Butler et al. used a novel cadaveric testing apparatus to quantify each knee ligament's individual contribution to resisting anterior and posterior tibial drawer. The study asks: which structures are primary versus secondary restraints, and what happens to stability when the primary restraint is lost? Tests were conducted at 90° and 30° of flexion in both intact knees and after cruciate sectioning at larger displacements.
Every clinical exam you perform rests on this paper's framework. Before Butler 1980, there was no quantitative framework for understanding why a knee with a torn ACL could have a negative drawer test — clinicians debated which ligaments actually mattered and in what order.
When you perform an anterior drawer and it's negative after an acute knee injury, do not be falsely reassured. Secondary restraints, joint effusion, and hamstring spasm can all mask ACL insufficiency under the low forces of a clinical exam. Upgrade your suspicion with a Lachman test (30° flexion, lower hamstring tension) or flexion-rotation drawer. Both load the knee more selectively.
When you see a PCL injury, check carefully for the posterior sag sign before performing an anterior drawer. What looks like a positive anterior drawer may simply be the tibia starting from a posteriorly subluxed position. Test the correct direction first.
The finding that no single secondary restraint adequately substitutes for the ACL under functional loads is the biomechanical argument for ACL reconstruction rather than rehabilitation alone in active patients. Secondary structures stretch over time, and progressive laxity follows.
Butler et al. used a novel cadaveric testing apparatus to quantify each knee ligament's individual contribution to resisting anterior and posterior tibial drawer. The study asks: which structures are primary versus secondary restraints, and what happens to stability when the primary restraint is lost? Tests were conducted at 90° and 30° of flexion in both intact knees and after cruciate sectioning at larger displacements.
Every clinical exam you perform rests on this paper's framework. Before Butler 1980, there was no quantitative framework for understanding why a knee with a torn ACL could have a negative drawer test — clinicians debated which ligaments actually mattered and in what order.
When you perform an anterior drawer and it's negative after an acute knee injury, do not be falsely reassured. Secondary restraints, joint effusion, and hamstring spasm can all mask ACL insufficiency under the low forces of a clinical exam. Upgrade your suspicion with a Lachman test (30° flexion, lower hamstring tension) or flexion-rotation drawer. Both load the knee more selectively.
When you see a PCL injury, check carefully for the posterior sag sign before performing an anterior drawer. What looks like a positive anterior drawer may simply be the tibia starting from a posteriorly subluxed position. Test the correct direction first.
The finding that no single secondary restraint adequately substitutes for the ACL under functional loads is the biomechanical argument for ACL reconstruction rather than rehabilitation alone in active patients. Secondary structures stretch over time, and progressive laxity follows.