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Sports Medicine

Anterior Cruciate Ligament Injuries in Skeletally Immature Patients: A Meta-analysis Comparing Repair Versus Reconstruction Techniques

Knapik, Derrick M. MD*,†; Voos, James E. MD*,†,‡

Author Information
Journal of Pediatric Orthopaedics: October 2020 - Volume 40 - Issue 9 - p 492-502
doi: 10.1097/BPO.0000000000001569
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Abstract

Anterior cruciate ligament (ACL) injury rates in skeletally immature patients have increased substantially over the last 2 decades, with children and adolescents accounting for 0.5% to 3% of all ACL injuries.1–3 Multiple investigations have demonstrated high rates of progressive meniscal and chondral damage in the ACL-deficient knee in children treated nonsurgically or with surgical management delayed until skeletal maturity.4,5 Moreover, recurrent knee instability as a result of nonsurgical management has been shown to lead to high sport dropout rates, with up to 94% of pediatric athletes unable to participate at preinjury levels and up to 50% unable to return to play.4,6

As such, restoration of ACL anatomy and function are critical to restore functional stability to the knee, minimizing the incidence of progressive intra-articular injuries in the pediatric patient while enabling an effective return to play.7,8 However, surgical management in the skeletally immature patient presents unique challenges due to the presence of the open, active distal femoral and proximal tibial physes, shown to contribute the greatest length to the growth of the lower extremity.9 As these physes are located in the areas reserved for graft fixation in skeletally mature patients, traditional transphyseal techniques possess the risk for iatrogenic damage to one or both physes. Disruption to the physes in children with multiple years of growth remaining has been shown to increase the risk of growth abnormalities, resulting in leg-length discrepancy (LLD) or angular deformity of the lower extremity.10,11

To preserve normal physeal function during skeletal development while restoring functional stability to the knee, a number of physeal-sparing surgical techniques have been developed. These techniques include all-epiphyseal (AE) reconstruction, first described by Anderson,12 consisting of femoral and tibial tunnel drilling isolated to the epiphyses; extraphyseal reconstruction, introduced by Kocher et al,13 consisting of nonanatomic iliotibial band graft harvest and placement over the top of the femur and under the intermeniscal ligament on the tibia; and ACL repair.

The purpose of this study was to systematically review the literature to evaluate outcomes following physeal-sparing ACL reconstructive procedures (AE reconstruction and extraphyseal reconstruction) while analyzing outcomes following ACL repair in skeletally immature patients. Specifically, this study sought to determine differences in reconstructive techniques based on: (1) reported patient chronologic age and bone age; (2) postoperative outcome scores; (3) return to sport rate; and (4) postoperative complications, primarily rerupture. The authors hypothesized comparable ages, outcome scores, return to sport rate and complication incidences between AE versus extraphyseal reconstruction.

METHODS

A systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines using a PRISMA checklist.14 All literature pertaining to skeletally immature pediatric patients undergoing surgery for documented ACL ruptures using either AE reconstruction, extraphyseal reconstruction or ACL repair published between January 1990 and August 2019 was identified. The 2 authors (D.M.K., J.E.V.) independently conducted a literature search in August 2019 using the following databases: PubMed, Biosis Previews, SPORTdiscus, MEDLINE, Ovid, PEDRO, and EMBASE. Each search included various combinations of the following terms: pediatric AND immature AND athlete AND anterior cruciate ligament AND rupture AND tear AND reconstruction AND all-epiphyseal AND extra-physeal AND repair.

