Resorbability of rigid beta-tricalcium phosphate wedges in open-wedge high tibial osteotomy: a retrospective radiological study

Combined use of beta-tricalcium phosphate with different porosities can accelerate bone remodelling in open-wedge high tibial osteotomy

Background/Objective

Beta-tricalcium phosphate (β-TCP) is often used as a gap filler in open-wedge high tibial osteotomy (OWHTO). The aim of the present study was to investigate the effects of using β-TCP with different porosities on bone remodelling after OWHTO.Methods: We evaluated 29 knees in 26 patients that underwent OWHTO using β-TCP with porosities of 60% and 75% (combined group). A further 30 knees in 28 patients that underwent OWHTO using β-TCP with 60% porosity alone were allocated as a control group. In the combined group, a β-TCP block with 75% porosity was inserted into the gap at the cancellous bone site and a β-TCP block with 60% porosity was inserted into the medial cortical bone side. In the control group, a β-TCP block with 60% porosity was inserted into the osteotomy gap. The bone remodelling phases of the inserted β-TCP blocks were evaluated on standard anteroposterior radiographs using the modified van Hemert classification at 3 and 6 months post-operatively.

Results

The rate of satisfactory bone remodelling at the cancellous bone sites was 86.2% (25/29) in the combined group and 0% (0/30) in the control group at 3 months post-operatively (p<0.05), progressing to 96.6% (28/29) in the combined group and 20% (6/30) in the control group at 6 months post-operatively (p<0.05).

Conclusion

The present study demonstrated that combined use of β-TCP with high and low porosities can significantly enhance bone formation. The combined use of artificial bones with different porosities is useful for early bone remodelling in OWHTO.

β-tricalcium phosphate for bone substitution: Synthesis and properties

β-tricalcium phosphate (β-TCP) is one the most used and potent synthetic bone graft substitute. It is not only osteoconductive, but also osteoinductive. These properties, combined with its cell-mediated resorption, allow full bone defects regeneration. Its clinical outcome is sometimes considered to be "unpredictable", possibly due to a poor understanding of β-TCP physico-chemical properties: β-TCP crystallographic structure is not fully uncovered; recent results suggest that sintered β-TCP is coated with a Ca-rich alkaline phase; β-TCP apatite-forming ability and osteoinductivity may be enhanced by a hydrothermal treatment; β-TCP grain size and porosity are strongly modified by the presence of minute amounts of β-calcium pyrophosphate or hydroxyapatite impurities. The aim of the present article is to provide a critical, but still rather comprehensive review of the current state of knowledge on β-TCP, with a strong focus on its synthesis and physico-chemical properties, and their link to the in vivo response. STATEMENT OF SIGNIFICANCE: The present review documents the richness, breadth, and interest of the research devoted to β-tricalcium phosphate (β-TCP). β-TCP is synthetic, osteoconductive, osteoinductive, and its resorption is cell-mediated, thus making it one of the most potent bone graft substitutes. This comprehensive review reveals that there are a number of aspects, such as surface chemistry, crystallography, or stoichiometry deviations, that are still poorly understood. As such, β-TCP is still an exciting scientific playground despite a 50 year long history and > 200 yearly publications.

Lateral hinge fracture delays healing of the osteotomy gap in opening wedge high tibial osteotomy with a beta-tricalcium phosphate block

BACKGROUND

The purpose of this study was to investigate the healing process of synthetic bone grafts in opening wedge high tibial osteotomy (OWHTO) and to identify the factors that affect bone healing in OWHTO. It was hypothesized that lateral hinge fracture (LHF) is associated with delayed bone healing after OWHTO with synthetic bone grafting.

METHODS

The subjects included 350 knees of 283 patients who underwent OWHTO using two wedged blocks of beta-tricalcium phosphate (β-TCP) with 60% porosity. The healing of the osteotomy gap using a radiologic rating system for OWHTO with synthetic bone grafts and the presence of an LHF were assessed up to postoperative 24 months.

RESULTS

LHFs were found in 49 knees (14%). The osteotomy gap showed slower progression of radiographic healing with an LHF than without an LHF (P < .05). In the knees with LHFs, initial radiographic change in the osteotomy gap was observed almost at the same time as healing of the LHF. Multivariate logistic regression analysis identified LHF as the factor preventing the progression of bone healing (OR = 46.78, P < .05).

