Importance Rupture of the anterior cruciate ligament (ACL) of the knee is a commonly occurring injury in the athletic population. Associated meniscal and chondral injury is well recognised. This occurs at both the time of index injury and secondarily over time in the ACL-deficient knee. There are different treatment options to manage meniscal tears during ACL reconstruction (repair, meniscectomy, lesion left in situ) and the place of the non-operative treatment of such meniscal lesions remains unclear.
Objective This article reviews the contemporary literature about the indications and results of leaving meniscal lesions without treatment during ACL reconstructions.
Evidence review PubMed was searched for eligible studies. 15 studies met the inclusion criteria, including 1485 untreated meniscal tears (843 lateral meniscus, 642 medial meniscus).
Findings The outcomes of untreated meniscus lesions during ACL reconstruction demonstrated low rates of failures for lateral meniscus tears (between 0% and 7% if the lesion remains posterior to the popliteus tendon), whereas 12–15% of untreated medial meniscus tears underwent reoperation.
Conclusions and relevance This systematic review was in favour of leaving small lateral meniscus lesions during ACL reconstruction without additional risk of subsequent meniscectomy.
For the medial meniscus, the risk might be still present, even for small lesions.
What is already known
Meniscus lesions left untreated is a common, but underevaluated, occurrence in surgical procedures for anterior cruciate ligament (ACL) reconstruction.
What are the new findings
The rate of untreated meniscus lesions during ACL reconstruction is from 11% to 35% in the literature.
When left untreated, the risk of subsequent surgery of these lesions is low, especially on the lateral meniscus. This ‘treatment’ could be used more often without additional risk of subsequent surgery.
There is still a need for long-term and comparative studies.
In the most recent studies, the mean prevalence of meniscal injuries at the time of anterior cruciate ligament (ACL) reconstruction is 35–40% for the medial meniscus and 40–45% for the lateral meniscus.1–4
The healing potential of a torn meniscus depends on the location of the tear, the type and length of tear, stability, the blood supply and the degree of meniscus degeneration: stable, partial and vertical tears in the peripheral zone have a greater potential to heal.5
The treatment of meniscal lesions and ACL is inter-related. ACL reconstruction in an unstable knee plays a key role in the healing of the concomitant meniscal lesion and its consequences for the natural history of the joint. On the other hand, the type of treatment of these meniscal lesions can affect the outcome (stability, function, symptoms) of an ACL reconstruction.
The rationale of treatment during an ACL reconstruction is always to preserve as much of meniscal tissue as possible, and a meniscectomy would be justified only if the meniscus lesion cannot be repaired or is left untreated. Although meniscal preservation is important for both stability and chondroprotection, leaving meniscal lesions untreated during ACL reconstruction may be beneficial when compared with performing meniscectomy. The purpose of this study was to investigate the outcomes of meniscal lesions left untreated during ACL reconstruction. Our hypothesis was that there would be differences in outcome according to the side of the meniscal lesion (medial or lateral).
An electronic search of PubMed was performed for articles published from January 1980 to November 2015 on clinical studies looking at outcomes of meniscus tears left in situ at the time of ACL reconstruction. Search strategies were created to include the Medline keywords ‘knee’, ‘Anterior Cruciate ligament’, ‘meniscus tear’ or ‘meniscal tear’, ‘left in situ’ or ‘let alone’ or ‘non-operative’. The flow chart in figure 1 shows the review process from the original search to those included in the final study. The initial search yielded 224 eligible studies. Review of the abstracts of the identified studies was performed. Letters, biomechanical studies and non-English language papers were excluded. All the remaining manuscripts were reviewed (30). Literature reviews, non-clinical studies and studies with no possibilities of subgroup extraction of data were also excluded. Using the above criteria, this process of exclusion yielded 15 studies. Citation tracking did not add any studies.
Data from the original articles were extracted using a standardised extraction form, including study design, number of patients, mean age at time of surgery, mean duration of follow-up, timing of surgery, surgical method used, clinical outcome, functional outcome, anatomical outcome, and complications such as reoperation rate and persisting pain.
