Metabolic bone diseases, such as osteoporosis and osteopetrosis, result from an imbalanced bone remodeling process. In vitro bone models are often used to investigate either bone formation or resorption independently, while in vivo, these processes are coupled. Combining these processes in a co-culture is challenging as it requires finding the right medium components to stimulate each cell type involved without interfering with the other cell type's differentiation. Furthermore, differentiation stimulating factors often comprise growth factors in supraphysiological concentrations, which can overshadow the cell-mediated crosstalk and coupling.

To address these challenges, we aimed to recreate the physiological bone remodeling process, which follows a specific sequence of events starting with cell activation and bone resorption by osteoclasts, reversal, followed by bone formation by osteoblasts. We used a mineralized silk fibroin scaffold as a bone-mimetic template, inspired by bone's extracellular matrix composition and organization. Our model supported osteoclastic resorption and osteoblastic mineralization in the specific sequence that represents physiological bone remodeling.

We also demonstrated how culture variables, such as different cell ratios, base media, and the use of osteogenic/osteoclast supplements, and the application of mechanical load, can be adjusted to represent either a high bone turnover system or a self-regulating system. The latter system did not require the addition of osteoclastic and osteogenic differentiation factors for remodeling, therefore avoiding growth factor use.

Our in vitro model for bone remodeling has the potential to reduce animal experiments and advance in vitro drug development for bone remodeling pathologies like osteoporosis. By recreating the physiological bone remodeling cycle, we can investigate cell-cell and cell-matrix interactions, which are essential for understanding bone physiology and pathology. Furthermore, by tuning the culture variables, we can investigate bone remodeling under various conditions, potentially providing insights into the mechanisms underlying different bone disorders.

It is well known that environmental cues such as mechanical loading and/or cell culture medium composition affect tissue-engineered constructs resembling natural bone. These studies are mostly based on an initial setting of the influential parameter that will not be further changed throughout the study. Through the growth of the cells and the deposition of the extracellular matrix (ECM) the initial environmental conditions of the cells will change, and with that also the loads on the cells will change. This study investigates how changes of mechanical load or media composition during culture influences the differentiation and ECM production of mesenchymal stromal cells seeded on porous 3D silk fibroin scaffolds. ECM formation, ECM mineralization and cell differentiation in 3D tissue-engineered bone were analyzed using microscopic tools. Our results suggest that mechanical stimuli are necessary to differentiate human mesenchymal stromal cells of both bone marrow and adipose tissue origin into ECM producing osteoblasts which ultimately become ECM-embedded osteocytes. However, the influence of this stimulus seems to fade quickly after the onset of the culture. Constructs which were initially cultured under mechanical loading continued to deposit minerals at a similar growth rate once the mechanical stimulation was stopped. On the other hand, cell culture medium supplementation with FBS was identified as an extremely potent biochemical cue that influences the mechanosensitivity of the cells with regards to cell differentiation, ECM secretion and mineral deposition.

Only through a thorough understanding on these influences over time will we be able to predictably control tissue development in vitro.

Novel biomaterials are being developed and studied, intended to be applied as bone graft substitute materials. Typically, these materials are being tested in in vitro setups, where among others their cytotoxicity and alkaline phosphatase activity (as a marker for osteoblastic differentiation) are being evaluated. However, it has been reported that in vitro tests correlate poorly with in vivo results and therefore many promising biomaterials may not reach the clinic as a bone graft substitute product. One of the reasons for the poor correlation, may be the minimal complexity of the in vitro tests, as compared to the in vivo environment. Ex vivo models, mimicking the natural tissue environment whilst maintaining control of culture parameters, may be a promising alternative to assess biomaterials for bone formation. Assess the possibility of an ex vivo culture platform to test biomaterials on their potential to stimulate new bone formation. Osteochondral plugs (cylinders n=10, Ø 10 mm, height 15 mm) were drilled from fresh porcine knees, from the slaughterhouse. A bone defect (Ø 6 mm) was created and which was filled with a biomaterial graft (S53P4 bioactive glass (n=3); collagen sponges loaded with BMP-2 (n=3, as positive control)) or kept empty (n=4). The explants were cultured in custom-made two-chamber bioreactors for six weeks (LifeTec Group BV). Cartilage and bone were physically separated, similar to the in vivo situation, by a sealing ring. The two tissues were cultured in separate compartments, allowing for specific culture medium for each tissue. Medium was changed every 2–3 days and weekly micro computed tomography (µCT) images were obtained to longitudinally monitor the formation of new bone. An MTT assay was performed on half of the samples after six weeks of culture. The other samples were fixed for histology, to determine which cells were present after six weeks. The MTT metabolic assay showed that a number of cells in the bone were viable after six weeks. The further away from the border, the fewer living cells were observed. The cells in the cartilage also survived. No significant bone formation was observed with µCT in either of groups, even though abundant bone formation was expected in the BMP-2 group. Explanations of the negative results of the positive group might be that too few viable cells remain after six weeks, or that the cells that are still present are not able to form bone. No significant bone formation was observed in the bone defects in osteochondral explants that were cultured with, or without, biomaterials for six weeks. However, the platform showed that it is capable to successfully culture osteochondral explants for six weeks.

