Although once thought to be uncommon, anterior cruciate ligament (ACL) injuries are increasingly recognized in the pediatric and adolescent athletic population. In total, 12% to 36% of children and adolescents presenting with a hemarthrosis after a knee injury have evidence of an ACL injury on magnetic resonance imaging (MRI).
Studies have demonstrated that the incidence of pediatric ACL tears has increased at a significantly higher rate than that seen in adults over the last 20 years. This is likely because of a combination of factors including an increase in the number of females participating in competitive sports since the passage of Title IX in 1972, earlier single-sport specialization, increased participation in year-round sports, more intense and frequent training, and improved awareness on the part of medical professionals. One large study demonstrated that the rate of ACL tears in children and adolescents averaged 121 per 100,000 person-years. In that study, there was a 2.3% rate of annual increase in diagnosis over the study period (1994–2013). Furthermore, surgical treatment of ACL reconstruction (ACLR) in patients under 15 years of age has also increased dramatically. One large study demonstrated a 28% increase in the rate of ACLRs in patients between the ages of 10 and 14 from 2007 to 2011. Another demonstrated a 924% increase in rates of ACLR in patients under the age of 15 from 1994 to 2006. ,
Surgeon attitudes regarding the treatment of pediatric ACL tears have changed dramatically. A recent survey of the Pediatric Research in Sports Medicine society demonstrated that only 3% of members would treat an 8-year-old child with an ACL tear nonoperatively. This shift is caused in part by the understanding that nonoperative management of children with complete ACL ruptures leads to an increased rate of secondary pathology, such as meniscal or chondral injury. In addition, there is a 50% rate of failure to return to sports in young athletes treated nonoperatively.
Despite the collective agreement that ACL tears in young athletes are best treated with surgical management, the optimal surgical technique remains controversial. The most commonly used techniques in this setting include extraphyseal reconstruction with a combined extra- and intraarticular approach using an iliotibial band autograft, all-epiphyseal reconstruction, partial or “hybrid” transphyseal reconstruction, “physeal-respecting” transphyseal reconstruction, or traditional adult-type reconstruction.
For patients who are Tanner stage I and II or patients with 2 to 3 years of growth remaining (boys younger than 13–14 years and girls younger than 12–13 years), previous studies and literature have recommended extraphyseal (iliotibial band) or all-epiphyseal techniques. , However, there are multiple case series which demonstrate that transphyseal ACLR can be a safe technique, even in Tanner stage I and II patients.
The “physeal-respecting” transphyseal technique is similar to the standard adult-type technique used, but there are several important differences, as outlined later ( Fig. 15.1 ). , , , Most commonly, a 4-strand hamstring autograft is used. Quadriceps and patellar tendon autograft, as well as multiple allograft options, have also been described. , , Graft options and potential complications are discussed in this chapter.
There is the potential for similar intraoperative complications as those seen in the adult population, including graft truncation during autologous hamstring harvest, patellar fracture during autologous patellar tendon or quadriceps tendon harvest, damage to the infrapatellar branch of the saphenous nerve, fixation hardware breakage or complication, posterior femoral tunnel “blowout,” inappropriate placement of graft tunnels, and failure to appropriately tension the graft.
Quadriceps autograft is being used more often because of the robust volume and reliable length of the quadriceps tendon. The graft can be harvested with or without an attached bone plug from the superior patella. As discussed subsequently, it is imperative that the surgeon not place bone blocks across the physis, to avoid tethering and subsequent growth disturbance. A potential intraoperative complication when harvesting a bone block is patella fracture. Fu et al. noted an 8.8% incidence of patella fracture following quadriceps harvest in 55 patients. It should be noted that two of the five fractures were asymptomatic and were noted on research-computed tomography at 6 months postsurgery. Lee et al. noted only three patellar fractures among 350 patients. One option to mitigate patellar fracture is to harvest a soft tissue only graft. If a bone block is used, it should be taken from the central aspect of the patella because fractures most frequently occur when the bone block is taken laterally. The depth of the cut should be less than 30% to 50% of the patellar thickness, whereas the length should be less than 50% of the patellar length. Additionally, the defect should be bone grafted with autograft when possible.
