Middle and ring fingers are more exposed to pulley rupture than index and little during sport-climbing: A biomechanical explanation Laurent Vigouroux a, * , Franck Quaine b , Florent Paclet b , Floren Colloud c , Franc ßois Moutet d a Movement and Perception Laboratory, CNRS UMR 6152, University of the Mediterranean, Faculte des Sciences du Sport, Case postale 910, 163, avenue de Luminy, 13288 Marseille, France b GIPSA-lab, CNRS UMR 5216, Control Systems Department, Grenoble, France c Laboratory of Solid Mechanics, CNRS UMR 6610, University of Poitiers, Poitiers, France d SOS Hand, Unit of Hand Surgery, CHU A. Michallon, Grenoble, France Received 3 October 2007; accepted 19 December 2007 Abstract Background. Finger pulley injury is a common incident observed during sport-climbing. The total rupture of one or several pulleys is highly debilitating and requires surgical reconstruction and/or rehabilitation programs. Literature reports show that fingers are not equally exposed to this injury. The ring and middle fingers are usually injured while the index and little fingers are less exposed. The objective of this study was to determine the biomechanical factors leading to the enhanced exposure of ring and middle finger pulleys. Method. Eight subjects were required to exert maximal four-finger force in a specific sport-climbing finger posture. External fingertip forces and finger joint postures were used as input data of a specifically developed biomechanical model of the four fingers (i.e., index, middle, ring and little). This model was based on classical Newton static laws and used an optimization process to quantify the flexor tendon tensions and the pulley forces in each finger. Passive participation of ligaments was also considered into mechanical equations. Findings. Results showed that two main factors could explain the enhanced exposure of ring and middle fingers. Firstly, the fingertip force intensities applied by these two fingers were higher than those observed for the index and little fingers. Secondly, results show that the pulley forces of the ring and middle fingers were close to their rupture thresholds, while it was not the case for the two other fingers. This could be explained by a specific localisation of the finger pulleys of the ring and middle fingers leading to enhanced pulley forces. Interpretation. These results are relevant and could help clinicians to understand finger pulley pathologies and adapt the surgical inter- ventions to reconstruct the fingers pulleys. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Finger pulley system; Finger injury; Sport-climbing; Finger biomechanical model 1. Introduction The biomechanical functioning of the finger pulleys is one of the most complicated problems of the human mus- culo-skeletal system (Moutet, 2003). The role of the pulleys is crucial in maintaining the tendons of both principal finger flexors (Flexor Digitorum Superficialis, FDS and Flexor Digitorum Profundus, FDP) close to the bone allow- ing a harmonious transmission of forces along the finger whatever the joint postures (Manske and Lesker, 1977; Tropet et al., 1990). Injury/rupture of the pulley during sport-climbing causes tendon bowstringing which is debili- tating and may require surgical intervention and/or reha- bilitation programs to recover the full set of functions for the injured fingers (Gabl et al., 2000; Scho ¨ffl et al., 2003; Scho ¨ffl et al., 2006). 0268-0033/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2007.12.009 * Corresponding author. E-mail address: laurent.vigouroux@univmed.fr (L. Vigouroux). www.elsevier.com/locate/clinbiomech Available online at www.sciencedirect.com Clinical Biomechanics 23 (2008) 562–570