[Misinterpretation of the anteversion in computer-assisted acetabular cup navigation as a result of a simplified palpation method of the frontal pelvic plane]. / Fehleinschätzung der Anteversion bei der bildfreien, computerassistierten Hüftpfannen-Navigation als Folge einer vereinfachten Palpationsprozedur der frontalen Beckenebene.

AIM: Computer assisted navigation of the acetabular cup in THR requires reliable digitalisation of bony landmarks defining the frontal pelvic plane by user driven palpation. According to the system recommendations the subcutaneous fat should be held aside during epicutaneous digitalization. To improve intraoperative practicability this is often neglected in the symphysis area. In these cases the fat is just compressed and not pushed aside. METHOD: In this study soft tissue thickness was assessed by ultrasound and pelvic geometry was measured in 72 patients to quantify potential misinterpretation of cup anteversion triggered by the simplified palpation. As reference we employed data of the same patients that had been acquired by recommended palpation. RESULTS: Anteversion misinterpretation averaged at 8.2 degrees with extremes from 2 to 24 degrees. There were no correlations between soft tissue thickness or misinterpretation and body weight, height and pelvic size. Anteversion misinterpretation was highly significant worse compared to the reference data. CONCLUSION: In 31 % of the patients the anteversion misinterpretation of a navigation system would have been wrong by over 10 degrees and in 81 % over 5 degrees . Therefore the simplified palpation should not be utilized. For epicutaneous digitalization of the bony landmarks it is mandatory to push the subcutaneous fat aside.

Interactive effects of tunnel dilation on the mechanical properties of hamstring grafts fixed in the tibia with interference screws.

The effect of dilation of the tibial tunnel on the strength of hamstring graft fixation using interference screws was evaluated. In all, 28 RCI screws were tested in male human tibia-hamstring constructs with tibial tunnels reamed or dilated to the respective size of the graft diameter. Dilation of the tibial tunnel failed to significantly enhance hamstring fixation. Grafts secured in dilated tunnels displayed an 11% greater resistance to the initiation of graft slippage (174+/-112 N) compared to their undilated controls (156+/-77 N, P=0.63). Dilation of the tibial tunnel increased the failure load by an average of 4%, independent of screw diameter (dilated specimens: 360+/-120 N, controls: 345+/-88 N, P=0.74). Biomechanical research on the effect of tibial tunnel dilation in hamstring fixation has not provided satisfactory evidence as to the benefits of this additional surgical step during anterior cruciate ligament (ACL) reconstruction.