J. Hoher et al., Mechanical behavior of two hamstring graft constructs for reconstruction of the anterior cruciate ligament, J ORTHOP R, 18(3), 2000, pp. 456-461
We compared the mechanical behavior of two common hamstring graft construct
s that are frequently used for reconstruction of the anterior cruciate liga
ment-Graft A: quadrupled semitendinosus tendon fixed with titanium button/p
olyester tape and suture/screw post, and Graft B: a double semitendinosus a
nd double gracilis tendon fixed with a cross pin and two screws over washer
s. The experimental protocol used to evaluate each graft construct included
stress relaxation (with and without preconditioning), cyclic loading, and
a tensile load-to-failure test. The amount of stress relaxation without pre
conditioning was 60.6% for Graft A and 53.8% for Graft B. With precondition
ing, it significantly decreased (p < 0.05) to 38.7 and 42.3%. respectively.
Elongation of the graft construct in response to 100 cycles of loading (20
-150 N) was 1.8 and 0.6% of the original length for Grafts A and B, respect
ively. However, after a series of five cyclic loading tests, the residual p
ermanent elongation for each construct was 3.8 +/- 1.2 and 0.3 +/- 0.2 mm,
a significant difference (p < 0.05) between the two graft constructs. Furth
er analysis found more than 90% of the permanent elongation in the proximal
and distal regions of Graft A, which consisted of polyester tape tied to a
titanium button (proximal) and sutures tied around a screw post (distal).
The tensile load-to-failure tests also revealed significant differences (p
< 0.05) between the two graft constructs. Linear stiffness was 32 +/- 1 and
119 +/- 19 Nmm and ultimate load was 415 +/- 36 and 658 +/- 128 N for Craf
ts A and B, respectively. For Graft A, the polyester tape consistently fail
ed; for Graft B, slippage or tearing from the washers was the mode of failu
re. We conclude that a quadruple-hamstring graft Fixed over a cross pin pro
ximally and with metal washers distally (Graft B) has less permanent elonga
tion in response to cyclic loading and has structural properties superior t
o those of a graft construct that includes suture and tape material (Graft
A). The large permanent elongation following repetitive loading of a graft
construct with tape and suture material during the early postoperative peri
od is of concern.