Hydroxyapatite/Calcium Carbonate (HA/CC) vs. Plaster of Paris: A Histomorphometric and Radiographic Study in a Rabbit Tibial Defect Model

The search for an ideal bone substitute is ongoing. Multiple osteoconductive bone substitutes are available today. Plaster of Paris (POP) (calcium sulfate) has been used for more than 100 years for treatment of skeletal defects. This implant is compared to a new material, hydroxyapatite/calcium carbonate (HA/CC), in a rabbit tibia model. HA/CC is made from partial conversion of coralline calcium carbonate to hydroxyapatite and has an outer hydroxyapatite layer and an inner calcium carbonate core, a combination that leads to faster resorption than that of pure hydroxyapatite. This study compares the histomorphometric and radiographic properties of POP and HA/CC in a rabbit tibial defect. Both implants preferentially restore bone to the cortex relative to the canal. Plaster of Paris was fully resorbed by 6 weeks both radiographically and histometrically and HA/CC was substantially resorbed by 42 weeks. No significant difference was noted in volume fraction of bone between the two implants at 42 weeks postimplantation. Hydroxyapatite/calcium carbonate is a biocompatible bone graft substitute with a rate of resorption significantly slower than plaster of Paris.     

Repair of Osteochondral Defects in a Rabbit Model Using a Porous Hydroxyapatite Collagen Composite Impregnated With Bone Morphogenetic Protein‐2

Articular cartilage has a limited capacity for spontaneous repair, and an effective method to repair damaged articular cartilage has not yet been established. The purpose of this study was to evaluate the effect of transplantation of porous hydroxyapatite collagen (HAp/Col) impregnated with bone morphogenetic protein‐2 (BMP‐2). To evaluate the characteristics of porous HAp/Col as a drug delivery carrier of recombinant human BMP‐2 (rhBMP‐2), the rhBMP‐2 adsorption capacity and release kinetics of porous HAp/Col were analyzed. Porous HAp/Col impregnated with different amounts of rhBMP‐2 (0, 5, and 25 μg) was implanted into osteochondral defects generated in the patellar groove of Japanese white rabbits to evaluate the effect on osteochondral defect regeneration. At 3, 6, 12, and 24 weeks after operation, samples were harvested and subjected to micro‐computed tomography analysis and histological evaluation of articular cartilage and subchondral bone repair. The adsorption capacity was 329.4 μg of rhBMP‐2 per cm³ of porous HAp/Col. Although 36% of rhBMP‐2 was released within 24 h, more than 50% of the rhBMP‐2 was retained in the porous HAp/Col through the course of the experiment. Defects treated with 5 μg of rhBMP‐2 showed the most extensive subchondral bone repair and the highest histological regeneration score, and differences against the untreated defect group were significant. The histological regeneration score of defects treated with 25 μg of rhBMP‐2 increased up to 6 weeks after implantation, but then decreased. Porous HAp/Col, therefore, is an appropriate carrier for rhBMP‐2. Implantation of porous HAp/Col impregnated with rhBMP‐2 is effective for rigid subchondral bone repair, which is important for the repair of the smooth articular surface.     

富血小板血浆／人工骨修复兔桡骨骨缺损的实验研究

目的探讨富血小板血浆和羟基磷灰石生物陶瓷复合物修复兔桡骨节段性骨缺损的疗效。方法新西兰大白兔12只,切除兔双前肢桡骨中下段1 cm连同骨膜的骨质造成骨缺损,选择左侧前肢为实验侧,右侧前肢为对照侧。实验侧缺损区植入富血小板血浆加羟基磷灰石生物陶瓷,对照侧缺损区单纯植入羟基磷灰石生物陶瓷。术后第2、4、8和12周分别处死3只实验动物,进行大体观察、X线片、组织学、新生骨面积图像分析和透射电镜等观察两侧桡骨愈合情况。结果术后所有动物无感染、死亡,植入物无脱落。大体标本和X线片显示：术后2周实验侧和对照侧在人工骨与宿主骨交界处均有较多肉芽组织,实验侧略多。第4、8周实验侧人工骨表面及孔隙被新生骨组织包裹填充,人工骨与自体骨吻合好;对照侧骨痂主要限于人工骨两端,与对侧比较相对较幼稚。第12周,实验侧骨缺损修复完全,人工骨表面被皮质骨完全包裹;对照侧在人工骨两端区域有板层骨形成,表面未见连续性骨痂。组织学和透射电镜观察显示：随着术后时间的延长,实验侧骨细胞生长明显优于对照侧,有统计学差异。结论富血小板血浆加人工骨复合对管状骨缺损的修复有明显的加速愈合功能。     

