Discoid Lateral Meniscus Tear And Concomitant Articular Cartilage Lesions In The Knee

BackgroundMeniscus tear is one of the most common athletic injuries in the knee. In western countries, medial meniscus tears are more common than lateral meniscus tears. But, lateral meniscus tears are more frequent than medial meniscus tears in China. One reason may be that discoid lateral meniscus is frequent in China. Meniscus tears may lead to articular cartilage lesions. Articular cartilage is hyaline cartilage, and is very difficult to repair when damaged. Articular cartilage repair is still a tough medical problem now. When lateral meniscus was torn, cartilage was easy to be damaged if one didn’t receive treatment in time. There are no reports about the relationship between the time course after lateral meniscus tear and articular cartilage lesions now.Discoid meniscus is very common in arthroscopic surgery of lateral meniscus. Discoid meniscus is an abnormal morphology of the meniscus. Because of the hypertrophic body, it looks like a discoid, and is called discoid meniscus. The etiology of discoid meniscus is still controversial. Discoid meniscus occurs more often in the lateral meniscus than in the medial meniscus. The incidence of discoid meniscus is about 16.6% in Japanese populations and 10.9% in Korean populations, but is quite low in Caucasians populations (0.4%-5%). The basic number of Chinese population is very large, so the number of patients with discoid meniscus is also very large.Discoid lateral meniscus covers most or the entire lateral tibial plateau compared with normal lateral meniscus, which changes the transmission of the mechanical stress force in the knee. Recent studies have also demonstrated a decrease in the number of collagen fibers and discontinuity and inhomogeneity of the circumferential collagen network in the discoid meniscus in comparison with the normal meniscus. So, discoid lateral meniscus is more vulnerable to injury and very frequent in knee injuries. When meniscus is torn, it loses the normal function. Articular cartilage may be vulnerable and degeneration may be unavoidable without normal meniscal protection. When discoid lateral meniscus was torn, arthroscopic meniscal plastic operation, partial meniscectomy, subtotal meniscectomy or total meniscectomy was done according to the degree of tears. Many studies have reported a high incidence of radiographic knee osteoarthritis after total meniscectomy and lateral meniscectomy is a more risky procedure than medial meniscectomy. The etiology of OA is not clear until now. In peoples more than 60 years old, more than 50% of them show OA in the radiologic image. The knee will be diastrophic in the late stage knee OA, and people will lose the locomotor activity. Knee OA is very harmful to the health and quality of life.PurposeThis study examined the characteristics of isolated discoid lateral meniscus (DLM) tears and concomitant articular cartilage lesions in the knee. The associations between the DLM tears and the presence of articular cartilage lesions were also investigated. This will provide important information for the diagnosis, making a reasonable treatment protocol, operation and evaluating prognosis of lateral meniscus tears or DLM.MethodsPart I:The relationship between time course after lateral meniscus tear and articular cartilage lesionsAll the patients diagnosed as lateral meniscus tears were enrolled in this study from January 2010 to September 2011. According to patient’s ID, we logged in the "doctor station", and get the electronic medical record (EMR). From the EMR, the time course was recorded (the time from the onset of symptoms to arthroscopic surgery). They were divided into three groups:acute phase (<2 months), subacute phase (2-12 months), chronic phase (> 12 months). The grade of cartilage lesions and location of cartilage lesions were gained from the arthroscopic surgery records. Then the relationship between time course and articular cartilage lesions were investigated.Part II:The characteristics of discoid meniscus tears and articular cartilage lesions in the knee of 252 patientsFrom January 2010 to December 2011,252 consecutive patients diagnosed with an isolated DLM tear under an arthroscopic procedure in our center were enrolled in this study. According to patient’s ID, we logged in the "doctor station", and get the electronic medical record (EMR). From the EMR, demographic variables, including