Background: Posterolateral corner injuries can be difficult to diagnose. The external rotation recurvatum test was one of the first clinical tests described to diagnose these injuries. Since its earliest description, it has been reported that a positive test result occurred with posterior translation of the proximal tibia with respect to the distal femur as the knee went into recurvatum, external rotation, and varus angulation.
Purpose: To document the sagittal plane relationship of the tibiofemoral joint in patients with posterolateral knee instability and a positive external rotation recurvatum test finding, and to determine possible injury patterns associated with this test.
Study Design: Case series; Level of evidence, 4.
Materials and Methods: In a series of 134 consecutive patients with posterolateral knee injuries, all patients demonstrating a positive external rotation recurvatum test result were identified, and bilateral hyperextension lateral radiographs were subsequently obtained to assist with preoperative planning for surgical reconstruction of their knee injuries.
Results: Of the 134 patients with posterolateral knee injuries, 10 demonstrated a positive external rotation recurvatum test finding. All 10 patients were noted to have a combined anterior cruciate ligament and posterolateral knee injury, with the proximal tibia noted to be subluxated anterior with respect to the distal femur on all hyperextension lateral knee radiographs. The percentage of patients with combined anterior cruciate ligament and posterolateral knee injuries with a positive external rotation recurvatum test result was 30%.
Conclusion: Posterolateral corner knee injuries are often difficult to diagnose, and as a result, correct interpretation of pertinent clinical knee examination findings is essential. Regarding posterolateral knee injuries, the interpretation of a positive external rotation recurvatum test result needs to be redefined to demonstrate that the tibia actually subluxates anterior to the femur, which produces an increase in genu recurvatum clinically. Moreover, the presence of a positive external rotation recurvatum test finding should alert the clinician to the presence of a probable combined posterolateral knee and anterior cruciate ligament injury.