The Effects of Donor Age and Strain Rate on the Biomechanical Properties of Bone-Patellar Tendon-Bone Allografts

Abstract

Over 50% of all knee injuries involve partial or complete tear of the anterior cruciate ligament. Surgical reconstruction of this ligament using an isometrically placed bone-patellar tendon-bone autograft is the current technique of choice; however, harvest of patellar tendon as a free graft can lead to increased morbidity. To address this issue, allogenic patellar tendon grafts have been introduced as alternatives to autogenic graft material. The purpose of this study was to examine effects of age and strain rate on tensile strength, modulus, and failure mode of bone-patellar tendon-bone allografts from a typical population of tissue donors. Eighty-two, fresh-frozen, bone-patellar tendon-bone allografts were harvested from 25 different donors, aged 17 to 54. Paired grafts from individual patellar tendons were assigned randomly to tensile testing at either 10% or 100% elongation per second. Tensile strength, modulus, and failure mode were not significantly different for tests conducted at these 2 strain rates. Correlations between tensile strength and age were not significant for tests conducted at either strain rate. Specimens tested at a strain rate of 100% per second exhibited weak but significant negative correlation between modulus and age, with modulus decreasing 25% over the age range examined.

Comparative Analysis of the Structural Properties of the Collateral Ligaments of the Human Knee

“…16 While the preponderance of avulsion failures may also reflect the relatively slow loading rate employed in the current investigation (500 mm/min or approximately 20%/s), 21 it is worthy to note that the ultimate tensile strength and stiffness values of the LCL and MCL are comparable to those reported in the literature for isolated tests (TABLE 1), despite considerable differences in the age of specimen donors and the loading rates employed. Thus, these findings tend to support those of previous studies, in which the properties of knee ligaments have been shown to be only weakly influenced by age 2 and were relatively insensitive to loading rates ranging from 1%/s to 100%/s. 5 Although the loading rate employed in the current study was encompassed within the wide range of elongation rates (30 to 90 000 mm/min) thought to induce traumatic loading of the human knee joint, 6 there was considerable between-specimen variability in the tensile strength of the 2 ligaments, as shown in TABLE 3.…”

Investigating the effects of anterior tibial translation on anterior knee force in the porcine model: Is the porcine knee ACL dependent?

“…However, this slower speed is not expected to dramatically affect tissue forces as it has been shown previously that soft tissue samples transmit similar forces when tested at 10%/s versus 100%/s. 27 (3) Alignment of the anatomical axes with robot and load cell axes was controlled accurately but could have varied from limb to limb. This is not expected to be a major factor due to the small variance in our force data within and among specimens.…”

Strain rate effect on the mechanical behavior of the anterior cruciate ligament–bone complex

“…The measurement of the linear tangent moduli did not show significant differences with respect to the strain rates and confirmed the observation that the strain rate effect acts mainly in the toe region. A direct consequence of this result is that the linear tangent moduli can not be used to quantify the effect of strain rate in a soft tissue as proposed for the patellar tendon specimens [22]. The quantification of the strain rate effect should use an independent variable, as the "supplemental stress" or should use a continuum mechanics approach as proposed in a recent paper [23].…”