Quantitative Magnetic Resonance Imaging UTE-T2* Mapping of Cartilage and Meniscus Healing After Anatomic Anterior Cruciate Ligament Reconstruction

Abstract

Background: An anterior cruciate ligament (ACL) injury greatly increases the risk for premature knee osteoarthritis (OA). Improved diagnosis and staging of early disease are needed to develop strategies to delay or prevent disabling OA.

Purpose: Novel magnetic resonance imaging (MRI) ultrashort echo time (UTE)-T2(*) mapping was evaluated against clinical metrics of cartilage health in cross-sectional and longitudinal studies of human participants before and after ACL reconstruction (ACLR) to show reversible deep subsurface cartilage and meniscus matrix changes.

Study design: Cohort study (diagnosis/prognosis); Level of evidence, 2.

Methods: Forty-two participants (31 undergoing anatomic ACLR; 11 uninjured) underwent 3-T MRI inclusive of a sequence capturing short and ultrashort T2 signals. An arthroscopic examination of the medial meniscus was performed, and modified Outerbridge grades were assigned to the central and posterior medial femoral condyle (cMFC and pMFC, respectively) of ACL-reconstructed patients. Two years after ACLR, 16 patients underwent the same 3-T MRI. UTE-T2(*) maps were generated for the posterior medial meniscus (pMM), cMFC, pMFC, and medial tibial plateau (MTP). Cross-sectional evaluations of UTE-T2(*) and arthroscopic data along with longitudinal analyses of UTE-T2(*) changes were performed.

Results: Arthroscopic grades showed that 74% (23/31) of ACL-reconstructed patients had intact cMFC cartilage (Outerbridge grade 0 and 1) and that 90% (28/31) were Outerbridge grade 0 to 2. UTE-T2(*) values in deep cMFC and pMFC cartilage varied significantly with injury status and arthroscopic grade (Outerbridge grade 0-2: n = 39; P = .03 and .04, respectively). Pairwise comparisons showed UTE-T2(*) differences between uninjured controls (n = 11) and patients with arthroscopic Outerbridge grade 0 for the cMFC (n = 12; P = .01) and arthroscopic Outerbridge grade 1 for the pMFC (n = 11; P = .01) only and not individually between arthroscopic Outerbridge grade 0, 1, and 2 of ACL-reconstructed patients (P > .05). Before ACLR, UTE-T2(*) values of deep cMFC and pMFC cartilage of ACL-reconstructed patients were a respective 43% and 46% higher than those of uninjured controls (14.1 ± 5.5 vs 9.9 ± 2.3 milliseconds [cMFC] and 17.4 ± 7.0 vs 11.9 ± 2.4 milliseconds [pMFC], respectively; P = .02 for both). In longitudinal analyses, preoperative elevations in UTE-T2(*) values in deep pMFC cartilage and the pMM in those with clinically intact menisci decreased to levels similar to those in uninjured controls (P = .02 and .005, respectively), suggestive of healing. No decrease in UTE-T2(*) values for the MFC and new elevation in UTE-T2(*) values for the submeniscus MTP were observed in those with meniscus tears.

Conclusion: This study shows that novel UTE-T2(*) mapping demonstrates changes in cartilage deep tissue health according to joint injury status as well as a potential for articular cartilage and menisci to heal deep tissue injuries. Further clinical studies of UTE-T2(*) mapping are needed to determine if it can be used to identify joints at risk for rapid degeneration and to monitor effects of new treatments to delay or prevent the development of OA.

Keywords: ACL reconstruction; MRI; UTE-T2*; anterior cruciate ligament tear; articular cartilage; joint injury; mapping; osteoarthritis; posttraumatic OA; quantitative MRI.

Figure 1

Five regions of interest were evaluated in this work (white outlines). The central and posterior medial femoral condyle (cMFC and pMFC, respectively), central and posterior (submeniscus) medial tibial plateau (cMTP and pMTP, respectively), and posterior medial meniscus (pMM). Zonal cartilage differences were assessed by further segmenting cartilage regions of interest into superficial and deep halves.

