Not a whole lot has changed in surgical options for the treatment of canine cruciate injuries in quite a while.
A few years back, the Triple Tibial Osteotomy (TTO) made its debut in New Zealand. It’s a hybrid between the TPLO and TTA surgeries and I actually quite liked it even though it still quite invasive. However, whether it is actually better or not is moot because it’s still not available around here.
In England and New Zealand, they are overall more adventurous and have come up with modifications to the TTA surgery idea, such as the Modified Maquet Procedure (MMP).
Improvements to the TPLO led to the Cora-based Leveling Osteotomy (CBLO) and the TightRope technique underwent an upgrade.
Simitri Stable in Stride
The way I found out about this new technique for the treatment of cruciate tears in dogs was nothing short of amazing. Almost as if destiny knocked on the door.
Cookie was with Jasmine’s vet getting her platelet-rich plasma (PRP) in the attempt to encourage the ligament to heal. During the discussion about advances in veterinary medicine, we talked about progress in the treatment of canine cruciate ligament injuries. The veterinarian brought up a new technique he’s been reading about, the hinge technique.
That very day I received an email from the co-inventor of the procedure–Simitri Stable in Stride stifle internal stabilization system. What are the odds of that happening?
My first impression
My first impression was that there is still a lot of hardware involved. The more closely I looked, however, the more I was intrigued. No bones are being cut and original anatomy is preserved. The hinge stabilizes the joint immediately.
I was fortunate to get in touch with Dr. Neil Embleton, co-inventor of the procedure, and he was happy to answer all my questions. Our talks grew into an interview.
Q: Dr. Neil, what is your veterinary background?
A: I graduated from the Ontario Veterinary College in 1987. I began my career in mixed animal practice in Ontario and migrated to Alberta and towards small animal surgery, especially orthopedics, the following year. Unfortunately, as a result of a lack of funds and a young family, a residency was not an option. Instead, I pursued many continuing education courses over the last 29 years. I am certified in AO/ASIF techniques, spinal surgery, arthroscopy, TPLO, and total hip replacement. In fact, I performed the first canine cemented total hip replacement procedure in Alberta.
Q: What got you interested in orthopedics?
A: The practice owner I worked for when I graduated had no interest in orthopedic cases so I ended up treating them and fortunately I had an aptitude for it and enjoyed the challenge. When I bought my own practice in Alberta two years later, referral to Saskatoon was not a viable option for most clients so, I spent a great deal of time with my orthopedic books (it was not unusual for them to be in the surgery room with me) and attending as many orthopedic courses as possible.
What is your experience treating cruciate injuries?
A: That began 29 years ago. My partner, Dr. Veronica Barkowski first taught me how to do cruciate surgery. I refined the technique over the years and expanded repair options to include the TPLO procedure (15 years ago) and now Simitri Stable in Stride®.
Q: How many cruciate repairs have you performed and what types?
A: Conservatively I would say more than six thousand repairs, including the lateral fabellar suture (LFS) technique and TPLO.
Q: How many TPLO’s?
A: Again conservatively, I’d say close to 2500.
Q: How pleased were you with the outcomes of the existing cruciate procedures?
A: Actually I was reasonably pleased with the results using both procedures. Complication rates were relatively low although, I did notice that stifle (knee) range of motion never fully recovered and degenerative joint disease (arthritis) always progressed. While I still perform the LFS procedure on smaller patients (that will change now that the Simitri implant is available in a smaller version), my feelings toward the TPLO procedure evolved over time as new scientific evidence began to come to light. I began to question what the goal of cruciate surgery was and what exactly the TPLO procedure accomplished.
Q: What led you to develop a different option?
A: When TPLO became available more than 20 years ago, it was touted as the ‘gold standard’ for cruciate repair. Surgeons were looking for an alternative for larger dogs because of the high rate of failure of LFS. It was adopted very quickly with little or no scientific evidence to support its use. There is still no scientific evidence to suggest one procedure has benefits over another. Over time I began to question the geometry modifying procedures themselves.
