Ovine Knee Research Articles

Microporous calcium phosphate ceramics as tissue engineering scaffolds for the repair of osteochondral defects: Biomechanical results

This work investigated the suitability of microporous β-tricalcium phosphate (TCP) scaffolds pre-seeded with autologous chondrocytes for treatment of osteochondral defects in a large animal model. Microporous β-TCP cylinders (Ø 7mm; length 25mm) were seeded with autologous chondrocytes and cultured for 4weeks in vitro. Only the upper end of the cylinder was seeded with chondrocytes. Chondrocytes formed a multilayer on the top. The implants were then implanted in defects (diameter 7mm) created in the left medial femoral condyle of ovine knees. The implants were covered with synovial membrane from the superior recess of the same joint. For the right knees, an empty defect with the same dimensions served as control. Twenty-eight sheep were split into 6-, 12-, 26- and 52week groups of seven animals. Indentation tests with a spherical (Ø 3mm) indenter were used to determine the biomechanical properties of regenerated tissue. A software-based limit switch was implemented to ensure a maximal penetration depth of 200μm and maximal load of 1.5N. The achieved load, the absorbed energy and the contact stiffness were measured. Newly formed cartilage was assessed with the International Cartilage Repair Society Visual Assessment Scale (ICRS score) and histomorphometric analysis. Results were analysed statistically using the t-test, Mann–Whitney U-test and Wilcoxon test. Statistical significance was set at p<0.05. After 6weeks of implantation, the transplanted area tolerated an indentation load of 0.05±0.20N. This value increased to 0.10±0.06N after 12weeks, to 0.27±0.18N after 26weeks, and 0.27±0.11N after 52weeks. The increase in the tolerated load was highly significant (p<0.0001), but the final value was not significantly different from that of intact cartilage (0.30±0.12N). Similarly, the increase in contact stiffness from 0.87±0.29Nmm−1 after 6weeks to 3.14±0.86Nmm−1 after 52weeks was highly significant (p<0.0001). The absorbed energy increased significantly (p=0.02) from 0.74×10−6±0.38×10−6Nm after 6weeks to 2.83×10−6±1.35×10−6Nm after 52weeks. At 52weeks, the International Cartilage Repair Society (ICRS) scores for the central area of the transplanted area and untreated defects were comparable. In contrast, the score for the area from the edge to the centre of the transplanted area was significantly higher (p=0.001) than the score for the unfilled defects. A biomechanically stable cartilage was built outside the centre of defect. After 52weeks, all but one empty control defect were covered by bone and a very thin layer of cartilage (ICRS 7 points). The empty hole could still be demonstrated beneath the bone. The histomorphometric evaluation revealed that 81.0±10.6% of TCP was resorbed after 52weeks. The increase in TCP resorption and replacement by spongy bone during the observation period was highly significant (p<0.0001). In this sheep trial, the mechanical properties of microporous TCP scaffolds seeded with transplanted autologous chondrocytes were similar to those of natural cartilage after 52weeks of implantation. However, the central area of the implants had a lower ICRS score than healthy cartilage. Microporous TCP was almost fully resorbed at 52weeks and replaced by bone.

Estudo biomecânico da fixação transcortical ou transesponjosa do enxerto de tendão patelar com pinos bioabsorvíveis na reconstrução do LCA em ovinos

OBJETIVO: Determinar a resistência inicial de fixação do sistema RigidFix® e comparar com o método tradicional de fixação que utiliza parafusos de interferência metálicos. Avaliar a resistência da fixação com o sistema RigidFix® ao se modificar o posicionamento rotacional do bloco ósseo no interior do túnel femoral. MÉTODOS: 40 espécimes de joelhos (soldras) de ovinos, foram submetidos à reconstrução do ligamento cruzado anterior (LCA)utilizando enxerto osso-tendão-osso. Em 20 espécimes utilizou-se o método RigidFix®, este grupo foi subdividido em dois, 10 joelhos foram utilizados para fixação através da esponjosa e 10 para fixação cruzando a tábua óssea cortical. Nos 20 espécimes restantes fixou-se o enxerto com parafusos de interferência metálico de 9mm. RESULTADOS: A comparação do método RigidFix® com o método de fixação com parafuso de interferência metálico não mostrou diferenças estatisticamente significativas ao se considerar carga máxima e rigidez, também não houve diferenças estatisticamente significativas ao se modificar o posicionamento rotacional do bloco ósseo no interior do túnel femoral. Para estas avaliações considerou-se o p < 0,017. CONCLUSÃO: A fixação do enxerto osso-tendão-osso com dois pinos bioabsorvíveis, independente do posicionamento rotacional no túnel femoral, permite uma fixação comparável em termos de resistência inicial ao parafuso de interferência metálico neste modelo experimental.

