Comet C/1996 B2 Hyakutake was extensively observed at the Pic du Midi observatory during late March of 1996. Bright condensations were observed in the near-nucleus coma. We have performed a detailed data analysis in order to derive the position of these features with respect to the nucleus. We make the hypothesis that they are induced by fragments of the nucleus. Despite the frequency of fragmentation of cometary nuclei, the dynamics of the fragments is not yet well understood. We propose a general approach in order to study the motion of the fragments in the orbital plane of the comet. An estimate of the non-gravitational forces is used to describe the motion of the fragment and of the nucleus with respect to their centre of mass. Then the equations of the theory of perturbed Keplerian motion are solved in order to study the motion of the centre of mass. This approach is applied to Comet C/1996 B2 Hyakutake. The results are in good agreement with the observations. An excellent fit is obtained for a fragment size of 20 m, assuming a density of 300 kg m-3.