|Beitragstitel||A METHOD FOR A C-ARM CONTROLLED INTRAOPERATIVE EVALUATION OF THE HIP TILT FOR TOTAL ENDOPROSTHESIS IMPLANTATION|
For a successful total hip prosthesis implantation the physiologic alignment of the acetabular cup is inevitably. The crucial impact is the correct inclination and anteversion of the acetabular cup. Differences in the angle of orientation of this load-bearing part leads commonly to postoperative problems in hip-luxation. Here, the anterior movement of the femoral implant is the most documented problem.
Therefore, this study evaluates the radiologic projection of the obturator foramen in regards to the retroversion/anteversion tilt positions of the pelvis in order to define the angle intraoperatively.
To perform the study, a custom designed device simulating an inclined plane was used to simulate the tilt of isolated, formalin-fixed pelvic samples in 5° steps. After an anatomical orientation of the samples on the device, C-arm as well as CT-images were obtained in predefined tilts. The retrieved projections were evaluated with the image analysing Software VG Studio Max® 2.2 and the relation of the defined longest diameter to the longest perpendicular extension was assessed.
The results reveal that a C-arm centered projection of the unilateral hip joint depicts the obturator foramen with different dimensions of the longest paramedian diameter and its perpendicular extension in a constant relation in accordance to the pelvic tilt. The defined measurement technique proved to be more concise and reliable in comparison to C-arm centered projections of the bilateral hip joint and defines a mathematical relation as well as a high Coefficient of determination. Via tilt angles of the pelvic bones from 25° retroversion to 25° anteversion and the mathematical analysis of the defined diameters, we found the angle of pelvic tilt (x) to be in relation to the ratio (y) of the longest paramedian diameter to the perpendicular extension to be:
y = -0.0216x + 1.09 (right side)
y = -0.0232x + 1.16 (left side)
The raised intra- and interobserver reliability of the confidence intervals (2σ) showed average ratios of 2.7 %.
In order to realize a significant relationship of importance for the hip-TEP implantation during orthopaedic procedures, follow-up studies presenting the results of a larger and statistically significant sample collection are already in preparation. A confirmation of the found linear function could be used to determine the deviation of the pelvic tilt for a precise calculation and alignment of the acetabular cup orientation.