Rib fractures and flail chest

What it is

Isolated rib fractures are common after thoracic trauma and usually heal without fixation. A flail chest occurs when two or more adjacent ribs are each fractured (or dislocated) in two places, dorsally and ventrally. The segment between the fractures loses its connection to the rest of the thoracic wall and moves paradoxically: it is sucked inward during inspiration and pushed outward during expiration. The flail segment reduces ventilation, but in most dogs the main cause of hypoxaemia is the underlying pulmonary contusion, together with pneumothorax or haemothorax.

Who it affects

Dogs of any age and breed after blunt or penetrating thoracic trauma. Bite wounds in small dogs attacked by larger dogs are a classic cause; vehicle accidents are the other main one.

Anatomy involved

The dog has 13 pairs of ribs (costae). Ribs 1 to 9 are sternal ribs, whose costal cartilages articulate with the sternum; ribs 10 to 12 are asternal and form the costal arch, and rib 13 is usually floating. Each rib articulates dorsally with the vertebral bodies (head) and the transverse process (tubercle). The intercostal artery, vein and nerve run along the caudal border of each rib, which matters for intercostal nerve blocks and for passing sutures or wires around a rib. Bite wounds may look small on the skin while hiding extensive damage to muscles, ribs and lung beneath.

Clinical signs

Tachypnoea and dyspnoea, a visible segment of chest wall moving in the opposite direction to the rest of the thorax, pain on palpation, crepitus, subcutaneous emphysema and signs of shock. Bite wounds may be open into the thorax.

Diagnosis

• Observation of the breathing pattern and careful palpation.
• Point-of-care ultrasound of the thorax to detect pneumothorax, haemothorax and contusion while stabilising the patient.
• Thoracic radiographs once the patient can tolerate them: rib fractures, pulmonary contusion, pneumothorax, pleural effusion.
• Arterial blood gases or pulse oximetry to assess oxygenation.

Treatment

Oxygen supplementation, analgesia (opioids and intercostal nerve blocks cranial and caudal to the fractures), thoracocentesis for pneumothorax or haemothorax, and positioning the dog with the affected side down. Many flail segments become stable within a few weeks with conservative care. Stabilisation is indicated when the paradoxical movement compromises ventilation: an external splint attached to the ribs with sutures, or internal fixation with wires or plates when a thoracotomy is required anyway, as with penetrating bite wounds, which should be explored surgically.

In the cat

Like the dog, the cat has 13 pairs of ribs: nine sternal, three asternal that form the costal arch and one floating. Rib fractures and flail chest occur mainly after dog bites, road traffic accidents and falls from height, and are almost always accompanied by pulmonary contusion and pneumothorax. Bite wounds may leave minimal skin wounds with extensive tearing of the intercostal muscles, ribs and lung, so they are explored surgically.

A dyspnoeic cat tolerates handling very poorly: it is stabilised first with oxygen in a quiet environment, opioid analgesia and thoracocentesis for pneumothorax, and radiographs are delayed until it can tolerate them. Local anaesthetic doses for intercostal blocks must be adjusted, because cats are more sensitive to their toxicity. The principles of stabilisation with an external splint or internal fixation are the same as in the dog, with smaller implants and sutures.

Key studies in the cat

• Kraje et al. (2000), 75 cats with traumatic rib fractures. When the cause was known, 58% were injured by another animal. 87% had intrathoracic injuries, 47% had concurrent orthopaedic injuries and 13% had a flail chest. 78% of the treated cats survived; flail chest, pleural effusion and diaphragmatic hernia were associated with death.
• Frykfors von Hekkel and Halfacree (2020), 22 cats with thoracic dog bite wounds. 6 of 21 had no external wound, pneumothorax was the most common radiographic finding, and 3 or more radiographic lesions were associated with a penetrating wound. Mortality was 27%. It is a small single-centre series.
• Mansbridge et al. (2024), 137 cats with blunt trauma and thoracic CT at UK referral hospitals. 69% were road traffic accidents. CT showed atelectasis in 34%, pulmonary contusion in 33%, pneumothorax in 29% and pleural effusion in 20%. 33% of cats had a normal thoracic examination but lesions on CT, and six of them needed treatment.
• Vidal et al. (2024), 111 traumatised cats with thoracic point-of-care ultrasound and radiographs within 24 hours. 74.4% had lesions, most often pulmonary contusion. Agreement between the two tests was moderate, and only fair for pleural effusion, which supports ultrasound in the initial assessment.