The inclusion criteria consisted of English language articles or articles with English translation, skeletally immature patients sustaining ACL ruptures treated using AE reconstruction, extraphyseal reconstruction or ACL repair with minimum 2-year follow-up. Only cases in which patients were classified as skeletally immature with specific documentation of open physes at the distal femur and proximal tibia at the time of surgery were included in the final analysis. Exclusion criteria consisted of: non-English language articles, literature reviews, animal studies, cadaveric or in vitro investigations, biomechanical studies, technical notes or technique papers, patients sustaining partial ACL tears, patients undergoing nonoperative management or delayed surgical treatment, patients with <2-year follow-up, patients undergoing partial transphyseal or transphyseal ACL reconstruction, patients treated using hybrid techniques, studies involving skeletally mature patients or those without specific mention regarding physeal appearance, and studies not separating outcomes in skeletally mature versus skeletally immature patients. As the purpose of this review was to compare demographics and outcomes of skeletally immature patients undergoing AE, extraphyseal or ACL repair, that is, methods in which neither the distal femoral nor proximal tibial physes were violated. We believe that by excluding studies undergoing any physeal disruption, either transphyseal through the distal femoral and proximal tibia physes, or hybrid techniques, we would be able to perform more meaningful analyses on patients treated with true physeal-sparing surgery, utilizing a more homogenous population of patients, especially in regards to the incidence of complications such as LLD or angular deformities.

Following the 2 independent authors’ search of the literature, a total of 427 citations were identified. The search process is shown in the flow diagram (Fig. 1). Following title and abstract evaluation, a total of 73 articles were selected for further evaluation. Of these studies, a total of 59 studies were excluded due to: patients undergoing transphyseal reconstruction (n=4), management using hybrid techniques (n=3), nonoperative management (n=3), studies not documenting skeletal maturity (n=7), studies with <2-year follow-up (n=8), failure to separate skeletally mature from immature patients (n=8), cadaveric studies (n=5), biomechanical studies (n=4), reviews (n=11), technical/technique studies (n=2), or animal studies (n=3). One study was excluded due to the reporting of redundant patients present in a later publication. Following the application of the inclusion/exclusion criteria, a total of 14 studies were identified for further analyses. To ensure that all available studies were identified, references cited in the included articles were cross-referenced for inclusion if they were overlooked during the initial search.

FIGURE 1
FIGURE 1:
Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of study.

To assess the quality of the studies, the modified Coleman Methodology Score (MCMS) was used, which allows for evaluation study methodology based on 10 criteria, giving a total score between 0 and 100.15 The subsections that comprise the CMS are based on the subsections of the Consolidated Standards of Reporting Trials (CONSORT) statement (for randomized controlled trials) which are modified to allow for other trial designs. The Coleman criteria were modified to make them reproducible and relevant for the systematic review of ACL reconstruction or repair in skeletally immature patients (Table 1). Each study was independently scored in duplicate by the 2 authors (D.M.K., J.E.V.) for each of the criteria adopted. Any disagreements were resolved by discussion.

TABLE 1 - Modified Coleman Methodology Score15
Category Options Score
Part A: Only one score to be given for each of the 7 sections
 Study size—number of <20 0
20-50 4
50-100 7
>100 10
 Mean follow-up (mo) <12 0
12-36 4
37-60 7
> 61 10
 Surgical approach Different approach used and outcome not reported separately 0
Different approach used and outcome reported separately 7
Single approach used 10
 Type of study Retrospective cohort study 0
Prospective cohort study 10
Randomized controlled trial 15
 Description of indications for technique Described without % specified 0
Described with % specified 5
 Descriptions of surgical technique Inadequate (not stated, unclear) 0
Fair (technique only stated) 5
Adequate (technique stated, details of surgical procedure given) 10
 Description of postoperative rehabilitation Described 5
Not described 0
Part B: Scores may be given for each option in each of the 3 section if applicable
 Outcome criteria Outcome measures clearly defined 2
Timing of outcome assessment clearly stated 2
Use of outcome criteria that has reported reliability 3
General health measure included 3
 Procedure of assessing outcomes Subjects recruited 5
Investigator independent of surgeon 4
Written assessment 3
Completion of assessment by patients themselves with minimal investigator assistance 3
 Description of subject selection process Selection criteria reported and unbiased 5
Recruitment rate reported >90% 5
Recruitment rate reported <90% 0

Statistical analysis was performed comparing demographic data and outcomes between skeletally immature patients undergoing AE reconstruction versus extraphyseal reconstruction. An unpaired Student t test was used to compare differences for continuous variables [mean chronologic age, mean final follow-up, Lysholm, International Knee Documentation Committee (IKDC) and Tegner activity scores], while categorical variables (incidence of a range of motion deficits, the incidence of LLD based on postoperative long-leg standing radiographs, return to play rates, and incidence of ACL reruptures and contralateral ACL ruptures requiring surgery) were evaluated using a χ2 test. A P-value <0.05 was used to determine statistical significance. All statistical analyses were performed using SPSS (Version 23; IBM Corp., Armonk, NY) software.

