Goals
Acetabular position
Affects dislocation / liner wear / impingement / ROM
Lewinnek safe zone
- inclination 40+/-10 degrees
- anteversion 15+/-10 degrees
Minimize leg length discrepancy
Causes gait disturbance and lower back pain
Restore offset
Measuring acetabular position
Cup inclination
Cup anteversion
Methods for measuring cup anteversion on xray PDF
Options for component positioning
Mechanical navigation / intra-operative landmarks
Intra-operative fluoroscopy
Image-less optical navigation
CT based navigation
Results
Fluoroscopy versus no imaging
Lecoultre et al Arthroplasty 2023
- systematic review of 10 papers and 1400 papers
- fluoroscopy did not improve cup position / offset or LLD
Fluoroscopy versus image-less navigation
- fluoroscopy versus image-less navigation in 640 anterior hips
- navigation improved cup anteversion and LLD
CT versus fluoro versus no navigation
Matsuki et al J Orthop Sci 2023
- 171 hips with post op CT
- CT navigation most accurate in cup placement versus fluoro or mechanical guides
CT versus image-less navigation
Hasegawa et al Computer Assist Surg 2021
- cup anteversion and inclination more accurate with CT
- accuracy equal if both ASIS included in image-less navigation
Conventional alignment guides
Stryker Trident Acetabulum guide
Intra-operative fluoroscopy
Advantage
- assesses femoral fit and fill
Issues
- 2 dimensional image
- easier in supine position / direct anterior THA
- parallax and distortion
- less accurate for acetabular anteversion
Image-less optical navigation
Smith&Nephew RI Hip Navigation
Method
- insert trackers
- register anatomy
- produce an intra-operative 3D image
Advantage
- easy to use supine or lateral position
Issues
- dependent on registration of bony landmarks
- affected by patient body habitus
- longer surgical times
Accuracy
Naito et al BMC Musculoskeletal Disord 2021
- 107 navigated THA with postoperative CT
- inclination within 3 +/-3 degrees
- anteversion within 6 +/-5 degrees
CT based navigation
Advantage
- can identify bony osteophytes that can cause bony impingement
- highly accurate
Issues
- radiation from CT
- longer surgical times
Accuracy
Hasegawa et al J Orthop Surg Res 2023
- 65 THA with computer navigation and post op CT
- inclination within 2.5+/-2 degrees
- anteversion within 2.5+/-2 degrees
Robotics
Stryker Mako Hip System - CT based
Zimmer Rosa Hip System - intra-operative fluoroscopy based
Advantage
- robot reams acetabulum
- can minimize medial reaming