Traumatic Onset of Medial Meniscus Posterior Root Tears Is Associated With Younger Age While Insidious Onset Is Associated With Chronic Overload and Bone Bruising

Abstract

Purpose: To evaluate clinical and radiographic findings for medial meniscus posterior root tears (MMPRTs) and investigate their associations with traumatic and insidious etiologies.

Methods: Patients who underwent arthroscopic isolated MMPRT repair by one fellowship-trained surgeon from 2019 to 2023 were retrospectively identified. Clinical variables included history of present illness (HPI), medical history, and physical examination findings. Radiographic variables included Kellgren-Lawrence grade, bone bruise, ghost sign, truncation sign, linear hyperintensity perpendicular to the meniscus, meniscal extrusion, tibial slope, and mechanical axis. Patients were stratified by inciting event versus insidious onset for subgroup analysis.

Results: Of 72 patients (mean age 56.7 ± 8.9 years, mean BMI 32.3 ± 5.7 k/m²), recollection of an inciting event was reported in 45.8% of patients. The most prevalent findings in the HPI were knee swelling (72.2%) followed by mechanical symptoms (62.5%) and episodes of perceived instability (45.8%), whereas medial joint line tenderness (93.1%) and a positive McMurray's test (69.4%) were commonly observed on physical examination. On MRI, ghost sign was identified in 91.7% of cases followed by truncation sign (83.3%) and a linear signal perpendicular to the meniscus (68.1%). The average measured meniscal extrusion was 4.18 ± 1.09 mm. Cases with an inciting event were more likely to be younger (P = .021), present acutely (P = .039), and have a positive McMurray test (P = .036). Cases with an insidious presentation were found to have higher rates of bone bruising at the medial femoral condyle (P = .016) and medial plateau (P = 0.029).

Conclusions: Patients with MMPRT associated with an inciting event are typically younger and more likely to present acutely, with a positive McMurray's test. Conversely, patients with insidious presentation are older, present chronically, and exhibit higher rates of bone bruising, particularly when there is varus malalignment.

Level of evidence: Level IV, prognostic case series.

Fig. 1

Magnetic resonance imaging findings for medial meniscus posterior root tears. (A) Ghost sign on sagittal T2 sequence, when the slice plane is in line with the meniscal tear close to the root, generating the partial or complete signal loss of the triangular shape of the posterior horn (dotted white line). (B) Truncation sign or (cleft sign) when there is a vertical linear high-intensity signal close to the root on T2 sequence. (C) Radial tear in close proximity (<1 cm) to the root attachment on axial T2 view. (D) Bone marrow edema or “bone bruising” on the medial femoral condyle (∗).

Fig 2

Meniscal extrusion measurement on magnetic resonance imaging. The coronal T2 slice plane at the mid-point of the medial femoral condyle is located; the meniscal extrusion is quantified by the horizontal distance from the margin of the medial tibial plateau to the peripheral margin of the medial meniscus, in millimeters. ∗, subchondral bone bruising on the medial tibial plateau.

Fig 3

Tibial slope measurement on magnetic resonance imaging. (A) Sagittal T2 slice representing the central sagittal image identified by the posterior cruciate ligament, intercondylar eminence, and the anterior/posterior tibial cortices. The longitudinal axis traverses through the center of the 2 circles positioned at the tibial head. (B) The slope of the medial plateau represented by the angle between the line tangent to the medial tibial plateau and the line perpendicular to the longitudinal axis as proposed by Hudek et al.