Outcomes Following Primary Anterior Cruciate Ligament Reconstruction Using a Partial Transphyseal (Over-the-Top) Technique in Skeletally Immature Patients

Abstract

Background

The incidence of anterior cruciate ligament (ACL) injuries in skeletally immature patients is increasing, with ACL reconstruction preferred in this population due to reported chondroprotective benefits. Due to concerns with growth disturbance following ACL reconstruction in skeletally immature patients, various physealsparing and partial transphyseal techniques have been developed. Currently, there is no consensus on the most effective ACL reconstruction technique in skeletally immature patients. The purpose of the current study was to report the outcomes of a partial-transphyseal over-the-top (OTT) ACL reconstruction in a cohort of skeletally immature patients.

Methods

All patients with radiographic evidence of open tibial and femoral physes that underwent primary ACL reconstruction using a partial-transphyseal OTT technique between 2009-2018 at a single tertiary-care institution with at least twelve months of clinical follow-up were retrospectively reviewed. Patient demographics, physical examination findings, graft ruptures, return to sport, and Tegner activity levels were analyzed. Statistical significance was defined as p<0.05.

Results

Overall, 11 males and 1 female (12 knees) with a mean age of 12.8±1.8 (range: 10-16) years were included in the study. The mean postoperative follow-up of the cohort was 2.3±1.2 (range: 1.1-5.2) years. All ACLs were reconstructed with hamstring autograft with allograft augmentation utilized in a single patient. There were two cases of ACL graft rupture (16.7%). All patients were able to return to the same or higher level of sporting activity at an average of 7.4+2.7 months. There were no cases of clinically significant longitudinal or angular growth disturbance.

Conclusion

Partial transphyseal ACL reconstruction using a transphyseal tibial tunnel and an extra-articular OTT technique on the femur in skeletally immature patients affords minimal risk of growth disturbance with a graft rupture rate consistent with what has been reported in this high-risk population. All patients were able to return to sport at the same or higher level.

Level of Evidence: IV

Introduction

The incidence of anterior cruciate ligament (ACL) injuries in skeletally immature patients is increasing secondary to the surge in competitive sport participation at younger ages.^1-6 ACL deficient knees, particularly in young, active individuals, are at increased risk for subsequent cartilage, meniscal, and ligamentous injuries.^3,7-13 In this skeletally immature population, several studies have recommended early ACL reconstruction over nonoperative management in the setting of acute ACL injury despite the presence of open physes.^3,9,14-17

Numerous ACL reconstructive techniques for skeletally immature patients have been described, including physeal-sparing, partial-transphyseal, or complete transphyseal techniques.^18-32 The aim of these techniques is to restore knee stability while minimizing iatrogenic physeal injury and subsequent growth disturbance.^3,32 Currently, there is no consensus on the most effective ACL reconstructive technique in the skeletally immature population.^3,5,33,34

In 1972, Galway and colleagues described an anterolateral stabilization technique for ACL insufficiency using a strip of the iliotibial band (ITB) secured to the distal femur.³⁵ This technique was later modified by Bertoia et al. to include a longer, intra-articular graft that went ‘over-the-top’ (OTT) of the lateral femoral condyle and into the notch.³⁶ In 1994, Andrews et al. reported their outcomes using a transphyseal tibial tunnel with OTT, extra-articular fixation on the femur.³⁷ A similar technique has been utilized frequently at our institution. Reported outcomes using this technique in skeletally immature patients are limited to small case series’ with a total of 36 patients identified throughout the available literature.^11-13,37,38 Therefore, the purpose of this study is to report the clinical outcomes, return-to-sport, and graft rupture rates after primary ACL reconstruction using a transphyseal tibial tunnel and an OTT extraarticular technique on the femur in skeletally immature individuals.

