Introduction

The treatment of meniscus tears in conjunction with anterior cruciate ligament (ACL) reconstruction requires a thorough understanding of the different types of meniscus tears and their capacity for healing. The factors to consider are whether the tear is medial or lateral, degenerative or nondegenerative, or stable or unstable, as well as the vascular zone of the meniscus. The treatment choices are to remove, repair, or leave the tear in situ.

Meniscus tears with ACL injuries are different than meniscus tears in ACL intact knees. For a meniscus to tear, either (1) the knee is unstable, causing excessive movement, which in turn causes the meniscus to become caught between the femur and the tibia or (2) the knee is stable, and the meniscus has a degenerative component to it. In general, meniscus tears in ACL intact knees have extensive degeneration. Meniscus tears with an acute ACL injury are traumatic and occur mostly in the posterior and peripheral part of the meniscus. Meniscus tears in chronic ACL deficient knees can be degenerative or nondegenerative, depending on the number and severity of instability episodes.

The incidence of lateral meniscus tears has been reported to be higher than the incidence of medial meniscus tears with acute ACL injuries.¹ Shelbourne and Gray² found that of 448 patients with acute ACL injuries, 62% had lateral meniscus tears and 42% had medial meniscus tears, whereas in 609 patients with chronic ACL deficiency, 49% had lateral meniscus tears and 60% had medial meniscus tears. Cipolla et al³ found that of 218 acute injuries, 59% had lateral meniscus tears and 28.5% had medial meniscus tears, whereas in 552 chronic ACL injuries, 41.6% had lateral meniscus tears and 74% had medial meniscus tears. The lateral meniscus is mobile and translates 9 to 11 mm in the anteroposterior plane, whereas the medial meniscus translates only 2 to 5 mm.⁴ The lateral meniscus is more frequently injured acutely because of its extreme mobility, and the peripheral and posterior portions of the meniscus are prone to getting caught in the joint during an ACL instability episode, which may explain the high incidence of posterior horn avulsion tears with acute ACL injuries. The less mobile medial meniscus is less injured with acute ACL injuries, and it may take consecutive giving-way episodes for the peripheral posterior third of the meniscus to become caught in the joint. When patients do have a medial meniscus tear with an acute ACL injury, it is typically a peripheral vertical tear in the posterior third of the meniscus. This tear can extend anteriorly with additional giving-way episodes and eventually become a bucket-handle tear.

The fact that more lateral meniscus tears are seen with acute ACL injuries than with chronic ACL deficiency can be explained by the fact that most lateral meniscus tears with acute ACL injuries can heal without treatment. In fact, many medial meniscus tears seen at the time of acute ACL reconstruction can heal without repair. With the advent of knee arthroscopy, surgeons have felt compelled to treat many meniscus tears seen at the time of ACL reconstruction that would have been unobserved and left alone before knee arthroscopy was invented. The high meniscus repair success rate with ACL reconstruction can partially be explained by the fact that many menisci are being repaired that probably do not need any treatment at all.

This chapter will discuss the types of meniscus tears seen with ACL reconstruction, which meniscal tears can be left in situ, which tears to repair and the repair success rates, and finally the timing of meniscus repair with ACL reconstruction surgery.

Meniscus Tears to Leave in Situ

With acute ACL injuries, most meniscus tears are not symptomatic for the patient. The patient’s inability to fully extend the knee is usually due to the ACL stump being lodged in the intercondylar notch. Shelbourne et al⁵ found that joint line tenderness observed at the time of acute ACL injury does not correlate to the presence or absence of meniscus tears at the time of surgery. Over a 2-year period, 173 patients were seen for acute injury and were evaluated for joint line tenderness, and then the type of meniscus tear was recorded at the time of surgery. The investigators found that medial joint line tenderness was 45% sensitive and 34% specific for a medial meniscus tear. Lateral joint line tenderness was 58% sensitive and 49% specific for a lateral meniscus tear.⁵ We now delay ACL surgery until the patient’s knee has full range of motion and no swelling and the patient has good leg control. On the day of surgery, very few patients have joint line tenderness but about 50% have a meniscus tear.⁶ It appears that meniscus injuries in conjunction with acute ACL injuries are difficult to determine preoperatively based on joint line tenderness exam.

