Case submission – ground data
In general, the following information will be required: body weight (kg), breed, age and expected activity level in the postoperative period (this might influence the design of the implant) and whether the dog is expected to function as a working dog.
Background on image acquisition
Customization of implants aims for the best anatomical fit of the made to measure implant with the host anatomy. To achieve this, detailed knowledge of the host anatomy is mandatory. Usually, CT images of the affected area provide the basis for 3D modelling and subsequent planning and construction of the dedicated implant and/or surgical guide(s). However, MRI might also be used in case CT is not available. Plain radiographs with some reference scale might be sufficient for preliminary case assessment, but for detailed planning and final implant design CT or MRI are mandatory.
CT vs. MRI
We prefer CT over MRI data because image resolution is better and (bony) segmentation is faster and more reliable. Even for planning a patient specific synthetic osteochondral implant (chondroTECH), we would use CT to define the extent of the lesion to be reconstructed, as well as the physiological three-dimensional curvature of the pathologic joint surface. When using CT, information on the extent of cartilage loss can be achieved, by scanning twice. Once using your established scanning protocol for joints and the second scan by adding some contrast media intra- articularly. This sort of arthrography usually provides a good estimate of full thickness cartilage loss. Ideally, this information would be complemented by some good arthroscopic pictures, giving the full set of necessary information.
In case MRI images have to be used, scanning parameters should be based on any form of 3D-sequence with thin slicing and no gap between the slices.
Imaging Protocols for Specific Applications
Ideally, axial CT acquisition will be done with small slice thickness (0.5 to 1 mm) and overlapping increment, resulting in a net slice thickness of 0.4 to 0.8 mm. The field of view should be as close to the joint as possible, to provide high in-plane image resolution. Images should be reconstructed using a bone algorithm and a bone level-window setting. If possible, data of the controlateral (healthy) joint should also be provided. This will serve as a template to calculate the surface shape of the customized synthetic osteochondral implant as anatomically precise as possible. In case both sides are affected or other reasons preclude bilateral image acquisition, we will use statistical shape models to extrapolate the missing anatomy.
For CT arthrography a 1:3 ratio of iodine based contrast media and sterile water for injection, resulting in an iodine concentration of 75 mg iodine/ml, is recommended. After injection, the joint should be manipulated through its ROM for several times, and subsequently be positioned mimicking the conditions of the native scan as closely as possible.