Acute Knee Flexion Limitation After Sudden Extension: A Clinical Framework Integrating Effusion Decompression and Rotatory Tibial Realignment.

BACKGROUND: Acute inability to flex the knee following a sudden extension event is commonly attributed to structural pathology. However, some patients present with non-mechanical flexion limitation that resolves without invasive intervention, suggesting potentially reversible functional mechanisms. PURPOSE: To synthesize current concepts and integrate them into a clinically applicable framework that distinguishes effusion-related inhibition from transient alignment-dependent restriction in acute knee flexion limitation. METHODS: Narrative review and conceptual synthesis of published literature addressing arthrogenic muscle inhibition, knee effusion, and rotational knee biomechanics, integrated with clinical observations to develop an interpretive framework for bedside assessment. RESULTS: A four-component interpretive framework is described comprising: (1) identification and aspiration of knee effusion to reduce capsular distension; (2) gravity-assisted passive flexion assessment; (3) pain-limited, alignment-facilitated motion involving medial compression, controlled external rotation, posterior translation, and oscillatory flexion; and (4) validation through restoration of symmetric gravity-assisted motion. CONCLUSION: Acute knee flexion limitation following sudden extension may not always reflect fixed mechanical obstruction. The proposed framework integrates established concepts of arthrogenic muscle inhibition with observations from rotational knee biomechanics to support clinical reasoning in selected cases. As a conceptual and hypothesis-generating model, it has not undergone prospective clinical, imaging, or biomechanical validation, and further investigation is required to determine its validity, safety, reproducibility, and clinical utility.