Biomechanical Comparison of Tibial Eminence Fracture Fixation With High-Strength Suture, EndoButton, and Suture Anchor

To biomechanically compare anterior cruciate ligament (ACL) tibial bony avulsion fixation by suture anchors, EndoButtons (Smith & Nephew, Andover, MA), and high-strength sutures subjected to cyclic loading. Type III tibial eminence fractures were created in 49 ovine knees, and 7 different types of repairs were performed. Each repair group contained 7 specimens. The repair groups were as follows: No. 2 FiberWire (Arthrex, Naples, FL); No. 2 UltraBraid (Smith & Nephew); No. 2 MaxBraid (Arthrotek, Warsaw, IN); No. 2 Hi-Fi (ConMed Linvatec, Largo, FL); No. 2 OrthoCord (DePuy Mitek, Raynham, MA); Ti-Screw suture anchor (Arthrotek); and titanium EndoButton. These constructs were cyclically loaded (500 cycles, 0 to 100 N, 1 Hz) in the direction of the native ACL and loaded to failure (100 mm/min). Endpoints included ultimate failure load (in Newtons); pullout stiffness (in Newtons per millimeter); cyclic displacement (in millimeters) after 100 cycles, between 100 and 500 cycles, and after 500 cycles; and mode of failure. Bone density testing was performed in all knees. Bone density was not different among the groups. The EndoButton group had a higher ultimate failure load than the FiberWire, UltraBraid, Hi-Fi, and suture anchor groups (P < .05). The MaxBraid and OrthoCord groups had higher failure loads than the suture anchor group (P < .05). The MaxBraid group also had a higher failure load than the Hi-Fi group (P < .05). Stiffness was not statistically different for the various tested constructs. After 100 cycles, the EndoButton group had less displacement than the FiberWire, UltraBraid, MaxBraid, and Hi-Fi groups (P < .05). The suture anchor group had less displacement than the Hi-Fi and FiberWire groups (P < .05). The displacements of the different tested constructs between 100 and 500 cycles and total displacements after 500 cycles were not statistically different. The predominant failure mode was suture rupture. Under cyclic loading conditions in an ovine model, EndoButton fixation of tibial eminence fractures provided greater initial fixation strength than suture anchor fixation or fixation with various high-strength sutures except for OrthoCord. During initial cyclic loading of ACL tibial eminence fractures, the strength of the repair construct should be taken into consideration because conventional suture repair even with ultrahigh-molecular-weight polyethylene sutures may not provide enough strength.

A study of the anatomy and injection techniques of the ovine stifle by positive contrast arthrography, computed tomography arthrography and gross anatomical dissection

Although ovine stifle models are commonly used to study osteoarthritis, meniscal pathology and cruciate ligament injuries and repair, there is little information about the anatomy of the joint or techniques for synovial injections. The objectives of this study were to improve anatomical knowledge of the synovial cavities of the ovine knee and to compare intra-articular injection techniques. Synovial cavities of 24 cadaver hind limbs from 12 adult sheep were investigated by intra-articular resin, positive-contrast arthrography, computed tomography (CT) arthrography and gross anatomical dissection. Communication between femoro-patellar, medial femoro-tibial and lateral femoro-tibial compartments occurred in all cases. The knee joint should be considered as one synovial structure with three communicating compartments. Several unreported features were observed, including a communication between the medial femoro-tibial and lateral femoro-tibial compartments and a latero-caudal recess of the lateral femoro-tibial compartment. No intermeniscal ligament was identified. CT was able to define many anatomical features of the stifle, including the anatomy of the tendinous synovial recess on the lateral aspect of the proximal tibia under the combined tendon of the peroneus tertius, extensor longus digitorum and extensor digiti III proprius. An approach for intra-articular injection into this recess (the subtendinous technique) was assessed and compared with the retropatellar and paraligamentous techniques. All three injection procedures were equally successful, but the subtendinous technique appeared to be most appropriate for synoviocentesis and for injections in therapeutic research protocols with less risk of damaging the articular cartilage.