The meniscus has a blood supply provided by the perimeniscal capillary plexus, and these capillaries extend into 20% to 30% of the body of the medial meniscus and 10% to 25% of the lateral meniscus.^7,8 Tears in the peripheral vascular zone of the meniscus are thought to be ideal for meniscus repair, but many can heal without specific repair treatment. The acuteness or chronicity of the ACL injury is not the deciding factor for determining the treatment of the meniscus. Rather, it is the location of the tear and the degenerative nature of the tear that help determine treatment.

Lateral Meniscus Tears

Complete removal of a torn lateral meniscus has a poor prognosis.⁹ In the early 1980s, the senior author observed the almost 100% success with repair of lateral meniscus tears and came to the conclusion that many of the lateral meniscus tears being repaired probably did not need repair. Therefore the senior author began to change his treatment of lateral meniscus tears from repairing 80% of the tears in 1984 to repairing 15% in 1992. During that same time, he changed his treatment from leaving lateral meniscus tears in situ in 4% of tears in 1984 to 70% in 1992. The types of lateral meniscus tears left alone included posterior horn avulsions (52 tears; Fig. 62-1), stable vertical tears that were posterior to the popliteus tendon (99 tears; Fig. 62-2), and nondisplaced vertical tears that extended anterior to the popliteus tendon (27 tears).¹⁰ With a follow-up at a mean of 2.6 years (range 1–9 years), Fitzgibbons and Shelbourne¹⁰ found that no patients returned to the clinic reporting symptoms of a lateral meniscus tear. One patient twisted his knee playing basketball at 114 days after ACL reconstruction and had a displaced bucket-handle medial meniscus tear. At the time of follow-up arthroscopy, the original vertical lateral meniscus tear had progressed to a complex T-type tear, but the tear did not extend anterior to the popliteus.

Fig. 62-1 Posterior horn avulsion tear of the lateral meniscus commonly seen with acute anterior cruciate ligament (ACL) injuries.

Fig. 62-2 Superior surface of the lateral meniscus, showing a stable vertical tear.

Shelbourne and Heinrich¹¹ performed another long-term follow-up of 332 patients who had lateral meniscus tears left in situ or treated with abrasion and trephination without suture repair. The patients also had no medial meniscus tears or chondromalacia greater than grade II to isolate the factor of lateral meniscus tears in the long-term follow-up analysis. At a mean of 5.1 years after surgery, 162 patients (95%) had normal radiographs, six patients had nearly normal radiographs, and two patients had abnormal radiographs for lateral joint space narrowing using IKDC criteria. Of 70 patients with posterior horn avulsion tears left in situ, two (2.9%) underwent a subsequent procedure to remove the tear. Of 50 patients with radial flap tears, three patients (6%) needed a subsequent surgery for the tear. Of 169 patients with peripheral or posterior tears left in situ, three patients (1.8%) required subsequent surgery for the tear. None of the 43 patients who had peripheral or posterior tears treated with abrasion and trephination required further surgery.¹¹

Medial Meniscus Tears

Medial meniscus tears seen at the time of acute ACL reconstruction are traumatic in nature and are usually in the vascular zone of the meniscus. A common type of tear seen with acute ACL injury is a peripheral or posterior stable medial meniscus tear, which can be easily missed (Fig. 62-3). This type of tear is not symptomatic for the patient, and it is possible that many of these tears heal on their own in patients who do not undergo an ACL reconstruction acutely or semi-acutely.

Fig. 62-3 Inferior surface of the medial meniscus, showing a peripheral vertical posterior third tear commonly seen with acute anterior cruciate ligament (ACL) injuries.

Shelbourne and Rask¹² performed a follow-up study to determine the outcome of nondegenerative peripheral vertical medial meniscus tears that were stable and were treated either by leaving the tear in situ or with abrasion and trephination without suture repair. All the tears were greater than 1 cm long but could not be displaced into the intercondylar notch. Between 1982 and 1988, 139 tears were treated by leaving the tears in situ. Between 1989 and 1997, the tears were treated with abrasion and trephination. At a mean of 4.8 years after surgery, the number of patients who underwent subsequent arthroscopy for symptoms of a meniscus tear was 15 (10.8%) for the tears left in situ and 14 (6%) for the tears treated with abrasion and trephination. The mean time after ACL reconstruction that patients experienced symptoms was 2.5 years for the tears left in situ and 2.3 years for the tears treated with abrasion and trephination. As part of the same study, 176 patients had the same type of meniscus tear, but it was unstable and required suture repair. The failure rate of the repaired group was 13.6%.¹²

Trephination has been shown in both animal and clinical studies to enhance meniscal healing by creating vascular channels.^13–15 Fox et al¹⁶ treated 26 incomplete peripheral vertical meniscus tears by trephination alone and had 90% clinical success, but all of the tears were less than 1 cm long. Weiss et al¹⁷ showed that medial meniscus tears of 1 cm or less can heal if left alone, but the study did not evaluate tears greater than 1 cm long.

