Complications and Pitfalls of ACL Reconstruction and Graft Failure in Young Athletes

Anterior cruciate ligament injury and subsequent reconstruction surgery are becoming more common among young athletes in the setting of early sports specialization, intensive involvement, and year-round training. Children and adolescents have a higher rate of graft failure compared to adults and this may be due to differences in graft choice, surgical technique, timing of surgery, neuromuscular development, psychological readiness, compliance with physical therapy, and/or longer duration of exposure to high-risk activities. The purpose of this article is to discuss potential complications and pitfalls of anterior cruciate ligament reconstruction as well as methods to decrease the risk of graft failure in young athletes.

Introduction

Anterior cruciate ligament (ACL) injury and subsequent surgical reconstruction are rapidly increasing in the pediatric and adolescent population. ^, This is postulated to be multifactorial, including increased injury recognition and hightened susceptibility to injury through early sports specialization and year-round participation in sports. ^, Historically, skeletally immature patients with ACL injuries were treated conservatively until physeal closure because of concern for growth disturbances from utilizing adult reconstructive techniques. However, delayed reconstruction in this age group has been associated with poor outcomes including instability, pain, and subsequent meniscal and/or chondral injury.

As a result, a wide range of surgical techniques have been developed to reestablish stability to the knee while minimizing the risk of growth disturbances that result in angular deformity or leg length discrepancy. Wong et al. performed a meta-analysis of complications after pediatric ACL reconstruction and found a growth disturbance rate of 4.1% in a combined cohort of nearly 1400 ACL reconstructions. A systematic review by Patil et al. consisting of 2693 pediatric ACL reconstructions found a similarly low rate of growth disturbances of 2.6% with valgus deformity of the distal femur being the most common disturbance in both studies. Varus deformity, tibial recurvatum, limb shortening, and overgrowth are various growth disturbances that can be seen. It is also important to counsel parents that overgrowth of the surgical limb may occur as a potential growth disturbance, specifically with intraepiphyseal reconstruction, as many parents may assume shortening is most common. There are a myriad of factors associated with growth disturbance, including utilization of large tunnels across the physis, more oblique placement of tunnels across the physis, utilization of bone blocks across the physis, hardware crossing the physis, violation of the tibial tubercle with premature utilization of patellar tendon autograft, and dissection near the distal femoral or proximal tibial physis ( Fig. 1 ).

Although there are differentiating factors influencing outcomes between younger and older populations, including injury patterns and bony anatomy, perhaps the most challenging difference in outcomes to address is the higher rate of graft failure in children and young adults. Ho et al. performed a retrospective review of 561 pediatric ACL reconstructions and found a graft failure rate of 9.6% with soft tissue grafts, such as hamstring, failing nearly twice as often as bone patellar tendon bone grafts. Similarly, Dekker et al. reviewed their series of pediatric ACL reconstructions and found a nearly 20% graft failure rate as well as a 13% rate of contralateral tear. Furthermore, DeFrancesco et al. examined their series of 419 pediatric ACL reconstructions and found a failure rate of 10.3%, nearly half of which occurred before clearance to full activity. It is also important to recognize that the rate of graft failure varies within the pediatric and adolescent population. Cordasco et al. examined re-tear rates in 3 cohorts of patients (mean ages 12, 14.3, and 16.2 years) and found that the middle cohort had the highest rate of 20% compared to the youngest and oldest cohorts that both demonstrated rates of 6%.

There are many hypotheses explaining the increased graft failure rate in young athletes compared to their adult counterparts, including differences in graft choice, surgical technique, timing of surgery, neuromuscular development, psychological readiness, and compliance with physical therapy. Return to high-risk activities, such as cutting and pivoting sports, for a longer exposure in young athletes is likely a major contribution. Allahabadi et al. found that pediatric patients had a re-tear rate that more closely mirrored that of professional athletes than that of the general adult population. The orthopaedic surgeon must therefore not only counsel families about the increased risk of graft failure but also be well-versed in revision reconstructive techniques in the younger population.

Clinical Presentation and Workup

Many patients with graft failure may have sustained an acute traumatic injury leading up to the event and report immediate pain, swelling, and instability. However, it is important to recognize that a certain percentage of patients will present with complaints of recurrent instability, swelling, and/or pain without an associated acute trauma. This warrants careful investigation because many younger patients will be able to compensate for a compromised graft with effective motor control and strength.

A careful workup must be performed to determine an appropriate treatment plan while taking into consideration history and timeline of instability events, physical therapy type and compliance, brace utilization, medical history including collagen disorders, and activity goals. A standard radiographic evaluation including comprehensive views of the knee, full-length alignment films, bone age radiographs, and an MRI should be performed. In addition, a CT scan can be performed to further evaluate tunnel position and widening.

If graft failure is diagnosed, the potential for social and emotional distress for a young athlete and their family must be recognized, and appropriate psychosocial support resources should be offered. Although most patients will undergo revision reconstruction, delayed revision surgery may be warranted if the family and/or patient do not possess the ability to invest the time needed for successful revision; particularly if noncompliance led to failure of the index surgery. ACL injury in general can have a significant psychosocial impact on young athletes. Even in the absence of graft failure, the fear of reinjury and various psychosocial barriers can negatively affect the ability of a young athlete to return to sport.

