Methods for selecting knee prosthesis elements and device therefor
Method for selecting one or several knee prosthesis elements, by acquiring spatial data concerning spacing and tensioned femorotibial position, including the corresponding HKA angle, for at least three angular positions, of 20°, of 0°, and of the order of 90° in flexion, processing the data thus obtained to verify whether the HKA angles are substantially equal and included within the tolerable limits, and processing the data, in particular those corresponding to extension and flexion of 90° to determine the dimensions and/or positions of the implant.
1. A method for selecting one or more knee prosthesis elements, comprising:
tensioning femoro-tibial spacing and acquiring with acquiring means spatial data concerning the tensioned femore-tibial spacing and position with a knee cap in position or dislocated, including a corresponding HKA angle, for at least three angular positions of the knee, including an intermediate position, an extended position if possible with 0° degrees of flexion, and a significantly flexed position;
processing with determining means the data thus obtained, corresponding to the intermediate position and the extended position, to indicate whether, in these two positions, the HKA angles are substantially equal and are within tolerable limits of genu varum and of genu valgum; and
processing with processing means the data corresponding to the extension and significant flexion to determine sizes and/or positions of an implant and, or a choice of a thickness of a tibial insert for optimum filling of a space between a prosthetic condyle and a tibial cut or a choice of the size of a femoral implant.
2. The method according to claim 1 , wherein the angle of flexion at the intermediate position is 20°±10°.
3. The method according to claim 1 , wherein the angle when extended is 0°±5°.
4. The method according to claim 1 , wherein the angle of significant flexion is 90°±15°.
5. The method according to claim 1 , wherein the data is acquired in the following order:
data at 20°, then data at 0°, then data at 90°.
6. The method according to claim 1 , further comprising verifying by means of a computer that the angles at which the data is acquired actually correspond to desired angles, acquisition being denied if the corresponding angle is not observed.
7. The method according to claim 1 , further comprising determining whether, at extension angles and angles of flexion of 20°, the HKA angle is substantially equal in both positions and between 175° and 180° in the case of genu varum and between 180° and 184° in the case of genu valgum, and if so, considering whether anatomical properties are appropriate.
8. The method according to claim 1 , wherein processing relating to determination of most appropriate elements of the prosthesis of the method is not carried out until the data corresponding to 0° and 20° are acceptable, as indicated by absence of substantial flexum and HKA angles which are substantially equal and within permitted values.
9. The method according to claim 1 , wherein said data is processed by modelling means to determine an antero-posterior position of a femoral prosthesis such that:
an upper edge of a prosthetic trochlea is in contact with an anterior femoral cortical bone;
an axial rotation of a femoral prosthesis is such that posterior prosthetic condyles are parallel to an actual tibial cut,
the tibial insert selected from the set best fills a space between the prosthetic condyles and the tibial cut;
a medio-lateral position is such that the implant is centred on an anatomical notch,
and a distal position of the femoral implant is chosen using a selected tibial plate and the extended position is stored so that laxity is substantially zero in the extended position;
a femoral varus is such that, when extended, the distal prosthetic condyles are parallel to the tibial cut.
10. The method according to claim 1 , wherein a result of the processing indicates an exact choice of various elements of a prosthetic set.
11. The method according to claim 1 , wherein the method further comprises preselecting by means of controlling parameters inherent in the set, including a size of the femoral implant, a height of the tibial insert, axial rotation, femoral varus, flexum, antero-posterior position, lateral position or a height of a distal femoral cut to be made.
12. The method according to claim 1 , wherein internal and external laxities estimated in flexion and in extension are displayed continuously, at least for the three angular positions.
13. The method according to claim 1 , wherein the knee prosthesis elements comprise at least one of a prosthetic femoral portion, a tibial prosthetic plate or a femoral or tibial thickness template.
14. The method according to claim 1 , wherein the significant flexed position has a flexion of approximately 90°.