Based upon the data published by Maquet and Nisell, Montavon and Tepic proposed that a similar situation existed in the dog, and tibial tuberosity advancement (TTA) was proposed to neutralize cranial tibial femoral shear force in a cranial cruciate ligament (CCL) deficient stifle joint in the dog. A PTA of 90 degrees was suggested as the crossover point at 135 degrees of stifle joint extension, thus the TTA technique was developed so as to achieve this PTA. These assumptions have since been validated in experimental models. These models were used to evaluate cranial tibial femoral shear force either indirectly with cranial tibial subluxation or directly with cranial tibial thrust under varying loading conditions.^3,4,5 

 

A decrease in retropatellar pressure after a TTA has recently been demonstrated experimentally in the dog.^5,12 In theory this diminished force can protect the articular cartilage of both the patella and the femur from subsequent damage. Femorotibial contact pressure and location have been evaluated in vitro using an experimental model of a CCL deficient stifle joint, which demonstrated a 40% decrease in contact area with an associated 100% increase in peak pressure; furthermore, the positioning of the peak pressure was found to shift caudally.⁵ The TTA appeared to restore the normal femorotibial contact and pressure, which may spare the meniscus from risk of trauma after TTA. This study also suggested that because TTA did not change the geometry of the joint, and the pressure distributions essentially remained unchanged, there may be less development of osteoarthritis. All of these findings may support the clinical studies that implied an absence of problems with the patellar tendon and the joint surfaces after TTA.^6,7,8

As the resultant PTA is crucial to the determination of the amount of TTA, there has been a recent suggestion that the PTA is more accurately determined by the method of the common tangent (PTACT)as opposed to the method using the tibial plateau angle (PTATPA). The former method has been proposed to be clinically more accurate as it takes into account the anatomic relationship between the femoral condyles and tibial plateau, as opposed to a static relationship of the tibial plateau with the patellar tendon. Based upon these suppositions, this method has been recommended for clinical use. Support for this concept has been demonstrated experimentally whereby less variability was observed with PTACT vs. PTATPA when compared to the target PTA of 90 degrees.^10,11 

 

There are FIVE primary considerations when selecting the appropriate case for a TTA/CCL repair. The FIRST is the location of the patellar tendon insertion, low vs.high. The tibial tuberosity is at greater risk of fracture with a TTA in a case with a low patellar tendon insertion point. This anatomy necessitates a smaller plate be applied to the tibial crest. Then the usual position of the interspersed cage is above the most proximal position of the  plate resulting in little bone to support it. With that anatomy a TPLO would be a better application for the CCL repair in those cases. Dogs with a high insertion point a TTA/CCL repair is ideal because a larger TTA plate can be applied leaving adequate bone to support the cage. 

 

                        Left 43 degree TPA                     Right 25 degree TPA

Figure 5: We have already discussed the recommended approach to ligament remnants and the medial meniscus. Next the proximal medial tibia is exposed and the osteotomy is started. The osteotomy must be straight across from the medial side to the lateral side. Oblique osteotomies are undesirable. The osteotomy must be caudal enough such that the tibialtuberosity fragment is big enough to allow safe placement of the fork and the cage screw without risk of fracture. It must be cranial enough to avoid the long digital extensor tendon and the menisci.¹⁵ 

Figure 6: To achieve this, the osteotomised tuberosity is held in the advanced position by titanium, plate, fork, screws, and cage.These are very light weight and have minimal temperature conductivity in their exposed ( no muscle coverage on the proximal medial tibia). Subjectively large stainless steel TPLO plates may cause cold climate intermittent lameness.¹⁵

 

 

In all studies, two major points are discussed: early technical errors with the procedure and meniscal injury. Elimination of technical errors, which were associated with the early learning curve in performing this surgical procedure, would have significantly reduced the number of major complications; attention to the technical details of the procedure is paramount. The issue with the meniscus is more confounding, as there is much controversy as to the best method of approach: meniscal release or no meniscal release. The TTA was originally performed without a meniscal release, but it appears that the majority of complications occurring postoperatively in two of the studies were because of meniscal tears, either those that may have been missed at the time of the original surgery or those that subsequently occurred. A suggestion was made that meniscal release may eliminate this issue. Furthermore, it was reported that dogs with/without meniscal debridement (meniscal tears or not) were not different based upon clinical outcome. Therefore, it was suggested a meniscal release might be appropriate as minimal morbidity could be expected; however, this supposition needs to be further evaluated with long- term follow-up.Whatever the opposing mechanisms proposed regarding the meniscus, debate remains as to whether or not to perform a medial meniscal release. It appears there are two opposing opinions regarding the necessity of meniscal release at this time with TTA.⁹

