To investigate the effectiveness of MRI findings in order to evaluate lateral meniscus posterior root tear (LMPRT) in anterior cruciate ligament (ACL) injury, 231 patients who underwent primary ACL reconstruction were assessed. Though MRI findings in coronal and sagittal plane have low sensitivity, the sensitivity was increased with high specificity by evaluating the image in both planes together.
A lateral meniscus posterior root tear (LMPRT) occurs in 6~10% of anterior cruciate ligament (ACL) injuries. LMPRT causes loss of hoop function and possible osteoarthritic change, so an accurate preoperative diagnosis for LMPRT is important. However, it is difficult to detect LMPRT using only MRI specific findings including cleft signs, truncated triangle signs, and ghost signs individually due to low sensitivity. Furthermore, it has been reported that there is a relationship between bone bruising and meniscal tears in acute ACL injury. The purpose of this study was to investigate the effectiveness of MRI findings in evaluations of LMPRT in ACL injury and the relationship between LMPRT and bone bruising.
We retrospectively assessed 231 patients who underwent primary ACL reconstruction (126 men: 105 women, age 25.1 ± 11.2), 32 of whom had complicated LMPRT, between February 2010 and June 2016. LMPRT was defined as a radial tear within 10 mm from the lateral meniscus posterior root attachment. The clinical information regarding sex, age, body mass index (BMI), time from injury to MRI, and time from MRI to surgery between LMPRT and no LMPRT groups were assessed. LMPRT was evaluated using MRI findings: the presence of cleft signs in the coronal plane, ghost signs, and truncated triangle signs in the sagittal plane and the number of bone bruises occurring in the medial or lateral condyles of the femur or the tibia. The significance level was set at p < 0.05.
There were no differences between LMPRT and no LMPRT groups in sex (18 men: 14 female, 108 men: 91 female, p = 0.835), BMI (23.5 ± 3.8 kg/ m2, 23.0 ± 3.3 kg/ m2, p = 0.476), the time from injury to MRI (52 ± 54 day, 66 ± 63 day, p = 0.214), and the time from MRI to surgery (11 ± 16 day, 19 ± 29 day, p = 0.195); on the other hand, there were significant differences between the two groups in age (22.1 ± 10.3, 25.6 ± 11.3, p < 0.05) and the number of bone bruises (2.5 ± 1.1, 1.4 ± 1.2, p < 0.01). The sensitivities of cleft sign, ghost sign, and truncated triangle sign were 65.6, 34.4 and 59.4%, and the specificities were 95.5, 97.0 and 94.0%, respectively. However, sensitivity and specificity when at least one of the three specific signs were positive were 84.4 and 90.5%, respectively.
In the LMPRT group, there was a tendency towards younger age and increased bone bruising. When there is a large number of bone bruises, it is important to assess LMPRT. Though the specificity of cleft signs, ghost signs, and truncated triangle signs in MRI findings of LMPRT were high, the sensitivity was low. However, sensitivity and specificity were both high when at least one of the three specific signs was positive. Therefore, it is important to evaluate MRI findings in both the coronal and sagittal plane in order to assess LMPRT in ACL injury.