BIOMECHANICAL STUDY OF TRANSCORTICAL OR TRANSTRABECULAR BONE FIXATION OF PATELLAR TENDON GRAFT WITH BIOABSORBABLE PINS IN ACL RECONSTRUCTION IN SHEEP

Objective: To determine the initial resistance of fixation using the Rigid Fix® system, and compare it with traditional fixation methods using metal interference screws; and to evaluate the resistance of the fixation with the rigid fix system when the rotational position of the bone block is altered in the interior of the femoral tunnel. Methods: forty ovine knee specimens (stifle joints) were submitted to anterior cruciate ligament reconstruction (ACL) using a bone-tendon-bone graft. In twenty specimens, the Rigid Fix method was used; this group was subdivided into two groups: ten knees the pins transfixed only the spongious area of the bone block, and ten for fixation passing through the layer of cortical bone. In the twenty remaining specimens, the graft was fixed with 9mm metal interference screws. Results: comparison of the RIGIDFIX® method with the metal interference screw fixation method did not show any statistically significant differences in terms of maximum load and rigidity; also, there were no statistically significant differences when the rotational position of the bone block was altered inside the femoral tunnel. For these evaluations, a level of significance of p < 0.017 was considered. Conclusion: fixation of the bone-tendon-bone graft with 2 bioabsorbable pines, regardless of the rotational position inside the femoral tunnel, gave a comparable fixation in terms of initial resistance to the metal interference screw, in this experimental model.

Critical‐size defect induces unicompartmental osteoarthritis in a stable ovine knee

Animal models simulating osteoarthritis are frequently associated with irreversible changes in biomechanics. Although these models successfully induce osteoarthritis, results of experimental repair procedures are impaired by biomechanical problems. The aim of this study was to define the critical size of a chondral lesion to induce unicompartmental osteoarthritis in a stable joint. Sixteen sheep were randomly divided into four treatment groups. A cartilage defect (7- or 14-mm diameter) was created in the weight-bearing zone of the medial femoral condyle. The sheep were mobilized for 6 or 12 weeks. Osteoarthritis was determined by gross assessment, India ink staining, histology (Mankin score), and analysis of COMP in the serum. In the 6-week group, only minor osteoarthritis was registered for either defect size. After 12 weeks, the 14-mm defect induced minor osteoarthritis at the femoral condyle and caused significant degenerative changes at the tibial articular cartilage and the meniscus. The 7-mm defect created focal unicompartmental osteoarthritis at the medial femoral condyle and minor degenerative changes at the corresponding tibia. A 7-mm full-thickness chondral defect with a weight-bearing regimen of 12 weeks induced local osteoarthritis at the medial compartment in an otherwise stable joint as aimed.

Investigating the effects of anterior tibial translation on anterior knee force in the porcine model: Is the porcine knee ACL dependent?

This study sought to determine anterior force in the porcine knee during simulated 6-degree-of-freedom (DOF) motion to establish the role of the anterior cruciate ligament (ACL). Using a 6-DOF robot, a simulated ovine motion was applied to porcine hind limbs while recording the corresponding forces. Since the porcine knee is more lax than the ovine knee, anterior tibial translations were superimposed on the simulated motion in 2 mm increments from 0 mm to 10 mm to find a condition that would load the ACL. Increments through 8 mm increased anterior knee force, while the 10 mm increment decreased the force. Beyond 4 mm, anterior force increases were non-linear and less than the increases at 2 and 4 mm, which may indicate early structural damage. At 4 mm, the average anterior force was 76.9 ± 10.6 N (mean ± SEM; p < 0.025). The ACL was the primary restraint, accounting for 80-125% of anterior force throughout the range of motion. These results demonstrate the ACL dependence of the porcine knee for the simulated motion, suggesting this model as a candidate for studying ACL function. With reproducible testing conditions that challenge the ACL, this model could be used in developing and screening possible reconstruction strategies.