Histology needs to be performed to evaluate which cells were present at the end of the culture and this will be compared to the cells present directly after drilling the explants.

Bone tissue engineering has the intent to grow bone copies in the laboratory that could be used either for bone regeneration or as model systems to study bone physiology and pathology. Bone marrow- or adipose derived derived mesenchymal stromal cells are commonly used as they have been shown to be capable to differentiate into osteoblasts and depositing a calcium phosphate rich extracellular matrix. However, real bone is more than that: there are commonly three cell types described that are essential contributors to the tissue's native function: osteoblasts, osteocytes and osteoclasts. While all three cell types are being investigated separately, co-cultures of them including their precursors and inactive forms still provide a huge challenge these days, both in terms of culturing and (quantitative) evaluation. In addition, the matrix deposited by the osteoblasts in vitro is still far from bone's hierarchical organization in vivo that contributes to bone's impressive mechanical properties. Using a large set of microscopic tools (micro-computed tomography, SEM, 3D FIB/SEM, TEM and fluorescence), combined with spectroscopic (FTIR) and molecular tools (qPCR) we show that our 3D model system develops the main features of bone by human stromal cells differentiating first into osteoblasts who further embed themselves to become osteocytes. In their right environment and when stimulated mechanically, the cells are embedded within a collagenous matrix which is mineralized with carbonated hydroxyapatite. While this system still needs the addition of osteoclasts to represent ‘real’ bone, it allows to study the interaction between osteoblasts and osteocytes and to invest parameters contributing to collagen mineralization in high resolution and cryogenic conditions.

Purpose: 2–5 years results in the treatment of deep infection of total knee arthroplasty (TKA) after two-stage reimplantation are presented. An articulating antibiotic spacer prosthesis and a standardized antibiotic therapy were used.

Material and Methods: In a prospective study 33 consecutive patients were treated with the articulating spacer, which was made on the table by cleaning and autoclaving removed parts of the infected TKA. A parenteral double antibiotic therapy in combination with rifampin was given for 10 days, followed by oral therapy for 4 weeks.

Results: At a mean follow-up period of 47 months (31 to 67) three patients had reinfection (success rate 91 %). We could increase the average Hospital for Special Surgery knee score from 67 points (44 to 84) to 87 points (53 to 97) after reimplantation.

Based on these results, 25 knees (76 %) were rated excellent, 5 knees (15 %) were rated good, 2 knees (6 %) were rated fair and one patient (3 %) had a poor result. Complications were one temporary peroneal palsy, one luxation of the spacer due to insufficient extensor mechanism and one fracture of the tibia due to substantial primary metaphyseal bone loss.

Conclusion: Using articulating spacer prosthesis disadvantages of joint fixation between the two stages could be reduced. There is no difference in the reinfection rate compared to procedures using fixed spacer blocks. It facilitates the reimplantation and gives good functionel results.

Aims: In this prospective study, we determined whether corrective surgery for rotational malalignment of femoral prosthesis components would benefit patients that had previously undergone total knee arthroplasty.

Methods: 68 consecutive patients with a painful total knee arthroplasty were screened with computed tomography. All patients were offered plain radiographs, tangential radiographs and stress radiography for valgus/varus stability in 20° and 90° flexion. No patient had signs of infection or loosening. 14 patients were selected that had isolated internal malrotation of the femoral component. No other malpositions could be found. Two patients with mild (≤3°) internal mal-rotation were excluded due to conservative treatment. Revision surgery was performed to replace prosthetic components in 12 patients with internal malrotation ≥ 4° within 3 years of the primary arthroplasty

Results: The corrective surgery resulted in an increase in the average Knee Society Score from 51/65 to 86/86 points and an improvement in the average Hospital for Special Surgery knee score from 64 to 83 points. The mean follow-up was 57 (range 46 to 89) months.

