Purpose: The purpose of this study was to determine whether the incidence of posterolateral knee injuries, as well as other concurrent knee ligament injuries, could be obtained from a prospective evaluation of magnetic resonance imaging scans in patients with an acute knee injury with a hemarthrosis.
Methods: We prospectively documented all patients with acute (within 30 days) knee injuries with a hemarthrosis over a 90-day period who underwent 1.5-T magnetic resonance imaging at a large referral imaging facility with 6 sites, effectively covering a large metropolitan area. The anterior cruciate ligament, superficial medial collateral ligament, and posterior cruciate ligament (PCL) and the following individual structures of the posterolateral corner were evaluated for high-grade injury: fibular collateral ligament, popliteus tendon, and popliteofibular ligament.
Results: Out of 331 consecutive acute knee injuries with a hemarthrosis, 265 ligament injuries occurred in 187 patients (56%). Of these 187 patients with ligament injuries, 126 had isolated ligament injuries and 61 (33%) had combined multiple ligament injuries. Of the 187 patients with knee ligament injuries, 83 (44%) had isolated anterior cruciate ligament tears, 28 (15%) had isolated superficial medial collateral ligament tears, 11 (5%) had isolated PCL tears, and 4 (2.1%) had isolated posterolateral knee tears. Of the patients with posterolateral knee structure injuries, 87% (26/30) had multiple ligament injuries, with the overall incidence of posterolateral knee injuries among all knee ligament injuries being 16% and among all acute knee injuries with a hemarthrosis being 9.1%. Of the 27 patients with PCL tears, 16 (52%) had combined multiple ligament injuries.
Conclusions: This study shows that in this population, the incidence of posterolateral knee injuries in patients with acute knee ligament injuries with a hemarthrosis was 9.1%. It also verified that most PCL and posterolateral corner injuries occur in combination with other ligament injuries.
Level of evidence: Level II, development of diagnostic criteria on the basis of consecutive patients with a universally applied gold standard.