The classifications for adult both bone forearm fractures apply descriptive terms about the location of the fracture in bone, whether one or both bones are fractured, the degrees of comminution, displacement ,angulation and whether the fracture is open or closed.
OTA basic Fracture Course Expert

"Fractures of the ulna,22-Radius/Ulna Diaphysis"

AONA posting of the AO Classification of Long Bone Fractures Highly Reputable

See
- Pediatric Both Bone Fractures
- Deforming Forces:
- Discussion of Blount Fractures:
- Implants for Fractures of the Radius and Ulna:
- Plating Techniques:
- Indications for Operative Treatment:
- all displaced, unstable fractures of the radius and ulna in adults;
- radial shaft fractures: all displaced fractures of the radius with greater than 10 deg of angulation or with subluxation of proximal or distal R-U joint
- ulnar shaft fracture: isolated fractures of the ulna with angulation greater than 10 deg;

- radial head fracture plus dislocation of distal RU joint (& interosseous membrane disruption);
- mechanism: fall from height;
- in this type of frx, radius will also migrate proximally if radial head is excised;
- if injury is not found when it is acute, pt may develop severe wrist pain from radial migration and subluxation, of upto 5-6 mm;
- there may be loss of forearm pronation, supination, and extension;
- late reconstruction(> 4 weeks) of radial instability yields poor results;
Wheeless Textbook of Orthopaedics

The radius/ulna section of the AO Surgery Reference. The whole surgical management described, including decision-making support, approaches, and surgical procedures. Highly Reputable

- fracture of radial shaft (between middle and distal 1/3's) & dislocation of distal radioulnar joint;
- usually the dislocation is dorsal, but in some cases can be palmar;
- fracture is almost always located just above proximal border of pronator quadratus;
- usually there is anterior angulation w/ transverse or short oblique configuration;
Wheeless' Textbook of Orthopaedics

Giovanni Monteggia (1814) first described fracture of proximal 1/3 of ulna in association with anterior dislocation of radial head;
- hence dislocation of radial head with fracture of proximal 1/3 of ulna is known as Monteggia's deformity.
- Mechanism:
- proposed mechanisms include direct blow & hyperpronation injuries as well as the hyperextension theory;
Wheeless' Textbook of Orthopaedics

radius & ulna lie parallel to each other when forearm is supinated;
- during pronation radius crosses ulna, rotating on axis that passes from capitulum through the distal end of ulna;