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. 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.Introduction
Materials and Methods
In a previous study of subjects with no history of lower extremity injury or disease we found a linear relationship between body weight and peak hip, knee, and ankle joint forces during the stance phase of gait. To investigate the effect of total knee arthroplasty (TKA) on forces in the operated joints as well as the other joints of the lower extremities, we tested TKA subjects during gait and performed inverse dynamics analyses of the results. TKA subjects (3 M, 1 F; 58 ± 5 years; body mass index range (BMI): 26–36 kg/m2) participated in this investigation following institutional review board approval and informed consent. One subject had bilateral knee replacement. Each patient received the same implant design (4 PS, 1 CR). Data from previously tested control subjects (8 M, 4 F; 26 ± 4 years; BMI: 20–36 kg/m2) were used for comparison. Retro-reflective markers were placed over bony landmarks of each subject. A nine-camera video-based opto-electronic system was used for 3D motion capture as subjects walked barefoot at a self-selected speed on a 10 meter walkway instrumented with three force plates. Data were imported into a 12-body segment multibody dynamics model (AnyBody Technology) to calculate joint forces. Each leg contained 56 muscles whose mechanical effect was modeled by 159 simple muscle slips, each consisting of a contractile element. The models were scaled to match each subject's anthropometry and BMI. For the control subjects, only one limb was used in determining the relationship between body mass and peak joint force at the hip, knee, and ankle. For the TKA subjects, the peak joint forces were calculated for both the TKA limb and the contralateral limb.Introduction
Materials and Methods
