Single Incision Arthroscopic ACL Reconstruction in Skeletally Immature Patients With Direct Visualization of the Femoral and Tibial Physes
Matthew Thompson, MD, BS; John Flynn, MD; Lawrence Wells, MD; Theodore J. Ganley, M
Visualization and precise measurement of the tibial tunnel allows for appropriate placement of the soft-tissue interference screw.
Within the past three decades, the diagnosis of anterior cruciate ligament (ACL) injuries in skeletally immature patients has become more common due to increased participation in competitive, contact sports and improvements in imaging. Research on ACL reconstruction in children has mirrored the rise in injuries. A literature search shows that among >150 studies related to ACL reconstruction in skeletally immature patients, two-thirds have been published in the past 10 years. This research has raised awareness of issues that are specific to pediatric ACL reconstruction.
Prior to the advent of arthroscopic-assisted ACL reconstruction, children traditionally were treated with bracing, rehabilitation, and activity modification. The results of long-term nonoperative treatment studies in this patient population have shown increased instability and laxity, significant meniscal and osteochondral damage, and osteoarthritic changes.1,2
Placement of guide for transverse femoral bioabsorbable pins.
Transphyseal reconstruction with modifications to minimize damage to the physes has been shown to be successful in patients at or near skeletal maturity.3-6 The subject of debate regarding ACL reconstruction in children who are at or near skeletal maturity is no longer whether it results in successful outcomes, but when and how to safely perform this procedure.
Following accepted orthopedic principles can avoid untoward damage to the growth plate. Reports exist on leg-length discrepancies and angular deformities with the placement of fixation hardware and bone plugs across wide-open physes.7,8 At our institution, we initially treat patients with wide-open physes and an immature chondroepiphysis with activity restriction and bracing. Recent evidence suggests that delaying surgery up to 26 weeks will not result in additional knee injuries, as long as activity restriction protocols are followed.9 We treat patients approaching skeletal maturity (specifically girls with a bone age of 13 and boys with a bone age of 14) with a transphyseal ACL reconstruction using a soft-tissue graft and fixation that avoids hardware placement or bone plugs across the femoral and tibial physes.
Materials and Methods
The proximal cross pin and distal interference screw technique described in this paper has been used for three years at The Children’s Hospital of Philadelphia. This procedure has been performed in 30 adolescents with isolated ACL injuries who were at or near skeletal maturity. A slight modification is made for patients with insufficient distal tibial bone quantity due to small patient size. In these patients, a distal screw and barbed washer are used for tibial fixation instead of an interference screw.10
During the development of this procedure, the primary focus was to take steps to protect the femoral and tibial physes. Also of importance was choosing femoral and tibial fixation that would provide sufficient strength for a return to full activity.
Figure 2: Trocar placement (white arrow) is verified above the femoral physis (small black arrow) (A).
The tibial physis is visualized (large black arrow) (B).
After placement under general anesthesia, examination, and diagnostic arthroscopy, a single incision arthroscopic ACL reconstruction is performed. A soft-tissue graft is initially prepared using quadrupled hamstring autograft or an Achilles tendon allograft of approximately 12-cm in length. The calcaneal bone is removed and two horizontal mattress stitches are placed that will be pulled through the tunnels first. The other end of the graft is whip-stitched, and the graft is tubularized and trimmed to a 10-mm diameter. Excess length in the graft on this end is trimmed after it has been secured in the knee. When using the hamstring autograft, the gracilis and semitendinosus are harvested and prepared in the standard fashion. The graft is preconditioned on a preparation board using 15 lbs of tension (Graft Preparation System; Mitek, Westwood, Mass) during tunnel preparation to help eliminate of graft tension loss after fixation in the knee.
With the knee in 90° of flexion, the torn ACL is debrided with an arthroscopic curved full-radius shaver, a straight biter, and a pituitary rongeur. A notchplasty is performed and the ACL guide is set at the ACL footprint. The tibial guide is placed at a 55° angle to create a tibial tunnel of sufficient length and to avoid problems with graft impingement. A 55° angle, as opposed to a smaller, sharper angle, allows for more bone distally for more secure tibial fixation.
When this is completed, the guide pin is placed within the ACL footprint and a 10-mm cannulated drill bit is used to create the tibial tunnel. The distal portion of the tibial guide is set at a position midway between the posteromedial border of the tibia and the anterior tibial tubercle. Next, a 7-mm femoral offset aimer is used to place the guide pin for drilling the femoral tunnel. The guide pin is placed in the 10 o’clock position for the right knee and the 12 o’clock position for the left knee. Both the pin and the drill are placed at the same flexion angle with at least 90° of flexion. The pin then is over-drilled with a 10-mm cannulated bit. This femoral tunnel is drilled to 35-40 mm in length. This is longer than the customary 30-mm tunnel to allow for more proximal placement of the femoral fixation pins.
Figure 3: Measurement of the distance to the tibial physis.
After the femoral and tibial tunnels are drilled, the femoral guide for the transverse femoral fixation system (Rigidfix Cross Pin System, Mitek, Westwood, Mass) is placed (Figure 1). The femoral guide is placed so that the proximal tip of the guide is positioned 40 mm within the femoral tunnel to ensure that the trocars are proximal to the femoral physis. The two transverse femoral tunnels are drilled using the femoral guide and cannulae.
When the two transverse femoral tunnels are drilled, the arthroscopic camera is placed through the graft tunnel to visualize the location of the transverse tunnels proximal to the femoral physis. The drill bit or a K-wire placed through each cannula demonstrates appropriate transverse tunnels (Figure 2A). Plain radiographs confirm the position of the trocars, specifically to note their position in relation to the femoral physis at their insertion in the lateral femur.
