High-load preconditioning of soft tissue grafts: an in vitro biomechanical bovine tendon model.
OBJECTIVE
No consensus exists regarding the optimal preconditioning protocol that will minimize postoperative elongation while creating a graft that is biomechanically equivalent to the native anterior cruciate ligament (ACL). It was hypothesized that a preconditioning protocol of specific mode and magnitude would create a graft with equivalent stiffness to the native ACL.


METHODS
Thirty-six bovine extensor tendon grafts were randomly allocated among six preconditioning groups (n = 6 per group) including three cyclic (10 cycles at 0.5 Hz between 10-80, 100-300, and 300-600 N) and three static loading protocols (20 s at 80, 300, and 600 N). Grafts were then cyclically loaded between 50 and 250 N at 0.5 Hz for 500 cycles to simulate an early rehabilitation protocol.


RESULTS
Cyclic 300-600 N and static 600 N loading protocols both demonstrated significantly less elongation during simulated rehabilitation when compared to lower, current clinical standard preconditioning levels of 10-80 N (-62% Δ) and 80 N (-69% Δ). The same high-load preconditioning protocols demonstrated statistical equivalence in stiffness when compared to the previously reported stiffness of the native ACL.


CONCLUSIONS
In this experimental model, increased force applied to soft tissue grafts during preconditioning significantly decreased the subsequent elongation experienced during simulated early rehabilitation. A static load of 600 N removed the most graft elongation during preconditioning, had the least amount of cyclic displacement during simulated early rehabilitation, and was statistically equivalent to the native ACL stiffness. Implementation of high-load preconditioning of soft tissue grafts may help improve outcomes following ACL reconstruction by reducing residual knee laxity resulting from postoperative graft elongation and the intrinsic viscoelastic properties of the graft tissue while imparting biomechanical characteristics (e.g. stiffness) equivalent to the native ACL.
Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA.|The Steadman Clinic, 181 West Meadow Drive, Suite 400, Vail, CO, 81657, USA.
Jeffrey R
JR
Jaglowski
Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA.
Brady T
BT
Williams
Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA.
Travis Lee
TL
Turnbull
Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA. drlaprade@sprivail.org.|The Steadman Clinic, 181 West Meadow Drive, Suite 400, Vail, CO, 81657, USA. drlaprade@sprivail.org.
Robert F
RF
LaPrade
Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO, 81657, USA.
Coen A
CA
Wijdicks
D000818:Animals; D016118:Anterior Cruciate Ligament / Q000502:physiology; D001696:Biomechanical Phenomena; D002417:Cattle; D004548:Elasticity; D064593:Heterografts / Q000502:physiology; D023421:Models, Animal; D013710:Tendons / Q000502:physiology*; D019737:Transplants / Q000502:physiology*; D016474:Weight-Bearing
ACL reconstruction; Hamstring grafts; Preconditioning; Soft tissue grafts