I had issues with inflicting a hard tissue injury (cutting a healthy bone) and forever changing the biomechanics of the joint. Good scientific evidence began to come to light in recent years that suggested that the TPLO procedure did not provide the stability we claimed it did and in fact the procedure caused a backward shift in the shin bone movement called (caudal tibial translation) – more information here. It made me reevaluate what it was we were trying to achieve. I began to think about what the role of the cranial cruciate ligament was and how we could reproduce its function and maintain joint biomechanics in as least an invasive method as possible. That process began 6 years ago. The result was the Simitri Stable in Stride® implant.
Q: What is this new procedure and how does it work?
A: The new procedure is called Simitri Stable in Stride®. It is a three-part, modular stifle (knee) stabilizing implant that is designed to provide immediate and continuous translational and rotational stability while minimally affecting stifle kinematics (movement). It consists of surgical grade femoral and tibial plates and an ultra-high molecular weight polyethylene (UHMWPE) sliding articulating insert. UHMWPE is the same material used in hip and knee replacements in humans.
The femoral plate has a ball and stem which interconnects with the tibial plate via an 8 mm travel channel within the articulating insert. The implant is attached to the medial (inner) side of both the femur (thigh) and tibia (shin) using six cortical locking screws. The implant does not go into the joint and, no bones or muscles are cut during the procedure making it a less invasive option.
Joint biomechanics (function) are not significantly altered during the procedure. Once implanted it provides immediate and continuous translational and rotational stability while allowing the joint the freedom to flex, extend, compress, expand and move side to side in as normal a manner as possible.
Q: What inspired you to design it this way?
A: In my mind, there were a number of criteria that the implant had to meet. It needed to be completely extracapsular (remain outside the joint), be well tolerated by the dog, provide continuous translational and rotational stability throughout the entire phase of stride, be biocompatible, long lasting and easy to implant without specialized orthopedic equipment.
Through the entire 6-year development process, Veronica and I have tried to be as evidenced based as possible. Implant design engineering was done using CT scans and CAD software, the implant design was tested and refined using 3D computer modelling and biomechanical testing. In fact, a scientific paper written by Dr. Gina Bertocci and Dr. Nathan Brown on the 3D computer modelling work has just been published in the March issue of Veterinary Surgery. Finally, cadaver work was used to establish the surgical procedure before going anywhere near a live patient. We also purposefully kept the project away from the public eye until we felt we were ready to begin initiating the conversation.
Q: How do you feel does Simitri Stable in Stride Stifle Stabilization System compare with existing procedures?
A: That is a really hard question to answer, an evidence-based comparison would require a randomized blinded clinical trial. Comparisons of clinical trials of other procedures to our clinical trial is also difficult due to differences in study designs and population of dogs. That said, our clinical trials have shown that after Simitri surgery, dogs regain normal range of motion which has not been shown in studies of any of the current procedures.
There is no osteotomy with Simitri so it could be considered less invasive than procedures like TPLO and TTA. Simitri is designed to provide stability at all times not just during weight bearing which we feel may protect the joint from further damage especially the menisci (cartilages), to date we have not seen any dogs develop clinical signs of meniscal tears after Simitri surgery.
Meniscal tears are a commonly reported postoperative complication with existing procedures, this has lead some surgeons to perform meniscal releases to reduce the incidence of postoperative tears but this procedure has also been scientifically shown to adversely affect joint biomechanics, there are no meniscal releases done in conjunction with Simitri.
Q: How does the post-op rehab compare with existing procedures?
A: “Night and day.” That’s exactly how one client responded to that very question. His dog’s first cruciate tear was treated by me with a TPLO (complication free) and when Riley tore his second knee we were able to do a Simitri Stable in Stride® procedure. The owner felt his dog was more comfortable and the aftercare was minimal compared to the TPLO.
Basically the Simitri Stable in Stride® rehabilitation program comes downs to controlled exercise, massage and passage range of motion exercises. All of which are designed to strengthen the hind end and increase range of motion of the ankle, knee and hip. Because there is no cutting of bone the post-op restrictions are not as onerous.
Q: How long is the post-op period?
