The meniscus is frequently damaged in anterior cruciate ligament (ACL) injuries or in the degenerative process over a period of several years. The predominance of lateral meniscal tears has been demonstrated with acute ACL rupture, whereas the incidence of medial meniscal tears significantly increases with chronic ACL insufficiency.¹

The lateral meniscus is relatively loosely attached to the tibial plateau, which allows it to be quite mobile, and performs little or no stabilizing function on the knee.

The medial meniscus, however, is firmly attached to the tibia, especially at the posterior horn.² This firm attachment allows the medial meniscus to serve as a knee stabilizer, and various studies have shown that it is a significant restraint to anterior tibial translation in ACL-deficient knees.³ Biomechanical studies have indicated that the meniscus performs this function by acting as a mechanical block or wedge.⁴ Their results suggest that the loss of ACL function increases anterior tibial translation, allowing the meniscus to engage the femoral condyle and act as a wedge against the tibia.

Radiographic studies have shown that there is a linear relationship between posterior tibial slope (PTS) and anterior tibial translation during weight bearing: the greater the PTS, the greater the anterior tibial translation, in both ACL-intact and ACL-deficient knees.⁵ Our hypothesis is that secondary medial meniscal tears occur more frequently in ACL deficient knees with greater PTS.

In this study we recorded the incidence of meniscal tears in ACL deficient knee joints and related our findings to the time elapsed since injury. Aim of the study was to determine the relation between the incidence of meniscal injuries in ACL deficient knee and the time of surgery after injury. We also analyzed the site of meniscal tears, whether medial or lateral, in acute and chronic ACL deficient knees.

This is a Prospective study consist of 50 patients with internal derangement of knee, who underwent ACL reconstruction arthroscopically.

Study Population

The present study recruits, the patients in the age group of 18 - 50 years with internal derangement of knee. Both male & female patients were included for the study.

Sample Size and Sampling

50 patients were chosen for the present study

INCLUSION & EXCLUSION CRITERIA

The patients were included with the predefined inclusion and exclusion criteria in the present study, with diagnosis of ACL tears managed by Arthroscopy at our centre.

Inclusion criteria

1. Age: 18 - 50
2. Gender:
3. Patient’s nature ACL tears managed by Arthroscopic
4. Acute and chronic internal derangement of Knee

Exclusion criteria

1. Patients less than 18 years of age and above 50 years of
2. Patients with associated bony injuries on the ipsilateral limb

 Methodology

It is a descriptive study to evaluate the incidence of meniscal injuries in ACL deficient knee joints. Patients come with complaints of knee pain, instability, difficulty in squatting and sitting crossed leg, to our OPD and Emergency Department. These patients were then assessed with proper history and clinical examination. Patients who underwent Arthroscopy within 6 months of injury were grouped into acute or early group, whereas beyond 6 months were pooled in chronic or late group.

Of the 50 patients, 45 were males and 5 were females with 28 patients injuring the right knee and 22 injuring their left knee. The mean age of ACL repair was 28.78 years (range 18-50 years).  There were 34 patients in the early group and 16 patients in the   late group.   The overall incidence of   meniscal tears in ACL deficient knees was 35 out of 50 patients (70%). 20 out of 34 patients in the early group (58.8%) had meniscal injuries as compared to 15 out of 16 patients (93.75%) in the late group.  In the early group there were only 5 cases of medial meniscal   tear (14.7%) compared   to   13   cases   of lateral   meniscal   tears (38.2%).   In   the   late   group   there   were   11   cases of medial meniscal tears (68.75%) compared to 2 cases of lateral meniscal tears (12.5%).

Patients with both meniscal tears in the early group were 2 (5.9%) and in the late group were 2 (12.5%). Patients with isolated ACL tears were 14 (41.1%) in the early group and 1 patient (6.25%) in the late group.

Table 1: Age distribution

Table 2: Sex distribution

Table 3: Side involved

Table 4: Mode of injury

Table 5: Comparison of incidence meniscal injuries in early and late group

Table 6: Duration of injury

BELOW 6 MONTHS = EARLY GROUP

• MONTHS AND ABOVE = LATE GROUP

Table 7: Comparison of the incidence and side of meniscal tears in early and late group

The study comprised of 45 males and 5 females with the male to female ratio of 9:1. The youngest patient in the study was 18 years and the oldest was 48 years. Most of the patients (64%) were in the 21- 30 years age group. The patients were divided into an early (surgery within 6 months of injury) and a late group (surgery more than 6 months after injury). 68% of the patients belonged to the early group and 32% belonged to the late group. The commonest mode of injury was road traffic accidents (46%), closely followed by sports injury (38%).

      Noyes et al¹¹ had suggested that meniscal tears are common following ACL disruption and that the patients showed functional deterioration with time. In our study 35 out of 50 patients had meniscal tears (70%) following ACL deficiency, the incidence of meniscal tears was more common in patients who presented 6 months after injury (late group) 93.75%.

