“Max” is a 7 year-old, German Shepherd. Max presents, having had lumbosacral surgery 1 year previously. Max has lameness in the right hind leg at this time. No drawer sign can be elicited but a partial cranial cruciate tear is suspected.
Sequences include T2-weighted sequences, STIR sequence, and T1-weighted sequences. All planes are represented.
A small amount of joint effusion is seen. For the most part, normal anatomy is visualized. Critical structures, including the cranial and caudal cruciate ligaments, medial and lateral menisci, long digital extensor tendon, straight patellar ligament, and femoral meniscal ligament are visualized and are found to be normal. Figure 1 shows a T1-weighted sagittal image of the stifle with the caudal and cranial cruciate ligament labeled. Figure 2 is a STIR sequence in the same location. The synovial fluid is bright white and the infrapatellar fat body has been suppressed and is now dark. There is excellent contrast between the fat body and the synovial fluid on this sequence. Again, the cranial and caudal cruciate ligaments have been labeled.
The cranial cruciate ligament is never seen as well as the caudal cruciate ligament due to its fan-shaped origin and the volume average with the synovial fluid that envelopes the cranial portion of the ligament. Figure 3 is a T2-weighted image of the stifle medial of midline. The cranial and caudal horns of the meniscus are labeled. Damage to the meniscus is readily detected via magnetic resonance imaging. Figure 4 is a dorsal plane looking at the knee from the front. The lateral and medial collateral ligaments are identified with the arrows. No abnormalities are seen.
The fact that only a mild joint effusion is seen indicates that this animal would not benefit from surgery. Partial tears of the cruciate ligament are readily identified on magnetic resonance imaging as the tear extends into the bone and an abnormality can be seen at the origin and insertion of the ligament. Since that was not detected, this animal merely has a mild degree of osteoarthrosis of the stifle (knee joint).
As our physician colleagues have found, magnetic resonance imaging prior to stifle surgery often indicates that there is not a need for invasive surgery. Procedures to correct stifle instability are both expensive and create significant pain with the potential for complications. Magnetic resonance imaging prevented Max from having unwarranted surgery. While cruciate ligament ruptures and meniscal damage are common in the dog, magnetic resonance imaging can be utilized to confirm that diagnosis prior to surgery and if it is not present, will negate the need for surgery.