Medically speaking, the complainant must prove the physical harm/ damage in the form of a tear, abrasion, blood vessel rupture and/ or other injuries. This can be done by examination of the part penetrated i.e. anus, mouth and/ or urethra. Such a medical examination should be carried out at the earliest opportunity.
This might be similar to a claim of ‘attempt to murder’ which should be accompanied by a medico legal case (MLC) at a hospital, preferably a government one.
A news item likely to be useful might be accessed at https://www.huffingtonpost.in/2016/08/09/can-a-husband-be-punished-for-having-unnatural-sex-with-his-wi_a_21447742/
Hope this helps. Please let me know if you have further questions. Thanks!