Differential Diagnosis for SI Pain after Fall Down Stairs

Single Most Likely Diagnosis

• Sacroiliac Joint Sprain: This is the most likely diagnosis given the mechanism of injury (fall down stairs) which can cause a sudden, forceful movement that strains the ligaments surrounding the sacroiliac joint, leading to pain.

Other Likely Diagnoses

• Sacroiliac Joint Dislocation: A fall down stairs can also cause a dislocation of the sacroiliac joint, which would result in significant pain and potentially instability in the pelvis.
• Gluteal or Pelvic Contusion: A direct blow to the buttocks or pelvis during the fall could result in a contusion, leading to pain in the SI region.
• Lumbar Strain: The fall could also cause a strain to the lumbar muscles, which might refer pain to the SI area.

Do Not Miss Diagnoses

• Pelvic Fracture: Although less common, a fracture of the pelvis could occur from a fall down stairs, especially in older adults or those with osteoporosis. Missing this diagnosis could lead to significant morbidity.
• Cauda Equina Syndrome: A severe injury from the fall could potentially cause cauda equina syndrome, a condition where the nerves in the spinal canal are compressed, leading to severe pain, numbness, and potentially permanent neurological damage if not promptly treated.
• Internal Bleeding (e.g., Hematoma): Significant trauma from the fall could lead to internal bleeding in the pelvic region, which is a medical emergency.

Rare Diagnoses

• Avulsion Fracture of the Sacrum or Ilium: A rare possibility where a fragment of bone is pulled off by a tendon or ligament, which could happen in the context of a severe fall.
• Stress Fracture of the Sacrum: Although more common in long-distance runners, a stress fracture of the sacrum could theoretically occur from a sudden, forceful impact like a fall down stairs, especially in individuals with predisposing factors such as osteoporosis.
• Infection (e.g., Osteomyelitis, Septic Sacroiliitis): While rare and not directly related to the trauma of the fall, if the SI joint or surrounding bone becomes infected, it could present with pain in the SI region, although this would typically be accompanied by other symptoms such as fever and redness.