Lateral Anatomic Structures at Risk During Transepiphyseal Reconstruction of the Anterior Cruciate Ligament (SS-47)

Abstract

Transepiphyseal reconstruction of the ACL allows for anatomic placement of the femoral tunnel and avoids damage to the distal femoral physis. To our knowledge there is no published study describing the lateral structures at risk during this technique. The popliteus tendon and lateral collateral ligament are at greatest risk during guide pin placement for the posterolateral bundle femoral tunnel. The lateral collateral ligament and gastrocnemius tendon are at risk during placement of the anteromedial bundle guide pin. A better understanding of the lateral knee anatomy can help avoid damage to the lateral structures during transepiphyseal ACL reconstruction. The purpose of the present study is to describe the lateral anatomic structures at risk during transepiphyseal preparation of the anterior cruciate ligament femoral tunnel. We utilized 6 fresh frozen cadaveric knees. We first excised the ACL and identified the anatomic footprints of the anteromedial (AM) and posterolateral (PL) bundles. A guide pin, oriented parallel to the ground, was then passed through the center of each bundle's footprint, exiting the lateral femoral cortex. Subsequently, the anatomic structures on the lateral aspect of the knee were exposed. We then measured the distance from the AM and PL bundle guide pins to the lateral collateral ligament, popliteus and gastrocnemius tendons. We also measured the angle of the guide pin with respect to the lateral epicondyle in the axial plane (epicondyle angle). The mean length from the AM bundle guide pin to the LCL, popliteus and gastrocnemius tendons were 0.76, 6.32, and 2.67 mm, respectively. The guide pin pierced the LCL in 2 out of 6 specimens. The gastrocnemius tendon was pierced in 1 of 6 specimens. The AM bundle mean epicondyle angle measured 15.5 degrees. The mean length from the PL bundle guide pin to the LCL, popliteus and gastrocnemius tendons were 0.72, 1.14, and 8.11 mm, respectively. The guide pin pierced the LCL in 4 of 6 specimens. The popliteus tendon was pierced in 3 out of 6 specimens. The mean PL bundle epicondyle angle measured 17.7 degrees. Anterior cruciate ligament (ACL) reconstruction in the preadolescent patient is becoming more commonplace. Anderson described a transepiphyseal technique for anatomic reconstruction of the ACL which avoids the distal femoral physis. We have shown that multiple structures are at risk with transphyseal drilling of the ACL femoral tunnel. The LCL is most at risk during guide pin placement for the AM bundle. Both the LCL and popliteus tendons are at risk during guide pin placement for the PL bundle. A transepiphyseal femoral tunnel is a promising option for anatomic reconstruction of the ACL in the skeletally immature patient. This technique avoids the distal femoral physis, thus decreasing the incidence of distal femoral growth arrest that can be seen following transphyseal reconstruction techniques. It also allows for anatomic placement of the ACL femoral tunnel. Several retrograde drilling devices are now available that allow for minimally invasive, inside-out placement of the ACL femoral tunnel. With retrograde devices a poke and spread technique should be utilized to reach the lateral femoral cortex, thus avoiding several important structures. Violation of the lateral cortex should also be avoided to preserve the lateral anatomic structures. Alternatively an outside in approach can be utilized. With the outside-in technique, we recommend a small incision to facilitate exposure and retraction of the important lateral structures. It is our hope that a better understanding of the lateral soft tissue anatomy will avoid injury to the vital lateral structures.