Lag Screw for Weber B Frx



- Discussion:
    - see: lag screw theory:
    - when the fibular fracture is sufficiently oblique, is not comminuted, and is not osteoporotic, then sufficient fixation can be achieved w/ only two lag screws;
           - the oblique fracture should be longer than 2x diameter of bone inorder for the fracture to be fixed with 2 lag screws alone;
           - when these criteria are not met, then application of a lateral plate will be necessary;
    - advantages:
           - allows for a smaller incision;
           - the hardware is not prominent and usually does not have to be removed;
           - lag screws will not interfere w/ syndesmotic screws (if they are needed);

- Technique:
    - flouroscopy is required if there is a concomitant syndesmotic injury
    - generally lag screws are inserted from anterior to posterior to produce intrafragmentary compression;
    - 3.5 mm cortical screw are used most often, but 2.7 mm screws can be used in smaller patients;
    - after reduction, fracture is fixed with 1 or 2 lag screws, using standard techniques;
           - it is essential that the reduction clamps be locked in a stable position, which will not interfere w/ the drill;
           - also note that the anterior fibula is shaped like a narrow mountain ridge;
                   - ensure that enough soft tissue has been stripped at the gliding holesite, so that the drill position is perfect;
           - if two lag screws are to be used, then insert both screws in a position midway between perpendicular to the bone and perpendicular to the fracture;
                   - this will "create more room" for both screws;
                   - it is important to avoid splitting the posterior spike on the distal fragment;
           - if only one lag screw is to be inserted then place it perpendicular to the fracture line for maximal compression;
                   - when only one lag screw is used, then it will be necessary to apply a 1/3 tubular plate inorder to neutralize rotational & axial forces on the fibula;
           - apply the countersink to make the screw head to improve seating on the anterior fibula and to make the head less prominent;
                   - the countersink will cause the screw to sink deeper, causing it to be more proud;
    - screws must engage the posterior cortex for secure fixation but must not protrude far enough posteriorly to encroach on the peroneal tendon sheaths;
           - often lag screws are overmeasured and appear proud on postop x-rays;
           - when a proud lag screw is recognized intraoperatively, the surgeon may find that replacing the screw with a smaller one does not achieve the same screw bite;

- Alternative Technique:
    - if the incision is slightly posterior, it may be difficult to place the lag screw due to the tightness of the soft tissues anteriorly;
    - a solution to this problem involves creation of a stab incision directly in line with the proposed site of lag screw insertion;

           



- Case Examples:
    - preoperative AP, mortise, and lateral views:

         

    - postoperative films demonstrating an anatomic reduction:

         


         
         


         


         



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Monday, November 26, 2012 3:29 pm