 

TTA's in the hands of our three surgeons BVS/CCVS with over 6 years experience and well over a 1500 cases the complication rate is very low. We have no residents in training so all the cases are done by very experienced surgeons. The consensus among the three surgeons is to do a medial meniscal ligament release which greatly minimizes to post-operative complication rate. Our major complication rate is consistent with previously published (infection, tibial fractures, meniscal injury, and catastrophic implant failure), is very low. Because all the TTA implants are titanium they almost never require removal due metallurgical reaction. All our TTA cases are examined at 2, 4, 8-10, or 10-12 weeks post- op depending on the surgeon's preference and the age of the patient. Post-operative confinement for 8-10 weeks is restricted to short leash walks , no off leash running or jumping, and confinement to a crate, child's play area, pantry, half bathroom when alone indoors. All TTA cases are  sedated and radiographed at 10-12 weeks post-op to confirm the osteotomy is healed. Bilateral CCL injuries are often repaired at a 6 week interval. Autogenous cancellous graft material is harvested from the adjacent proximal caudal tibial metaphyseal bone and placed in the adjacent osteotomy gap below the cage. However, a recent publication would indicate bone grafting does  not enhance osteotomy healing.¹⁴ Subjectively, weight bearing occurs earlier and more normally than in TPLOs. We currently do many more TTAs than TPLOs each week.

¹ Maquet P: Tibial tuberosity advancement. Clin Orthop Rel Res 115:225-230, 1979

² Nisell R: Mechanics of the knee. A study of joint and muscle load with clinical applications. Acta Orthop Scand Supp 56:3-42, 1985

³ Nisell R, Németh G, Ohlsén H: Joint forces in the extension of the knee: Analysis of a mechanical model. Acta Orthop Scand 57:41-46, 1986

⁴Shirazi-Adl A, Mesfar W: Effect of tibial tubercle elevation on biomechanics of the entire knee joint under muscle loads. Clin Biomech 22:344-351, 2007

⁵ Kim SE, Pozzi A, Banks SA, et al: Effect of tibial tuberosity advancement on femorotibial contact mechanics and stifle kinematics. Vet Surg 38:33-39, 2009

⁶Hoffmann DE, Miller JM, Ober CP, et al: Tibial tuberosity advancement in 65 canine stifles. Vet Comp Orthop Traumatol 19:219-227, 2006

⁷ Lafaver S, Miller NA, Stubbs WP, et al: Tibial tuberosity advancement for stabilization of the canine cranial cruciate ligament-deficient stifle joint: surgical technique, early results and complication in 101 dogs. Vet Surg 36:573-586, 2007

⁸ Stein S, Schmoekel H: Short-term and eight to 12 months results of a tibial tuberosity advancement as treatment of canine cranial cruciate ligament damage. J Sm Anim Pract 49:398-404, 2008

⁹ Boudrieau RJ. Surgical Treatment: Tibial Tuberosity Advancement. In: Advances in Veterinary Surgery: The Canine Cranial Cruciate Ligament, Muir P (ed.). Wiley- Blackwell, Ames; in press, 2010.

¹⁰ Hoffmann DR, Kowaleski MP, Johnson KA, et al: In vitro biomechanical evaluation of the canine CrCL deficient stifle with varying angles of stifle joint flexion and axial loads after TTA. Abstracts of the 18th Annual Scientific Meeting of the European College of Veterinary Surgeons. Nantes, France. July 2-4, 2009; pp 557-559

¹¹ Kipfer NM, Damur DM, Guerrero T, et al: Effect of tibial tuberosity advancement on femorotibial shear in cranial cruciate-deficient stifles: an in vitro study. Vet Comp Orthop Traumatol 21:385-390, 2008

¹² Guerrero TG, Pozzi A. Dunbar N et al: Effect of Tibial Tuberosity Advancement On the Contact Mechanics and the Alignment of the Patellofemoral Joint Proceedings AVCS 2008

¹³ Steinberg EJ, Prata RG, Palazzini K et al: Tibial Tuberosity Advancement for Treatment of Cranial Cruciate LigamentInjury in 193 Consecutive Surgeries Complications and Owner Satisfaction. Proceedings of the VOS 2009