Comparative Study on Osteoconductivity by Synthetic Octacalcium Phosphate and Sintered Hydroxyapatite in Rabbit Bone Marrow

Octacalcium phosphate (OCP) is thought to be a precursor of the mineral crystals in biological apatite. Synthetic OCP has been shown to be converted into an apatite structure when implanted in murine calvarial bone, to enhance bone regeneration more than synthetic hydroxyapatite (HA), and to degrade faster than biodegradable β-tricalcium phosphate. This study was designed to investigate whether OCP implantation enhances the formation and resorption of new bone (remodeling) concomitant with OCP degradation when implanted intramedullary in a rabbit femur for 12 weeks, compared to sintered HA ceramic. Histological and histomorphometric analyses using undecalcified specimens showed that the area of bone apposition was significantly higher on OCP than on HA between 2 and 3 weeks, whereas it subsequently became smaller on OCP than on HA. The area attacked by multinucleated giant cells, including tartrate-resistant acid phosphatase (TRAP)-positive cells, was significantly higher for OCP than for HA at 8 weeks. Radiography revealed resorption of OCP but not of HA. The results disclose some osteoconductive characteristics of synthetic OCP in the bone marrow space: (1) enhancement of bone regeneration at the initial bone apposition stage and (2) stimulation of resorption of the newly formed bone coupled with OCP biodegradation mediated by TRAP-positive osteoclast-like cells. These results suggest that synthetic OCP would be a more useful bone substitute than HA in implant applications where rapid bone formation and concomitant implant resorption are important considerations.     

外固定架及重组合异种骨植骨治疗胫骨骨缺损与骨不连

目的：探讨外固定架和重组合异种骨(RBX)植骨治疗胫骨骨缺损、伴肢体短缩的胫骨骨不连及先天性胫骨假关节的临床疗效。方法：应用外固定架共治疗胫骨骨缺损、伴肢体短缩性骨不连及先天性胫骨假关节20例。胫骨断端清理后短缩长度2—9cm，平均4．8cm。断端应用RBX植骨12例。结果：20例病人随访8个月-7年，平均4年3个月，患肢功能恢复满意。12例应用RBX植骨治疗骨不连的平均愈合时间4．8个月。结论：本手术方法治疗胫骨骨缺损、伴肢体短缩的胫骨骨不连及先天性胫骨假关节，创伤小、操作简单，肢体功能恢复满意；RBX植骨治疗骨不连，安全，对促进骨愈合疗效可靠。     

Comparison of Hydroxyapatite Granules to Autogenous Bone Graft in Fusion Cages in a Goat Model

Background

With the increased use of fusion cages to achieve lumbar intervertebral fusion, the question arises as to the potential for bone ingrowth from the host bone through the entire cage. Is it even necessary to have an autogenous graft to achieve total bone incorporation?

Methods

Nine adult male goats had fusion cages implanted into three vertebral bodies. The design was Surgical Dynamics/Ray Fusion Cage, measuring 21 mm × 14 mm. In each animal, one fusion cage was filled with autogenous graft, one with hydroxyapatite, porous granules, and the other with nonporous granules. Amount of new bone formation was determined by backscatter electron microscopy at 3 months post implantation in all animals.

Results

The histologic section shows that there was total incorporation in all specimens at 3 months. There was slightly more new bone (43%) with the nonporous granules compared with the porous granules (35%). The amount of residual void space was about the same in all specimens, indicating that the amount of new bone formation was similar and not statistically different in cages filled with hydroxyapatite granules versus granules of autogenous bone.

