Simple pertrochanteric fractures with posteromedial involvement
Simple pertrochanteric fractures with posteromedial involvement and an intact lateral wall are classified by AO/OTA as 31A1.3.
In these fractures, the fracture line can start laterally anywhere on the greater trochanter and run towards the medial cortex, broken in two different places. This results in the detachment of a third fragment, which is usually a coronal fragment including part of the posteromedial cortex. In rare cases, the lesser trochanter is avulsed.
Lateral wall height of greater trochanter
The coding system separates the pertrochanteric fractures into two groups (A1 and A2) defined by the lateral wall height (d) of the greater trochanter.
Lateral wall height or thickness is defined as the distance in millimeters (mm) from a reference point 3 cm below the innominate tubercle of the greater trochanter angled 135° upward to the fracture line on the AP x-ray. The thickness (d) must be less than 20.5 mm for the fracture to be considered an A2 fracture (Hsu et al 2013). It is recommended that the measurement for the lateral wall be taken using the traction view with the leg in neutral rotation. This can be difficult to obtain preoperatively but should be assessed fluoroscopically following operative closed reduction but before implant selection. Alternatively, preoperative 3-D CT provides detailed mapping of fracture location and planes.
Fractures with an intact lateral wall (>20.5 mm) may be considered stable after anatomical reduction.
Additional coronal fragment
In addition to a primary trochanteric fracture, often a secondary coronal fracture on the posterior aspect of the greater trochanter can be observed. These coronal fragments may start at the summit of the greater trochanter and exit through some point along the trochanteric crest or even at the posteromedial cortex.
Irreducible intertrochanteric fracture
Superolateral displacement of the shaft after high-energy trauma is a sign of an irreducible intertrochanteric fracture.
The displacement of the medial neck spike causes button-holing anteromedially through the iliofemoral ligament, anterior capsule, and iliopsoas.
This case shows an irreducible fracture with shearing displacement and avulsion of the lesser trochanter.
The 3-D CT image of the same case shows the fracture morphology more clearly, especially on the posterior aspect.
Occult hip fractures
An undisplaced fracture may also be referred to as occult fracture as it is often not visible and may not be diagnosed correctly.
If clinical assessment indicates a neck fracture, but the x-ray does not show clear signs of it, CT or MRI imaging is recommended.