Isolated meniscus extrusion associated with meniscotibial ligament abnormality

Purpose: The purpose of this study was to describe meniscus extrusion, present imaging characteristics, and provide clinical correlations for patients with isolated meniscus extrusion. Methods: Of the 3244 MRI reports identified as having meniscus extrusion, 20 patients were identified to have isolated meniscus extrusion (0.62%). Patients with moderate to severe chondromalacia, meniscus tears, intra-articular fractures, tumours, and ligament tears were excluded. Radiographs were reviewed and graded using Kellgren–Lawrence (K–L) scores. MRI’s were reviewed for the extent of extrusion and whether or not the meniscotibial ligament was intact. Clinical presentation and management were recorded. Results: The study population consisted of 12 females and 8 males with a mean age of 40.5, diagnosed with meniscus extrusion and minimal concomitant knee pathology. 68% of patients were considered symptomatic as their knee pain correlated with the side of their meniscus extrusion and no other reason for pain was identified. The mean amount of meniscus extrusion was 2.5 mm (SD ± 1.1 mm) with 45% (9 of 20) having 3 + mm of extrusion. Meniscotibial ligament abnormality was identified in 65% of cases (13 of 20). Patients with 3 + mm of meniscus extrusion were much more likely to have associated meniscotibial ligament abnormality (100%, 9 of 9) compared to those with < 3 mm of extrusion (36%, 4 of 11) (RR 2.75, p = 0.048). The mean K–L grade obtained at the initial visit was 0.9 (95% CI 0.7–1.4) and the mean K–L grade obtained on final follow-up was 1.3 (95% CI 0.8–2.8) (n.s.) at a mean of 44.7 months. No correlation was found between K–L grade, gender, age, acute injury, and BMI in relation to meniscotibial ligament abnormality or amount of meniscal extrusion. Conclusions: Meniscus extrusion often occurs in the presence of significant knee pathology, predominantly with meniscus tears or osteoarthritis. Isolated meniscus extrusion is a rare occurrence that may present clinically with knee pain, commonly to the side in which the extrusion occurs. In patients with three or more millimetres of meniscus extrusion, an intact meniscus and minimal knee pathology, meniscotibial ligament abnormality is likely. This may provide an opportunity to treat the meniscotibial ligament abnormality with meniscus centralisation technique and decrease the amount of meniscus extrusion.