Conclusion

This study confirms that total incorporation by ingrowth of new bone can be expected in fusion cages. The amount of ingrowth is about the same for autogenous graft versus hydroxyapatite granules. Apparently, it is not necessary to use bone graft to achieve successful bone incorporation if an acceptable biocompatable lattice, such as hydroxyapatite granules, is used.     

Effect of Electrical Polarization of Hydroxyapatite Ceramics on New Bone Formation

Large surface charges can be induced on hydroxyapatite (HAp) ceramics by proton transport polarization, but this does not affect β-tricalcium phosphate (TCP) because of its low polarizability. We wished to examine differences in osteogenic cell activity and new bone growth between positively or negatively surface-charged HAp and HAp/TCP plates using a calvarial bone defect model. In the first group of rats, test pieces were placed with their positively charged surfaces face down on the dura mater. In the second group, test pieces were placed with their negatively charged surfaces face down on the dura mater. A third group received noncharged test pieces. Histological examination, including enzymatic staining for osteoblasts and osteoclasts, was carried out. While no bone formation was observed at the pericranium, direct bone formation on the cranial bone debris and new bone growth expanded from the margins of the sites of injury to bridge across both the positively and negatively charged surfaces of HAp and HAp/TCP plates occurred. Electrical polarization of implanted plates, including positive charge, led to enhanced osteoblast activity, though decreased osteoclast activity was seen on the positively charged plate surface. Thus, polarization of HAp ceramics may modulate new bone formation and resorption.     

Low-intensity Pulsed Ultrasound Enhances Bone Repair in a Rabbit Model of Steroid-associated Osteonecrosis

Background

Steroids are a leading cause of femoral head osteonecrosis. Currently there are no medications available to prevent and/or treat steroid-associated osteonecrosis. Low-intensity pulsed ultrasound (LIPUS) was approved by the FDA for treating delayed union of bone fractures. Some studies have reported that LIPUS can enhance bone formation and local blood flow in an animal model of fracture healing. However, whether the effect of osteogenesis and neovascularization by LIPUS can enhance the repair progress in steroid-associated osteonecrosis is unknown.

Questions/purposes

We hypothesized that LIPUS may facilitate osteogenesis and neovascularization in the reparative processes of steroid-associated osteonecrosis. Using a rabbit animal model, we asked whether LIPUS affects (1) bone strength and trabecular architecture; (2) blood vessel number and diameter; and (3) BMP-2 and VEGF expression.

Methods

Bilateral femoral head necrosis was induced by lipopolysaccharide and methylprednisolone in 24 rabbits. The left femoral heads of rabbits received LIPUS therapy (200 mW/cm²) for 20 minutes daily and were classified as the LIPUS group. The right femoral heads of the same rabbits did not receive therapy and were classified as the control group. All rabbits were euthanized 12 weeks after LIPUS therapy. Micro-CT, biomechanical testing, histologic evaluation, immunohistochemistry, quantitative real-time PCR, and Western blot were used for examination of the effects of LIPUS.

Results

Twelve weeks after LIPUS treatment, the loading strength in the control group was 355 ± 38 N (95% CI, 315–394 N), which was lower (p = 0.028) than that in the LIPUS group (441 ± 78 N; 95% CI, 359–524 N). The bone tissue volume density (bone volume/total volume) in the LIPUS group (49.29% ± 12.37%; 95 % CI, 36.31%–62.27%) was higher (p = 0.022) than that in the control group (37.93% ± 8.37%; 95 % CI, 29.15%–46.72%). The percentage of empty osteocyte lacunae in the LIPUS group (17% ± 4%; 95% CI, 15%–20%) was lower (p = 0.002) than that in the control group (26% ± 9%; 95% CI, 21%–32%). The mineral apposition rate (μm/day) in the LIPUS group (2.3 ± 0.8 μm/day; 95% CI, 1.8 2.8 μm/day) was higher (p = 0.001) than that in the control group (1.6 ± 0.3 μm/day; 95% CL, 1.4–1.8 μm/day). The number of blood vessels in the LIPUS group (7.8 ± 3.6/mm²; 95% CI, 5.5–10.1 mm²) was greater (p = 0.025) than the number in the control group (5.7 ± 2.6/mm²; 95% CI, 4.0–7.3 mm²). Messenger RNA (mRNA) and protein expression of BMP-2 in the LIPUS group (75 ± 7, 95% CI, 70–79; and 30 ± 3, 95% CI, 28–31) were higher (both p < 0.001) than those in the control groups (46 ± 5, 95% CI, 43–49; and 15 ± 2, 95% CI, 14–16). However, there were no differences (p = 0.114 and 0.124) in mRNA and protein expression of vascular endothelial growth factor between the control (26 ± 3, 95% CI, 24–28; and 22 ± 6, 95% CI, 18–26) and LIPUS groups (28 ± 2, 95% CI, 26–29; and 23 ± 6, 95% CI, 19–27).

