Tibial Tuberosity Advancement (TTA) and Modified Maquet Procedure (MMP)
What is TTA surgery?
The TTA or ‘Maquet’ procedure itself does have different versions, but these all share many of the same principles as detailed below.
How does TTA surgery work?
In a normal dog’s knee during weightbearing, it is the cranial cruciate ligament that acts to prevent the shin bone from slipping forwards relative to the thigh bone (what is called cranial tibial thrust).
In dogs with cranial cruciate ligament ruptures, this movement is not resisted, and this allows the tibia to ‘slide forwards’ causing instability, pain and lameness.
The mechanism by which TTA helps dogs with cruciate disease is to advance the tibial tuberosity to alter the direction of the force transmitted through the patellar tendon: to change what is called the patellar tendon angle (PTA) and realign the ‘dynamic forces’ that occur in the knee joint when the foot is placed on the ground. (Apelt, Kowaleski, & Boudrieau, 2007).
In a knee in which a TTA procedure has been performed, the forces exerted by the quadriceps muscles through the patella tendon serve to improve the stability of the knee, without repair or replacement of the injured cruciate ligament itself.
This stability prevents the sensation of the knee ‘giving way’ when the foot is placed on the ground and should improve the lameness seen pre-surgery.
What does TTA surgery involve?
The procedure may vary slightly depending on your surgeon and the specific implant system they use. They will be able to provide you with more specific information.
All TTA procedures are performed under a general anaesthetic. Specialised X-rays are be taken if not already performed. These are taken at specific limb positions/angles to allow measurement for planning and successfully performing the TTA procedure. These measurements are unique to your pet and vary greatly depending on the breed and size of your dog.
For surgery your pet will need to have a full clip of the affected leg stretching from the hip down to the ankle.
The first stage of surgery involves looking in the joint (through a small incision (arthrotomy), or with a keyhole camera (arthroscopy)) to confirm the nature of the injury that has occurred inside the knee. It is not uncommon for the medial meniscus (the shock absorber on the inside of the knee) to be damaged at the time of cruciate injury, with between 30% – 83% of medial menisci reported at being torn at the time of surgical assessment by probing (Mccready & Ness, 2016).
If damage to the medial meniscus is apparent, then this will be trimmed before the TTA is performed. The shin bone is then more fully exposed and marks for the ‘cut’ are made based upon the pre-operative X-rays and surgical plans. There are different versions of the TTA or ‘Maquet’ procedure but these all share many of the same principles.
The key step is that the shin bone is cut, either completely or incompletely, using a straight saw blade and the cut portion of the shin bone is gently ‘advanced’ a precalculated distance, and a surgical ‘spacer’ device is then placed in the gap to hold the front section of the shin bone in this new position.
A surgical implant spacer is then placed and the construct is reinforced by one of various means such as a plate and screws, or pin/staple to hold the bone in place in this new position while it heals.
X-rays are taken at the end of surgery to make sure the implants are in the correct position and the biomechanical aim of the surgery has been achieved.
What does post-operative care involve?
Your dog will require a course of pain relief and sometimes antibiotics following surgery; these are typically given orally in tablet or liquid form.
Exercise is beneficial during the recovery, although this must be strictly controlled and will be significantly reduced during the first eight weeks following surgery. A period of very strict exercise restriction is likely immediately after surgery and will require your dog to be crate-rested or confined to a small room without access to furniture. Your surgeon will provide you with more detailed instructions on how to manage your dog’s exercise following surgery.
Follow up visits
Dependent on how your pet’s surgical wound has been repaired, a follow-up visit to your vet is often needed around two weeks after surgery. Most dogs will need to wear a buster collar until this time to prevent interference with the wound which may lead to infection.
Depending on progress, post-operative X-rays are usually performed around eight weeks after surgery to check healing is progressing well.
Unfortunately, regardless of treatment (or lack of treatment), all dogs are likely to be predisposed to the development of osteoarthritis in the affected joint following cranial cruciate ligament disease. Because of this, it is recommended that they maintain a slim body condition. Your vet will be able to give you more information regarding weight control plans if this is required.
Hydrotherapy and/or physiotherapy can be useful in the post-operative period and can be considered once the skin wound has healed. Your vet can advise you if this is appropriate for your pet.
What is the prognosis following TTA?
TTA surgery has a very high success rate, with outcome considered good to excellent in 90% of dogs, and activity level improved in 90% of patients (Hoffmann et al., 2006b) One study described 97.8% of pet owners would choose to have the TTA surgery performed again ‘without hesitation’ if their dog was faced again with a similar injury (Lafaver, Miller, Stubbs, Taylor, & Boudrieau, 2007).
All dogs with cranial cruciate ligament rupture are expected to eventually develop at least some signs of osteoarthritis in the affected joint but this is likely to be reduced or delayed in dogs who have had a surgical procedure.
Around 38% of dogs will develop cranial cruciate ligament disease in the other leg following the initial injury (Grierson, Asher, & Grainger, 2011).
What are the risks of a TTA?