Methods

Patient selection

Institutional review board (IRB) approval was obtained for this study. All electronic medical records of patients less than 18 years old that underwent primary ACL reconstruction between 2009 and 2018 at a single tertiarycare institution were retrospectively reviewed. Patients with radiographic evidence of open tibial and femoral physes that were treated with the partial-transphyseal OTT technique using autograft tendon with at least twelve months of clinical follow-up were included for analysis. Exclusion criteria consisted of closure of either the distal femur or proximal tibia physis, OTT ACL reconstruction using allograft, and clinical follow-up of less than one year. Suspected ACL injuries were diagnosed on physical examination and confirmed with preoperative magnetic resonance imaging (MRI). Demographic variables, including sex, age, body mass index (BMI), and medical comorbidities, were documented for each patient. Surgical variables, including graft type, graft diameter, and concomitant injuries, were also recorded. The time elapsed from ACL reconstruction to return-to-sport participation, as well as preinjury and postoperative Tegner activity levels, were documented. The current study received no external funding.

Surgical technique

All partial-transphyseal OTT ACL reconstructions were performed by board-certified, sports fellowship-trained orthopaedic surgeons. All patients were treated with hamstring autograft, which was harvested in standard fashion. One patient’s graft was noted to be small intraoperatively and augmented with allograft. The graft was prepared using #2, non-absorbable, braided sutures in a locking fashion on both sides of the tendon. It was then doubled over and sized based on surgeon preference. A standard diagnostic arthroscopy was then carried out to assess ACL integrity and concomitant injuries, all of which, if present, were treated prior to ACL reconstruction.

The tibial tunnel was drilled utilizing a tip-pointing tibial guide centered in the anatomic footprint of the ACL and set at 55-60 degrees. Fluoroscopy was utilized to ensure the tunnel was oriented vertically to reduce the obliquity across the physis and to confirm that the starting point was distal to the proximal tibial physis.

Next, a three-centimeter (cm) lateral incision was made sharply through skin and subcutaneous tissue just proximal to the palpable lateral femoral epicondyle. The ITB was divided longitudinally and the vastus lateralis was mobilized and elevated anteriorly off the intermuscular septum. The posterior aspect of the femur was bluntly dissected until the posterior aspect of the femoral notch was palpable.With the use of a gaff hook, a passing suture was then passed around the back of the femur and into the notch. The ACL graft was then pulled into the knee joint through the tibial tunnel and notch and over the top of the lateral femoral condyle, until it was palpable posteriorly. The graft was then delivered out of the skin wound on the lateral aspect of the femur. Utilizing fluoroscopy, the graft was secured to the femur approximately 1.5-3.0 cm proximal to the distal femoral physis using a fully threaded AO cancellous screw and washer (Synthes, Switzerland), or cannulated cancellous screw and spiked washer (ConMed Corporation, NY, USA) (Figure 1A/1B). While applying a posterior drawer, the graft was tensioned with the knee in approximately 15° of flexion and secured distal to the proximal tibial physis using a Richard’s staple (Smith and Nephew, London, UK) or a fully threaded AO cancellous screw with washer (Synthes, Switzerland) (Figure 2A/B). Both femoral and tibial fixation methods were based on surgeon preference. The knee was copiously irrigated, and incisions were closed in standard fashion. Standard anteroposterior (AP) and lateral radiographs were obtained two weeks postoperatively (Figure 3A/B).

Figure 1.

(A) Intraoperative anteroposterior radiograph showing fixation of the ACL graft proximal to the distal femoral physis in the over-the-top position. (B) Intraoperative lateral radiograph showing fixation of the ACL graft proximal to the distal femoral physis in the over-the-top position.

Figure 2.

(A) Intraoperative anteroposterior radiograph showing fixation of the ACL graft distal to the proximal tibial physis. (B) Intraoperative lateral radiograph showing fixation of the ACL graft distal to the proximal tibial physis.

Figure 3.

(A) Standing anteroposterior radiograph 2 weeks postoperatively. (B) Standing lateral radiograph 2 weeks postoperatively.

Isolated ACL reconstructions were made weightbearing and range of motion (ROM) as tolerated without the use of a brace. Patients that underwent concomitant procedures, such as meniscal repair, had restricted weight bearing, range of motion, and brace use for a minimum of 6 weeks postoperatively.

