Background: One of the most useful clinical tests for diagnosing an isolate
d injury of the posterior cruciate ligament is the posterior drawer maneuve
r performed with the knee in 90 degrees of flexion. Previously, it was thou
ght that internally rotating the tibia during posterior drawer testing woul
d decrease posterior laxity in a knee with an isolated posterior cruciate l
igament injury. In this study, we evaluated the effects of internal and ext
ernal tibial rotation on posterior laxity with the knee held in varying deg
rees of flexion after the posterior cruciate and meniscofemoral ligaments h
ad been cut.
Materials and Methods: Twenty cadaveric knees were used. Each knee was moun
ted in a fixture with six degrees of freedom, and anterior and posterior fo
rces of 150 N were applied. The testing was conducted with the knee in 90 d
egrees, 60 degrees, 30 degrees, and 0 degrees of flexion with the tibia in
neutral, internal, and external rotation. All knees were tested with the po
sterior cruciate and meniscofemoral ligaments intact and transected. Repeat
ed-measures analysis of variance was used for statistical analysis.
Results: At 30 degrees, 60 degrees, and 90 degrees of flexion, there was a
significant increase in posterior laxity following transection of the poste
rior cruciate and meniscofemoral ligaments. At 60 degrees and 90 degrees of
flexion, there was significantly less posterior laxity when the tibia was
held in internal compared with external rotation. At 0 degrees and 30 degre
es of flexion, there was no significant difference in posterior laxity when
the tibia was held in internal compared with external rotation.
Conclusions: After the posterior cruciate and meniscofemoral ligaments had
been out, posterior laxity was significantly decreased by both internal and
external rotation of the tibia. Internal tibial rotation resulted in signi
ficantly less laxity than external tibial rotation did at 60 degrees and 90
degrees of knee flexion.
Clinical Relevance: An isolated injury of the posterior cruciate ligament i
s best detected when a posterior drawer test is performed with the knee in
90 degrees of flexion. Repeating this test with the tibia internally rotate
d will result in a substantial decrease in the amount of posterior laxity a
t 60 degrees and 90 degrees of knee flexion.