglycan content between treated discs and time-matched, nontreated discs. CONCLUSIONS Our results demonstrate that percutaneous plasma discectomy alters the expression of inflammatory cytokines in degenerated discs, leading to a decrease in IL-1 and an increase in IL-8. Whereas both IL-1 and IL-8 have hyperalgesic properties, IL-1 is likely to be a more important pathophysiologic factor in painful disc disorders than IL-8. Therefore, the alteration in cytokine expression that we observed is consistent with this effect as a mechanism of pain relief after discectomy. In addition, given that IL-1 is catabolic in injured tissue and IL-8 is anabolic, our results suggest that a percutaneous plasma discectomy may be capable of initiating a repair response in the disc.

Hospital readmission after spine fusion for adult spinal deformity.

Study Design. Retrospective cohort study. Objective. To assess the rate, causes, and risk factors of unplanned hospital readmission after spine fusion for the treatment of adult spinal deformity. Summary of Background Data. Hospital readmissions in the elderly are common, and with increasing emphasis on the quality of health care, readmission rates are used to assess hospital performance. Spine surgery has seen rapidly increased utilization during the past 2 decades. Surgical treatments of complex spinal deformity are known to have higher rates of complications than other types of spine surgery. However, there are no reports describing the rates and causes of hospital readmission after deformity surgery. Methods. Patients were identified at a single institution from 2006 through 2011 that received a spine fusion for the treatment of adult spinal deformity. All hospital readmissions within 90 days of discharge were reviewed for cause. Unplanned readmission rates were calculated via Kaplan-Meier failure analysis. Rates were compared across patients receiving different lengths of spine fusion (short: 2–3 vertebra, medium: 4–8, long: 9 or more). Risk factors were assessed using a Cox proportional hazards multivariate model. Results. Eight hundred thirty-six patients were enrolled (111 short, 402 medium, and 323 long fusions). The overall unplanned readmission rate was 8.4% at 30 days and 12.3% at 90 days. Patients with long spine fusion had higher rates of readmission than patients with medium or short length fusions. Surgical site infection accounted for 45.6% of readmissions. Risk factors for readmission include longer fusion length, higher patient severity of illness, and specific medical comorbidities. Conclusion. Unplanned hospital readmissions after spine fusion for adult spinal deformity are common, and are most often due to surgical site infection. Patient medical comorbidities are an important part of assessing risk and can be used by providers and patients to better assess individual risk prior to treatment. Level of Evidence: 3

Proximal junctional kyphosis and clinical outcomes in adult spinal deformity surgery with fusion from the thoracic spine to the sacrum: a comparison of proximal and distal upper instrumented vertebrae

