Fracture of capitellum and humeral trochlea - Mckee double arc sign
Presentation
Fall onto right elbow.
Patient Data
Right elbow
Anteroposterior radiograph showed only a distal humeral fracture involving medial and lateral epicondyles.
Lateral radiograph showed a half-moon-shaped fragment that is displaced upwards, representing an intra-articular displaced fracture of humeral trochlea. Anterior fat pad sign is also noted.
Mckee double arc sign of combined capitellum and trochlea fracture:
the inner arch (green arrow) represents the lateral half of trochlea
the outer arch, the larger (yellow arrow) represents the subchondral bone of capitellum
Case Discussion
A case of fracture elbow shows a combination of medial and lateral epicondyles fractures and a displaced intra-articular fracture of the capitellum and lateral half of the humeral trochlea. Mckee double arc sign refers to the characteristic appearance of this fracture. It represents less than 1% of elbow fractures and about 3-6% of distal humeral fractures. It occurs due to coronal shear injury of the distal humerus that forms axial loading on capitello-trochlear area. It is a rare type of fracture that occurs due to a fall on the outstretched hand.
This fracture is considered type C3 according to AO/OTA classification of distal humeral fractures, as it involves not only the capitellum and trochlea but also the epicondyles. Open reduction and internal fixation (ORIF) were recommended.