Posterior horn medial meniscal root tear: the prequel.

Objective: To determine whether subarticular marrow changes deep to the posterior horn medial meniscal root anchor might predict subsequent medial meniscal root tear.
Materials and Methods: Fifteen patients with MR-diagnosed posterior horn medial meniscal root (PHMMR) tear and a knee MRI antecedent to the tear were identified at three imaging centers over a 7-year period. The pre- and post-tear MR images were evaluated for marrow signal changes deep to the root anchor, meniscal root signal intensity, medial compartment articular cartilage thinning, and meniscal body extrusion. Images of 29 age- and gender-matched individuals with two MRIs of the same knee were reviewed as a control group.
Results: MRI in 11 of 15 (73%) cases with subsequent PHMMR tear demonstrated linear subcortical marrow edema deep to the meniscal root anchor on the antecedent MRI compared to only 1 of 29 (3%) non-tear controls (p < 0.0001). The abnormal signal resolved on post-tear MRI in all but two patients. Cyst-like changes deep to the PHMMR were present on initial MRI in three of 15 (23%) cases and three of 29 (10%) controls, persisting in all but one case on follow-up imaging. The PHMMR was gray on the initial MRI in seven of 15 (47%) of cases that developed tears compared to four of 29 (14%) controls (p < 0.0001). There was medial meniscal extrusion (MME) prior to tear in two of 15 (13%) patients and in ten of 15 (67%) patients after PHMMR failure. In the control group, MME was present in one (3%) and three (10%) of 29 subjects on the initial and follow-up MRIs, respectively. Articular cartilage loss was noted in two of 15 (15%) cases before tear and nine of 15 (69%) on follow-up imaging, as compared to one (3%) and four (14%) of 29 subjects in the control group.
Conclusions: Subcortical marrow edema deep to the PHMMR may result from abnormal stresses and thus be a harbinger of meniscal root failure. This hypothesis is supported by resolution of these marrow signal changes after root tear. Following tear, extrusion of the meniscal body results in increased stress on the medial weight-bearing surfaces often leading to articular cartilage loss; we observed this sequence in six of our 15 patients with PHMMR tears.