Green Classification of First Metacarpal Base Fractures

Type I	Bennett Fracture (displaced fracture), first proposed by Bennett in 1882. The fracture line goes from the base of the metacarpal upwards diagonally outward, entering the joint. A triangular bone fragment forms on the ulnar side of the metacarpal base. Due to the ligament connection between the hook of the hamate and the majority of the carpal bones, this fragment remains in position, or only slightly rotates. The distal end of the fracture moves dorsally and laterally due to the pull of the abductor pollicis longus, resulting in dislocation of the first carpometacarpal joint. The proximal end of the fracture is displaced radially due to the pull of the abductor pollicis longus, while the distal end is displaced ulnarly due to the pull of the flexor pollicis longus and adductor pollicis, resulting in dorsal and radial angulation deformity.
Type II	Rolando Fracture (comminuted fracture), described by Rolando in 1910, is a “T” or “Y” shaped intra-articular fracture at the base of the first metacarpal and can be regarded as a comminuted Bennett fracture.
Type III	a) Transverse fracture; b) Oblique fracture.
Type IV	Injury to the epiphyseal plate. Types I and II are intra-articular fractures, while Types III and IV are extra-articular fractures. The Rolando fracture is an intra-articular fracture, and for intra-articular fractures, a comprehensive understanding of the direction of joint surface displacement and the degree of comminution is the basis for reasonable reduction and effective fixation, which will directly affect healing and final functional outcomes. This is also true for the treatment of Rolando fractures. The Green classification only focuses on describing the mechanisms and geometric changes of the fractures and does not directly reflect the state of the joint surface fracture fragments.