CONCLUSIONS

LHF is associated with delayed bone healing after OWHTO with synthetic bone grafting.

Osteoclastic Bioresorption of Biomaterials: Two- and Three-Dimensional Imaging and Quantification

Purpose

Bioresorbable materials have been developed in the hope that the body will replace them with newly formed tissue. The first step of this remodeling process in bone is the bioresorption of the material by osteoclasts. The aim of this study was to analyze osteoclastic resorption of biomaterials in vitro using the commonly used two-dimensional methods of light-microscopy (LM) and scanning electron microscopy (SEM) in comparison with infinite focus microscopy (IFM), a recently developed imaging method allowing for three-dimensional surface analysis.

Methods

Human hematopoietic stem cells were cultivated in the presence of the cytokines M-CSF and RANK-L for 4 weeks directly on dentin and a calcium phosphate cement. Osteoclast development was surveyed with standard techniques. After removal of the cells, resorption was characterized and quantified by LM, SEM and IFM.

Results

Osteoclast cultures on the biomaterials presented the typical osteoclast-specific markers. On dentin samples LM, SEM as well as IFM allowed for discrimination of resorption. Quantification of the resorbed area showed a linear correlation between the results (LM vs. SEM: r=0.996, p=0.004; SEM vs. IFM: r=0.989, p=0.011; IFM vs. LM: r=0.995). It was not possible to demarcate resorption pits on GB14 using LM or SEM. With IFM, resorption on GB14 could be visualized and quantified two- and three-dimensionally.

Conclusions

In this paper we introduce IFM as a technology for three-dimensional visualization and quantification of resorption of biomaterials. Better understanding of the bioresorption of biomaterials may help in the design of better materials and might therefore constitute an important step on the avenue to the development of artificial bone.

Radiographic and computed tomographic evaluation of bone union after medial opening wedge high tibial osteotomy with filling gap

BACKGROUND

We evaluated bone union and remodelling in patients undergoing opening-wedge high tibial osteotomy (OWHTO) with bone gaps filled with beta-tricalcium phosphate. We examined the effectiveness of radiography and computed tomography (CT) for the evaluation of bone union and remodelling, and investigated whether lateral hinge fractures affected bone union.

METHODS

Sixty-six cases underwent OWHTO with a combination of a TomoFix plate and a bone substitute. Bone union and remodelling were assessed using the rating system for OWHTO at three and six months, postoperatively.

RESULTS

Radiographic evaluation showed that bone union of the lateral hinge was 85% and 100% at three and six months, respectively. Based on CT evaluation, bone union of the lateral hinge and the flange was achieved in all cases at six months, and the bone union of the posterior cortex reached Zone 3 in 83% at six months. Based on radiographic evaluation, bone remodelling phases of bone substitute had progressed in each zone in six months compared with three months. Radiographic and CT analyses identified a Takeuchi type I hinge fracture in fourteen (21.2%) and five (7.6%) knees at two weeks postoperatively, respectively. There were no differences in bone union with and without the lateral hinge fracture.

CONCLUSIONS

The use of CT enabled us to evaluate the bone union of the flange and the extent of the bone union of the posterior cortex. Plain radiographs are useful to evaluate bone union of the lateral hinge similar to CT analysis. The presence of a Takeuchi type I hinge fracture did not affect bone union.

Incorporation of BMP-2 loaded collagen conjugated BCP granules in calcium phosphate cement based injectable bone substitutes for improved bone regeneration

The objective of the present study was to incorporate surface modified porous multichannel BCP granule into CPC to enhance its in vivo biodegradation and bone tissue growth. The multichannel BCP granule (15wt%) was first coated with collagen subsequent to BMP-2 loading (ccMCG-B). It was then embedded into CPC to form CPC-ccMCG-B system. The newly developed CPC-ccMCG-B system was then examined for SEM, EDX, XRD, setting time, compressive strength, injectability, pH change, BMP-2 release, in vitro as well as in vivo studies and further compared with CPC. Optimized CPC (0.45mL/g) was found based on setting time and compressive strength studies. In vivo studies exhibited improved new bone formation and better degradation of CPC after 2 and 4weeks of implantation as compared to CPC as resulted from effective BMP-2 signaling. Our results suggest that CPC-ccMCG-B system might be used as a promising injectable bone substitutes in clinical applications.

