Ankle Sprain: This is the most common injury in the foot and ankle region, often resulting from inversion or eversion of the ankle, leading to ligamentous injury. The absence of an acute fracture on imaging, combined with symptoms of pain, swelling, and difficulty walking, makes this a highly plausible diagnosis.

Ligamentous Injury (other than ankle sprain): Injuries to the ligaments supporting the foot's arch or the toes can occur from similar mechanisms as ankle sprains and may not always be associated with a fracture.
Tendinopathy or Tendon Rupture: Conditions affecting the tendons, such as Achilles tendinopathy or rupture, can present with pain and dysfunction in the foot and ankle region without an associated fracture.
Contusion or Bruising: Direct trauma to the foot can result in soft tissue injury, including contusions and bruising, without necessarily causing a fracture.
Overuse Injuries (e.g., Stress Reaction): While often associated with chronic symptoms, overuse injuries can present acutely, especially if there's been a recent increase in activity level, and might not show a fracture on initial imaging.

Compartment Syndrome: A serious condition that can result from increased pressure within the compartments of the foot or leg, leading to nerve and muscle damage. It is crucial to identify early due to its potential for long-term disability.
Neurovascular Injury: Damage to nerves or blood vessels can occur with foot injuries and may not be immediately apparent. These injuries can have significant consequences if not promptly addressed.
Infection (e.g., Cellulitis, Abscess): Especially in patients with open wounds or those who are immunocompromised, infection is a critical diagnosis to consider and treat promptly to prevent serious complications.
Osteochondral Lesion: An injury to the cartilage and bone of the joint, which might not be visible on all types of imaging and could be missed if not specifically looked for.

Plantar Fascia Rupture: While more common in athletes, a rupture of the plantar fascia can occur and might not be associated with a fracture.
Fat Pad Contusion or Atrophy: Injury to the fat pads of the foot can cause significant pain and may not be immediately apparent on standard imaging.
Nerve Entrapment Syndromes: Conditions like tarsal tunnel syndrome can mimic other foot injuries and may not be associated with fractures.
Arthritis Flare: In patients with pre-existing arthritis, a flare can be precipitated by trauma, even without a fracture, and should be considered in the differential diagnosis.