Purpose: A new software based on computed tomography data has been developed for individual unicompartmental reconstruction. The puropse is to achieve custom-made anatomic reconstruction of the medial compartment of the knee and to restore the physiological kinetics of each specific knee. This system can also be used to provide individualised tools for implantation

Material and methods: Custom-made unicompartmental prostheses and their corresponding implantation patterns were designed by this software. The data were fed to a rapid prototyping machine to produce a two-piece (cobalt-chromium and polyethylene) unicompartmental prosthesis and the guides for anatomic cuts specific for each knee. This method was tested on ten cadaver specimens in order to verify the precision of the reconstruction and alignment. A specially designed software was used to establish 3D reconstructions of the knee specimen taking precisely into account the cartilage surfaces. Virtual bone cuts were established to obtain the future seat for the implant. The data of the virtual bone cut were recovered to obtain a brute form of the future implant. The joint surfaces which still presented the degenerative lesions were repaired and finalised by interpolation and by use of the mirror data obtained from the contralateral knee. An individual support system was then installed to perform the bone cuts established virtually. The final data were then fed to a rapid prototyping machine and the aleasing machine to produce a two-piece unicompartment prosthesis and the guides for the anatomic cuts specific for each knee. The operation was then performed via a medial parapatellar 8cm incision. The implants were inserted without other fixation onto the knees and tested immediately to determine function. Anatomic reconstruction of the knee was checked with standard x-rays and CT images compared with the initial data.

Results: The implants could be inserted rapidly and easily. The impact of exhibited an excellent press fit and reproduced the initial morphology of the healthy articulation.

Discussion: Movement of the knee prosthesis reproduced all the characteristic physiological movements. Furthermore, the knee prosthesis obtained with this method allowed individualised and minimalised bone cuts, optimising congurency and contact zones between the bone and the implant and thus reducing the difficulties of surgical alignment. This system appears to offer high-performance restoration of individual physiological joint kinetics.