RESULTS

A total of 14 studies16–29 composed of 443 patients were included within the review, comprising 164 patients undergoing AE reconstruction, 252 treated with extraphyseal reconstruction, and 27 treated with ACL repair (Table 2). The mean chronologic age of all patients was 11.5±1.6 years (range, 8.5 to 14 y). No significant difference in chronological age at the time of surgery was appreciated when comparing patients treated with AE versus extraphyseal reconstruction (P=0.65) (Tables 3, 4). Chronologic age based on patient sex was reported in only 2 studies.16,29 Patients undergoing AE reconstruction had a mean older bone age when compared with patients undergoing extraphyseal reconstruction, as reported in a single study,26 while no bone age was recorded in patients undergoing ACL repair. Mean final follow-up time among all patients was 52.1±16.1 months (range, 24 to 78 mo), with patients undergoing extraphyseal reconstruction possessing significantly greater follow-up compared with patients treated with AE reconstruction (P=0.04). Graft type was reported in 100% (n=164/164) of patients undergoing AE reconstruction, with 65% (n=107/164) treated using hamstring autograft. All patients (100%; n=252/252) undergoing extraphyseal reconstruction were treated using an iliotibial band autograft.

TABLE 2 - Overview of Included Studies
References Level of Evidence # of Patients Sex Age at Surgery [Mean±SD (Range)] (y) Tanner Stage (# of Patients) Skeletal Age [Mean±SD (Range)] Technique Graft Type Meniscal Tearing (# of Patients) Concomitant Procedure (# of Patients) MCMS
Anderson17 4 12 Male=10 Female=2 13.3 (11.1-15.9) 1 (3); 2 (4); 3 (5) NR AE Hamstring LMT (9) MMT (2) LMR (6) PLM (1) PLC repair (1) MMR (2) 59
Bonnard et al19 4 57 Male=43 Female=13 12.2 (6.8-14.5) NR 11.5 (7-15) AE Patellar tendon LMT (11) MMT (5) LMR (6) MMR (2) PMM (2) 58
Akinleye et al16 4 1 Female=1 10 NR NR AE Hamstring None None 44
Koch et al24 4 12 Male=10 Female=2 12.1 (10.4-13.4) NR NR AE Hamstring NR NR 49
Wall et al28 4 21 Male=23 Female=4 11 (8-15) NR 11.8±1.8 (8.5-14.0) AE Hamstring LMT (8) MMT (3) LMR (4) MMR (2) PLM (3) 59
Cordasco et al21 4 23 Male=17 Female=6 12.2 (9.9-14.5) NR Male=13.1 Female=11.7 AE Hamstring LMT (7) MMT (3) LMR (6) PLM (1) MMR (2) 60
Guzzanti et al23 4 8 Male=8 11.5 1 (8) 10.9 AE Hamstring MMT (1) PMM (1) 52
Pennock et al29 4 30 NR Male=12.2 (8.7-15.7) Female=11 (7.4-13.3) NR Male=12.2 (8-15) Female=10.7 (8-12) AE Hamstring NR NR 64
Kocher et al25 3 237 86% males (204) 11.2±1.7 1 or 2 NR EP ITB LMT (100) MMT (18) MMR (14) PMM (4) LMR (79) PLM (16) MR+PM (4) 58
Micheli et al26 4 8 Male=7 Female=1 10.9±3.8 NR 10.3±3.5 EP ITB LMT (1) MMT (3) PLM (1) PMM (1) PLC repair (1) MMR (2) 58
Nakhostine et al27 4 5 Male=5 14 (12-15) NR NR EP ITB LMT (1) PLM (1) 39
Chotel et al20 4 2 Male=2 8.5 (7-10) NR NR EP ITB MMT (1) MMR (1) 48
Gagliardi et al22 3 22 Male=12 Female=12 13.9±3.2 NR NR Repair LMT (12) PLM (6) LMR (6) 57
Bigoni et al18 4 5 Male=4 Female=1 9.2 (8-10) 1 or 2 NR Repair None None 57
AE indicates all-epiphyseal reconstruction; EP, extraphyseal reconstruction; ITB, iliotibial band; LMR, lateral meniscal repair; LMT, lateral meniscal tear; MCMS, modified Coleman Methodology Score; MMR, medial meniscal repair; MMT, medial meniscal tear; MR, meniscal repair with unspecified laterality; NR, not recorded; PLC, posterolateral compartment; PLM, partial lateral menisectomy; PM, partial menisectomy with unspecific laterality; PMM, partial medial menisectomy.

