Slocum and Larson analyzed 76 operatively verified knees to define rotatory instability, a pattern of abnormal external tibial rotation. They link the injury to forced valgus and external rotation of the flexed knee, tearing the medial capsular ligament. They propose a modified anterior drawer test performed in external rotation to detect this instability at the bedside.
A straight anterior drawer can miss a rotatory pattern, and this paper explains why: the medial capsular ligament, not the ACL, is the first structure to fail. The mental model to carry into an exam is the shifting pivot. Intact medial structures keep the tibia rotating about the medial tubercle. Once the capsule tears, that axis slides laterally and the medial tibia subluxates forward and out.
When you draw the tibia forward in 15 degrees of external rotation and see abnormal anterolateral drift, think medial capsular disruption, whether or not the ACL is intact.
Remember the meniscal trap: an intact posterior horn can mask instability, so a negative exam does not exclude it, and meniscectomy can unmask it. This is the conceptual ancestor of the anteromedial and anterolateral rotatory instability framework refined by Hughston and others.
Slocum and Larson analyzed 76 operatively verified knees to define rotatory instability, a pattern of abnormal external tibial rotation. They link the injury to forced valgus and external rotation of the flexed knee, tearing the medial capsular ligament. They propose a modified anterior drawer test performed in external rotation to detect this instability at the bedside.
A straight anterior drawer can miss a rotatory pattern, and this paper explains why: the medial capsular ligament, not the ACL, is the first structure to fail. The mental model to carry into an exam is the shifting pivot. Intact medial structures keep the tibia rotating about the medial tubercle. Once the capsule tears, that axis slides laterally and the medial tibia subluxates forward and out.
When you draw the tibia forward in 15 degrees of external rotation and see abnormal anterolateral drift, think medial capsular disruption, whether or not the ACL is intact.
Remember the meniscal trap: an intact posterior horn can mask instability, so a negative exam does not exclude it, and meniscectomy can unmask it. This is the conceptual ancestor of the anteromedial and anterolateral rotatory instability framework refined by Hughston and others.