ACL injuries in the pediatric population are not emergencies and rarely necessitate immediate surgical management [5]. However, patients and families should be counseled on the eventual need for surgery, as conservative management with bracing or activity modification rarely prevents progressive intra-articular damage [2, 5, 13]. This is particularly true for younger athletes and very active patients who are less likely to be compliant with activity modification [2]. A prospective study of skeletally immature patients treated nonoperatively for ACL reconstruction, with an average follow-up of 3.8 years, demonstrated that 32% eventually needed surgical reconstruction of the ACL and 19.5% required meniscal surgeries [21].

There is no consensus on the perfect timing of ACL repair to prevent associated injuries, and the decision to treat must be made on an individual basis, in discussion with the patient and his/her family while taking into consideration the pros and cons of delayed treatment [2, 16, 22]. Benefits of waiting include allowing closure of the growth plates and the development of a more mature patient for rehabilitation [19]. Skeletal maturity can be assessed physiologically by bone age and tanner stage and treatment may be delayed if the patient is approaching skeletally maturity [8, 23]. However, from the standpoint of concomitant pathology, the disadvantages of waiting include risk for further instability and subsequent damage, particularly to the meniscus and articular cartilage [10, 15–17, 19, 24].

The trend is towards early reconstruction and stabilization of concurrent ligamentous, meniscal, and chondral injuries in an effort to prevent further injuries [20]. Early reconstruction is recommended even in skeletally immature, especially if it will be more than 1 year until skeletal maturity is reached [14, 20, 25]. A physeal sparing technique can be used in these skeletally immature patients and has been shown to have good functional outcomes with low revision rates with minimal risk for growth disturbance [23]. However, in certain circumstances, such as concomitant MCL injury, the ACL reconstruction can be delayed until the concomitant injury is treated [4].

Approximately 40–60% of ACL injuries will have an associated injury of either meniscus [11, 21, 26]. While management of concomitant meniscal injuries is similar to isolated tears, they do not necessarily behave in the same way. In fact, combined injures tend to have better outcomes [26, 27]. Risk factors for meniscal injuries include adolescent age, male gender, type of sporting activity, higher BMI, and delayed ACL reconstruction [1, 3, 10, 16, 17, 19]. Patients with additional meniscal injuries have similar mechanisms of injury compared to isolated ACL tears, usually noncontact sporting activities such as pivoting and jumping [7].

Gender is also an important risk modifier for concomitant injuries, as males and females tend to have distinct injury patterns [5, 7, 25]. Though females are at higher risk for ACL injuries in general, they are at lower risk for sustaining concomitant intra-articular injuries [7]. A review of high school athletes revealed that compared to their male counterparts, female soccer players sustained fewer medial meniscal tears and female basketball players sustained fewer lateral meniscal and chondral injuries [7]. The reason for these differences between males and females is unknown but speculated to be due to differences in strength, size, weight, force generation, muscle recruitment, joint alignment, or differences in the resilience of either the ACL or meniscus [7]. There were no reported differences in the mechanisms of injury, history of popping, joint swelling, or return to play between males and females [7]. Males were more likely to sustain medial and lateral meniscal tears and undergo meniscectomy [25]. A higher rate of meniscectomy is perhaps explained by the fact that boys were more likely to have delayed treatment [25].

Evaluating for meniscal injuries should be undertaken early and with a high index of suspicion given the high incidence of repairable injuries and the fact that many can be found early in the patient’s course [2]. In a case series of patients with ACL injuries, an arthrogram was performed in 10 out of 12 skeletally immature patients with acute ACL tears and 10.7 days after the injury on average. These arthrograms revealed 10 meniscal tears in 7 patients. Subsequent arthroscopy confirmed 8 tears in 6 patients [2]. An important finding for stratifying risk for meniscal injuries is bone bruises , which are very common and occur in over 80% of acute ACL injuries [28–30]. The evidence of bone bruise on MRI is another important consideration as femoral size of a bone bruise has been correlated with a higher likelihood of sustaining meniscal injuries [28]. In addition, the presence of bone bruise in the posteromedial aspect of the tibial plateau may be a sign pointing towards meniscal root avulsion, which may otherwise go undiagnosed [31]. Once brought to the operating room, it is important to search thoroughly for a meniscal tear, as up to 40% of medial meniscal lesions may occur on the posterior horn, which is difficult to view from a standard approach. These lesions may be either “ramp lesions” which are not easily viewed on MRI or with normal inspection, or “hidden lesions,” which are only apparent after debridement or motorized shaving [32]. Undiscovered lesions may result in higher rates of treatment failure [32].

