Jt P-POSSUM. Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity. Surgical risk calculator described in 1998 by Prytherch et al as Portsmouth POSSUM in the British Journal of Surgery 1998. It was an adaption of the original POSSUM score by Copland, Jones and Walters in Br. J. Surg 1991.