The enhancement of periosteal chondrogenesis in organ culture by dynamic fluid pressure

Relationship between knee osteophytes and calcitonin gene-related peptide concentrations of serum and synovial fluid in knee of osteoarthritis

To explore the relationship between knee osteophytes of osteoarthritic knee and calcitonin gene-related peptide (CGRP) concentrations of serum and synovial fluid (SF). 65 patients with knee medial compartment osteoarthritis (OA) were recruited and examined with weight-bearing radiographs of the entire lower limb. The concentrations of CGRP in serum/SF were also detected in surgery. The relationship between the concentrations of CGRP in serum/SF and osteophyte scores were detected with Spearman rank correlation coefficient. CGRP concentrations in serum and SF were significantly correlated with osteophyte score of overall knee respectively (R = 0.462, P < .001; R = 0.435, P < .001). In addition, a correlation tended to be observed about the relationship between CGRP concentrations in serum and SF and osteophyte scores of medial compartment (R = 0.426, P < .001; R = 0.363, P = .003), and osteophyte scores of lateral compartment (R = 0.429, P < .001; R = 0.444, P < .001). In this study, the relationship between CGRP in serum/SF and knee osteophyte scores in different subregions were explored, which showed significant positive correlations, that possibly reflecting the contribution of CGRP influencing osteophyte formation. Positive correlations between osteophyte scores and CGRP suggest that CGRP promote the growth of osteophyte formation. It has the potential to be selected as a biomarker for the assessment of severity in knee OA patients and predict the progression of knee OA. It also provides a potential therapeutic target to delay the progression and relieve the symptom of OA.

Effects of and Response to Mechanical Loading on the Knee

Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, musculotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions, and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and specificity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation.

Enhanced chondrogenic phenotype of primary bovine articular chondrocytes in Fibrin-Hyaluronan hydrogel by multi-axial mechanical loading and FGF18

Current treatments for cartilage lesions are often associated with fibrocartilage formation and donor site morbidity. Mechanical and biochemical stimuli play an important role in hyaline cartilage formation. Biocompatible scaffolds capable of transducing mechanical loads and delivering bioactive instructive factors may better support cartilage regeneration. In this study we aimed to test the interplay between mechanical and FGF-18 mediated biochemical signals on the proliferation and differentiation of primary bovine articular chondrocytes embedded in a chondro-conductive Fibrin-Hyaluronan (FB/HA) based hydrogel. Chondrocytes seeded in a Fibrin-HA hydrogel, with or without a chondro-inductive, FGFR3 selective FGF18 variant (FGF-18v) were loaded into a joint-mimicking bioreactor applying controlled, multi-axial movements, simulating the natural movements of articular joints. Samples were evaluated for DNA content, sulphated glycosaminoglycan (sGAG) accumulation, key chondrogenic gene expression markers and histology. Under moderate loading, samples produced particularly significant amounts of sGAG/DNA compared to unloaded controls. Interestingly there was no significant effect of FGF-18v on cartilage gene expression at rest. Following moderate multi-axial loading, FGF-18v upregulated the expression of Aggrecan (ACAN), Cartilage Oligomeric Matrix Protein (COMP), type II collagen (COL2) and Lubricin (PRG4). Moreover, the combination of load and FGF-18v, significantly downregulated Matrix Metalloproteinase-9 (MMP-9) and Matrix Metaloproteinase-13 (MMP-13), two of the most important factors contributing to joint destruction in OA. Biomimetic mechanical signals and FGF-18 may work in concert to support hyaline cartilage regeneration and repair. STATEMENT OF SIGNIFICANCE: Articular cartilage has very limited repair potential and focal cartilage lesions constitute a challenge for current standard clinical procedures. The aim of the present research was to explore novel procedures and constructs, based on biomaterials and biomechanical algorithms that can better mimic joints mechanical and biochemical stimulation to promote regeneration of damaged cartilage. Using a hydrogel-based platform for chondrocyte 3D culture revealed a synergy between mechanical forces and growth factors. Exploring the mechanisms underlying this mechano-biochemical interplay may enhance our understanding of cartilage remodeling and the development of new strategies for cartilage repair and regeneration.

