Abstract
Aims
Accurate placement of acetabular and femoral stem components in total hip arthroplasty (THA) is an important factor in the success of the procedure. A variety of free hand or navigated techniques is reported. Survivorship and complications have been shown to be directly related to implant position during THA. The aim of this cadaver study was to assess the accuracy of the placement of the components in THA using patient specific instruments (PSI) in combination with a 3D planning software and the direct anterior approach.
Method
Patient specific instruments (PSI) were developed to guide the surgeon during THA that were 3D printed with their bone models following a 3D software planning protocol (LPH software V2.5.1, Onefit-Medical, Eos Imaging Company, Besancon, France). Acetabular guides: cup, offset and straight reamer handle and impactor, femoral- and chisel guides were used in each THA (Fig. 1). To define anatomic bone landmarks and to generate a 3D model of each hip joint CT scans were performed preoperatively. The planning of component position was done by one surgeon (AZ) preop. Surgery was performed by two experienced surgeons (AZ, SD) on cadaver specimen with 4 hips in two separate series. A total of 8 hip replacements were evaluated pre- and postoperatively using CT-scans of each hip joint to compare planned to achieved results. Mechanical simulations of the guides were carried out to verify that there were no conflicts between the different instruments. To meet the ISO standard 16061: 2015 the compatibility of the instruments with the guides has been checked. Parameters were evaluated in 3D pelvic and femoral planes: center cup position, inclination angle, anteversion angle, cutting height and plan orientation, anteversion angle, flexion/extension angle, varus/valgus angle, anatomical and functional leg length, offset. Acceptance criteria: postop. parameters evaluated must not have a deviation of more than 5 degrees, 2,5 mm according to preop. planning. For every THA the test protocol has been completely realized.
Results
The difference between the preop. and postop. measures in the first series of 4 hips revealed 2 outliers because of fractures of the acetabulum in 2 cases, related to bad cadaver quality. In the second series we found satisfactory results comparing the planned preop and postop component position (Fig. 2). For example difference of leg length showed a mean absolute of 1,58 mm, standard deviation 1,21 mm (min 0,62; max 3,34 mm). Offset revealed a mean absolute of 1,62 mm, standard deviation 0,57 mm (min 1,06; max 2,14 mm) concerning the difference between preop. planning and result postop.
Conclusion
Accurate and safe placement of total hip components in THA, both acetabular cup and stem, performing the direct anterior approach can be achieved using a 3D preoperative planning along with patient specific instruments. The results of the cadaver study tests are promising and that is to be proven in the clinical setting and by application in the future.
