Drop Sign and Radial Head Subluxation in Lateral Collateral Ligament Complex Injury: CT scan study in a cadaver model

Aim & BackgroundPosterolateral elbow instability can be difficult to diagnose.Drop sign and radial head subluxation are frequently reported after lateral collateral ligament complex(LCLc) injuries, however, their physiological ranges and diagnostic utility are not well established.This study aimed to define the physiological range of these markers using CT and correlate changes in these markers with progressive LCLc injury. MethodsNine adult cadaveric elbows were mounted on a setting that allows controlled postero-lateral distraction at 90 flexion.CT scans were performed before and after distraction to evaluate drop sign and radial head subluxation.Drop sign was measure as distance between Trochlear Sulcus and Olecranon (TSO).LCLc injuries were sequentially induced, including annular ligament division and progressive soft tissue lesions, up to complete LCLc disruption. ResultsThe physiological TSO was 3.3mm in normal elbow without distraction and increased to 3.8mm under distraction (p=0.02).TSO greater than 4.3mm was defined as a positive drop sign and an average TSO of 4.95 mm was observed with a lesion of the capsule and ulnar band of the LCL.The drop sign progressively increased after each stage of LCLc injury, reaching 9.7mm (95 % CI 8.8-10.5)after complete LCLc disruption.Radial head subluxation also rises from 2.1mm (95% J o u r n a l P r e -p r o o f CI 1.3-2.8)under distraction in normal elbow to 14.4mm following complete LCLc lesion(p<0.01). ConclusionCT imaging of the drop sign and radial head subluxation correlates with the severity of LCLc injury.These markers provide valuable diagnostic information for posterolateral elbow instability.