gender, age, body mass index (BMI), traumatic history, time course, and date of the DLM tear, were recorded. The type of discoid lateral meniscus(complete or incomplete), type of tears, locations of tears, grade of cartilage lesions and location of cartilage lesions were gained from the arthroscopic surgery records, and the above information were confirmed through the photos taken by the arthroscope.Outcome measures:1) the basic information of all patients; 2) the proportion of patients with different type of DLM tears; 3) the location of DLM tears; 4) the basic characteristics of cartilage lesions; 5) the characteristics of cartilage lesions in different locations; 6) the characteristics of cartilage lesions in patients with different type of DLM tear.Part Ⅲ:The relationship between discoid lateral meniscus tear and articular cartilage lesionsFrom the study of Part II, we could get the basic information of all patients including gender, age, BMI, traumatic history, time course and type of discoid lateral meniscus. The characteristics of DLM tears and articular cartilage lesions were also used in this part, which including the type of DLM tear, the location of DLM tear, the location of cartilage lesions, the grade of cartilage lesions and so on.Outcome Measures:1) the incidence of cartilage lesions in patients with different types of DLM tear; 2) the incidence of grade Ⅲ and grade IV cartilage lesions in different locations; 3) the incidence of grade Ⅲ and grade Ⅳ cartilage lesions in patients with different types of DLM tear; 4) Gender, age, body mass index (BMI), trauma history, time course, DLM type (complete or incomplete), and DLM tear types were analyzed as potential prognostic variables for the presence of articular cartilage lesions. The relationship between the above variables and the presence of articular cartilage lesions was investigated.ResultsPart Ⅰ:The relationship between time course after lateral meniscus tear and articular cartilage lesions1. One hundred and twenty-nine (34.3%) patients had articular cartilage lesions. Of these patients,5.43% were identified to have grade I cartilage lesions,32.56% were grade II, 45.73% were grade Ⅲ, and 16.28% were grade IV.2. The mean time course of patients with cartilage lesions was longer than that of patients without cartilage lesions (P<0.05).3. The incidence of cartilage lesions was 23.64% in patients of acute phase. The incidence of cartilage lesions was 23.64% and 42.38% in patients of subacute phase and chronic phase, respectively. The incidence of cartilage lesion in patients of chronic phase was higher than that of acute phase and subacrute phase (P<0.05).Part Ⅱ:The characteristics of discoid meniscus tears and articular cartilage lesions in the knee of 252 patients1. Characteristics of discoid meniscus tears1.1 In patients with DLM tears, the constituent ratio of female was higher than that of male (P<0.05); the constituent ratio of patients without traumatic history was higher than that of patients with traumatic history (P<0.05); the constituent ratio of patients with complete DLM was higher than that of patients with incomplete DLM (P<0.05).1.2 There were 118 patients had complex tears (46.8%),49 patients had BH tears (19.4%),42 patietents had horizontal tears (16.7%),20patients had radial tears (8.0%),16 patients had longitudinal tears (6.3%) and 7 patients had oblique tears (2.8%). In patients with horizontal tear, the constituent ratio of patients without traumatic history was higher than that of patients with traumatic history (P<0.05); in patients with radial tear, the constituent ratio of patients with incomplete DLM was higher than that of patients with complete DLM (P<0.05)1.3 In the 118 patients with complex tears,23 had horizontal tear,15 had BH tear and 69 had horizontal tear and BH tear simultaneously. So, actually 134 patients (53.2%) had horizontal tear and 133 (52.8%) had BH tear.1.4 Of all the patients,213 (84.5%) had tears in the body of DLM,173 (68.7%) had tears in the posterior horn and 100 (39.7%) had tears in the anterior horn.2. Characteristics of articular cartilage lesions2.1 The incidence of articular cartilage lesions was 26.6% in patients with DLM tears. The cartilage lesions were accounted for 44.4% in the patellofemoral joint, and were accounted for 42.6% and 13% in lateral compartment and medial compartment, respectively.2.2 The most frequent location of cartilage lesions was lateral tibial plateau (LTP) and the