Innovative Diagnostic Protocol Development for Ipsilateral Floating Hip and Knee: Diagnostic Floating Lower Limb Ipsilateral Protocol (D-FLLIP)

Purpose: The Floating Lower Limb (FLL) represents an exceptionally rare injury complex, and to date, no consensus has been established regarding optimal timing, fixation sequence, or prognostic expectations. In this study, we aim to present and evaluate the Diagnostic Floating Lower Limb Ipsilateral Protocol (D-FLLIP), a novel classification system specifically developed for patients with ipsilateral floating hip and knee injuries. Methods: A retrospective descriptive classification system, named D-FLLIP, was developed to evaluate injury patterns in polytraumatized patients with ipsilateral FLL. This system integrates existing classification criteria for isolated injuries of the pelvis, femur, tibia, and acetabulum, allowing for stratification of injury severity, prediction of complications, and support in clinical and surgical decision-making. A retrospective cross-sectional study was conducted to assess the utility of D-FLLIP. Results: Twenty-eight patients with ipsilateral FLL were classified using the D-FLLIP system. Based on their cumulative injury scores, seven patients (25%) were categorized as grade I, eleven (39.3%) as grade II, six (21.4%) as grade III, and two patients each (7.1%) as grades IV and V. Statistically significant associations were identified between the D-FLLIP grade and the occurrence of vascular injury (p < 0.01) and limb amputation (p < 0.01). A trend toward significance was observed for early fracture-related infections (p = 0.06). Conclusions: Our findings suggest that both the categorical classification and total score demonstrate good predictive value for acute complications, with the total score providing slightly better discriminative capacity. However, the limited number of cases in higher severity grades led to model instability in logistic regression.