On medio-lateral radiograph the density of the infrapatellar fat pad is increased leaving a narrow space between the patellar tendon and the fat pad the transparent lines of the popliteal fascia caudal to the joint is pushed backwards by a swollen joint capsule. TCT and drawer sign are slightly positive with the knee held in flexion. With the progression of the CrCL sprain, the palpation of the medial compartment of the knee shows a swelling between the femoral condyle and the tibial plateau that forms a buttress. Arthroscopic observation shows fibrillation of ligament fibers, usually in the medial band, and synovitis. Early ligament sprains are suspected radiographically in the mediolateral view because of increased infrapatellar fat pad density without any sign of other diseases, like OCD of the lateral femoral condyle, avulsion of the extensor digitorum pedis longus tendon, immune-mediated joint disease. The tibial compression test (TCT) is negative as it is the drawer sign.

In early partial rupture joint palpation is still normal and no swelling is felt on the caudomedial joint compartment were a separation between the femoral condyle and the tibial plateau is still well defined. Because of the subtile signs, most often partial CrCL rupture is overlooked until it progress to complete rupture with more dramatic clinical signs.

With the progression of the ligament sprain clinical signs become more evident with morning pain, incomplete weight bearing with central foot-pad lifted from the ground, lameness after exercise when jumping over a surface (like a pick-up car) the affected leg is landed not simultaneously with the unaffected leg and when sitting the affected knee is not completely flexed, keeping the hock away from the ischiatic tuberosity. Sit test is normal with complete flexion of the stifle and the dog can jump normally. In early CrCL partial rupture the dog runs normal, but in resting position the affected leg is held slightly off weight during walking few steps limping and then normal. In these dogs the cranial tibial thrust caused by the forces acting on the slope of the tibial plateau continuously stresses the CrCL and causes its partial rupture progressing with time in complete rupture.Д¬linical signs are different in intensity according to the degree and duration of CrCL partial rupture. CrCL of non-traumatic origin are caused by a chronic biomechanics imbalance of the forces acting on the CrCL as it is seen in large breed dogs, in overweight dogs, in bowlegged dogs and in dogs with straight rear leg conformation and open knee angle in standing and walking. Partial rupture usually evolves with time in complete rupture, because of the joint inflammation, of weakening of the ligament and of altered biomechanics imbalance that enhances the cranial tibial thrust. CrCL injuries of traumatic origin are caused by forced hyperextension and or internal torsion of the stifle high impact trauma causes the complete rupture of the ligament, while less intense trauma causes partial rupture. The ethiology of CrCL injures is traumatic and non traumatic. Cranial cruciate ligament (CrCL) injuries occur both as partial and as complete rupture.

Dog torn acl symptoms