The 15 original studies retrieved from our systematic search, with a total of 1485 participants (843 lateral meniscus, 642 medial meniscus), included 13 level IV and 2 level III evidence-based medicine studies. These studies were conducted among different study populations and included different outcome measures (questionnaire, patient satisfaction, residual pain, functional outcomes scales, return to sports, reoperation rate, healing rate of the meniscus). There were no studies with control groups of operatively treated meniscal lesions that could be left in situ without treatment.
The mean follow-up ranged from 16 to 72 months. The mean age at the time of surgery was 25 years (20–28).
Tears were mainly located peripherally in the vascularised area. When evaluated, the length of the tear ranged from 5 to 25 mm. The mean time from ACL injury to surgery varied between studies from 13 to 58 months.
For the lateral meniscus, there were 175 partial thickness tears and 417 complete or full-thickness tears. The remaining 242 tears could not be classified. For the medial meniscus, there were 160 partial thickness tears, 442 complete or full-thickness tears. Forty tears could not be classified.
Lateral meniscal tears left in situ
The results of the series included in this review showed that small stable lateral meniscus tears seen with ACL reconstruction may be left in situ without high risk of reoperation. The reoperation rate for either incomplete or small lesions (<1 cm) was from 0% to 1.5%, and from 0% to 7.1% for larger lesions.5 ,7 ,10–14 ,16–19 ,22 ,23
There was only one case–control study (level III) available in the literature.17 This study concluded that stable posterior segment tears of the lateral meniscus left untreated at the time of ACL reconstruction revealed successful clinical outcomes compared with isolated ACL injuries without meniscus tear, and showed considerable healing and functional restoration of tears with repeat MRI and second-look arthroscopy.
Another important factor is that lateral meniscus tears are often well tolerated and can be left untreated hoping they will continue to provide support. Indeed, the rate of residual meniscal symptoms (minor discomfort or pain) after such untreated lesions is low, from 0% to 5.7% on the lateral side.
If the lesion is located posteriorly to the popliteal hiatus, it could be left untreated,6 whatever the size of the lesion (from partial thickness tears to longitudinal tears up to 2 cm in length), with good results and no additional risk of subsequent surgery (figure 2, see online supplementary video 1).
Medial meniscal tears left in situ
The results of these series on medial meniscus were slightly different from those of the series on the lateral meniscus (table 2). Residual pain and/or need for a subsequent meniscectomy were reported in up to 15% of cases. The results were not different when considering partial thickness and full thickness lesions separately.6 ,12 ,14–16 ,18–21 ,23
Duchman et al13 recently reported a trend towards more reoperations in medial compartment tears as compared with lateral compartment tears left untreated (12.7% vs 5.1%, respectively; p=0.052).
This could be explained by the influence of the posterior segment of the medial meniscus on anteroposterior (AP) stability and rotational laxity. Ahn et al,15 in an experimental study, reported that longitudinal lesions of the posterior segment of the medial meniscus in an ACL-deficient knee altered knee kinematics and that repair of these lesions improved AP translation (figure 2).
Treatment options of meniscal lesions during ACL reconstruction
There are very limited data in the literature comparing meniscectomies, repairs and lesions left in situ during ACL reconstruction.24 This might be due to the insufficient available data to analyse the effects of tear size, and patient and surgeon characteristics.
Kluczynski et al,3 in 2015, reported a total of 211 lateral meniscal tears (35.3% untreated, 48.3% meniscectomised, 16.4% repaired) and 197 medial meniscal tears (25% untreated, 52% meniscectomised, 23% repaired) among 541 ACL reconstructions. They analysed predictors of associated intra-articular injuries (meniscal lesions, chondral lesions) at the time of ACL reconstruction. Male sex predicted lateral meniscal tears and management. Male sex, sport injuries 6 weeks from surgery and preoperative episodes of instability, predicted medial meniscal tears and management.
Therefore, to be a male would be the worst prognosis factor of having a meniscectomy of a torn meniscus during ACL reconstruction. What about the type of lesion?
