Posterior shoulder instability is heterogeneous and historically lacked a satisfactory classification. This prospective study tests the comprehensiveness and reliability of the ABC classification, which sorts PSI by etiology and pathomechanism. Four raters classified 100 consecutive cases to assess reproducibility across experience levels.
When you evaluate posterior instability, first ask three questions that map directly onto the ABC system: Is this a first-time event (A), recurrent dynamic instability (B), or chronic static decentering (C)? That single framework organizes a confusing pathology into actionable buckets, each with its own workup and treatment implications.
The key mental model is progression: an untreated acute dislocation (A2) can slide into structural dynamic instability (B2) and ultimately fixed static subluxation (C2). Catching and treating patients early may prevent that slide.
Practically, the scapulohumeral subluxation index of 0.61 is your imaging tiebreaker between dynamic and static disease, and the absence of structural defects on MRI plus a positive show-me test points to functional B1 instability, which is treated with rehab, not surgery.
The main caveat: this came from a high-volume referral center, so subtype frequencies may not reflect general practice, and the classification's originator led the study.
Posterior shoulder instability is heterogeneous and historically lacked a satisfactory classification. This prospective study tests the comprehensiveness and reliability of the ABC classification, which sorts PSI by etiology and pathomechanism. Four raters classified 100 consecutive cases to assess reproducibility across experience levels.
When you evaluate posterior instability, first ask three questions that map directly onto the ABC system: Is this a first-time event (A), recurrent dynamic instability (B), or chronic static decentering (C)? That single framework organizes a confusing pathology into actionable buckets, each with its own workup and treatment implications.
The key mental model is progression: an untreated acute dislocation (A2) can slide into structural dynamic instability (B2) and ultimately fixed static subluxation (C2). Catching and treating patients early may prevent that slide.
Practically, the scapulohumeral subluxation index of 0.61 is your imaging tiebreaker between dynamic and static disease, and the absence of structural defects on MRI plus a positive show-me test points to functional B1 instability, which is treated with rehab, not surgery.
The main caveat: this came from a high-volume referral center, so subtype frequencies may not reflect general practice, and the classification's originator led the study.