Functional approaches for the localisation of the hip centre (HC) are widely used in Computer Assisted Orthopedic Surgery (CAOS). These methods aim to compute the HC defined as the centre of rotation (CoR) of the femur with respect to the pelvis. The Least-Moving-Point (LMP) method is one approach which consists in detecting the point that moves the least during the circumduction motion. The goal of this paper is to highlight the limits of the native LMP (nLMP) and to propose a modified version (mLMP).

A software application has been developed allowing the simulation of a circumduction motion of a hip in order to generate the required data for the computation of the HC. Two tests have been defined in order to assess and compare both LMP methods with respect to (1) the camera noise (CN) and (2) the acetabular noise (AN).

The mLMP and nLMP error is respectively: (1) 0.5±0.2mm and 9.3±1.4mm for a low CN, 21.7±3.6mm and 184.7±13.1mm for a high CN, and (2) 2.2±1.2mm and 0.5±0.3mm for a low AN, 35.2±18.5mm and 13.0±8.2mm for a high AN.

In conclusion, mLMP is more robust and accurate than the nLMP algorithm.

The hip centre (HC) in Computer Assisted Orthopedic Surgery (CAOS) can be determined either with anatomical (AA) or functional approaches (FA). AA is considered as the reference while FA compute the hip centre of rotation (CoR). Four main FA can be used in CAOS: the Gammage, Halvorsen, pivot, and least-moving point (LMP) methods. The goal of this paper is to evaluate and compare with an in-vitro experiment (a) the four main FA for the HC determination, and (b) the impact on the HKA.

The experiment has been performed on six cadavers. A CAOS software application has been developed for the acquisitions of (a) the hip rotation motion, (b) the anatomical HC, and (c) the HKA angle. Two studies have been defined allowing (a) the evaluation of the precision and the accuracy of the four FA with respect to the AA, and (b) the impact on the HKA angle.

For the pivot, LMP, Gammage and Halvorsen methods respectively: (1) the maximum precision reach 14.2, 22.8, 111.4 and 132.5 mm; (2) the maximum accuracy reach 23.6, 40.7, 176.6 and 130.3 mm; (3) the maximum error of the frontal HKA is 2.5°, 3.7°, 12.7° and 13.3°; and (4) the maximum error of the sagittal HKA is 2.3°, 4.3°, 5.9°, 6.1°.

The pivot method is the most precise and accurate approach for the HC localisation and the HKA computation.

Opening-wedge High Tibial Osteotomy (HTO) has been shown to be an effective procedure to treat mild to moderate osteoarthritis of the medial compartment of the knee in active individuals. It has also become a mandatory surgical adjunct to articular cartilage restoration when there is preoperative mal-alignment. However, its efficacy is directly correlated with the accuracy of the correction, which must be within 3° of the preoperative target. Achieving this goal is a significant challenge with conventional techniques. Therefore, computer-assisted navigation protocols have been developed; however, they do not adequately address the technical difficulties associated with this procedure. We present an integrated solution dedicated to the opening-wedge HTO. Advantages to the technique we propose include: 1) a minimum number of implanted bone trackers, 2) depth control of the saw, 3) improved 3-D accuracy in the location of the lateral tibial hinge, and 4) micrometric adjustment of the degree of correction. The proof of concept has been completed on all six specimens. The following key points have been validated: a) Compatibility with a minimally-invasive (5–6 cm) surgical incision b) The compact navigation station can be placed close to the operative field and manipulated through a sterile draping device c) Only two trackers are necessary to acquire the required landmarks and to provide 3-D control of the correction. These can be inserted within the surgical wound without any secondary incisions d) The optimised guide accurately controlled the external tibial hinge in all six cases e) The implant cavity could be milled effectively f) The distractor used to complete the desired realignment maintained stability of the distraction until final fixation with the PEEK implant g) The PEEK implant could be fixed to the tibia with excellent stability in a low-profile fashion. The solution presented here has the potential to help surgeons perform a medial opening-wedge HTO more safely and accurately. This will likely result in an increase in the number of HTOs performed for both isolated medial compartment osteoarthritis as well as for lower extremity realignment in association with cartilage restorative procedures.

INTRODUCTION

In orthopedic surgery, the lower limb alignment defined by the HKA parameter i.e. the angle between the hip, knee and ankle centers, is a crucial clinical criterion used for the achievement of several surgeries. It can be intraoperatively determined with Computer Assisted Orthopedic Surgery (CAOS) systems by computing the 3D location of these joint centres. The hip centre used for the computation of the HKA is defined by the experts as the anatomical centre of the femoral head. However, except for Total Hip Replacement procedure, the hip joint is not accessible and the hip center is computed using functional methods. The two most common are the Least Moving Point (LMP) and the Pivoting (PIV).