Degree Name

Doctor of Philosophy


Department of Biomedical Science


Treatment of anterior cruciate ligament deficient (ACLD) patients is complicated by difficulty in accurately predicting those patients who will be functionally impaired by ACL rupture and those who will have minimum symptoms. Although the effects of ACL rupture on knee function during locomotor tasks have been studied, no research was located which examined whether the use of compensatory adaptations by ACL D subjects to perform dynamic tasks could be associated with knee function during knee laxity assessment. Therefore, the purpose of the thesis was to establish the relationship between knee function during arthrometric knee laxity assessment and knee function during a dynamic movement known to stress the ACL, namely abrupt deceleration. To achieve this three studies were conducted to establish a standardised arthrometric knee laxity assessment protocol using the Dynamic Cruciate Tester (DCT) and to verify reliability of the protocol (Experimental Section A). In Study 1 active and passive knee laxity was assessed for 10 uninjured subjects before and after the subjects cycled for 10 minutes and then performed hamstring stretches. As there were no significant differences between anterior tibial translation (ATT), knee extension force, or hamstring activity pre- compared to post-warm up it was concluded that a warm up suitable for use with ACLD patients was not required before arthrometric knee laxity assessment. In Study 2 active and passive knee laxity of 12 controls and 12 ACL D subjects was assessed with the subjects in three torso positions: vertical, reclined, and supine; while electromyographic (EMG) data were collected for the hamstring and quadriceps muscles. Although there was no significant difference in mean ATT as a function of torso position, subjects displayed significantly greater hamstring activity when seated vertically or reclined compared to when supine. As torso position also significantly affected knee extension force, it was recommended patients be supine during arthrometric knee laxity assessment to minimise muscle guarding. In Study 3 reproducibility of ATT and knee extension force data were examined for 13 ACLD subjects and 16 controls. The ATT and knee extension force results were found to be highly reproducible between and within test days. However, as a significant main effect of trial was found on ATT, a pretrial was recommended before knee laxity assessment to enhance reproducibility of the results. It was concluded that, following the standardised protocol, the DC T was a reliable tool to characterise ATT and isometric knee extension deficits and to monitor hamstring guarding by chronic ACL D subjects during active and passive arthrometric knee laxity assessment.

Once the arthrometric assessment protocol was established, a kinematic, kinetic, and neuromuscular analysis was conducted of 11 chronic functional ACL D subjects and 11 matched controls performing a deceleration task (landing in single-limb stance after catching a ball) after each subject's lower extremity strength and knee laxity were assessed (Experimental Section B). Compared to the controls, the ACLD subjects displayed: lower Lysholm knee scores; significantly lower peak knee extension torques assessed isokinetically (60°-s1); no evidence of knee flexion strength deficits and no significant reduction in thigh circumference; a significantly greater mean passive gap but a negligible limb-to-limb difference in active ATT; greater hamstring cocontraction during anterior tibial drawer to restrict excessive ATT; and took longer during active assessment to deactivate rectus femoris and vastus lateralis after reaching their maximal knee extension effort. During the deceleration task no significant alterations were evident in the kinematic parameters analysed at either Initial Contact (IC) or Peak Resultant Ground Reaction Force (PRGRF) or in the ground reaction forces generated by the ACL D subjects. However, compared to the controls, the ACL D subjects displayed: significantly less knee flexion motion from IC to PRGRF; a higher tibiofemoral compressive force (Fc) at IC caused by higher knee flexion moments; a delay in hamstring activation so that peak hamstring activity was more synchronous with IC and with the high tibiofemoral shear forces (F,) which occurred post IC; but no evidence of quadriceps-avoidance nor any increase in hamstring cocontraction intensity. These between-subject group differences were thought to be functional adaptations employed by the ACL D subjects to stabilise their involved knee against a giving-way episode via increased joint compression and posterior tibial drawer in preparation to withstand, rather than reduce or avoid, the high anterior F, generated during deceleration.

Landing technique adaptations displayed by ACL D subjects were evident only at IC with the hamstring and quadriceps muscles activated before IC. These findings supported the notion that subjects preprogrammed their deceleration strategy before landing in anticipation of the joint loads. Although increased hamstring guarding during arthrometric knee laxity assessment and restricted knee flexion motion during deceleration were displayed bilaterally, alterations in Fc, knee flexion moments, and hamstring sequencing during deceleration were not transferred to the contralateral limb. It was postulated that task novelty or upper extremity motion involved in catching the ball may have interfered with the ACL D subjects' motor programs developed to control lower extremity muscle function during deceleration.

Thirty five correlations between variables characterising knee laxity and deceleration were significant across the pooled subject group results. However, the correlations were low (r = 0.299 - 0.483) such that most of the variance within the variables characterising knee function during deceleration could not be explained by their relationship to the variables characterising knee function during arthrometric knee laxity assessment. Therefore, although providing information pertaining to functional status during a closed isometric knee extension effort or during passive anterior tibial loading, it was concluded that the DC T could not be used to predict knee function of ACL D subjects during an open dynamic deceleration task.

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