1. How do I make sure that my osteotomy is in the correct position? Is there a mental checklist to go through before the blade starts cutting?
There are a few landmarks. Ideally you want to imagine the centre of the blade’s arc over the very caudal aspect of the tibial plateau. The cranial border of the osteotomy should aim to preserve the size of the tibial crest- leaving too small an arc of bone on the crest can predispose to tibial crest fracture. (a hohmann retractor inserted behind the patella ligament helps protect it during cutting, and ensures that the positioning of the cut is not too close to the crest).The caudal aspect of the osteotomy should make roughly a right angle to the tibial cortex. And finally, you should aim have a sufficiently large proximal portion to accommodate the plate and screws. Use templates on your lateral radiograph to ensure that your blade size is correct for the size of dog, following these landmarks.
2. Is it best to start slow or just go for it? I have heard that the blade skates around.
It can be difficult to start the osteotomy. Remember that you are not cutting a flush surface- the tibal is roughly triangular in cross section proximally, and your cut will begin in the caudal tibial cortex. It can be tempting to lean the blade over so starts cutting all the tibial surface at the same time, but you must ensure that you remain right-angular to the tibal long axis- so you will typically have gone through a significant amount of the caudal cortex before you begin to engage the proximal tibial crest region. Starting without pressure but at a reasonably high speed should help you get an initial groove started. Do not place the saw blade on the bone and then start the saw- it’ll shake you all over the place!
3. How do I make sure that the osteotomy is proceeding at the correct angles relative to the tibia?
Some surgeons find the jig very helpful for this. However, it all comes down to eyeball. Arranging the limb so it is horizontal, and having assistants calling your saw blade at vertical helps- particularly if you have the jig in situ, as it gives a reference point- the blade should be parallel to the jig fixation pins. I feel that the jig is of most use in establishing confidence with early procedures. Once you then have the feel for the alignment and angulation, it becomes less important
4. What happens if the cut is in the wrong place or at the wrong angle? Is there anything I can do?
If the cut is at the wrong angle, the osteotomy can be fixated at the correct angle, with either gapping at the cis- or tran- cortex, and the deficit filled with bone graft. Some surgeons routinely bone graft the caudal aspect of the tibial osteotomy anyway. If the cut yields an overly small tibial crest, a pin and tension band may be placed in case of fracture, just as though you were dealing with a tibial crest avulsion fracture. If the cut should start within the tibial plateau, (hard to see how that could happen) you might be better advised to simply fixate the bone in situ, maintaining an articular surface, and perform a lateral fabella suture instead.
5. How do I reduce the risk of thermal necrosis at the osteotomy
1. if using the biradial blade, sharpen it between each use
2. Pause regularly uring the osteotomy to clean any caked debris from the teeth. You will often find deposits filling the teeth at the caudal aspect of the osteotomy- they reduce the effective cut and therefore create heat.
3. Take the osteotomy slowly- the blade sharpnes should cut without the need for undue pressure
4. have an assistant with a 20ml syringe and an iv cannula dribbling saline onto the saw blde as you make your cut
6. Can I use self tapping screws?
Yes- I see no reason why not, provided the screw heads tally with the compression holes on the plate. IN younger dogs a cancellous screw may be preferred at the most proximal screw hole, but they can be more prone to screw heading bending and/or fracture having a smaller shaft- I typically use cortical screws at all holes.
7. Do you have to use the min-caudomedial arthrotomy?
NO. A conventional craniomedial parapatellar arthrotomy can also be performed within the same approach, giving a better field of view for meniscal examination. The caudomedial arthrotomy does greatly facilitate meniscal release, however. Equally, the CrCL and menisci can be examined arthroscopically as part of the procedure.
8. Are there particular concerns regarding sterility? I’ve heard that TPLOs carry a higher than average infection rate.
Orthopaedic sterility must be very strictly maintained. Some of the concerns regarding post-op infectin rate may relate to metallurgy of the early plates used, and to the cutting efficiency of the blades, generating extra heat. I pay particular attention to copious lavage of the plate in situ, and to closure of the soft tissue layers from periosteum upwards over the plate. The caudal insertion of sartorius is reconstructed over the proximal plate aspect also, and infection rates have not been elevated.
9.Is this a Totally Pointless Leg Operation, designed to bring the most common canine orthopaedic condition back within the realms of the referral orthopaedic surgeon rather than the general practitioner?
I don’t think so. The post-op outcomes, particularly in treating partial tears, where the progression of CrCL disease can be genuinely arrested, are tremendously exciting. Prior to performing TPLO, in wedge, and then curved cut form, I had been relatively happy with lateral fabellar suture as a technique. Whilst the lateral fabellar suture, amongst other procedures, can have very good outcomes, I believe that for larger dogs, partial tears, performance animals and excessive tibial plateau angles, TPLO is the treatment method if choice. And I continue to be excited by the outcomes at post-op checks!
10. DO I need diathermy?
It helps for some of the medial stifle fascial vessels, and periosteal vessels, but it is by no means essential.
11. Angulation of the proximal screw- I’ve heard reports of this screw entering the joint surface.
This is a reported complication, but entirely avoidable. Aiming this drill hole at the fibular head, wither by feel or by an aiming device, will ensure that you never impact the joint surface. You will need to stock some significantly longer screws for this- I have usd up to 60mm for a giant dog.