Conclusions

The results of this study indicate that LIPUS promotes osteogenesis and neovascularization, thus promoting bone repair in this steroid-associated osteonecrosis model.

Clinical Relevance

LIPUS may be a promising modality for the treatment of early-stage steroid-associated osteonecrosis. Further research, including clinical trials to determine whether LIPUS has a therapeutic effect on patients with early-onset steroid-associated osteonecrosis may be warranted.     

不同颗粒大小β-TCP植骨材料对于修复腔隙性骨缺损的影响

目的探讨不同颗粒大小的β-TCP植骨材料对腔隙性骨缺损骨修复的影响。方法将多孔β-TCP制备成粒径不同的三种形态:大颗粒组(A组),颗粒直径3.5~4.5 mm,小颗粒组(B组),颗粒直径1.5～2.5 mm,整块植骨组(C组),植骨块为圆柱体,直径6mm,高7 mm,并以无填充组(D组)为空白对照,随机植入到60只新西兰大白兔胫骨近端圆柱状骨缺损(直径7 mm,深6 mm)处,于术后第2、4和8周取材,进行影像学、显微CT定量分析(micro-CT)、组织学检测分析,观察骨缺损区β-TCP降解和新骨形成情况,并进行统计学分析。结果影像学、显微CT及组织学检结果显示:在2周时,A组在新生骨生成量方面仅仅在2周时少于C组,多于其他两组;4周时A组和C组一致,多于其他两组;8周时A组为最多的一组。在降解速率上,三组植入物组2周、4周都趋于平缓,B组在8周时显示降解速率增快。结论多孔β-TCP的颗粒大小对兔长骨腔隙性骨缺损的修复产生影响,适当调整植骨粒径将有利于新骨的形成。     

Negative Effect of Rapidly Resorbing Properties of Bioactive Glass-Ceramics as Bone Graft Substitute in a Rabbit Lumbar Fusion Model

Background

Bioactive glass-ceramics have the ability to directly bind to bones and have been widely used as bone graft substitutes due to their high osteoconductivity and biocompatibility. CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics are known to have good osteoconductivity and are used as bone graft extenders.

Methods

This study aimed to evaluate the effects of the resorbing properties of glass-ceramics in bone fusion after producing and analyzing three types of CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics with high osteoconductivity that had enhanced resorption by having an increased B₂O₃ content. The three types of CaO-SiO₂-P₂O₅-B₂O₃ glass-ceramics with B₂O₃ contents of 8.0, 9.0, and 9.5 weight % were designated and grouped as P20B80, P10B90, and P5B95, respectively. Glass-ceramic types were tested for fusion rates and bone formation by employing the lumbar 5-6 intertransverse process fusion model in 51 New Zealand male rabbits. Bioactivity was assessed by soaking in simulated body fluid (SBF).

Results

In vitro study results showed sufficient hydroxycarbonate apatite layer formation occurred for P20B80 in1 day, for P10B90 in 3 days, and for P5B95 in 5 days after soaking in SBF. For the rabbit lumbar spine posterolateral fusion model, the autograft group recorded a 100% fusion rate with levels significantly higher than those of P20B80 (29.4%), P10B90 (0%), and P5B95 (14.3%), with high resorbing properties. Resorbing property differences among the three glass-ceramic groups were not significant. Histological results showed new bone formation confirming osteoconductivity in all three types of glass-ceramics. Radiomorphometric results also confirmed the resorbing properties of the three glass-ceramic types.

