The HIPGEN study funded under EU Horizon 2020 (Grant 7792939) has the aim to investigate the potential of the first regenerative cell therapy for the improvement of recovery after muscle injury in hip fracture patients. For this aim we intramuscularly injected placental derived mesenchymal stromal cells during hip fracture arthroplasty. Despite not having reached the primary endpoint, which was the Short Physical Performance Battery, we could observe an increase in abductor muscle strength and a faster return to balance looking at symmetry in insole measurements during follow up.

Years ago, we identified the need of a dedicated group and conference for advanced therapies with musculoskeletal indications. We saw a disconnect between high-level science and the criticality of actual medical need, thus creating a gap between research and industry – a gap that needed to be bridged.

To achieve this goal, a vehicle to connect and amplify the expertise of key opinion leaders in advanced therapies in orthopaedics was needed. With that purpose in mind and after years of preparation, the “Advanced Therapies in Orthopaedics Foundation” (ATiO) was established with the aim to create a network consisting of all important stake holders in the field, ranging from clinics & research, to corporates, finance and regulators – an Alliance for Advanced Therapies in Orthopaedics to form the future.

Aims

The aim of the HIPGEN consortium is to develop the first cell therapy product for hip fracture patients using PLacental-eXpanded (PLX-PAD) stromal cells.

Aim

Two stage revision is the most commonly used surgical treatment strategy for periprosthetic hip infections (PHI). The aim of our study was to assess the intra- and postoperative complications during and after two stage revision using resection arthroplasty between ex- and reimplantation.

Despite its intrinsic ability to regenerate form and function after injury, bone tissue can be challenged by a multitude of pathological conditions. While innovative approaches have helped to unravel the cascades of bone healing, this knowledge has so far not improved the clinical outcomes of bone defect treatment. Recent findings have allowed us to gain in-depth knowledge about the physiological conditions and biological principles of bone regeneration. Now it is time to transfer the lessons learned from bone healing to the challenging scenarios in defects and employ innovative technologies to enable biomaterial-based strategies for bone defect healing. This review aims to provide an overview on endogenous cascades of bone material formation and how these are transferred to new perspectives in biomaterial-driven approaches in bone regeneration.

Cite this article: T. Winkler, F. A. Sass, G. N. Duda, K. Schmidt-Bleek. A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge. Bone Joint Res 2018;7:232–243. DOI: 10.1302/2046-3758.73.BJR-2017-0270.R1.

Introduction

Despite the lack of data regarding the diagnostic validity of synovial aspiration in Girdlestone hips a Girdlestone-aspiration is often performed before reimplantation to detect a possible persistence of infection during two staged revision total hip arthroplasty (THA). The aim of this study was to assess the diagnostic performance of the synovial aspiration in Girdlestone hips, without a PMMA-Spacer, for the detection of infection persistence prior to THA reimplantation.

Background

The main reasons for hip prosthesis failure are aseptic loosening and periprosthetic joint infection (PJI). The real frequency of PJI is probably largely underestimated because of non-standardized definition criteria, diagnostic procedure, treatment algorithm and other confounders. Therefore, data from joint registries are not reflecting the frequency of PJI and can be misleading; particularly low-grade PJI can be frequently misdiagnosed as aseptic failure. Therefore, prospective clinical studies with standardized protocol, comprehensive diagnostic procedure and sufficient follow-up should be performed. Sonication of explanted prosthesis is highly sensitive for detection of biofilms on prosthetic surface and allows quantitative analysis of biofilm formation. We hypothesize that by using sonication, ceramic components (BIOLOX®delta, BIOLOX®forte) will show higher resistance against biofilm adhesion compared to polyethylene (PE) and metal (CoCrMo).