Postoperative rehabilitation and return-to-sport

Postoperatively, patients initiated the Multicenter Orthopaedic Outcomes Network (M.O.O.N.) ACL rehabilitation protocol.³⁹ The time elapsed from ACL reconstruction to return-to-sport participation, as well as preinjury and postoperative Tegner activity levels, were documented.

Clinical outcomes

The Lachman test, anterior drawer, pivot shift test, varus and valgus stability, and knee ROM were assessed and recorded. The Lachman test was defined as negative (< 3 millimeters [mm] of laxity), grade 1 (3-5 mm of laxity), grade 2 (5-10 mm of laxity), and grade 3 (> 10 mm of laxity). The pivot shift was defined as negative (no instability), grade I (glide), grade II (clunk) and grade III (gross clunk with locking).⁴⁰

Statistical analysis

Statistical analysis was performed using Statistical Package for Social Sciences (SPSS) version 25 (Chicago, IL). Fisher’s exact test was used for categorical variables, and Student’s t-test (2-tailed) was used for continuous variables with statistical significance defined as p<0.05.

Results

Demographics

Overall, 11 males and 1 female (12 knees) with a mean postoperative follow-up of 2.3±1.2 (range: 1.1-5.2) years were included in the study. Mean age and BMI at the time of surgery were 12.8±1.8 (range: 10-16) years and 20.3±3.7 (range: 15.7-27.7) kg/m², respectively. Patients indicated the sport at the time of injury as American football (n=6), basketball (n=2), motocross (n=2), soccer (n=1), and snow skiing (n=1). Lateral meniscus tears were the most common concomitant injury (n=4; 33.3%), followed by injury to the medial meniscus (n=1; 8.3%) and medial collateral ligament (MCL) (n=1; 8.3%). The MCL injury was treated with concomitant repair at the time of OTT ACL reconstruction while all but one meniscus tear was managed with arthroscopic all-inside repair. One lateral meniscus injury consisted of a small radial white-white tear amenable to debridement. All patients underwent ACL reconstruction with hamstring autograft with one patient’s graft reinforced with allograft due to small diameter. The average graft diameter was 7.1 (range: 6.0-10.0) mm.

Clinical outcomes

Following ACL OTT reconstruction, 11 patients exhibited a stable Lachman exam with a firm endpoint and one patient had Grade I anterior translation with a firm endpoint. No patients demonstrated a clinical pivot shift. By a mean 3.5 months (range: 0.5-6.4) postoperatively, all knees had at least 0-125º of active motion.

Surgical outcomes

A total of 2 (16.7%) patients (1 male, 1 female) sustained an ACL graft rupture at 0.7 and 1.0 years after surgery. The mechanism of re-injury was competitive basketball and American football. Patient and operative characteristics of the patients stratified by graft tear can be found in Table 1.

Table 1.

Patient and Operative Characteristics in Graft Tear vs Intact Graft Groups

	Graft tear	Intact graft
Number of Patients (%)	2 (16.7)	10 (83.3)
Male, n (%)	1 (50.0)	10 (100)
Female, n (%)	1 (50.0)	0 (0)
Laterality, right, n (%)	2 (50)	9 (42.9)
Average Age (years)	13.5 (range: 13-14)	12.6 (range: 10-16)
Body Mass Index (kg/m2)	18.5 (range: 18.4-18.6)	20.7 (range: 15.7-27.7)

Return-to-Sport

The average time to return-to-sport was 7.4+2.7 months (range: 4.6-12.7). The mean preinjury Tegner activity level was 8.8 (range: 7.0-9.0) and mean postoperative Tegner activity level at final follow-up was 8.9 (range: 7.0-10.0). All patients either maintained (n=11) or increased (n=1) their Tegner activity level scores following OTT ACL reconstruction.

