Explant analysis and implant registries are both needed to further improve patient safety.

In the early days of total joint replacement, implant fracture, material problems and wear presented major problems for the long-term success of the operation. Today, failures directly related to the implant comprise only 2-3% of the reasons for revision surgeries, which is a result of the material and design improvements in combination with the standardization of pre-clinical testing methods and the post-market surveillance required by the legal regulation. Arthroplasty registers are very effective tools to document the long-term clinical performance of implants and implantation techniques such as fixation methods in combination with patient characteristics. Revisions due to implant failure are initially not reflected by the registries due to their small number. Explant analysis including patient, clinical and imaging documentation is crucial to identify failure mechanisms early enough to prevent massive failures detectable in the registries. In the past, early reaction was not always successful, since explant analysis studies have either been performed late or the results did not trigger preventive measures until clinical failures affected a substantial number of patients. The identification of implant-related problems is only possible if all failures are reported and related to the number of implantations. A system that analyses all explants from revisions attributed to implant failure is mandatory to reduce failures, allowing improvement of risk assessment in the regulatory process.

Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the "race for the surface" theory.

OBJECTIVES: Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the 'race for the surface' theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied. METHODS: We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis. RESULTS: Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria. CONCLUSIONS: The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence.Cite this article: M. Martinez-Perez, C. Perez-Jorge, D. Lozano, S. Portal-Nuñez, R. Perez-Tanoira, A. Conde, M. A. Arenas, J. M. Hernandez-Lopez, J. J. de Damborenea, E. Gomez-Barrena, P. Esbrit, J. Esteban. Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the "race for the surface" theory. Bone Joint Res 2017;6:315-322. DOI: 10.1302/2046-3758.65.BJR-2016-0226.R2.

Meniscal degeneration in human knee osteoarthritis: in situ hybridization and immunohistochemistry study.

OBJECTIVE: Meniscus injury is one of the causes of secondary osteoarthritis (OA). However, the role of meniscus is still unclear. Human meniscal distribution of cells and cartilage oligomeric matrix protein (COMP) and their changes in advanced OA were analyzed. PATIENTS AND METHODS: Thirty-one medial menisci from patients with knee OA that underwent a total knee arthroplasty were studied. Normal meniscal tissue was obtained from partial arthroscopic meniscectomy. Meniscal samples were processed for histology, immunohistochemistry and in situ hybridization, for cell assessment including density, active divisions, apoptosis, COMP distribution and proteoglycan content. RESULTS: Osteoarthritic menisci demonstrated areas of cell depletion and significant decrease in COMP immunostaining. Actively dividing cells were only found in the meniscectomy group, but not in the osteoarthritic group. Proteoglycan staining was less prominent in menisci from the osteoarthritis group. CONCLUSIONS: Our results show a decreased cell population, with low COMP and altered matrix organization in osteoarthritis menisci that suggest an altered meniscal scaffold and potential impairment of meniscal function. These meniscal changes may be associated with the development of knee osteoarthritis.

The relevance of biomaterials to the prevention and treatment of osteoporosis.

Osteoporosis is a worldwide disease with a very high prevalence in humans older than 50. The main clinical consequences are bone fractures, which often lead to patient disability or even death. A number of commercial biomaterials are currently used to treat osteoporotic bone fractures, but most of these have not been specifically designed for that purpose. Many drug- or cell-loaded biomaterials have been proposed in research laboratories, but very few have received approval for commercial use. In order to analyze this scenario and propose alternatives to overcome it, the Spanish and European Network of Excellence for the Prevention and Treatment of Osteoporotic Fractures, "Ageing", was created. This network integrates three communities, e.g. clinicians, materials scientists and industrial advisors, tackling the same problem from three different points of view. Keeping in mind the premise "living longer, living better", this commentary is the result of the thoughts, proposals and conclusions obtained after one year working in the framework of this network.

Factors influencing regional variability in the rate of total knee arthroplasty.

