A 30-year-old professional footballer sustains an acute knee injury during a tackle. MRI shows bone contusions in the lateral femoral condyle and posterior lateral tibial plateau with a characteristic kissing pattern. There is also complete disruption of the anterior cruciate ligament fibres with the ligament lying horizontally. What additional MRI finding confirms the associated pivot shift mechanism?
- A The lateral femoral condyle-posterior lateral tibial plateau kissing bone contusion pattern
- B Posterior cruciate ligament buckled appearance
- C Segond fracture — avulsion of the lateral tibial rim ✓
- D Medial collateral ligament deep fibre tear
Explanation
The Segond fracture is a small elliptical avulsion fracture of the lateral tibial plateau rim, representing avulsion of the anterolateral ligament or iliotibial band. It is virtually pathognomonic of an anterior cruciate ligament tear caused by internal rotation with valgus stress — the pivot shift mechanism. On MRI, it appears as a small cortical bone fragment adjacent to the lateral tibial rim. The kissing bone contusions (lateral femoral condyle and posterior lateral tibial plateau) are also characteristic of ACL injury through the pivot shift mechanism, but the Segond fracture specifically confirms this injury mechanism with very high specificity for ACL rupture (approaching 100% association).
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.