Execution
- 1Position the patient supine.
- 2Flex both hips and knees to 90 degrees.
- 3Support both legs under the heels or lower legs.
- 4View both knees from the side and front.
- 5Observe whether the tibia on the affected side sags posteriorly relative to the femur.
Positive outcome
A posterior drop of the tibia or loss of the normal tibial step-off is positive. The sign suggests PCL insufficiency. It should be assessed before anterior drawer so a reduced posterior sag is not mistaken for anterior translation.
Studies
| Study | Reliability | Sn | Sp | LR+ | LR− |
|---|---|---|---|---|---|
| Rubinstein et al. (1994) | NA | 79 | 100 | infinity | 0.21 |
CommentPosterior sag is highly specific when obvious, but subtle partial injuries can be missed. The 100% specificity estimate creates an infinite LR+ that should be read cautiously. It remains a high-value observation because it changes interpretation of anterior drawer and active drawer tests.
High Clinical Value