PURPOSE: This study proposes a simple and noninvasive instrument called the "Rotatometer" to measure tibiofemoral rotation and investigates its clinical applicability to the assessment of static rotational knee laxity.
METHODS: The degree of tibiofemoral rotation was measured for a sample of 94 healthy volunteers with 188 knees by using the Rotatometer. The measurement was made by two independent and blinded examiners in three sessions at one-month intervals. The normative rotational profile and its relationship with gender and age were evaluated, and inter-observer reliability and intra-observer reliability were calculated.
RESULTS: Males showed 62° ± 5° of external rotation, whereas females, 64° ± 5°. Males showed 44° ± 5° of internal rotation, whereas females, 49° ± 4°. Females showed significantly higher degrees of rotation than males. Tibiofemoral rotation was not correlated with age, and external rotation and internal rotation had a moderate positive relationship. Inter-observer reliability ranged from 0.84 to 0.91 for external rotation and 0.90 to 0.95 for internal rotation, and intra-observer reliability ranged from 0.69 to 0.89 for external rotation and 0.87 to 0.95 for internal rotation.
CONCLUSIONS: The results suggest the Rotatometer to be a simple and noninvasive device with high inter- and intra-observer reliability. The device can provide a normative rotational profile for reference purposes and thus can be used to determine the preoperative and postoperative rotational status of knees with anterior cruciate ligament injuries and compare results from different reconstruction techniques.