Intra- and extra-articular planes of reference for use in total hip arthroplasty: a preliminary study

Purpose Acetabular component malalignment in total hip arthroplasty can lead to potential complications such as dislocation, component impingement and excessive wear. Computer-assisted orthopaedic surgery systems generally use the anterior pelvic plane (APP). Our aim was to investigate the reliability of anatomical landmarks accessible during surgery and to define new potential planes of reference. Methods Three types of palpations were performed: virtual, on dry bones and on two cadaveric specimens. Four landmarks were selected, the reproducibility of their positioning ranging from 0.9 to 2.3 mm. We then defined five planes and tested them during palpations on two cadaveric specimens. Results Two planes produced a mean orientation error of 5.0° [standard deviation (SD 3.3°)] and 5.6° (SD 2.7°). Conclusions Even if further studies are needed to test the reliability of such planes on a larger scale in vivo during surgery, these results demonstrated the feasibility of defining a new plane of reference as an alternative to the APP.