Laxity measurements using stress radiography to assess anterior cruciate ligament tears

Abstract

Introduction: The clinical diagnosis of the anterior cruciate ligament (ACL) tear is based on demonstrating anterior subluxation of the tibia on the femur. In any of the following perspectives, diagnostic (cutoff value confirming rupture), prognostic (treatment efficacy), and therapeutic (laxity influencing the treatment), this laxity can be measured on stress X-rays.

Working hypothesis: The diagnostic value of dynamic radiographs is low for ACL rupture. Passive Telos(®) X-rays have better diagnostic value, better radiologic quality, and are easier to carry out than active Franklin-type X-rays.

Material and methods: A cohort of 112 patients (28 females, 84 males; mean age, 33.7 years [range, 18-72 years]) with an indication for knee arthroscopy were studied prospectively. Before undergoing the arthroscopic treatment, two series of images of both knees were taken: one series of passive anterior drawer dynamic X-rays on a Telos(®) device at 250 N and a series of active anterior drawer dynamic X-rays according to Franklin (contraction of the quadriceps against 7 kg of weight at the ankle). The arthroscopic evaluation of the ACL (reference status) was compared to the anterior laxity measurements (absolute and differential) of each knee compartment (medial, lateral, and average) to determine the diagnostic value of the two radiological tests.

Results: We found 70 patients with an "arthroscopically ruptured ACL", 32 with an "arthroscopically healthy ACL", and 10 with a "partial rupture". The measurement of the anterior drawer values on the dynamic X-rays (active and passive) by two independent observers was reliable and reproducible (ICC>0.80), particularly when using the medial compartment (ICC=0.96) and the differential values eliminating the interobserver measurement error and interindividual laxity variations. In terms of X-ray technique, the active images were more frequently painful and the radiographic result showed less good quality than the Telos images. The anterior drawer values in the "healthy ACL" group were significantly less than in the "ruptured ACL" group for the Telos(®) images, whether the measurements were absolute or differential. For the Franklin images, this difference was only significant for the absolute values. Used for diagnosis (4-mm differential on the medial compartment), the passive dynamic images had lower diagnostic values (Se=59% and Sp=90%) than the series reported in the literature, which were marked by great heterogeneity.

Conclusion: The measurement of anterior drawer values on Telos(®) and Franklin dynamic X-rays is a reliable and reproducible measurement, particularly when using the medial compartment and differential measurements. This small series did not demonstrate a diagnostic value for the Franklin images, contrary to the Telos(®) X-rays. Used for diagnostic purposes, the Telos(®) images had a low sensitivity; consequently, they should be used preferentially for prognostic or therapeutic purposes.

Level of evidence: Level III, prospective case-control study.

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