The cruciate ligament is located in the knee and helps to stabilise the joint. It is made up of a tough band of fibrous tissue which attaches to the femur and connects to the tibia. Its purpose is to prevent the tibia moving forwards relative to the femur which stops the joint from over extending or rotating. Cruciate ligament damage can degenerate slowly over time as the fibres start to fray and weaken. Genetic factors, sudden trauma, obesity, hormone imbalances, sudden twisting or pressure on the joint and breed predisposition may all play a role.

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When the ligament becomes torn it is a sprain and graded as follows:-

 

Grade 1 - minimal tear, likely to  heal with activity restrictions in place and reviews of the dogs daily routine (ADL’s).

Grade 2 - partial tear, which can easily progress to full tear so management of the dogs daily activities is crucial.

Grade 3 - complete rupture and surgery will be required.

Grade 4 - complete rupture and the ligament takes with it small pieces of bone which again requires surgery.

 

When the cruciate ligament is damaged it allows the femur to slide down the slope of the tibia causing pain and weakness when any weight is put on the joint. It also often damages a pair of cartilages called the menisci as the femur can crush and tear them as it slides down the tibia.