Introduction: The goal of meniscal transplantation is to prevent progressive joint degeneration that predictably follows meniscectomy. The meniscal transplant’s ability to transfer load effectively depends on its ability to bear circumferential loading. Purpose of this study was thus to investigate the influence of intraoperative pre-tensioning on the chondroprotective of meniscal transplants in a sheep model.

Methods: Thirty-six sheep were divided into 6 groups (n = 6), subjected to a sham operation (group A), a meniscectomy (group B), or a meniscal autograft using tag sutures with different levels of pre-tensioning (group C, 0 N; group D, 20 N; group E, 40 N; group F, 60 N). Macroscopic (International Cartilage Repair Society score) and histological evaluation (Mankin score) of the articular cartilage was performed after 6 months.

Results: Higher suture pretension (40 N, 60 N) resulted in less cartilage degeneration than in meniscectomized (P =.047; P =.036) and non-pre-tensioned (P =.028; P =.015) knees, with International Cartilage Repair Society scores of 1.63 +/− 0.57 and 1.66 +/− 0.51 in groups E and F, respectively, and scores of 2.40 +/− 0.27 and 2.68 +/− 0.46 observed after meniscectomy and meniscal transplantation with no pre-tensioning, respectively. Group F had a significantly better Mankin score of 6.66 +/− 2.15 (P =.05) compared with group D. Regarding criterion cells, trends toward less degeneration compared with meniscectomized and non-pretensioned knees (P =.054 and P =.055) were found. The coefficient of variation of the Mankin scores was greater than that of the International Cartilage Repair Society score. Group A had significantly better cartilage than all other groups.

Conclusion: Adequate intraoperative pre-tensioning has an influence on the chondroprotective effect of meniscal transplants but did not prevent the development of articular cartilage degeneration.

Clinical Relevance: The results suggest that intraoperative pre-tensioning could improve the chondroprotective effect of meniscal transplantation.

Introduction Non-invasive prediction of load bearing capacity is an important issue in the advanced clinical treatment of distraction osteogenesis in order to define the appropriate point of time for the removal of the external fixateur. Therefore, non-invasive stiffness measurements were recommended as a promising tool due to the high correlation between strength and various kinds of stiffness: Torsional, bending and compressive.

However, previous experiments only analysed the relationship between a single type of stiffness. This approach neglects the multi-dimensional characteristics of bone loading in compression, bending and torsion.

This study investigates how compressive, bending (ap and ml) and torsional stiffness are related to the torsional load bearing capacity of healing callus tissue using a common set of bone regenerate samples of sheep treated with distraction osteogenesis. In addition, this study compares the evolution of the various kinds of stiffness.

This study provides insight into how the various stiffness modes are suited to predict the load bearing capacity by in-vivo stiffness measurement.

Material and Methods Mid-diaphyseal osteotomies were performed in 26 right tibiae of mature, female domestic sheep. Tibiae were then stabilized using an external half-ring Ilizarov fixator. After a 4-day latency period the tibiae were distracted at a rate of 1.25 mm per day in two increments for 20 days. As a result of a parallel study, the callus was treated with different combinations of growth factors and carrier material resulting in four treatment groups plus a contralateral control group. The sheep were sacrificed and the tibiae were harvested on the 74th day.

The ends of the tibiae were embedded in PMMA and mounted to a sequence of special custom made jigs for compressive testing, 4-point-bending and torsion in a material testing machine.

Stiffness was calculated by regression of the initial linear part of the load-displacement curves.

In a final experiment, the specimens were loaded in torsion until failure to record the ultimate torsional moment.

Results Torsional stiffness exhibits the highest correlation with the ultimate torsional moment (r2 = 0.77), while the ones for compressive (r2 = 0.60) and bending (ap (r2 = 0.70); ml (r2 = 0.66)) are only slightly lower.

Discussion This ex-vivo study in sheep shows that torsional, bending (ap and ml) and compressive stiffness measurements are all suitable means to predict the load bearing capacity of healing callus tissue. Our results show that torsional stiffness measurements perform slightly better than compressive and bending stiffness measurements. However, further studies are necessary to underline the superior performance of torsional stiffness measurements, since the sheep-tibiae were failed by applying torsional stress.

Introduction: The long consolidation phase of patients undergoing distraction osteogenesis (DO) causes a high risk of side effects and contributes to high costs. Thus, the development and evaluation of treatments that accelerate the bone consolidation process is of great interest. Evidence suggests that recombinant human bone morphogenetic protein 2 (rhBMP-2) increases the mechanical integrity of the callus. However, the potential benefits of rhBMP-2 on trabecular microarchitecture during DO have not been investigated up to date. In this study the regenerate microarchitecture was assessed using 3D micro-computed tomography (CT).

