Bone Morphogenetic Proteins, Carriers, and Animal Models in the Development of Novel Bone Regenerative Therapies

Bone morphogenetic proteins (BMPs) possess a unique ability to induce new bone formation. Numerous preclinical studies have been conducted to develop novel, BMP-based osteoinductive devices for the management of segmental bone defects and posterolateral spinal fusion (PLF). In these studies, BMPs were combined with a broad range of carriers (natural and synthetic polymers, inorganic materials, and their combinations) and tested in various models in mice, rats, rabbits, dogs, sheep, and non-human primates. In this review, we summarized bone regeneration strategies and animal models used for the initial, intermediate, and advanced evaluation of promising therapeutical solutions for new bone formation and repair. Moreover, in this review, we discuss basic aspects to be considered when planning animal experiments, including anatomical characteristics of the species used, appropriate BMP dosing, duration of the observation period, and sample size.

Preclinical studies on pleiotropic functions of erythropoietin on bone healing

Erythropoietin (ЕPО) is a glycoprotein hormone, mainly known for its haemopoietic function. For orthopaedics, its pleiotropic effects – osteogenic and angiogenic potential, are of primary interest. The exact mechanism of EPO action is still unclear. The effects of EPO on bone healing were investigated through experiments with rats, mice, rabbits and pigs. Each of used models for experimental bone defects (calvarial models, long bone segmental defects, posterolateral spinal fusion and corticosteroid-induced femoral head osteonecrosis) has specific advantages and flaws. Obtaining specific and correct results is largely dependent on the used model. The brief evaluation of models could serve for standardisation of preclinical studies on bone regeneration.

Long-term (> 10 years) clinical outcomes of instrumented posterolateral fusion for spondylolisthesis

Purpose Despite the rapid increase in instrumented spinal fusions for a variety of indications, most studies focus on short-term fusion rates. Long-term clinical outcomes are still scarce and inconclusive. This study investigated clinical outcomes > 10 years after single-level instrumented posterolateral spinal fusion for lumbar degenerative or isthmic spondylolisthesis with neurological symptoms. Methods Cross-sectional long-term follow-up among the Dutch participants of an international multicenter randomized controlled trial comparing osteogenic protein-1 with autograft. Clinical outcomes were assessed using the Oswestry Disability Index (ODI), EQ-5D-3L and visual analogue scale (VAS) for leg and back pain, as well as questions on satisfaction with treatment and additional surgery. Results The follow-up rate was 73% (41 patients). At mean 11.8 (range 10.1–13.7) years after surgery, a non-significant deterioration of clinical outcomes compared to 1-year follow-up was observed. The mean ODI was 20 ± 19, mean EQ-5D-3L index score 0.784 ± 0.251 and mean VAS for leg and back pain, respectively, 34 ± 33 and 31 ± 28. Multiple regression showed that diagnosis (degenerative vs. isthmic spondylolisthesis), graft type (OP-1 vs. autograft) and 1-year fusion status (fusion vs. no fusion) were not predictive for the ODI at long-term follow-up (p = 0.389). Satisfaction with treatment was excellent and over 70% of the patients reported lasting improvement in back and/or leg pain. No revision surgeries for non-union were reported. Conclusion This study showed favourable clinical outcomes > 10 years after instrumented posterolateral spinal fusion and supports spondylolisthesis with neurological symptoms as indication for fusion surgery.

Preparation of Hydroxyapatite/Silk Fibroin Composite and Its Adoption in Posterolateral Spinal Fusion of Rats

Hydroxyapatite/silk fibroin (HAp/SF) composite was prepared and applied to the posterolateral spinal fusion model in rats to observe the effect of bone fusion. Method: Calcium chloride, diammonium phosphate, SF, and polyvinyl alcohol were used as raw materials, HAp/SF composites were prepared by chemical precipitation. The microstructure of the composite, crystal phase composition, and chemical structure were analyzed by the scanning electron microscope (SEM) and X-ray diffraction (XRD), and fourier transform infrared spectrometer (FTIR Spectrometer). Through the cultivation of osteoblasts MC3T3-E1 in vitro, the adhesion and proliferation (A&P) of cells on the face of materials were investigated. Thereby, the biocompatibility of the material was characterized. HAp/SF material was applied to the rat posterolateral spinal fusion model. The osteogenesis and spinal fusion were evaluated by the imaging observation, histological observation and manual palpation. The results showed that the rod-shaped HAp with uniform size and high purity was obtained, with a diameter of 20∼40 nm and a length of 200∼500 nm, similar to the apatite crystal in natural bone tissue (BT). In composite materials, a spatial network structure was formed by the interweaving of the SF fibers, and HAp was deposited on the face of the SF or in the middle of its network structure. In the obtained HAp/SF materials, the calcium ions of HAp and the carbonyl groups of SF were used to form thermally stable complexes through strong chemical bonds. Besides, SF was a template for the directional induction of HAp crystal growth, and the growth of HAp crystal along the C axis was regulated by SF. The growth direction was parallel to the long axis of SF fibers, and was consistent with the structure of apatite crystals deposited on the face of collagen fibers in natural BT. The results of cell culture in vitro showed that: after comparison with the control group (CG) with pure Hap, the adhesion ability of cells to HAp/SF material was significantly improved. The proliferation capacity of bone artificial bone (BAM) material and HAp/SF material was also significantly improved. The nuclear and skeletal staining results of MC3T3-E1 cells on the face of three groups of materials (HAp, BAM and HAp/SF) were combined, and the results also indicated that BAM and HAp/SF materials had good ability to promote cell A&P. The results of posterolateral spinal fusion in rats showed that HAp/SF materials group palpated the posterolateral spine for fusion. The formation of new BT on the posterolateral side of the spine was revealed by the Micro-computed tomography (Micro-CT) examination. In conclusion, HAp/SF composite had good osteoblastic compatibility and can achieve good spinal fusion effect.

Fusion and Healing Prediction in Posterolateral Spinal Fusion Using 18F-Sodium Fluoride-PET/CT

This study measures the total graft of 18F-sodium fluoride (NaF) uptake in non-instrumented posterolateral lumbar fusion (niPLF) patients one month after surgery and correlates it with the difference in the clinical findings between the baseline and one year after surgery. The walking distance (WLK-D), visual analog scale of back pain (VAS-B), VAS score of leg pain (VAS-L), tandem test (TAN), Oswestry Disability Index questionnaire (ODI), and European Quality of Life-5 Dimensions questionnaire (EQ-5D) were assessed before surgery and one year after. The graft NaF uptake was analyzed quantitatively with a fixed threshold algorithm resulting in the total graft uptake (SUVtotal) and partial volume corrected SUVtotal (cSUVtotal). Only 4 out of 18 patients experienced fusion; they had an insignificantly lower median total graft uptakes, i.e., 1178 SUVtotal vs. 1224 SUVtotal (p = 0.73) and 1282 cSUVtotal vs. 1231 cSUVtotal (p = 0.35), respectively. Similarly, fused patients experienced insignificantly larger pain decreases, i.e., median VAS-B 4.3 vs. 3.8 (p = 0.92) and VAS-L −6.4 vs. −4.4 (p = 0.2). We found an insignificant trend for a lower NaF uptake and less pain in fused patients. The NaF uptake did not correlate with the chronological change in the clinical parameters.