Tibial Plateau Levelling Osteotomy (TPLO) was originally developed by Barclay Slocum in the 1980s. Slocum realised that given the standing angle of the dog’s knee, the cranial cruciate ligament deficient stifle had a tendency to subluxate cranially because of the opposing forces generated between the tibial plateau and the femoral condyles. He speculated that making a corrective osteotomy and changing (flattening) the tibial plateau angle should neutralise cranial tibial thrust and therefore the instability resulting from cranial cruciate ligament rupture. The osteotomy was originally designed as a wedge ostectomy, which still exists as a separate procedure for cranial cruciate ligament rupture and has its own advantages and disadvantages; see other section on CWO-TPLO on page 192. The wedge ostectomy then evolved into the curved / cresenteric osteotomy that differs by separating the tibial plateau from both the tibial metaphysis and the tibial tuberosity. A radial saw blade with a TPLO specific oscillating saw is used that makes the crescentic osteotomy (see page 197 for saws and blades). Once the tibial osteotomy is made, it is rotated by a calculated amount by inserting a rotation pin (tables are available to determine the correct amount of rotation for each blade size, see page 195.The aim is to achieve a Tibial Plateau Angle (TPA) of 5 to 7 degrees. Once rotated, the tibial plateau segment is temporarily held in position by a single K-wire, or fracture reduction forceps. Then the plate and screws are applied for definitive stabilisation.
TPLO was originally developed with many claims, including complete return of function, re-gaining full muscle mass, and the halting of progression of degenerative joint disease. Nowadays it is accepted that whilst TPLO does not achieve all these goals as it does not restore completely normal stifle biomechanics, it is arguably the best surgical procedure available for addressing the cranial cruciate ligament deficient stifle. For this reason, it is very popular amongst specialist surgeons, and evidence is starting to emerge that it offers the best outcome compared to other surgical techniques, including other osteotomies, to address cranial cruciate ligament rupture such as TTA or extra-capsular stabilisation.
The original TPLO surgical technique was very specific, and surgeons all followed a very similar protocol. With the passage of time, surgeons have evolved individual variations on the original technique. For example, use of a jig is no longer universal, many surgeons have adopted a minimal soft tissue elevation technique as compared to the original extensive soft tissue elevation and packing technique, and stabilisation of the rotated tibial plateau can be achieved using pointed fracture reduction forceps rather than placement of a temporary stabilising K-wire.
The procedure can also be modified to address concurrent patellar luxation with cranial cruciate ligament disease, by axially rotating the tibial tuberosity and diaphysis relative to the tibial plateau, although this may cause a concurrent internal / external rotational deformity of the distal limb.
The TPLO procedure can be performed in almost any dog. For many surgeons, TPLO is the procedure of choice for the majority of patients with cranial crucial ligament disease. The higher the TPA, the greater the rotation required to achieve a TPA of 5 to 7 degrees. It has been suggested that when the TPA exceeds 30 degrees, the amount of rotation required becomes excessive, and this could lead to fracture of the tibial tuberosity. This has lead to some surgeons to choose the CWO-TPLO procedure for such dogs. Also a double osteotomy comprising a combination of wedge ostectomy and crescentic osteotomy has been described, but this is not for the feint hearted.
Reasons not to choose a TPLO would include inexperience or lack of familiarity with the technique, uncontrollable skin disease or pyoderma that increases the risk of surgical site infection, inability of the owner to restrict the patient appropriately post-operatively that could lead to implant failure and failure of reduction, or ability of the owner to accept the list of potential complications associated with an osteotomy procedure, or the associated cost.