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 The prosthesis is an anatomic right and left
prosthesis with a 135 ° sloping angle and an 10 °
anteversion angle.The titanium alloy metaphysiary part drawing
(TA16V4) provides a suited metaphysiary filling, as, when
installed, it comes to rest both on the lateral face of the
greater trochanter and on the front and rear side of the
metaphysis ; its surface has horizontal fissures in order to
prevent sinking. Its rough surface is covered with a layer
of 70 micron hydroxyapatite intended to facilitate its
secondary fastening.The shaft part is also titanium ; it is smooth,
without hydroxyapatite, rather short and is available in 7
sizes : it is used for temporary centring pending the final
metaphysiary anchoring.70 combinations are possible, matching most
standard femurs.The fastening of both parts has been the
subject of numerous studies. The parts are cylindrically
inserted in one another and screwed.A finished element study has been conducted
prior to the use of the prosthesis. The purpose of the study
was to study the behaviour of both fastened parts in terms
of warping and constraints, mainly at the shaft / metaphysis
unit. Various components were studied: alumina ball,
metaphysis parts, shaft parts, cortical bones, upper spongy
bone and lower spongy bone. All 6 components were subjected
to a 2 000 N stress applied to the alumina ball (Pauwels'
diagram). The results show that the level of stress is very
low. The maximum figures (15.4 daN/mm2) were found on the
metaphysis part, in the area connecting the stem holding the
ball and the massive section. With the assembly of both
parts, the maximum stress value reached 8 daN / mm2, in
spots only. It was found that the maximum stress values (15
daN / mm2) were not dangerous for the metaphysis and the
shaft since the value is much lower than the elastic limit
of the respective material. In the same way, the low level
of stress found on the metaphysis / shaft assembly shows the
durability of that combination.Additionally, during tests conducted by the
Laboratoire National d'Essai, France, a modified endurance
test was performed, as there were no ISO standards for that
type of prostheses ; the tested prostheses resisted 5
million cycles, confirming that the cylindrical insertion
absorbed most of the stress reaching that level, without
transmitting it to the threading.
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