The dynamic hip screw (DHS) is a metal plate-screw construct that is attached to the femur. This procedure is one of several osteosynthesis options that reattach fractured bones using inserted materials.
What is the dynamic hip screw?
A fracture of the neck of the femur is repaired by surgery that preserves the femoral head. There are several therapeutic approaches, but plates and nails are most commonly used. One disadvantage is that most procedures require the patient to take weight off the operated leg for three months and restrict movement. Plates and nails are used mainly in young people who have suffered an accident or fall. To restore the patient’s mobility as quickly as possible, a Dynamic Hip Screw and Side Plate construct is inserted at the neck of the femur.
Function, effect and goals
The Dynamic Hip Screw (DHS) is a metal plate-screw construct that is attached to the femur. The Dynamic Hip Screw is a construct that consists of a metal plate and a screw. It is an implant that stabilizes fractures near the hip joint. The most common use is for fractures of the neck of the femur and fractures near the hip (petrochanteric fracture). The core of the Dynamic Hip Screw is a femoral neck screw that stabilizes the fracture. A metal plate fixes the hip joint to the outside of the bone shaft. It is placed distally, toward the end of the bone near the knee, and fixed to the bone shaft with four screws or nails. An angled sleeve is inserted into the femoral neck at the upper end of the plate, near the hip, so that the femoral neck screw can slide back and forth along this sleeve. After repositioning (direction) of the fracture, the Dynamic Hip Screw is attached to the femoral neck bone through an incision approximately 10 centimeters long. The difference with the equally commonly used Gammanagel method is that the fracture is stabilized by a metal plate attached to the outside of the bone shaft, whereas with the Gammanagel, stabilization is provided by an intramedullary nail located inside the bone. The Dynamic Hip Screw uses the sliding mesh principle. There is sliding of the screw shaft inside the plate cylinder, which ensures dynamic compression. The operation is performed on an extension table. The fractured leg is held by a leg holder and counter traction bar. The patient is positioned in a well-padded position, paying particular attention to the parts of the body at risk of pressure, the pubic region (counter traction bar) and the ankle joints. The arm located on the side to be operated on is held by an anesthesia bar to prevent nerve injury. The basic instrumentation includes scalpels, 2 broad-spritz, 2 narrow-spritz, 2 long-pelvic hooks, 2 roux hooks, 2 sharp hooks as 5-prongs, reduction forceps and bone scraper (raspatory). The surgical tools used are an aiming device with a T-handle, threaded guide wires, a three-step drill, a tap, a wrench with a centering sleeve, a cylindrical guide shaft with a connecting screw, connecting screws, impact bolts, a hammer, a neutral drill sleeve 3.2 mm and a 3.2 mm drill. The surgical area is covered with four sterile drapes. After the skin incision below the bony prominence on the thigh (greater trochanter), sharp hooks are used for pre-preparation to open the surface (facie). In this way, the surgeon exposes the thigh bone (femur) according to the principle of the so-called “posterior mailbox approach”. The sharp hooks are then removed again. In the next step, the threaded guide wire is inserted into the neck of the femur using the image converter control and a 135-degree targeting gauge. The gauge provides information on how long the wire needs to be in the bone (lateral cortex joint). A 10 mm screw is required. The three-step drill is adjusted to the length of the screw, i.e. the 10 millimeters of screw length must be subtracted when adjusting the drill length. The screw ends 10 millimeters before the joint. The DHS screw channel is drilled out. In the first stage, the channel is opened for the femoral neck screw, and in the second stage, the hole is drilled for the portion of the plate cylinder.In the third stage, the headspace milling is produced to connect the cylinder and plate. Only in the case of very hard cancellous bone, a thread is cut using a T-handle with centering sleeve and tap. The Dynamic Hip Screw is assembled using the cylindrical guide shaft, centering sleeve and connecting screw. At this point, the guide wire is removed again, the plate holes are filled, the measured screws (cortex) are inserted and then tightened manually. Image converter control is performed at all levels. The wound cavity is irrigated and a redon drainage is performed. In the final step, a layer-by-layer atraumatic wound closure and a sterile wound dressing with compresses are performed. The Dynamic Hip Screw allows collapse at the fracture site. In combination with a side plate, it provides maximum support at the outer site of the femur. However, experts believe that the ability to rotate still needs improvement. Another treatment option is multiple screw fixation, but this provides little lateral support for the fracture. Medical experts consider the Targon FN implant to be the best solution, combining the advantages of dynamic and multiple screw fixation.
Risks, side effects, and hazards
With the Dynamic Hip Screw, prompt and complete weight-bearing of the operated leg is possible and desirable. The primary goal is to preserve the femoral head joint to avoid follow-up surgery, especially at a young age. In contrast to the Gammanagel procedure, there is no leaching of fat, which can lead to fat embolism in older patients with lung damage. The intramedullary nail inside the bone spares the delicate bone tissue and periosteum. This gentle approach is less given with the Dynamic Hip Screw. Therefore, the DHS procedure with multiple nails or screws is not recommended in patients with severe osteoporosis. There is a risk of further fracture due to the metal plate and fixation screws attached to the femoral shaft.
