Abstract
Introduction
The sit-to-stand (STS) movement is a physically demanding activity of daily living and is performed more than 50 times per day in healthy adults. Several studies have shown that the normal ‘screw-home’ mechanism is altered after total knee arthroplasty (TKA). However, these studies have been criticized due to their limitations of the movement being non-weight-bearing or atypical daily activity (lunge maneuver). We analyzed TKA subjects during a STS activity to determine if the internal-external rotation of their TKA knees differed from the knees of control subjects.
Materials and Methods
Six TKA subjects (3 M, 3 F) participated following institutional review board approval and informed consent. One subject had bilateral knee replacement. Surgery was performed by the same surgeon using the same type of implant (6 posterior-stabilized, 1 cruciate-retaining). The control group included eight healthy subjects (6 M, 2 F).
Retro-reflective markers were placed over bony landmarks of the torso, pelvis, and lower extremities, and arrays of four markers were attached to the thighs and shanks using elastic wrap. A digitizing pointer was used to create virtual markers at the anterior superior iliac spines. A nine camera video-based opto-electronic system (Qualisys) was used for 3D motion capture. Subjects were barefoot and seated on a 46 cm armless bench with one foot on each force plate (AMTI). Subjects rose from their seated position, paused, and returned to the seated position at a self-selected pace repeatedly for 30 seconds. Subjects did not use their arms to push off the bench. Only the STS portion of the task was analyzed. The start of the STS cycle was defined when the C7 marker began to move forward in the sagittal plane and ended at the point of maximum knee extension. Only the right leg of the control subjects was used for analysis.
Results
Femurs rotated internally as control subjects rose from the bench. Two of the TKA knees displayed a similar pattern of internal rotation as the knees extended. However, four TKA knees displayed the opposite pattern, and one TKA knee showed no rotation. For ease of comparison I/E rotation was normalized to zero at full extension (Figure 1).
Discussion
Our results of a reverse tibio-femoral rotational pattern in TKA knees compared to normal knees are similar to those reported in fluoroscopic studies in which a single leg lunge activity is performed. Finding a similar reversal in STS is significant due to the necessity and frequency of the STS activity during daily living and warrants further investigation.