Methods: Mid-diaphyseal osteotomies were created in the right limb of twenty-four skeletally mature sheep, which were stabilized with an external fixator. After a latency period of 4 days, the tibiae were distracted at a rate of 1.25 mm daily over a period of 20 days. The operated limbs were randomly assigned to three treatment groups and one control group: (A) triple injection of rhBMP-2/NaCl, (B) single injection of rhBMP-2/Hydroxylapatite, and (C) single injection of buffer/Hydroxylapatit, (D) no injection. Groups A and C were injected at day 27. Group B was injected on days 3, 10 and 17. The animals were sacrificed after 74 days. The tibiae were analyzed by CT and for bone volume/total volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th.), trabecular separation (Tb.Sp.) and Connectivity. The BV/TV was maesured for the total volume of the distraction zone (BV/TVtotal) respectively in a subvolume with emphasize on the cortical bone region (BV/TVcortical). All other microarchitecture parameters were measured in the cortical weighted subvolume.

Results: The stereologic evaluation revealed a significant higher BV/TVcortical, Tb.N and Connectivity in the triple rhBMP-2 injected group A than in the control (D). Furthermore, the Tb.Sp. in group A was significant lower than in group D. The single injections of rhBMP-2/carrier in group B showed a significant higher BV/TVcortical, Tb.N and Connectivity than the control (D). Although the BV/TVcortical was increased in group A and B, there was no significant difference in BV/TV total between the rhBMP-2 treated groups (A, B) and the control (D).

Discussion: In this DO model a triple injection of rhBMP-2 has been demonstrated to induce significant changes in trabecular microarchitecture. RhBMP-2 does not increase the total amount of newly formed bone, but it enhances the formation of the corticalis. The microstructural changes in the cortical volume: increase of Tb.N and Connectivity, decrease of Tb.Sp., are discussed to be biomechanically highly relevant. This study suggests that rhBMP-2 optimizes the trabecular microarchitecture, which might explain the advanced mechanical integrity of newly formed bone under rhBMP-2 treatment.

Introduction: Despite advances in endoprosthesis fixation by implant surface alteration, the problem of aseptic implant loosening still exists. Especially in patients with revisions osseointegration and filling of gaps at the bone-implant interface is mandatory for implant survival. Simple BMP-2 immersion has been introduced previously to act as an osteoinductive coating for advanced osseointegration. However, because of the uncontrolled release kinetics and subsequent molecular action and activity of BMP-2, purely osteoinductive actions are hard to differentiate from osteoclastic BMP-actions leading to bone remodelling, which could counteract the implant fixation process and might be the reason for failed attempts to use BMP-2 for implant fixation. In this study we investigated the osteoinductive potency of BMP-2 bound to titanium surfaces by a highly controlled molecular coupling with specifically designed polymers, allowing a slow controlles release kinetics. We present the first results of two different polymers that were implanted in the tibia and femora of New Zealand White Rabbits.

Methods: In this study we designed cylindrical titanium-implants with an inner thread (Ti6-Alï·& #8220;4V, 3 mm hight x 3 mm diameter) and an electropolished outer surface that were coated with different polymers. The polymers were fixed to the surface using the photochemical method of grafting. The implants were implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The anatomical locations of the implants were alternated to test their osseointegration in different quality of bone (cancellous vs. cortical bone). After 4 weeks the animals were sacrificed and DEXA-scans (Dual-energy X-ray absorptiometry), micro-CT and histological analysis were performed. ANOVA and t-test were used for statistic analysis.

Results: In high-resolution DEXA-scans we found a difference in bone mineral density (BMD) between PVBP and a control implant in the distal femora (PVBP 0,720 g/cm², control 0,661 g/cm²) and in the proximal tibia (PVBP 0,633 g/cm², control 0,431 g/cm²) with an increase of bone mineral density. In the histological investigation we found an increase of osteoblasts around the implants coated with PVBP and PVBP-Co-Acryloxysuccimid. Furthermore, the micro-CT scans showed an increase of BV/TV (bone volume/total volume) for both polymers.

Discussion: In this study we present the first results of the investigation of polymer-coated titanium-implants implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The results of DEXA-scans, micro-CT and histological analysis showed an increase of osseointegration. We suggest that controlled release kinetics after coupling of these polymers with BMP-2 can additionally increase osseointegration. To get a closer look on the polymers, their characteristics in-vivo, and coupling with BMP-2 further investigations are conducted.

The ability to predict load-bearing capacity during the consolidation phase in distraction osteogenesis by non-invasive means would represent a significant advance in the management of patients undergoing such treatment. Measurements of stiffness have been suggested as a promising tool for this purpose. Although the multidimensional characteristics of bone loading in compression, bending and torsion are apparent, most previous experiments have analysed only the relationship between maximum load-bearing capacity and a single type of stiffness. We have studied how compressive, bending and torsional stiffness are related to the torsional load-bearing capacity of healing callus using a common set of samples of bone regenerate from 26 sheep treated by tibial distraction osteogenesis.

Our findings showed that measurements of torsional, bending and compressive stiffness were all suitable as predictors of the load-bearing capacity of healing callus. Measurements of torsional stiffness performed slightly better than those of compressive and bending stiffness.