Dynamic condylar screw is an implant assembly that consists of a lag screw, angled barrel plate fixed to the bone [usually distal femur] by 4.5 cortical screws.
DCS and DHS work on the same principle of the sliding nail that allows impaction of the fracture. This is due to the insertion of wide diameter into the condyle [or femoral head]. A side plate, which has a barrel at a fixed angle is slid over the screw and fixed to the femoral shaft.
In fact, it has all other components the same as DHS. Just the side plate is different. Plate barrel angle is 95 degrees and plate is shaped to accommodate lateral aspect of the lateral condyle.
Indications for Dynamic Condylar Screw
Dynamic condylar screw was mainly developed for fractures of distal femoral condyles.
Hence the name.
It is also used in fixation of subtrochanteric fractures of the femur.
Sometimes, it can be used in revision surgeries of selected intertrochanteric fractures.
Parts of DCS
Lag Screw
The lag screw is same as that of dynamic hip screw.
The screws are available in various lengths of 50 to 145 mm. It has a thread diameter of 12.5 mm and a thread length of 22 mm.
The shaft is slotted [has two flat sides] to fit the barrel and has a length of 8.0 mm. The shaft and barrel slots fit each other so that the screw is able to slide inside the barrel but cannot rotate.
On the distal aspect of the shaft of the lag screw, the inner side is threaded. This is for placing compression screw after the screw and plate assembly has been fixed.
The purpose of the compression screw is to pull the lag screw towards barrel as the compression screw is tightened.
Side plate
The plates are made of 316L stainless steel and are cold-worked for strength. The two holes closest to the barrel accept 6.5 mm cancellous Bone Screws. This enhances stability.
Similar to dynamic hip screw, the inside of barrel plate has two flats correspond to the two-flat design of the lag screw. This prevents the rotation of the lag screw within the barrel and eases the insertion too.
The DCS plates are available with 6 to 16 holes, for varied clinical situations.
Technique of Dynamic Condylar Screw For Distal Femur
The exact nature of the fracture should be determined before surgical intervention and all major fracture fragments should be identified
Preoperative planning allows one to determine optimum placement of the entry point and determine the appropriate lengths of the blade and side plate.
After exposure through a lateral incision on the distal femur, the fractures are temporarily stabilized with k-wires and guidewires. If required cancellous screws are used to fix the small intercondylar fragments.
Correct placement of guide wire for the lag screw is very important. For this, under image intensifier control, pass one guide wire lateral to medial along the tibiofemoral joint line (red). Pass a second guide wire over the anterior surface of the knee to indicate the plane of the patellofemoral condyles (green).
The ideal position of the DCS is shown by the yellow wire.
The guide wire for the DCS is positioned at 2 cm proximal to the distal end of the femur.
The tip of the guide wire should just engage the medial cortex, and so will appear short of the medial condylar cortex on the AP intensifier image.
Using the direct measuring device over the guide wire, lag screw length is measured.
DCS triple reamer is a reamer like DHS triple reamer used for reaming for the lag screw.
After tapping, the lag screw is inserted over the guide wire, keeping its outer end visible 2-3 mm outside the lateral cortex of the distal femur.
This is followed by plate insertion. The plate barrel is slid over the screw shaft and fixed to the bone after positioning.
Technique of Dynamic Condylar Screw For Proximal Femur
Dynamic condylar screw is used to fix subtrochanteric fractures of the femur. The insertion point for dynamic condylar screw on the proximal femur is higher than DHS. Apart from these other steps are similar.
Leave a Reply