Why should we use osteotomies to treat CrCR in small dogs?

A survey of British veterinarians has shown that only 15% of cases of cruciate ligament rupture in a small dog (<15kg) are primarily proposed for surgical care (Commerford at al., VCOT 6/2013). Conservative treatment is often considered sufficient in other countries as well, and surgical stabilization is done if there is insufficient improvement. Most dogs are then treated with an extracapsular technique (ECS), a proximal tibial osteotomy is only performed in about 1/3 of the operated patients (Commerford at al., VCOT 6/2013).

It is widely acknowledged that the tibial plateau angle (TPA) generates a cranial tibial thrust (CTT) that causes a dog to be unable to stabilize the stifle after an anterior cruciate ligament tear (Scott et al., JOR, 2004). Therefore, in larger dogs, a surgical procedure for the unstable stifle is recommended. However, as small dogs have on average a greater TPA than large dogs (30°-32° vs 22°-25°), we must assume a significant CTT in small dogs that challenges conservative treatment.

Theoretically, there are some problems with the ECS. The large TPA puts the lateral suture material under stress. Since a correct isometric placement of the string is not possible, there is a cyclic loading stress (P.G. Witte, VCOT 2015; Fischer et al.,VetSurg 2010). There is currently no material that is both elastic enough and has the necessary strength. Therefore, patients suffer pain and the suture breaks often early after application (Boettcher et al., ESVOT meeting, 2006; S. Roe, VCOT 2013).

Unfortunately, there are no published objective data on the success rate of an ECS in small dogs. Comparative studies in larger dogs show that there is not the expected large difference between TPLO and ECS in the load on the operated hind limb after one to two years. Despite the theoretical problems of the ECS, in most cases improvement of the knee function occurs (AU et al., Vet Surg 2010; Gordon-Evans et al., JAVMA 2013; Conzemius et al., JAVMA 2005; Nelson et al., Vet Surg 2013). [...]