An ultrasound approach to digitizie bony landmarks in navigation assisted total hip arthroplasty

An imageless Computer-Assisted Navigation System (iCNS) in Total Hip Arthroplasty (THA) has been shown to help increase the accuracy of cup placement. iCNS relies on the location of the Anterior Superior Iliac Spines (ASISs) and the Pubic Symphysis (PS) to establish the pelvic coordinate system for operation. However, palpated location of these landmarks can be the inaccuracy in establishing the pelvic coordinate system due to the substantial amount of the soft tissue and may increase the possibility of misalignment of the hip prostheses, resulting in the failure of THA. The objective of this study was to initially evaluate an alternative solution in palpating the bony landmarks using an ultrasound probe. Bony landmarks on pelvis were measured using 3 methods, manual palpating probe of the iCNS, two ultrasound modes ('surface' ultrasound mode, 'point' ultrasound mode). The X (Right), Y (Anterior) and Z (Superior) coordinates of IASIS, RASIS, PS, and the acetabular Abduction and Anteversion of cup orientation were calculated in the pelvic coordinate system established on the bony landmarks to assess the potential effect on calculating the cup orientation using landmarks obtained from different methods. The results show the cup orientation did not generate significantly different values from two ultrasound modes and manual palpation, which approves these two ultrasound methods can be an alternative solution to digitizie bony landmarks in navigation assisted total hip arthroplasty.