The three treatment options for meniscal injuries are to leave the tear in situ, meniscectomy, and meniscal repair [33]. Meniscectomy is performed most often during ACL reconstruction, at a rate of two to three times as often as repair [26]. As many as 65% of concomitant meniscal injuries are trimmed, compared to 26% that are repaired and 9% left in situ [26]. Between 2007 and 2011, there was a rising incidence of meniscal pathology treatment in pediatric patients [1]. The incidence of meniscal repair increased by 54.8% and the incidence of meniscectomy increased by 37.7% [1].

Patient characteristics are important factors to consider when deciding the best treatment option [18]. Nonoperative management of meniscal injuries during ACL reconstruction is unlikely to be successful in younger patients, especially young athletes, who are unwilling to comply with activity modification [1, 13]. Younger patients with ACL injury are less likely to have tears left in situ and are more likely to undergo partial meniscectomy or meniscus repair compared to older patients [1]. A review of a national database of pediatric ACL reconstructions found that nearly half of all patients undergoing ACL reconstruction also underwent a concomitant meniscectomy and a quarter underwent meniscal repair [1]. Though meniscectomy is more common, there is a trend towards meniscal repair in younger patients due to a higher success rate compared to adults and the desire to reduce the risk of subsequent osteoarthritis [1, 34]. This is reflected in the fact that the rates of meniscectomy increase with advancing age (38.8% in 10–14-year-olds vs. 52.% in 20–45-year-olds) and the rates of meniscal repair decrease with increasing age (27.6% in 10–14-year-olds vs. 16.2% in 20–45-year-olds) [1].

Certain types of meniscal tears can be left in situ during ACL reconstruction. Leaving tears alone is usually more appropriate for lateral meniscal tears [3, 10]. This is reasonable considering lateral meniscal tears are more common in the acute setting, and the incidence does not significantly increase as time to treatment increases [10, 19, 25]. Medial meniscal injuries, on the other hand, are more common in the chronic setting and are more likely to require treatment [10, 19]. Certain tear characteristics that are associated with being left in situ include partial tears, location of the tears, orientation, and tear type [33]. A prospective, multicenter study demonstrated that lateral meniscus tears, partial tears, tears in the peripheral one-third of the meniscus, and longitudinal tears were more likely to be left in situ compared to oblique, complex, or radial tears [33]. In addition, every additional 1 mm in length of a tear decreased the likelihood of a tear being left in situ by 22% [33]. No bucket handle tears were left in situ. For the medial meniscus, the only two factors associated with being left in situ were length, with each 1 mm increase in tear length decreasing the likelihood of being left in situ by 28%, and partial tears, which were more likely to be left in situ than complete tears [33].

A systematic review of meniscal tears left in situ found that medial meniscal tears left in situ required a secondary procedure at a rate of between 0 and 33% and that patients reported significant pain in an average of 14.8% of cases [35]. On the other hand, lateral tears developed either subsequent pain or need for an operation at a much lower rate of 4.8% of cases on average [35]. In addition, lateral meniscal tears left in situ tend to have an improved prognosis compared to attempted treatment [36]. A large multicenter study reported good outcomes for meniscal tears left in situ, with 97.8% and 94.4% of lateral and medial meniscal tears, respectively, requiring no additional surgery at 6 years follow-up [33]. However, the pediatric population may fare worse than older patients, as the average age of those needing additional surgeries in this cohort was 18.6 years compared to 25.1 years for those who needed no additional surgery [33].

