There has been an increase of anterior cruciate ligament (ACL) injuries in the pediatric population due to multiple factors. The potential complications of traditional ACL reconstructions have led to the development of physeal-sparing techniques. The goal with this technique is to preserve growth potential while provide long-term knee stability. This procedure involves a small, centrally-placed tibial transphyseal suture fixation with an all-epiphyseal graft tunnel on the tibial side along with an all-epiphyseal femoral tunnel. Over a 7-year period of this physeal-respecting technique being performed, no clinically significant growth disturbances, angular deformities, or major leg length discrepancies were reported. The most common finding has been mild overgrowth of the surgical side (<15 mm) but has led to no functional concerns. As pediatric ACL injuries continue to rise, improving surgical approaches to enhance both safety and function should remain a priority. However, further research is needed to review patient long-term outcomes.
Introduction
Anterior Cruciate Ligament (ACL) injuries, once thought rare among pediatric and adolescent populations, have seen a notable increase in the last 2 decades. This rise has been attributed to multiple factors, including the advent of high-demand, year-round sports at younger ages, improved clinician awareness, and better recognition of the signs and symptoms of ACL injuries. When ACL tears occur in skeletally immature patients, the priority is to stabilize the knee; however, the optimal technique has not been completely agreed upon.
The physes of the knee provide a significant majority of lower extremity growth, with the distal femoral physis contributing 70% of femoral growth and the proximal tibial physis contributing 60% of tibial growth annually. Historically, the potential for growth disturbances associated with traditional ACL tunnels led to a preference for nonoperative treatments or delayed reconstruction until skeletal maturity. However, studies have shown poor outcomes from non-operative management of complete ACL tears in skeletally immature patients, including progressive meniscus and cartilage damage, instability symptoms, and decreased activity levels. A 2016 meta-analysis reported that patients treated non-operatively had a 12-fold greater risk of developing meniscal tears and were 33.7 times more likely to report instability compared to those undergoing early operative treatment. Furthermore, delaying ACL reconstruction for more than 12 weeks significantly increases the risk of meniscal injuries and irreparable meniscal tears, with secondary tears observed in 17% to 44% of non-operatively treated patients. The potential complications of traditional ACL reconstructions, along with the past tendency to delay surgery, have led to the development of new “physeal-sparing” and “physeal-respecting” surgical techniques designed to protect the growth potential of the physes.
Choosing the optimal ACL reconstruction technique depends on several factors, but most importantly, the skeletal age of the patient. It is our recommendation that physiologically younger patients with substantial growth remaining should undergo physeal-sparing techniques to mitigate the risk of significant growth disturbances.
Iatrogenic physeal bar formation, leg length inequality, and angular deformity, although rare, are a concern with any skeletally immature ligamentous reconstruction. The all-epiphyseal Anderson technique and the Micheli-Kocher physeal sparing technique with iliotibial band have been the leading procedures in skeletally immature ACL reconstruction. , McCarthy et al. studied the risks of the all-epiphyseal technique and found that there is frequently an injury to the perichondral ring on the anteromedial tibia, concerning for developing an angular deformity with continued growth. Other authors have demonstrated low risk of growth disturbance with transphyseal soft-tissue grafts, but these more vertical tunnels may result in a non-anatomic reconstruction. Transphyseal suture fixation of tibial spine fractures has similarly shown minimal risk for physeal bar formation, even using two 3 mm diameter tunnels.
Building on these previous efforts and with the goal of creating a biomechanically-stable, anatomic ACL graft that respects further growth potential., the senior author developed this novel technique. The technique combines a centrally-placed epiphyseal socket with transphyseal suture fixation on the tibia and an all-epiphyseal graft tunnel on the femur using a quadriceps tenon-bone autograft. This technique is described below and shown in Figure 1 .
Technique
After induction of general anesthesia and regional nerve block, the patient is positioned supine with footrest and side post to allow knee positioning at 90 degrees of flexion for the ease and consistency of femoral tunnel targeting and tunnel placement. The leg is then prepped and draped in standard fashion. Arthroscopic portals are established, and diagnostic arthroscopy performed. The integrity of the ACL is evaluated, as well as any other concomitant pathology, prior to graft harvest.
Following exposure of the distal quadriceps tendon, two parallel longitudinal incisions are made in the tendon at a width of 10 mm. Incisions are continued distally onto the periosteum of the patella, and then an oscillating saw is used to make trapezoidal cuts in the superior pole of the patella along the incisions. A transverse cut is made to create a bone plug of 15 mm in length. An osteotome is then used to gently lever the bone plug out of the patella. Retracting the bone plug proximally, the quadriceps graft is elevated off the underlying capsule and transected proximally. For a physeal-respecting or a true all-epiphyseal tunnel a total graft length of 55 mm is obtained with 15 mm of bone and 40 mm of tendon. An adjustable-length suture button (BTB TightRope, Arthrex: Naples FL) is placed through a small drill hole in the bone plug, and a second adjustable-length button (RT TightRope, Arthrex: Naples FL) is attached to the tendinous end of the graft. As the graft is being prepared, a standard diagnostic arthroscopy of the knee is performed, and any cartilage or meniscal work is performed during this time window. Preparation of the notch is then finalized, using a notchplasty as needed if the notch is too narrow.
