Historically, CrCL rupture in dogs has been considered an accidental injury, with the subsequent development of stifle arthritis. However, since the early 1990s this paradigm has been challenged. It was established that a high risk of contralateral CrCL rupture existed in affected dogs and that the typical history and clinical signs of CrCL rupture could not be easily explained by traumatic injury. Recent studies have clearly shown that stifle arthritis precedes the development of CrCL rupture and associated stifle instability in the majority of affected dogs.⁸  

The point of this discussion is that often dogs presented with intermittent mild rear leg lamenesses should be radiographed to determine the presence of the infrapatellar fat pad changes bilaterally. Early diagnosis of unilateral CrCL rupture is very advantageous in avoiding acute bilateral complete CrCL ruptures. We frequently see dogs who had a subtle intermittent hindlimb lameness in one or both legs in our referral practices. They may have had either a current radiographic study or a past radiographic study for hip dysplasia and the lameness was attributed to CHD. When these dogs are presented to us with an acute rear leg non-weight bearing lameness from a CrCL injury, we want to know the status of the contralateral CrCL. The reason for this is the post-op recovery restrictions must be adhered to in order to avoid a contralateral CrCL tear. If the contralateral stifle is normal the patient is at risk of rupturing that CrCL until the ipsilateral stifle is normal or nearly normal following surgery. We now have the fastest recovery to normal or nearly normal function post-op with TTA or TPLO repairs, 8-12 weeks in many cases. If the contralateral stifle has a radiodense infrapatellar fat pad and is palpably unstable, we know that patient has bilateral CrCL disease and will need bilateral repairs. Often we stage them 6 weeks apart resulting a very comfortable/functionally active patient in 3-4 months post-op. Bilateral disease impacts our financial discussion with the owner. We feel responsible in helping the owner understand how to try and avoid a contralateral CrCL tear if that stifle is radiographically normal, ie. leash walks primarily and avoidance of strenuous exercise with other dogs, ball play, squirrel chasing, etc. These efforts are not a guarantee of avoiding a contralateral CrCL tear. If the contralateral stifle is free of the infrapatellar fat pad density radiographically we are more lenient in the exercise restrictions. If the contralateral stifle has an infrapatellar fat pad density and is palpably stable, we know we have a partial tear that will completely rupture unless the exercise consists of just leash walks. Often, for financial reasons, an owner will elect restriction to leash walks only in hopes of avoiding a second surgery or to delay the financial impact of two surgeries in a short space of time. If the owner has good insurance coverage or the financial ability to surgically repair a contralateral partial tear preemptively prior to significant OA or meniscal injury, the surgical outcome is much better. Another reason for radiographing both stifles early in the CrCL disease process is to have a dated record of their integrity. If they have one radiographically normal knee and purchase Trupanion insurance and avoid a CrCL injury for 18 months in that limb via exercise restriction, it is not considered a pre-existing injury, and Trupanion will pay 90% of the second surgery if that becomes necessary (Should be mutually determined by the owner and Trupanion immediately following confirmation of a radiographic normal contralateral knee).

¹ Fuller, Mark C. et al: Evaluation of the radiographic infrapatellar fat pad sign of the contralateral stifle joint as a risk factor for subsequent contralateral cranial cruciate ligament rupture in dogs with a unilateral rupture: 96 cases (2006-2007). JAVMA, Vol. 244, No. 3, February 1, 2014 328-338.

² Cabrera SY, et al. Comparison of tibial plateau angles in dogs with unilateral versus bilateral cranial cruciate ligament rupture; 150 cases (2000-2006),  JAVMA 2008; 232: 889-892.

³ Buote N., et al Age, tibial plateau angle, sex, and weight risk factors for contralateral rupture of the cranial cruciate ligament in Labradors. Vet. Surg. 2009; 38: 481-489.

⁴ Muir P, et al. Contralateral cruciate survival in dogs with unilateral non-contact cranial cruciate ligament rupture. PLoS ONE 2011; 6 : e25331.

⁵ de Bruin T, et al. Radiographic assessment of the progression of osteoarthritis in the contralateral stifle joint of dogs with a ruptured cranial cruciate ligament. Vet. Rec. 2007; 161: 745-750.

⁶ Widmer WR. et al. Radiographic and magnetic resonance imaging of the stifle joint in experimental osteoarthritis of dogs. Vet. Radiol. Ultrasound 1994; 35: 371-383.

⁷ Kowaleski MP, et al. Stifle Joint. In Tobias KM et al. Veterinary Surgery: Small Animal. St Louis: Saunders Elsevier, 2012; 914-920. 

⁸ Bleedorn J A, et al. Synovitis precedes development of joint instability in dogs with degenerative cranial cruciate ligament rupture. Vet. Surg. 2009; 38: E26

⁹ Doverspike M, et al. Contralateral cranial cruciate ligament rupture: incidence in 114 dogs. JAAHA 1993; 29: 167-170.