As discussed subsequently, one surgical “pearl” is avoidance of fixation hardware crossing the physis. For this reason, perhaps the most common fixation device for femoral-sided fixation is a suspensory button. A variety of options are available, including fixed-loop and adjustable-loop. As with any fixation device, there are specific potential intraoperative complications related to the use of a suspensory button fixation. Pulling too rapidly or with too much force on the leading sutures can lead to the button advancing past the iliotibial band. At a minimum, this leads to a prolonged operative time and potentially a larger skin incision. Conversely, failure to advance the button past the lateral femoral cortex can lead to the button remaining intraosseous or within the tunnel ( Fig. 15.2 ). This will ultimately lead to graft laxity and failure.
This technical complication can be avoided with careful surgical technique. The surgeon should measure the intraosseous distance, defined as the distance between the lateral femoral cortex and the aperture of the intraarticular femoral tunnel. This length can then be marked on the button-graft construct. When advancing the graft, the surgeon knows the button has advanced past the lateral cortex when this mark reaches the edge of the intrarticular femoral tunnel ( Fig. 15.2 ). There is also usually distinct tactile feedback once the button has “flipped.” Intraoperative fluoroscopy can also be used to verify the correct position of the button. Alternatively, the arthroscope can be placed into the anteromedial portal, and the button can be directly visualized as it passes the lateral cortex.
Growth disturbance, including angular deformity and overgrowth, is a potential complication of transphyseal reconstruction. Recent systematic reviews have noted a 1.4% to 2.7% rate of growth disturbance following transphyseal reconstruction. , The most common deformities are genu valgum and proximal tibial recurvatum. Kocher et al. surveyed the Herodicus Society and reported 15 cases of growth disturbance. They reported that all of these complications resulted from common technical errors, such as those discussed later.
Animal model studies have demonstrated that injury to more than 7% of the physis can lead to permanent growth disturbance. , Studies have demonstrated that commonly used techniques result in physeal violations under this “threshold.” Wang et al. used an 8-mm tibialis anterior allograft placed through an accessory anteromedial portal. They demonstrated that the mean physeal violation was 3.95% of the distal femoral physis and 3.65% of the proximal tibial physis. Several MRI-based studies have also demonstrated physeal violations of less than 5% during “simulated” transphyseal tunnel placement. ,
There are several important technical pearls that should be considered when performing the transphyseal reconstruction to minimize the risk of growth disturbance. The surgeon should attempt to use bone tunnels 8 mm in diameter or smaller. Shea et al. demonstrated that 6-, 7-, 8-, and 9-mm–diameter tunnels produced physeal violations of 1.6%, 2.2%, 2.9%, and 3.8%, respectively, for the tibia and 2.4%, 3.2%, 4.2%, and 5.4%, respectively, for the femur.
Similarly, to minimize physeal damage, the surgeon should attempt to orient the tunnel as vertically as possible, while still placing the graft in the appropriate anatomic location. Tunnels placed using an accessory anteromedial portal or an “outside-in” technique have been shown to be more “oblique” when compared with tunnels placed using a transtibial technique ( Fig. 15.3 ) or with a flexible reaming system through an anteromedial portal. , A more vertically directed tunnel will create a more circular or concentric physeal traverse, whereas a more oblique or eccentric traverse is created with an oblique oriented tunnel. Thus transtibial drilling may produce less physeal disruption than a “femoral-independent technique,” such as outside-in drilling or drilling from an anteromedial accessory portal. , Cruz et al. examined patients treated with either an outside-in technique or a transtibial technique using a 9-mm tunnel. They demonstrated that the mean femoral tunnel angle in the coronal plane was 32 degrees versus 73 degrees, and the mean physeal disruption was 2.11% versus 4.93%, respectively. The transphyseal technique also resulted in a more centralized tunnel. This is not to say that appropriate tunnel placement cannot be achieved with an outside-in or anteromedial technique, especially with the use of knee hyperflexion or a flexible reamer. However, the surgeon should be cognizant and aware of the potential for a more oblique and peripheral physeal “traverse” or violation with these techniques. The tunnel length can provide a good indicator of the tunnel trajectory. More horizontal drilling will create shorter tunnel lengths, usually around 25 mm, whereas increasingly more oblique angles of drilling will result in increased tunnel lengths, frequently greater than 35 mm.