The camera is then transferred to the medial portal. The femoral drill guide, set at 85 degrees, is passed into the knee through the lateral portal. The femoral drill guide is then placed on the lateral wall of the notch at the anatomic footprint of the femoral attachment of the ACL, posteriorly, leaving 1-2mm of posterior wall behind the femoral tunnel.
The guide is then positioned along the lateral cortex of the femoral epiphysis through a small anterolateral incision. Care is taken to only incise the Iliotibial (IT) band, avoiding excessive dissection that may damage the femoral origins of the Lateral Collateral Ligament (LCL), Popliteus, Anterolateral ligament (ALL), or perichondrial Ring of Lacroix. A retrograde reamer (Flipcutter III; Arthrex, Naples, FL) is then passed through this guide, adjusting as needed to confirm ideal placement. The retrograde reamer is extended to the desired tunnel size (usually 10mm), line-to-line for the bone block diameter. The chuck is then disengaged from the drill bit. Intra-operative fluoroscopy is then used to obtain a perfect lateral and a simulated 45° PA notch view of the knee to confirm drill position will not cross the distal femoral physis ( Fig. 1 A). The socket is then drilled to a depth of 20-22 mm (5 mm longer than the measured patellar bone block length) while viewing from the lateral portal and the shaver in the medial portal. A trap (GraftNet, Arthrex; Naples, FL) is placed on the shaver to capture the bone debris created by the femoral socket preparation which will be used to fill the patellar bone defect from the graft harvest. A passing suture is then exchanged for the retrograde drill. This suture is withdrawn out through the anterolateral portal and a hemostat is placed to hold securely. The scope is then transitioned to the lateral portal and the medial portal is extended to allow for ease of passage of the graft after the tibial tunnel has been drilled.
The tibial drill guide is set to 60° and is then placed into the knee through the medial portal. The targeting tip is positioned in line with the posterior aspect of the anterior root of the lateral meniscus. This is also centered in the posterior aspect of the ACL footprint from medial to lateral which allows the tunnel to be positioned in the center of the physis, minimizing the risk of iatrogenic growth disturbance. The guide sleeve is used to indent the skin on the anterior surface of the tibia just distal to the tibial tubercle and about 1/3 of the distance from the tubercle to the posterior border of the tibia. An 8 mm skin incision is made longitudinally centered over this location, and blunt dissection down to periosteum is performed. The drill guide is inserted down to bone, and the retrograde reamer is passed through the drill guide into the knee joint at the ACL tibial footprint. The tip of the retrograde drill is extended to the planned line-to-line size of the tibial tunnel needed for the soft tissue ended the graft (usually 9-10 mm). The retrograde drill is spun by hand to confirm correct location of the tibial tunnel and that all surrounding structures will be protected. The drill guide is then seated into the proximal tibia, and reaming is performed to a depth of 5-10 mm. Lateral fluoroscopy is obtained to confirm the proximity of the proximal tibial physis during the remainder of socket preparation ( Fig. 1 B). Drilling of the all-epiphyseal socket continues under fluoroscopy until reaching 3-5 mm proximal to the physis. Bone debris is again harvested with the shaver during reaming, and passing sutures are placed through the tibia and out the medial portal. The tibial socket is evaluated arthroscopically to ensure no part of the proximal tibial physis is visible.
Both sets of passing sutures are retrieved together out of the medial portal. The graft is then passed through the medial portal and seated into the femoral and tibial sockets, respectively. The suture buttons are provisionally tensioned with the knee in 10-15° of flexion and a posterior drawer applied. The Lachman exam is then evaluated. The knee is cycled 25 times from full flexion to full extension and the Lachman exam is evaluated again. Final tensioning of the suspensory fixation is performed near full extension. A final Lachman and pivot shift exam are tested to ensure stability of the knee has been restored. Tibial fixation may be backed up with the addition of a metaphyseal screw or suture anchor at the discretion of the surgeon.
Postoperative Protocol
Postoperative rehabilitation protocol includes immobilization in a hinged knee brace locked in extension during ambulation and sleeping until quadriceps control returns. In the absence of concomitant pathology, immediate weightbearing as tolerated is permitted postoperative day one. Early range of motion is crucial. The brace may be unlocked to allow full range of motion, and PT is initiated within 1-10 days after surgery.
Postoperative Monitoring Strategies for Growth-Related Complications
Given the potential risks associated with any surgical intervention involving the physis, rigorous postoperative monitoring is essential. Standardized follow-up protocol for this technique includes:
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Serial knee radiographic imaging to assess for physeal bar formation, limb length discrepancies, and angular deformities.
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Preoperatively, 6 weeks, 3 months, 6 months, 12 months and every 6 months until skeletal maturity has been reached. ,
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Functional assessments to monitor for knee instability, range of motion deficits, and quadriceps strength recovery.
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Long-term surveillance through skeletal maturity to ensure that growth disturbances do not develop over time.
Outcomes
In the past 7 years of performing the physeal respecting technique we have followed 8 male patients with an average age of 10.6 (±1.5 yrs) for a minimum of 5-7 years. We have not observed any evidence of clinical or radiographic growth disturbance, either angular or leg length inequality. Our most common complication has been mild overgrowth of the surgical side less than 15 mm which was observed in 2 patients ( Table 1 , Fig. 2 ).
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