It is accepted that peripheral vertical medial meniscus tears less than 1 cm long that are found at the time of ACL reconstruction can be left in situ or treated with trephination. Shelbourne and Rask¹² have now shown that tears longer than 1 cm long can also be left in situ or treated with trephination and still have a very low rate of causing subsequent symptoms of a meniscus tear. Trephination is a simple technique to provide vascular channels in the meniscus for healing, and it avoids the risks associated with meniscus repair using sutures.

Meniscus Tears to Repair

It would be ideal to attempt to repair all torn menisci because the menisci transmit load across the medial and lateral compartments of the knee. As more of the meniscus is removed, the more contact surface between the femur and tibia is lost and contact stress increases. Meniscus repair of all menisci, however, does not ensure that the repaired meniscus performs normally for distributing load and absorbing stress.

McCarty et al¹⁸ published an extensive review of the different types of meniscus repair techniques and their results. It appears that most techniques can be successful, with rates ranging from 73% to 99% for clinical success and 25% to 90% for success of meniscal healing. The factors for success were similar for the different types of repairs: success was dependent on meniscus tear type, size, and location. To determine the success of meniscus repair, it would be most helpful for investigators to study specific types of meniscus tears instead of combining all types together.

Cannon and Vittori¹³ evaluated meniscal healing in 90 repairs done in conjunction with ACL reconstruction and 27 repairs in ACL intact knees, and the healing was related to rim width (vascular versus avascular zones), tear length (stable versus unstable), and joint compartment (lateral versus medial). Rim widths up to 2 mm had a healing success rate of 96%. Rim widths of 2 to 4 mm had a healing success rate of 84%, and rim widths of 4 to 5 mm had a success rate of 50%. Tear length less than 2 cm had a 94% success rate, and tear lengths of 2 to 4 cm had an 86% success rate. When the tear length was more than 4 cm, the healing rate was only 50%. Lateral meniscus tears successfully healed 93% of the time, whereas medial meniscus tears healed 73% of the time. Meniscus repair done with ACL reconstruction was more successful (93%) than repairs done in ACL intact knees (50% success), but there was no information provided as to the differences in rim width, tear length, or joint compartment between the two groups.¹³

Asahina et al¹⁹ also evaluated the factors that affected healing of meniscal repair of unstable, full-thickness, vertical, longitudinal tears longer than 15 mm in 98 patients evaluated by second-look arthroscopy. Of the 98 repairs, 73 completely healed, 13 incompletely healed, and 12 did not heal. Healing was achieved in 78% of medial meniscus repairs and 63% of lateral meniscus repairs. Repairs in the peripheral third zone had a statistically significant better healing rate of 87%, compared with 59% for repairs in the central third zone. The statistically significant factors in healing were rim width and meniscal locking. Meniscus tears in the central third zone that had been locked in the knee or could be locked at the time of surgery had a negative correlation to healing.¹⁹

Unstable meniscus tears, such as bucket-handle tears, are common with chronic ACL instability (Fig. 62-4). Most bucket-handle meniscus tears are degenerative, which is why they are very seldom seen with acute ACL injuries. It is possible for a bucket-handle tear to be nondegenerative in a patient with chronic ACL laxity if he or she has been able to protect the knee from instability episodes and has just suffered a recent giving-way episode prior to the evaluation. In a series of 55 bucket-handle meniscus tears seen with chronic ACL deficiency, 43 tears (78%) were in the white-white nonvascular zone of the meniscus, 11 were in the red-white vascular zone, and one was in the red-red vascular zone.²⁰

Fig. 62-4 Bucket-handle medial meniscus tear. A, Superior surface of the medial meniscus tear, showing the bucket-handle separation. B, Inferior surface of the tear being trephinated. C, Meniscus after repair with sutures.

