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The Endobutton (Smith & Nephew), which was launched in 1990, undoubtedly played an important role in the fixation of the femoral end of anterior cruciate ligament reconstruction. This changed the fixation method of the femoral end of the anterior cruciate ligament, and the suspension fixation method was also proven to be effective in subsequent studies. Better mechanical strength and prognosis.
As major companies on the market launch new suspension fixation devices such as RIGIDLOOP (Johnson & Johnson), TightRope (Arthrex), Procinch (Stryker) etc., more and more surgeons may slowly forget the depth of the femoral end tunnel during fixation measurement.
Calculation method
First of all, we need to know that the lengths of the Endobutton’s loops are 15mm, 20mm, 25mm, and 30mm.
Secondly, the loop length of the Endobutton is determined based on the length of the internal opening of the lateral femoral condyle bone tunnel and the lateral cortical outlet. Generally, the transplanted tendon should be placed 2-3 cm within the bone channel. Therefore, the length of the bone channel of the lateral femoral condyle minus 2-3 cm is the loop length of the Endobutton.
Calculation formula
Loop length = 4.5mm, total length of drill tunnel – femoral drill bit drilling depth + 10mm
Therefore, in order to make the length of the lateral condylar tunnel as long as possible, when creating the lateral condylar tunnel, the knee should be bent as much as 120 degrees to ensure the required length of the tunnel.
When drilling the grafting tendon-bone channel, it is sufficient to retain 1 cm of lateral bone cortex, which facilitates the turning of the Endobutton.
Example of calculation
Scenario 1: First determine the specifications of Endobutton
Use a 4.5mm Endobutton drill bit at the femoral end to drill through the femur and measure the depth to 40mm. Select the 20mm Endobutton CL:
Then the loop length is 40mm (4.5mm femoral tunnel depth) – 20 (loop length) + 7mm (space required to turn the loop) = 26mm
Scenario 2: Finally select the specifications of Endobutton
The femoral end 4.5mm Endobutton drill bit drills through the femur to a measured depth of 40mm, and the femoral drill bit drills into 28mm:
Then the loop length is 40-28+7=19mm, the Endobutton length must be greater than 19mm, use 20mm.
Other methods
The simplest method is to divide the measured tunnel by 2 and take the smaller value, because if the drilling is accurate, it is usually between 35-60mm. Divided it by 2 is 17.5-30mm, so choose 15-25mm.
As for whether to add 10 for flipping, it depends on the length of the tunnel. If the tunnel is long, there is no problem in adding 10; but if the tunnel is smaller than 44mm, take a 20mm loop and the ligament in the tunnel is 24mm; or if the tunnel is shorter, use a 15mm loop. If you continue to add 10, the angle between the drill and the tunnel may cause cortical damage. There is a risk of breaking, so it is advisable to consider adding 7-8. for reference only.
Suggestion
If the patient is really short, the tunnel is not expected to be long, and the femoral tunnel is not in a good position after drilling. For example, if the femoral tunnel is less than 40mm in special circumstances, using a 15mm loop will be risky no matter how you insert it. You can use a small incision to directly suspend it without turning it over.