Purpose: Evaluation of the inter- and intra-observer reliability of a new developed knee laxity measurement device for tibiofemoral rotation.

Methods: 30 healthy subjects (15m, 15w, mean age of 24 years) were examined with the Rotameter knee laxitiy measurement device. The Beigthon score was reported to test the general laxitiy of the subjects.

After fixation of the device on the lower extremity and positioning of the patient in the starting position the device was first externally and then internally rotated at an applied torque of 5,10 and 15 Nm. To decrease the measurement error the procedure was repeated 5 times. Afterwards 5 measurements were performed by a second examiner in the same way to measure the inter-observer reliability. All 30 patients were measured again after a mean of 31 ± 43 days by the same examiners to test the intra-observer reliability. Statistical analysis was performed using the intra class correlation coefficient (ICC). Pearson correlation coefficient were used to compare the measurements of the left and the right knee.

Results: The Beigthon Score showed a mean of 0.8 ± 1.1 (0–4). At an applied torque of 5 Nm the ICC for the intra-observer reliability of was 0.81 for the external rotation and 0.67 for the internal rotation, the ICC for the inter-observer reliability was 0.94 for the external and 0.94 for the internal rotation. At 10 Nm of rotation torque an ICC for the intra-observer reliability of 0.79 was reached for internal and 0.88 for external rotation, the ICC for the inter-observer reliability was 0.97 for internal and 0.95 for external rotation. At the highest applied torque of 15 Nm an ICC for the intra-observer reliability of 0.93 was observed for the external rotation and 0.83 was found for internal rotation. For the inter-tester reliability the ICC was 0.95 for external and 0.98 for internal rotation.

The comparison of the measurements of the left and the right knee showed high Pearson correlation (.90) at all applied torques.

Conclusion: The Rotameter testing device for the measurement of tibiofemoral rotation showed a high inter-observer and intra-observer reliability. It is easy to perform and might be used in a wide field to examine the rotational stability of the knee.