Alterations in medial-lateral postural control after anterior cruciate ligament reconstruction during stair use.

BACKGROUND: Dynamic postural control during everyday tasks is poorly understood in people following anterior cruciate ligament reconstruction (ACLR). Understanding dynamic postural control can provide insight into potentially modifiable impairments in people following ACLR who are at increased risk for second ACL injury and/or knee osteoarthritis. RESEARCH QUESTION: Determine whether measures indicative of dynamic postural control differ between individuals with and without ACLR during stair ascent and descent. METHODS: Seventeen individuals with ACLR (>1 yr post-surgery) and 16 age and sex-matched healthy controls participated. Centre of pressure (COP) measures included: i) COP excursion, ii) COP velocity, and iii) dynamic time-toboundary (TTB). Mixed linear models were used to compare COP measures for the ACLR leg, non-ACLR leg, and healthy controls during stair ascent and stair descent. RESULTS: There were no statistically significant differences observed during stair ascent (all p > 0.05). Several statistical differences were found during stair descent for individual with ACLR, but not between those with ACLR and healthy controls. The ACLR leg had higher medial-lateral COP excursion (mean difference 1.06 cm, [95 %CI 0.08-2.06 cm], p = 0.036; effect size = 0.38) compared to the non-ACLR leg during stair descent. In addition, the ACLR leg had a lower medial-lateral TTB (mean difference -13 ms [95 %CI -38 to 2 ms], p = 0.005; effect size = 0.49) and medial-lateral TTB normalized to stance time (mean difference -5.8 % [95 %CI -10.3 to 1.3 %], p = 0.012; effect size = 0.80) compared to the non-ACLR leg during stair descent. No statistical differences were observed for anterior-posterior measures during stair descent (all p > 0.05). SIGNIFICANCE: Taken together, findings indicate that there are small to large differences in medial-lateral postural control in the ACLR leg compared to the non-ACLR leg during stair descent. Further work is required to understand clinical implication of these novel observations.

Kinematic and Kinetic Indicators of Sit-to-Stand.

Variation in the timing indicators separating sit-to-stand (STS) into movement phases complicates both research comparisons and clinical applications. The purpose of this study was to use kinetic reference standards to identify accurate kinematic and kinetic indicators for STS movement analysis such that consistent indicators might be used for STS from varied initial postures. Healthy adults performed STS using 4 foot placements: foot-neutral, foot-back, right-staggered, and left-staggered. Kinetic and kinematic data were collected from force platforms and an 8-camera video system. Initiation, seat-off, vertical posture, and termination were detected with 5% start and 7.5% end thresholds for changes in kinetic and kinematic STS indicators. Timing differences between kinetic and kinematic indicator time points and the reference vertical seated reaction force end point (seat-off) were determined. Kinematic indicators were compared with selected kinetic indicators using timing differences, statistical similarity, and internal consistency measures. Our results suggest that a single force platform system measuring vertical GRF or a simple camera system to evaluate the shoulder marker position and velocity can accurately and consistently detect STS initiation, seat-off, and vertical posture. In addition, these suggested STS indicators for initiation, seat-off, and vertical posture were not dependent upon foot placement.

Muscle activity amplitudes and co-contraction during stair ambulation following anterior cruciate ligament reconstruction.

The purpose of this study was to compare muscle activity amplitudes and co-contraction in those with anterior cruciate ligament (ACL) reconstruction to healthy controls during stair negotiation. Eighteen participants with unilateral ACL reconstruction and 17 healthy controls performed stair ascent and descent while surface electromyography was recorded from knee and hip musculature. During stair ascent, the ACL group displayed higher gluteus maximus activity (1-50% stance, p = 0.02), higher vastus lateralis:biceps femoris co-contraction (51-100% stance, p = 0.01), and higher vastus lateralis:vastus medialis co-contraction (51-100% stance, p = 0.05). During stair descent, the ACL group demonstrated higher gluteus maximus activity (1-50% stance, p = 0.01; 51-100% stance, p < 0.01), lower rectus femoris activity (1-50% stance, p = 0.04), higher semimembranosus activity (1-50% stance, p=0.01), higher gluteus medius activity (51-100% stance, p = 0.01), and higher vastus medialis:semimembranosus co-contraction (1-50% stance, p = 0.02). While the altered muscle activity strategies observed in the ACL group may act to increase joint stability, these strategies may alter joint loading and contribute to post-traumatic knee osteoarthritis often observed in this population. Our results warrant further investigation to determine the longterm effects of altered muscle activity on the knee joint following ACL reconstruction.

