title: Central-third bone-patellar tendon-bone allografts demonstrate superior biomechanical failure characteristics compared with hemi-patellar tendon grafts.
abstract: BACKGROUND
  Reconstruction of the anterior cruciate ligament (ACL) is commonly performed with a bone-patellar tendon-bone (BTB) allograft. However, grafts may result from harvesting the central region of a whole graft (C-BTB), the medial 10 mm of a lateral hemi-BTB (L-BTB) graft, or the lateral 10 mm of a medial hemi-BTB (M-BTB) graft.
  
  
  OBJECTIVE
  To quantify potential differences in graft biomechanical properties when comparing whole versus hemi-BTB grafts.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Ten pairs of human BTB allografts (irradiated with 1.0-1.2 Mrad) were randomized to preparation as whole grafts or hemigrafts. From these, 10-mm grafts were prepared from the center or the most central portion, respectively. After measurements of tendon thickness, width, and length, specimens underwent cyclic tensile testing, followed by load-to-failure analysis. Biomechanical outcomes included cyclic elongation and creep strain along with the following failure characteristics: maximum load, elongation at maximum load, maximum stress, strain at maximum stress, and linear stiffness.
  
  
  RESULTS
  Regionally, the mean thickness of the C-BTB (5.18 ± 0.75 mm), M-BTB (5.08 ± 0.56 mm), and L-BTB (5.32 ± 0.62 mm) grafts were comparable (P > .72). Similarly, the mean length of the C-BTB (47.4 ± 6.73 mm), M-BTB (47.0 ± 5.45 mm), and L-BTB (50.7 ± 6.42 mm) grafts were alike (P > .43). While differences in cyclic elongation and strain were not significant, the M-BTB graft tended to elongate more (0.204 ± 0.13 mm; P = .075) and experience greater strain (0.56% ± 0.32%; P = .054) compared with the C-BTB graft (0.09 ± 0.03 mm and 0.23% ± 0.07%, respectively). Load-to-failure testing demonstrated a higher maximum load (2293 ± 531 N) and stiffness (356 ± 46 N/mm) of the C-BTB graft as compared with the M-BTB graft (1575 ± 325 N [P < .007] and 275 ± 37 N/mm [P < .008], respectively) and L-BTB graft (1585 ± 452 N [P < .008] and 277 ± 65 N/mm [P < .009], respectively). No differences were noted with respect to elongation or stress at maximum load among the grafts. Maximum stress in the C-BTB graft (45.4 ± 11.5 MPa) was greater than in the L-BTB graft (29.7 ± 10.6 MPa) (P < .03) and tended to be greater than the M-BTB graft (34.1 ± 6.27 MPa) (P = .087).
  
  
  CONCLUSIONS
  Biomechanical failure properties (maximum load, stress, and stiffness) of the central portion of a whole BTB graft are superior to those of the medial portion of a lateral hemi-BTB graft and the lateral portion of a medial hemi-BTB graft. However, cyclic loading characteristics did not differ between grafts.
  
  
  CONCLUSIONS
  Although the true central-third BTB graft is biomechanically superior to hemi-BTB grafts, future studies are necessary to determine if the use of hemigrafts leads to an increased incidence of clinical failure.
authors.affiliation: Adam B. Yanke, Department of Orthopedic Surgery, Rush University Medical Center, 1611 West Harrison Street, Suite 300, Chicago, IL 60612. basworth@mac.com.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Yanke
authors.forename: Rebecca
authors.initials: R
authors.lastname: Bell
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Lee
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Shewman
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Wang
authors.forename: Bernard R
authors.initials: BR
authors.lastname: Bach
mesh_terms: D000328:Adult; D064591:Allografts / Q000502:physiology*; D001696:Biomechanical Phenomena; D050376:Bone-Patellar Tendon-Bone Grafting; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013314:Stress, Mechanical; D055815:Young Adult
keywords: ACL; allografts; anterior cruciate ligament; biomechanics of ligament; bone–patellar tendon–bone allograft; knee; ligaments; morphology