CASE 157
By: Dr. NIZAR AL-NAKSHABANDI MD, FRCPC
HISTORY: 25-year-old male football player had previous reconstruction of the ACL present after acute knee trauma while playing football.
What are your findings?
What is the differential diagnosis?
What are the causes?
FINDINGS:
Coronal T2-weighted images with fat saturation [A] demonstrate bone contusion in the medial tibial condyle presenting as high signal intensity.
Sagittal oblique gradient echo images [B] and T1 [C] demonstrate fiber discontinuity of the ACL graft. The ACL angle is no longer parallel to Blumensaat’s line.
DIAGNOSIS:
ACL graft tear.
PEARLS AND DISCUSSION:
Tears of the ACL graft can be divided into primary and secondary signs. The primary signs are swelling, fiber discontinuity, and change in the course of the ACL where the ACL angle is no longer parallel to Blumensaat’s line. Other signs, as in our case here, is bone contusion. More than 7 mm of anterior tibial translation. Look for other signs such as Segond fracture. Buckling of the PCL.
The O’Donahue unhappy triad constitutes:
Tear of the anterior cruciate ligament. Tear of the medial collateral ligament, and Medial meniscal tear.
Triad has been revisited considering surgical findings where lateral meniscal injury is more common than injury to the medial meniscus. This makes more sense from a biomechanical point of view.
On plain radiographs look for the deep sulcus sign, the anterior tibial translation sign, Segond fracture, and arcuate fracture, or joint effusion.
MRI is critical in the evaluation of the post-operative knee, and the ACL reconstruction patient is no exception. Common indications for utilizing MRI in the post-operative ACL patient include acute reinjury, persistent instability, limitation of motion, or simply persistent pain. In cases of acute reinjury, such as the current example, MRI often directly visualizes the edema and laxity of a recurrent tear. In cases where a graft tear is poorly visualized, any of the secondary signs of ACL disruption such as pivot-shift bone bruises or PCL buckling may also be utilized in the ACL graft patient. As with native ACL injuries, MRI allows evaluation of associated meniscal, chondral, or osseous abnormalities in patients who have suffered an ACL graft tear.
FURTHER READING:
1. Sanders TG, Medynski MA, Feller JF et-al. Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 2000;20 Spec No (suppl 1): S135-51.
2. Shelbourne KD, Nitz PA. The O'Donoghue triad revisited. Combined knee injuries involving anterior cruciate and medial collateral ligament tears. Am J Sports Med. 1992;19 (5): 474-7.
3. O’DONOGHUE DH. Surgical treatment of fresh injuries to the major ligaments of the knee. J Bone Joint Surg Am. 2004;32 (A:4): 721-38.
