A.F. Anderson replies:
I appreciate Dr. Parikh's thoughtful questions regarding transepiphyseal ACL reconstruction.
Dr. Parikh's first question concerns the safety of this technique for children at Tanner stage I of sexual maturity. Unfortunately, the orthopaedic literature is deficient both with regard to age-specific basic science on the effects of physeal injury and with regard to clinical studies demonstrating the safety of the various surgical techniques that can be used to reconstruct the ACL in pediatric patients. Although the methods of treatment remain controversial, it is widely accepted that the consequences of iatrogenic growth disturbance, should they occur following ACL reconstruction, are greater for younger children. Consequently, my bias in the presence of this uncertainty is to treat high-risk, prepubescent patients in Tanner stages I or II and intermediate-risk patients in early Tanner stage III with this "physeal sparing" procedure. I have performed fifty transepiphyseal ACL reconstructions, thirty-one of which were in patients who were in Tanner stages I or II. I have observed no growth disturbances, and the youngest patient was an eight-year-old boy. It seems logical to me that this procedure would be as safe in a five-year-old child as it is in an eight-year-old child, although I have no experience to support this assumption.
Dr. Parikh also asked how transepiphyseal ACL reconstruction is performed in younger children. I use the same technique in younger children as I use for older patients with an ACL tear prior to tibial tubercle ossification. In the paper, I emphasized the presence of the tibial tubercle apophysis only because the illustrative case was that involving an older child. Even so, it is important to remember that rotation of the c-arm fluoroscope will show the position of the guide pin more distinctly. In pubescent children with ossification of the tibial tubercle, the guide pin may appear to be transgressing the apophysis when the image is made with the c-arm positioned in the lateral plane.
I agree with Dr. Parikh's opinion that the height of the tibial epiphysis is of concern when performing this procedure. I have not measured, nor do I have minimum criteria for, tibial epiphyseal height. However, I think the more important factor is the height of the epiphysis relative to the size of the drill bit being used, and not simply the height of the epiphysis. The smallest appropriate drill bit should be used to minimize the potential for physeal injury. Consequently, both ends of each of the hamstring tendons are sutured together with a single number-2 FiberWire suture (Arthrex, Naples, Florida) rather than using a FiberWire suture in each end of both tendons. This technique decreases the tendon suture mass that must be pulled into the tibial hole. Ironically, tibial epiphyseal height is less of a concern in younger children because they have greater epiphyseal height relative to the size of their quadruple hamstring tendons.
The basic-science literature on the effects of graft tension illustrates why Dr. Parikh's concern about iatrogenic growth disturbance caused by compression of the physis after screw-and-post fixation is valid. There may be several explanations for why growth disturbance is not being caused by the metaphyseal graft fixation used in our technique. First, it is difficult to tie the sutures with enough tension to inhibit longitudinal growth. Second, the creep and decreased stiffness of this method of fixation make it more forgiving. More importantly, the graft maintains some cellular viability and undergoes biomechanical and histological transformation that is related to the mechanical and biochemical environments. Stretching of the graft, without revascularization and remodeling, would result in failure of the reconstruction or a growth disturbance caused by a tethering effect. Again, we have observed no growth disturbances in our series. Consequently, it may be reasonable to presume that the graft progresses through the stages of maturation and continues to grow until the time of skeletal maturity.
Finally, Dr. Parikh asked why an alternative method of fixation, such as an interference screw, is not used in the tibial tunnel. We initially considered interference screw fixation as a method to secure the graft to both the femur and the tibia. Our primary reason for rejecting this method of fixation was due to the concern that the screw might compress the physis and cause growth disturbance. Additionally, without the drilling of a transphyseal hole, an epiphyseal screw would have to be used on the tibial side. The retrograde screw insertion technique, an even more demanding procedure, requires the drilling of a guide pin through the tibial physis. Although not optimal, screw-and-post fixation is technically easier and, in my experience, is a safe and effective method for ACL reconstruction in the pediatric age group.