Conclusion: This study showed that correction of isolated internal malrotation of the femoral component will lead to better clinical and functional outcomes.

Purpose: There is a growing demand on revision surgery in the last decade. 60 – 80% of these revisions are performed for early failure within the first three years. We are a referral center for painful and failed TKAs and have performed more then 400 revision surgeries between 2000 and 2005. In this paper we have analysed the cause(s) of failure(s) in patients with painful or failed TKAs.

Material and Methods: 100 consecutive revision surgeries were analysed using a standardized diagnostic algorithm. This included extended history, clinical evaluation with special tests and laboratory examinations. Radiographic analysis included standard x-rays, full leg standing weight bearing x-rays and special fluoroscopic views. Patients with suspicion of implant malrotation received a special computer tomography and stress x-rays. In patients with suspicion of infection aspiration of the joint and if negative a dynamic technetium and leucocyte bone scan was performed. The suspected cause(s) of failure(s) was analysed during revision surgery in all cases.

Results: In 48% malalignment (> 4°) caused overloading, pain and/or PE-wear. In 26% malrotation (> 3°) of the tibia and/or femoral component caused either patella malttracking, stiffness or flexion gap instability. In 23% pain was caused by instability either in extension, midflexion and/or full flexion. In 19% the cause of pain was infection. In 24 % several other rare causes could be identified. Only in 9% there was aseptic loosing over the time without any implantation failure. 78% of all revisions were performed within 3 years after the primary surgery.

Conclusions: Aseptic loosing, PE-wear and instability had been described as the main failure mechanisms in TKA. In this study it could be shown, that these are only secondary phenomena’s for the three main implantation failures of malalignment, malrotation and mismatch of the flexion/extension gaps. In most of the early failures within 3 years after primary implantation these revision surgeries might be prevented by a more precise primary implantation.

Minimal Invasive Surgery (MIS) in total knee arthroplasty (TKA) has gained much attention in the scientific community and the public in the last few years. There still exists confusion in the related terminology and different surgical techniques are recommended. Cost effectiveness and risk/benefit analysis are not available at the moment. There still remains controversy whether these new techniques represent only a modern trend or the future of TKA.

MIS Unicondylar replacement has shown significant faster rehabilitation but the same reproducible radiographic and clinical results compared with the conventional open technique. In Oct 2003 we have started using MIS TKA in our hospital. After a significant learning curve the decision was made to do only MIS TKA from Nov. 2004 up to now. More than 300 cases were performed. Only few definite data are available at this stage. In 20% of the patients we performed the so called quad sparing (QS) technique. This offers a less invasive but very demanding and time consuming approach, where most of the surgery has to be performed from the side using complete new side cutting instruments. In the majority of our patients (80%) we performed a modified mini midvastus (MMI) approach, using standard 4 in 1 front cutting instruments. Electromagnetic navigation (EM) might be a helpful tool for MIS surgery in TKA. We have limited experience with this new EM navigation system in combination with the new MIS TKA surgical techniques.

In a pilot study with two groups of patients the direct comparison between QS and MMI was evaluated. Clinical evaluation was performed by two scores (KSS and WOMAC) and five additional functional tests including straight leg raising, active motion, raising a chair, stair climbing and functional gait analysis. Testing was performed pre-op and at 1, 6 and 12 weeks post-op. Patients and investigators were blinded to the surgical technique (either QS or MMI).

The average OR time was 92 min (70 to 130) for MMI and 110 (85 to 165) for QS respectively. There were no complications in the MMI and 1 (wound healing) in the QS group. There were no differences in the different scores and in the functional tests between the groups at any time.

There is still controversy in the benefit-risk analysis for the different minimal invasive techniques. In our hospital the MIS future for TKA has already started. Patients’ satisfaction and significant earlier rehabilitation are the key advantages of these new surgical techniques. The much easier MMI technique is now the standard. Only in selected cases the more demanding QS technique is performed. According to the learning curve these new MIS techniques are for specialized surgeons only and require additional training programmes. Despite these facts, we do believe that MIS is the future of TKA surgery.

