11 Moreover, a meniscal tear is the only demonstrated predisposing factor to meniscal extrusion in non-arthritic knees.12, 14, 15 In fact, there is a high prevalence of meniscal root tears in patients with meniscal extrusion. However, it has recently been demonstrated that meniscal extrusion is much more common in non-OA knees than had been thought previously. Osteoarthritic (OA) knees are known to present a high incidence of meniscal extrusion. Little has been reported about the incidence and predisposing factors relative to meniscal extrusion. 12 considered 3 mm as the physiological limit of meniscal subluxation and it is only beyond this limit that the meniscus is considered extruded. 14 considered meniscal extrusion minor when the meniscus is extruded ≤ 3 mm and major when the meniscus is extruded >3 mm. Several studies used 3 millimeters as a threshold value for meniscal extrusion. 7 This condition has been found to be associated with joint space narrowing,8, 9 osteophyte formation, 10 the presence of chondral lesions11, 12 and meniscal tears.12, 13, 14 There is no agreement with respect to the amount of meniscal subluxation that can be considered physiological. This might imitate the effect of a meniscectomy, which alters the physical behaviour of the knee joint. 6 In this scenario, the meniscus does not adequately absorb the load applied to the tibial cartilage. 6 It has been suggested that if the meniscus is extruded beyond the edge of the tibial plateau, leaving the articular surface of the tibia uncovered, it will not fulfill all its functions.
5 When the meniscus is partially or totally displaced beyond the tibial margin, it is defined as meniscal extrusion. It plays a crucial role in sharing the force load by increasing the contact surface area and providing uniform distribution of weight bearing across the articular surfaces.4, 5 Damage or loss of the meniscus alters this function by modifying the pattern of load distribution, and contributes to compartmental instability. Knee injuries are common following trauma, and such structures as ligaments and menisci can be damaged.1, 2, 3 The meniscus is an integral part of the knee biomechanics.
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