Medial meniscal root tears and meniscal extrusion transverse length ratios on MRI

Abstract

Objective: To evaluate the clinical utility of the meniscal extrusion transverse ratio of the medial meniscus in the diagnosis of meniscal root tear compared with the gold standard of arthroscopic diagnosis.

Methods: This retrospective study sample included 32 males and 35 females who underwent MRI at our institution. There were 24 meniscal root tear cases. The control groups were 18 cases of medial meniscal tears without root tears and 25 cases of negative meniscal findings on arthroscopy. Meniscal extrusion (L) and maximal transverse lengths (T) of the medial meniscus were measured, and L/T ratios were calculated. These results were correlated with arthroscopic findings and analysed statistically. With arthroscopic findings used as the standard of reference, the sensitivity and specificity of 10%, 11% and 12% extrusion thresholds, and 3 mm of medial meniscal extrusion (MME) as diagnostic thresholds, were calculated.

Results: The mean length of the meniscal extrusions of meniscal root tears was twice as long as the control group. The mean L/T ratio of the meniscal root tears was approximately 13%, while those of the control groups were 5%. The differences in the L and L/T between the meniscal root tears and normal and meniscal root tears and other meniscal tears were statistically significant (p<0.001), but those between normal and other meniscal tears were not. The best diagnostic discrimination was achieved using an extrusion ratio threshold of 10% (79% sensitivity, 86% specificity). The 3 mm of MME threshold demonstrated high specificity (98%), but not high sensitivity (54%).

Conclusion: The mean L/T ratio of the meniscal root tears was approximately 13% and was statistically significant. The best diagnostic discrimination was achieved using an extrusion ratio threshold of 10%. Advances in knowledge The use of the L/T ratio in combination with MME can be a useful method for evaluating medial meniscal root tears.

Figures

Figure 1

Schematic showing medial meniscal extrusion. Meniscal extrusion is measured by the distance from the perpendicular line to the edge of the tibial plateau and the outer edge of the meniscus (at the point of the mid-portion of its maximal thickness).

Figure 2

Schematic demonstrating the maximal transverse length of the medial meniscus.

Figure 3

A 25-year-old male with knee pain. (a) Proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) of the knee at the mid-point demonstrates no definite extrusion of the medial meniscus. A medial collateral ligament tear is seen. (b) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) 15 mm behind (a) shows a 26.2 mm transverse meniscus length. The meniscal extrusion transverse ratio was 0. An intact medial meniscus was confirmed arthroscopically.

Figure 4

A 59-year-old male with knee joint swelling. (a) Proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) of the knee at the mid-point shows extrusion of the medial meniscus with a distance of 4.39 mm. (b) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) 15 mm behind (a) shows a 27.7 mm transverse meniscus length. The meniscal extrusion transverse ratio was 0.16. Complete disruption of the medial meniscal root is seen. (c) Fat-saturated proton density imaging (repetition time, 3000 ms; echo time, 36 ms) reveals a definite tear of the posterior root of the medial meniscus. The posterior root tear was confirmed arthroscopically.

Figure 5

A 35-year-old female with knee joint pain. (a) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) of the knee at the mid-point shows extrusion of the medial meniscus with a distance of 2.83 mm. (b) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) 15 mm behind (a) shows a 22.9 mm transverse meniscus length. The meniscal extrusion transverse ratio was 0.12. (c) Arthroscopic imaging demonstrates a retracted and avulsed tear of the posterior root of the medial meniscus.

Figure 6

A 55-year-old female with knee joint pain. (a) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) of the knee at the mid-point shows extrusion of the medial meniscus with a distance of 2.19 mm. (b) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) 15 mm behind (a) shows a 24.5 mm transverse meniscus length. The meniscal extrusion transverse ratio was 0.09. A small radial tear of the posterior horn of the medial meniscus was seen on arthroscopy but a root tear was not observed.

Figure 7

A 42-year-old female with knee joint pain lasting for 3 months. (a) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) of the knee at the mid-point shows extrusion of the medial meniscus with a distance of 2.50 mm. (b) A proton density coronal image (repetition time, 3000 ms; echo time, 35 ms) 15 mm behind (a) shows a 23.3 mm transverse meniscus length. The meniscal extrusion transverse ratio was 0.11. A posterior root tear of the medial meniscus was diagnosed on arthroscopy.