The lattice parameters, distortion modes and volume collapse happening in LaMnO3 unit cell have been investigated by a modified anisotropic Potts model in terms of two forms of orbital interactions. The model has further been modified to investigate the variation of the lengths of Mn-O bonds as a function of temperature. The Mn-O bond lengths depend on the type of the Mn-Mn orbital interaction. It has been shown that the collapse happened in the unit cell volume depends on the change in the bonds lengths with the temperature increase particularly around the transition. Our results proved that the understudying parameters decrease with increasing temperature in a narrow temperature range below TJT, and then undergoes a collapse at TJT with weak first order transition. These results are in a good agreement with the published experimental results.