Pivot shift injury and resultant unhappy triad

Case contributed by Bálint Botz

Presentation

Sport injury. Plain film unremarkable. ?ACL and meniscal tear

Patient Data

Age: 20 years
Gender: Female

Bone edema of the posterolateral and posteromedial corners of the tibia condyles, as well as the ventral aspect of the lateral femoral condyle. Bone bruise pattern is partially in line with pivot shift, but suggests an even more complex twisting mechanism. 

Complete anterior cruciate ligament tear. 

Complex, radial and longitudinal tears of the lateral meniscus without displacement. 

Subtle horizontal tear of the medial meniscus at the border between the body and the posterior horn, only seen well in the coronal sequence. 

Complete disruption of the medial collateral ligament with adjacent soft tissue high signal due to edema on PD FS. 

Thin fluid signal along the medial gastrocnemius attachment, but no tendon disruption/retraction. 

Equivocal inhomogeneity of the popliteus tendon, suggesting partial injury. 

Moderate joint effusion with subtle synovial irregularity. 

Annotated image

Annotated images sequentially show some of the key findings: 

1. ACL tear

2. Medial meniscal horizontal tear

4-5. Lateral meniscal vertical longitudinal and radial tears

6. MCL tear

7. Medial gastrocnemius insertion injury

Case Discussion

Altogether the injuries match (and in fact go well beyond) the criteria for an unhappy triad complex knee injury. 

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