BACKGROUND AND PURPOSE: Geographic variations in knee arthroplasty have been detected through international surveys. We aim to investigate in this study the influence of aging index, health budget, and number of orthopedic surgeons in the regional variations of the primary and revision TKA rate in a single European country, Spain. MATERIAL AND METHODS: Inpatient database of knee arthroplasty procedures for years 1997 to 2010 was obtained from the Spanish Ministry of Health, including 393,714 primaries and 37,037 revisions, segregated for each of the 17 regional health services in Spain. Crude and adjusted rates (direct method with total Spanish population per year) were calculated and used as dependent variables. Aging index, regional health budget, and number of orthopedic surgeons per region were used as independent variables in a Kruskal-Wallis test and a negative binomial regression analysis model. RESULTS AND CONCLUSIONS: With a mean crude rate for Spain of 76 primary TKA and 7 revision surgeries per 10(5) population and year, the mean adjusted rate per region oscillated between 702 and 27 primary TKA and 87 and 3 revisions per 10(5). A model was adjusted confirming the influence of aging index, health budget, and number of surgeons, but regional variations remained partly unexplained by these factors.

Evaluation of a minimally aggressive method of patellofemoral osteoarthritis treatment at 10 years minimum follow-up.

BACKGROUND: Knee osteoarthritis mainly affecting the lateral facet of the patella, especially in young patients, is a definite challenge to the surgeon. Our purpose was to investigate the long-term outcome of a simple operation such as the partial lateral facetectomy on middle-aged to elderly patients with predominant lateral patellofemoral osteoarthritis. METHODS: A retrospective, long-term study of 39 knees (28 females, mean aged at surgery 61yearsold) with a minimum follow-up of 10years was performed. Evaluations included preoperative and postoperative questionnaires, physical examinations, and radiographs. RESULTS: The main outcomes included the initial anterior pain relief, with higher scores using the Knee Society Score (that improved in 84% of the knees), and the eventual failure of the technique, including percentage of patients that required secondary total knee replacement (30% of the knees). CONCLUSION: Partial lateral facetectomy aiming to decrease the high pressure in the lateral facet of the patella confirmed frequent pain relief. This surgical procedure being minimally invasive, relatively simple, and effective in selected patients, is a valid early alternative to more complex operations and does not preclude further reconstructive surgery in case of disease progression.

Parámetros de marcha en una muestra de referencia de escolares sanos españoles: descripción multivariante y asimetrías entre ciclos izquierdos y derechos / Gait parameters in a reference sample of healthy Spanish schoolchildren: multivariate descriptive statistics and asymmetries observed in left and right cycles

Introducción: El análisis instrumental de marcha (AIM) es una tecnología de uso creciente en la evaluación de trastornos motores infantiles. La evaluación de pacientes requiere una base de referencia de normalidad, pero existen pocas referencias infantiles españolas. Objetivo: Descripción de 16 variables de marcha de relevancia clínica en una muestra de referencia de escolares sanos. Estudio de sus relaciones lineales y asimetrías izquierda-derecha. Sujetos y métodos: Se midieron con AIM 16 variables de marcha en escolares sanos (n = 27, 5-13 años). Se estudiaron las asimetrías en cada variable (t de Student, muestras dependientes) y sus intervalos de confianza (95% de la media de diferencia estandarizada derecha menos izquierda, dz). Se representaron los valores y las asociaciones entre variables mediante «heatmap». Resultados: Se aportan tablas de normalidad para 16 variables del ciclo de marcha. Son significativamente asimétricos los valores medios de flexión mínima de cadera (dz: 0,25 IC del 95%, 0,11-0,39) y de máxima abducción de cadera en el balanceo (dz: -1,05 IC del 95%, —1,71; —0,27). Existen asociaciones funcionales entre las variables de marcha. Conclusiones: Presentamos una muestra de normalidad de escolares españoles donde se observan asimetrías entre los lados izquierdo y derecho y organización funcional entre sus variables (AU)

