Résumé
Background: Methods of objectively measuring rotational knee laxity are either experimental or difficult to use in daily practice. A new method has been developed to quantitatively assess rotatory laxity using an open MRI system and new tool, the KneeM device.
Purpose/Hypothesis: To perform a preliminary evaluation of a novel knee rotation measurement device to assess knee kinematics during flexion in an MRI field, in both anterior cruciate ligament (ACL)-deficient and healthy contralateral knees. The hypothesis was that the KneeM device would allow in vivo reproduction and analysis of knee kinematics during flexion in healthy and ACLdeficient knees.
Study Design: Controlled laboratory study.
Methods: Ten subjects (7men and 3 women; mean age +/- standard deviation, 32.3 +/- 9.4 years) with ACL-deficient knees and contralateral uninjuredknees participated in the study. AnopenMRIwas performedwith theKneeMdevice at amean 4.9months (range, 3.0-7 months) after ACL injury. The device exerted on the knee an anterior drawer force of 100 N, with an internal rotation of 20 degrees, through the range of flexion (0 degrees, 20 degrees, 40 degrees, and 60 degrees). Both ACL-deficient and healthy contralateral knees were analyzed using the Iwaki method.
Results: There was no statistical difference of anterior translation in the medial compartment between intact and ACL-deficient knees at all degrees of flexion. However, significant differences in the anterior translation of the lateral compartment were observed between ACL-deficient and intact contralateral knees at 0 degrees and 20 degrees of flexion (P =.005 and P =.002, respectively). Between 20 degrees and 40 degrees, the lateral plateau of ACL-deficient knees translated 7.7 mm posteriorly, whereas the medial compartment remained stable, reflecting a sudden external rotation of the lateral plateau under the femoral condyle.
Conclusion: This preliminary study suggests that measurement of tibiofemoral movements in both compartments during flexion using the KneeM device was useful for quantifying rotatory laxity in ACL-deficient knees. Moreover, this device seemed to allow a "mechanized pivot shift'' and allowed reproduction of the "pivot'' phase in the MRI field between 20 degrees and 40 degrees of flexion.
Clinical Relevance: This device could be used for diagnostic purposes or to investigate the outcomes of ACL reconstructions.