Subtrochanteric fractures account for about 10% of all fractures in the proximal femur. This fracture occurs between the lesser trochanter and a point 5 cm distal to the lesser trochanter. The subtrochanteric region is the worst area on the femur for the fracture to occur. There is high compression and tensile forces in the area, as well as less vascularity, less healing potential, and ability. This area is made of hard cortical bone that does not heal well. There are a lot of deforming forces on the proximal fragment. The subtrochanteric fracture is flexed by the iliopsoas muscle, abducted by the gluteus medius and minimus muscles, and externally rotated by the short rotator muscles. Additionally, there is a high risk of implant failure. A bone to bone transfer may be necessary in this area, especially if the fracture is going to be opened.
There are two types of fractures, atypical and typical. Atypical fractures are associated with bisphosphonate use. Patients will experience thigh pain and usually there is no history of trauma. The fracture may be seen on an MRI. Using bisphosphonate for a long period of time may cause this atypical subtrochanteric fracture of the femur. The fracture may appear as a localized thickening on the lateral side of the femur. When you bend a bone, there will be two parts, a compression component and tension component. In an x-ray, the compression component will signal an oblique “spike” on the medial side and there will be no comminution. The tension component will be on the lateral side. Typical fractures usually occur due to high energy trauma such as car accidents or from a fall.
In the majority of subtrochanteric fractures, either typical or atypical, we will use a rod. Because the rod is inside the bone, and not outside the bone like a plate, this area is suitable for IM nailing. The rod location will result in a shorter lever arm and lower bending moment on the device. The rod will be closer to the center of motion of the body than a plate, which is on the lateral surface of the bone, further away from the center of motion of the body. Therefore, rods are subjected to smaller bending loads and less likely to result in fatigue failure. The IM rod is minimally invasive and they do not destroy the extramedullary blood supply. IM rods are load sharing so you can initiate weightbearing. IM rods are stronger than plates. You must reduce the fracture before reaming and insertion of the rod.
The disadvantage is that an IM rod may create varus and procurvatum deformity (flexion). There is more varus with trochanteric entry. There may also have perforation at the anterior cortex distally due to mismatch between the radius of curvature of the nail and femur. The IM rod is not preferred in the treatment of subtrochanteric fracture that extends into the piriformis fossa or the greater trochanter. A fixed angle plate may need to be used to avoid excessive dissection medially. A bone graft may be used to avoid nonunion. A bone to bone transfer will be necessary medially. The patient should try to avoid early weightbearing. The plate induces fracture healing through primary bone healing. The rod induces endochondral ossification, secondary bone healing (more abundant bone healing). If there is enough segment of the proximal fragment that you can place a diagonal screw, this means that you have a large piece of bone and a standard IM nail may be used. If there is not enough bone segment to place a diagonal screw, then you need to place the screws on the head, called cephalomedullary nailing. If the fracture extends to the piriformis fossa or the greater trochanter, then you probably need to use a fixed angle plate.