A Case Report of an Osteoid Osteoma on the Bearing Surface of the Talus Treated with Arthroscopic Resection Associated with Autologous Iliac Crest Graft

Osteoid osteomas are most likely to occur in the talar neck and can be classified as cortical, cancellous, or subperiosteal according to the position of the tumor nidus. However, cases located on the bearing surface of the talus are rare. Herein, the patient presented with an osteoid osteoma on the bearing surface of the talus and achieved good curative effects with arthroscopic resection associated with autologous iliac crest graft.

The vascularized periosteum flap as novel tissue engineering model for repair of cartilage defects

Periosteum is a promising tissue engineering scaffold in research of cartilage repair; so far however, periosteum transfers have not been realized successfully because of insufficient nourishment of the graft. In a translational approach we, for the first time, designed a vascularized periosteum flap as ‘independent’ biomaterial with its own blood supply to address this problem and to reconstruct circumscript cartilage defects. In six 3-month-old New Zealand rabbits, a critical size cartilage defect of the medial femur condyle was created and covered by a vascularized periosteum flap pedicled on the saphenous vessels. After 28 days, formation of newly built cartilage was assessed macroscopically, histologically and qualitatively via biomechanical compression testing, as well as on molecular biological level via immunohistochemistry. All wounds healed completely, all joints were stable and had full range of motion. All flaps survived and were perfused through their pulsating pedicles. They showed a stable attachment to the bone, although partially incomplete adherence. Hyaline cartilage with typical columnar cell distribution and positive Collagen II staining was formed in the transferred flaps. Biomechanical testing revealed a significantly higher maximum load than the positive control, but a low elasticity. This study proved that vascularization of the periosteum flap is the essential step for flap survival and enables the flap to transform into cartilage. Reconstruction of circumscript cartilage defects seems to be possible. Although these are the first results out of a pilot project, this technique, we believe, can have a wide range of potential applications and high relevance in the clinical field.

Continuous passive motion following cartilage surgery: does a common protocol exist?

Continuous passive motion (CPM) devices have the potential to improve the histological content as well as the rate and volume of chondrogenesis in repair tissue following chondral injury. However, clinical evidence is lacking to support broad implementation of CPM following cartilage restoration procedures. We searched PubMed, CINAHL, SPORTDiscus, and Cochrane for such terms as knee, continuous passive motion, CPM, ACI, ACT, autologous chondrocyte implantation, autologous chondrocyte transplantation, microfracture, marrow-stimulation technique, mosaicplasty, osteochondral autograft, and osteochondral allograft. Inclusion criteria were all English-language studies of human subjects, evidence levels I to IV, reporting the use of CPM following cartilage repair or restoration surgery in the knee. One hundred and seven studies met inclusion criteria. Sixty-three studies reported the use of CPM following autologous chondrocyte implantation; 28 reported the use of CPM following microfracture; 13 reported the use of CPM following osteochondral autograft; and 15 reported the use of CPM following osteochondral allograft (several studies reported > 1 type of cartilage procedure, which explains why the sum of all studies reporting a particular procedure [119] is greater than the number of studies included in the review [107]). Of the 5723 patients included, 60.8% were treated with autologous chondrocyte implantation, 23.1% were treated with microfracture, 6.4% were treated with osteochondral autograft, and 9.7% were treated with osteochondral allograft. Of the 6612 total defects, 5043 (76.3%) were tibiofemoral and 1569 (23.7%) were patellofemoral. Most reports of CPM use after cartilage restoration procedures did not include specific information on how it was implemented. Overall, the description of CPM protocols in published knee articular cartilage surgery studies was disappointing. The majority of studies did not describe common variables such as the duration of CPM therapy, the initiation of CPM therapy, and the initial range of motion used. The most commonly prescribed parameters within a CPM regimen are initiated on the first postoperative day, with an initial range-of-motion of 0 to 30 degrees and a frequency of 1 cycle per minute, and for 6 to 8 hours daily over 6 weeks. The lack of consistent standardized reporting of postoperative CPM protocols provides an impetus to researchers and clinicians to more clearly define and describe their use following knee articular surgery.