TABLE 3 - Reported Clinical Outcomes Following ACL Surgery Based on Technique
References Follow-up [Mean±SD (Range)] (mo) Lysholm [Mean±SD (Range)] IKDC [Mean±SD (Range)] Tegner [Mean±SD (Range)] Range of Motion Return to Sport (Mean Timing) (mo) LLD (# of Patients) (Mean) (mm) # of Patients With LLD ≥1 cm Mean Angular Deformity (# of Patients) (deg.) Complications Subsequent Surgery
Anderson17 49.2 (24-96) NR 96.5 (86-100) NR N=5 with flexion deficit <8 degrees N=8, very strenuous; N=4, strenuous +7; 3 −3; 1 1 None Superficial infection (n=1) None
Bonnard et al19 66 (24-168) NR 94 6.75 (4-9) NR N=50/57 (11 mo) −0.4; 55 0 0.7 varus (55) Graft rerupture (n=3) Revision ACLr (n=2)
Akinleye et al16 36 NR NR NR Full motion N=1/1 (12 mo) None 0 None Stiffness (N=1) Contralateral ACLr (n=1) Manipulation under anesthesia for stiffness (n=1)
Koch et al24 54 (39-80) 93 (73-100) 88.5 (74.7-98) 7.7 N=4 with flexion deficit of 5-10 degrees NR +21; 1 +16; 1 +5-10; 4 2 1.5 varus (1) Graft rerupture (n=2) Revision ACLr (n=2) Meniscal repair (n=1)
Wall et al28 43.2±16.8 (24-79.2) NR 94±11 (49-100) NR Full extension and all within 5 degrees full flexion N=17/21 +22.3; 3 3 Valgus (1)* Graft rerupture (n=3) Graft laxity (n=1) MMT (n=2) LMT (n=3) Notch impingement (n=2) Prominent hardware (n=2) Skin infection (n=2) Patellar dislocation (n=1) LFC fracture (n=1) Genu valgum (n=1) Revision ACLr (n=4) Notchplasty (n=1) LMR (n=1) MMR (n=1) Hemiepiphysiodesis (n=1) Distal femoral epiphysiodesis (n=1) MPFL reconstruction (n=1) Proximal tibial osteotomy (n=1) Contralateral ACLr (n=2)
Cordasco et al21 24 (24-45) 97.9±4.0 94.6±4.9 NR NR N=22/23 (13.5 mo) >+5; 6 NR None Graft rerupture (n=1) Contralateral ACL rupture (n=1) MMT (n=1) Revision ACLr (n=1) Contralateral ACLr (n=1) PLM (n=1)
Guzzanti et al23 69.2 (48-84) NR NR NR NR N=5/5 None 0 None None None
Pennock et al29 38.4 (24-60) 93.6 NR 7.6±1.0 NR N=25/26 +12; 1 1 None Graft rerupture (n=4) Contralateral ACL rupture (n=3) Revision ACLr (n=4) Contralateral ACLr (n=3)
Kocher et al25 74.4 (25.2-298.8) 93.4±9.9 93.3±11.0 7.8 (2-10) NR 96.5% None 0 None Graft rupture (n=9) Arthrofibrosis (n=5) Septic arthritis (n=1) Wound dehiscence (n=1) Meniscal/chondral pathology (n=13) Contralateral ACLr (n=13)
Micheli et al26 62.9 (25-168) 97.8 (93-100) NR NR Full N=8/8 (range, 9-15 mo) None 0 None None None
Nakhostine et al27 52.8 (24-72) NR NR NR N=2 with 5 degrees extension deficit N=5/5 None 0 None None None
Chotel et al20 78 (60-96) NR 88 (82-94) NR NR NR +15; 1 +10; 1 2 6 valgus (1) Genu valgum (n=1) Epiphysiodesis (n=1) Hardware removal (n=2)
Gagliardi et al22 38.4 (26.8-40.8) 100 (89.5-100) 90.8 (83.9-97.7) NR Full in 98% NR (11.9) NR NR NR Graft rerupture (n=9) NR
Bigoni et al18 43.4 (25-56) 93.6 (68-100) 93.3 (67.8-95) NR Full N=4/5 None 0 None NR None
*Measurement values not provided.
− indicates limb shortening against contralateral leg; +, limb overgrowth against contralateral leg; ACL, anterior cruciate ligament; ACLr, anterior cruciate ligament reconstruction; IKDC, International Knee Documentation Committee; LFC, lateral femoral condyle; LLD, limb-length discrepancy; LMR; lateral meniscal repair; LMT, lateral meniscal tear; MMR, medial meniscal repair; MMT, medial meniscal tear; MPFL, medial patellofemoral ligament; NR, not recorded; PLM, partial lateral menisectomy.

