Differential Diagnosis for Patient with Left Posterior Shoulder Pain

The patient's presentation of left posterior shoulder pain, sharp pain with breathing, and initial numbness in the right arm after a fall from a horse suggests several possible diagnoses. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Rib Fracture: The patient's sharp pain that worsens with breathing (pleuritic chest pain) and the mechanism of injury (fall from a horse) make rib fracture a highly plausible diagnosis. The presence of superficial abrasions and the patient's grunting in pain also support this diagnosis.

• Other Likely Diagnoses

  • Scapular Fracture: Given the location of the pain (left posterior shoulder) and the mechanism of injury, a scapular fracture is a possible diagnosis. The patient's ability to actively flex the left shoulder above the head does not rule out this diagnosis, as some scapular fractures may still allow for significant shoulder mobility.
  • Clavicle Fracture: Although the pain is described as posterior, clavicle fractures can sometimes present with pain referred to the posterior shoulder area, especially if the fracture is more proximal. The mechanism of injury is consistent with a clavicle fracture.

• Do Not Miss Diagnoses

  • Pneumothorax: The patient's pleuritic chest pain and history of trauma necessitate consideration of a pneumothorax, which could be life-threatening if not promptly diagnosed and treated. Although lungs are clear to auscultation, this does not entirely rule out a small pneumothorax.
  • Spinal Injury: The patient's initial numbness in the right arm and the fact that he does not remember the event raise concerns about a potential spinal injury. The inability to assess the patient's back due to the c-spine brace highlights the need for careful consideration and further evaluation of the spine once it is safe to do so.
  • Aortic Dissection: Although less common, the mechanism of injury and the initial numbness could, in rare cases, suggest an aortic dissection, especially if there were any signs of mediastinal widening on imaging or if the patient had a pre-existing condition like hypertension.

• Rare Diagnoses

  • Brachial Plexus Injury: While the patient's sensation is intact in the bilateral upper extremities, and the initial numbness has improved, a brachial plexus injury could still be considered, especially if there were any signs of neurological deficit that were not immediately apparent.
  • Diaphragmatic Rupture: This is a rare but possible injury following severe trauma, which could present with shoulder pain due to referred pain from the diaphragm. However, this diagnosis would typically be associated with more significant respiratory distress or abdominal symptoms.