The Porto Ankle Testing Device is reliable to measure ankle laxity with concurrent magnetic resonance imaging.

OBJECTIVES

The purpose of this study was to assess the reliability of a new arthrometer - the Porto Ankle Testing Device (PATD) - that is compatible with magnetic resonance imaging (MRI) assessment to measure ankle joint laxity.

METHODS

This cross-sectional study enrolled 33 ankles without a history of sprain or symptoms of instability. All ankles underwent ankle instrumented stress testing with the PATD with concurrent MRI. The PATD protocol compares the ankle rest position against the ankle stress under the anterolateral drawer or the talar tilt test. Tibiotalar and subtalar laxity measurements were calculated as the difference in joint position before and after stress testing. Tibiotalar laxity measurements included the anterior talus translation (ATT) and the talar tilt (TT). The ATT was measured in the anterior, diagonal, and inferior directions. Subtalar laxity measurements included anterior calcaneus translation (ACT), the subtalar tilt (STT), the subtalar opening distance, and the subtalar rotation. The intraclass correlation coefficient (ICC) was computed to evaluate the inter and intra-rater reliability, and the standard error measurement (SEM) to estimate the amount of random error associated with laxity measurements.

RESULTS

All tibiotalar and subtalar laxity measurements were classified as excellent reliability for inter (ICC, 0.77-0.98) and intra-rater (ICC, 0.87-0.99). Only the ATT in the inferior direction showed suboptimal inter-rater reliability (ICC, 0.59-0.70). The SEM values showed a low risk of associated random error from measurement and were higher for inter-rater than for repeated measures, suggesting that repeated measures result in a lower risk of random error.

CONCLUSION

The measurement of tibiotalar and subtalar laxity with the PATD provides excellent reliability between different assessors and after repeated measures. The PATD can overcome the limitations of previous devices while offering the correlation of structural integrity with a reliable assessment of functional competence of ankle ligaments (joint laxity) within the same exam.

LEVEL OF EVIDENCE: Level IV.