Abstract
Objectives
Few reports were shown about the position of the cup in total hip arthroplasty (THA) with CT-based navigation system. We use minimally invasive surgery (MIS) technique when we perform cementless THA and the correct settings of cups are sometimes difficult in MIS. So we use CT-based navigation system for put implants with correct angles and positions. We evaluated the depth of cup which was shown on intra-operative navigation system.
Materials and Methods
We treated 30 hips in 29 patients (1 male and 28 females) by navigated THA. 21 osteoarthritis hips, 6 rheumatoid arthritis hips and 3 idiopathic osteonecrosis hips were performed THA with VectorVision Hip 2.5.1 navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Japan Medical Materials, Osaka). Appropriate angles and positions of cups were decided on the 3D model of pelvis before operation. According to the preoperative planning, we put the implants with navigation system. We correct the pelvic inclination angle and measured the depth of cups with 3D template software.
Results
The average distance from the surface of the cup to the edge of medial wall of pelvis was 3.4mm (0.0-8.0mm) on the axial plane which include the center of femoral head on postoperative CT. The average distance from the surface of the cup to the edge of medial wall of pelvis was 6.4mm (1.5-15.0mm) on intraoperative navigation. The average error was 2.9mm (0.0-9.0mm). The cup positions of post operative CT were deeper than that of intraoperative navigation in twenty six hips (86%).
Conclusions
The shallow setting of cups caused the instability of cups. Deep setting caused damage of acetabular fossa. The positions of cups on the navigation system tend to be shown shallower than actual positions, so we should take care of deeper setting.