Ankle joint distraction arthroplasty: why and how?

For select patients, distraction ankle arthroplasty may be a promising treatment approach for ankle osteoarthritis; however, there is still limited literature addressing its efficacy and clinical long-term results. In this article, the literature regarding the outcome after ankle distraction arthroscopy is reviewed, the indications and contraindication for this procedure are listed, our surgical technique is described, and our preliminary results with this procedure are presented.

Concise review: the periosteum: tapping into a reservoir of clinically useful progenitor cells

Elucidation of the periosteum and its regenerative potential has become a hot topic in orthopedics. Yet few review articles address the unique features of periosteum-derived cells, particularly in light of translational therapies and engineering solutions inspired by the periosteum's remarkable regenerative capacity. This review strives to define periosteum-derived cells in light of cumulative research in the field; in addition, it addresses clinical translation of current insights, hurdles to advancement, and open questions in the field. First, we examine the periosteal niche and its inhabitant cells and the key characteristics of these cells in the context of mesenchymal stem cells and their relevance for clinical translation. We compare periosteum-derived cells with those derived from the marrow niche in in vivo studies, addressing commonalities as well as features unique to periosteum cells that make them potentially ideal candidates for clinical application. Thereafter, we review the differentiation and tissue-building properties of periosteum cells in vitro, evaluating their efficacy in comparison with marrow-derived cells. Finally, we address a new concept of banking periosteum and periosteum-derived cells as a novel alternative to currently available autogenic umbilical blood and perinatal tissue sources of stem cells for today's population of aging adults who were "born too early" to bank their own perinatal tissues. Elucidating similarities and differences inherent to multipotent cells from distinct tissue niches and their differentiation and tissue regeneration capacities will facilitate the use of such cells and their translation to regenerative medicine.

A novel recirculating flow-perfusion bioreactor for periosteal chondrogenesis

PURPOSE

Previous research indicated that engineered cartilage was soft and fragile due to less extracellular matrix than native articular cartilage. Consequently, the focus of this study was mostly confined to application in vitro function. In order to generate 3D engineered cartilage resembling native articular cartilage, we developed a recirculating flow-perfusion bioreactor to simulate the motion of a native diarthrodial joint by offering shear stress and hydrodynamic pressure simultaneously.

MATERIALS

The bioreactor we developed offers steady oscillating laminar flow (maximum shear stress of 250 dyne/cm(2)) and hydrodynamic pressure (increased from 0 to 15 psi) simultaneously. The periosteal explants were harvested from the proximal medial tibiae of rabbits and fixed onto PCL scaffold with four corner sutures and cambium layer facing upward, then these periosteal composites (periosteum/ PCL) were placed into the culture chamber of our bioreactor for six weeks in vitro culture.

RESULTS

The cartilage yield in our recirculating bioreactor was 75-85%. The outcome was better than the 65-75% in the spinner flask bioreactor (shear stress only) and 17% in static culture. In addition, there was a significant difference in the cell morphology and zonal organisation among the three methods of culture; the engineered cartilage in the recirculating bioreactor presented many more characteristics of native articular cartilage.

CONCLUSIONS

If the environment of culture provides the shear stress and hydrodynamic pressure simultaneously, the composition of the engineered cartilage resembles native articular cartilage, including their ECM composition, cell distribution, zonal organisation and mechanical properties.

