26- Le système Hip Nav 1.2 : Perspectives et évolutions - Perspective evolution of the HipNav system for THR

J Essig, G Asencio (Toulouse)

The systems of hip navigation have been under development for a few years. The HipNav System from Stryker has been developed for 3 years. It is an active imageless system which makes it possible to control the cup and femoral implant positioning and to regulate the functionality of the hip (control of ROM, stability and leg length).

The cup positioning is referred to the anterior pelvic plan (Lewineck APP) (anatomical measurement) and for last version 1.2 correlate to the position of the pelvis compare to the trunk (functional measurement). The positioning of the prosthetic femoral stem is referred in the femoral sagital plan and the anatomical axis of the femur proximal.

Several studies evaluated the benefit of a navigation control on the cup positioning. Comparative studies with CT scan control demonstrate that the benefit on the cup positioning with the use of a navigation system compared with a manual ancillary.

Today, the development of the HipNav system goes in 3 ways :

– To improve the precision of the imageless system : The imageless navigation do not require the realization of a preoperative CT scan. The inaccuracy of the system rests on the quality of digitalization of the reference landmarks and planes. The anatomical landmarks are sometimes difficult to digitalize at an obese subject and according to the per operative position of the patient (supine position or lateral position). Spencer demonstrate the inter observer consequences on the cup positioning (more in anteversion than in abduction). On the other hand, a CT scan system necessite some preoperative constraints for the patient (implantation of a preoperative of a landmark on the pelvis and/or the femur) or an inaccuracy at the time of the per operative matching.

– To find a more functional pelvic reference on the cup positioning: Many studies demonstrate that the cup orientation cannot be referred only with the APP. The more functional orientation of the cup must hold of the pelvic tilt which is variable according to the individuals, to the functional activities and during the same activity. Version 1.2 of the HipNav. system makes it possible to digitalize a spine axis to simulate the trunk and in consequence to give a functional measurement to the cup orientation. In the future, the development navigation system will be done in a compromise between the functionality (maximum ROM and stability) and the respect of the stability zone (Lewineck) and of the cup minimal wear zone.

– To give more functionality on the femoral slope: At the femoral side, the development of the modular collar on ancillary and implant will allow a better adjustment of leg length and femoral offsets.

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