A: Most dogs return to their preoperative activity level within four months. This is dependent on age, breed, degree of preexisting disease and rehabilitation effort by the owners.
Q: How does the knee stability and function compare with existing procedures?
A: Simitri knees are stable immediately after surgery and they remain stable throughout the entire phase of stride. With TPLO and TTA the knee is purported to be “dynamically stable” which means it is stable during only the weight bearing phase of stride.
During the non weight bearing phase of stride the knee is unstable. In our study Simitri knees recovered their stifle range of motion after surgery. With all other procedures range of motion actually decreases and never recovers.
Q: Would an extremely athletic dog be able to function at full capacity?
A: I think that would depend on what extremely athletic and full capacity means. My goal is to have every dog return to full pre-injury function. To me that means running, playing and performing the function they were bred to. However, we need to remember that there would be a number of factors to consider, age, breed, level of pre-existing disease, time from injury to repair, etc.
Our clinical trial dogs were representative of the dogs we normally see in our practice with cruciate injuries, including family pets and working dogs, however we did not see any dogs that compete at high levels of competition.
Q: How does success and complications rates of Simitri Stable in Stride compare with existing procedures?
A: During our initial study of the first 66 cases, which is currently under scientific review for publication in Veterinary Surgery, we reported a 15% major complication rate (needed a revision surgery) and a 10% minor complication rate. We also reported a complete resolution of lameness (0/5 no clinical lameness noted at the walk) in 85% of cases. The remaining 15% scored a 1/5 (mild lameness noted at the walk).
The complication values compare very closely with what is currently reported for TPLO and TTA. However, the types of complications we encountered were significantly different and generally less serious than TPLO or TTA.
Q: What are potential complications and how they compare with existing procedures?
A: The main potential complication specific to Simitri surgery is disarticulation of the implant. Think of the implant being like a ski binding, under normal circumstances it remains solidly attached. However; if the knee joint is placed under excessive stress the implant is designed to release. If it didn’t the knee could potentially be injured. This would only occur however, if the patient has excessive tibial torsion (ie. born with abnormal twist in the shin bone), suffered severe trauma to the joint, or the implant was incorrectly positioned.
In early cases we also saw screw breakage but this was caused by using to small of a screw in larger dogs (>40 kg). It is difficult to compare Simitri Stable in Stride® complications to those of existing procedures as each has specific procedure related complications.
However, with Simitri there are no osteotomy related complications (eg. higher rates of infection, ….) and postoperative meniscal tearing has not occurred. Minor complications such as incision site breakdown, swelling, bleeding can be expected to occur at similar rates after any procedure.
Q: What are minor complications and how long do they last?
A: Mostly seroma formation, which is a fluid filled swelling. Seromas all spontaneously resolved within 3-5 days. These mostly occurred in our earlier cases while we were still working on improving our surgical technique with this new procedure.
We had the skin incision partially breakdown in one dog after she was allowed to lick at the incision, this healed without treatment once the owner complied with proper use of the Elizabethan collar.
Q: What are the major complications and how are they addressed?
A: They were two main complications noted early on: Screw fracture and implant disarticulation. To eliminate screw fracturing, we made changes to the surgical technique. We now use 4.0 mm screws. These screws are 189% stronger than the previously used screws. As a result, we no longer see any screw fracturing.
To reduce implant disarticulation, we redesigned the UHMWPE articulating insert and made it four times stronger than the original. We also refined the implantation process which allowed us to be much more accurate at locating the femoral plate.
Q: What happens in case of an infection or implant rejection?
A: After 175 cases, we have yet to have a documented case of post operative infection. Rejection is unlikely as both surgical grade stainless steel plates and the UHMWPE are both extremely biocompatible. If an infection occurred, we would initially aggressively treat with antibiotics. If we were unable to resolve the infection, then the implants would need to be removed.
Q; If the implant needs to be removed, what can be done for the knee?
A: If the knee was clinically stable, nothing would need to be done. However, if the knee was unstable, any other cruciate repair procedure could be employed. Simitri does not alter the joint architecture and therefore would not interfere.
Q: What materials are used for the implant and why?
