Experimental study of the optimal angle for arthrodesis of fingers based on kinematic analysis with tip-pinch manipulation Paul Arauz a,n , Sue Ann Sisto b , Imin Kao a a Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11790, United States b School of Health Technology and Management, Stony Brook University, Stony Brook, NY 11794, United States article info Article history: Accepted 22 October 2016 Keywords: Proximal interphalangeal joint fusion Finger function Manipulability Manipulation finger range of motion abstract To evaluate the appropriate angle for arthrodesis of the index finger proximal interphalangeal (PIP) joint, the functional range of motion (ROM) of the joints and manipulabilities at three selected tip-pinch manipulation postures of the finger were studied experimentally under imposed PIP joint arthrodesis angles. A kinematic model of the index finger was used in experiments which involved three postures. Experiments were conducted using seven healthy subjects in tip-pinch manipulation tasks to obtain the measurements of finger motions under imposed angles of joint constraint, including the functional ROM of the joints and the three criteria of kinematic manipulability. Data show that the functional ROM and the shape of the kinematic manipulability ellipses at the fingertip were influenced significantly by the imposed PIP joint constraint in the tip-pinch manipulation tests. Results suggest that a PIP arthrodesis angle between 40° and 60° led to the optimal performance of fingers in grasping and manipulation of fine objects. This theoretical and experimental study can help surgeons and clinicians to make more informed decisions on the appropriate constraint angles before the arthrodesis operation, and to cus- tomize this angle for individual patients in order to enhance not only the capability of manipulation of the finger but also the quality of life after such intervention. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Rheumatoid arthritis and osteoarthritis may lead to painful instability of fingers, making movement and even simple tasks difficult to perform. Symptomatic cases of hand osteoarthritis are a major public health concern reported for 5–25% of the population (Sisto and Malanga, 2006). This pathology induces a degradation of articular cartilage and surrounding tissues resulting in loss of grip strength, reduce range of motion, severe pain, and other impairments regarding daily tasks such as precision manipulation (Goislard de Monsabert et al., 2014; Sisto and Malanga, 2006; Bullock et al., 2015). Arthrodesis, an artificial induction of joint ossification between two bones via surgery, provides a pain-free stable joint but sacrifices motion after the surgery (Brutus et al., 2006; Mantovani et al., 2008; Rizzo et al., 2009; Sisto and Malanga, 2006; Woodworth et al., 2006). Although the impact of arthrodesis on hand and finger function remains a matter of debate among surgeons, preoperative planning has to include a decision on the appropriate angle for arthrodesis (Leibovic, 2007; Leibovic et al., 1994; Uhl, 2007; Woodworth et al., 2006; Yao et al., 2012; Arauz et al., 2016). Obviously, constraining a finger joint reduces functionality by limiting the ability to perform important everyday tasks such as writing, delivering medication, key-insertion, and among others. While previous studies have significantly contributed to the understanding of finger and hand movement capabilities (Yokogawa and Hara, 2004; Woodworth et al., 2006; Domalain et al., 2011; Arauz et al., 2016), the effect of arthrodesis angles on the functional ROM of the joints and precision tip-pinch manipulation has not been reported before. Precision manipulation, the hall- mark of human's superior dexterity, is key to the ability to perform a large number of daily tasks such as writing, key insertion, or picking up and holding a very fine object like a pill (medication) or pin (Arauz et al., 2016; Bullock et al., 2015; Yokogawa and Hara, 2004). Consequently, precision manipulation under imposed joint constraints needs to be investigated in order to make more informed decisions on the appropriate angle for arthrodesis. In this article, a kinematic evaluation was conducted on the index finger to determine the optimal PIP joint arthrodesis angles for precision in tip-pinch manipulation. Precision tip-pinch manipulation, involving repositioning a fine object in the finger- tips, is used in everyday tasks (Bullock et al., 2015). The objective of this research was to study a methodology for determining an Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics http://dx.doi.org/10.1016/j.jbiomech.2016.10.047 0021-9290/& 2016 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: paulusgon@gmail.com (P. Arauz). Please cite this article as: Arauz, P., et al., Experimental study of the optimal angle for arthrodesis of fingers based on kinematic analysis with tip-pinch manipulation. Journal of Biomechanics (2016), http://dx.doi.org/10.1016/j.jbiomech.2016.10.047i Journal of Biomechanics ∎ (∎∎∎∎) ∎∎∎–∎∎∎