Rib Fracture: This is the most common injury following blunt chest trauma, and the left side is as likely as the right to be affected. The pain is typically sharp and worsens with deep breathing or coughing.

Pulmonary Contusion: A bruise of the lung tissue caused by trauma, which can lead to left chest pain if the contusion is located in the left lung. Symptoms can include shortness of breath and cough.
Hemothorax: Accumulation of blood in the pleural space, which can cause chest pain, shortness of breath, and decreased breath sounds on the affected side.
Pneumothorax: Air in the pleural space, which can lead to partial or complete lung collapse. Symptoms include sudden chest pain and shortness of breath.

Myocardial Contusion: A bruise of the heart muscle, which can lead to arrhythmias, heart failure, or even cardiac arrest. Although less common, it's critical to diagnose due to its potential severity.
Aortic Dissection: A tear in the inner layer of the aorta, which can lead to a life-threatening condition if not promptly treated. Chest pain is often severe and tearing in nature.
Splenic Injury: Given the spleen's location under the left diaphragm, trauma can cause splenic rupture or laceration, leading to left upper quadrant pain, which can radiate to the left chest.

Diaphragmatic Rupture: A tear in the diaphragm, which can allow abdominal organs to herniate into the chest cavity, causing chest pain, abdominal pain, and respiratory distress.
Esophageal Injury: A tear or rupture of the esophagus, which can lead to chest pain, difficulty swallowing, and potentially severe infection if not promptly treated.
Spinal Injury: Fractures or dislocations of the thoracic spine can cause chest pain due to the involvement of the spinal nerves or the instability of the spine itself.