TABLE 4 - Patient Age and Postoperative Follow-up Outcomes Based on Technique
All-epiphyseal Extraphyseal Repair P*
Chronologic age (y)
 Mean±SD 11.7±1.0 11.2±2.3 11.6±3.3 0.65
 Range 10-13.3 8.5-14 9.2-13.9
Bone age (y)
 Mean±SD 11.6±0.5 10.3±0 NR —†
 Range 10.9-12.4
Final follow-up (mo)
 Mean±SD 47.5±15.3 67±11.5 40.9±3.5 0.04
 Range 24-69.2 2.8-78 38.4-43.4
Lysholm
 Mean±SD 94.8±2.7 95.6±3.1 96.8±4.5 0.80
 Range 93-97.9 93.4-97.8 93.6-100
International Knee Documentation Committee
 Mean±SD 93.5±3.0 90.1±3.7 92.1±1.8 0.46
 Range 88.5-96.5 88-93.3 90.8-93.3
Tegner
 Mean±SD 7.4±0.5 7.8 NR —†
 Range 6.8-7.7
*Analysis performed for all-epiphyseal versus extraphyseal only.
†No analysis performed due to presence of a single study reporting bone age in extraphyseal reconstruction group.
NR indicates not recorded.

Concurrent medial meniscal tearing was present in 14 patients treated with AE reconstruction, 22 with extraphyseal reconstruction, and no patients undergoing ACL repair, while lateral meniscal tearing was recorded in 35 patients undergoing AE, 102 with extraphyseal reconstruction, and 12 with ACL repair (Table 2). The most common concomitant procedures included: lateral meniscal repair (n=22), medial meniscal repair (n=8), and partial lateral menisectomy (n=5) for AE reconstruction; lateral meniscal repair (n=79) and partial lateral menisectomy (n=18) for extraphyseal reconstruction; and lateral meniscal repair (n=6) and partial lateral menisectomy (n=6) for ACL repair.

At final follow-up, no significant differences in mean Lysholm (P=0.80) or IKDC (P=0.46) outcome scores were appreciated between patients treated with AE or extraphyseal reconstruction (Table 4). There was no significant difference in the incidence of patients with any reported range of motion deficits in knee flexion or extension between either reconstructive technique at final follow-up (P=0.82) (Table 5).