Another key point of consideration during femoral fixation is to take care to avoid the perichondrial ring of Lacroix. Toward this goal, the surgeon should avoid placing suspensory fixation at the level of the physis. Great care should also be taken to avoid the tibial tuberosity to prevent a recurvatum deformity from occurring. Furthermore, placement of fixation screws or bone blocks across the closing physis should be avoided. Transphyseal reconstruction has been described using bone-patellar tendon-bone (BPTB) and quadriceps tendon-bone autograft; however, it is imperative that the bone blocks are not “fixed” across the physis, to prevent tethering. ,
Although uncommon, growth disturbance is a known complication. The surgeon should counsel the patient and family regarding this potential complication. Furthermore, consideration should be given to performing preoperative hip-to-ankle alignment radiographs, as well as postoperative radiographs every 6 months following the procedure until physeal closure. Shifflett et al. reported on four cases of genu varum and tibial recurvatum, three of which required epiphysiodesis. They noted that all four patients were asymptomatic, thus highlighting the importance of surveillance and diligence. Recognition of growth disturbance (genu valgum, tibial recurvatum, and leg-length discrepancy) while the patient is still growing allows for less-invasive treatment options, such as guided growth or hemiepiphysiodesis. If the deformity is not diagnosed until after skeletal maturity, a more extensive osteotomy may be needed.
Rerupture or Graft Rupture
Similar to adult patients, graft rupture is a potential complication of transphyseal reconstruction. Adolescents are 2.5 times more likely to undergo a revision reconstruction compared with a similar adult cohort. Adolescent athletes are more active and more likely to return to cutting and pivoting sports, activities which may lead to a 4-fold greater risk of graft rupture. Recent systematic reviews noted a 6.2% to 7.2% rate of graft rupture following transphyseal reconstruction. , In adult patients, a graft size smaller than 7 to 8 mm has been shown to be a risk factor for failure. However, the skeletally immature patient will frequently have a quadrupled hamstring graft of less than 7 mm in diameter. Weight less than 50 kg, height less than 140 cm, and body mass index less than 18 are known predictors for a graft diameter less than 7 mm. When faced with a graft size of less than 7 to 8 mm, potential options include accepting the smaller graft and augmenting with allograft. However, recent literature has shown that “augmenting” a smaller graft with allograft may increase the failure rate, even when compared with autografts smaller than 7 mm. ,
Engelman et al. reviewed the results of their transphyseal reconstructions in adolescent patients. They reported a 29% failure rate in the allograft group compared with 11% in the autograft group. The risk of graft failure was 4.4 (95% confidence interval, 1.23–18.89) times greater in the allograft group and continued to increase during postoperative months 24 to 48. Larson et al. also demonstrated a 38% rupture rate following allograft reconstruction compared with 9% for autograft, although this was not statistically significant, given the small group sizes.
Although somewhat controversial, the adult literature also supports the use of autograft in younger, more active patients. Kaeding et al. demonstrated a 5.2-fold greater risk of rupture in allograft reconstructions compared with BPTB autograft in a review of 2683 patients with an average age of 27 years. In a systematic review of seven studies of patients younger than 25 years or with a high activity level (military, Marx activity score >12 points, collegiate or semiprofessional athletes), Wasserstein et al. demonstrated a 25% failure rate in allograft reconstructions compared with 10% in autograft reconstructions.
Therefore, autograft is highly recommended in transphyseal reconstructions. Based upon the work of Pennock et al., it would be preferable to accept a slightly “smaller” autograft (6–7 mm) than “augment” with allograft. As an alternative, an all-inside technique could be used whereby the hamstring tendons, which would have been less than 7 mm, are fashioned into a 4-, 6-, or even 8-stranded graft, which is shorter but of greater diameter.