Introduction: Instrumental gait analysis is an emerging technology used increasingly to evaluate motor disorders in children. Normal reference data is necessary in order to evaluate patients, but there are few reference resources for the Spanish paediatric population. Objective: We aim to describe the values of 16 clinically relevant gait variables in healthy Spanish schoolchildren, and identify any linear associations or left-right asymmetries. Subjects and methods: The values of 16 gait variables were determined in schoolchildren (n = 27, aged 5-13 years) using instrumental gait analysis. We analysed asymmetries for each variable (Student’s t-test for dependent samples) and calculated their confidence intervals (95% of the standardised difference in right and left means [SMD]). Values and associations between variables were represented using a heat map. Results: Our project presents normal values tables for 16 variables in the gait cycle. Significant asymmetries were detected in the mean values for minimum hip flexion (SMD: 0.25 95% CI, 0.11-0.39) and peak hip abduction in swing (SMD: −1.05 95% CI: −1.71- − 0.27). Functional associations among gait variables are present. Conclusions: We present a reference dataset for Spanish school-aged children in which leftright asymmetries and functional associations may be observed for different variables (AU)

Gait parameters in a reference sample of healthy Spanish schoolchildren: multivariate descriptive statistics and asymmetries observed in left and right cycles.

INTRODUCTION: Instrumental gait analysis is an emerging technology used increasingly to evaluate motor disorders in children. Normal reference data is necessary in order to evaluate patients, but there are few reference resources for the Spanish paediatric population. OBJECTIVE: We aim to describe the values of 16 clinically relevant gait variables in healthy Spanish schoolchildren, and identify any linear associations or left-right asymmetries. SUBJECTS AND METHODS: The values of 16 gait variables were determined in schoolchildren (n=27, aged 5-13 years) using instrumental gait analysis. We analysed asymmetries for each variable (Student's t-test for dependent samples) and calculated their confidence intervals (95% of the standardised difference in right and left means [SMD]). Values and associations between variables were represented using a heat map. RESULTS: Our project presents normal values tables for 16 variables in the gait cycle. Significant asymmetries were detected in the mean values for minimum hip flexion (SMD: 0.25 95% CI, 0.11-0.39) and peak hip abduction in swing (SMD: -1.05 95% CI: -1.71--0.27). Functional associations among gait variables are present. CONCLUSIONS: We present a reference dataset for Spanish school-aged children in which left-right asymmetries and functional associations may be observed for different variables.

Sonication of intramedullary nails: clinically-related infection and contamination.

BACKGROUND AND AIM: Sonication is currently considered the best procedure for microbiological diagnosis of implant-related osteoarticular infection, but studies in nail-related infections are lacking. The study aim was to evaluate implant sonication after intramedullary nail explantation, and relate it to microbiological cultures and clinical outcome. PATIENTS AND METHODS: A study was performed in two University Hospitals from the same city. Thirty-one patients with implanted nails were prospectively included, whether with clinical infection (8 cases) or without (23 cases). Retrieved nails underwent sonication according a previously published protocol. The clinical and microbiological outcome patient was related to the presence of microorganisms in the retrieved implant. RESULTS: Positive results appeared in 15/31 patients (9 with polymicrobial infections) almost doubling those clinically infected cases. The most commonly isolated organisms were Staphylococcus epidermidis (19.2 %) and Staphylococcus aureus (15.4 %). A significant relationship was found between the presence of positive cultures and previous local superficial infection (p=0.019). The presence of usual pathogens was significantly related to clinical infection (p=0.005) or local superficial infection (p=0.032). All patients with positive cultures showed pain diminution or absence of pain after nail removal (15/15), but this only occurred in 8 (out of 16) patients with negative cultures. CONCLUSIONS: In patients with previously diagnosed infection or local superficial infection, study of the hardware is mandatory. In cases where pain or patient discomfort is observed, nail sonication can help diagnose the implant colonization with potential pathogens that might require specific treatment to improve the final outcome.

DLC coatings for UHMWPE: relationship between bacterial adherence and surface properties.