The most common treatment for meniscal injuries is meniscectomy [1, 26]. In a review of a national ACL injury registry, it was found that the youngest age group of 10–14-year-olds had the most pronounced increase in meniscectomy, although this group retains the lowest rates of meniscectomy overall [1]. The reason for this increase is multifactorial and perhaps related to the increased intensity of athletics and earlier specialization [1, 13, 37]. While it is generally ideal to preserve the meniscus, this is not always possible. Not all tear types are amenable to repair and leaving certain tears in situ may lead to high failure rates, particularly in medial tears or lateral tears larger than 10 mm [33]. Meniscal injuries associated with chronic ACL deficiency are more likely to be irreparable and require meniscectomy [11]. As the time from injury increases, the complexity of the tears tends to increase, making the lesion harder to repair, and these are more likely to be treated with meniscectomy [11]. Complex tears have been associated with a higher rate of failure following repair and therefore are often better managed with meniscectomy [27]. The amount of meniscus trimmed can have an impact on future outcomes [36]. Counterintuitively, small medial resections (<33%) had poor outcomes, whereas large medial and lateral meniscal resections (>50%) actually had better outcomes compared to patients without meniscal pathology in a 6-year follow-up study after ACL reconstruction [36].

The meniscus protects the knee from injury by acting to reduce contact pressure in the knee [18]. Every attempt should be made to preserve the meniscus when possible, as meniscectomy is associated with an increased risk and acceleration of osteoarthritis [26, 34, 35, 38]. Repair of stable peripheral tears may always be indicated for medial meniscal injuries since there is low risk for complications [35]. Studies of patients at the time of revision ACL surgery have shown that prior meniscectomy is associated with higher likelihood of chondral lesions, whereas prior meniscal repair is not [38]. Factors associated with an increased likelihood of undergoing meniscal repair during ACL reconstruction include younger patient age, lower patient BMI, involvement of both menisci, sports medicine fellowship training of the surgeon, higher surgeon case volume, and higher site volume [18].

It is also important to understand that meniscal injuries associated with ACL injuries do not behave in the same way as isolated meniscal injuries. Meniscal repairs during ACL reconstruction have a higher success rate compared to isolated meniscal injuries [27, 39]. It is also important that both injuries be treated since meniscal repair has a much higher failure rate if the ACL tear is not addressed [39]. In a review of patients younger than 18 years old treated with surgical repair of meniscal tears with concomitant ACL reconstruction, there was an overall 74% success rate, with a 90.9% freedom from failure rate at 2 years and 76.8% freedom from failure rate at 5 years [27]. Risk for repair failure include complex tears, bucket handle tears, medial tears, and skeletal immaturity [27]. However, complex tears associated with ACL injuries have a higher success rate than isolated injuries, perhaps due to increased perfusion secondary to the ACL ruptures [27].

Several techniques are available to the surgeon to repair meniscal injuries, including inside-out, outside-in, and all-inside approaches [27, 40–42]. A randomized controlled trial comparing all three demonstrated 100% healing rate for outside-in technique, 95% healing rate for the inside-out technique, and only 65% healing rate for the all-inside technique with a minimum follow-up of 1 year [43]. Mean surgical times were 38.5 min, 18.1 min, and 13.6 min for the outside-in, inside-out, and all-inside approaches, respectively [43].

The inside-out technique has the advantage of being able to treat nearly all types of tears in any location, including both simple and complex tears and even in those extending into the avascular zone [41, 42]. Vanderhave et al. reported on excellent results in 43 of 45 skeletally immature athletes who were all treated with inside-out approach regardless of tear pattern or location [40]. This approach may be used in young, active patients who may otherwise receive meniscectomy and be put at higher risk for loss of function from early osteoarthritis [41]. However, the inside-out approach has the disadvantage of increased risk of damaging neurovascular structures [42]. The outside-in technique avoids this risk to the neurovascular structures, but it has the disadvantage of requiring an additional small incision and difficulty with treating posterior tears [42]. The all-inside approach has become more popular with the rise of various devices [42]. A long-term follow-up study demonstrated that all-inside approach still offered protection from osteoarthritis and even with initial incomplete healing [44].

Meniscal repair should be attempted whenever possible to avoid meniscectomy, especially in younger, more active patients [41]. While all-inside approach may offer fast, easier fixation, suturing techniques may be necessary for more difficult or complex tear patterns [43].

