MR imaging of osteochondral grafts and autologous chondrocyte implantation

Surgical articular cartilage repair therapies for cartilage defects such as osteochondral autograft transfer, autologous chondrocyte implantation (ACI) or matrix associated autologous chondrocyte transplantation (MACT) are becoming more common. MRI has become the method of choice for non-invasive follow-up of patients after cartilage repair surgery. It should be performed with cartilage sensitive sequences, including fat-suppressed proton density-weighted T2 fast spin-echo (PD/T2-FSE) and three-dimensional gradient-echo (3D GRE) sequences, which provide good signal-to-noise and contrast-to-noise ratios. A thorough magnetic resonance (MR)-based assessment of cartilage repair tissue includes evaluations of defect filling, the surface and structure of repair tissue, the signal intensity of repair tissue and the subchondral bone status. Furthermore, in osteochondral autografts surface congruity, osseous incorporation and the donor site should be assessed. High spatial resolution is mandatory and can be achieved either by using a surface coil with a 1.5-T scanner or with a knee coil at 3 T; it is particularly important for assessing graft morphology and integration. Moreover, MR imaging facilitates assessment of complications including periosteal hypertrophy, delamination, adhesions, surface incongruence and reactive changes such as effusions and synovitis. Ongoing developments include isotropic 3D sequences, for improved morphological analysis, and in vivo biochemical imaging such as dGEMRIC, T2 mapping and diffusion-weighted imaging, which make functional analysis of cartilage possible

Inducible nonviral gene expression in the treatment of osteochondral defects.

OBJECTIVE: The repair of osteochondral defects with chondrocytes genetically modified to express desired growth factors promises great potential in orthopaedic therapy. Controlled expression of the transgenes is required in many instances. The objective of the present study was to demonstrate the inducibility of tetracycline-responsive transgene expression in osteochondral defects in the knee joint filled with genetically modified chondrocyte implants. METHODS: An expression plasmid containing the lacZ gene under the control of the minimal CMV promoter fused to the Tet-responsible element (TRE) as well as the reverse transactivator (rtTA2s-M2) was constructed and used to transfect isolated articular chondrocytes from New Zealand white rabbits. rtTA2s-M2 binds to the TRE in the presence of tetracycline and leads to the transcription of the transgene. Different concentrations of DNA and various DNA:lipid ratios were tested to determine best transfection conditions. Transfection efficiency and inducibility were analysed by histochemical analysis and flow-cytometry. To evaluate the system in vivo, collagen-sponges were seeded with transfected autologous chondrocytes and implanted in osteochondral defects in the knees of NZW-rabbits. Gene expression was induced by doxycycline and 3 weeks later, LacZ-expression in isolated knee joints was evaluated in histological sections by X-gal staining. RESULTS: In vitro 13.5% (+/-1.32) of induced primary chondrocytes were LacZ-positive, while non-induced controls showed a background-staining in 0.6% (+/-0.2). In vivo, upon doxycycline treatment, induction of lacZ-gene-expression could be demonstrated in chondrocytes in 3-week-old, well-integrated implants. CONCLUSION: For the first time, tetracycline-inducible gene expression is demonstrated to work in the treatment of osteochondral defects. This demonstrates the feasibility for a gene therapy-assisted approach using controlled expression of therapeutic growth factors from transplanted genetically modified chondrocytes

Retrograde cartilage transplantation on the proximal and distal tibia.

The authors, with experience with more than 400 osteochondral autograft transplantation (OATS) cases since 1996, report a new technique of a retrograde osteochondral autograft transplantation for the treatment of isolated osteochondral lesions of the proximal and the distal tibia started in 1999. We treated 5 patients, 3 who presented with painful traumatic chondral defects in the central weight-bearing portion of the tibial plateau (1 in the medial and 2 in the lateral compartment), and 2 who presented with painful chondral lesions on the distal tibia. An anterior cruciate ligament (ACL) drill guide positioned in the center of the defect was used to accurately prepare the cartilage surface, in one case arthroscopically and in 4 cases through an open incision. A guide-wire was introduced and drilled through the tibia, and a cannulated reamer equal to the diameter of the defect was advanced. An osteochondral cylinder was harvested from the non-weight-bearing zone of the femoral trochlea at the angle that corresponded to the angle on the ACL drill guide. The autograft was inserted in a retrograde fashion from the cortical window into the tibial tunnel to be flush with the articular surface in press-fit technique. The remaining tunnel defect between the cortical window on the tibia and the distal aspect of the autograft was filled with a cancellous bony cylinder and secured with a diagonal bioabsorbable screw. A concomitant varus deformity with the lesion on the medial tibial plateau was corrected in the same surgery using a high tibial osteotomy to relieve stress on the graft. Patients were followed up for 6 to 35 months. A complete healing of the grafts was seen in control magnetic resonance images (MRIs). All patients were satisfied with the surgery. Control arthroscopies showed the osteochondral cylinders well integrated and flush with the articular surface

In vivo analysis of retroviral gene transfer to chondrocytes within collagen scaffolds for the treatment of osteochondral defects.

To examine a retroviral gene transfer to chondrocytes in vitro and in vivo in tissue-engineered cell-collagen constructs articular chondrocytes from rabbits and humans were isolated and transduced with VSV.G pseudotyped murine leukemia virus-derived retroviral vectors. Viral supernatants were generated by transient transfection of 293T cells using the pBullet retroviral vector carrying the nlslacZ gene, a Moloney murine leukemia virus gag/pol plasmid and a VSV.G coding plasmid. Transduction efficiency was analyzed by fluorescence-activated-cell-sorter analysis and transduced autologous chondrocytes from rabbits were seeded on collagen-scaffolds and implanted into osteochondral defects in the patellar groove of the rabbit's femur (n=10). LacZ-expression was analyzed by X-gal staining on total knee explants and histological sections. Retroviral transduction efficiency exceeded 92.3% (SEM+/-3.5%) in rabbit articular chondrocytes, 74.7% (SEM+/-1.8%) in human articular chondrocytes and 52.7% (SEM+/-5.8%) in osteoarthritic human chondrocytes. Reporter gene expression remained high after 15 weeks in 75.7% (SEM+/-8.2%) of transduced rabbit articular chondrocytes. In vivo, intraarticular beta-galactosidase activity could be determined in the majority of implanted chondrocytes in the osteochondral defects after 4 weeks