Directional fluid flow enhances in vitro periosteal tissue growth and chondrogenesis on poly-epsilon-caprolactone scaffolds

The purpose of this study was to investigate the effect of directional fluid flow on periosteal chondrogenesis. Periosteal explants were harvested from 2-month-old rabbits and sutured onto poly-epsilon-caprolactone (PCL) scaffolds with the cambium layer facing away from the scaffolds. The periosteum/PCL composites were cultured in suspension in spinner flask bioreactors and exposed to various fluid flow velocities: 0, 20, 60, and 150 rpm for 4 h each day for 6 weeks. The application of fluid flow significantly increased percent cartilage yield in periosteal explants from 17% in the static controls to 65-75% under fluid flow (there was no significant difference between 20, 60, or 150 rpm). The size of the neocartilage was also significantly greater in explants exposed to fluid flow compared with static culture. The development of zonal organization within the engineered cartilage was observed predominantly in the tissue exposed to flow conditions. The Young's modulus of the engineered cartilage exposed to 60 rpm was significantly greater than the samples exposed to 150 and 20 rpm. These results demonstrate that application of directional fluid flow to periosteal explants secured onto PCL scaffolds enhances cell proliferation, chondrogenic differentiation, and cell organization and alters the biomechanical properties of the engineered cartilage.

Tuning the differentiation of periosteum-derived cartilage using biochemical and mechanical stimulations

OBJECTIVE

In this study, we aim at tuning the differentiation of periosteum in an organ culture model towards cartilage, rich in collagen type II, using combinations of biochemical and mechanical stimuli. We hypothesize that addition of TGF-β will stimulate chondrogenesis, whereas sliding indentation will enhance collagen synthesis.

DESIGN

Periosteum was dissected from the tibiotarsus of 15-day-old chick embryos. Explants were embedded in between two agarose layers, and cultured without stimulation (control), with biochemical stimulation (10 ng/ml TGF-β1), with mechanical stimulation (sliding indentation), or both biochemical and mechanical stimulations. Sliding indentation was introduced as a method to induce tensile tissue strain. Analysis included quantification of DNA, collagen and GAG content, conventional histology, and immunohistochemistry for collagen type I and II at 1 or 2 weeks of culture.

RESULTS

Embedding the periosteal explants in between agarose layers induced cartilage formation, confirmed by synthesis of sGAG and collagen type II. Addition of TGF-β1 to the culture medium did not further enhance this chondrogenic response. Applying sliding indentation only to the periosteum in between agarose layers enhanced the production of collagen type I, leading to the formation of fibrous tissue without any evidence of cartilage formation. However, when stimulated by both TGF-β1 and sliding indentation, collagen production was still enhanced, but now collagen type II, while sGAG was found to be similar to TGF-β1 or unloaded samples.

CONCLUSIONS

The type of tissue produced by periosteal explants can be tuned by combining mechanical stimulation and soluble factors. TGF-β1 stimulated a chondrocyte phenotype and sliding indentation stimulated collagen synthesis. Such a combination may be valuable for improvement of the quality of tissue-engineered cartilage.

Continuous Passive Motion, Early Weight Bearing, and Active Motion following Knee Articular Cartilage Repair: Evidence for Clinical Practice

OBJECTIVE

To systematically review the literature regarding postoperative rehabilitation for articular cartilage repair: (1) does the use of continuous passive motion (CPM) enhance healing, and if so, what parameters should be applied? (2) Can active range of motion (AROM) be used in place of or with CPM? (3) When can individuals safely resume weight bearing (WB) following repair?

DATA SOURCES

A search using Medline, SportsDiscus, and CINAHL databases was performed with the following keywords: articular cartilage, AROM, CPM, microfracture, osteochondral allograft, autologous chondrocyte implantation, rehabilitation, weight bearing, and knee.

STUDY SELECTION

Basic science or clinical outcomes examining the effects of CPM, AROM, or WB on knee articular cartilage healing.

DATA EXTRACTION

Selected articles were rated using the Strength of Recommendation Taxonomy (SORT) to determine evidence for clinical application.

DATA SYNTHESIS

Sixteen articles met selection criteria: 12 were basic science studies; 4 were clinical studies. Basic science evidence supporting CPM exists. However, few patient-oriented outcomes have been documented resulting in a SORT rating of C. Early WB and AROM received a SORT rating of B based on limited clinical research and patient-oriented outcomes.