A novel MSC‐seeded triphasic construct for the repair of osteochondral defects

Mesenchymal stem cells (MSC) are increasingly replacing chondrocytes in tissue engineering based research for treatment of osteochondral defects. The aim of this work was to determine whether repair of critical-size chronic osteochondral defects in an ovine model using MSC-seeded triphasic constructs would show results comparable to osteochondral autografting (OATS). Triphasic implants were engineered using a beta-tricalcium phosphate osseous phase, an intermediate activated plasma phase, and a collagen I hydrogel chondral phase. Autologous MSCs were used to seed the implants, with chondrogenic predifferentiation of the cells used in the cartilage phase. Osteochondral defects of 4.0 mm diameter were created bilaterally in ovine knees (n = 10). Six weeks later, half of the lesions were treated with OATS and half with triphasic constructs. The knees were dissected at 6 or 12 months. With the chosen study design we were not able to demonstrate significant differences between the histological scores of both groups. Subcategory analysis of O'Driscoll scores showed superior cartilage bonding in the 6-month triphasic group compared to the autograft group. The 12-month autograft group showed superior cartilage matrix morphology compared to the 12-month triphasic group. Macroscopic and biomechanical analysis showed no significant differences at 12 months. Autologous MSC-seeded triphasic implants showed comparable repair quality to osteochondral autografts in terms of histology and biomechanical testing.

Accuracy of MRI vs CT imaging with particular reference to patient specific templates for total knee replacement surgery

The present study compares the accuracy of MRI and CT imaging for the manufacture of patient-specific templates for total knee replacement surgery. A total of 10 ovine knees were imaged using MRI and CT scanners. Each set of images was reconstructed in 3D and then used to manufacture physical models of each bone, using rapid prototyping technology. After imaging the soft tissues were removed and specific measurements of the bony anatomy compared with measurements from the MRI and CT models. Bone models generated from MRI scans were dimensionally less accurate than those generated from CT scans. Furthermore, the bone models generated from MRI scans were visibly inferior to those generated from the CT scans. Current MRI scans do not offer a viable alternative to CT. Although adaptation of the template system to accommodate MRI imaging is possible, the changes required are neither practical nor desirable.

Effects of Low-Intensity Pulsed Ultrasound on Tendon–Bone Healing in an Intra-articular Sheep Knee Model

This study reports the mechanical and histologic properties of intra-articular tendon-bone healing with the application of low-intensity pulsed ultrasound (LIPUS) in an ovine knee model. A single digital extensor tendon autograft from the right hoof was used as the graft in 89 adult sheep. Femoral fixation was achieved with an EndoButton (Smith & Nephew Endoscopy, Andover, MA) and tibial fixation by tying over a bony post. LIPUS treatment was performed daily for 20 minutes over the femoral and tibial tunnels until sacrifice in all groups, apart from the 26-week group, which was treated only for the first 12 weeks. Histology was performed at 3, 6, 12, and 26 weeks. Mechanical testing was performed at 6, 12, and 26 weeks. The LIPUS-treated group showed increased cellular activity at the tendon-bone interface and general improvement in tendon-bone integration and vascularity. Stiffness and peak load were greater compared with the control group at 26 weeks after surgery (P < .05). The application of LIPUS appears to improve healing at the tendon-bone interface for soft tissue grafts fixed with a suspensory fixation technique. Histology supports a benefit based on increased integration between tendon and bone and a biologically more active interface, which would account for the improved mechanical properties. The indications of LIPUS may be expanded to include tendon-bone healing, for example, in anterior cruciate ligament reconstruction.

Ingrowth of osteochondral grafts under the influence of growth factors: 6-month results of an animal study

In the age of growth factors and gene therapy, the induction of cartilage healing remains an unsolved problem. Even in autologous grafting, one of the preferred methods of treatment for focal osteochondral lesions, chondral integration remains difficult. This study aims to define a possible positive influence of growth factor augmentation on the ingrowth of these transplants. In an ovine model, questions regarding the healing of osteochondral transplants under the influence of two different growth factors were to be addressed. Two osteochondral autologous transplantations (OAT), one in the weight-bearing surface of each femoral condyle, were performed on the ovine knee using the standard operative protocol. One of the grafts was bathed in augmented PBS containing 50 microg bFGF or bone morphogenetic protein (BMP)-2 directly prior to implantation, while the other condyle served as the control. Two groups, consisting of eight sheep each, were evaluated for each growth factor after 6 months. During the evaluation of all the specimens, neither osteophytes nor synovial changes were observed. The mechanical consistency of the cartilaginous tissue began to reach a level equivalent to the surrounding tissue at 6 months, independent of the use of growth factor. Macroscopically, the superficial border of the transplanted osteochondral plug could easily be outlined in all groups, while the cartilage interface of the bFGF specimens was determined to be less demarcated than the BMP augmented plugs or the controls. Radiographically, a solid osteointegration of the graft could be documented at 6 months in the native and augmented groups. In contrast, integration of the chondral surface of the OAT was not seen macro- or microscopically in any specimen, even though cartilage surfaces remained viable. A firm physical interdigitation of the reconstructed joint surface could not be demonstrated in either of the two augmented groups or the control population. The augmentation with bFGF and BMP-2 stimulated the osseous ingrowth and seems to expedite the remodelling process, but was not able to improve chondral healing. The lack of integration of the cartilaginous portion of the transplanted plugs into the reconstructed joint surface, even following the augmentation with bFGF and BMP-2, does not bode well for the long-term survival of the joint itself.

