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Information about project titled 'Material properties of the quadriceps tendon: Full-thickness vs partial-thickness graft'

Material properties of the quadriceps tendon: Full-thickness vs partial-thickness graft

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Project status: Ongoing
Project manager: Marc Strauss
Supervisor(s): Robert LaPrade, Lars Engebretsen, Gilbert Moatshe


Background: Despite increasing interest in utilizing quadriceps tendon graft in ACL reconstruction, data on the optimal quadriceps graft thickness is still lacking. While some authors utilize a full-thickness quadriceps tendon, others advocate for a partial-thickness tendon graft. It is important that the graft being utilized in ACL reconstruction have comparable biomechanical properties as the native ACL. In this study, we will characterize the mechanical properties for the quadriceps tendon; and compare a full-thickness tendon graft (10x8 mm) to a half-thickness (12x5 mm) graft and compare these properties to the native ACL. 

Materials and methods
A total of 24 fresh frozen quadriceps allograft tendons without bone block and 12 fresh frozen patella tendon allografts (Allosource, CO) with no prior injury, surgical history and gross anatomic abnormality from donors < 40 years of age will be used for this study. We will utilize young adult cadavers primarily because the majority of patients treated with ACL reconstruction are <40 years of age. In addition, it is difficult to obtain very young cadavers (adolescent) in sufficient quantity. 

Specimen preparation: The grafts will be stored at -20oC and thawed at room temperature on the day of testing. One tendon of each pair will be randomly assigned to either of the two groups (Group 1: Patella tendon with bone block, Group 2: full thickness quadriceps tendon 10x7 mm. Group 3:12x5 mm quadriceps tendon graft) for testing. After randomization of the quadriceps tendons, the graft will be prepared to the allocated size. Each specimen’s native ACL will be separated with bone plugs and similarly tested with load to failure testing. 

Biomechanical testing methods: The free ends of the quadriceps tendon of each prepared specimen will be mounted to the actuator of a dynamic testing machine (Instron ElectroPuls E10000, Instron Systems, Norwood, Massachusetts) while secured within previously validated custom cryo-clamps, to prevent graft slippage. The patella tendons will be potted. The potted bone block will be secured within a custom rotating fixture with the application of the tensile force along the axis of the tendons. Before tensile testing to failure is performed, specimens will be preconditioned for 10 cycles between 2-10 Newtons (N) at 0.1 Hz. The grafts will then be loaded for 500 cycles between 50 and 250 N at a frequency of 1 Hz. Surviving grafts will be further displaced at 20 mm/min until failure. For each specimen, the mechanical properties including cyclic displacement/elongation (mm), cyclic stiffness (N/mm), initial failure load (N), ultimate load (N), pullout displacement (mm), and stiffness at failure (N/mm) will be recorded. 

The mechanical properties of each tendon will be calculated from force displacement graphs that are recorded. In addition, the location and mechanism of failure (pullout, intra-substance tendon stretch) of each tendon will be noted. This method is validated and has been utilized in previous studies (references). 

Statistics: Statistical analysis will be performed with the use of Predictive Analytics SoftWare (PASW) Statistics Version 18 (IBM Corporation, Armonk, New York). The study compares data for each group using a one-way analysis of variance (ANOVA). 

Results: The stiffness, tensile strength, elongation/displacement of each tendon graft size group will be determined and compared to each other and to those of the adult ACL.