CONCLUSIONS

Basic science evidence supports CPM to maintain ROM, reduce pain, and promote healing. Patient-oriented research is needed to strengthen CPM's recommendation. Limited evidence exists regarding early WB and AROM post cartilage repair. There is insufficient evidence to confidently address when to begin WB for maximum healing. Appropriate basic science and patient-oriented research are needed for rehabilitation protocols to maximize benefits of cartilage repair procedures.

Improving chondrogenesis: potential and limitations of SOX9 gene transfer and mechanical stimulation for cartilage tissue engineering

Articular cartilage injuries and degeneration affect a large proportion of the population in developed countries world wide. Stem cells can be differentiated into chondrocytes by adding transforming growth factor-beta1 and dexamethasone to a pellet culture, which are unfeasible for tissue engineering purposes. We attempted to achieve stable chondrogenesis without any requirement for exogenous growth factors. Human mesenchymal stem cells were transduced with an adenoviral vector containing the SRY-related HMG-box gene 9 (SOX9), and were cultured in a three-dimensional (3D) hydrogel scaffold composite. As an additional treatment, mechanical stimulation was applied in a custom-made bioreactor. SOX9 increased the expression level of its known target genes, as well as its cofactors: the long form of SOX5 and SOX6. However, it was unable to increase the synthesis of sulfated glycosaminoglycans (GAGs). Mechanical stimulation slightly enhanced collagen type X and increased lubricin expression. The combination of SOX9 and mechanical load boosted GAG synthesis as shown by (35)S incorporation. GAG production rate corresponded well with the amount of (endogenous) transforming growth factor-beta1. Finally, cartilage oligomeric matrix protein expression was increased by both treatments. These findings provide insight into the mechanotransduction of mesenchymal stem cells and demonstrate the potential of a transcription factor in stem cell therapy.

Repair of articular cartilage defects: review and perspectives

Articular cartilage defects heal poorly and lead to catastrophic degenerative arthritis. Clinical experience has indicated that no existing medication substantially promotes the healing process and the cartilage defect requires surgical replacement, preferably with an autograft. However, there is a shortage of articular cartilage that can be donated for autografting. A review of previous unsuccessful experiences reveals the reason for the current strategy to graft cartilage defects with regenerated cartilage. Autologous cartilage regeneration is a cell-based therapy in which autogenous chondrocytes or other chondrogenic cells are cultured to constitute cartilaginous tissue according to the principles of tissue engineering. Current studies are concentrating on improving such techniques from the three elements of tissue engineering, namely the cells, biomaterial scaffolds, and culture conditions. Some models of articular cartilage regeneration have yielded good repair of cartilage defects, in animal models and clinical settings, but the overall results suggest that there is room for improvement of this technique before its routine clinical application. Autologous cartilage regeneration remains the mainstay for repairing articular cartilage defects but more studies are required to optimize the efficacy of regeneration. A more abundant supply of more stable cells, i.e. capable of maintaining the phenotype of chondrogenesis, has to be identified. Porous scaffolds of biocompatible, biodegradable materials that maintain and support the presentation of the chondrogenic cells need to be fabricated. If the cells are not implanted early to allow their in vivo constitution of cartilage, a suitable in vitro cultivation method has to be devised for a consistent yield of regenerative cartilage.

In vivo mechanical condition plays an important role for appearance of cartilage tissue in ES cell transplanted joint

The objective of this study was to evaluate the effects of the mechanical environment on the formation of cartilage tissue in transplanted embryonic stem (ES) cells. Full-thickness osteochondral defects were created on the patella groove of SD rats, and ES cells (CCE ES cells obtained from 129/Sv/Ev mice and Green ES FM260 ES cells obtained from 129SV [D3] - Tg [NCAG-EGFP] CZ-001-FM260Osb mice) were transplanted into the defects embedded in collagen gel. The animals were randomly divided into either the joint-free group (JF group) or the joint-immobilized group (JI group) for 3 weeks after a week postoperatively. The results showed that cartilage-like tissue formed in the defects of the JF group whereas large teratomatous masses developed in the defects of the JI group. Some parts of the cartilage-like tissue and the teratomatous masses were positively stained with immunostain for GFP when the Green ES FM260 ES cells were transplanted. It is suggested that the environment plays an important role for ES cells in the process of repairing cartilage tissue in vivo.