A: Surgical grade stainless steel and UHMWPE. The UHMWPE is the same material as used in hip replacements and knee replacements. It has good wear characteristics and a low coefficient of friction. We used surgical grade stainless steel, because of the familiarity of the product. As new materials become available the implant could be switched as long as they provide the same characteristics.
Q: Why stainless steel and not titanium?
A: Titanium is actually a very brittle metal. It couldn’t handle the shear stresses placed on the implant.
Q: How many Simitri Stable in Stride repair have you performed so far? With what results?
A: Personally, I’ve performed 175 cases. The results to date have been excellent. After a brief review of the medical records of my last 50 cases: The minor complication rate was 2%. The major complication rate was 4%. This is an extremely low major complication rate. Documented major complication rate for TPLO and TTA range from 12-38%.
Q: How long has the implant been known to keep the joint stable?
A: Longest cases are now out over three years.
Q: How does the surgery affect bone integrity and the surrounding tissues?
A: It doesn’t appear to have any effect.
Q: What are the potential ways in which the implant could fail and would a repeat procedure to address the problem?
A: There are three potential ways the implant could fail: metal fracturing, screw fracturing, or insert failure. If a failure occurred, the individual case would be evaluated and an appropriate revision procedure employed such as replacement of all or parts of the implant or implant removal followed by another procedure as discussed above.
Q: If for any reason the implant didn’t work out and other repair had to be performed, how would the existing screw holes affect the outcome of the other repair?
A: The screw holes would have no effect on the outcome of any revision procedure.
Q: Which repair would be recommended in such case.
A: The recommendation would be based on the needs of the patient on a case by case basis.
Q: If an infection or rejection occurred a year or more post-op, with TPLO or TTA the joint shouldn’t need the implants any longer. What about this procedure?
A: Good question. I can’t really answer that. My hope is that if enough time has passed (6-12 months) the knee joint itself and the surrounding tissues will have strengthened to the point that they would be able to take over.
Q: Can this implant be used for any dog or are there restrictions?
A: Simitri could not be used in cases of neoplasia or in the face of a known infection. Otherwise it can be used on any dog that fits the currently available implants. The currently available implants fit most dogs between 20 and 36 kg. A smaller design is now available and should allow us to treat dogs as small as 10 kg. Larger size implants are currently in the design process.
Age is not a restriction. In fact, Simitri is ideal for older patients; our oldest patient treated to date was 14 years old. He was walking within 24 hours of surgery. The procedure itself is indicated as a primary treatment for cranial and or caudal cruciate ligament injury. It can also be used in cases with concurrent collateral ligament injuries and luxating patella. However, they would need a primary repair of the concurrent injuries prior to implanting Simitri.
Q: When do you think Simitri Stable in Stride Stifle Stabilization System might be available for larger dogs?
A: Hopefully by the end of this year.
Q: Please summarize why you believe this procedure is better than other existing options?
A: I hate the idea of comparing or competing against another procedure. Let me say this. Simitri provides immediate and continuous translational and rotational stability while minimally affecting stifle kinematics. No bones, or muscles are cut during the procedure, making it a less invasive alternative to current techniques and the complication rate is extremely low. I think Simitri provides us with another option to manage canine cranial cruciate ligament disease.
You can ask Dr. Neil directly at firstname.lastname@example.org.
Dr. Neil A. Embleton, BSc, DVM received his doctorate at the Ontario Veterinary College, University of Guelph and holds a Bachelor Degree in Science. Dr. Neil has been a veterinarian for almost 30 years.
His continuing education includes ASIF/AO certification, Spinal decompression surgery certification, Interlocking nail certification, Biometrix Total Hip Replacement certification, Tibial Plateau Leveling Osteotomy certification, and Arthroscopy certification.
Dr. Veronica J Barkowski, DVM received her doctorate at the Ontario Veterinary College, University of Guelph. She’s been a veterinarian for 27 years.
Her continuing education includes veterinary dentistry, laparoscopic surgery, arthroscopic surgery, ultrasonography, and anesthesiology. \
Simitri Stable in Stride: Islay’s Knee Injury and Repair