Sickle Cell Disease Has No Impact on 10-Year Cumulative Incidence and Indications for Revision Lumbar Fusion.

STUDY DESIGN: Retrospective Cohort Study. OBJECTIVES: Patients with sickle cell disease (SCD) experience distinct physiological challenges that may alter surgical outcomes. There has been no research establishing 10-year lumbar fusion (LF) implant survivorship rates among individuals with SCD. This study aims to determine the 10-year cumulative incidence and indications for revision LF between patients with and without SCD. METHODS: A national database was queried to identify patients with and without SCD who underwent primary LF. SCD patients undergoing LF were propensity-score matched in a 1:4 ratio by age, gender, and Charlson Comorbidity Index (CCI) to a matched LF control. In total, 246 SCD patients were included along with 981 and 100,000 individuals in the matched and unmatched control cohorts, respectively. Kaplan-Meier survival analysis was utilized to determine the 10-year cumulative incidence rates of revision LF. Furthermore, multivariable analysis using Cox proportional hazard modeling was performed to compare indications for revisions and surgical complications between cohorts including hardware removal, drainage and evacuation, pseudoarthrosis, and mechanical failure. RESULTS: No significant differences were found in the cumulative incidence of 10-year all-cause revision LF between patients in the SCD cohort and either of the control cohorts (P > .05 for each). Additionally, there were no significant differences between the SCD cohort and either of the control cohorts in regards to the indications for revision or surgical complications in LF (P > .05 for each). CONCLUSIONS: This study indicates that SCD patients do not have increased risk for revision LF, nor any of its indications.

Evaluation of autologous platelet concentrate for intertransverse process lumbar fusion.

Data on the role of platelet concentrate (PC) in spinal fusion are limited. Using the New Zealand white rabbit model, we compared fusion rates at L5-L6 using 2 different volumes (1.5 cm(3), 3.0 cm(3)) of iliac crest autograft with and without PC (4 groups total, 10 animals in each). PC was collected from donor rabbits and adjusted to a concentration of 1 x 10(6) platelets/mL. Bone growth and fusion were evaluated using biomechanical, radiographic, and histologic testing. At 1.5 cm(3), autograft alone had a 29% fusion rate, compared with autograft plus PC, which had a 57% fusion rate (P = .06). At 3.0 cm(3), the fusion rate approached 90% in both groups. Radiologic fusion had a 70% correlation with biomechanical test results. Huo/Friedlaender scores were 4.3 (SD, 2.9) for 1.5-cm(3) autograft alone; 5.0 (SD, 3.5) for 1.5-cm(3) autograft plus PC; 4.7 (SD, 2.5) for 3.0-cm(3) autograft alone; and 7.7 (SD, 0.6) for 3.0-cm(3) autograft plus PC. For 1.5-cm(3) autograft, a trend toward improvement in biomechanically defined fusion was found when PC was added, which suggests that, when the amount of bone graft is limited, PC may function as a graft extender in posterolateral fusion. At higher volumes of bone graft, no appreciable difference was noted between groups. Although radiography revealed fusion masses, the technique was not useful in identifying pseudarthrosis. On histologic analysis, adding PC seemed to result in more mature bone at both volumes, with the most mature bone in the group with 3.0-cm(3) autograft plus PC.

Biomechanics of two-level Charité artificial disc placement in comparison to fusion plus single-level disc placement combination.