HISTOLOGICAL ASSESSMENT OF THE CHONDRAL AND CONNECTIVE TISSUES OF THE KNEE BY CONFOCAL ARTHROSCOPE

Conventional histological assessment of tissue requires the removal of tissue from its physiological environment for pathological processing. In this study we report on the development and application of a laser scanning confocal arthroscope (LSCA) capable of in situ histological assessment by confocal microscopy. The knee joints of three euthanasied adult Merino sheep were imaged using the LSCA and a combination of fluorescent contrasting agents. LSCA images of various tissues were examined for common histological characteristics. The confocal histology images from the ovine knee acquired during the course of our study illustrated some of the major histological features of chondral and connective tissues. Our study demonstrates the efficacy of the LSCA for the histological assessment of the chondral and connective tissues of the ovine knee. The LSCA provides an easy and rapid method for assessing the in situ structure of cartilage, muscle, tendon, ligament, meniscus and synovium in their native and unaltered physiological environment. By obviating the need for mechanical biopsy, the LSCA provides a method for the non-destructive assessment of the chondral and connective tissues of the knee, and may be of great benefit in the investigation of orthopedic diseases or in the assessment of newly emerging cartilage repair techniques.

Dimensional measurement of structural features of the ovine knee using three-dimensional reconstructed imaging: intra- and inter-observer repeatability

Purpose The aim of this study was to establish intra- and inter-observer repeatability in the direct linear measurement of knee structures displayed using three-dimensional (3-D) reconstructed computer imaging. Methods To test inter-observer repeatability, using a commercially available image reconstruction software package, seven observers were asked to record measurements for each of 30 individual structural features identified from a previously generated series of MR-based 3-D computer reconstructions of a single, complete, ovine knee. To test intra-observer repeatability, a single observer was asked to record measurements of the same 30 features on three separate occasions. Results Statistical analysis of the collected data suggests a high degree of repeat measurement agreement both within ( P=0.76) and between observers ( P=0.87). Conclusion The findings of this study suggest that defined linear measurements can be generated from 3-D MR images created using the new reconstructive system, by imaging technologists, with a high degree of both intra- and inter-observer repeatability. This result, linked with the outcome of ongoing validity and clinical testing, will contribute to support the wider acceptance and use of this new cost-effective 3-D technique, and form a platform onto which ongoing work in this area can be built.

Dimensional measurement of structural features of the ovine knee using three-dimensional reconstructed imaging: intra- and inter-observer repeatability

<h2>Abstract</h2><h3>Purpose</h3> The aim of this study was to establish intra- and inter-observer repeatability in the direct linear measurement of knee structures displayed using three-dimensional (3-D) reconstructed computer imaging. <h3>Methods</h3> To test inter-observer repeatability, using a commercially available image reconstruction software package, seven observers were asked to record measurements for each of 30 individual structural features identified from a previously generated series of MR-based 3-D computer reconstructions of a single, complete, ovine knee. To test intra-observer repeatability, a single observer was asked to record measurements of the same 30 features on three separate occasions. <h3>Results</h3> Statistical analysis of the collected data suggests a high degree of repeat measurement agreement both within (<i>P</i>=0.76) and between observers (<i>P</i>=0.87). <h3>Conclusion</h3> The findings of this study suggest that defined linear measurements can be generated from 3-D MR images created using the new reconstructive system, by imaging technologists, with a high degree of both intra- and inter-observer repeatability. This result, linked with the outcome of ongoing validity and clinical testing, will contribute to support the wider acceptance and use of this new cost-effective 3-D technique, and form a platform onto which ongoing work in this area can be built.

