Patients with sacroiliac joint dysfunction exhibit altered movement strategies when performing a sit-to-stand task.

OF BACKGROUND DATA: The ability to rise from a chair is a basic functional task that is frequently compromised in individuals diagnosed with orthopedic disorders in the low back and hip. There is no published literature that describes how this task is altered by sacroiliac joint dysfunction (SIJD). PURPOSE: The objective of this study was to compare lower extremity biomechanics and the onset of muscle activity when rising from a chair in subjects with SIJD and in healthy persons. STUDY DESIGN: Six women with unilateral SIJD and six age-matched healthy controls performed a sit-to-stand task while we measured kinematics, kinetics, and muscle activity. MATERIALS AND METHODS: Subjects stood up at a preferred speed from a seated position on an armless and backless adjustable stool. We measured kinematics with a 10-camera motion capture system, ground reaction forces for each leg with force plates, and muscle activity with surface electromyography. Joint angles and torques were calculated using inverse dynamics. Leg-loading rate was quantified as the average slope of vertical ground reaction (VGRF) force during the 500-millisecond interval preceding maximal knee extension. RESULTS: Between-leg differences in loading rates and peak VGRFs were significantly greater for the SIJD group than for the control group. Maximal hip angles were significantly less for the SIJD group (p=.001). Peak hip moment in the SIJD group was significantly greater in the unaffected leg (0.75±0.22 N⋅m/kg) than in the affected leg (0.47±0.29 N⋅m/kg, p=.005). There were no between-leg or between-group differences for peak knee or ankle moments. The onset of activity in the latissimus dorsi muscle on the affected side was delayed and the erector spinae muscles were activated earlier in the SIJD group than in the control group. CONCLUSIONS: Subjects with SIJD have a greater VGRF on the unaffected leg, generate a greater peak hip moment in the unaffected leg, use a smaller range of motion at the hip joint of the affected leg, and delay the onset of a key muscle on the affected side when rising from a seated position.

The Functional Roles of Muscles, Passive Prostheses, and Powered Prostheses During Sloped Walking in People With a Transtibial Amputation.

Sloped walking is challenging for individuals with transtibial amputation (TTA) due to the functional loss of the ankle plantarflexors. Prostheses that actively generate ankle power may help to restore this lost function. The purpose of this study was to use musculoskeletal modeling and simulation to quantify the mechanical power delivered to body segments by passive and powered prostheses and the remaining muscles in the amputated and intact legs during sloped walking. We generated walking simulations from experimental kinematic and kinetic data on slopes of 0, ±3 deg and ±6 deg in eight people with a TTA using powered and passive prostheses and eight nonamputees. Consistent with our hypothesis, the amputated leg hamstrings generated more power to both legs on uphill slopes in comparison with nonamputees, which may have implications for fatigue or overuse injuries. The amputated leg knee extensors delivered less power to the trunk on downhill slopes (effect size (ES) ≥ 1.35, p ≤ 0.02), which may be due to muscle weakness or socket instability. The power delivered to the trunk from the powered and passive prostheses was not significantly different (p > 0.05), However, using the powered prosthesis on uphill slopes reduced the contributions from the amputated leg hamstrings in all segments (ES ≥ 0.46, p ≤ 0.003), suggesting that added ankle power reduces the need for the hamstrings to compensate for lost ankle muscle function. Neither prosthesis replaced gastrocnemius function to absorb power from the trunk and deliver it to the leg on all slopes.

The correlation between metabolic and individual leg mechanical power during walking at different slopes and velocities.

During level-ground walking, mechanical work from each leg is required to redirect and accelerate the center of mass. Previous studies show a linear correlation between net metabolic power and the rate of step-to-step transition work during level-ground walking with changing step lengths. However, correlations between metabolic power and individual leg power during step-to-step transitions while walking on uphill/downhill slopes and at different velocities are not known. This basic understanding of these relationships between metabolic demands and biomechanical tasks can provide important information for design and control of biomimetic assistive devices such as leg prostheses and orthoses. Thus, we compared changes in metabolic power and mechanical power during step-to-step transitions while 19 subjects walked at seven slopes (0°, +/-3°, +/-6°, and +/-9°) and three velocities (1.00, 1.25, and 1.50m/s). A quadratic model explained more of the variance (R(2)=0.58-0.61) than a linear model (R(2)=0.37-0.52) between metabolic power and individual leg mechanical power during step-to-step transitions across all velocities. A quadratic model explained more of the variance (R(2)=0.57-0.76) than a linear model (R(2)=0.52-0.59) between metabolic power and individual leg mechanical power during step-to-step transitions at each velocity for all slopes, and explained more of the variance (R(2)=0.12-0.54) than a linear model (R(2)=0.07-0.49) at each slope for all velocities. Our results suggest that it is important to consider the mechanical function of each leg in the design of biomimetic assistive devices aimed at reducing metabolic costs when walking at different slopes and velocities.