**1. Introduction**

Meniscus is a fibrocartilaginous structure which provides many functions to the knee joint such as distributing load to the knee, increased stability of the tibiofemoral articulation, lubrication, provides nutrient and a strong shock absorption. Without the meniscus, load to the articular cartilage will increase and progress to osteoarthritis. Meniscus root tear is one of the tear patterns which are increasingly important due to an increasing number of patients and the rapid progression of the osteoarthritis similar to total meniscectomy [1]. Hence, early detection and treatment may improve outcome of the patient.

#### **1.1 Definition**

The bone which avulsed from the attachment at tibial plateau which represent meniscus root tear, was first described in 1935 by Weaver by plain radiograph [2]. However, ligament or soft-tissue injury at the insertion site of meniscal root on tibial plateau was described later after the use of magnetic resonance imaging (MRI). In 1991, Pagnani reported a medial subluxation of the meniscus associated with an avulsion injury to the posterior horn medial meniscus in an athlete [3]. The modern

definition commonly used for "meniscus root tear" is defined as avulsion of the meniscal attachments to the tibia or radial tears within 1 cm from the bony insertion [4].

### **1.2 Epidemiology**

In the past, medial meniscus root tear has been neglected due to difficulties in diagnosis. The prevalence might be lower than it should be. With increasing recognition of the medial meniscus root tear, the prevalence is higher. In a study by Matheny et al., in 673 arthroscopic surgeries, they found 50 patients with meniscus root tear equivalent to 7% [5]. Another study by Ozkoc et al. found that prevalence of radial tear of the posterior horn of the medial meniscus in 7,148 patients who underwent partial menisectomy of the knee was about 10% (722 patients) [6]. The prevalence may be up to 15% in Asia which is a more common injury [7]. In case of traumatic knees, a study by Ho Jong Ra found 7 medial meniscus posterior root tear out of 51 patients who had multiple ligaments knee injury [8]. Most of the medial meniscus root tear were degenerative change. However, traumatic tear of the medial meniscus root is also common. The incidence of medial meniscus posterior root tear was up to 78% in patient underwent total knee arthroplasty. In addition, severity and varus deformity correlated with the root tear [9].

## **1.3 Natural history**

As we know meniscus is a strong shock absorber. Without meniscal root attachment, hoop stress is lost and can lead to rapid progression of osteoarthritis [10]. Five-year follow up study of non-operative treatment in 52 patients with posterior meniscus root tear revealed association with low functional outcome and 31% of the patients need conversion to total knee arthroplasty [11]. In case of partial meniscectomy of the meniscus, long term follow up (5-8 years) also showed osteoarthritis progression about one-third of the patients [7]. The meniscus extrusion in a sign that showed impairment of the meniscus function and the degree of extrusion might be associated with severity of osteoarthritis [9, 12]. The longer the symptom, the degree of extrusion might be worse. According to a study by Furumatsu et al., in early period (<1 month) mean extrusion was 3.0 mm. In subacute (1-3 months) and chronic (3-12 months), the mean extrusion was 4.2 and 5.8 mm respectively [13]. The increasing rate of meniscus extrusion was studied by okazaki et al. which reviewed MRI of 33 patients who were diagnosed with medial meniscus posterior root tear and had done MRI twice at a mean interval of 48 days, the mean extrusion increased from 3.4 mm to 4.5 mm. The progression of the extrusion rate was 0.02 mm per day [14]. There is also an association between the presence of medial meniscus root tears and articular cartilage damage of the knee with an Outerbridge grade 2 or greater changes. Patients with a medial root tear were approximately five times more likely to also have an articular cartilage defect of the knee with an Outerbridge grade 2 score or higher [5]. In addition, osteonecrosis, bone contusion, and subchondral insufficiency fracture are commonly associated with the medial meniscus root tear [10, 15].

#### **1.4 Biomechanics**

As mentioned above, the complete medial meniscus posterior root tear had similar biomechanics with total meniscectomy due to impairment of hoop stress function of the meniscus (**Figure 1**). Normal load to the meniscus is about 50% of body weight and the other 50% transfers directly to the articular cartilage [16]. *Medial Meniscus Root Tear: Current Update Review DOI: http://dx.doi.org/10.5772/intechopen.98763*

**Figure 1.**

*Hoop stress function of meniscus. (A) Normal load distribution of meniscus with intact meniscal root. (B) With meniscal root tear, load is directly transferred to the articular cartilage.*

**Figure 2.**

*Fairbank phenomenon after meniscectomy. Finding included narrowing of joint space, squaring of femoral condyle and antero-posterior osteophyte.*

The body and posterior horn of the medial meniscus take most of the force applied to the medial compartment and are the least mobile parts. With knee flexion, the pressure to the posterior horn of meniscus is the highest this is due to the femoral roll back mechanism of the knee. That explains why posterior horn and posterior root injuries have been found to be more common compared to the anterior horn injury [17]. In case of torn medial meniscus posterior root or total menisectomy, the peak pressure to the medial articular cartilage increased 25% [1, 18]. Hence, this may lead to osteoarthritis change which was called "Fairbank's phenomenon" [19] (**Figure 2**). The biomechanics test of medial meniscus posterior root repair can restore the tibiofemoral contact pressure compared with intact meniscus knee [20, 21].
