Original Article Proc IMechE Part H: J Engineering in Medicine 227(3) 302–309 Ó IMechE 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954411912468540 pih.sagepub.com Haptically guided robotic technology in total hip arthroplasty: A cadaveric investigation Danyal H Nawabi 1 , Michael A Conditt 2 , Amar S Ranawat 1 , Nicholas J Dunbar 3 , Jennifer Jones 2 , Scott Banks 3 and Douglas E Padgett 1 Abstract The longevity of total hip arthroplasty (THA) continues to improve with advancements in design and bearing materials. However, the incidence of dislocation and impingement-related failures continue to rise, with the inability of the surgeon to achieve optimal component orientation cited as a cause. Computer-assistance has been shown to increase the accuracy of component orientation and robotic-assistance has been developed to translate this advantage into precise surgical execution. We sought to validate a haptically-guided robotic arm system in performing THA with the aim of comparing the accuracy of robotic-assisted acetabular cup placement to manual placement. We implanted 12 acetabular components in 6 cadaveric pel- vises comparing robotic-assistance on one side with manual implantation on the other. We measured planned and actual center of rotation (COR), cup position, leg-length equalization and offset for each THA using computed tomography and the robotic platform. The root-mean-square (RMS) error for the robotic-assisted system was within 3° for cup placement and within 1mm for leg-length equalization and offset when compared to computed tomography. The robotic-assisted sys- tem was significantly more accurate than manual implantation in reproducing the COR and cup orientation, as determined by a preoperative plan. The RMS error for manual implantation compared to robotic-assistance was 5 times higher for cup inclination and 3.4 times higher for cup anteversion (p \ 0.01). Robotic-assistance is more accurate than manual implanta- tion in achieving optimal cup orientation. It has the ability to eliminate human error from THA and should be considered in light of THA failures due to component malposition. Keywords Total hip arthroplasty, robotic assistance, haptics, accuracy Date received: 18 March 2012; accepted: 26 October 2012 Introduction Total hip arthroplasty (THA) is widely accepted as the most successful surgical intervention in orthopedics. Long-term follow-up studies in the literature report patient satisfaction, functional outcome and implant longevity in excess of 90% at a minimum of 10 years follow-up. 1 The improvement in cementless technology, with regard to bone ingrowth–promoting stems and cups, has demonstrated excellent survivorship deep into the second decade, even in young patients. 2 In the second decade, failures of THA are predomi- nantly attributed to wear. This phenomenon has been addressed to some extent by designers and manufactur- ers through the introduction of modular femoral com- ponents to replicate native joint mechanics, larger heads to reduce impingement-related wear and better bearing surfaces, such as highly cross-linked polyethy- lene, modern ceramics and oxidized zirconium. Despite these technological advances, it is estimated that revision rates in the United States will increase by 137% in the next 20 years. 3 This is not surprising in part due to the fact that the number of primary THAs is 1 Adult Reconstruction and Joint Replacement Division, Hospital for Special Surgery, New York, USA 2 Department of Clinical Research, MAKO, Surgical Corp., Fort Lauderdale, FL, USA 3 Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL, USA Corresponding author: Douglas E Padgett, Department of Adult Reconstruction and Joint Replacement, Hospital for Special Surgery, New York, NY 10021. Email: padgettd@hss.edu This paper was submitted as part of the Orthopaedic navigation technol- ogy and biomechanical evaluation for total hip replacement Special Issue.