Reconstructed three-dimensional MR images: application to simulated tibial plateau depression fractures

Purpose The aim of this study was to test the accuracy of measurements obtained from three-dimensional (3-D) reconstructed magnetic resonance images in the setting of a depressed tibial plateau fracture. Methods A simulated bilateral tibial plateau depression fracture was surgically induced in a disarticulated ovine knee. An attached perspex spacer was used to allow controlled fragment displacement, while maintaining a constant fracture gap. Ten identical intermediate-T2-weighted acquisitions (2.0 mm slice thickness) were acquired at different fragment displacement levels. Using a commercially available software package, these data were then used to generate 10 corresponding sets of 3-D images. Computer measurements were made of the volume of bony fragments, the width of the fracture gap, the degree of infero-medial and infero-lateral fragment depression and these findings were compared with caliper and volume displacement measurements taken from the phantom itself. Results Mean volumes derived from 3-D reconstructed MR images for the two bony fragments were 10,363.26 mm 3 and 8273.27 mm 3 (percentage measurement error (PME) of 2.21% and 2.49%, respectively). The mean fragment separation was 2.97 mm (PME 3.98%). The mean raw measurement error when measuring the degree of fragment depression was 0.31 mm and this was considered clinically acceptable. Conclusion The findings of this study suggest that 3-D reconstructed MR imaging may be sufficiently accurate for the evaluation of tibial plateau depression, fracture gap and fragment volume.

Histochemical visualization of the cartilage hyaladherins using a biotinylated hyaluronan oligosaccharide bioaffinity probe.

Hyaluronan (HA) binding proteins (HABPs) were localized in cartilaginous ovine tissues (articular cartilage, intervertebral disc) using a biotinylated HA (bHA) oligosaccharide bioaffinity probe. The bHA oligosaccharide probe was prepared by partial digestion of HA with ovine testicular hyaluronidase, and the oligosaccharides were labeled with biotin hydrazide and purified by a combination of aggrecan G1 domain and avidin affinity chromatography. Hyaladherins were prominently visualized in tissue sections using the bHA oligosaccharide probe as pericellular components in hypertrophic epiphyseal and vertebral growth plate chondrocytes and in the enlarged cells of the cartilaginous end plate of the intervertebral disc. Weaker extracellular staining was also evident in the matrix of the ovine newborn hip and knee joint cartilages. The bHA oligosaccharide probe also visualized intracellular HABPs (IHABPs) in the hypertrophic growth plate chondrocytes of the primary ossification centers. Monolayer cultures of ovine chondrocytes rapidly internalized the bHA oligosaccharide affinity probe to discrete cytoplasmic, nuclear, and perinuclear regions, which were visualized by indirect fluorescent microscopy. This bHA oligosaccharide affinity probe may be useful in future investigations designed to characterize these novel cartilage IHABPs and the role that HA endocytosis plays in cellular regulatory processes in cartilage homeostasis.

Filling of osteochondral donor site defects. Experimental study with tricalcium phosphate cement and BMP-2

Osteochondral grafting procedures have developed into one of the preferred methods of treatment for focal osteochondral lesions, although the management of the donor site remains problematic. In this animal study, an attempt at sealing the donor site with a fully-resorbable tricalcium phosphate bone cement was evaluated. Autologous osteochondral transplantation of the medial and lateral condyle was performed on the ovine knee using a standard operative protocol. The ensuing defect was filled with the original beta-TCP cement laterally, while medially the cement was augmented with 50 micro g BMP-2. Two groups, consisting of 10 sheep each, were evaluated after three and 6 months, respectively. The clinical evaluation of the specimens revealed an improved reconstruction of the joint surface following the application of the augmented biomaterial. Macroscopically, the superficial border of the original donor site could easily be outlined at both time periods in both groups. Solid osteointegration of the bone cement could be documented radiographically as early as three months following implantation. The beta-TCP bone cement represents a promising resorbable filler for osteochondral defects. The augmentation with BMP-2 seems to expedite the remodelling process and improve the surface reconstruction.