Gait analysis post anterior cruciate ligament reconstruction: knee osteoarthritis perspective.

Individuals with anterior cruciate ligament (ACL) reconstruction are at increased risk to develop knee osteoarthritis (OA). Gait analysis describing kinetics of the lower extremity during walking and stair use (stair ascent and stair descent) can provide insight to everyday dynamic knee joint loading. In this study, we compared lower extremity gait patterns of those with ACL reconstruction (>1 year) to a control group. Fifteen ACL reconstructed individuals and 17 healthy controls participated in this study. Knee extensor and flexor strength were assessed. Using inverse dynamics, lower extremity moments were calculated during the stance phase of walking and during two steps of stair ascent and descent. Univariate ANOVA was used to test for main effects between (1) injured leg and control group and (2) non-injured leg and control group. Student paired t-tests were used to determine differences between the injured and non-injured leg. Those with ACL reconstruction exhibited reduced initial knee flexion angles during stair descent, reduced knee extension moments during stair descent and stair ascent (second step), and increased hip extension moments during stair ascent (second step) and walking as compared to controls. Knee flexor strength was significantly reduced in the ACL group, but no differences were found in knee extensor strength. No kinematic or kinetic differences were observed between the injured and non-injured leg of the ACL group. Walking and stair ambulation highlight altered joint loading in those with ACL reconstruction surgery. Individuals appeared to compensate for lower knee extension moments by increasing hip extension moments. Furthermore, the load distribution on the articular cartilage is likely shifted as evidenced by reduced knee flexion angles in the ACL reconstructed leg.

Lower extremity joint moments during carrying tasks in children.

Farm youth often carry loads that are proportionally large and/or heavy, and field measurements have determined that these tasks are equivalent to industrial jobs with high injury risks. The purpose of this study was to determine the effects of age, load amount, and load symmetry on lower extremity joint moments during carrying tasks. Three age groups (8-10 years, 12-14 years, adults), three load amounts (0%, 10%, 20% BW), and three load symmetry levels (unilateral large bucket, unilateral small bucket, bilateral small buckets) were tested. Inverse dynamics was used to determine maximum ankle, knee, and hip joint moments. Ankle dorsiflexion, ankle inversion, ankle eversion, knee adduction, and hip extension moments were significantly higher in 8-10 and 12-14 year olds. Ankle plantar flexion, ankle inversion, knee extension, and hip extension moments were significantly increased at 10% and 20% BW loads. Knee and hip adduction moments were significantly increased at 10% and 20% BW loads when carrying a unilateral large bucket. Of particular concern are increased ankle inversion and eversion moments for children, along with increased knee and hip adduction moments for heavy, asymmetrical carrying tasks. Carrying loads bilaterally instead of unilaterally avoided increases in knee and hip adduction moments with increased load amount.

The effects of symmetric and asymmetric foot placements on sit-to-stand joint moments.

The purpose of this study was to determine the effects of symmetric and asymmetric foot placements on joint moments during sit-to-stand movements. Three symmetric (foot-neutral, foot-back, and foot-intermediate) and three asymmetric foot placements (preferred stagger, nonpreferred stagger, and intermediate stagger) were tested. Standard (46 cm) and low (41 cm) seat heights were chosen to represent an average public seat height and a 10% lower seat height. Using inverse dynamics, maximum ankle plantarflexion, knee extension, hip extension, and hip abduction moments were calculated. Hip extension moments were significantly increased when using foot-neutral as compared to foot-back. Ankle plantarflexion and knee extension moments were significantly increased when a foot was placed in the posterior position as compared to the anterior position for preferred and nonpreferred stagger. Knee extension moments were significantly increased at the low seat height as compared to the standard seat height. When shifting the feet anterior or posterior for symmetric placements during sit-to-stand, the most dramatic effect was an increase in hip extension moments when the feet are shifted anteriorly. Utilizing asymmetric foot placements during sit-to-stand produced increases in ankle plantarflexion and knee extension moments for the posteriorly placed limb, with reductions in the anteriorly placed limb.