Size of meniscal lesions
In the MOON cohort study, Duchman et al13 reported that tears measuring more than 10 mm underwent reoperation more frequently than tears measuring 10 mm or less (11.5% vs 3.2%, respectively; p=0.035). This relationship was not seen when excluding tears treated in the setting of concomitant revision ACL reconstruction.
The aim of rasping, proposed by Ochi et al8 20 years ago, was to induce vascularity from the peripheral vascular area to tears in the avascular zone without drastically changing the meniscal architecture. The described procedure involved rasping the surface of the meniscus from the parameniscal synovium to the inner portion, including the longitudinal tear, using an electrical diamond burr without sutures.9 Experimental study showed that this procedure promoted synovial ingrowth on the rasped meniscal surface to the tear in the avascular zone, leading to good meniscal healing. Several cytokines were noted on the rasped meniscal surface; these are closely related to the healing mechanism.
Trends and factors associated with meniscal treatment during ACL reconstruction
Recently, in the Norwegian registry, 2520 lateral meniscal lesions were found in 10 468 primary ACL reconstructions. Of these, a meniscectomy was performed in 71.2% of cases, a meniscal repair in 12.8%, and the meniscus was left in situ in 15.5% of cases.4 Of the 3208 medial meniscal lesions found in the same cohort, 24.3% were repaired, 64% were resected and 11.6% were left in situ.
In 2013, Abrams et al25 published a review on the trends of knee arthroscopic procedures performed from 2005 to 2011, using a national database compiled from a collection of private insurance records. There was no significant increase in the total number of meniscectomies performed (p=0.712), while the incidence of meniscectomies increased 14% from 2005 to 2011. There were no significant changes in the number of meniscus repairs performed at the same time as ACL reconstruction during the study frame. This indicates that there is no recent trend towards meniscal repair instead of meniscectomy during ACL reconstruction. Nevertheless, the total number and incidence of secondary meniscectomies after repair significantly decreased, indicating that the accuracy of the meniscal repair procedure improved in this period.
In 2012, Noyes and Barber-Westin26 performed a systematic literature review of articles on the treatment of meniscus tears during ACL reconstruction. There were 19 531 patients with 11 711 meniscus tears who met the inclusion criteria. This study reported that 26% of meniscus tears were repaired, 65% were treated by meniscectomy and only 9% were left in situ. The difference between lateral and medial menisci was not clearly seen.
In a study on meniscal repair and ACL reconstruction by Wyatt et al,27 meniscectomies and meniscus tears left in situ were pooled in the same control group and referred to as alternative treatment. However, four different subgroups according to the meniscus status must always be addressed separately during ACL reconstruction: no meniscal lesion, meniscal repair, meniscectomy and meniscal lesion left untreated.28
There are a high number of limitations in this literature review.
All the case series were retrospective and non-homogenously described. Not all of the parameters analysed in the tables were reported in every article, these include: tear length, distance of the lesion to the meniscosynovial junction, high number of unclassified medial and lateral meniscus lesions, time from injury to surgery and even postoperative rehabilitation. In the referenced studies, there were no clear differences between studies of meniscus lesions left in situ without any treatment compared with lesions left in situ without suture but with a concomitant synovial abrasion to promote healing.
The rationale for treatment during an ACL reconstruction is always to preserve as much meniscal tissue as possible, and a meniscectomy would be justified only if the meniscus cannot be repaired or the tear was left in situ without treatment.
Regarding this literature review, leaving small meniscal lesions alone without treatment can be recommended, especially on the lateral side, unless they are causing symptoms that warrant treatment. During ACL reconstruction, a meniscal lesion should first be considered for preservation (meniscal lesion that can be left in situ in 30–40% of cases, meniscal repair in 40–45% of cases), and only as a last resort referred for resection (unsalvageable lesions in 15–20% of cases). If a meniscectomy is needed, the amount of removed tissue should involve only the lesion (partial meniscectomy).
Future papers should consider the use of standardised classification, for example, the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS) classification of meniscal tears. This may help to provide more homogeneous and comparable data in different studies.
Moreover, there is a need for long-term follow-up studies, in order to determine if these recommendations can prevent degenerative changes in the joint after an ACL reconstruction.
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.