Aims: To evaluate the clinical signiþcance of isolated femoral malrotation after otherwise well performed painful TKAñs. Methods: 11 painful TKAñs (5 female, 6 male, mean 61 years, range 41 to 73) with normal mechanical axis, patella tracking, stability in extension and no signs of infection or loosening were included in this prospective study. The knees were evaluated by routine clinical and radiographic examinations in combination with a standardized computer tomography (CT) to measure the rotation of the components, using the transepicondylar axis as a reference for the femur. Results: All patients had progressive persistent pain from the time of surgery which was resistant to conservative therapy. There were two groups according to the clinical symptoms: limited ßexion and medial pain at the proximal tibia (4) or ßexion > 90û with anterior knee pain during stairs descending or raising from a chair (7). Standard x-rays were normal but in the special CT all patients showed isolated internal malrotation of the femoral component mean 7û (2 to 10). 9 patients required revision surgery with correction of the malrotated femoral component. The two patients who did not want revision surgery had only minor malrotation (< 4û).Conclusions: In painful TKAñs with unknown persistent pain but limited ßexion and/or lateral instability in the ßexion gap evaluation of the femoral component rotation with a special CT should be performed.

Introduction: Bone marrow edema (BME) is a common cause of pain in the knee with restricted treatment options. The authors performed a double-blind, randomized, active-controlled study in order to explore the clinical effects of the prostacyclin analog iloprost (Schering AG, Germany)

Materials and Methods: Forty-one patients with painful bone marrow edema associated with osteonecrosis, osteoarthritis, bone bruise or axis deformities were evaluated. Patients were randomized either to iloprost (n=21, 15 male, 6 female; mean age 53 years) or to Tramadol (n=20, 12 male, 8 female; mean age 51 years). An individual dose adjustment was allowed within the range of 100–300 μg of iloprost, and 100–300 mg of Tramadol. The treatment duration was 4 weeks. The treatment period was followed by an 8-week treatment-free follow-up. During and after treatment, full weight bearing was allowed as tolerated. Efficacy of treatment was assessed by 10 cm visual analog scales for pain at rest and on exertion, Larson’s knee score, and magnetic resonance imaging.

Results: The results are presented below.

These clinical effects were sustained over the entire follow-up. At the end of study, 53% of iloprost patients showed healing of at least one BME affected bone as compared to only 19% of Tramadol patients. Regression of subchondral lesions occurred in 4 iloprost patients. No serious adverse events occurred; however, three Tramadol patients discontinued the treatment prematurely due to adverse events.

Discussion: The authors conclude that the oral application of the vasoactive drug iloprost results in substantial treatment effects on pain relief and joint function improvement. These effects were similar for iloprost and Tramadol. Iloprost treatment was associated more often with BME regression than Tramadol. Oral iloprost may offer a new and safe treatment option for patients with painful BME.

Introduction: The purpose of this study was to compare two methods for the quantification of bone marrow edema (BME) of the knee.

Materials and Methods: Forty-one patients with Bone Marrow Edema (BME) of the knee due to osteonecrosis, osteoarthritis, bone bruise or stress were included in the study. Coronal STIR images of the affected knees were obtained using either a 1.0 Tesla or a 1.5 Tesla Magnetic Resonance (MR) scanner. To monitor the BME’s progression, every knee was examined twice at a 3-month interval. Size and signal intensity of BME were semi-quantitatively assessed in consensus by two radiologists and two orthopaedic surgeons. Independently, size and signal intensity were calculated using a new computer assisted method based on grey value analysis and calculation of a threshold value between normal and edematous bone marrow. The results of the semi-quantitative method were correlated with those of the computer assisted method.

Results: The correlation coefficient was 0.89 (ìstrongî) for BME size and 0.72 (ìmedium to strongî) for BME signal intensity. For the progression of size and signal intensity, correlation coefficients of 0.78 (ìstrongî) and 0.67 (ìmediumî) were found.

Conclusion: Good correlation between semi-quantitative and quantitative methods of assessment of both size and intensity of BME was found. While the computer assisted method is time-consuming and reserved for scientific purposes, the semi-quantitative method is simple and offers to the experienced examiner a fast and simple means for BME recording in clinical practice.