TPLO radiograph positioning

Lateral Radiograph PoSITIONING

The lateral radiograph is the most important for determining the Tibial Plateau Angle (TPA) which allows us to determine how far we need to rotate the osteotomy to correct for cranial tibial thrust. Studies have shown that an osteotomy which is not rotated appropriately allows for continued subtle tibial thrust and hence may reduce the effectiveness of the procedure. A difference of only 5 degrees may make this difference.

The most important factor which affects measurement of the slope is rotation. In order to reduce these inaccuracy it is important to have a true lateral of the stifle. Overlapping femoral condyles is representative of a true lateral. If you can visibly see two condyles NOT overlapping then this is going to affect the TPA measurement.

Both the stifle and the hock should ideally be at 90 degrees and need to be included in the radiograph to allow determination of the tibial axis.

It is also VERY important that the xrays be labelled left or right so we can confirm we are evaluating the correct limb (the left marker was cropped out of this photo for the website).

The radiograph here shows increased stifle effusion, some mild osteoarthritis and mild cranial trasnlation of the tibia relative to the femur all suggestive of cranial cruciate insufficency.

In many cases to obtain accurate radiographs the patient needs to be sedated. In some instances it may make sense to perform radiographs at the patient visit prior to scheduling surgery. This helps us confirm that the findings are consistent with cruciate injury and rule out other pathology (cancer). It also can help to confirm that the patient does not have excessive TPA which can alter the procedure and therefore price and risk of complications. It is not unreasonable to take a “screening radiograph” and then perform more accurate radiographs on the day of the procedure before heading in to surgery.

AP Radiograph positioning

The AP radiograph allows us to assess for femoral and tibial torsion and also evaluate for any other pathology. This allows us to assess if there are any additional corrections we may need to take in to consideration during the osteotomy. The patella should be central (provided the patient does not have concurrent patella luxation) indicating a straight AP or PA of the stifle. The location of the calcaneus then allows us to assess for torsion. Again it is important to label with left or right markers. Knowing the length of your markers can help when we import the images in to some of the planning software and so letting us know the length for reference can be helpful.

POST OPERATIVE radiographs

Immediate post operative radiographs should ideally be positioned similar to the pre operative films. This allows the post operative angle to be measured and also alignment to be assessed.

Radiographs at 8 weeks post op are mainly to allow assessment of the stifle structures and osteotomy healing therefore lateral and AP of the stifle are