Objectives: Skeletal muscle trauma leads to severe functional deficits. Present therapeutic treatments are unsatisfying and insufficient posttraumatic regeneration is a problem in trauma and orthopaedic surgery. Mesenchymal stem cell (MSC) therapy is a promising tool in the regeneration of muscle function after severe trauma. Our group showed increased contraction forces compared to a non-treated control group 3 weeks after MSC transplantation (TX) into a skeletal muscle trauma. In addition we demonstrated a dose-response relationship of the amount of MSC and force enhancement. We furthermore investigated the fate of the transplanted MSC labelled with very small iron oxide particles using 7 Tesla-MRI. Histological analysis revealed fusion events between existing myofibers but only to a low amount. The increase of muscle force can not be explained by these events only. Before further steps are taken the impact of paracrine effects and the homing to the site of trauma of the MSC has to be evaluated. Experimental studies about the functional regeneration of traumatized skeletal muscule after systemic MSC-TX do not exist.

Methods: 36 female SD-rats received open crush trauma of the left soleus muscle. One week after trauma 2.5 x 106 autologous MSC, harvested from tibial biopsies, were transplanted intraarterially (i.a., femoral arte-ria, group 1) or intravenously (i.v., tail vein, group 2) (n=18). Control animals received saline (i.a.: group 3; i.v.: group 4) (n=18). Histological analysis and biomechanical evaluation by in vivo muscle force measurement was performed 3 weeks after TX.

Results: Twitch stimulation of the healthy right soleus muscles resulted in a contraction force of 0.52±0.14 N. Forces of tetanic contraction in the uninjured muscles reached 0.98±0.27 N. The i.a. MSC-TX improved the muscle force of the injured soleus significantly compared to control (twitch: 82,4%, p=0.02, tetany: 61.6%, p=0.02). Contraction forces of muscles treated i.v. (MSC vs. saline) showed no significant difference. The histological analysis showed no differences in the amount of fibrotic tissue.

Conclusions: The presented study demonstrates the effect of systemic MSC-TX in the treatment of severe skeletal muscle injuries. Interestingly, the functional regeneration could only be increased by i.a. application. The entrapment of MSC in the lungs and the dilution effect in the circulation, when injecting the MSC i.v. could be the reason. For possible future therapeutic approaches a systemic application is considered to be favourable compared to local injections due to the better distribution of the cells in the target muscle.

Skeletal muscle injuries often lead to severe functional deficits. Mesenchymal stem cell (MSC) therapy is a promising but still experimental tool in the regeneration of muscle function after severe trauma. One of the most important questions, which has to be answered prior to a possible future clinical application is the ideal time of transplantation. Due to the initial inflammatory environment we hypothesized that a local injection of the cells immediately after injury would result in an inferior functional outcome compared to a delayed transplantation.

Twenty-seven female Sprague Dawley rats were used for this study. Bone marrow was aspirated from both tibiae of each animal and autologous MSC cultures obtained from the material. The animals were separated into three groups (each n=9) and the left soleus muscles were bluntly crushed in a standardized manner. In group 1 2×106 MSCs were transplanted into the injured muscle immediately after trauma, whereas group 2 and 3 received an injection of saline. Another week later the left soleus muscles of the animals of group 2 were transplanted with the same number of MSCs. Group 1 and 3 received a sham treatment with the application of saline solution in an identical manner. In vivo functional muscle testing was performed four weeks after trauma to quantify muscle regeneration.

Maximum contraction forces after twitch stimulation decreased to 39 ± 18 % of the non injured right control side after crush trauma of the soleus muscles as measured in group 3. Tetanic stimulation showed a reduction of the maximum contraction capacity of 72 ± 12 % of the value obtained from intact internal control muscles. The transplantation of 2 x 106 MSCs one week after trauma improved the functional regeneration of the injured muscles as displayed by significantly higher contraction forces in group 2 (twitch: p = 0.014, tetany: p = 0.018). Local transplantation of the same number of MSCs immediately after crush injury was able to enhance the regeneration process to a similar extent with an increase of maximum twitch contraction forces by 73.3 % (p = 0.006) and of maximum tetanic contraction forces by 49.6 % (p = 0.037) compared to the control group.

The presented results underline the effectivity of MSC transplantation in the treatment of severe skeletal muscle injuries. The most surprising finding was that despite of the fundamental differences of the local environment into which MSCs had been transplanted, similar results could be obtained in respect to functional skeletal muscle regeneration. We assume that the effect of the MSC after immediate injection can partly be explained by their known immunomodulatory competences. The data of our study provide evidence for a large time window of MSC transplantation after muscle trauma.

