School of Engineering and Materials Science
Research Student Awards
PhD Thesis: A multi-media approach to establish the mechanical integrity of the ACL deficient knee
Author: HUDSON, Z
Supervisor(s): Dan Bader
The Anterior Cruciate Ligament (ACL) helps to maintain the dynamic integrity of the knee joint. This study investigated the ACL in two distinct conditions: in vivo using the Knee Signature System (KSS) and in vitro, using a novel mechanical test jig on different model systems. The force-displacement curves derived from both conditions were evaluated and associated measurement parameters established.
The KSS was used to evaluate normal and ACL deficient knees during the Lachman test and measurement parameters and errors were derived from a pilot study. In a prospective study of 2 groups of control and ACL deficient subjects (both n = 45), the groups could be differentiated to a side-to-side difference of 2.5 mm measured at an anterior tibial displacement (ATD) of 178 N. The sensitivity and specificity at this threshold was 89% and 80%, respectively. In a double blind, randomised controlled study, the KSS was also used to test the effect on ATD of open and closed kinetic chain exercises following bone-patella-bone ACL reconstruction. After a training period of 4 weeks, initiated 2 weeks after surgery, there was not significant difference (p<0.05) between the 2 exercise modalities.
A test jig was used to evaluate the porcine ACL in vitro. Tensile testing was conducted on immature (n = 20) and mature (n = 8) specimens at 2 crosshead rates. Skeletal maturity had a greater influence than test rate on the ultimate tensile load (UTL), deformation at failure and stiffness. For example, median stiffness values of 93 Nmm-1 and 348 Nmm-1 were recorded for immature and mature specimens, respectively. The in vitro test methodology was adapted to evaluate a novel tissue engineered device designed for a biological repair of the ACL (BioACL). In cadaveric and in vivo studies in an ovine model, the median UTL and stiffness for the normal ACL (n = 5) was 2040 N and 255 Nmm-1, respectively. The corresponding values for contralateral knees with BioACL implants were 885 N and 81 Nmm-1. In addition, mechanical integrity decreased dramatically over the period of 3 to 12 weeks post implantation.