Surrogate Outcome Measures of In Vitro Osteoclast Resorption of β Tricalcium Phosphate

Introduction of porosity to calcium phosphate scaffolds for bone repair has created a new challenge when measuring bioresorption in vitro, rendering traditional outcome measures redundant. The aim of this study is to identify a surrogate endpoint for use with 3D scaffolds. Murine RAW 264.7 cells are cultured on dense discs of β-tricalcium phosphate in conditions to stimulate osteoclast (OC) formation. Multinucleated OCs are visible from day 6 with increases at days 8 and 10. Resorption pits are first observed at day 6 with much larger pits visible at days 8, 10, and 12. The concentration of calcium ions in the presence of cells is significantly higher than cell-free cultures at days 3 and 9. Using linear regression analysis, Ca ion release could account for 35.9% of any subsequent change in resorption area. The results suggest that Ca ion release is suitable to measure resorption of a beta-tricalcium phosphate ceramic substrate in vitro. This model could replace the more accepted resorption pit assay in circumstances where quantification of pits is not possible, e.g., when characterizing 3D tissue engineered bone scaffolds.

Bone grafts and bone substitutes for opening-wedge osteotomies of the knee: a systematic review

PURPOSE

To establish the rate of use of various void fillers in the setting of opening-wedge osteotomy around the knee, the types of fixation used, and the rates of delayed union or nonunion related to these variables. In addition, this review addressed short-term to midterm outcomes and complication rates associated with such procedures.

METHODS

The electronic databases Medline, Embase, and PubMed were searched using the methodology for systematic review as recommended by the Cochrane Collaboration. The search terms used were as follows: knee, osteotomy, knee joint, bone grafting, opening osteotomy, opening wedge, tibial osteotomy, femoral osteotomy, and bone substitute. We screened 1,383 articles and applied exclusion criteria. Fifty-six articles were included.

RESULTS

We included 3,033 cases of osteotomy in 2,910 patients. The mean age of patients was 50 years, with a mean follow-up period of 42 months. Male patients comprised 52% of patients. The mean alignment change was 10.8°, shifting the mechanical axis to 5.1° valgus. Delayed union/nonunion rates were 2.6%, 4.6%, and 4.5% for autograft, allograft bone, and synthetic bone substitutes, respectively (P = .03). Delayed union/nonunion rates were significantly lower for autograft compared with allograft (P = .03) and for autograft and allograft compared with synthetic bone substitutes (P < .0001). Non-locking plates (n = 2,148) had a rate of delayed union/nonunion of 3.7% and a mean loss of correction over time of 0.5°. Locking plates (n = 681) had a rate of delayed union/nonunion of 2.6% and a loss of correction of 2.3°. All mean knee outcome scores improved, and an overall complication rate of 14% was found.

CONCLUSIONS

Opening-wedge osteotomy had good short-term to midterm outcomes with acceptable complication rates. The lowest rates of delayed union/nonunion were in autograft bone-filled osteotomies. Plate type does not appear to affect osteotomy union or loss of correction.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I to IV studies.

A novel evaluation system to monitor bone formation and β-tricalcium phosphate resorption in opening wedge high tibial osteotomy

PURPOSE

The aim of this study was to establish an evaluation system to monitor bone formation and beta-tricalcium phosphate (TCP) resorption in opening high tibial osteotomy (HTO).

METHODS

From 2003 to 2005, opening HTO was performed in 36 patients using a Puddu plate and β-TCP blocks with 60 and 75 % porosity. Thirty-one patients were used for evaluation. All patients underwent CT examination at 2 weeks and 6 years. The CT image data were divided into three areas, and CT values of each area were analysed using the imaging software, Osirix.

RESULTS

CT image analysis at 2 weeks showed that the mean CT-attenuation values (in Hounsfield units) of the implanted area with β-TCP of 60 % porosity, the implanted area with β-TCP of 75 % porosity, and cancellous bone were, 1,694.0 ± 94.2, 1,010.9 ± 81.1, and 178.0 ± 45.1, respectively. Six years after surgery, these values were 574.1 ± 273.5, 168.8 ± 75.1, and 174.9 ± 69.3, respectively.

CONCLUSION

β-TCP with 75 % porosity was completely resorbed and replaced by bone. β-TCP with 60 % porosity was resorbed, but approximately 1/3 still remained even 6 years after surgery. The imaging software, Osirix, enabled scanning of the whole area to measure CT values. This system is the first to quantitatively evaluate β-TCP resorption and bone formation in opening HTO.