Background: Autologous mesenchymal stem cells (MSC) have been shown to improve the functional outcome after severe skeletal muscle trauma. The reasons for this improvement have yet not been revealed. Up to now insufficient techniques of cell labelling, which could only be used for histologic analysis ex vivo, have been a problem.

The development of iron oxide nanoparticles, which are taken up and endosomally stored by stem cells, allows the evaluation of cellular behaviour in the muscle with the use of magnetic resonance imaging (MRI). Previous work has shown that labelling does not affect the proliferation and neurogenic differentiation capacity of embryonic stem cells. In the present study we are currently investigating the in vivo distribution and migration of locally transplanted MSC after blunt muscle trauma in a rat model.

Methods: MSC cultures are derived from tibial biopsies of Sprague Dawley rats via plastic adherence. A standardized open crush injury of the left soleus muscle is performed in each animal. 24 hours before transplantation cells are labelled with very small superparamagnetic iron oxid particles (VSOP-C200, Ferropharm, Teltow, Germany) and Green Fluorescent Protein (GFP). One week after trauma different amounts of stem cells (5×105, 1×106 and 5×106) are transplanted into the soleus muscle by local injection. Distribution and migration of the cells are evaluated over time by the repeated performance of high resolution-MRI at 7 Tesla (Bruker, Rheinstetten, Germany). At the endpoint of the study, three and six weeks after transplantation, the muscles are harvested and histologically and immunohistochemically analysed.

Results: Cells could be visualised inside the soleus muscle in the MRI 24 hours after transplantation showing characteristic signal extinctions in T2*-weighed images. The hypointense signal could be followed over the longest investigated time of six weeks and could be easily discriminated from the structures of the injured muscle. Preliminary results show that the cell pool changed its shape over time with the loss of an initially depicted injection canal and an increase in the surface/volume ratio. First histologic Prussian Blue stained sections showed co-localisation of the respective MRI signal and nanoparticle labelled cells. Fusion events of marked cells with regenerating myofibers could be observed.

Conclusion: Magnetic labelling of MSC is a powerful tool to analyse the in vivo behaviour of the cells after transplantation into a severly injured skeletal muscle. For the first time the observation of an intraindividual time course of the distribution of the transplanted cells is possible. Our preliminary results are promising and the ongoing work will further characterise migration processes and the correlation of the MRI results with muscle function evaluated by contraction force measurements.

Background: Scientific investigation of muscle trauma and regeneration is in need of well standardised models. These should mimic the clinical situation and be thoroughly described histologically and functionally. Existing models of blunt muscle injury are either based on segmental muscle damage or in case of whole muscle injury also affect the innervating structures. In this study we present a modified model of open crush injury to the whole soleus muscle of rats sparing the region of the neuromuscular junctions.

Methods: The left soleus muscles of male Sprague-Dawley rats were crushed with the use of a curved artery forceps. Functional regeneration was evaluated 1, 4 and 8 weeks after trauma (n = 6 per group) via in vivo measurement of muscle contraction force after fast twitch and tetanic stimulation of the sciatic nerve. The intact right soleus muscle served as an internal control. H & E staining was used for descriptive analysis of the trauma. The amount of fibrosis was determined histomorphologically on Picro-Sirius Red stained sections at each point of time.

Results: Across the evaluated regeneration period a continuous increase in contraction force after fast twitch as well as after tetanic stimulation could be observed – describing the functional regeneration of the traumatized soleus muscle over time. Tetanic force amounted to 0.34 ± 0.14 N, which are 23 ± 4% of the control side one week after trauma, and recovered to 55 ± 23% after eight weeks. Fast twitch contraction was reduced to 49 ± 7% of the control side at one week after injury and recovered to 68 ± 19% during the study period. Fibrotic tissue occupied 40 ± 4% of the traumatized muscles after the first week, decreased to approximately 25% after four weeks and remained at this value at eight weeks.

Conclusion: The trauma model characterised morphologically and functionally in the presented study allows the investigation of muscle regeneration caused by highly standardized injury exclusively to muscle fibers.