Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech Does navigated patellar resurfacing in total knee arthroplasty result in proper bone cut, motion and clinical outcomes? Belvedere Claudio a, ⁎ , Ensini Andrea a,b , Tamarri Silvia a , d'Amato Michele b , Barbadoro Paolo b , Feliciangeli Alessandro b , Rao Anish b , Leardini Alberto a a Movement Analysis Laboratory, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy b Department of Orthopaedic Surgery, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy ARTICLE INFO Keywords: Total knee arthroplasty Computer-assisted surgery Surgical navigation Patellar resurfacing Tibio-femoral kinematics Patello-femoral kinematics ABSTRACT Background: In total knee arthroplasty with patellar resurfacing, patellar bone preparation, component posi- tioning and motion assessments are still not navigated. Only femoral/tibial component positioning is supported by computer-assistance. The aim of this study was to verify, in-vivo, whether knee surgical navigation extended to patellar resurfacing, by original instrumentation and procedures for patellar-based tracking, could achieve accurate patella preparation in terms of original thickness restoration, bone cut orientation, and normal knee motion. Methods: An additional navigation system for patellar data acquisition was used together with a standard na- vigation system for total knee arthroplasty in 20 patients. This supported the surgeon for patellar resurfacing via measurement of removed bone thickness, three-dimensional patellar cut orientations, and patello-femoral mo- tion. Radiological and clinical examinations at 6 and 24-month follow-up were also performed. Findings: The medio-lateral patellar-bone cut orientation was respectively 0.5° (standard deviation: 3.0°) and 1.4° (1.7°) lateral tilt, as measured via navigation and post-operatively on the Merchant x-ray view. The cranio- caudal orientation was 3.8° (7.2°) of flexion. The thickness variation between patellar pre- and post-implantation was 0.2 (1.3) mm. Immediately after implantation, patello-femoral as well as tibio-femoral kinematics was within the normality. Good radiological and clinical examinations at 6 and 24-month follow-up were also ob- served. Interpretation: For the first time, the effect of patellar navigation for its resurfacing was assessed in-vivo during surgery, with very good results for thickness restoration, proper cut orientation, and normal knee motion. These results support the introduction of patella-related navigation-based surgical procedures for computer-assisted total knee arthroplasty. 1. Introduction Patellar abnormalities are generally considered the most frequent reasons for failure in total knee arthroplasty (TKA) (Malo and Vince, 2003). After TKA, the correct functioning of the patello-femoral joint (PFJ) depends on the accurate positioning of the femoral and tibial prosthesis components and on the appropriate balancing of the re- maining soft tissues. It is well known that anterior knee pain is gen- erally caused by patellar maltracking, mainly due to malrotation of the prosthetic components (Berger et al., 1998) and altered knee kinematics (Komistek et al., 2000). In TKA with patellar resurfacing, patellar bone preparation and corresponding component implantation are additional critical issues: when not addressed carefully, reduced knee flexion, PFJ maltracking, increased patellar polyethylene wear, and aseptic com- ponent loosening were observed (Baldini et al., 2006; Baldini et al., 2007; Bracey et al., 2015; Kawano et al., 2002; Merican et al., 2014; Merkow et al., 1985; Nakamura et al., 2017; Pagnano and Trousdale, 2000; Ranawat, 1986). From a more specifically biomechanical point of view, improper estimation of the patellar resection level and in- adequate patellar component thickness and positioning (Anglin et al., https://doi.org/10.1016/j.clinbiomech.2019.07.026 Received 17 April 2019; Accepted 23 July 2019 Abbreviations: BC, Belvedere Claudio; EA, Ensini Andrea; TS, Tamarri Silvia; DM, d'Amato Michele; PB, Barbadoro Paolo; FA, Feliciangeli Alessandro; RA, Rao Anish; LA, Leardini Alberto ⁎ Corresponding author at: Movement Analysis Laboratory, Centro di Ricerca Codivilla-Putti, IRCCS Istituto Ortopedico Rizzoli, Via di Barbiano 1/10, 40136 Bologna, Italy. E-mail address: belvedere@ior.it (B. Claudio). Clinical Biomechanics 69 (2019) 168–177 0268-0033/ © 2019 Elsevier Ltd. All rights reserved. T