BACKGROUND CONTEXT: Biomechanical studies of artificial discs that quantify parameters such as load sharing and stresses have been reported in literature for single-level disc placements. However, literature on the effects of using the Charité artificial disc (ChD) at two levels (2LChD) as compared with one-level fusion (using a cage [CG] and a pedicle screw system) plus one-level artificial disc combination (CGChD) is sparse. PURPOSE: To determine the effects of the 2LChD and CGChD across the implanted and adjacent segments. STUDY DESIGN: A finite element model of a L3-S1 segment was used to compare the biomechanical effects of the ChD placed at two lower levels (2LChD model) with L5-S1 fusion (using a CG and a pedicle screw system) plus L4-L5 level ChD placement combination (CGChD model). METHODS: We used our recently published and experimentally validated L3-S1 finite element model for the present study. The intact model was subjected to 400 N axial compression and 10.6 Nm of flexion/extension moments. The experimental constructs described above were then subjected to 400 N axial compression and a moment that produced overall motion equal to the intact model predictions (hybrid testing protocol). Resultant motion, loads across facets, and other parameters were analyzed at the experimental and adjacent levels. RESULTS: In flexion, the bending moments for the CGChD and 2LChD models were 15.4 Nm (fusion effect) and 7.3 Nm (increase in flexibility effect), respectively in comparison to 10.6 Nm for the intact model. The corresponding values in the extension mode were 11.2 Nm and 7.2 Nm. The predicted flexion rotations across the L5-S1 segment for the CGChD decreased by 76% (fusion effect), and increased at the L4-L5 and the L3-L4 levels by 68.5% and 28%, respectively. In the extension mode, motion across the L5-S1 segment decreased by 96.4% whereas it increased 74.6% and 18.2% across the L4-L5 and L3-L4 levels, respectively. For the 2LChD model, the flexion rotation across the L5-S1 segment increased by 28.2%. The motions across the L4-L5 and L3-L4 segments decreased by 12% and 24%, respectively. In extension, the corresponding changes were 10% increase, 10% increase, and 21% decrease at the L5-S1, L4-L5, and L3-L4 levels, respectively. The facet loads were in line with the changes in motion, except for the 2LChD case. CONCLUSIONS: The changes at L3-L4 level for both of the cases were of similar magnitude (approximately 25%), although in the CGChD model it increased and in the 2LChD model it decreased. The changes in motion at the L4-L5 level were large for the CGChD model as compared with the 2LChD model predictions (approximately 70% increase vs. 10% increase). It is difficult to speculate if an increase in motion across a segment, as compared with the intact case, is more harmful than a decrease in motion.

Effects of charité artificial disc on the implanted and adjacent spinal segments mechanics using a hybrid testing protocol.

STUDY DESIGN: Finite element model of L3-S1 segment and confirmatory cadaveric testing were used to investigate the biomechanical effects of a mobile core type artificial disc (Charité artificial disc; DePuy Spine, Raynham, MA) on the lumbar spine. OBJECTIVE: To determine the effects of the Charité artificial disc across the implanted and adjacent segments. SUMMARY OF BACKGROUND DATA: Biomechanical studies of artificial discs that quantify parameters, like the load sharing and stresses, are sparse in the literature, especially for mobile-type core artificial disc designs. In addition, there is no standard protocol for studying the adjacent segmental effects of such implants. METHODS: Human osteo-ligamentous spines (L1-S1) were tested before and after L5-S1 Charité artificial disc placement. The data were used to validate further an intact 3-dimensional (3-D) nonlinear L3-S1 finite element model. The model was subjected to 400-N axial compression and 10.6 Nm of flexion/extension pure moments (load control) or pure moments that produced the overall rotation of the L3-S1 Charité model equal to the intact case (hybrid approach). Resultant motion, load, and stress parameters were analyzed at the experimental and adjacent levels. RESULTS: Finite element model validation was achieved only with the load-controlled experiments. The hybrid approach, believed to be more clinically relevant, revealed that Charité artificial disc leads to motion increases in flexion (19%) and extension (44%) at the L5-S1 level. At the instrumented level, the decrease in the facet loads was less than at the adjacent levels; the corresponding decrease being 26% at L3-L4, 25% at L4-L5, and 13.4% at L5-S1 when compared to the intact. Intradiscal pressure changes in the L4-L5 and L3-L4 segments were minimal. Shear stresses at the Charité artificial disc-L5 endplate interface were higher than those at S1 interface. However, in the load control mode, the increase in facet loads in extension was approximately 14%, as compared to the intact case. CONCLUSIONS: The hybrid testing protocol is advocated because it better reproduces clinical observations in terms of motion following surgery, using pure moments. Using this approach, we found that the Charité artificial disc placement slightly increases motion at the implanted level, with a resultant increase in facet loading when compared to the adjacent segments, while the motions and loads decrease at the adjacent levels. However, in the load control mode that we believe is not that clinically relevant, there was a large increase in motion and a corresponding increase in facet loads, as compared to the intact.

The 2002 Marshall Urist Young Investigator Award Paper. Lumbar arthrodesis gene expression: a comparison of autograft with osteogenic protein-1.