O’Shea and Shelbourne²⁰ evaluated meniscal healing of repairs done on bucket-handle meniscus tears that were unstable and locked in the intercondylar notch in patients with chronic ACL deficiency. Patients underwent meniscus repair followed by rehabilitation to regain full knee range of motion, strength, and function before undergoing an ACL reconstruction at a later date. The menisci were evaluated with arthroscopy at the time of the ACL reconstruction, which occurred at a mean of 77 days after meniscus repair. Of 43 repairs done in the avascular zone of the meniscus, only five menisci showed no healing at the repair site. Of 11 repairs done in the red-white vascular zone of the meniscus, only one repair showed no healing. The one repair done in the red-red zone of the meniscus healed completely. At a subsequent follow-up at a mean of 4.3 years after repair, four patients had a failed repair that required subsequent arthroscopies to remove repairs done in the avascular zone of the meniscus (Fig. 62-5).

Fig. 62-5 Meniscus at 3 months after repair of bucket-handle tear. No sutures are present, and the meniscus appears healed on the superior surface (A) and inferior surface (B).

Rubman et al²¹ found similar success rates of meniscal repair in 198 meniscus tears that had a rim width of 4 mm or more. Most of the tears were either single (N = 92) or double (N = 40) longitudinal tears. Clinical success, defined as the patient being asymptomatic for tibiofemoral joint symptoms, was found in 80%. Arthroscopic follow-up evaluation of 91 of the tears found that 23 (25%) had completely healed, 35 (38%) had partially healed, and 33 (36%) failed. The authors concluded that repairs of the meniscus in the avascular zone is preferred over partial meniscectomy, especially in young athletic patients or patients with varus or valgus lower extremity malalignment. Noyes and Barber-Westin²² in a similar study found that 26 of 33 repairs of tears in the avascular zone remained asymptomatic at a mean of 33 months postoperatively for patients 40 years or older.

Thus it appears that meniscus tears, even in the avascular zone of the meniscus, can heal or remain asymptomatic with repair. The question remains as to whether repaired menisci, especially large bucket-handle tears in the avascular zone, function well enough to protect the joint and not cause symptoms for the patient in the long term. Shelbourne and Carr²³ compared the results of meniscus repair versus partial meniscectomy of bucket-handle medial meniscus tears in ACL reconstructed knees. The patients had no other intraarticular pathology such as lateral meniscus tears or articular cartilage damage greater than Outerbridge grade 2. One would expect that patients who underwent meniscus repair would have better results than patients who had a partial meniscectomy. The mean modified Noyes subjective score was identical for the two groups, 90.9 points, at 8 years after surgery. Of note, however, was that when the repair group was analyzed based on whether the bucket-handle tear was degenerative or nondegenerative, patients who had a degenerative meniscus tear had a mean score of 87.1 points, which was statistically significantly lower than the mean of 93.9 points for patients who had a nondegenerative meniscus tear. Radiographic evaluation showed that 11 of 12 patients (92%) in the nondegenerative group had normal radiographs at follow-up versus only nine of 12 patients (75%) in the degenerative group. Interestingly, 41 of 52 patients (79%) who had partial meniscectomy of the bucket-handle tear also had normal radiographs. Therefore the authors concluded that repaired degenerative bucket-handle medial meniscus tears may not function normally in the knee to provide any advantage over partial meniscectomy.²³

In a similar study, Shelbourne and Dersam²⁴ compared the results of partial meniscectomy versus repair for bucket-handle lateral meniscus tears with ACL reconstruction. The patients had no other intraarticular pathology, such as medial meniscus tears or articular cartilage damage greater than Outerbridge grade 2. The mean time of subjective follow-up was 7 years for the repair group and 11 years for the removal group. The mean total subjective score for 57 patients in the repair group was 92.5 points, and the mean total score for the removal group was 88.7 points, which was not statistically significantly different. Patients in the removal group did have statistically significantly lower pain subscores on the subjective survey than patients in the repair group. Radiographic evaluation using IKDC criteria found that 83% of the removal group (8 years postoperatively) and 87% of the repair group (6 years postoperatively) had normal radiographs. The longer follow-up time for the removal group should have accentuated any detriment of meniscus removal of the tears versus meniscus repair. Although the subjective scores between groups were not statistically significantly different, we believe the P value of 0.2014 indicates a trend toward lower scores in the removal group.²⁴

Conclusions

Not all meniscus tears require a formal repair. Many stable menisci can be left in situ or treated with trephination to create vascular channels for healing. The surgeon must consider what would happen to the torn meniscus if arthroscopic evaluation of the knee were not done at the time of ACL reconstruction. Although degenerative medial meniscus tears in the avascular zone can heal, they may not function normally and may cause a loss of knee range of motion or other adverse symptoms for patients.