Complications and Subsequent Injuries

Complications after surgery included one superficial wound infection that resolved after a five-day course of oral antibiotics and one hardware removal for a painful staple on the medial aspect of the tibia (Table 2). Subsequent injuries following primary ACL reconstruction included ACL graft rupture (n=2), contralateral ACL rupture (n=2), ipsilateral lateral meniscus tear treated with an all-inside repair (n=1), and patella dislocation treated with physical therapy (n=1).

Table 2.

Complications and Subsequent Injuries After Primary ACL Reconstruction with the Over-the-top Technique

Complications	n, (%)
ACL Graft Tear	2 (16.7)
Contralateral ACL Rupture	2 (16.7)
Superficial Wound Infection	1 (8.3)
Painful Hardware	1 (8.3)
Patella Dislocation	1 (8.3)
Lateral Meniscus Tear After Primary ACL Reconstruction	1 (8.3)
Total	8

Discussion

The incidence of ACL injuries in patients 6 to 18 years of age is approximately 121 per 100,000 persons per year and continues to increase.⁴¹ Conservative management of ACL tears in skeletally immature individuals leads to an unacceptably high rate of subsequent knee morbidity, including meniscal tears, cartilage damage, and instability.^3,7-13 Traditional ACL reconstruction techniques involve transosseous tibial and femoral tunnels which confer a risk of physeal closure in the skeletally immature patient. Here, we describe a cohort of skeletally immature patients that underwent primary ACL reconstruction using a transphyseal tibial tunnel and a physeal-sparing OTT technique on the femur. We observed a 100% return to at least preinjury sporting level with a 16% ipsilateral ACL re-rupture rate. No growth disturbances or cases of angular deformity were observed.

Bertoia and colleagues were the first to describe an ACL reconstruction with an OTT technique using the ITB.³⁶ This was a modification of MacIntosh’s lateral extra-articular tenodesis (LET), first published in 1972.^42,43 In 1994, Andrews et al. reported their results after ACL reconstruction with Achilles allograft using a transphyseal tibial tunnel and an extra-articular, OTT technique on the femur in eight skeletally immature patients with a mean age of 13.5 years.³⁷ At 4.8-year follow-up, they found six excellent, one good, and one fair result. One of the patients with an initial ‘excellent’ outcome sustained a graft rupture four years postoperatively playing competitive soccer. All patients returned to some level of sport postoperatively, but only 4/8 (50%) were able to return-to-sport at the same level or greater. To date, few studies have reported outcomes utilizing this partial-transphyseal OTT technique in skeletally immature patients.^11-13,38

In 1997, Lo et al. reported seven year outcomes of five patients that underwent an autograft reconstruction using a transphyseal tibial tunnel and OTT technique on the femur³⁸ IKDC grade was A in four patients and C in one patient who sustained a subsequent patella dislocation.³⁸ There were no graft tears and all patients returned to sport.³⁸ Shortly after this, Bisson and colleagues reported three year outcomes on nine patients.¹² Seven had excellent results and returned to sport.¹² The other two patients sustained graft tears after returning to sport ten months and three years postoperatively.¹² In a more recent study with 18-year follow-up, Demange and Camanho described outcomes in twelve immature patients in both Tanner Stage 1 (n=4) and Tanner Stage 2 (n=8) at the time of surgery.¹³ Three (25%) patients sustained a graft tear at a mean 6.6 years (range 4.79) postoperatively. Graf and colleagues also reported good outcomes in two patients that underwent a partialtransphyseal technique with semitendinosus autograft.¹¹

