Knochenersatz: Transplantate und Ersatzmaterialien – ein Update

Experimental magnesium phosphate cement paste increases torque of trochanteric fixation nail advanced™ blades in human femoral heads

BACKGROUND

The use of polymethylmethacrylate cement for in-situ implant augmentation has considerable disadvantages: it is potentially cytotoxic, exothermic and non-degradable. Therefore, the primary aim of this study was to develop a magnesium phosphate cement which meets the requirements for in-situ implant augmentation as an alternative. Secondly, this experimental cement was compared to commercial bone cements in a biomechanical test set-up using augmented femoral head blades.

METHODS

A total of 40 human femoral heads were obtained from patients who underwent total hip arthroplasty. After bone mineral density was quantified, specimens were assigned to four treatment groups. A blade of the Trochanteric Fixation Nail Advanced™ was inserted into each specimen and augmented with either Traumacem™ V+, Paste-CPC, the experimental magnesium phosphate cement or no cement. A rotational load-to-failure-test (0° to 90°) was performed.

FINDINGS

A conventional two-component magnesium phosphate cement failed in-situ implant augmentation consistently due to filter pressing. Only a glycerol-based magnesium phosphate paste was suitable for the augmentation of femoral head blades. While the blades augmented with Traumacem™ V+ yielded the highest maximum torque overall (22.1 Nm), the blades augmented with Paste-CPC and the magnesium phosphate paste also showed higher maximum torque values (15.8 and 12.8 Nm) than the control group (10.8 Nm).

INTERPRETATION

This study shows for the first time the development of a degradable magnesium phosphate cement paste which fulfills the requirements for in-situ implant augmentation. Simultaneously, a 48% increase in stability is demonstrated for a scenario where implant anchorage is difficult in osteoporotic bone.

Comparison of degradation behavior and osseointegration of 3D powder-printed calcium magnesium phosphate cement scaffolds with alkaline or acid post-treatment

Due to the positive effects of magnesium substitution on the mechanical properties and the degradation rate of the clinically well-established calcium phosphate cements (CPCs), calcium magnesium phosphate cements (CMPCs) are increasingly being researched as bone substitutes. A post-treatment alters the materials’ physical properties and chemical composition, reinforcing the structure and modifying the degradation rate. By alkaline post-treatment with diammonium hydrogen phosphate (DAHP, (NH4)2HPO4), the precipitation product struvite is formed, while post-treatment with an acidic phosphate solution [e.g., phosphoric acid (PA, H3PO4)] results in precipitation of newberyite and brushite. However, little research has yet been conducted on newberyite as a bone substitute and PA post-treatment of CMPCs has not been described in the accessible literature so far. Therefore, in the present study, the influence of an alkaline (DAHP) or acid (PA) post-treatment on the biocompatibility, degradation behavior, and osseointegration of cylindrical scaffolds (h = 5.1 mm, Ø = 4.2 mm) produced from the ceramic cement powder Ca0.75Mg2.25(PO4)2 by the advantageous manufacturing technique of three-dimensional (3D) powder printing was investigated in vivo. Scaffolds of the material groups Mg225d (DAHP post-treatment) and Mg225p (PA post-treatment) were implanted into the cancellous part of the lateral femoral condyles in rabbits. They were evaluated up to 24 weeks by regular clinical, X-ray, micro-computed tomographic (µCT), and histological examinations as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis and compared with tricalcium phosphate (TCP). All materials showed excellent biocompatibility and rapid osseointegration. While TCP degraded only slightly, the CMPCs showed almost complete degradation. Mg225d demonstrated significantly faster loss of form and demarcability from surrounding bone, scaffold volume reduction, and significantly greater degradation on the side towards the bone marrow than to the cortex than Mg225p. Simultaneously, numerous bone trabeculae have grown into the implantation site. While these were mostly located on the side towards the cortex in Mg225d, they were more evenly distributed in Mg225p and showed almost the same structural characteristics as physiological bone after 24 weeks in Mg225p. Based on these results, the acid post-treated 3D powder-printed Mg225p is a promising degradable bone substitute that should be further investigated.

