ACL Reconstruction with Open Growth Plates
Abstract & Commentary
Synopsis: A tensioned soft tissue graft across wide open growth plates resulted in severe angulation and growth disturbance apparently due to the compressive effect across the physis.
Source: Edwards BT, et al. The effect of placing a tensioned graft across open growth plates. J Bone Joint Surg. 2001; 83-A(5):725-734.
Most of the literature regarding ACL reconstruction in skeletally immature patients focuses on individuals with less than 1 year of growth remaining. It is clear that these patients do well with conventional ACL reconstruction techniques for the most part. However, there really are no good clinical series with athletes having more than 2 or 3 years of growth remaining who undergo ACL reconstruction. Edwards and colleagues at LSU addressed that specific scenario with a dog model. They used 12 10-week-old beagles and performed ACL reconstruction in open fashion with a fascia lata soft tissue graft placed through transphyseal 4 mm drill-holes. These tunnels were basically in the same position as conventional endoscopic ACL reconstruction tunnels. The graft was fixed at both ends with a bicortical screw used as a post placed well away from each physis. The grafts were tensioned to 80 N before fixation to restore stability and to determine the effect of a tensioned graft across the growth plates.
One animal was lost due to infection. The others were sacrificed at 4 months postoperatively and evaluated radiographically and by gross dissection with careful measurements of the length of both medial and lateral sides of the femur and the tibia. Finally, histological sections of the growth plates were compared.
Findings were notable for severe growth disturbance. The femurs all went into valgus, procurvatum, and were shortened. The tibiae went into varus but were not shortened, suggesting that the varus angulation was more due to overgrowth laterally to compensate for the valgus deformity of the femur. Histological sections revealed that the growth plates were thinner peripherally in the femur on the lateral side where they were compressed by the tensioned graft as it passed toward the lateral aspect of the femur. In similar fashion, the growth plates were thinner than controls in the central portion of the tibia where the tunnel passed creating compression at the physis. Interestingly, no osseous bar formation was observed in any specimen. Thus, the tensioned graft with the resulting compression of the growth plate resulted in inhibition of growth without the presence of an osseous bar. This is termed the Heuter-Volkmann principle.
Comment by David R. Diduch, MS, MD
This study by Edwards et al substantially increases our understanding of the risks of ACL reconstruction in skeletally immature athletes. Previously, most of the attention regarding this issue has been directed toward potential osseous bar formation with transphyseal tunnels. As such, conventional recommendations have been to use a soft-tissue graft rather than bone-tendon-bone to prevent osseous bar formation. This may still be true. However, this study demonstrates that the osseous bar is really only part of the risk. A much bigger concern is that tensioning the graft across the growth plates inhibits growth directly. This Heuter-Volkmann principle was readily demonstrated in these skeletally immature dogs by the femurs going into dramatic valgus and procurvatum with shortening over just a 10-week time frame. The tibia appeared to overgrow laterally rather than shorten medially to compensate for the femoral valgus. This is apparently due to the fact that the femoral tunnel travels obliquely in the lateral direction creating compression across the lateral aspect of the physis, whereas the tibial tunnel is much more central.
Edwards et al conclude that they cannot recommend transphyseal reconstruction of the ACL for individuals with significant growth remaining. So what are we to do? Other studies have clearly documented the risks of leaving a young patient with an unstable knee in terms of potential meniscal and chondral injury. There have also been studies clearly demonstrating the decrease in function of these unstable knees. The existing recommendation that is popularly held to use smaller tunnels with soft-tissue grafts with fixation distant to the growth plates needs to be re-examined in light of this study. Others have also recommended nonanatomical reconstruction such as bringing the graft under the roof of the notch with fixation on the side of the femur without a tunnel. While this avoids potential damage from tunnel drilling, it still does not eliminate the fact that tension is across the growth plate and could create the same procurvatum and valgus deformity. This would need to be specifically examined to be confirmed but seems likely in light of these findings. Probably the next step would be to examine the effect of various tensions across the growth plate to see if tension somewhere less than 80 N would still provide graft stability without the same growth arrest. This should continue to be an active area of research because the problem is yet to be solved.
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