Aetiology

Rib fractures most commonly result from motor vehicle accidents (MVAs), falls, assaults, and industrial accidents.[13] A flail chest is defined as consecutive, segmental (i.e., multiple fractures in the same rib) ipsilateral rib fractures, classically causing paradoxical motion of the chest wall during inspiration and expiration. These are usually the result of high-energy MVAs with concomitant injuries leading to increased morbidity and mortality.[21][22]​ Significant intrusion of the steering column can apply dramatic force to the thoracic cage.

Traumatic fractures can also occur due to cardiopulmonary resuscitation (CPR).[23][24]​​​ However, incidence of rib fractures following CPR in children, who have a much more flexible chest wall, is estimated to be <2%.[23]

In young children, studies have shown rib fractures are a result of child abuse 65% to 100% of the time.​[2]​[3]​[4]​[5]​[6]​ The positive predictive value of rib fractures for child abuse in children younger than 3 years was 95% in one retrospective study.[4]​ The probability of abuse in children with intracranial injury and retinal haemorrhage alone is about 33%, but this probability increases to about 98% with the addition of rib fractures.[8]​[9] Although much less common, rib fractures can also occur after serious accidental injuries, birth trauma, or secondary to bone fragility.[10]​

Posterior rib fractures commonly occur in elder abuse as a result of punches and kicks to the patient’s back and have a low probability of resulting from accidental trauma.[25]​[26]​ In a study of 92 elder abuse victims, approximately 93% of rib fractures were observed to occur posteriorly.[25]​[26]​

Metastasis from lung, prostate, breast, and liver cancer can also involve the ribs, accounting for 12.6% of metastatic lesions.[27] Furthermore, there are numerous primary bone tumours that can present as pathological rib fractures, including osteochondroma, enchondroma, plasmacytoma, chondrosarcoma, and osteosarcoma. About 37% of these lesions are malignant.[28] Multiple myeloma can present with rib fractures and even with a flail chest.[29]​​[30]

Stress fractures can result from severe coughing, and from sporting activities such as golf, swimming, baseball, and competitive rowing.[31][32][33][34]​​ Rib stress fractures occur in 2% to 12% of rowers as a result of cyclic loading to the rib cage.[35]​ Diagnosis is suggested by continued pain despite the absence of trauma.

As age increases, the absolute risk of sustaining a fragility fracture is inversely proportional to the bone mineral density of the patient, with about 27% of these fractures occurring in the ribs.[15]

Pathophysiology

There are 12 ribs on each side of the normal human thorax (24 ribs in total) that function to protect the intrathoracic and upper abdominal organs and to aid in respiration. The first 2 ribs are shorter than ribs 3 to 10 and are intimately associated with the subclavian artery and the brachial plexus. Greater force is required to fracture these 2 ribs than the others, and such fractures should alert the physician to the possibility of vascular or neurological injury.[36]​​[37][38][39]​​​ Upper rib injuries tend to injure the lung parenchyma by direct penetration. Fractures of ribs 10-12 are more likely to be associated with injuries to the liver, spleen, and kidneys.[40][41]​ The presence of multiple rib fractures involving the lower ribs has a high association with solid organ injury (about 50%).[41]​​

On the inferior surface of each rib are the intercostal nerve, artery, and vein. This neurovascular bundle has the potential to be injured with fractures of the rib, resulting in haemothorax and substantial pulmonary insufficiency.

Ultimately, rib fractures impair adequate ventilation, resulting in atelectasis, poor oxygenation, and respiratory compromise.[42]

Ribs and costal cartilage are more elastic in children, making substantial force necessary to cause a fracture. Therefore, in the absence of a known traumatic event, non-accidental injury should be suspected.

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