CT SCAN KNEE JOINT

CT SCAN TECHNIQUE OF KNEE JOINT:

INDICATIONS:

1. The primary indication for a knee CT is to assess the alignment and degree of displacement of fracture fragments, particularly at the articular surfaces. It demonstrates bony anatomy such as the evaluation of bony morphological abnormalities, patellofemoral tracking and fractures. (For this reason, the Field Of View <FOV> must include the entire patella, both femoral condyles in their entirety, the proximal tibia through the level of the fibular head. Unless specified, it is not necessary to image fractures along entire length of the femoral/tibial shafts).
2. The other major indication for a knee CT is to assess the integrity of the bone around a prosthesis (i.e. Total Knee Arthroplasty or "TKA"). The accurate localisation of the bony anatomy to calculate the mechanical axes of long bones and the relationships of the joints. This information may be useful for pre-operative planning of joint replacements. In the setting of protocol, you may want to modify the standard protocol : increasing the kV to 140, increasing the mAs, making the slices as thin as possible 0.625 or less).
3. On rare occasions, a CT will be done immediately after an arthrogram of the knee performed with iodinated contrast and/or air. The standard scanning and reconstruction protocols can be followed. The top slices must include the entire contrast filled supra-patella pouch. 
4. Intraosseous tumor, for example the nidus of osteoid ostemoa.
5. Tumore matrix calcification and ossification.
6. Sequestra in osteomyelitis
7. Osteochondral lesions 

POSITIONING:

1. Patient supine, feet first into scanner.
2. It is not necessary to bend the contralateral knee out of the way. It is more comfortable for the patient to lay with knees extended, side by side. Taping the feet together helps to keep the knees from moving.
3. Plaster casts/splints are not a problem. If possible, slide the patient so that the knee being scanned is in the center of the table.
4. Scout in two planes.
5. Select slices to cover FOV.

SCANNING PARAMETERS:

1.  Collimation: 1.25 cm
2. Interval spacing: 0.625 cm
3. KV: 120 KV
4. mA: 200 mA
5. Rotation time: 0.8 sec (This should yield around 200 slices; more if covering the length of a fracture).
6. Use a relatively small display field of view. Most knee bones will fit in a 16 cm FOV. If knee can be centered, try using the "small" scanning FOV.
7. Create "Bone+" and "Standard" algorithm data using FOV and slice spacing parameters.
8. Do not use "Priority Recon". (It creates confusion).

2-DIMENSIONAL RECONSTRUCTION IMAGES:

1. All knee bone CTs get 2D Recons in all three planes.
2. Coronal and sagittal recons are made off an axial slice.(Parallel and perpendicular to a line through the backs of the femoral condyles. Axials are made off a mid-coronal slice, parallel to the top of the tibial plateau.
3. Additional planes may be requested as per required.

HARD COPY FILMING:

1. Film only the 2D reconstruction images. (Do not film any of the original helical images).
2. Film using a 24-on-1 format (4 rows, 6 columns). Annotate "Right" or "Left". Larger formats may be chosen as per required.
3. Endeavor to select the number of reconstruction images to be  23, for then when filming with the reference image, the entire series occupies one or two sheets of film exactly.