Healing of osteochondral grafts in an ovine model under the influence of bFGF

Purpose: The well-recognized limitations in cartilage healing have lead to the development of a number of resurfacing techniques for defects of joint surfaces. Autologous grafting has developed into 1 of the preferred methods of treatment for focal osteochondral lesions, although basic research on this topic remains sparse. Type of Study: In an animal study, questions regarding the healing of osteochondral transplants under the influence of basic fibroblast growth factor (bFGF) were addressed. Methods: Two osteochondral autologous transplantations (OAT), 1 in the weight-bearing surface of each femoral condyle, were performed on the ovine knee using a standard operative protocol. One of the grafts was bathed in phosphate buffered sulfate (PBS) containing 50 μg of recombinant human bFGF (rh-bFGF) directly before implantation. Two groups consisting of 10 sheep each were evaluated after 3 and 6 months, respectively. Results: During the evaluation of the specimens, neither osteophytes nor synovial changes were observed. Macroscopically, the superficial border of the transplanted osteochondral plug could easily be outlined at both time periods, even though the cartilage interface of the rh-bFGF specimens was less demarcated. Radiographically, a solid osteointegration of the graft could already be documented at 3 months in the control group. In contrast, integration of the chondral surface of the OAT was not seen macroscopically or microscopically at any point. A firm physical interdigitation of the reconstructed joint surface could not be demonstrated in either of the 2 groups. The augmentation with rh-bFGF stimulated the osseous ingrowth, but was not able to improve chondral healing. Conclusions: The lack of integration of the cartilaginous portion of the transplanted plugs into the reconstructed joint surface, even following augmentation with bFGF, leads to questions regarding the long-term survival of the joint itself.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 2 (February), 2003: pp 182–187

The accuracy of three-dimensional reconstructions of the ovine knee: dissectional validation

A single, complete, ovine knee was imaged using conventional MRI then dissected allowing comprehensive dimensional measurement of the intra-articular structures. A three-dimensional (3-D) computer model of the knee was generated from the MR sections. Thirty-two individual structural measures were recorded from the image output for which there was an available surgical measure for direct comparison. The results of Pearson's correlation testing show a rounded score of 1.00, suggesting an exceptional linear correlation between direct anatomical measurement and the 3-D image output. Further analysis of the data revealed an average error of measurement of 0.2 mm across the 32 measures. The findings of this preliminary study suggest that 3-D reconstruction from MR data may be an appropriate, and accurate, means for making dimensional measurements of the bony and soft tissue structures of the ovine knee. It is unlikely that the measurement error would be of any great clinical significance. There is evidence in the literature to suggest that an ovine knee may be considered an acceptable model for substitution for the human knee in diagnostic assessment studies. Therefore, such findings may be considered clinically relevant in the field of human knee assessment.

Long term in-vivo studies of a photo-oxidized bovine osteochondral transplant in sheep.

BackgroundArticular cartilage has limited capacity to repair. Defects greater than 3 mm heal with formation of inferior fibrous cartilage. Therefore, many attempts have been made to find the ideal graft for larger cartilage lesions. Different grafts, such as untreated or cryopreserved osteochondral transplants, have been used with variable success.MethodsPhoto-oxidized osteochondral grafts were implanted in both femoral condyles of one ovine knee. Untreated xenogeneic and autogeneic grafts served as controls. Three groups of 8 sheep each were formed and they were sacrificed 6, 12 or 18 months after surgery.ResultsThe macroscopic evaluation of the condyle and graft showed a well-maintained cartilage surface in most grafts at all time points. However, the host cartilage matrix deteriorated considerably in all xenogeneic, most autogeneic and fewer of the photo-oxidized grafts at 12 and 18 months, respectively. The blue colour of the photo-oxidized grafts resulting from the process of photo-oxidation was visible in all grafts at 6 months, had diminished at 12 months and had completely disappeared at 18 months after surgery. Histologically a loss of matrix staining was almost never noticed in untreated xenografts, transiently at 6 months in photo-oxidized grafts and increased at 12 and 18 months. Fusion between graft and host cartilage could be seen in photo-oxidized grafts at 12 and 18 months, but was never seen in autografts and xenografts.ConclusionsThe photo-oxidation of osteochondral grafts and its use as transplant appears to have a beneficial effect on cartilage and bone remodelling. Osteochondral grafts pre-treated with photo-oxidation may be considered for articular cartilage replacement and therefore may delay artificial joint replacements in human patients.