TABLE 5 - Postoperative Outcomes Based on ACL Surgery Technique
n/N (%)
All-epiphyseal (N=164) Extraphyseal (N=252) Repair (N=27) P*
ROM reported 46 (28) 12 (4.8) 27 (100)
 # of patients with full ROM 37/46 (80) 10/12 (83) 26/27 (96) 0.82
Return to activity reported 152 (93) 250 (99) 5 (19)
 # of patients return to full activity 132/152 (87) 242/250 (97) 4/5 (80) <0.001
Postoperative limb length reported 164 (100) 252 (100) 5 (17)
 # of patients with LLD 20/164 (12) 2/252 (0.8) 0 (0) <0.001
 # of patients with limb overgrowth 17/20 (85) 2/2 (100)
 # of patients with limb shortening 3/20 (15)
 # of patients with limb length disturbance ≥10 mm 7/164 (4.3) 2/252 (0.8) 0/5 (0) 0.02
Postoperative angular deformity reported 164 (100) 252 (100) 5 (17)
 # of patients with varus malalignment 1/164 (0.6) 0/252 (0)
 # of patients with valgus malalignment 1/164 (0.6) 1/252 (0.4)
Complications reported 164 (100) 252 (100) 22 (81)
 # of patients with rerupture 13/164 (7.9) 9/252 (3.6) 9/22 (41) 0.52
 # of patients with contralateral ACL rupture 4/164 (2.4) 0/252 (0) 0
*Analysis performed for all-epiphyseal versus extraphyseal only.
ACL indicates anterior cruciate ligament; LLD, limb-length discrepancy; ROM, range of motion.

Return to activity rate was significantly higher in patients undergoing extraphyseal reconstruction compared with AE reconstruction (P<0.001) (Table 5) The incidence of any reported LLD was significantly higher in patients following AE reconstruction when compared with extraphyseal (P<0.001), with no reports of any LLDs following ACL repair. Overgrowth of the operative limb was reported in 85% (17/20) of patients with LLD following AE reconstruction, and 100% (2/2) patients following extraphyseal reconstruction. LLDs measuring ≥10 mm at final follow-up were significantly higher following AE reconstruction compared with extraphyseal reconstruction (P=0.02). Varus or valgus malalignment was reported in 0.6% and 0.6% of patients undergoing AE reconstruction, respectively; while only a single study reported the development of genu valgum following extraphyseal reconstruction. No angular deformities were reported following ACL repair.

The presence or absence of a complication was reported in all but one study.18 ACL rerupture was the most commonly reported complication and while nonsignificant, was more likely to occur following AE reconstruction when compared with extraphyseal reconstruction (P=0.52) (Table 5). Contralateral ACL ruptures requiring surgery were reported in 2.4% of patients undergoing AE reconstruction and no patients treated with extraphyseal reconstruction.

The mean MCMS score was 54.4 (range, 39 to 64) demonstrating that the quality of the studies was poor. No significant difference was appreciated between the mean values of MCMS calculated by the 2 examiners.

DISCUSSION

The principles findings from this investigation were that in 14 studies comprising 443 skeletally immature patients undergoing ACL surgery, no significant differences in chronologic age was appreciated between patients undergoing AE versus extraphyseal reconstruction. At final follow-up, no significant differences in Lysholm or IKDC outcomes scores were reported between the 2 reconstruction groups, while the return to activity rate was higher following extraphyseal reconstruction when compared with AE reconstruction. There was a significantly higher rate of reported LLD and LLD measuring ≥10 mm following AE reconstruction, while ACL reruptures were more common in patients undergoing AE reconstruction.

No significant differences in chronologic age were appreciated when comparing the 2 reconstructive groups. While mean bone age was younger following extraphyseal reconstruction, data was only available in a single investigation,26 preventing further statistical analysis. Prior studies have advocated for the use of extraphyseal reconstruction as opposed to AE reconstruction in younger patients with >2 to 4 years of growth remaining due to the absence of any transosseous tunnels during reconstruction, minimizing the potential for iatrogenic physeal injury.30,31 Furthermore, extraphyseal reconstruction allows for less complicated revision surgery due to the absence of tunnels and the preservation of autograft sources.13

Determination of bone age is crucial in patients undergoing surgical intervention near open physes, necessitating assessment of skeletal maturity and remaining growth in all pediatric patients.7 Bone age was assessed in all reporting studies using the Greulich-Pyle Bone Age atlas, which has been shown to be the most accurate method of assessing skeletal maturity and remaining skeletal growth in the pediatric patient.7,32 In contrast, maturity assessment using the Tanner staging system was frequently reported,13,17,18,23,25 however, the Tanner staging system has not been shown to accurately predict remaining skeletal growth.19,33 Moreover, the evaluation of the Tanner stage has been shown to be highly unreliable among clinicians, and specifically, in orthopaedic surgeons.33 The influence of remaining skeletal growth in patients undergoing ACL repair remains largely unknown, necessitating further research to better understand the impact of age in regards to ACL repair outcomes in relation to AE and extraphyseal reconstruction in skeletally immature patients.