Characterization of Naturally Occurring Bioactive Factor Mixtures for Bone Regeneration

In this study, the bone-regenerative potential of bioactive factors derived from adipose tissue, platelet-rich plasma (PRP) and conditioned medium from hypoxia-treated human telomerase immortalized bone-marrow-derived mesenchymal stem cells (hTERT-MSC) was investigated in vitro with the aim to develop cost-effective and efficient bone substitutes for optimized regeneration of bone defects. Adipose tissue was harvested from human donors undergoing reconstructive surgery, and adipose tissue extract (ATE) was prepared. Platelet lysates (PL) were produced by repeated freeze-thaw cycles of PRP, and hypoxia-conditioned medium (HCM) was obtained by culturing human telomerase immortalized bone-marrow-derived mesenchymal stromal cells for 5 days with 1% O2. Besides analysis by cytokine and angiogenesis arrays, ELISA was performed. Angiogenic potential was investigated in cocultures of bone-marrow-derived (BM)-MSC and human umbilical vein endothelial cells. Multiple angiogenic proteins and cytokines were detected in all growth factor mixtures. HCM and ATE contained high amounts of angiogenin and CCL2/MCP-1, whereas PL contained high amounts of IGFBP-1. Culturing cells with HCM and ATE significantly increased specific ALP activity of BM-MSC as well as tubule length and junctions of endothelial networks, indicating osteogenic and angiogenic stimulation. To achieve a synergism between chemoattractive potential and osteogenic and angiogenic differentiation capacity, a combination of different growth factors appears promising for potential clinical applications.

Osteointegration of porous absorbable bone substitutes: A systematic review of the literature

Biomaterials' structural characteristics and the addition of osteoinductors influence the osteointegration capacity of bone substitutes. This study aims to identify the characteristics of porous and resorbable bone substitutes that influence new bone formation. An Internet search for studies reporting new bone formation rates in bone defects filled with porous and resorbable substitutes was performed in duplicate using the PubMed, Web of Science, Scielo, and University of São Paulo Digital Library databases. Metaphyseal or calvarial bone defects 4 to 10 mm in diameter from various animal models were selected. New bone formation rates were collected from the histomorphometry or micro-CT data. The following variables were analyzed: animal model, bone region, defect diameter, follow-up time after implantation, basic substitute material, osteoinductor addition, pore size and porosity. Of 3,266 initially identified articles, 15 articles describing 32 experimental groups met the inclusion criteria. There were no differences between the groups in the experimental model characteristics, except for the follow-up time, which showed a very weak to moderate correlation with the rate of new bone formation. In terms of the biomaterial and structural characteristics, only porosity showed a significant influence on the rate of new bone formation. Higher porosity is related to higher new bone formation rates. The influence of other characteristics could not be identified, possibly due to the large variety of experimental models and methodologies used to estimate new bone formation rates. We suggest the inclusion of standard control groups in future experimental studies to compare biomaterials.

Allogenic bone grafting for augmentation in two-part proximal humeral fracture fixation in a high-risk patient population

INTRODUCTION

The surgical fixation of unstable, varus displaced two-part fractures of the proximal humerus remains challenging.

MATERIALS AND METHODS

In a case series of 10 non-compliant, high-risk patients (median age 63 years; range 52-78), a cancellous allograft was used to augment plate fixation of the fractures.

RESULTS

After a median follow-up of 28.5 months, all but one fracture were healed, with the bony allografts incorporated without any systemic or local complications. No significant loss of reduction or evidence of avascular necrosis of the humeral head was seen. The median Constant-Murley Score was 72.0 (range 45-86). Median pain on a visual analog scale was 1 (range 0-7). Median values for the range of motion were flexion: 155° (range 90-170), abduction: 168° (range 95-180) and external rotation: 43° (range: 30-50). Compared to the uninjured contralateral side, flexion was impaired by 13 %, abduction by 14 %, and external rotation by 15 %. Median abduction power was 64 % of the uninjured side. The median varus displacement was 51° (range 45-59) preoperatively, 4° (range -5 to 19) intraoperatively, and 13° (range 1-18) at the time of the final follow-up, relating to an improvement of 38° compared to the preoperative status.

CONCLUSIONS

The augmentation of proximal humeral fracture fixation using a cancellous allograft might be a viable and reliable alternative to prevent early varus failure and to, moreover, lead to bony union in a non-compliant or high-risk patient population.