Abstract
Knee arthroscopy is a common and generally safe procedure for treating ligamentous, meniscal and cartilaginous knee injuries, yet rare complications such as irrigation fluid extravasation and compartment syndrome can occur when the posterior joint capsule is violated. Because posterior capsular injury is often under-recognized on clinical examination and conventional MRI, failure to identify these tears may lead to instability, accelerated cartilage degeneration and functional limitations. In this narrative review, we first outline the complex anatomy of the posterior capsule, including its integration with the semimembranosus and popliteus complexes and attachments to cruciate ligaments, and then characterize key injury mechanisms (multi-ligament tears, pivot-shift, dashboard, hyperextension and valgus “clip” injuries). For each mechanism, we describe characteristic MRI findings, such as focal or gross extracapsular fluid collections, specific bone-bruise patterns and associated ligamentous injuries that should prompt careful evaluation for capsular disruption. We discuss implications for surgical planning, including the trade-offs between early repair (enhanced landmark identification versus increased arthrofibrosis) and delayed intervention (improved capsular healing versus more challenging dissection). Finally, we highlight the need for standardized MRI protocols, reporting templates and risk-stratification tools that integrate imaging findings with injury patterns to guide timing and technique of arthroscopic reconstruction and improve patient outcomes.
•Under-recognized MRI Signs: Highlights key MRI patterns, from overt extracapsular fluid collections to subtle focal capsular defects—that signal posterior capsule tears across various knee injury mechanisms.•Mechanism-Specific Imaging Correlates: Defines characteristic bone-bruise distributions and ligament-capsule tear configurations for multi-ligament, pivot-shift, dashboard, hyperextension, and valgus (“clip”) injuries.•Clinical Impact on Surgical Planning: Emphasizes how identifying posterior capsular disruption guides optimal timing (early vs. delayed), irrigation-pressure adjustments, and consideration of staged or tailored arthroscopic approaches to minimize complications.