Development of intrinsically antibacterial surfaces is of key importance in the context of prostheses used in orthopedic surgery. This work presents a thorough study of several plasma-based coatings that may be used with this functionality: diamond-like carbon (DLC), fluorine-doped DLC (F-DLC), and a high-fluorine-content-carbon-fluor polymer (CF(X)). The coatings were obtained by a radio-frequency plasma-assisted deposition on ultra high molecular weight polyethylene (UHMWPE) samples and physicochemical properties of the coated surfaces were correlated with their antibacterial performance against collection and clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The fluorine content and the relative amount of C-C and C-F bonds were controlled by X-ray photoelectron spectroscopy, and hydrophobicity and surface tension by contact angle measurements. Surface roughness was studied by Atomic Force Microscopy. Additional nanoidentation studies were performed for DLC and F-DLC coatings. Unpaired t test and regression linear models evaluated the adherence of S. aureus and S. epidermidis on raw and coated UHMWPE samples. Comparing with UHMWPE, DLC/UHMWPE was the least adherent surface with independence of the bacterial species, finding significant reductions (p ≤ 0.001) for nine staphylococci strains. Bacterial adherence was also significantly reduced in F-DLC/ UHMWPE and CFx/UHMWPE for six strains.

Bacterial adhesion on biomedical surfaces covered by micrometric silver Islands.

A set of Cu-Mn-O and Ag-Cu-Mn-O films were sputter-deposited onto polished Ti-6Al-4V coupons and the microbiological adherence of Staphylococcus sp. was studied in these biomedical surfaces modified by using advanced ternary and quaternary oxides, these latter incorporated micrometric silver islands. Silver is known to have a natural biocidal character and its presence in the surface of Ti-6Al-4V forming large micrometric islands. In principle, predicted to enhance the antimicrobial properties of biomedical surfaces. Microbial adhesion tests were performed using collection strains and six clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The adherence study was performed using a previously published protocol by Kinnari et al. Collection strains and clinical strains showed decreased adherence to modified materials; however, only on the clinical strains were there statistically significant differences between Cu-Mn-O and Ag-Cu-Mn-O containing silver islands. Nanocrystalline silver dissolves and releases both Ag(+) and Ag(0) whereas other silver sources release only Ag+. We can conclude that nanocrystalline silver coating, confirmed by XRD, appears to alter the biological properties of the solution, particularly antimicrobial activity.

Mullins effect behaviour under compression in micelle-templated silica and micelle-templated silica/agarose systems.

The mechanical properties of bioceramic conformed pieces based on micelle-templated silica (MTS) such as SBA15, MCM41 and MCM48 as well as MTS/agarose systems have been evaluated under static and cyclic compressive tests. The MTS pieces exhibited a brittle behaviour. Agarose, a biocompatible and biodegradable hydrogel, has been used to shape ceramic-agarose pieces following a low temperature shaping method. Agarose conferred toughness, ductility and a rubbery consistency up to a 60% strain in ceramic MTS/agarose systems leading to a maximum strength of 10-50 MPa, without losing their initial cylindrical structure. This combination of ceramic and organic matrix contributes to avoiding the inherent brittleness of the bioceramic and enhances the compression resistance of hydrogel. The presence of mechanical hysteresis, permanent deformation after the first cycle and recovery of the master monotonous curve of MTS/agarose systems indicate a Mullins-like effect similar to that found in carbon-filled rubber systems. We report this type of mechanical behaviour, the Mullins effect, for the first time in MTS bioceramics and MTS bioceramic/agarose systems.

An experimental study of COMP (cartilage oligomeric matrix protein) in the rabbit menisci.

INTRODUCTION: Secondary knee osteoarthritis (OA) is currently associated with meniscal injuries, but the pathogenesis is unclear. We analyzed the distribution of cells and cartilage oligomeric matrix protein (COMP) and its changes in the early stages of degeneration in meniscus. METHOD: Ten New Zealand rabbits underwent anterior cruciate ligament (ACL)-transection of the right knee-joint. Left knee-joints were used as controls. The animals were killed at 4 and 12 weeks. Gross injuries in meniscus and articular cartilage were scored. Meniscal tissues were immunostained with a specific antibody against COMP, with Ki-67, using TUNEL-assay and alcian blue stain. The number of cells was counted. RESULTS: At 4 weeks post-ACL-transection, 2/5 of the operated knees showed articular damages and medial menisci tears. Menisci showed a weak increase of cells, higher in cells under division and an increase of apoptosis, COMP and proteoglycans. At 12 weeks, 5/5 of the medial menisci and 2/5 of lateral menisci presented tears, and osteoarthritic changes were seen in the cartilage of all the operated knees. Meniscal cells reverted to normal number, while active cell division decreased below normal, apoptotic events were still high, COMP remained elevated, and glycosaminoglycans were even more elevated. CONCLUSION: Extracellular matrix changes and altered cell distribution occur early in the degenerative meniscus. There is a close relationship between changes in the articular cartilage and the menisci at the onset of secondary OA.

