Quantifying catch‐and‐release: The extensor tendon force needed to overcome the catching flexors in trigger fingers

Abstract

The extensor tendon forces required to overcome the catching flexors in trigger fingers are unknown. A biomechanical model with moment equilibrium equations and method of least squares was developed for estimating the tendon force at triggering in trigger fingers. Trigger fingers that exhibited significant catching and sudden release during finger extension were tested. A customized "pulling tester" was used to pull the finger from flexion to extension and provide synchronic measurement of the pulling force. The displacement of the tested finger was measured by a motion capture system. This preliminary study presents kinematic and kinetic data at triggering of 10 trigger fingers. The distal and proximal interphalangeal (PIP) joints presented sudden release while the metacarpophalangeal (MCP) joint started extension in the early phase of finger extension. The tendon tension of flexor digitorum profundus was greater than that of flexor digitorum superficialis (FDS) in six fingers, and less than that of FDS in three fingers. The tension of two flexor tendons was almost equal in one finger. At the PIP and MCP joints, 1.54 times the force of flexors was needed for the extensors to overcome the catching flexors in trigger fingers. This biomechanical model provides clinicians with a clearer idea of the tendon force at triggering. The quantitative results may help in the understanding of movement characteristics of trigger fingers. These findings are useful to better understand the etiology and nature of trigger finger development, and thus aid in further development of better assessments and treatments related to this. #

Carpal Tunnel Syndrome Impairs Thumb Opposition and Circumduction Motion

“…Such an advanced motion analysis method has the potential to identify subtle kinematic changes associated with pathological hand conditions. For example, it has been shown that osteoarthritis of the thumb CMC joint results in reduced adduction and extension in the affected joint [6,18] and that MCP joint extension precedes the sudden extension of the distal and proximal IP joints in trigger finger [17]. Using similar motion analysis methods to investigate carpal tunnel syndrome-related impairments may quantify abnormalities that potentially are undetectable using traditional approaches.…”

A Finite Element Model for Trigger Finger

“…When considering the forces acting on the FDS tendon during trigger finger, the results in this study were compared with Lu et al [23]. The results from this study are particularly meaningful as it is the only study detailing the direct correlation between trigger finger and its effect on the forces acting on the tendon.…”

“…There is agreement in the literature that tension in the FDP tendon is greater than that in the FDS tendon for healthy fingers [25,27]. More specifically, in a study by Lu et al, tension generated during passive extension modelling was estimated in the FDP tendon as 1.41 to 22.93 N compared to 0.78 to 11.97 N in the FDS tendon [23]. If the FDS tendon is inflamed, as experimented with in this study, the overall strain on the FDP tendon would be greater, leading to significant long-term damage.…”

“…Others explore the finger extensor tendon network but do not model trigger finger [2]. Arguably, the most comprehensive model is provided by Lu et al [23] to evaluate the forces within different tendons, predicting higher tension in the FDP tendon than in the FDS tendon when both tendons were triggering. There is scope, though, to evaluate the effect of trigger finger on the tension in the tendons of the hand during a range of movements.…”

Tendinosis in Trigger Finger

“…Some patients experience pain, while others only notice a trigger phenomenon 8,105 . Even if only one digit is affected, the coordination of all the digits can be altered 106,107 .…”