34th Annual Scientific Meeting proceedings

Stifle arthroplasty – more commonly referred to as canine total knee replacement - is now accepted as a viable option for the surgical management of end-stage degenerative joint disease (DJD) in dogs. This presentation will highlight recent developments in surgical planning, the use of patient-specific guides, and common challenges faced by surgeons performing TKR. It will also look forward to the future and consider how innovations such as surgical robotics and navigation can be used to improve patient outcomes and enhance the adoption of canine TKR as a clinical procedure.

Surgical planning
While standard radiographic templating remains the gold standard for surgical planning in TKR, we are seeing a growing trend towards the use of 3D planning methods, based on CT data. For dogs with complex stifle deformity or trauma, the benefits of 3D planning are clear, and it is relatively simple to extend this planning to include the development of patient-specific guides (see below). Clinical studies are needed to evaluate the relative accuracy of radiographic versus CT planning in canine TKR. While it is likely that “standard” TKR cases can still be planned effectively with plain films, there is compelling argument for 3D planning to become the gold standard for more complex cases, especially when they involve prior surgery or concurrent deformity (e.g. DFO plus TKR).

Patient-specific guides (PSGs)
The use of PSGs has become widely accepted practice in many areas of veterinary orthopaedics, including the management of angular limb deformity^1,2, atlantoaxial instability³ and placement of transcondylar screws across the humeral condyle⁴. Laboratory studies have demonstrated the potential value of PSGs in canine TKR⁵ but multicentre clinical trials are now needed to determine whether the potential benefits of PSGs in improving implant placement translate into meaningful improvements in short- or long-term clinical outcomes and implant function.

Surgical learning curve
In humans, the surgical learning curve for TKR has been shown to be longer/less steep than for THR. Equivalent data for canine TKR have not been reported, but the data for canine THR suggest 44 cases in order to become proficient⁶. None of the surgeons currently performing canine TKR has a caseload that would meet this expectation, and it is unlikely that any of us has an annual caseload that is large enough to support remaining on the learning curve over time. The introduction of a specialist fellowship in total joint replacement is one step in the right direction, but a strong case can be made for supporting the development of centres of excellence where referrals of canine TKR can be managed in an efficient and effective manner. Clinical training could also be re-imagined, with an increased emphasis on the use of virtual surgical training to develop and reinforce key skills in surgical technique and decision-making.

Modular solutions to facilitate revision surgery
One of the most pressing and consistent challenges faced in performing canine TKR is the risk of inadvertent injury to the collateral ligaments. Damage to the collaterals can be a potentially devastating complication, leading to static and dynamic joint instability and lameness. We recently performed an anatomic study to define the relationship between the origins/insertions of the collateral ligaments and the cutting planes used to implant femoral and tibial TKR components. While it is possible to make minor adjustments to the cutting planes in the operating room – for example, by carefully changing the flexion-extension alignment of the femoral component – the reality is that the footprints of the collateral ligaments are always going to be close to the cutting planes used for TKR. With virtual surgical planning in 3D it is possible to incorporate maps of the collateral footprints and avoid these with careful selection of implant sizing and positioning, but there may also be value in improving the design of TKR components to provide an anatomic and more conservative fit against the femoral condyles. It could also prove possible to change from the current focus on planar cuts to a curved cut approach that harnesses the precision and accuracy of robotic milling. In parallel with this, there could be real value in the development of a modular, off-the-shelf TKR system that supports primary TKR but with the potential for conversion to a more constrained implant geometry in the event of intra-operative or post-operative collateral injury.

Navigation, virtual/augmented reality, and robot-assisted TKR
Given the nature of the caseload in canine TKR – mostly end-stage stifle joints with significant collapse/deformity and soft tissue compromise – the use of computerised surgery, with image-guided or image-free navigation, offers real potential as a means of improving the accuracy and the repeatability of implant alignment and post-operative outcomes (range of motion, joint function and implant longevity). Many of the challenges associated with developing a navigation solution for canine THR and TKR have now been overcome, opening up possibilities for developing a clinical system within the next few years. For those wanting a more interactive, visual experience, it should be feasible to combine pre-operative imaging data with virtual/augmented reality to provide an immersive experience in the operating room. With either approach, the introduction of robot-assisted drilling and cutting would be expected to further improve technical accuracy and precision hopefully with attendant benefits in clinical outcomes, as has been shown in human TKR.

Conclusions
Canine TKR has been available as a clinical procedure for over 15 years, yet it continues to struggle to fully penetrate the veterinary market. Uptake of the procedure continues to be hampered by concerns over the complexity and complication profile of the procedure, with many veterinarians seeing it as “too risky” for consideration except in the most extreme cases. Despite this, most referral surgeons undertaking canine TKR see its value and want to see it become more accepted as an option for dogs with DJD or non-reconstructible stifle joint trauma. Four key hurdles need to be overcome to make this happen: case selection needs to expand to include cases with earlier and less severe pathology; surgeries should be performed at specialist centres with a particular focus on TKR; virtual surgical training with simulation and VR/AR are needed to allow surgeons to overcome the surgical learning curve for the procedure; and technological innovations in surgical planning, navigation, robotics and implant design need to be harnessed to reduce surgical complications and improve clinical outcomes. Finally, none of these iterations will mean anything without effective communications within and from the veterinary community – this should be based on clinical trial data with objective outcomes, something that has been sorely lacking from the canine TKR field in recent years.

References

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