OBJECT Proximal junctional kyphosis (PJK) is a common and significant complication after corrective spinal deformity surgery. The object of this study was to compare-based on clinical outcomes, postoperative proximal junctional kyphosis rates, and prevalence of revision surgery-proximal thoracic (PT) and distal thoracic (DT) upper instrumented vertebra (UIV) in adults who underwent spine fusion to the sacrum for the treatment of spinal deformity. METHODS In this retrospective study the authors evaluated clinical and radiographic data from consecutive adults (age > 21 years) with a deformity treated using long instrumented posterior spinal fusion to the sacrum in the period from 2007 to 2009. The PT group included patients in whom the UIV was between T-2 and T-5, whereas the DT group included patients in whom the UIV level was between T-9 and L-1. Perioperative surgical data were compared between the PT and DT groups. Additionally, segmental, regional, and global spinal alignments, as well as the sagittal Cobb angle at the proximal junction, were analyzed on preoperative, early postoperative, and final standing 36-in. radiographs. Patient-reported outcome measurements (visual analog scale, Scoliosis Research Society Patient Questionnaire-22, Oswestry Disability Index, and the 36-Item Short-Form Health Survey) were compared. RESULTS Eighty-nine patients, 22 males and 67 females, had a minimum follow-up of 2 years, and thus were eligible for participation in this study. Sixty-seven patients were in the DT group and 22 were in the PT group. Operative time (p = 0.387) and estimated blood loss (p < 0.05) were slightly higher in the PT group. The overall rate of revision surgery was 48.0% and 54.5% in the DT and PT groups, respectively (p = 0.629). The prevalence of PJK according to radiological criteria was 34% in the DT group and 27% in the PT group (p = 0.609). The percent of patients with PJK that required surgical correction (surgical PJK) was 11.9% (8 of 67) in the DT group and 9.1% (2 of 22) in the PT group (p = 1.0). The onset of surgical PJK was significantly earlier than radiological PJK in the DT group (p < 0.01). The types of PJK were different in the PT and DT groups. Compression fracture at the UIV was more prevalent in the DT group, whereas subluxation was more prevalent in the PT group. Postoperatively, the PT group had less thoracic kyphosis (p = 0.02), less sagittal imbalance (p < 0.01), and less pelvic tilt (p = 0.04). In the DT group, early postoperative radiographs demonstrated that the proximal junctional angle of patients with surgical PJK was greater than in those without PJK and those with radiological PJK (p < 0.01). Clinical outcomes were significantly improved in both groups, and there was no significant difference between the groups. CONCLUSIONS Both PT and DT UIVs improve segmental and global sagittal plane alignment as well as patient-reported quality of life in those treated for adult spinal deformity. The prevalence of PJK was not different in the PT and DT groups. However, compression fracture was the mechanism more frequently observed with DT PJK, and subluxation was the mechanism more frequently observed in PT PJK. Strategies to avoid PJK may include vertebral augmentation to prevent fracture at the DT spine and mechanical means to prevent vertebral subluxation at the PT spine.

Adjacent Segment Motion After Anterior Cervical Discectomy and Fusion Versus ProDisc-C Cervical Total Disk Arthroplasty : Analysis from a Randomized, Controlled Trial

Study Design. Post hoc analysis of data acquired in a prospective, randomized, controlled trial. Objective. To compare adjacent segment motion after anterior cervical discectomy and fusion (ACDF) versus cervical total disc arthroplasty (TDA). Summary of Background Data. TDA has been designed to be a motion-preserving device, thus theoretically normalizing adjacent segment kinematics. Clinical studies with short-term follow-up have yet to demonstrate a consistent significant difference in the incidence of adjacent segment disease. Methods. Two hundred nine patients at 13 sites were treated in a prospective, randomized, controlled trial of ACDF versus TDA for single-level symptomatic cervical degenerative disc disease (SCDD). Flexion and extension radiographs were obtained at all follow-up visits. Changes in ROM were compared using the Wilcoxon signed-rank test and the Mann-Whitney U test. Predictors of postoperative ROM were determined by multivariate analysis using mixed effects linear regression. Results. Data for 199 patients were available with 24-month follow-up. The groups were similar with respect to baseline demographics. A significant increase in motion at the cranial and caudal adjacent segments after surgery was observed in the ACDF group only (cranial: ACDF: +1.4° (0.4, 2.4), P = 0.01; TDA: +0.8°, (−0.1, +1.7), P = 0.166; caudal: ACDF: +2.6° (1.3, 3.9), P < 0.0001; TDA: +1.3, (−0.2, +2.8), P = 0.359). No significant difference in adjacent segment ROM was observed between ACDF and TDA. Only time was a significant predictor of postoperative ROM at both the cranial and caudal adjacent segments. Conclusion. Adjacent segment kinematics may be altered after ACDF and TDA. Multivariate analysis showed time to be a significant predictor of changes in adjacent segment ROM. No association between the treatment chosen (ACDF vs. TDA) and ROM was observed. Furthermore clinical follow-up is needed to determine whether possible differences in adjacent segment motion affect the prevalence of adjacent segment disease in the two groups.