The association between the sagittal femoral stem alignment and the resulting femoral head centre in total hip arthroplasty

Adequate stem alignment is essential for the success of Total Hip Arthroplasty (THA) to avoid dislocation and impingement. One factor that has not been sufficiently investigated so far is the stem tilting in the sagittal plane, which has an influence on the position of the centre of the femoral head and thus also on prosthesis torsion. We aimed to evaluate sagittal stem position using 3D-CTs in patients with THA and to develop a mathematical-geometrical model to simulate the functional correlation between sagittal stem tilting and the influence on functional anteversion. Thirty patients with THA underwent a CT-scan. By 3D-reconstruction of the CT-data, femoral-/prosthesis-axis, torsion and sagittal tilt were determined. In accordance with the position of the femoral and prosthesis axes, the rotatory (rAV) (surgically adjusted) and functional (depending on sagittal tilt) anteversion (fAV) was measured. A three dimentional-coordinate transformation was also performed using the Euler-angles to derive a mathematical-geometrical correlation between sagittal stem tilting and corresponding influence on anteversion. The mean rAV was 8° (-11.6 - 26°), the fAV 18° (6.2 - 37°), and the difference 10° (8.8 - 18°). The mean degree of stem tilting was 5.2° (0.7 - 9°) anterior towards the femoral axis. The individually measured parameters are reflected in the mathematical-geometrical model. Depending on the extent of the sagittal deviation, a clear influence on the torsion emerges. For example, a stem implanted at a 15° anteverted angle with a sagittal tilt by two degrees towards anterior results in a fAV of 20°. A clear association between the sagittal stem alignment and the impact on the fAV was demonstrated. Hence, the rotatory anteversion intended by the surgeon may be functionally significantly different. This might pose an increased risk of dislocation or impingement. The sagittal tilt of the prosthesis should therefore be considered in the context of impingement and dislocation diagnosis. In this respect, we recommend a 3D-analysis of stem alignment

Enhanced acetabular component positioning through computer-assisted navigation

Optimal positioning of the acetabular component improves the long-term success of total hip arthroplasty by reducing the rate of adverse outcomes, such as component wear and dislocation. Mechanical guides designed to facilitate proper component orientation are inadequate, as they do not account for variations in patient position and pelvic motion during surgery. Pioneering image-guided surgical navigation systems were developed to provide surgeons with improved methods for intraoperatively measuring orientation and alignment. Although enhanced orientation has been reported with such systems, they require preoperative CT scans and are therefore limited by the need for preplanning, the necessitiy of matching CT data with the actual patient position, and the additional costs associated with CT. The recent development of CT-free navigational tools addresses these disadvantages and offers real-time surgical feedback regarding the actual position of the acetabular component and instruments relative to the pelvis. Proper training and enhanced identification of bony landmarks will improve upon the success of these systems

Image-guided pedicle screw insertion accuracy: a meta-analysis

Improved pedicle screw insertion accuracy has been reported with the assistance of computer tomography-based navigation. Studies also indicated that fluoroscopy-based navigation offers high accuracy and is comparable to CT-based assistance. However, different population characteristics and assessment methods resulted in inconsistent conclusions. We searched OVID, Springer, and MEDLINE databases to conduct a meta-analysis of the published literature specifically looking at accuracy of pedicle screw placement with different navigation methods. Subgroups and descriptive statistics were determined based on the subject type (in vivo or cadaveric), navigational method, and spinal level. A total number of 7,533 pedicle screws were summarised in our database with 6,721 screws accurately inserted into the pedicles (89.22%). Overall, the median placement accuracy for the in vivo CT-based navigation subgroup (90.76%) was higher than that with the use of two-dimensional (2D) fluoroscopy-based navigation (85.48%). We concluded that CT-based navigation could provide a higher accuracy in the placement of pedicle screws for all subgroups presented. In the lumbar level, 2D fluoroscopy-based navigation was comparable with CT-based navigation. Discrepancy between the two navigation types increased in the thoracic level for the in vivo populations, where there was less potential in the use of 2D fluoroscopy-based navigation than CT-based navigation