[The primary stability between manual and robot assisted implantation of hip prostheses: A biomechanical study on synthetic femurs].
OBJECTIVE
We investigated the initial stability of cementless stems implanted with robotic milling and conventional manual broaching.


METHODS
Proximally porous structured stems (G2, ESKA-Implants, Luebeck, Germany) were implanted into synthetic femora. In one group, the femoral cavity was prepared by a CT-based robot (CASPAR, URS-Ortho, Germany) with a high-speed milling head. In the other group, femora were rasped manually with broaches. The broaches had 1 mm proximal press-fit, the robotic cavities 1.5 mm. The implants were exposed to 15 000 loading cycles with 1 000 +/- 500 N. The direction of forces on the implant head were chosen to simulate stair climbing. Internal rotation and translation (caudal, dorsal and lateral) of the implants were measured by linear transducers.


RESULTS
The robotic group showed significantly less reversible motion regarding translation in caudal, dorsal and lateral directions. The standard deviations of implant motions were smaller in the robotic group.


CONCLUSIONS
Using robotic preparation of the femur, initial stability was higher and more consistent than with manual broaching, but differences in undersizing of the cavities created in the femur in relation to the implant may have contributed to these differences for the most part. In-vitro-loading experiments focusing on femoral cavities with varying press-fits are recommended before the introduction of new implants or operating procedures.
Decking
J
J
Orthopädische Klinik und Poliklinik der Universität Mainz, Mainz. decking@mail.uni-mainz.de
Gerber
A
A
Kränzlein
J
J
Meurer
A
A
Böhm
B
B
Plitz
W
W
D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D001696:Biomechanical Phenomena / Q000379:methods; D019544:Equipment Failure Analysis / Q000295:instrumentation / Q000379:methods; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D011474:Prosthesis Design / Q000379:methods; D015203:Reproducibility of Results; D012371:Robotics / Q000295:instrumentation* / Q000379:methods*; D012399:Rotation; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D016474:Weight-Bearing