BackgroundImpingement can be a serious complication after total hip arthroplasty (THA), and is one of the major causes of postoperative pain, dislocation, aseptic loosening, and implant breakage. Minimally invasive THA and computer-navigated surgery were introduced several years ago. We have developed a novel, computer-assisted operation method for THA following the concept of "femur first"/"combined anteversion", which incorporates various aspects of performing a functional optimization of the cup position, and comprehensively addresses range of motion (ROM) as well as cup containment and alignment parameters. Hence, the purpose of this study is to assess whether the artificial joint's ROM can be improved by this computer-assisted operation method. Second, the clinical and radiological outcome will be evaluated.Methods/DesignA registered patient- and observer-blinded randomized controlled trial will be conducted. Patients between the ages of 50 and 75 admitted for primary unilateral THA will be included. Patients will be randomly allocated to either receive minimally invasive computer-navigated "femur first" THA or the conventional minimally invasive THA procedure. Self-reported functional status and health-related quality of life (questionnaires) will be assessed both preoperatively and postoperatively. Perioperative complications will be registered. Radiographic evaluation will take place up to 6 weeks postoperatively with a computed tomography (CT) scan. Component position will be evaluated by an independent external institute on a 3D reconstruction of the femur/pelvis using image-processing software. Postoperative ROM will be calculated by an algorithm which automatically determines bony and prosthetic impingements.DiscussionIn the past, computer navigation has improved the accuracy of component positioning. So far, there are only few objective data quantifying the risks and benefits of computer navigated THA. Therefore, this study has been designed to compare minimally invasive computer-navigated "femur first" THA with a conventional technique for minimally invasive THA. The results of this trial will be presented as soon as they become available.Trial registration numberDRKS00000739

BackgroundThere is a complex interaction among acetabular component position and antetorsion of the femoral stem in determining the maximum, impingement-free prosthetic range-of-motion (ROM) in total hip arthroplasty (THA). By insertion into the femoral canal, stems of any geometry follow the natural anterior bow of the proximal femur, creating a sagittal Femoral Tilt (FT). We sought to study the incidence of FT as measured on postoperative computed tomography scans and its influence on impingement-free ROM in THA.MethodsThe incidence of the postoperative FT was evaluated on 40 computed tomography scans after cementless THA. With the help of a three-dimensional computer model of the hip, we then systematically analyzed the effects of FT on femoral antetorsion and its influence on calculations for a ROM maximized and impingement-free compliant stem/cup orientation.ResultsThe mean postoperative FT on CT scans was 5.7° ± 1.8°. In all tests, FT significantly influenced the antetorsion values. Re-calculating the compliant component positions according to the concept of combined anteversion with and without the influence of FT revealed that the zone of compliance could differ by more than 200%. For a 7° change in FT, the impingement-free cup position differed by 4° for inclination when the same antetorsion was used.ConclusionsA range-of-motion optimized cup position in THA cannot be calculated based on antetorsion values alone. The FT has a significant impact on recommended cup positions within the concept of “femur first” or “combined anteversion”. Ignoring FT may pose an increased risk of impingement as well as dislocation.

Periprosthetic or bony impingement in total hip arthroplasty (THA) has been correlated to dislocation, increased wear, reduced postoperative functionality with pain and/or decreased range of motion (ROM). We sought to study the accuracy and assess the reliability of measuring bony and periprosthetic impingement on a virtual bone model prior to the implantation of the acetabular cup with the help of image-free navigation technology in an experimental cadaver study. Impingement-free ROM measurements were recorded during minimally invasive, computer-assisted THA on 14 hips of 7 cadaveric donors. Preoperatively and postoperatively the donors were scanned using computed tomography (CT). Impingement-free ROM on three-dimensional CT-based models was then compared with corresponding, intraoperative navigation models. Bony/periprosthetic impingement can be detected with a mean accuracy limit of below 5°for motion angles, which should be reached after THA for activities of daily living with the help of image-free navigation technology.