Abstract
The traditional stem in cement-less total hip replacement was designed as a straight stem. This design was chosen to compensate for lack of initial stability provided by cement. Specifically the box shape of the implant achieved rotational stability and the wedge shape promised proximal press fit. Therefore also the first robot-assisted surgeries were performed using straight stems.
Primarily those surgeons using the antero-lateral approach soon felt limitations of the use of straight stems during robot-assisted surgery. The reamer, in order to guarantee a straight positioning of the implant, used a straight approach to the proximal femur, thereby damaging the insertion site of the gluteus muscle in some cases. This then led to persisting muscular deficit with a consecutive positive Trendelenburg sign.
Surgeons began to monitor during computer–assisted planning not only the final position, but also the cutting path, which was – as requested by the surgeons – displayed on the screen. At the same time anatomic stems became available for computer-assisted planning and surgery. With the introduction of anatomic stems also oblique cutting became available, thus avoiding compromising the greater Trochanter.
Clinical results of anatomic stems in robot-assisted surgery seem to be satisfactory. Although most users allow immediate weight bearing, no loosening or visible subsidence was reported. Cadaver studies and animal experiments suggest that exactness of robot-assisted preparation with the resulting close fit of the implant – no press fit though – provide sufficient stability to allow for anatomic designed stems in cement-less procedures.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