Osteophytes: relevance and biology

OBJECTIVE

Osteophytes are common features of osteoarthritis. This review summarizes the current understanding of the clinical relevance and biology of osteophytes.

METHOD

This review summarizes peer-reviewed articles published in the PubMed database before May 2006. In addition this review is supplemented with own data and theoretical considerations with regard to osteophyte formation.

RESULTS

Osteophytes can contribute both to the functional properties of affected joints and to clinical relevant symptoms. Osteophyte formation is highly associated with cartilage damage but osteophytes can develop without explicit cartilage damage. Osteophytes are mainly derived from precursor cells in the periosteum and growth factors of the TGFbeta superfamily appear to play a crucial role in their induction.

CONCLUSION

Osteophyte formation is an integral component of OA pathogenesis and understanding the biology of osteophyte formation can give insights in the disturbed homeostasis in OA joints.

Effect of low loading and joint immobilization for spontaneous repair of osteochondral defect in the knees of weightless (tail suspension) rats

BACKGROUND

Mechanical stimulation has a great influence on articular cartilage regeneration. The objective of this study was to clarify the temporal sequences of spontaneous repair of weightless or immobilized joints.

METHODS

An osteochondral defect was created in the femoral patellar groove of F344 rats. A tail-suspension procedure was performed to control the mechanical environment of the hindlimbs. The experimental knee joints were classified into three conditions: CONT, normal gait; LLB, low load-bearing; LLI, low load and immobilized. The repair processes up to 4 weeks were evaluated histologically.

RESULTS

The knee defects in the CONT and LLB conditions were repaired to a smooth surface with fibrous tissue and highly developed subchondral bone. The knees in the LLI condition had the lowest reformation rate of subchondral bone, although partial regeneration of hyaline cartilage-like tissue was seen at 4 weeks after the operation. Bulges of fibrous tissue from the defects were observed in the LLI condition.

CONCLUSIONS

These results, combined with our previous report, suggest that dynamic compressive strain stimulates regeneration of the joint surface structures. They also suggest that the contact condition of the defect with surface cartilage may play a role in the hyaline cartilage repair.

Repair of large full-thickness articular cartilage defects in the rabbit

We produced large full-thickness articular cartilage defects in 33 rabbits in order to evaluate the effect of joint distraction and autologous culture-expanded bone-marrow-derived mesenchymal cell transplantation (ACBMT) at 12 weeks. After fixing the knee on a hinged external fixator, we resected the entire surface of the tibial plateau. We studied three groups: 1) with and without joint distraction; 2) with joint distraction and collagen gel, and 3) with joint distraction and ACBMT and collagen gel.

The histological scores were significantly higher in the groups with ACBMT collagen gel (p < 0.05). The area of regenerated soft tissue was smaller in the group allowed to bear weight (p < 0.05). These findings suggest that the repair of large defects of cartilage can be enhanced by joint distraction, collagen gel and ACBMT.

On bone adaptation due to venous stasis

This paper addresses the question of whether or not interstitial fluid flow due to the blood circulation accounts for the observed periosteal bone formation associated with comprised venous return (venous stasis). Increased interstitial fluid flow induced by increased intramedullary pressure has been proposed to account for the periosteal response in venous stasis. To investigate the shear stresses acting on bone cell processes due to the blood circulation-driven interstitial fluid flow, a poroelastic model is extended to the situation in which the interstitial fluid flow in an osteon is driven by the pulsatile extravascular pressure in the osteonal canal as well as by the applied cyclic mechanical loading. Our results show that under normal conditions, the pulsatile extravascular pressure in the osteonal canal due to cardiac contraction (10mm Hg at 2Hz) and skeletal muscle contraction (30mm Hg at 1Hz) induce peak shear stresses on the osteocyte cell processes that are two orders of magnitude lower than those induced by physiological mechanical loading (100 microstrain at 1Hz). In venous stasis the induced peak shear stress is reduced further compared to the normal conditions because, although the mean intramedullary pressure is increased, the amplitude of its pulsatile component is decreased. These results suggest that the interstitial fluid flow is unlikely to cause the periosteal bone formation in venous stasis. However, the mean interstitial fluid pressure is found to increase in venous stasis, which may pressurize the periosteum and thus play a role in periosteal bone formation.

