Comparative Efficacy of Commonly Available Human Bone Graft Substitutes as Tested for Posterolateral Fusion in an Athymic Rat Model.

BACKGROUND: Insufficient data exist on bone graft substitute materials efficacy; two thirds lack any clinical data.1,2 This prospective animal study identified efficacy differences among commercially available materials of several classes. METHODS: Historically validated muscle pouch osteoinduction study (OIS) and posterolateral fusion (PLF) were performed in an athymic rat model. Grafting material products implanted were demineralized bone matrix (DBM)-based allografts (Accell EVO3, DBX Mix, DBX Strip, Grafton Crunch, Grafton Flex, Grafton Matrix, Grafton Putty, Magnifuse, and Progenix Plus), allografts (OsteoSponge, MinerOss), cellular allograft (Osteocel Plus), ceramics (Mozaik Strip), or activated ceramics (Actifuse ABX Putty, Vitoss BA). After 4 weeks, OIS specimens were evaluated ex vivo by histologic osteoinductivity. After 8 weeks, PLF ex vivo specimens were evaluated for fusion by manual palpation (FMP), radiography (FXR), and histology (FHISTO). RESULTS: OIS: No materials exhibited a rejection reaction on histology. All DBM-based materials exhibited osteoinductive potential as new bone formation at > 88% of implanted sites. One plain allograft (OsteoSponge) formed bone at 25% of sites. No bone formed for one ceramic (Mozaik Strip), three activated ceramics (Actifuse ABX Putty), or one cellular allograft, regardless of human bone marrow aspirate (hBMA) when added. PLF: Among the 10 DBMs, 6 had FMP of 100% (Accell EVO3, DBX Mix, DBX Strip, Grafton Flex, Grafton Putty, Magnifuse), 2 had FMP of 94% (Grafton Crunch, Grafton Matrix), and 2 conditions had FMP of 0% (Progenix Plus, Progenix Plus + athymic rat iliac crest bone graft [arICBG]). Ceramics (Mozaik Strip), activated ceramics (Actifuse ABX Putty, Vitoss BA), plain allograft (OsteoSponge, MinerOss (PLF study), and cellular allograft (Osteocel Plus) demonstrated 0% FMP. ArICBG demonstrated 13% FMP. CONCLUSIONS: Eight DBM-based materials (Accell EVO3, DBX Mix, DBX Strip, Grafton Crunch, Grafton Flex, Grafton Matrix, Grafton Putty, Magnifuse) demonstrated excellent (> 90% FMP) efficacy in promoting fusion via bone healing. Two DBM conditions (Progenix Plus, Progenix Plus + arICBG) showed no manual palpation fusion (FMP). Systematically, over the 2 studies (OIS and PLF), cellular (Osteocel Plus), plain allografts (OsteoSponge, MinerOss; PLF study), ceramic (Mozaik Strip), and activated ceramics (Actifuse ABX Putty, Vitoss BA) demonstrated poor FMP efficacy (< 10%). CLINICAL RELEVANCE: When selecting DBMs, clinicians must be cognizant of variability in DBM efficacy by product and lot. While theoretically osteoinductive, cellular allograft and activated ceramics yielded poor in vivo efficacy. Whole allograft and ceramics may provide osteoconductive scaffolding for mixed-material grafting; however, surgeons should be cautious in using them alone. Direct clinical data are needed to establish efficacy for any bone graft substitute.

Correcting in situ chlorophyll fluorescence time-series observations for nonphotochemical quenching and tidal variability reveals nonconservative phytoplankton variability in coastal waters.

