Quantitative mapping of acute and chronic PCL pathology with 3 T MRI: a prospectively enrolled patient cohort

Abstract

Background: The diagnosis of incomplete acute and chronic posterior cruciate ligament (PCL) tears can be challenging with conventional magnetic resonance (MR) imaging, particularly for injuries in which the ligament appears continuous as occurs with chronic PCL tears that have scarred in continuity. Quantitative mapping from MR imaging may provide additional useful diagnostic information in these cases. The purpose of this study was to assess the feasibility of quantifying transverse relaxation time (T2) mapping values at 3 Tesla (T) in a prospectively enrolled patient cohort with chronic PCL tears.

Methods: Twelve subjects with acute or chronic functionally torn PCL, confirmed on clinical exam and posterior knee stress radiographs (with 8 mm or more of increased posterior tibial translation), were enrolled prospectively over a span of 4 years (age: 28-52 years, injury occurred 2 weeks to 15 years prior). Unilateral knee MR images were acquired at 3 T, including a multi-echo spin-echo T2 mapping scan in the sagittal plane. For the six subjects with a continuous PCL on MR imaging the PCL was manually segmented and divided into proximal, mid and distal thirds. Summary statistics for T2 values in each third of the ligament were compiled.

Results: Across the six patient subjects with a continuous ligament, the mean T2 for the entire PCL was 36 ± 9 ms, with the highest T2 values found in the proximal third (proximal: 41 ms, mid 30 ms, distal 37 ms). The T2 values for the entire PCL and for the proximal third subregion were higher than those recently published for asymptomatic volunteers (entire posterior cruciate ligament: 31 ± 5 ms, proximal: 30 ms, mid: 29 ms, distal: 37 ms) with similar methodology.

Conclusion: Mean T2 values were quantified for acute and chronic PCL tears in this prospectively enrolled patient cohort and were higher than those reported for asymptomatic volunteers. This novel approach of using quantitative mapping to highlight injured areas of the posterior cruciate ligament has potential to provide additional diagnostic information in the challenging case of a suspected posterior cruciate ligament tear which appears continuous, including chronic tears that have scarred in continuity and may appear intact on conventional magnetic resonance imaging.

Keywords: Knee; Magnetic resonance imaging; Posterior cruciate ligament; T2 mapping.

Fig. 1

Example images from two subjects with complete PCL tears. Subject A had a chronic injury in which the PCL was detached from the femoral attachment (white arrow). Subject B had a chronic injury in which the PCL was partially torn at its tibial attachment (black arrow). Images shown are from three consecutive slices of i) a PD FS TSE sequence (sagittal plane; TR/TE: 5300/40 ms; interpolated resolution: 0.19 × 0.19 mm; slice thickness: 3.0 mm; FOV: 120 mm; TA: 2 min 50 s) and ii) a PD TSE sequence (sagittal plane; TR/TE: 2500/32 ms; interpolated resolution: 0.16 × 0.16 mm; slice thickness: 3.0 mm; FOV: 125 mm; TA: 3 min 19 s)

Fig. 2

Example MR images in the six individual patients with PCL insufficiency showing a continuous ligament. Images show the closest sagittal slice through the middle of the injured PCL for each of the following sequences: PD FS TSE, PD TSE and color-mapped T2 mapping image

Fig. 3

Example images of subject 2 showing three consecutive slices of the PCL from four MR imaging sequences, including i) PD TSE sagittal, ii) PD FS TSE sagittal, iii) PD FS TSE axial, iv) PD FS TSE coronal. This subject was a 28-year old male with a chronic PCL injury from a fall. On original imaging evaluation the radiologist noted minimal focal increased signal within the mid PCL substance likely indicative of mild scarring and/or degeneration. However, a secondary review of the images identified some irregularity in the proximal region of the PCL (white arrows)