While the ACL is the most common ligamentous injury to require surgery, it is the MCL that is the most common ligament injured in the knee [45, 46]. The MCL is also the most common ligament to be injured concurrently with an ACL injury [46]. Over half of all MCL injuries that occur with ACL tears will also present with a meniscal injury as well in what is called the “Unhappy Triad,” with the most common injured meniscus being a tear to the lateral meniscus [6, 8, 9].

The diagnosis of an MCL injury can be made on the basis of the history and physical alone, with no need for advanced imaging or arthroscopy [6]. MCL injuries can be categorized as grade I, II, or III. The MCL is fully intact in grade I lesions, with no instability, a firm endpoint, only mild to moderate pain, and no radiographic changes [6, 45]. Grade II lesions are partial tears of the MCL and are associated with mild functional impairment, particularly in the acute period following the injury [45]. Valgus instability may be present in 30° of flexion, but there will be a firm endpoint with valgus stress testing [6, 45]. Grade III lesions are complete tears of the MCL, which may be accompanied by an avulsion of the femur or tibia, instability of the joint, no firm endpoint, and widening of joint space [6, 45]. Pain is often not proportional to the severity of the injury in grade III injuries whereas incomplete tears may be very painful but will not reveal instability when stressed [45, 47].

The treatment of MCL injuries can include surgical reconstruction or conservative management with brace or cast immobilization of the knee. The associated ACL injury can be treated simultaneously or at a later time [46]. However, there is evidence to suggest that operative management of both the ACL and MCL leads to higher rates of knee stiffness and decreased range of motion [6]. Instead, subacute ACL reconstruction is recommended to avoid the increased risk for arthrofibrosis [6].

Two randomized control clinical trials compared nonoperative and operative management of concomitant ACL and grade III MCL injuries and demonstrated similar outcomes in terms of ROM, quadriceps strength, valgus stability, return to activity, and subjective function as measured with Lysholm and IKDC scores. However, operative management requires more aggressive physical therapy and nonoperative management allowed patients to regain ROM and strength faster [48, 49]. In addition a meta-analysis of studies on combined ACL/MCL injuries showed that 38% of patients undergoing operative management of MCL injuries required additional procedures to regain ROM [46]. However, there may still be a role for surgical management in rare or more unusual presentations. For instance, Desai et al. described the case of a child with a complete disruption of the MCL that presented with intra-articular entrapment of the injured ligament requiring surgical repair and eventually return to full activity [50].

The MCL injury is treated first with immobilization to allow for decreased swelling, resolution of the acute inflammatory process, and return of full motion of the knee before reconstruction of the ACL [4, 6, 46]. A retrospective review of 12 pediatric patients treated for combined ACL-MCL injuries demonstrated good outcomes when the MCL was treated with a hinged brace followed by delayed ACL reconstruction [4]. At a mean follow-up of 5.3 years, all patients had stable Lachman tests, no laxity with valgus stress, a mean Lysholm score of 96°, and an average range of motion (ROM) of 146° [4].

Evidence also suggests that nonoperative management of the MCL injury yields favorable results compared to the reconstruction of both ligaments [6, 46]. This is the case for all grades of injury, but most injuries that present will be grade II or III since grade I injuries usually resolve without coming to medical attention [6, 46]. The key principle for the treatment of grade II injuries is to allow for restoration of motion while protecting the knee with immobilization, limited weight bearing, and the use of cruthches [6]. Physical therapy should be initiated to work on range of motion and improve knee stability and quadriceps strength [6]. Subsequent reconstruction of the ACL is recommended, particularly for younger patients and athletes [4, 6]. Grade III injuries are treated in a similar fashion to grade II lesions but with an increased emphasis on protection of the knee [6].

The treatment and natural history of the injuries is also affected by which portion of the MCL is avulsed in grade III injuries [6]. Avulsion of the femoral end of the ligament and midsubstance injuries have a tendency for more stiffness and less laxity. These injuries are treated with a short period of immobilization followed by physical therapy for ROM and protection of the knee with a hinged brace [6]. Tibial avulsions tend to have more laxity and should be treated with 2–4 weeks of immobilization in a cast. Laxity can be reassessed at 2-week intervals, and immobilization can be continued if there is no firm endpoint with valgus stress testing at 30° of knee flexion [6].