Anterior cruciate ligament tear: reliability of MR imaging to predict stability after conservative treatment

Abstract

Objective: The aim of this study is to evaluate the reliability of MR imaging to predict the stability of the torn anterior cruciate ligament (ACL) after complete recovery of the ligament's continuity.

Materials and methods: Twenty patients with 20 knee injuries (13 males and 7 females; age range, 20-54) were enrolled in the study. The inclusion criteria were a positive history of acute trauma, diagnosis of the ACL tear by both the physical examination and the MR imaging at the initial presentation, conservative treatment, complete recovery of the continuity of the ligament on the follow up (FU) MR images and availability of the KT-2000 measurements. Two radiologists, who worked in consensus, graded the MR findings with using a 3-point system for the signal intensity, sharpness, straightness and the thickness of the healed ligament. The insufficiency of ACL was categorized into three groups according to the KT-2000 measurements. The statistic correlations between the grades of the MR findings and the degrees of ACL insufficiency were analyzed using the Cochran-Mantel-Haenszel test (p < 0.05).

Results: The p-values for each category of the MR findings according to the different groups of the KT-2000 measurements were 0.9180 for the MR signal intensity, 1.0000 for sharpness, 0.5038 for straightness and 0.2950 for thickness of the ACL. The MR findings were not significantly different between the different KT-2000 groups.

Conclusion: MR imaging itself is not a reliable examination to predict stability of the ACL rupture outcome, even when the MR images show an intact appearance of the ACL.

Fig. 1

A 25-year-old man with a completely healed anterior cruciate ligament that was confirmed by arthroscopy. A, B. Oblique sagittal (A) and coronal (B) proton density-weighted images obtained on the day of the knee trauma show complete tear at the proximal anterior cruciate ligament and associated fracture at the lateral tibial plateau. C, D. Follow up oblique sagittal (C) and coronal (D) images after four-months reveal a nearly normal-looking anterior cruciate ligament. The anterior cruciate ligament appears to show a low signal intensityspotted with a high signal intensity, a sharp contour, a straight course and a normal thickness. Arthroscopy performed 2-months later, due to contracture of the knee joint by the hypertrophy of ligamentum mucosum, demonstrated a normal appearance with normal tension of the anterior cruciate ligament. The side-toside difference of the KT-2000 measurement was 3 mm at the time of arthroscopy.

Fig. 2

A 54-year-old man with partial tear of anterior cruciate ligament that was confirmed by arthroscopy. A, B. Sagittal (A) and oblique coronal (B) proton density-weighted images 15 days after the trauma show complete tear at the proximal anterior cruciate ligament and marrow contusion at the posterior aspect of the proximal tibia. C, D. Four-months later, the sagittal (C) and oblique coronal (D) images demonstrate restored continuity of anterior cruciate ligament, which shows a band-like high signal intensity within the ligament, a partly obscure contour, mild sagging and an increased thickness. Partial tear of the anterior cruciate ligament was confirmed during arthroscopy 5-months later. The side-to-side difference of the KT-2000 measurement was 5 mm at the time of arthroscopy.