Triple tibial osteotomy
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The Triple Tibial Osteotomy is a surgical procedure used to treat dogs that have ruptured their cranial (anterior) cruciate ligament. The cranial cruciate ligament is a ligament connecting the femur with the tibia, and it functions to stop internal rotation of the tibia, cranial (anterior) movement of the tibia with respect to the femur, and overextension of the stifle (knee) joint.
The cranial cruciate ligament is composed of two bands, a craniomedial band and a caudolateral band. Along with the caudal cruciate ligament and the two collateral ligaments, it functions to stabilise the canine stifle joint from the forces put on it during exercise and weight bearing; the cranial cruciate ligament is thought to be able to resist a force equivalent to four times the weight of the dog before it ruptures, but often the ligament is weakened by arthritis that is occuring in the joint. This leads to inflammation of the joint and the production of a joint fluid that is less viscous and less able to both protect against shock and to provide nutrition to the cartilage and the cruciate ligaments, which sit within the joint.
The other intra-articular structures (i.e. within the joint) that help to stabilise the joint and help to distribute load evenly are the menisci; crescent-shaped discs of cartilage that are thicker at the outside and with a thin inner aspect, they also have nerve fibres that help to tell the brain how much load is getting transmitted through the joint. The medial (inside) meniscus is often damaged when the cruciate rupture has been long standing because it is firmly attached to the tibia and gets crushed during abnormal cranial movement of the tibia. The lateral (outside) meniscus is more firmly attached to the femur and does not get crushed.
The triple tibial osteotomy was developed by a New Zealand veterinary orthopaedic specialist, Dr Warrick Bruce, while he was working in Adelaide, South Australia. It aims to neutralise the shear force that acts on the stifle during weight-bearing, by changing the geometry of the forces that act on the joint. These forces are (1) the sum of muscle tension and (2) gravity acting through the tibial plateau, which in the dog is sloped caudally (downwards towards the back of the joint). In the TTO, by reducing the tibial plateau slope, and advancing the tibial tuberosity such that the tibial plateau slope becomes perpendicular to the patellar ligament, shear forces within the joint are neutralised.
The procedure has been developed as a hybrid of two previously available orthopaedic procedures, the tibial tuberosity advancement (TTA) and the tibial plateau levelling operation(TPLO). The TTA neutralises shear force within the stifle by advancing the tibial tuberosity and the TPLO neutralises shear force by rotating the tibial plateau so that it is nearly horizontal with respect to the tibia. The TTO combines both of these procedures and as such less radical changes in tibial tuberosity advancement and plateau levelling are required.
The triple tibial osteotomy (TTO) procedure involves removing a horizontal small wedge of bone (average 12 degrees) halfway along an vertical osteotomy (cut in the bone) in the tibial tuberosity. By removing the wedge of bone, the tibial plateau is levelled, and as the horizontal defect created by removing the wedge is closed down, the tibial tuberosity is itself advanced by several millimetres. This compares with an average of 20 degrees plateau levelling with the TPLO and 9-12mm tibial tuberosity advancement with the TTA.
Return to normal function is rapid, with most dogs having good use of the leg and a normal appearing gait within 3-4 months; long-term progression of arthritis is minimal.
[edit] References
1. Vet Comp Orthop Traumatol. 2007;20(3):159-68.