Bacterial adherence on UHMWPE with vitamin E: an in vitro study.

Orthopaedic materials may improve its capacity to resist bacterial adherence, and subsequent infection. Our aim was to test the bacterial adherence to alpha-tocopherol (frequently named vitamin E, VE) doped or blended UHMWPE with S. aureus and S. epidermidis, compared to virgin material. Collection strains and clinical strains isolated from patients with orthopaedic infections were used, with the biofilm-developing ability as a covariable. While collection strains showed significantly less adherence to VE-UHMWPE, some clinical strains failed to confirm this effect, leading to the conclusion that VE doped or blended UHMWPE affects the adherence of some S. epidermidis and S. aureus strains, independently of the concentration in use, but the results showed important intraspecies differences and cannot be generalized.

Early point of significantly higher lesions in insufficient anterior cruciate ligament knees

An experimental study was designed to determine the impact of the instability in the rabbit knee.Ten mature white New Zealand male rabbits were studied. Anterior cruciate ligament-transection of the right knee joint was performed. Animals were sacrificed at 4 weeks (group 1: five animals) and 12 weeks (group 2: five animals) after the surgery. Left knee joints were used as controls. Gross injuries in articular cartilage and in menisci were scored. Forty percent of the knees from the group 1 showed fibrillation. In the group 2, all the knees were damaged and 2/5 showed full-thickness erosion. Tears were observed in 2 internal menisci from the group 1 and in 2 external menisci and 5/5 internal menisci from the group 2. The earliest point of significantly higher incidence of knee damage was 3 months post injury. Therefore, when an anterior cruciate ligament reconstruction is indicated it should carry out as soon as possible (AU)

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The C-terminal fragment of parathyroid hormone-related peptide promotes bone formation in diabetic mice with low-turnover osteopaenia.

BACKGROUND AND PURPOSE: Current data suggest that parathyroid hormone (PTH)-related peptide (PTHrP) domains other than the N-terminal PTH-like domain contribute to its role as an endogenous bone anabolic factor. PTHrP-107-139 inhibits bone resorption, a fact which has precluded an unequivocal demonstration of its possible anabolic action in vivo. We thus sought to characterize the osteogenic effects of this peptide using a mouse model of diabetic low-turnover osteopaenia. EXPERIMENTAL APPROACH: PTHrP-107-139 was administered to streptozotocin-induced diabetic mice, with or without bone marrow ablation, for 13 days. Osteopaenia was confirmed by dual-energy X-ray absorptiometry and microcomputed tomography analysis. Histological analysis was performed on paraffin-embedded bone tissue sections by haematoxylin/eosin and Masson's staining, and tartrate-resistent acid phosphatase immunohistochemistry. Mouse bone marrow stromal cells and osteoblastic MC3T3-E1 cells were cultured in normal and/or high glucose (HG) medium. Osteogenic and adipogenic markers were assessed by real-time PCR, and PTHrP and the PTH(1) receptor protein expression by Western blot analysis. KEY RESULTS: PTHrP-107-139 reversed the alterations in bone structure and osteoblast function, and also promoted bone healing after marrow ablation without affecting the number of osteoclast-like cells in diabetic mice. This peptide also reversed the high-glucose-induced changes in osteogenic differentiation in both bone marrow stromal cells and the more differentiated MC3T3-E1 cells. CONCLUSIONS AND IMPLICATIONS: These findings demonstrate that PTHrP-107-139 promotes bone formation in diabetic mice. This mouse model and in vitro cell cultures allowed us to identify various anabolic effects of this peptide in this scenario.

Bone regeneration and stem cells.