       Hart (1982) reviewed 142 patients with laxity of the anterior cruciate ligament and found meniscal tears in 27% of those arthroscopies done soon after injury compared with 90% of those with chronic instability. These are similar to the results of McDaniel and Dameron (1980).^12,13 In our study, out of 50 patients with torn anterior cruciate ligament only 58.8% had meniscal tears who presented within 6 months of injury, compared with 93.75% presented after 6 months of injury.

        Church and Keating¹⁴ reviewed 183 patients who underwent ACL reconstruction between 1996 and 2002 at the Edinburgh Royal Infirmary. Their findings showed a highly significant increase in meniscal tears in patients undergoing ACL reconstruction more than 12 months after injury as compared to those in the early group (72% vs. 42%). In our study also we found a significant increase in meniscal tears in the late group as compared to the early group (94% vs 59%). Our study also supports the view of Millett, Willis and Warren.¹⁵ who showed that delayed reconstruction of ACL was associated with higher incidence of meniscal tears.

Studies have shown that the medial meniscus is more commonly injured as compared to the lateral meniscus. Robert Bray and David Dandy¹⁶ studied 47 patients with ACL injury and found medial meniscal tear in 30% of the patients, while lateral meniscal tear was seen in only 11%6. In Church and Keating‘s¹⁷ study 29% of the patients with ACL deficient knee had medial meniscal tears while only 19% had lateral meniscal tears. Our study also shows a higher incidence of medial meniscal tears in the late group, as compared to lateral meniscal tears in the late group (68.75% vs. 12.5%).

        The greater number of tears of the medial meniscus may reflect the fact that it is relatively immobile, being firmly attached to the tibial plateau; unlike the lateral meniscus, it acts as a restraint to anterior tibial translation in the cruciate deficient knee (Levy, Torzilli and Warren 1982).¹⁸

       Studies have also shown a difference between acute and chronic ACL deficient knees with regard to the site of meniscal tear. In Church and Keating’s study¹⁹ the incidence of medial meniscal tears was 20.4% in the early group as compared to 40% in the late group. The incidence of lateral meniscal tears was similar in both the groups; 17.5% in the early group versus 20% in the late group. In our study, the incidence of lateral meniscal tears did show a significant difference in both groups. The incidence was 38.2% in the early group and 12.5% in the late group.

       However, the incidence of medial meniscal tears showed a significant increase as the time since injury progressed. It was 14.7% in the early group as compared to 68.75% in the late group. And the incidence of both meniscal injuries in the same patient was 5.9% in the early group and 12.5% in the late group. The percentage of patients with no meniscal injuries was 41.1% in the early group and 6.25% in the late group.

      In acute injuries, lateral meniscal tears were more common (38.2% vs 14.7%) whereas in chronic ACL injuries, the medial meniscus was more commonly involved (68.75% vs 12.5%). Our findings support the views of Fowler, Woods and Chapman²⁰ who stated that lateral meniscal injury occurs more frequently in acute ACL tears, while the incidence of medial meniscal injury increases with time.

      This indicates that lateral meniscal tear occurs more commonly at the time of ACL injury or soon after, whereas medial meniscal injuries are mostly acquired after the knee has been ACL deficient for more than 6 months. This may be due to the derangement in ACL deficient knee which undergoes recurrent sub clinical injury.²¹

       The distribution of meniscal tears in chronic ACL insufficiency can be explained by anatomic and biomechanical factors. Medial meniscus is less mobile due to its secure attachment to the tibial surface and medial collateral ligament. In ACL deficient knee, anterior tibial translation causes the posterior horn of medial meniscus to wedge against the medial femoral condyle, restraining further anterior tibial translation. Higher forces result in medial meniscal tears, especially of posterior horn.

         The lateral meniscus is more mobile and is able to translate more freely; therefore it plays less significant role in stabilizing the ACL deficient knee. Hence it is not subjected to recurrent shear loads.²² Whereas the medial meniscus is less mobile due to its secure attachment to the tibial surface and medial collateral ligament. The mechanical factors contribute for and explain why there is an increased incidence of medial meniscal tears in a chronic ACL deficient knee. ^[23]

The incidence of meniscal tears is increased in ACL deficient knee joints. A delay in ACL reconstruction increases the risk of meniscal tear. The medial meniscus is more commonly injured than the lateral meniscus. The incidence of medial meniscal injuries increased significantly when the knee remained ACL deficient for a long time due to the deformed biomechanics. Therefore a delay in the ACL reconstruction leads to wear and tear in the knee joint which results in early osteoarthrosis. As our study was restricted to only 50 patients, it would have been better if it was done in a larger group, to study the incidence of early osteoarthrosis also.

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