percentage of grade III or grade IVcartialge lesions was 34.5%. The percentage of grade III or grade IVcartialge lesions was 58.8% in lateral femoral condyle (LFC). The percentage of grade III or grade IVcartialge lesions was 51.9% in patella (PAT). The percentage of grade Ⅲ or grade IVcartialge lesions was 61.9% in trochlea (TRO). The percentage of grade Ⅲ or grade Ⅳcartialge lesions was 61.5% in medial femoral condyle (MFC).2.3 In patients with cartilage lesions of lateral compartment,12 patients (35.3%) had kissing lesions (8 patients had bucket-handle tear), and 50% of the lesions were graded as Ⅲ or Ⅳ. In patients with cartilage lesions of patellofemoral joint,11 patients (30.6%) had kissing lesions (6 patients had bucket-handle tear), and 54.5% of the lesions were graded as Ⅲ or Ⅳ.2.4 There were 3 patients (18.75%) had cartilage lesions in patients with longitudinal tears. Fourteen (28.57%) had cartilage lesions in patients with BH tear; 5 (25%) had cartilage lesions in patients with radial tear; 3 (42.86%) had cartilage lesions in patients with oblique tear; 9 (21.43%) had cartilage lesions in patients with horizontal tear; and 33 (27.97%) had cartilage lesions in patients with complex tear.Part Ⅲ:The relationship between discoid lateral meniscus tear and articular cartilage lesions1. There was no significant difference in incidence of cartilage lesions between patients with different types of DLM tear (P> 0.05).2. There was no significant difference in proportion of grade Ⅲ and Ⅳ cartilage lesions between different locations (P> 0.05).3. There was no significant difference in proportion of grade Ⅲ and Ⅳ cartilage lesions between patients with different types of DLM tear (P> 0.05).4. After univariate logistic regression, three variables were excluded:(1) trauma history (OR= 1.047, P= 0.874); (2) DLM type (OR= 0.727, P= 0.333); and (3) DLM tear type (P= 0.874). Gender, age, BMI, and time course were possible prognostic variables for cartilage lesions (P< 0.2). After multivariate logistic regression, age (OR= 5.089, P=0.000) were still significantly associated with cartilage lesions.ConclusionsPart I:The relationship between time course after lateral meniscus tear and articular cartilage lesions1. Articular cartilage lesion was common in patients with lateral meniscus tear (34.3%). Most of the cartilage lesions were graded as Ⅲ and Ⅳ.2. The incidence of articular cartilage lesions would rise with the increased time course after lateral meniscus tears.Part Ⅱ:The characteristics of discoid meniscus tears and articular cartilage lesions in the knee of 252 patients1. In patients with DLM tears, female was more than male, patients without traumatic history was more than that with traumatic history and patients with complete DLM was more than that with incomplete DLM.2. In patients with DLM tears, the most frequent type of DLM tear was complex tear. Horizontal tear occurs more in patients without traumatic history. Radial tear occurs more in patients with incomplete DLM.3. In patients with DLM tears, the most frequent location of DLM tear was the body, then was posterior horn and anterior horn.4. The incidence of articular cartilage lesions was 26.6% in patients with DLM tears. Cartilage lesions more common occurred in the patellofemoral joint and lateral compartment of the knee. The most frequent location of cartilage lesions was LTP.5. In all the locations of cartilage lesions, the percentage of grade III or grade IVcartialge lesions was more than 50%(except for LTP and MTP).6. Kissing cartilage lesions were often occurred in patients with bucket-handle tears.Part Ⅲ:The relationship between discoid lateral meniscus tear and articular cartilage lesions1. There was no significant difference in incidence of cartilage lesions between patients with different types of DLM tear. There was no significant difference in proportion of grade Ⅲ and Ⅳ cartilage lesions between different locations. There was no significant difference in proportion of grade Ⅲ and Ⅳ cartilage lesions between patients with different types of DLM tear.4. Trauma history, DLM type, and DLM tear type were not significantly associated with the presence of articular cartilage lesions. Gender, age, BMI and time course were possible risk factors for articular cartilage lesions and age was an independent risk factor for articular cartilage lesions. Articular cartilage lesions occurred more frequently in patients who were more than 36 years of age.