Surgical Planning

A detailed evaluation of all potential factors that may have led to failure of the index ACL reconstruction is required to optimize the success of revision surgery. Environmental, biological, and technical factors should all be considered and addressed accordingly. The most common modes of graft failure will be discussed as follows.

Tunnel Position

The first step in planning for revision ACL reconstruction in the pediatric and adolescent population is careful examination of tunnel position. Malpositioned tunnels can contribute to graft failure due to inappropriate graft orientation that does not provide adequate stability ( Fig. 2 ) or due to impingement with the intercondylar notch or PCL ( Fig. 3 ). Patients with graft impingement may have a history of difficulty obtaining full knee range of motion in the postoperative period. Patients with nonanatomic graft orientation may present with medial meniscus pathology in the absence of lateral compartment bone bruising. It is important to note that although tunnels may have been anatomically positioned at the time of the index surgery, they may become nonanatomic due to variations in growth of the proximal tibia and distal femur that could occur after reconstruction as patients mature.

If tunnel position is nonanatomic then the surgeon has two options: (1) place a new and divergent tunnel if space exists, or (2) utilize staged bone grafting if there is inadequate room for new tunnel placement in a single-stage revision. The decision can be further complicated by the extent of skeletal maturity. If a patient is nearing skeletal maturity with less than two years of growth remaining, then new tunnels can be placed with minimal concern for physeal damage resulting in malalignment. In contrast, if the patient has substantial growth remaining, then new tunnels must be placed and/or bone grafting must be performed in a fashion that does not compromise the physis ( Fig. 4 ).

Anatomic femoral and tibial tunnel positions can be determined arthroscopically following bony and soft tissue landmarks. However, arthroscopic landmarks may be distorted and difficult to identify in the revision setting. A strategy to determine appropriate femoral tunnel position is with the lateral quadrant method using fluoroscopic guidance as described by Bernard et al. Similarly, fluoroscopy can be utilized to determine tibial tunnel position as described by Stäubli and Rauschning. Femoral and tibial tunnel position can be confirmed using guide pins under fluoroscopic guidance prior to reaming ( Fig. 5 ).

For anatomically positioned tunnels that present with acute graft failure, the existing tunnels can be reused. Careful examination should be done for tunnel widening that may require bone grafting. Other considerations include limited space relative to the physis for “up-sizing” a tunnel or changes in tunnel configuration that must be made to accommodate the chosen graft type.

Identification of Concurrent Injury and Hardware Failure

Identification of missed ligamentous and cartilage pathologies on MRI and during diagnostic arthroscopy should be undertaken. Associated injuries may include medial meniscus ramp lesions, medial or lateral meniscus posterior root tears, collateral ligament injuries, and posterolateral corner injuries. An aggressive approach should be taken to appropriately treat articular cartilage injury and meniscus pathology because of the young age of these patients. Hardware failure should also be assessed as a possible contributing factor to graft re-rupture with consideration for hardware removal as needed to achieve more anatomic revision reconstruction.

Bony Deformity

Valgus malalignment of the knee has been associated with an increased risk of ACL injury. ^, This may be due to preexisting angular deformity or deformity that may have been caused by ACL reconstruction when substantial growth was remaining. Patients who have a significant degree of valgus can either undergo guided growth if skeletally immature or corrective osteotomy if skeletally mature. Fabricant et al. demonstrated in a cohort of 9 patients that implant mediated guided growth can be safely performed at the same time as ACL reconstruction.

Increased posterior tibial slope has been shown to be associated with an increased risk of ACL graft failure in adult patients. However, a recent systematic review performed by Farid et al. found that increased posterior tibial slope was not associated with ACL tears in pediatric and adolescent patients. Further study is needed in the younger population to determine the contribution of sagittal plane knee malalignment to graft failure. If correction of tibial slope is warranted, techniques have been described for both skeletally immature and mature populations.

Graft Choice

Skeletal maturity will guide the first decision point in graft selection. For patients who have substantial growth remaining (more than 2 years), a soft tissue autograft with iliotibial band, hamstring tendon, or quadriceps tendon can be utilized. For those who have minimal growth remaining, the same graft choices exist with the addition of bone patellar tendon bone autograft. Allograft should be avoided if possible both in primary and revision settings in the young and active population due to high failure rates. Prior graft used, time from index surgery, type of revision reconstruction being performed (ie, physeal sparing, trans-physeal, hybrid, or adult techniques), and shared decision making will determine the ideal graft choice. Tightrope button or interference screw fixation may be utilized depending on the selected graft and available bone.

Limited data exists for the ideal graft choice in the revision setting for pediatric and adolescent patients. However, there is increasing data in the index setting that quadriceps tendon autograft has lower failure rates than hamstring tendon autograft in the skeletally immature population. ^, Furthermore, the adult literature has shown increased efficacy in the revision setting of patellar tendon and soft tissue autografts over allograft, with some data suggesting increased efficacy of quadriceps tendon and bone patellar tendon bone autograft over that of hamstring tendon autograft. Graft thickness should be no less than 8 mm. ^, Additionally, studies have shown that augmentation with suture tape potentially lowers the risk of graft failure in skeletally mature patients, but it is not yet known if this data translates to pediatric patients ( Fig. 6 ).