Osteophyte development--molecular characterization of differentiation stages

OBJECTIVE

Osteophytes are non-neoplastic osteo-cartilaginous protrusions growing at the margins of osteoarthritic joints. They can not only be considered as in situ repair tissue, but also represent an excellent in vivo model for induced cartilage repair processes. Our focus was to identify different steps of osteophyte development via analysis of expression patterns of marker genes of chondrocytic differentiation.

DESIGN

We performed an extensive analysis of the presence and expression of matrix components using histochemical, immunohistochemical and in situ hybridization technology.

RESULTS

Four different stages of osteophyte formation could be identified based on histomorphological and cell biological parameters: starting from mesenchymal condensates, chondrogenic differentiation is indicated by the onset of Col2A and aggrecan expression (stage I). Stage II shows fibrocartilage with an admixture of cartilaginous and fibrous matrix components such as Col2 and aggrecan on the one hand and Col1 on the other hand. The proliferating osteophyte (stage III) shows a zonal organization similar to the fetal growth plate cartilage with extensive chondrocyte hypertrophy in the zones next to ongoing endochondral bone formation. 'Mature' osteophytes (stage IV) resembled largely articular hyaline cartilage with a predominance of Col2 and aggrecan and Col6 found mainly pericellularily.

CONCLUSIONS

The development of osteophytes is a good in vivo model to pursue chondrocyte differentiation from pluripotent mesenchymal cells to mature or hypertrophic chondrocytes in situ in the adult. The analysis of marker molecules of mesenchymal differentiation allows to identify different stages of repair tissue development and the transformation from fibrous tissue to neo-cartilage. Tissue architecture and matrix composition in mature osteophytes suggests that metaplastic neo-cartilagenous tissue might be one potential source of cartilage repair tissue in the adult joint.

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects

OBJECTIVE

To review the basic scientific status of repair in articular cartilage tissue and to assess the efficiency of current clinical therapies instigated for the treatment of structural lesions generated therein as a result of trauma or during the course of various diseases, notably osteoarthritis (OA). Current scientific trends and possible directions for the future will also be discussed.

DESIGN

A systematic and critical analysis is undertaken, beginning with a description of the spontaneous repair responses in different types of lesion. Surgical interventions aimed at inducing repair without the use of active biologics will then be considered, followed by those involving active biologics and those drawing on autogenic and allogeneic tissue transplantation principles. Cell transplantation approaches, in particular novel tissue engineering concepts, will be critically presented. These will include growth-factor-based biological treatments and gene transfection protocols. A number of technical problems associated with repair interventions, such as tissue integration, tissue retention and the role of mechanical factors, will also be analysed.

RESULTS

A critical analysis of the literature reveals the existence of many novel and very promising biologically-based approaches for the induction of articular cartilage repair, the vast majority of which are still at an experimental phase of development. But prospective, double-blinded clinical trials comparing currently practiced surgical treatments have, unfortunately, not been undertaken.

CONCLUSION

The existence of many new and encouraging biological approaches to cartilage repair justifies the future investment of time and money in this research area, particularly given the extremely high socio-economic importance of such therapeutic strategies in the prevention and treatment of these common joint diseases and traumas. Clinical epidemiological and prospective trials are, moreover, urgently needed for an objective, scientific appraisal of current therapies and future novel approaches.