Figure 2

Ultrashort echo time (UTE)–T2* in deep articular cartilage varies with the degree of arthroscopic softening among participants with intact articular surfaces (Kruskal-Wallis test, P = .01). (A) Arthroscopic image of the medial femoral condyle (MFC) of an anterior cruciate ligament (ACL)–reconstructed patient with firm and intact cartilage (Outerbridge grade 0). (B) The MFC of an ACL-reconstructed patient with intact and softened cartilage (Outerbridge grade 1). (C) ACL-reconstructed patients with intact and firm cartilage (grade 0) demonstrate significantly higher UTE-T2* values in deep central MFC cartilage (P = .01) compared with uninjured controls. In the posterior MFC, deep cartilage of ACL-reconstructed patients with softened but intact cartilage (grade 1) is significantly elevated compared with that of uninjured controls (P = .01). Error bars indicate standard error of the mean.

Figure 3

Example ultrashort echo time (UTE)–T2* maps from (A) an uninjured control participant, (B) an anterior cruciate ligament (ACL)–reconstructed patient before surgery, and (C) the same patient 2 years after ACL reconstruction (ACLR). (D) UTE-T2* mapping suggests that injuries to deep cartilage and menisci of ACL-injured patients resolve over 2 years after ACLR. Before surgery, ACL-reconstructed patients demonstrated significantly elevated UTE-T2* values in the deep central medial femoral condyle (cMFC) and deep posterior MFC (pMFC) (P = .007 and .003, respectively) compared with uninjured controls. Two years after ACLR, UTE-T2* values decreased to levels consistent with those of asymptomatic controls in all compartments. UTE-T2* values for the deep cMFC and pMFC fell a respective 29% and 24% (P = .02 for both). Error bars indicate standard error of the mean. *P <.05. **P <.01.

Figure 4

Change in ultrashort echo time (UTE)–T2* values of articular cartilage at 2 years after anterior cruciate ligament reconstruction (ACLR) varied based on meniscus status at the time of surgery. (A) Mean UTE-T2* values decreased 29% for deep posterior medial femoral condyle (pMFC) cartilage (P = .01) and showed a trend toward a decrease for deep central MFC (cMFC) cartilage (P = .07) 2 years after ACLR in joints with intact medial menisci (n = 11). (B) In ACL-reconstructed joints with torn medial menisci, no significant change in the mean UTE-T2* value of the MFC was detected (n = 5; P = .14 and .5 for deep cMFC and deep pMFC, respectively). Error bars indicate standard error of the mean. *P <.05. †Denotes a trend.

Figure 5

Example ultrashort echo time (UTE)–T2* maps of the posterior medial menisci from (A) an uninjured control participant, (B) an anterior cruciate ligament (ACL)–reconstructed patient with an intact medial meniscus before surgery, and (C) the same patient 2 years after ACL reconstruction (ACLR). (D) UTE-T2* mapping demonstrates subsurface meniscus matrix changes in intact menisci of patients with ACL injuries. Before ACLR, UTE-T2* values in intact medial menisci of ACL-injured patients were 27% higher than those seen in uninjured controls (P = .02). Over 2 years after joint stabilization surgery, UTE-T2* values in intact menisci of ACL-reconstructed joints fell 17% (P = .03) to levels that did not differ from those of asymptomatic controls (P = .7). As expected, UTE-T2* values in torn menisci before surgery were significantly higher (95%) than those of uninjured controls (P <.0001). Two years after joint stabilization surgery, UTE-T2* values in torn menisci of ACL-reconstructed patients continued to demonstrate significant elevations compared with those in both asymptomatic controls (P = .02) and also intact menisci of ACL-reconstructed joints (P = .05). Error bars indicate standard error of the mean. *P <.05. **P <.01.