The return to activity rate was significantly greater following extraphyseal reconstruction when compared with patients undergoing AE reconstruction. While not specifically analyzed in this investigation, the etiology responsible for this finding is likely multifactorial. ACL reinjury was found to be more common in patients treated with AE reconstruction and has been shown to compromise return to activity in pediatric athletes.34,35 Other variables potentially affecting return to activity include type and frequency of postoperative rehabilitation,36 return to sport timing34 and type of activity,37 with a higher risk of reinjury inherent in return to a higher level, cutting and pivoting sports. Analysis of these variables and others, including skeletal age at the time of surgery, on return to activity rate and timing following physeal-sparing and ACL repair techniques, warrant investigation to identify risk factors for sport dropout, and delayed return to activity timing to maximize patient health and minimize time lost from activity.

The incidence of any LLD, as well as LLD measuring ≥10 mm, was significantly more common following AE reconstruction when compared with extraphyseal reconstruction at final follow-up, with no reported LLD following ACL repair. Moreover, the presence of angular deformities was reported in only 2 patients undergoing AE reconstruction, compared with only a single patient treated with extraphyseal reconstruction and no patients following ACL repair. Despite increased attention to physeal avoidance, physeal disruption remains a significant concern following AE reconstruction in skeletally immature patients. Multiple studies have reported subsequent LLD and angular deformity observed at follow-up secondary to physeal damage despite attempted physeal avoidance following AE reconstruction,21,24,28 with reported rates approaching 13% overall.38 Authors have speculated that despite epiphyseal tunnel placement, the proximity of the growth plates to the drill paths of the tunnels may cause heat damage, leading to premature physeal closure.10 Moreover, the systematic review of 27 studies comparing transphyseal (n=21 studies with tunnels through both the distal femoral and proximal tibial physes) to physeal-sparing techniques (n=6 studies; n=5 AE reconstruction; n=1 extraphyseal reconstruction) by Pierce et al39 reported no significant differences based on technique on the incidence of LLD and angular deformities. Meanwhile, the meta-analysis by Frosch et al10 of 55 articles consisting of 935 children and adolescent patients found transphyseal reconstruction to result in a significantly lower risk of LLD or axis deviations when compared with physeal-sparing techniques (AE, extraphyseal, ACL repair). The majority of patients with LLD were reported to possess limb overgrowth in the operative extremity, which has been attributed to an increase in vascularization and mitotic activity in the physis following surgery.40 As such, LLD following physeal-sparing reconstruction remains a concern, especially following AE reconstruction, while further investigations are warranted examining the incidence of LLD and angular deformity following ACL repair.

While nonsignificant, ACL rerupture was more likely to occur following AE reconstruction when compared with extraphyseal reconstruction. Previous studies have shown skeletally immature patients to be at higher risk for graft failure requiring subsequent revision, partially attributed to higher activity levels and noncompliance following surgery when compared with older patients.34,41 The 7.9% graft rerupture rate following AE and 3.6% rate following extraphyseal reconstruction in our study is within to slightly below the range of graft rerupture rates in children reported in prior studies, ranging between 4.5% to 17% and 4.4% to 14%, respectively.13,24,25,42,43 Meanwhile, the 41% rerupture rate following ACL repair was derived based on the findings from the only study reporting rerupture in this cohort.22 Prior studies have reported time from injury to ACL repair is critical, with the native ACL being amenable to repair within 3 months of injury when the remnant tissue is of high quality.22 Surgical delays result in contraction of the torn edges, resulting in consequent gapping at the repair site, increasing the risk for subsequent rerupture.44 While prior investigations have examined for associations between patient characteristic, graft variables, and the presence of concomitant injuries on rerupture rates following physeal-sparing reconstruction,42 further studies are necessary to identify additional modifiable risk factors accounting for the high rerupture rate following AE reconstruction and ACL repair in skeletally immature patients.