The effects of age and type of carrying task on lower extremity kinematics.

The purpose of this study was to determine the effects of age, load amount and load symmetry on lower extremity kinematics during carrying tasks. Forty-two participants in four age groups (8-10 years, 12-14 years, 15-17 years and adults) carried loads of 0%, 10% and 20% body weight (BW) in large or small buckets unilaterally and bilaterally. Reflective markers were tracked to determine total joint range of motion and maximum joint angles during the stance phase of walking. Maximum hip extension, hip adduction and hip internal rotation angles were significantly greater for each of the child/adolescent age groups as compared with adults. In addition, maximum hip internal rotation angles significantly increased when carrying a 20% BW load. The observation that the 8-10-year-old age group carried the lightest absolute loads and still displayed the highest maximum hip internal rotation angles suggests a particular necessity in setting carrying guidelines for the youngest children. STATEMENT OF RELEVANCE: Bucket-carrying tasks were analysed as a function of age group, load amount and load symmetry. Hip joint rotations significantly increased when carrying 20% BW loads and in children as compared to adults, which suggests a particular necessity in setting carrying guidelines for the youngest age group (8-10 year olds).

Upper extremity and lower back moments during carrying tasks in farm children.

Farm youth commonly perform animal care tasks such as feeding and watering. The purpose of this study was to determine the effects of age, bucket size, loading symmetry, and amount of load on upper body moments during carrying tasks. Fifty-four male and female participants in four age groups (8-10 years, 12-14 years, 15-17 years, and adults, 20-26 years) participated in the study. Conditions included combinations of large or small bucket sizes, unilateral or bilateral loading, and load levels of 10% or 20% of body weight (BW). During bucket carrying, elbow flexion, shoulder flexion, shoulder abduction, shoulder external rotation, L5/S1 extension, L5/S1 lateral bending, and L5/S1 axial rotation moments were estimated using video data. The 8-10 year-old group did not display higher proportional joint moments as compared with adults. Decreasing the load from 20% BW to 10% BW significantly decreased maximum normalized elbow flexion, shoulder flexion, shoulder abduction, shoulder external rotation, L5/S1 lateral bending, and L5/S1 axial rotation moments. Carrying the load bilaterally instead of unilaterally also significantly reduced these six maximum normalized joint moments. In addition, modifying the carrying task by using smaller one-gallon buckets produced significant reductions in maximum L5/S1 lateral bending moments.

Alternative foot placements for individuals with spinal cord injuries standing with the assistance of functional neuromuscular stimulation.

This study investigated the effects of altering foot placement for two individuals with spinal cord injuries (SCI) that stood using functional neuromuscular stimulation (FNS) as compared to an able-bodied subject group. FNS-assisted standers used parallel bars as needed for support, while the able-bodied group stood hands-free. Three different foot placements were tested: side-by-side, wide, and modified tandem. For SCI subjects, the percentage of body weight loaded on the feet was not greatly affected by foot placement, which potentially could be altered to provide postural benefits during functional tasks. Anterior/posterior (A/P) center of pressure (COP) origins tended to be located more anterior in the base of support for SCI subjects as compared to able-bodied subjects. SCI subjects also tended to have medial/lateral (M/L) COP excursions that were larger than able-bodied subjects. The sacrum appeared to hold some promise as a sensor location for monitoring A/P postural sway, but movements in the M/L direction were inconsistent and will require additional study. General guidelines such as positioning the A/P COP more posterior in the base of support and feedback concerning excessive M/L COP displacements may be useful to improve standing performance for SCI subjects. In addition, the modified tandem placement was an effective alternative for making postural adjustments in one SCI subject who experienced excessive right knee flexion with other foot placements.