Conclusions

The high resorbing properties and osteoconductivity of porous glass-ceramics can be advantageous as no glass-ceramics remain in the body. However, their relatively fast rate of resorption in the body negatively affects their role as an osteoconductive scaffold as glass-ceramics are resorbed before bony fusion.     

The Effect of Octreotide on Hepatic Ischemia-Reperfusion Injury in a Rabbit Model

Background

Hepatic ischemic-reperfusion injury (HIRI) is a major cause of morbidity and mortality following liver surgery. Octreotide (Oct) has been reported to improve hepatocellular energy metabolism in a rat HIRI model. This study was designed to evaluate whether Oct could protect the liver of rabbits against ischemic-reperfusion (I/R) injury.

Methods

Twenty-four adult New Zealand rabbits were randomly divided into a sham operated group (Control), an ischemia/reperfusion group (I/R), and an ischemia/reperfusion + Oct pretreatment group (I/R + Oct). The hemodynamic (mean arterial pressure [MAP] and heart rate [HR]) changes, liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], and lactate dehydrogenase [LDH]) release, inflammatory cytokines (tumor necrosis factor [TNF]α and interleukin [IL]-1β) levels, and endotoxin (ETX) levels were measured during I/R.

Results

Compared with the Control group, the MAP decreased and HR increased in I/R and I/R + Oct groups at ischemia 15 minutes (P < .05) but were less in the I/R + Oct group relative to the I/R group (P < .05). ALT, AST, LDH, IL-1β, and ETX levels were increased in the I/R and I/R + Oct groups at ischemia 30 minutes (P < .05), however, the increase was lower in the I/R + Oct group relative to the I/R group (P < .05). Bcl-2 expression in the I/R + Oct group was higher compared with other groups (P < .05) and Bax expression in the I/R group was reduced compared with other groups (P < .05). Hepatocellular damage in the I/R + Oct group appeared to be less than in the I/R group by microscopy.

Conclusions

Oct pretreatment attenuated hemodynamic changes and decreased liver enzyme changes induced by HIRI in a rabbit model. The protection mechanisms of Oct may be related to reduced ETX levels, down-regulation of the inflammatory cytokines TNFα and IL-1β, and inhibition of hepatocellular apoptosis, as well as the modulation of the mitochondrion-mediated Bcl-2/Bax apoptosis pathway. Based on our study it appears that Oct may be useful in decreasing liver injury after liver surgery and/or transplantation and may serve as a promising agent against HIRI.     

Locking Buttons Increase Fatigue Life of Locking Plates in a Segmental Bone Defect Model

Background

Durability of plate fixation is important in delayed union. Although locking plates result in stronger constructs, it is not known if locking affects the fatigue life of a plate. Two locking screws on either side of the nonunion could decrease working length and increase strain in the plate. However, the reinforcing effect of the locking head on the plate may compensate, so that it is unclear whether locking reduces fatigue life.

Questions/purposes

We determined whether locking screws, compression screws, and locking buttons reduce or increase the fatigue life of a plate.

Methods

We tested fatigue life of four constructs using an eight-hole locking plate in a segmental defect model: (1) all locking screws (Locked; n = 5); (2) all compression screws (Unlocked; n = 5); (3) six compression screws with two locking buttons in the central holes (Button; n = 6); and (4) six compression screws with two open central holes (Open; n = 6).

Results

The Button group had the longest fatigue life (1.3 million cycles). There was no difference between the Locked and Unlocked groups. All of the constructs failed by fracture of the plates through a screw hole adjacent to the defect.

Conclusions

Locking screws did not improve fatigue life, however a locking button increased the fatigue life of a locking plate in a segmental bone defect model.

Clinical Relevance

Locking buttons in holes adjacent to a defect may improve durability, which is important when delayed union is a possibility.