The increase interest in ACL repair must be balanced with the known limitations of the procedure. Despite its popularity in the 1960s and 1970s, ACL repair was largely abandoned due to multiple reports of high rerupture rates following repair.45 However, improvements in surgical implants and repair techniques,46 appropriate case selection,47 and improved healing utilizing biologic augmentation48,49 have renewed interest in ACL repair. ACL repair has been shown to possess the advantage of avoiding potential donor site morbidity associated with the autologous harvest, preserving the native biology of the ligament while averting potential for LLD secondary to physeal disruption.18,50

As such, appropriate patient selection, especially in the highly noncompliant pediatric patient population, based on lesion pattern is critical. Currently, ACL tears most amendable to repair are those in which the ACL has avulsed off the femoral footprint,22,51 estimated to account for ∼10% of ACL tears.52 Proximal avulsions have been shown to possess a superior environment for healing due to the proximity of the bone.46 When treated in a timely manner, proximal avulsions can allow for direct repair of viable remnant tissue capable of holding sutures without gapping across the repair site.53 ACL repair research has been further advanced by investigations analyzing various augmentation strategies using extracellular matrix scaffolds48,49 as well as intraligamentary stabilization inserts47,50 to enhance repair healing and outcomes. Despite limited data, promising outcomes have been demonstrated for skeletally mature adults undergoing ACL repair with augmentation for proximal ACL avulsions.54 However, further high-quality investigations are critical and necessary to better understand if ACL repair in the appropriately indicated patient should be readopted for the treatment of the skeletally immature, ACL-deficient patient.

This study was not without limitations. The small sample size and poor MCMS score was related to the strict inclusion/exclusion criteria utilized, namely including only patients in which open physes indicative of skeletal immaturity were explicitly reported. As a result, few skeletally immature patients undergoing ACL repair were identified, resulting in all statistical analyses comparing only AE versus extraphyseal reconstruction. Moreover, the poor MCMS score is a result of all studies in this investigation consisting of Level III or IV evidence. Since the MCMS criteria awards higher scores to larger, randomized prospective studies, this finding further emphasizes the need for large, multicenter, prospective investigations evaluating demographics and outcomes for skeletally immature patients undergoing ACL surgery. The return to activity rate was significantly higher for patients under extraphyseal reconstruction; however, this finding may be due to the significantly greater follow-up time in patients treated with extraphyseal reconstruction compared with those treated with AE reconstruction, warranting further studies with >2-year minimum follow-up. Due to the inherent heterogeneity of the reported data, studies varied in the degree of details reported regarding time from injury to surgery, stage of skeletally maturity at the time of surgery, return to play timing, KT-1000 testing results, physical examination results at final follow-up, total longitudinal growth following surgery until maturity and rehabilitation protocol. As such, the authors were limited in the ability to conduct any meaningful analysis of these variables. Moreover, inconsistent reporting of graft type limited the ability of the authors to perform any meaningful subgroup analysis in patients undergoing AE reconstruction, while the heterogeneity of complications reported between groups limited analysis of complications outside of rerupture between groups. In addition, the authors were unable to match cohorts of patients within each treatment group for chronologic age, bone age, or sex, making comparisons between the treatment groups difficult.

In conclusion, the treatment of ACL ruptures in the skeletally immature patient remains a challenge, and despite various physeal-sparing surgical techniques, no consensus on optimal treatment strategy currently exists. Data from 14 studies found no significant differences in chronologic age between treatment groups, while patients undergoing AE reconstruction had a significantly higher incidence of all LLD and LLD measuring ≥10 mm when compared with those treated with extraphyseal reconstruction. Results following AE reconstruction were comparable to extraphyseal reconstruction procedures based on Lysholm and IKDC scores, however, return to activity rate was significantly greater in patients treated with extraphyseal reconstruction compared with those undergoing AE reconstruction. High rerupture rates remain a significant concern following AE reconstruction and ACL repair. As ACL repair techniques and instruments continue to advance, along with the evolution of novel augmentation strategies, further study is necessary to determine the viability and safety of ACL repair in the appropriately selected skeletally immature patient when compared with traditional physeal-sparing reconstruction techniques.

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Keywords:

anterior cruciate ligament; repair; reconstruction; all-epiphyseal; extraphyseal; skeletally immature; athlete

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