Kissing knees - factors behind the attraction. Knee abduction in individuals with anterior cruciate ligament injury

Abstract: Anterior cruciate ligament (ACL) injury and patellofemoral pain (PFP) are common sports-related knee injuries. Their consequences include compromised health of the effected individual and substantial financial costs for society. Increased knee abduction or a knee medial to foot position (KMFP), so called “kissing knees”, during weight-bearing activities is reported to be more common in patients with ACL injury or PFP than in non-injured individuals and is also reported to be associated with greater pain and worse function in these patients. Furthermore, increased knee abduction during activity is suggested to increase the risk of sustaining both primary and subsequent ACL injuries. However, the contributing factors for this altered movement pattern are not well understood. Therefore, the primary aim of this thesis was to investigate the association between sensorimotor factors, modifiable by training, and knee abduction in patients with ACL injury.Two systematic reviews with meta-analyses were conducted (papers I and II). These included patients with ACL injury or PFP and healthy individuals and investigated the association between sex, muscle strength, muscle activation, sensory function and joint range of motion (ROM), respectively, and knee abduction. The association between sensory function (n=51, 23 women), muscle strength and muscle activation (n=29, 11 women), respectively, and a knee abduction/KMFP in patients with ACL injury were investigated in three cross-sectional studies (papers III – V).This thesis shows that non-injured women and those with PFP perform weight-bearing activities with greater knee abduction compared to their male counterparts. In healthy individuals, lower trunk lateral flexion strength, lower gluteus maximus activation, increased hip external rotation ROM and reduced ankle dorsi-flexion range of motion were associated with increased knee abduction/KMFP. In individuals with ACL injury, reduced sensory function was associated with a KMFP, and lower vastus medialis (VM) activation and iliocostalis activation on the non-injured side but higher semitendinosus (ST) activation and ST/VM ratio were associated with increased 3D knee abduction during weight-bearing activities. Hip and knee strength was not, or only weakly, associated with knee abduction in healthy individuals and in those with knee injury.The result from this thesis indicates that sensorimotor function, such as proprioception and muscle activation patterns should be considered in the rehabilitation after ACL injury. Given that healthy women perform weight-bearing activities with increased knee abduction compared to men, there may need to be a greater focus on this movement pattern during prevention and rehabilitation training in women, whereas other factors may be more relevant in men. Further investigations are needed to confirm these results and to establish the factors, both structural and neuromuscular, that contribute to knee abduction in men and women with ACL injury.