Sensori-motor adaptation to knee osteoarthritis during stepping-down before and after total knee replacement

Abstract

Background: Stepping-down is preceded by a shift of the center of mass towards the supporting side and forward. The ability to control both balance and lower limb movement was investigated in knee osteoarthritis patients before and after surgery. It was hypothesized that pain rather than knee joint mobility affects the coordination between balance and movement control.

Methods: The experiment was performed with 25 adult individuals. Eleven were osteoarthritic patients with damage restricted to one lower limb (8 right leg and 3 left leg). Subjects were recruited within two weeks before total knee replacement by the same orthopedic surgeon using the same prosthesis and technics of surgery. Osteoarthritic patients were tested before total knee replacement (pre-surgery session) and then, 9 of the 11 patients were tested one year after the surgery when re-educative training was completed (post-surgery session). 14 adult individuals (men: n = 7 and women: n = 7) were tested as the control group.

Results: The way in which the center of mass shift forward and toward the supporting side is initiated (timing and amplitude) did not vary within patients before and after surgery. In addition knee joint range of motion of the leading leg remained close to normal before and after surgery. However, the relative timing between both postural and movement phases was modified for the osteoarthritis supporting leg (unusual strategy for stepping-down) before surgery. The "coordinated" control of balance and movement turned to be a "sequential" mode of control; once the body weight transfer has been completed, the movement onset is triggered. This strategy could be aimed at shortening the duration-time supporting on the painful limb. However no such compensatory response was observed.

Conclusion: The change in the strategy used when supporting on the arthritis and painful limb could result from the action of nociceptors that lead to increased proprioceptor thresholds, thus gating the proprioceptive inputs that may be the critical afferents in controlling the timing of the coordination between balance and movement initiation control.

Figure 1

Phases of the motor act in stepping down movement (A). Reference times were measured from 2 curves (B). Top, The reference times plotted on the vertical velocity curve of the malleolus marker of the leading leg (T2) and of the supporting leg (T3) correspond respectively to the onset and offset of the movement phase. Bottom: lateral CP curve (T1) corresponds to the onset of CP change and Tbal to the end of the ballistic CP shift.

Figure 2

Schema of the horizontal shift of the center of mass (CM) and associated center of pressure (CP) (left part) and description of the M/L and A/P CP curves (right part). The dotted lines show the time-relationships between each component. Note that the M/L thrust (T1-Peak) coincides with the first backward CP shift, and that during the unloading component of the M/L CP shift, the second backward shift occurs, which corresponds to heel off (T2).

Figure 3

Schema of the vertical ground reaction force recorded on the landing force platform. Weight acceptance was from the ground contact to the peak and was calculated in percentage relative to the body weight to normalize the data for all the subjects.

Figure 4

Kinetic and rectified EMG patterns recording with one control subject. The EMGs were recorded at a proximal level (VL, Vastus lateralis) for both sides. Note the supporting and leading VL activity prior to the ground contact.

Figure 5

Dynamic profiles of VL activation recorded on the forthcoming landing leg before and after surgery. EMG data are windowed each 150 ms from 300 ms before ground contact to 300 ms after ground contact (Arbitrary Units, AU).