Chlorophyll fluorometry is one of the most commonly implemented approaches for estimating phytoplankton biomass in situ, despite documented sources of natural variability and instrumental uncertainty in the relationship between in vivo fluorescence and chlorophyll concentration. A number of strategies are employed to minimize errors and quantify natural variability in this relationship in the open ocean. However, the assumptions underlying these approaches are unsupported in coastal waters due to the short temporal and small spatial scales of variability, as well as the optical complexity. The largest source of variability in the in situ chlorophyll fluorometric signal is nonphotochemical quenching (NPQ). Typically, unquenched nighttime observations are interpolated over the quenched daytime interval, but this assumes a spatial homogeneity not found in tidally impacted coastal waters. Here, we present a model that provides a tidally resolved correction for NPQ in moored chlorophyll fluorescence measurements. The output of the model is a time series of unquenched chlorophyll fluorescence in tidal endmembers (high and low tide extremes), and thus a time series of phytoplankton biomass growth and loss in these endmember populations. Comparison between modeled and measured unquenched time series yields quantification of nonconservative variations in phytoplankton biomass. Tidally modeled interpolation between these endmember time series yields a highly resolved time series of unquenched daytime chlorophyll fluorescence values at the location of the moored sensor. Such data sets provide a critical opportunity for validating the satellite remotely sensed ocean color chlorophyll concentration data product in coastal waters.

Effect of Oxy133, an osteogenic oxysterol, on new bone formation in rat two-level posterolateral fusion model.

PURPOSE: The aim of our study was to determine the effect of Oxy133 and rhBMP2 on fusion rates and new bone formation in a rat posterolateral fusion (PLF) model. Furthermore, we examined whether Oxy133 could inhibit the adipogenesis that is often present in rhBMP2-induced fusions. METHODS: Sixty-four male Lewis rats underwent two levels PLF (L3-L5). All animals were randomly divided into eight groups based on the test compound that they received: control (DMSO), low-dose rhBMP2 (0.5 µg), high-dose rhBMP2 (5 µg), low-dose Oxy133 (5 mg), high-dose Oxy133 (20 mg), low rhBMP2 + high Oxy133, high rhBMP2 + high Oxy133, and low rhBMP2 + low Oxy133. Fusion rates were assessed 8 weeks after surgery with manual palpation and plain radiographs. Bone parameters were measured using microCT. Histology was used to evaluate adipogenesis. RESULTS: No fusion was observed in the control group. Based on the manual palpation, 100% fusion was observed in all other groups except in the low-dose rhBMP2 group (69%). At 8 weeks based on X-rays, 100% fusion was observed in the following groups: high-dose rhBMP2, low-dose Oxy133, and low rhBMP2 + low Oxy133. In the other groups, the fusion rates were between 95 and 97%, except for the low rhBMP2 group (72%). We observed similar values in BV/TV ratio at L3-4 when Oxy133 groups were compared to rhBMP2 groups alone (44.62% in high-dose Oxy133 vs. 41.47% in high-dose rhBMP2 and 47.18% in low-dose Oxy133 vs. 54.98% in low-dose rhBMP2). Trabecular thickness was slightly lower in Oxy133 groups compared to rhBMP2 when comparing low- and high-dose groups from each group (118.44 µm for high-dose Oxy133 vs. 122.39 µm for high-dose rhBMP2 and 123.51 µm for low-dose Oxy133 vs. 135.74 µm for low-dose rhBMP2). At the same time, trabecular separation was lower in Oxy133 groups compared to rhBMP2 groups. Similar trends in bone parameters were observed at the L4-5 levels. Fusion masses with low- and high-dose Oxy133 had significantly less adipocytes than rhBMP2 groups that showed robust adipocyte formation. CONCLUSION: In our study, both low-dose and high-dose Oxy133 produced solid fusions with bone densities similar or higher than in the BMP2 groups. High-dose Oxy133 group had significantly less adipocytes than high- or low-dose rhBMP2 groups. Furthermore, high-dose Oxy133 was able to significantly inhibit high-dose BMP2-induced adipogenesis when combined together. Consistent with the previous reports, our preliminary findings suggest that Oxy133 has a significant potential as an alternative to rhBMP2 in spine fusion.

Effects of particle size and porosity on in vivo remodeling of settable allograft bone/polymer composites.