LEVEL OF EVIDENCE

Laboratory studies.

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 outcome of bone substitute wedges in medial opening high tibial osteotomy

BACKGROUND

Opening wedge high tibial osteotomy often requires bone grafting to improve the union rate and avoid instability at the osteotomy site. Autograft and allograft have both been associated with complications and the use of bone substitute wedges has been advocated to improve the outcome. This study investigated the clinical, radiological and histological outcomes of using biphasic calcium phosphate ceramic (Triosite) wedges in opening wedge high tibial osteotomy and determined whether the presence of the graft would compromise the satisfactory conversion to a total knee replacement.

METHODS

A consecutive cohort underwent radiological review to determine whether the osteotomy healed and the correction was maintained. Biopsies were performed on those undergoing second procedures. All patients converted to total knee arthroplasty were assessed separately as to any surgical complications attributed to the Triosite wedge.

RESULTS

There were 36 osteotomies in 33 patients with a minimum of 4 years follow up. All osteotomies healed. There was an average 90 (5-14) of correction, which was maintained. Histological assessment of 17 cases confirmed adequate bone replacement of the Triosite although some areas of tricalcium phosphate remained visible. Conversion to a total knee arthroplasty occurred in 11 cases with no complications.

CONCLUSION

Biphasic calcium phosphate ceramic wedges (Triosite) can be reliably used in opening wedge high tibial osteotomy with a low incidence of complications and satisfactory conversion to total knee arthroplasty.

Cell-based resorption assays for bone graft substitutes

The clinical utilization of resorbable bone substitutes has been growing rapidly during the last decade, creating a rising demand for new resorbable biomaterials. An ideal resorbable bone substitute should not only function as a load-bearing material but also integrate into the local bone remodeling process. This means that these bone substitutes need to undergo controlled resorption and then be replaced by newly formed bone structures. Thus the assessment of resorbability is an important first step in predicting the in vivo clinical function of bone substitute biomaterials. Compared with in vivo assays, cell-based assays are relatively easy, reproducible, inexpensive and do not involve the suffering of animals. Moreover, the discovery of RANKL and M-CSF for osteoclastic differentiation has made the differentiation and cultivation of human osteoclasts possible and, as a result, human cell-based bone substitute resorption assays have been developed. In addition, the evolution of microscopy technology allows advanced analyses of the resorption pits on biomaterials. The aim of the current review is to give a concise update on in vitro cell-based resorption assays for analyzing bone substitute resorption. For this purpose models using different cells from different species are compared. Several popular two-dimensional and three-dimensional optical methods used for resorption assays are described. The limitations and advantages of the current ISO degradation assay in comparison with cell-based assays are discussed.

High tibial osteotomy using polycaprolactone-tricalcium phosphate polymer wedge in a micro pig model

Medial open-wedge high tibial osteotomy has been gaining popularity in recent years, but adequate supporting material is required in the osteotomy gap for early weight-bearing and rapid union. The purpose of this study was to investigate whether the implantation of a polycaprolactone-tricalcium phosphate composite scaffold wedge would enhance healing of the osteotomy in a micro pig model. We carried out open-wedge high tibial osteotomies in 12 micro pigs aged from 12 to 16 months. A scaffold wedge was inserted into six of the osteotomies while the other six were left open. Bone healing was evaluated after three and six months using plain radiographs, CT scans, measurement of the bone mineral density and histological examination.

Complete bone union was obtained at six months in both groups. There was no collapse at the osteotomy site, loss of correction or failure of fixation in either group. Staining with haematoxylin and eosin demonstrated that there was infiltration of new bone tissue into the macropores and along the periphery of the implanted scaffold in the scaffold group. The CT scans and measurement of the bone mineral density showed that at six months specimens in the scaffold group had a higher bone mineral density than in the control group, although the implantation of the polycaprolactone-tricalcium phosphate composite scaffold wedge did not enhance healing of the osteotomy.