The aim of the partial transphyseal OTT technique is to restore knee stability and minimize growth disturbances in skeletally immature patients, particularly those with ‘wide open’ physes or in Tanner stages 1 and 2.⁴⁴ The ideal technique involves drilling a small vertical tunnel (< 8 mm in diameter), through the center of the tibial physis, using an all-soft tissue autograft, and securing it extra-articularly on the femur to avoid injuring the distal femoral physis.^13,45,46 However, this non-anatomic location for femoral fixation may portend to the slightly higher failure rate seen observed in this population.^13,37,38 Although evidence is limited, transphyseal techniques theoretically have a higher risk of physeal injury and subsequent growth abnormalities or deformity, with the distal femoral and proximal tibial physes contributing approximately 9 mm and 6 mm of growth per year, respectively. In 2002, Kocher et al. reported survey results from 140 orthopaedic surgeons who performed transphyseal and/or physeal sparing ACL reconstructions in skeletally immature patients.³⁴ A total of 15 cases of growth disturbances were identified (out of an unknown total number of reconstructions), of which 80% occurred on the femoral side.³⁴ In a more recent study published in 2016, Collins and colleagues identified 39 cases of growth abnormalities in a cohort of 313 patients (12.5%) following transphyseal and physeal-sparing reconstructions in skeletally immature patients.⁴⁷ Nearly a quarter of the growth abnormalities were reported in patients treated with physeal-sparing techniques.⁴⁷ Despite these reports, the majority of skeletally immature patients undergoing ACL reconstruction end up with an average LLD of < 1 cm and angular deformities less than 3 degrees.^{13,17,23-26,28,30,37,38,45,47-54}

In a recent systematic review by Pierce and colleagues that included 18 transphyseal and 6 physeal-sparing studies with over 600 total knees, leg length discrepancy _≥ 10 mm were only found in 0.81% and 1.23% of patients after transphyseal and physeal-sparing techniques, respectively.¹⁷ Furthermore, the incidence of angular deformity after transphyseal and physeal-sparing techniques was 0.61% and 0%, respectively.¹⁷ A meta-analysis of 55 studies (941 knees) by Frosch and colleagues estimated the overall risk of postoperative LLD >1 cm or angular deformity > 3 degrees at 2.1%.⁵¹ Previously identified risk factors for growth disturbances after transphyseal techniques include graft type, graft diameter and angular trajectory of the tibial tunnel.⁴⁵

The 16% graft tear rate found in our series is consistent with previously published partial-transphyseal OTT outcomes. Reported graft rupture rates after primary ACL reconstruction in skeletally immature patients ranges from 0-25% depending on the technique utilized.^13,20,55,56 We observed no cases of physeal closure although patients were not followed until skeletal maturity. Additionally, a large proportion of the patients in our series were able to return-to-sport at the same level or higher postoperatively. Given this information, we believe that the optimal ACL reconstructive technique should be dictated by graft failure rates, return-to-sport rates, and surgeon familiarity with the technique.

This study is limited by its retrospective nature and the use of clinical and surgical notes that rely on accurate and consistent documentation. Detailed information including ROM, Lachman exam, pivot-shift, return-to-sport, bilateral long-leg radiographs and graft diameter was not available for every patient included in this study. Additionally, “non-significant” univariate findings may indicate that the study in underpowered to detect difference. Due to the small sample size of graft ruptures, multivariate analysis was not possible and independent risk factors for graft failure were not able to be assessed. As mentioned previously, although we did not observe any cases of angular deformity during postoperative follow-up, patients were not clinically followed until radiographic confirmation of physeal closure. Lastly, a standardized protocol was not utilized to measure motor strength and functional movement prior to allowing patients to return to sport. However, this is the largest single series to date reporting on the outcomes of a partial transphyseal OTT technique for primary ACL reconstruction in skeletally immature patients.

Conclusion

ACL reconstruction using a transphyseal tibial tunnel and an extra-articular OTT technique on the femur in skeletally immature patients appears to be safe with minimal risk of growth disturbance. It is associated with a comparable graft rupture rate compared to other physeal-sparing or transphyseal techniques in the active, skeletally immature patient population. All patients were able to return to sport at the same level or higher in the current cohort. While the ideal technique for ACL reconstruction in skeletally immature patients continues to be a topic of debate, we believe it should be dictated by graft tear rates, return-to-sport rates, and surgeon familiarity with the technique, as opposed to risk of growth disturbances. Future studies are needed to directly compare the outcomes after the various ACL reconstruction techniques in patients with open physes.