Sacral fracture 4 months ago gp now suspects dvt have to have scan in morning would the fracture be the reason after this long?

Lack of mobilization: Virchow's triad remains the reason for dvts which include hemodynamic stasis (from lack of mobilization secondary to pain), vascular injury and hypercoaguable states. Doppler ultrasounds of the lower extremities is the cheapest way to evaluate dvts, but we can't look at the big vessels in the pelvis, which is a huge limitation to this evaluation modality.

Yes: It is possible that some clot formed back when you had your injury and were immobile but that was not occlusive (blocking the vessel). Clot itself is thrombogenic (makes more clot) and it is possible to have "acute" on chronic dvt. That would be new clot on top of older clot that could now be blocking or narrowing the blood vessel enough to cause symptoms.