Navigated total hip arthroplasty using a 3-D freehand ultrasound system : technical note and preliminary results

Ultrasound-navigated cementless total hip arthroplasty (THA) was performed in 10 consecutive patients with primary osteoarthritis of the hip between August 2008 and October 2009 (M:F, 6:4; median age, 61 years; age range, 30-86 years). The pelvic orientation was defined by preoperative digitization and registration of bony landmarks. Cup inclination and anteversion were documented for each patient intraoperatively (epidigitized vs ultrasound-assessed landmarks). The median difference between the palpated and ultrasound anterior pelvic plane was 8° (range, 4°-18°) for pelvic tilt (rotation around the transversal axis), 1° (range, -3° to 2°) for rotation around the longitudinal axis, and 0.25° (range, -2.0° to 5.0°) for rotation around the sagittal axis. The median difference in cup orientation resulting from pelvic tilt error was 6° (range, 3°-13°) for anteversion and 3° (range, -1° to 5°) for inclination. There were no intra- or postoperative complications. The measured width of soft tissue layer anterior to the pelvic symphysis correlated significantly with the measured difference in cup inclination and anteversion. One centimeter of soft tissue anterior to the symphysis resulted in a median 2° (range, 1.75°-2.3°) difference in pelvic tilt. Ultrasound-assisted navigation in THA is a promising technology able to eliminate systematic errors in anterior pelvic plane orientation, in contrast to conventionally navigated THA using percutaneous palpation of landmarks or THA without navigational support.