Volumetric analysis of osteoclastic bioresorption of calcium phosphate ceramics with different solubilities

Commonly, to determine osteoclastic resorption of biomaterials only the resorbed area is measured. The depth of the resorption pit, however, may also be important for the performance of a material. To generate such data we used two calcium phosphate ceramics (Ca(10) and Ca(2)). The solubility of the materials was determined according to DIN EN ISO 10993-14. They were scanned three-dimensionally using infinite focus microscopy and subsequently cultivated for 4 weeks in simulated body fluid without (control) or with human osteoclasts. After this cultivation period osteoclasts number was determined and surface changes were evaluated two- and three-dimensionally. Ca(10) and Ca(2) showed solubilities of 11.0+/-0.5 and 23.0+/-2.2 mgg(-1), respectively. Both materials induced a significant increase in osteoclast number. While Ca(10) did not show osteoclastic resorption, Ca(2) showed an increased pit area and pit volume due to osteoclastic action. This was caused by an increased average pit depth and an increased number of pits, while the average area of single pits did not change significantly. The deduced volumetric osteoclastic resorption rate (vORR) of Ca(2) (0.01-0.02 microm(3)microm(-2)day(-1)) was lower than the remodelling speed observed in vivo (0.08 microm(3)microm(-2)day(-1)), which is in line with the observation that implanted resorbable materials remain in the body longer than originally expected. Determination of volumetric indices of osteoclastic resorption might be valuable in obtaining additional information about cellular resorption of bone substitute materials. This may help facilitate the development of novel materials for bone substitution.

Outcome of opening wedge high tibial osteotomy augmented with a Biosorb® wedge and fixed with a plate and screws in 124 patients with a mean of ten years follow-up

The objective of this work was firstly to evaluate the long-term results of medial opening wedge high tibial osteotomy (HTO) and secondly to evaluate the tolerance and integration of a Biosorb® wedge (β Tricalcium Phosphate, SBM Company, Lourdes, France). The series consisted of 124 knees in 110 patients, 74 men and 36 women, with mean age of 53.23±10.68 years (range 32-74) and treated between June 1995 and November 2000 for medial compartment knee osteoarthritis by the senior author. The mean preoperative Lysholm and Tegner functional score was 65.44±13.32 (range 27-80) and the preoperative HKA angle was 172.51°±3.8° (range 162-179°). According to the modified Ahlbäck classification there were 27 stage I, 42 stage II, 44 stage III and 11 stage IV knees. All patients were reviewed clinically and radiologically with a mean follow-up of 10.39±1.98 years (range 8-14 years). Immediate postoperative complications consisted of nine undisplaced lateral tibial plateau fractures of no clinical significance, two deep vein thromboses and three pulmonary emboli which resolved with appropriate treatment. At a later stage, there were seven delayed unions without development of pseudarthrosis, and three screw breakages when the AO T-plate was used, leading to a secondary angulation in one case, requiring revision by femoral osteotomy. Postoperative mean weightbearing HKA angle was 182°±1.8° (range 178-186°) and 73.4% of axes were 184°±2°. Fifteen knees (12.1%) underwent total knee arthroplasty (TKA) after a mean delay of 8.87±3.04 years and were excluded from the final analysis. Concerning the long-term results (n = 107 knees), the mean Lysholm-Tegner score was 88±12.7 points (51-100) and the KOOS score was 86±14.6 points (25-100) with 94 patients satisfied or very satisfied (87.85%). In terms of the HTO survivorship curve, with failure consisting of revision to TKA or another operation, survival was 88.8% at five years and 74% at ten years. Concerning Biosorb®, this was completely integrated in 100% of cases and there was complete resorption in 12.1% of cases and greater than 50% resorption in 52.3% of cases.

Opening-wedge high tibial osteotomy without bone graft

Open wedge high tibial osteotomy has become the trend for correction of varus knee deformities. The drawbacks were the need of autogenous bone graft with its associated morbidity, and later the use of bone substitutes with their cost and delayed healing. In this study, a total of 58 consecutive patients underwent high tibial osteotomy with internal fixation by wedge (toothed) plate and screws without bone graft, from 2004 to 2008. Age of the patients ranged from 24 to 65 years. There were 37 women and 21 men. The osteotomy opening size ranged from 8 to 14 mm. The mean follow-up was 38 months. The osteotomy united in all patients. Average time to union was 12.4 weeks (range 8-16 weeks). Partial loss of correction occurred in one osteotomy. There was significant difference between the healing time and the size of the osteotomy opening. The results at the final follow-up using the HSS score were excellent in 51 knees (88%) and good in seven knees (12%). Despite the routine addition of bone graft as a part of the high tibial osteotomy procedure, this study supports medial opening-wedge high tibial osteotomy up to 14 mm without bone graft or bone substitutes, which shortens the operative time and avoids unnecessary morbidity.