title: An analytical expression for the D.I.P.-P.I.P. flexion interdependence in human fingers.
abstract: Empirical evidence shows that a strong correlation exists between the flexion angles of the distal and proximal interphalangeal (D.I.P., P.I.P.) joints of the human finger. Several authors measured this functional dependence, stating that the interdependence of D.I.P. and P.I.P. flexion is different for healthy individuals and patients displaying pathologies. The purpose of our study is to find an analytical expression for this correlation.
  
  
  METHODS
  Following closely the anatomical in situ relations, we developed a two-dimensional kinematical model which expresses analytically the D.I.P.-P.I.P. angle correlation. Numerical values for the model were extracted from one healthy and one pathological case data set.
  
  
  RESULTS
  The analytical form of the model allows for any P.I.P. angle not only to calculate the corre- sponding D.I.P. angle, but after first order differentiation with respect to the P.I.P. angle, it also shows the rate of change of the D.I.P. flexion. The model reproduces well the differences in the angular correlation of D.I.P. flexion of the two healthy-pathological data sets. Displaying the rate of change of D.I.P. flexion versus P.I.P. flexion provides an additional, clear-cut discriminatory tool between normal and pathological states.
  
  
  CONCLUSIONS
  Information on differences between normal and pathological flexion of fingers is more pronounced and easier accessible from the derivatives of the D.I.P.-P.I.P. flexion behaviour than from direct angular correlation data. The analytical form of our model allows one to establish the rate of change of the D.I.P. angles, resulting in a better analysis of the situations at hand.
authors.affiliation: Department of Anatomy, Morphology, BioMed Institute, University of Hasselt, Hasselt, Belgium.
authors.forename: Koos Jaap
authors.initials: KJ
authors.lastname: Van Zwieten
authors.affiliation: Department of Anatomy, Morphology, BioMed Institute, University of Hasselt, Hasselt, Belgium.
authors.forename: Klaus P
authors.initials: KP
authors.lastname: Schmidt
authors.affiliation: Database and Theoretical Computer Sciences Research Group, University of Hasselt, Hasselt, Belgium.
authors.forename: Geert Jan
authors.initials: GJ
authors.lastname: Bex
authors.affiliation: Department of Anatomy, Morphology, BioMed Institute, University of Hasselt, Hasselt, Belgium.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Lippens
authors.affiliation: Department of Neurosurgery, Jessa Hospital Hasselt, Hasselt, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Duyvendak
mesh_terms: D001696:Biomechanical Phenomena; D016208:Databases, Factual; D005384:Finger Joint / Q000502:physiology*; D005385:Fingers / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology; D016059:Range of Motion, Articular; D013710:Tendons / Q000033:anatomy & histology / Q000502:physiology