Data from animals have revealed that osteogenic protein-1 induces solid intertransverse process fusion more reliably than autograft, and has motivated the question: What is the difference in the fusion bed environment engendered by the addition of osteogenic protein-1? To address this question, an established New Zealand White rabbit model of spinal arthrodesis was used to evaluate the effect of iliac crest autograft, and alternatively osteogenic protein-1, on cytokine gene expression in the developing spinal fusion mass. The autograft group and the osteogenic protein-1 group had a similar pattern of gene expression for most of the cytokines investigated, highlighting the finding that the application of one bone morphogenetic protein to the fusion bed results in nearly the same gene expression as that resulting from application of autologous bone. Some differences in cytokine expression were observed at the fusion bed with the addition of osteogenic protein-1. The increased level of expression of particular osteogenic, chondrogenic, and angiogenic growth factors at the later stages of fusion may be responsible for the improved rate of solid fusion with osteogenic protein-1 as compared with autograft alone. Sequences for bone morphogenetic protein-5 and bone morphogenetic protein-7 were determined, and their respective expression in the developing spinal fusion mass was observed for the first time.

Comparison of posterolateral lumbar fusion rates of Grafton Putty and OP-1 Putty in an athymic rat model.

STUDY DESIGN: Posterolateral lumbar spine fusions in athymic rats. OBJECTIVES: To compare spine fusion rates of two different osteoinductive products. SUMMARY OF BACKGROUND DATA: Many osteoinductive bone graft alternatives are available. Grafton (a demineralized bone matrix [DBM]) and Osteogenic Protein-1 (OP-1, an individual recombinant bone morphogenetic protein) are two such alternatives. The relative efficacy of products from these two classes has not been previously studied. The athymic rat spine fusion model has been validated and demonstrated useful to minimize inflammatory responses to xenogeneic or differentially expressed proteins such as those presented by DBMs of human etiology. METHODS: Single-level intertransverse process fusions were performed in 60 athymic nude rats with 2 cc/kg of Grafton or OP-1 Putty. Half of each study group was killed at 3 weeks and half at 6 weeks. Fusion masses were assessed by radiography, manual palpation, and histology. RESULTS: At 3 weeks, manual palpation revealed a 13% fusion rate with Grafton and a 100% fusion rate with OP-1 (P = 0.0001). At 6 weeks, manual palpation revealed a 39% fusion rate of with Grafton and a 100% fusion rate with OP-1 (P = 0.0007). Similar fusion rates were found by histology at 3 and 6 weeks. Of note, one or two adjacent levels were fused in all of the OP-1 animals and none of the Grafton animals. CONCLUSIONS: Significant differences between the ability of Grafton and OP-1 to induce bone formation in an athymic rat posterolateral lumbar spine fusion model were found.

Bone grafting alternatives in spinal surgery.

BACKGROUND CONTEXT: Bone grafting is used to augment bone healing and provide stability after spinal surgery. Autologous bone graft is limited in quantity and unfortunately associated with increased surgical time and donor-site morbidity. Alternatives to bone grafting in spinal surgery include the use of allografts, osteoinductive growth factors such as bone morphogenetic proteins and various synthetic osteoconductive carriers. PURPOSE: Recent research has provided insight into methods that may modulate the bone healing process at the cellular level in addition to reversing the effects of symptomatic disc degeneration, which is a potentially disabling condition, managed frequently with various fusion procedures. With many adjuncts and alternatives available for use in spinal surgery, a concise review of the current bone grafting alternatives in spinal surgery is necessary. STUDY DESIGN/SETTING: A systematic review of the contemporary English literature on bone grafting in spinal surgery, including abstract information presented at national meetings. METHODS: Bone grafting alternatives were reviewed as to their efficacy in extending or replacing autologous bone graft sources in spinal applications. RESULTS: Alternatives to autologous bone graft include allograft bone, demineralized bone matrix, recombinant growth factors and synthetic implants. Each of these alternatives could possibly be combined with autologous bone marrow or various growth factors. Although none of the presently available substitutes provides all three of the fundamental properties of autograft bone (osteogenicity, osteoconductivity and osteoinductivity), there are a number of situations in which they have proven clinically useful. CONCLUSIONS: Alternatives to autogenous bone grafting find their greatest appeal when autograft bone is limited in supply or when acceptable rates of fusion may be achieved with these substitutes (or extenders) despite the absence of one or more of the properties of autologous bone graft. In these clinical situations, the morbidity of autograft harvest is reasonably avoided. Future research may discover that combinations of materials may cumulatively result in the expression of osteogenesis, osteoinductivity and osteoconductivity found in autogenous sources.