Established clinical approaches to treat bone voids include the implantation of autograft or allograft bone, ceramics, and other bone void fillers (BVFs). Composites prepared from lysine-derived polyurethanes and allograft bone can be injected as a reactive liquid and set to yield BVFs with mechanical strength comparable to trabecular bone. In this study, we investigated the effects of porosity, allograft particle size, and matrix mineralization on remodeling of injectable and settable allograft/polymer composites in a rabbit femoral condyle plug defect model. Both low viscosity and high viscosity grafts incorporating small (<105 µm) particles only partially healed at 12 weeks, and the addition of 10% demineralized bone matrix did not enhance healing. In contrast, composite grafts with large (105-500 µm) allograft particles healed at 12 weeks postimplantation, as evidenced by radial µCT and histomorphometric analysis. This study highlights particle size and surface connectivity as influential parameters regulating the remodeling of composite bone scaffolds.

Histological features of the degenerating intervertebral disc in a goat disc-injury model.

STUDY DESIGN: An in vivo study to develop a goat large-animal model for intervertebral disc (IVD) degeneration. OBJECTIVE: To determine an optimal method for inducing goat IVD degeneration suitable for testing disc regeneration therapies. SUMMARY OF BACKGROUND DATA: Although rodent, rabbit, and other small animal studies are useful, the narrow dimensions of IVDs in these species limit studies requiring injection of a relevant volume of therapeutics or implantation of engineered tissue constructs. For this study, the goat was selected because the size and shape of their IVDs are comparable with those of adult humans. METHODS: A minimally invasive approach that did not cause significant morbidity or mortality to adult goats (n = 6) was used. Under fluoroscopic guidance, goat lumbar IVDs were injured with a 4.5-mm drill bit or #15 or #10 surgical blades. Two months postinjury, the goats were killed and their IVDs with adjacent end plates were isolated, decalcified, and stained. RESULTS.: A numerical histologic scale to categorize the degree of goat IVD degeneration was developed on the basis of the histologic features of rabbit IVDs previously described by Masuda et al, goat IVDs described by Hoogendoorn et al, and human IVDs described by Boos et al. The interrater agreement of our scoring system was assessed (weighted kappa value = 0.6646). Mann-Whitney U tests were used to compare the injured IVDs with uninjured control. A 4.5-mm drill bit inserted to a 15-mm depth resulted in a significantly higher histologic score than uninjured controls (P = 0.01). Injury with a #15 or #10 blade did not result in increased histologic scores compared with uninjured controls. CONCLUSION: A comparison of the various injuries inflicted showed that the use of a 4.5-mm drill bit resulted in the most significant histologic changes.

Evaluation of mesenchymal stem cells following implantation in alveolar sockets: a canine safety study.

PURPOSE: The overall goal of this project was to evaluate culture-expanded bone-marrow-derived mesenchymal stem cells (MSCs) for alveolar bone repair in terms of safety and potential efficacy. MATERIALS AND METHODS: MSCs isolated from bone marrow aspirations were culture-expanded and cryopreserved. Thawed cells were incubated with 3.2 x 5-mm hydroxyapatite/tricalcium phosphate (HA/TCP) cylinders in a closed system containing 5 x 10(7) cells/mL. Cells alone, cell-free constructs, or cell-loaded constructs were rinsed in saline and implanted in extraction sockets in the mandibular second and fourth premolar sites of 14 beagle dogs. Acute reactions were evaluated histologically after 7 or 21 days, and bone formation was examined after 49 days. RESULTS: Neither implanted MSC-related inflammation nor ectopic osteogenesis was observed. At 7 and 21 days, dil-labeled canine MSCs were found in more than 80% of the implant sites. Few canine MSCs were found in neighboring tissue. Mild inflammation present at 7 days diminished by 21 days. After 49 days, measured bone formation was 34%, 25%, and 35% for cell-loaded, cell-free, and untreated sockets, respectively (P < .05). At 21 days, bone formation was evident in all sites. Wound dehiscence was a complication associated with cell exclusionary membranes and resulted in local inflammation. DISCUSSION: The extraction model indicates the safety of MSCs implanted adherent to HA/TCP. Local bone repair occurred in the absence of nonspecific differentiation or migration with distant osteogenesis. CONCLUSIONS: An alveolar socket model may be an appropriate model for initial clinical investigation of MSC-mediated bone repair.