**Core Concept**
Post-traumatic fat embolism syndrome (PTFES) is a clinical condition characterized by the presence of fat globules in the blood and their deposition in various organs, leading to systemic symptoms and complications. It typically occurs after a major trauma, such as long bone fractures, and is associated with significant morbidity and mortality.

**Why the Correct Answer is Right**
Option D is correct because diabetes mellitus is not a risk factor for post-traumatic fat embolism syndrome. The pathophysiology of PTFES involves the release of fat globules from damaged bone marrow and their entry into the bloodstream, which can lead to systemic hypoxia, neurological symptoms, and other complications. Diabetes mellitus does not have a direct relationship with the development of PTFES. In contrast, factors such as fracture mobility, which can lead to increased blood flow and fat globule release, and systemic hypoxia, which can occur due to the embolization of fat globules, are indeed risk factors for PTFES.

**Why Each Wrong Option is Incorrect**
**Option A:** Bradycardia is not typically associated with post-traumatic fat embolism syndrome. In fact, tachycardia and hypotension are more common due to the systemic effects of fat embolization.
**Option B:** Systemic hypoxia is a possible complication of post-traumatic fat embolism syndrome due to the embolization of fat globules in the lungs, which can impair gas exchange.
**Option C:** Fracture mobility is indeed a risk factor for post-traumatic fat embolism syndrome, as it can lead to increased blood flow and fat globule release from the damaged bone marrow.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the clinical presentation of post-traumatic fat embolism syndrome, which can include symptoms such as respiratory distress, neurological deficits, and petechial rash. Early diagnosis and treatment are critical to improving outcomes in patients with PTFES.

**✓ Correct Answer: D. Associated diabetes pose a risk**