Three-Dimensional Finite Element Analysis of Finger Boutonnière and Swan-Neck Deformities

Abstract

Finger deformities refer to the symptoms where a flexed or extended joint becomes fixed in one direction and is prevented from returning to a normal state due to muscle or tendon abnormalities around the joint as a result of trauma or a pathological abnormality. The deformities exist in numerous forms, and their causes are known to be either a muscle imbalance or tendon rupture. We focused on the finger deformity forms of the boutonnière and swan-neck deformity. To clarify the formation mechanisms of these deformities, conventional studies have used cadaveric fingers whereas in this study we used the finite element method to model the mechanism of human finger flexion and extension (extensor tendons, flexor tendons, phalanges, tendon pulleys, and ligaments). Using this model, flexion angles of the distal interphalangeal (DIP) and the proximal interphalangeal (PIP) joint were calculated with conditions for a tendon (central band, lateral band, flexor digitorum superficialis tendon) rupture and tendon tension abnormalities. The results have shown that the conditions which most resembled the boutonnière deformity were those of the central band removal model, and the conditions which most resembled the swan-neck deformity were those of the flexor digitorum superficialis tendon removal model and the tendon tension abnormalities. These results are in agreement with those from clinical observations and cadaveric finger experiments, and demonstrated that the finite element method was effective for clarifying the mechanisms for finger deformity formations.