This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.

Compression behaviour of biphasic calcium phosphate and biphasic calcium phosphate-agarose scaffolds for bone regeneration.

There is an acknowledged need for shaping 3-D scaffolds with adequate porosity and mechanical properties for biomedical applications. The mechanical properties under static and cyclic compressive testing of dense and designed porous architecture bioceramic scaffolds based on the biphasic calcium phosphate (BCP) systems and BCP-agarose systems have been evaluated. The dense and designed porous architecture scaffolds in BCP systems exhibited a brittle behaviour. Agarose, a biocompatible and biodegradable hydrogel, has been used to shape designed architecture ceramic-agarose scaffolds following a low-temperature shaping method. Agarose conferred toughness, ductility and a rubbery consistency for strains of up to 60% of in ceramic BCP-agarose systems. This combination of ceramic and organic matrix helps to avoid the inherent brittleness of the bioceramic and enhances the compression resistance of hydrogel. The presence of mechanical hysteresis, permanent deformation after the first cycle and recovery of the master monotonous curve indicate a Mullins-like effect such as that observed in carbon-filled rubber systems. We report this type of mechanical behaviour, the Mullins effect, for the first time in bioceramics and bioceramic-agarose systems.

Influencia del concentrado de plaquetas sobre la reconstrucción de defectos de cartílago articular en la rodilla de cordero / Influence of concentrated platelets on the reconstruction of cartilage defects in the lamb knee joint

Objetivo. Analizar el efecto de las plaquetas sobre el crecimiento de cartílago en los defectos articulares provocados en la rodilla ovina. Material y método. Se provocó un defecto de 4mm de diámetro y 3mm de profundidad en la tróclea femoral de ambas rodillas en corderos macho de 6 meses de edad. La distribución de los grupos fue: grupo A (n=6): el defecto de la rodilla derecha se rellenó con concentrado de plaquetas 5min después de ser activado con ClCa. Grupo B (n=6): el defecto se rellenó con colágeno y plaquetas. Material y método. Las plaquetas se obtuvieron por centrifugación de 10ml de sangre arterial obtenida de cada animal antes de la cirugía. En los defectos de la rodilla izquierda no se administraron plaquetas. Las ovejas fueron sacrificadas 10 semanas después de la cirugía. Se realizaron estudios macro y microscópicos. Resultados. En el grupo A, se observó cartílago hialino en 4 de los defectos de la rodilla derecha a las 10 semanas de la cirugía. Ninguno de los defectos de la rodilla izquierda mostró crecimiento de cartílago hialino. En el grupo B, no se observó cartílago hialino en nigún defecto. No obstante, todos los defectos presentaron mejor celularidad condral y menor fibrosis en los defectos tratados con plaquetas que en los no tratados. Conclusiones. Esta técnica para la reconstrucción con plaquetas de defectos articulares de oveja ha mostrado en nuestro estudio resultados esperanzadores que empeoran combinadas con un andamiaje de colágeno (AU)

Objective. To study the influence of platelets on cartilage growth in articular defects in the sheep knee. Material and methods. Male Rasa Aragonesa sheep (6 months) were operated under general anaesthesia. A 4mm diameter and 3mm deep defect was made in the femoral trochlea in both knees. The right knee defect was filled with platelet concentrate 5min after being activated with ClCa in group A (n=6), and similarly activated platelets + collagen scaffold in group B (n=6). Platelets were obtained by centrifuging 10ml arterial blood from the sheep prior to the surgical procedure. The left knee defect was not filled. The sheep were sacrificed 10 weeks after surgery. Macroscopic and microscopic studies were performed. Results. In group A, hyaline cartilage was observed in the right knee defect at the end of the experiment in four cases. None of the defects of the left knees showed hyaline cartilage growth. In group B, hyaline cartilage was not observed in any right knee defect. However, in group B, all sheep showed better chondral cellularity and regeneration and lower fibrosis in the defects treated with platelets than in non-treated ones. Conclusions. This technique for articular defect reconstruction with platelets has shown satisfactory results in our study. However, collagen scaffolds may decrease this positive effect (AU)