The forequarter lateral implosion injury: A diagnostic paradigm and Ch-Sh (chɛ-shɑ) classification

The lateral impaction force against the shoulder often causes multiple lesions to the forequarter including the chest wall. The purpose of this study is to describe the injury patterns and associated pathology in patients with combined chest wall and shoulder girdle injuries- forequarter lateral implosion injury and organize the findings into a classification framework to predict morbidity.

Three hundred fifty-four consecutive patients with two or more rib fractures and ipsilateral shoulder girdle injury from a Level 1 trauma center, between 2018-2022, were retrospectively reviewed. Ch-Sh is pronounced chɛ shɑ. Chest injuries were grouped into three categories: Ch1: 2-4 fractured ribs, Ch2: 5 + fractured ribs, or Ch3: 2 + fractured ribs with contralateral rib fractures and/or sternal fracture. Shoulder girdle injuries were grouped into: Sh1: clavicle or acromion fracture, and/or AC/SC joint dislocation, Sh2: scapula and/or proximal humerus fracture, or Sh3: combination of Sh1 and Sh2 injuries (clavicular chain and scapula/humerus). There were 9 total subgroups. Demographics, injury characteristics, associated injuries, and outcomes were recorded. Inter and intraobserver reliability of the classification system was studied.

As chest wall injuries scaled from Ch1 to Ch3, there were significantly higher rates of ICU admission, pneumothorax, pulmonary contusion, mechanical ventilation, and spinal or other orthopedic fractures. ISS and 30-day mortality also scaled similarly. The Sh2 classification was associated with increased morbidity and mortality relative to the Sh3 group. Reviewers had almost perfect interobserver agreement (kappa=0.81) and substantial intraobserver agreement (kappa=0.66).

In the Forequarter Lateral Implosion Injury classification, the Ch3-Sh2 group was associated with the greatest morbidity and mortality. The greater the chest wall injury, the greater the morbidity and mortality. However, that is not the case in shoulder injuries. Multiple disruptions in the Sh3 group may be associated with better outcomes due to dispersion of force from a "crumple zone" where the shoulder collapses with the rib cage sparing the thoracic organs. Examiners demonstrated high reliability for the Ch-Sh classification.

Prognostic Level III.