Potential complications include;
Any surgery carries a small risk of infection. Orthopaedic surgery carries a slightly higher risk because bacteria can stick to the metal implants which makes it difficult for the immune system to reach them. In order to reduce this risk, all dogs receive antibiotics during surgery. If your dog licks their wound after surgery, they can introduce infection.
Fracture or Implant Failure
There are different versions of the TTA procedure but all versions do have a potential risk of fracture of the tibial tuberosity, or the shaft of the tibia itself. This is due to mechanical weakening of the bone at the site of the cut in addition to implant insertion which can further weaken the bone.
Fracture of the tibial tuberosity or shaft of the tibia is a challenging complication to manage but can be treated successfully. The risk of such fractures may be minimised with increased surgeon experience performing TTA (Wolf et al., 2012) and consideration of the anatomical factors which may increase these risks (Rajala-schultz, Bergh, & Johnson, 2008).
In a small number of dogs, the implants which are holding the bone in its new position (screws, ‘wedge’, or staple) can become loose over time. If this happens, excessive movement of the bone segments against one another can delay healing and in the worst-case scenario the plate can break and require replacement. The risks of this complication increase substantially if exercise is not sufficiently restricted following surgery.
Delayed healing of the bone
The bone needs to heal to become strong enough to support your dog’s normal activity. In TTA this is especially important as a ‘space’ has been created to advance the tibial tuberosity.
In some versions of TTA, the space is ‘filled’ by a wedge-shaped spacer, other versions use a cage that fills a portion of the gap. Some surgeons use a bone graft to give additional stimulus to bone healing across the gap. The evidence is that bone graft may speed healing of this site, but not reduce complication risk (Bisgard, Barnhart, Shiroma, Kennedy, & Schertel, 2011)
All dogs heal at slightly different rates and sometimes patience is required. However, insufficient exercise restriction after surgery as well as some underlying health conditions can predispose a dog to slow healing.
Fracture of the tibial tuberosity
Possible suggested aetiologies for the development of post-TTA tibial tuberosity fracture include a reduced thickness of the cut tibial tuberosity, reduced osteotomy contact, placement implants too close to the osteotomy, large preoperative patellar tendon angle, and damage to the region during surgical dissection.
While this complication is a risk with TTA it does appear to generally have a favourable prognosis, although it can result in significant morbidity and in some cases revision surgery may be required (Calvo et al., 2014).
Patellar Tendon Damage/Inflammation
The advancement of the tibia may place additional strain upon the patella tendon and the tendon may also be irritated at the time of surgery. Both of these factors have been suggested to be a cause for patellar tendonitis. The reported risk of this is low in TTA (Wolf et al., 2012).
Subsequent meniscal injury
In up to 5.3-10% of patients treated with TTA procedures, the menisci appear normal at the time of surgery but are later damaged due to continued, mild degrees of joint instability. If this is the case, lameness may persist longer than expected post-surgery, or dogs may seemingly recover before suddenly becoming lame on the leg once more. If this occurs, repeat surgery will be required to inspect the meniscus for damage and cut away any torn portions (Hoffmann et al., 2006a) (Etchepareborde, Brunel, Bollen, & Balligand, 2011).
Which dogs will benefit from a TTA?
Developments and evolution of the equipment and implants used for TTA procedures have made it a suitable technique for most sizes of dogs.
As with all procedures however, the technique does need to be carefully tailored to the individual patient. The anatomy of the top of the shin bone does have to be carefully assessed and may make TPLO a more suitable technique for certain patients (Rajala-schultz et al., 2008)
Some studies have suggested that in dogs weighing over 50kgs, TTA may result in an increased incidence of a need for surgical revision compared to TPLO (Hans, Barnhart, Kennedy, & Naber, 2017).
While some studies have shown TTA to result in a similar short term outcome to TPLO (Ferreira, Ferrigno, de Souza, Caquias, & de Figueiredo, 2016) others suggest there may be a better long term outcome with the TPLO procedure (Christopher, Beetem, & Cook, 2013)(Moore, Weeren, & Paek, 2019).
While the specific surgical technique chosen will impact your pet’s recovery, it is important to also appreciate other factors are also important. These include your pet’s individual anatomy, their temperament, following veterinary guidance, if they have other injuries/health concerns, your pet’s body weight and the surgeons’ experience.
TTA involve a strict period of exercise rest and has a greater potential for serious complications if rest is not enforced during recovery compared to other procedures such as the lateral suture.
Contraindications for surgery may include:
· Dogs that are receiving medication that suppresses their immune system and makes them likely to experience delayed fracture healing.
· Dogs with limb deformities that may need to be corrected by other procedures.
Authors: Ross Allan BVMS PGCertSAS MRCVS
Ross qualified from Glasgow University in 2001, gained his BSAVA Certificate in Small Animal Surgery in 2014 and RCVS Advanced Practitioner status in 2015. Ross is Clinical Director of Referral Services at The Pets’n’Vets Family, Glasgow, where he leads Roundhouse Referrals surgical team.
Editor: RCVS Knowledge Communications Team
Reviewer: Dr Catrina Pennington BVM&S MRCVS and Mark Morton BVSc DSAS(Orth) MRCVS
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