Postoperative bracing following ACLR also remains controversial. Lowe et al. performed a systematic review of studies that reported clinical or in vivo biomechanical results of functional bracing versus nonbracing after ACLR. Their conclusion was that there is limited evidence supporting the use of routine functional bracing to decrease the rate of reinjury. Yellin et al. performed a systematic review of rehabilitation protocols following ACLR in children and adolescents and identified 15 articles that described physical therapy protocols following transphyseal reconstruction. Notably, four of 15 protocols recommended functional bracing for 12 to 24 months following surgery. However, there is concern that the skeletally immature athlete may be less compliant with activity restrictions following surgery. For example, DeFrancesco et al. demonstrated that 43% of retears or graft ruptures occurred before clearance to return to sport, somewhat implicating patient noncompliance. For this reason, many surgeons continue to use functional braces following transphyseal reconstruction. However, the duration of bracing and whether bracing is only performed during athletic activities will be based upon patient and surgeon factors, as there is limited evidence supporting an individual protocol or regimen. Bracing may help “slow the athlete down” when transitioning back into sports, but this has yet to be proven in the literature.
Similarly, there is much variation in the literature regarding postoperative physical therapy protocols following reconstruction, including variation in postoperative bracing, weight-bearing and range-of-motion restrictions, and return-to-sport (RTS) criteria. It is clear, however, that postoperative therapy is critically important to a successful outcome. The treating therapist should have experience working with young athletes and should work diligently to build rapport with the athlete and ensure compliance with a home exercise program and activity limitations. Furthermore, the importance of frequent discussion of patient expectations and the recovery timeline cannot be overstated.
Moksnes et al. described four important differences between adult and pediatric or adolescent rehabilitation protocols: (1) slower progression to running and jumping to reduce physeal strain, (2) less use of external loads during strength rehabilitation, (3) an emphasis on home-based exercise, and (4) a later return to sports when compared with the adult population. Many traditional rehabilitation protocols are time based, whereas more contemporary protocols require achievement of functional milestones before proceeding to the next stage or phase.
Likewise, the decision to return to sport has traditionally been time based. In contrast, modern protocols rely on functional assessment, with most children being cleared for return to sports between 6 and 12 months postoperatively. The most commonly used tests before clearance include the hop battery tests, y-balance test, drop-jump test, and measurement of isokinetic quadriceps strength. In a study of adult patients, Grindem et al. found a substantial reduction in reinjury rate with a protocol that did not allow patients to return to sport until they both passed RTS criteria and waited 9 months postoperatively. Their RTS criteria included a score greater than 90% on isokinetic quadriceps strength testing, four single-legged hop tests, and two self-report outcome scores. The reinjury rate was reduced by 51% for each month RTS was delayed until 9 months after surgery, after which no further risk reduction was observed. The correlation between time of return to sports and incidence of rerupture has also been demonstrated in a pediatric and adolescent cohort. A recent study demonstrated that, in this patient population, time to return to sport was the only significant predictor of a second ACL injury, with a slower return being protective. It is the authors’ opinion that return to sport should be delayed until at least 9 months to help combat the rate of reinjury.
Transphyseal reconstruction is a safe option for ACLR in the skeletally immature patient. Recent case series have demonstrated that it may even be safe in Tanner stage 1 and 2 patients. However, other options (extraphyseal iliotibial band or all-epiphyseal reconstruction) should also be carefully considered in this patient population.
The most common complication includes graft rupture, although there is also a risk for growth disturbance in the growing athlete. Thorough counseling should always be performed preoperatively, and consideration should be given to postoperative alignment radiographs at 6-month intervals.
To avoid potential complications, the following surgical “pearls” are recommended:
Use graft tunnels 8 mm in diameter or less.
Attempt to place the tunnel as vertical and central as possible while still recreating an “anatomic” footprint. Use caution when using an outside-in or an accessory anteromedial portal technique.
Avoid damage to the perichondrial ring of Lacroix or the tibial tuberosity to prevent genu valgum or tibial recurvatum, respectively.
Completely fill the portion of the tunnel “traversing” the physis with soft tissue graft.
Avoid placing bone blocks or fixation devices (interference screws) across the physis.
Use a soft tissue autograft when possible and avoid “augmentation” with allograft.
Consider postoperative alignment radiographs at 6-month intervals until skeletal maturity to assess for growth deformity. Many cases of growth disturbance are initially asymptomatic. Prompt identification allows for potentially less invasive growth modulation techniques (hemiepiphysiodesis), which will not be available after skeletal maturity.