title: Proximity of Lateral Critical Structures to the All-Epiphyseal Outside-In Femoral Tunnels in Pediatric Anterior Cruciate Ligament Reconstruction.
abstract: OBJECTIVE
  To describe the proximity of the lateral critical structures (peroneal nerve [PN], popliteus tendon [PT], lateral collateral ligament [LCL], and articular cartilage [AC]) to the femoral tunnel for outside-in all-epiphyseal anterior cruciate ligament (ACL) reconstruction in reference to knee flexion angle.
  
  
  METHODS
  All-epiphyseal ACL reconstructions were performed in 12 human cadaveric knees using arthroscopy and outside-in drilling for anatomic femoral tunnel placement that was ensured by identifying the center of the total ACL footprint. Fluoroscopy was used to confirm tunnel position and reconstructions were performed with quadrupled semitendinosus and gracilis autograft with Xtendobutton (Smith & Nephew, Andover, MA) fixation on the femoral side. After reconstruction, the lateral side of the knee was dissected and the LCL, PT, distal and posterior AC, and the PN were identified. The distances of these structures from the center of the exiting femoral tunnel were then measured using a digital caliper at 0°, 30°, 60°, 90°, and 120° of knee flexion. Any gross damage to these structures caused by the femoral drilling was also noted. Data were compiled and the mean and standard deviations (SD) of the distances from the pin to the structures of interest were calculated. The normality of the data at each flexion angle was assessed using Shapiro-Wilk tests (P > .05), and the relationship between flexion angle and average distance was evaluated using repeated measures analysis of variance (P < .05). Any significant relationships were then evaluated using paired t-tests (P < .05) with a Benjamini-Hochberg adjustment for each possible pair of flexion angles. Averages, SD, and P values are reported. A post hoc power analysis was performed.
  
  
  RESULTS
  The violation of the LCL was noted in 3 specimens and that of the PT in 1 specimen as a result of femoral tunnel drilling at flexion angles ranging from 90° to 120°. The distance between the PT and the femoral tunnel also decreased significantly (P < .001) with knee flexion with average distances to the center of 8.07 mm at 0°, 7.75 mm at 30°, 6.33 mm at 60°, 4.12 mm at 90°, and 1.89 mm at 120°. The mean ± SD for distances from the femoral tunnel to the center of the PT at 0° was 8.07 ± 7.15, at 30° 7.75 ± 6.66, at 60° 6.33 ± 6.79, at 90° 4.12 ± 5.71, and at 120° 1.89 ± 5.56. As the knee was progressively flexed, the distance between the LCL and the femoral tunnel decreased significantly (P < .001) with an average distance of 6.52 mm at 0°, 6.26 mm at 30°, 4.23 mm at 60°, 2.38 mm at 90°, and 0.4 mm at 120°. The mean ± SD for distances from the femoral tunnel to the center of the LCL at 0° was 6.52 ± 5.93, at 30° 6.26 ± 7.32, at 60° 4.23 ± 7.82, 90° 2.38 ± 7.31, and at 120° 0.4 ± 7.01. The PN was remote from the femoral tunnel at all flexion angles with a mean distance of 42.83 to 59.22 mm. The PN to guide pin distance increased significantly with progressive knee flexion (P < .001). The AC was not damaged in all specimens.
  
  
  CONCLUSIONS
  The LCL and PT are at significant risk during percutaneous femoral drilling for all-epiphyseal anatomic ACL reconstruction using an outside-in technique. This risk was maximized at 120° flexion and minimized in full extension. These findings suggest that the optimal position for femoral drilling in all-epiphyseal ACL reconstruction is full or near-full extension of the knee that can be accomplished by placing the knee in 30° of flexion (after using fluoroscopic guidance to pass the guide pin past the lateral critical structures) to visualize the footprint of the ACL.
  
  
  CONCLUSIONS
  Information garnered from this study may help clinicians better understand the risk to the lateral critical structures when an outside-in femoral tunnel is not drilled in the appropriate degree of knee flexion.
authors.affiliation: Children's Hospital of Michigan, Detroit, Michigan, U.S.A.; Department of Orthopaedic Surgery and Rehabilitation, Division of Sports Medicine, Detroit Medical Center, Detroit, Michigan, U.S.A.; Wayne State University, Detroit, Michigan, U.S.A.
authors.forename: Mark K
authors.initials: MK
authors.lastname: Lane
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, Division of Sports Medicine, Detroit Medical Center, Detroit, Michigan, U.S.A.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Mutch
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, Division of Sports Medicine, Detroit Medical Center, Detroit, Michigan, U.S.A.
authors.forename: Kaitlyn
authors.initials: K
authors.lastname: Ratkowiak
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, Division of Sports Medicine, Detroit Medical Center, Detroit, Michigan, U.S.A.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Lemos
authors.affiliation: Children's Hospital of Michigan, Detroit, Michigan, U.S.A.; Department of Orthopaedic Surgery and Rehabilitation, Division of Sports Medicine, Detroit Medical Center, Detroit, Michigan, U.S.A.. Electronic address: KKalra@dmc.org.
authors.forename: Kunal
authors.initials: K
authors.lastname: Kalra
mesh_terms: D000368:Aged; D016118:Anterior Cruciate Ligament / Q000033:anatomy & histology / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D002102:Cadaver; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000601:surgery; D002648:Child; D004838:Epiphyses / Q000033:anatomy & histology / Q000294:innervation / Q000601:surgery*; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D013710:Tendons / Q000033:anatomy & histology / Q000601:surgery*