Dynamic Hip Screw
A dynamic hip screw is commonly used to treat stable intertrochanteric hip fractures (figure 1). These are hip fractures that occur between the greater and lesser trochanter of the femur. Additionally, they must be non-comminuted and withstand a load applied to the leg without displacement.
Figure 1: X-ray showing the location of an inter-trochanteric hip fracture
A dynamic hip screw device consists of a large screw and plate system. The first part of the surgery involves realigning the two fragments of the fracture. Some intertrochanteric fractures are stable and in a good position, but many others are displaced and need to be repositioned. Repositioning the intertrochanteric hip fracture so that the fracture is aligned in its original position is done using a special operating table called a fracture table. This table allows traction and rotation to be applied to the leg so it may be appropriately repositioned. The final position of the fracture is evaluated using a special x-ray called fluoroscopy.
A guide wire (Krischner (K) wire), is then inserted through the lateral part of the upper thigh into the mid-femoral head. The K wire is finally placed into the layer of bone just beneath the cartilage (subchondral bone). The correct positioning of the K wire is determined by fluoroscopy. Once the K wire is placed, the length of the “hip screw” to be inserted is determined using the K wire and a measuring device. A drill with a hole through the middle (cannulated drill) is used to drill over the K wire. The dynamic hip screw is then inserted where the K wire is placed, and the wire is removed. The dynamic hip screw is held in place with a side plate that runs parallel to the shaft of the femur. Finally, the plate is fixed to the femur using additional screws that run through the center of the bone.
One advantage of the dynamic hip screw system includes the application of consistent and controlled dynamic pressure to promote healing of the fracture. The “hip screw” can “slide” through the plate so that the fracture site is compressed when the patient loads the implant during walking and standing. This application of force during the healing process encourages the cells responsible for bone formation (osteoblasts) to deposit new bone thereby increasing fracture healing. This results in a lower rate of nonunion, or failure of the fracture to heal. The system also offers consistent static, or fixed, pressure.
Surgical procedures performed to treat intertrochanteric hip fractures usually require 3-6 months of recovery. This is longer than most other types of hip surgeries because it takes time to form new bone. During the healing process pain medications such as oral and topical NSAIDs can be used as needed. Soon after surgery, weight bearing as tolerated using an assistive device such as crutches is encouraged to prevent stiffness and promote a full recovery. Early mobility is critical to a successful recovery, particularly in older patients. The surgeon will also prescribe physical therapy, which will promote a return to pre-fracture activity levels and ensure that the full range of motion is regained.
Potential complications of dynamic hip screw placement include:
- Failure of the ends of the fracture to join (nonunion)
- Surgical site infection
- Prominence or protrusion of the hardware
- Shortening of the affected leg