Brief exposure to high-dose transforming growth factor-beta1 enhances periosteal chondrogenesis in vitro: a preliminary report

BACKGROUND

Articular cartilage has limited potential for repair. There have been various attempts aimed at improving the repair process in articular cartilage. Transforming growth factor-beta1 (TGF-beta1) has a stimulatory effect on chondrogenesis in periosteal explants. The purpose of the present study was to determine the effect of brief exposures (i.e., thirty and sixty minutes) of high concentrations of TGF-beta1 on periosteal chondrogenesis.

METHODS

Five hundred and seventy-three periosteal explants were harvested from forty-six two-month-old male New Zealand White rabbits. Explants were exposed to 50 or 100 ng/mL of TGF-beta1 for thirty or sixty minutes. The amount of cartilage formed was then determined with use of a standardized six-week agarose culture assay.

RESULTS

There was a significant increase in the amount of cartilage formation (p < 0.01), Type-II collagen content (p < 0.05), and sulfate incorporation (p < 0.0001) in explants treated with TGF-beta1. Maximal stimulation occurred following exposure to 100 ng/mL of TGF-beta1 for thirty minutes. There was also an increase in chondrocyte proliferation as measured by [ (3) H-] thymidine incorporation on day 5 of culture (p < 0.049).

CONCLUSIONS

The findings of this study indicate that exposure to TGF-beta1 has a stimulatory effect on periosteal chondrogenesis. This stimulatory effect is observed even with a very brief exposure time of thirty minutes.

CLINICAL RELEVANCE

A possible clinical application of these findings is exposure of periosteal grafts that are currently utilized clinically to resurface articular defects to TGF-beta1 during the short time between graft procurement and implantation into the joint. This may obviate the need for intra-articular administration of TGF-beta1 and may enhance the ultimate graft incorporation and quality of cartilage repair.

Expression of beta1 integrins during periosteal chondrogenesis

OBJECTIVE

The interactions between integrins and extracellular matrix proteins are known to modulate cell behavior, and may be involved in regulating cartilage formation and repair. The purpose of this study was to determine the patterns and localization of expression of the beta1 integrins during cartilage formation by periosteum, which is used to repair articular cartilage.

DESIGN

Periosteal explants from 2-month-old rabbit medial proximal tibiae were cultured in agarose suspension for 0 to 6 weeks, with 10 ng/ml transforming growth factor-beta1 added for the first 2 days of culture. Integrin expressions were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and localized by immunohistochemistry.

RESULTS

Normal periosteum expressed the alpha1, alpha3, alpha5, beta1 subunits at low levels, and the proteins for all but the alpha3 subunits were identified by immunohistochemistry in the periosteum. Significant two- to five-fold up-regulation of the mRNA expression of the alpha1, alpha3, alpha5 and beta1 integrin subunits during the early proliferative stage of chondrogenesis was observed. The initial change was a five-fold increase in alpha5 expression on day 2 and a two-fold increase in alpha3 expression. On day 5, alpha1 expression was up-regulated (four-fold). beta1 expression was broadly up-regulated (three to four-fold) from day 5 to 14. In the early stage of chondrocyte differentiation, after day 14, alpha1 expression was down-regulated, while there was upregulation of alpha3 (three-fold), alpha5 (three-fold) and beta1 (four-fold) expressions. Thereafter, alpha1 expression was down-regulated, while alpha3, alpha5 and beta1 expressions were up-regulated again during matrix synthesis. Immunohistochemistry confirmed this late decrease in alpha1 levels and increase in alpha3, alpha5 and beta1 levels in chondrocytes.

CONCLUSIONS

These observations indicate that the beta1 integrins play an important role in the process of chondrogenesis in periosteum.

Technical considerations in periosteal grafting for osteochondral injuries

Periosteum has been used clinically for biologic resurfacing arthroplasty in small series of patients for almost two decades. The author's own experience with this technique in multiple joints, including the knee, has been similar to that already reported in the literature. Observations and considerations are discussed that might help avoid failure in future applications of this technique. Indications and surgical technique, including graft procurement and fixation, and postoperative treatment and possible complications are also described. The rationale for using periosteum as a chondrogenic tissue and the factors affecting its cartilage production are also outlined.