Evidence for differential control of tibial position in perturbed unilateral stance after acute ACL rupture

Abstract

Functional outcomes in anterior cruciate ligament-deficient "potential copers" and "non-copers" may be related to their knee stabilization strategies. Therefore, the purpose of this study was to differentiate dynamic knee stabilization strategies of potential copers and non-copers through analysis of sagittal plane knee angle and tibia position during disturbed and undisturbed unilateral standing. Ten uninjured potential coper and non-coper subjects stood in unilateral stance on a platform that translated anteriorly, posteriorly and laterally. Knee angle and tibia position with reference to the femur were calculated before and after platform movement. During perturbation trials, potential copers maintained kinematics that were similar to uninjured subjects across conditions. Conversely, non-copers stood with greater knee flexion than uninjured subjects and a tibia position that was more posterior than the other groups. Both non-copers and potential copers demonstrated small changes in tibia position following platform movement, but direction of movement was not similar. The similarities between the knee kinematics of potential copers and uninjured subjects suggest that potential copers compensated well from their injury by utilizing analogous dynamic knee stabilization strategies. In comparison to the other groups, by keeping the knee in greater flexion and the tibia in a more posterior position, non-copers appear to constrain the tibia in response to a challenging task, which is consistent with a "stiffening strategy".Based on the poor functional outcomes of non-copers, a stiffening strategy does not lead to dynamic knee stability, and the strategy may increase compressive forces which could contribute to or exacerbate articular cartilage degeneration.

Influence of Anticipation on Movement Patterns in Subjects With ACL Deficiency Classified as Noncopers

“…6,16 Possibly relevant to this study is the timing of the electromyographic activity after initiation of forward plate movement. 6,7 In previous studies, the noncoper subjects activated their muscles within 60 to 129 milliseconds after initiation of plate movement. 7 This suggests that subjects classified as noncopers are able to implement an abnormal movement pattern within the planning time (time from visual cue to force plate contact), estimated at approximately 350 milliseconds, that occurred in the current study.…”

“…6,7 In previous studies, the noncoper subjects activated their muscles within 60 to 129 milliseconds after initiation of plate movement. 7 This suggests that subjects classified as noncopers are able to implement an abnormal movement pattern within the planning time (time from visual cue to force plate contact), estimated at approximately 350 milliseconds, that occurred in the current study. Studies suggest that the causes of abnormal movement patterns in subjects classified as noncopers may be related to knee instability, deficits in knee strength, or deficits in neuromuscular control.…”

“…6 Studies of unanticipated tasks suggest that the abnormal movement patterns of the noncopers in response to force platform movement are in the intermediate reflex interval (60-129 milliseconds). 6,7 This suggests that noncopers are able to employ their abnormal movement patterns using feedback control when task demands are longer than this interval. 6,7 Although moving force platforms have validity for reproducing slip events, a criticism of this paradigm is that it lacks validity for simulating sports-related movements that do not involve slipping.…”

“…6,7 This suggests that noncopers are able to employ their abnormal movement patterns using feedback control when task demands are longer than this interval. 6,7 Although moving force platforms have validity for reproducing slip events, a criticism of this paradigm is that it lacks validity for simulating sports-related movements that do not involve slipping. 47 Unanticipated tasks have validity for simulating sports-related movements while inducing loads in the lower extremity that may challenge subjects that have an ACLD.…”

Sagittal Plane Knee Motion in the ACL-Deficient Knee During Body Weight Shift Exercises on Different Support Surfaces

“…That ability to stabilize the knee joint has been demonstrated before. 7,[19][20][21]29 We do not know if the results from the present study apply after ACL reconstruction. In addition, the method we used to measure dynamic translation gives no information about the stress on the ACL or a graft.…”