Measurement of the arc of digital flexion and joint movement ranges.

Dynamic digital flexion was examined by video recording healthy subjects making a fist. The arc of the fingertip sweep from full extension to full flexion was replayed frame by frame and plotted. A similar technique was employed to measure the MP, PIP and DIP joint angles throughout digital flexion. Graphs were plotted of MP against PIP, and PIP against DIP flexion. These results were related to a theoretical 45 degrees line. The fingertip appears to sweep through an elliptical pathway when flexing, rather than an equiangular curve. Graphs of joint flexion showed that male and female fingers flex in a similar fashion, as do the index and little finger. Graphs of PIP against DIP flexion suggest some limiting mechanism of either the extensor or flexor system. These graphs give useful insights into the complex mechanisms of dynamic digital flexion, and may be of diagnostic and prognostic importance.