The arthroscopic camera is placed within the tibial tunnel and the tibial physis is visualized (Figure 2B). A hook probe then is placed at all positions within the tunnel to the level of the physis to measure the shortest distance from the cortical bone of the tibia to the physis (Figure 3). The shortest distance is selected and a soft-tissue interference screw 8-10 mm in diameter with a length extending a few millimeters shy of the physis is selected.
The graft then is passed through the tibial and femoral tunnels using a Beath pin. The graft is held in position while two bioabsorbable cross pins are tamped lateral to medial across the graft and the femoral tunnel. The knee is placed in full extension as the distal limbs of the graft are pulled distally and a soft-tissue interference screw of the previously determined length is placed (Figures 4 and 5). Excess graft exiting the tibial tunnel is trimmed. In patients with insufficient tibial tunnel length beyond the physis, a cannulated screw and barbed washer are placed distal to the physis instead of an interference screw (Figure 6). If secure fixation is not obtained with the screw and washer, a second screw is placed distally. The second screw is used as a post and the sutures are tied to it. Arthroscopic photographs of the graft are taken with the knee in extension and flexion to verify that there is no impingement. A standard postoperative accelerated ACL protocol is instituted.
Over the past 3 years, this procedure has been performed on 30 patients, 5 of whom had screw and barbed washer tibial fixation. The age requirement for undergoing this procedure was a bone age of at least 13 for girls and 14 for boys. Criteria for a successful outcome consist of: 1) avoidance of hardware placed across the physes, 2) secure femoral and tibial fixation of the graft, 3) clinical absence of problematic laxity, and 4) at follow-up, absence of leg-length discrepancies, angular deformities, and symptomatic knee instability.
Figure 4: Placement of bioabsorbable tibial screw, secured into place with its tip several millimeters below the tibial physis.
Figure 5: Placement of a screw and barbed washer for tibial fixation.
No intraoperative complications, clinically significant leg-length discrepancies, angular deformities, symptomatic knee instability, or fixation failures have been noted. Physical examination has not shown pathological pivot shift tests, although two patients in the interference screw group had a positive pivot glide. A patient 15 months post-ACL reconstruction with screw and washer fixation had an ACL re-rupture during a martial arts competition, when a competitor’s kick transmitted a valgus force to the affected lower extremity that was planted. One patient had a knee-buckling episode while playing soccer 13 months postoperatively, and was found to have a new medial meniscus tear but an intact ACL by MRI and clinical criteria. Two patients had postoperative knee stiffness. One of those patients, with a family history of arthrofibrosis, had a concurrent posterior capsule rupture and a partial gastrocsoleus tear. The other patient with stiffness was not compliant with the postoperative protocol. Both patients were treated with arthroscopic lysis of adhesions followed by constant passive motion machine usage and an aggressive physical therapy regimen.
Figure 6: Diagram of soft-tissue graft ACL reconstruction.
Several reports in the literature have shown that in adolescents who are at or near skeletal maturity, ACL reconstruction can be performed safely with good results.3-6 These results are due to several factors, including improvements in diagnosis, modifications to the standard ACL reconstruction procedure used for adults, and proper selection of patients for surgery. Prompted by reports of growth deformities using transphyseal hardware and bone plugs, surgeons have modified the procedure specifically for adolescents, namely using a soft-tissue graft without bone on either end and avoiding the use of transphyseal hardware.
While several methods have been described, including femoral and tibial pin fixation, we use cross pins above the femoral physis and a bioabsorbable interference screw as the tibial anchor.10-12 This technique is not used in younger patients with wide open physes whose size generally prohibits placement of an interference screw distally. Patients with insufficient bone density also may require the use of a screw and washer distally. Bioabsorbable cross pins and interference screws have been shown to have comparable fixation strength, and recent studies show that multiple fixation methods exist that provide adequate strength for an accelerated postoperative ACL protocol.5,10,12
The benefits of our method include the use of a soft-tissue graft, avoidance of transphyseal hardware, and direct arthroscopic visualization of the femoral and tibial physes. Visualization of the femoral physis helps ensure that the transverse tunnels for bioabsorbable pins are above the physis. In addition, visualization and precise measurement of the tibial tunnel allows for appropriate placement of the soft-tissue interference screw.
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- Kocher MS, Saxon HS, Hovis WD, Hawkins RJ. Management and complications of anterior cruciate ligament injuries in skeletally immature patients: survey of the Herodicus Society and The ACL Study Group. J Pediatr Orthop. 2002; 22:452-457.
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- Coleridge SD, Amis AA. A comparison of five tibial-fixation systems in hamstring-graft anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2004; 12:391-397.
- Volpi P, Galli M, Bait C, Pozzoni R. Surgical treatment of anterior cruciate ligament injuries in adolescents using double-looped semitendinosus and gracilis tendons: supraepiphysary femoral and tibial fixation. Arthroscopy. 2004; 20:447-449.
- Zantop T, Weimann A, Rummler M, Hassenpflug J, Petersen W. Initial fixation strength of two bioabsorbable pins for the fixation of hamstring grafts compared to interference screw fixation: single cycle and cyclic loading. Am J Sports Med. 2004; 32:641-649.
Cover illustration © Scott Holladay
Dr Thompson is with DFP Orthopedic in KC, George Washington University, Washington, DC; and Drs Flynn, Wells, and Ganley are from the Dept of Orthopedic Surgery, The Children’s Hospital of Philadelphia, Pa.