title: Comparison of "inside-out" and "outside-in" interference screw fixation for anterior cruciate ligament surgery in a bovine knee.
abstract: Despite numerous advances in graft fixation with anterior cruciate ligament (ACL) reconstruction, few studies have compared the fixation strength of interference screws placed "outside-in" and from "inside-out" techniques. To compare techniques, a bovine model was designed to fail at the femoral tunnel bone-screw interface. Twenty-four fresh bovine knees were stripped of all soft tissues except the ACL. The native ACL was loaded the failure at a strain rate of 50 cm/min with the knee flexed 45 degrees. One standardized femoral tunnel was created on all specimens. A 3/32-inch guide pin was drilled into the center of the ACL femoral origin and overreamed with an 11-mm reamer from inside-out until the lateral cortex was reamed. Consistently sized patellar bone blocks were created (8 x 5 x 25 mm) with an 8-mm tendon width. The bone blocks were randomized to an "inside-out" (group 1) and "outside-in" (group 2) technique. Bone blocks were secured with a 7 x 25 interference screw. Specimens were mounted with the femoral tunnel and bone block aligned parallel to the tensile force and strained to failure at 50 cm/min. Failure of the native bovine ACL occurred at a mean of 2,304 N (SD +/- 472 N; n = 24). The mode of failure for group 1 was 9 of 13 at the bone-screw interface and 4 of 13 interligamentous failures. The mode of failure for group 2 was 7 of 11 at the bone-screw interface, 3 of 11 interligamentous, and 1 bone block failure. The mean load to failure for group 1 was 1,151 N (SD +/- 320 N, n = 13) including the four ligamentous failures and 1,143 N (SD +/- 306 N, n = 9) excluding the ligamentous failures. The mean load to failure for group 2 was 1,017 N (SD +/- 262 N, n = 11), including all specimens and 843 N (SD +/- 262 N, n = 7) excluding the interligamentous and bone block failure specimens. The "inside-out" technique averaged 100 N greater fixation strength than the "outside-in" technique. Statistical analysis using two-sample Student's t-test showed no statistically significant differences between group 1 and group 2. Both techniques demonstrate comparable maximum load to failure in a bovine model tested at 50 cm/min.
authors.affiliation: Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Bryan
authors.forename: B R
authors.initials: BR
authors.lastname: Bach
authors.forename: C A
authors.initials: CA
authors.lastname: Bush-Joseph
authors.forename: I M
authors.initials: IM
authors.lastname: Fisher
authors.forename: K Y
authors.initials: KY
authors.lastname: Hsu
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D020679:Arthroscopes; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002417:Cattle; D019723:Endoscopes; D004867:Equipment Design; D004868:Equipment Failure; D005269:Femur / Q000601:surgery; D013536:Suture Techniques / Q000295:instrumentation*; D013709:Tendon Transfer / Q000295:instrumentation; D013977:Tibia / Q000601:surgery; D016474:Weight-Bearing / Q000502:physiology