The following procedure will alter the angle of the tibial plateau to approximately 5 degrees
Take medial radiograph of whole tibia plus femoral condyles. Centre the beam over the stifle. Condyles should exactly overlap each other if positioning is correct. Use sandbags or foam wedges if necessary.
Draw line one to represent the level of the tibial articular surface. This line is used to calculate the angle of the tibial plateau and is most difficult to judge. We are essentially looking for a line that parallels the proximal tibia articular surface.
Second line is drawn along the long axis of the tibia which runs between the intercondylar eminence proximally and the hock centre of motion . If your beam does not colimate large enough you may have to use the centre of the distal tibia. The difference between the two lines is the angle of the plateau. Usually 20 to25 degrees sloping backwards.
Draw line three at right angles to line two at the level of the distal end of the tibial crest.
Draw line four parallel to line one meeting line three at the caudal cortex of the tibia.
Removal of the wedge deliniated will alter the tibial plateau angle to zero. Most authorities feel a 5 degree back slope to be the most appropriate. To achieve this remove 5 degrees from the wedge.
Measure the cranial border of the chosen wedge for reference during surgery.
Dog is placed in dorsal recumbancy
Remove remnants of ccl
Check menisci +/- removal if damaged
?Medial meniscus release? Somewhat controversial but allows the caudal horn to move back minimising trauma by the femur which remains unstable. ? no meniscus being better than a damaged one. Approach meniscus just caudal to medial co-lateral ligament. Small joint retractors are useful. Use No 11 or small pointed beaver blade to radially transect meniscus.
Many proponents of the Slocum technique do not routinely explore the stifle. They merely perform a medial meniscus release via a small arthrotomy caudal to the medial collateral ligament.
Extend cranio-medial incision to expose medial proximal tibia
Using above measurements and three-dimensional view of the joint alignment, plan a wedge shaped cut to alter tibial plateau angle and make any other appropriate corrections. By making the wedge an isosceles triangle (ie both long sides the same length) on reduction the cranial and caudal borders of the tibia should remain congruent. The important measurement is the dimension of the cranial edge. The two cuts will meet at the caudal border. The caudal dimension of the wedge will be zero.
Use an oscillating saw to remove tibial wedge. Take care that both cut surfaces are clean and smooth. Small bone spurs will create serious difficulties in reduction and compression of the osteotomy site. These spurs will typically occur as the cuts run out caudally. I.e. the most difficult area to see and deal with them. Use saw or rongeurs e.g. Lemperts to tidy up spurs.
Leave the fibula intact.
Reduce osteotomy using appropriately sized pointed reduction forceps. Use a drill hole to provide purchase point for forceps distal to osteotomy
Check alignment of foot in relation to the stifle & adjust as necessary. Large dogs especially Rotties often develop and inward rotation of the foot with CCL disease
Drive 'K' or 'A' wire across osteotomy for temporary stability. This may be left in place if providing some support.
An alternative to using a 'K' wire is to place a cranial figure of eight tension wire crossing the osteotomy site. As well as the temporary fixation the wire provides long term stability on what is the tension side of the 'fracture'.
Contour plate as necessary
Fix plate in compression mode. Consider the use of 4.0 cancellous screws in the proximal tibia.
Variations on a Theme
Analternative to using a 'k' wire for temporary stabilisation is to use a cranial tension wire band across the osteotomy. This band is left in situ and provides valuable cranial stability where tensile forces are greatest.
Dress for approx 3 days.
Strict lead exercise 3 weeks
Gradual increase in exercise over next 3 months
Philip Watt. "Tibial plateau levelling" Aust.Vet.Journal vol 78,no 6,June 2000
Barclay Slocum.Teresa Devine Slocum "Tibial Plateau Levelling Osteotomy for Cranial Cruciate ligament Rupture"in Bojrab M.J. Current Techniques in Small Animal Surgery 4th edition Williams and Wilkins 1997:1209-1215