Optimization of foot placement for individuals with total knee replacements during sit-to-stand transfers.

Sit-to-stand transfers are a fundamental activity of daily living, but it remains unknown how to systematically recommend a foot placement that matches an individual's physical capabilities. The first goal of this study was to measure biomechanical changes in sit-to-stand movements as a function of foot placement. The second goal was to develop a model that would optimize foot placement for ease of sit-to-stand and would determine challenging foot placements for strengthening. A female older adult who had undergone bilateral total knee replacement participated in the study. Video and force platform data were collected for sit-to-stand movements from foot-back, foot-neutral, right-staggered, and left-staggered placements. The optimal foot placement was determined by minimizing the highest strength percentage for any single joint torque. Strength-challenging foot placements were found by maximizing the highest strength percentages for targeted joint torques. The right-staggered placement was optimal and had a limiting factor of left hip extension torque (strength percentage 74.7%). Maximum left hip extension torque (76.7 Nm) was similar to the maximum right hip extension torque (79.5 Nm) for this foot placement. The strength-challenging foot placement with the highest strength percentage was for left ankle plantar flexion torque (89.4%) and occurred while using the left-staggered placement. The optimal right-staggered foot placement for this older adult balanced the hip extension torques between the stronger, painful right side and the weaker, less painful left side. This model-based technique has the potential to allow clinicians to select foot placements that may enhance the functional independence of older adults with osteoarthritis.

Support torques during simulated sit-to-stand movements.

Sit-to-stand movements are a fundamental daily activity and a prerequisite to upright posture. Previous simulations of spinal cord injured individuals using functional neuromuscular stimulation (FNS) suggested a forward foot placement would reduce hand-support forces. However, this recommendation has proved to be difficult for able-bodied individuals standing hands-free and for individuals with spinal cord injuries standing with a walker. This inverse model is a step towards the goal of using forward simulations to determine efficient sit-to-stand strategies. Initial seated postures varied from 80-110 degrees of knee flexion and 90-120 degrees of hip flexion. Realistic progressions of lower extremity joint angles including development of linear momentum were created using sigmoid functions. These kinematic values were used to estimate the required resultant joint torques to complete sit-to-stand. Joint torque values that act to raise the body were combined to indicate sit-to-stand difficulty from different seated postures. A representative foot-forward placement (knee 80 degrees, hip 90 degrees) resulted in a maximum combined torque of 544 Nm. In contrast, a representative foot-back placement (knee 110 degrees, hip 120 degrees) resulted in a maximum combined torque of 661 Nm. An intermediate seated posture (knee 97 degrees, hip 90 degrees) produced the lowest maximum combined torque of 401 Nm (2 Nm ankle plantarflexion, 201 Nm knee extension, 198 Nm hip extension). Foot-forward placement required substantial ankle dorsiflexion torques. The most efficient strategy appeared to be combining a foot back placement with momentum generation using hip flexion. By generalizing the sit-to-stand model beyond FNS-driven movements, further insight may be gained into other populations (i.e., elderly).

NMES-assisted standing model from varied seated postures.

After spinal cord injury (SCI), intact lower motor neurons can be electrically activated to produce functional muscular contractions and enhance one's capabilities beyond seated activities. Even with neuromuscular electrical stimulation (NMES), significant amounts of hand-support forces are commonly required to move from a sitting to standing position. The goal of this project was to determine initial seated postures that reduce vertical hand-support forces while keeping anterior/posterior hand-support forces below levels that would cause walker slipping or tipping. A multi-segment biomechanical model was further developed and expanded to test multiple combinations of initial postures. The muscles that were analyzed included the vastus lateralis and semimembranosus. Varying the initial knee and hip angles created alternative seated postures. For vastus lateralis stimulation, the lowest vertical hand-support forces (63-66% of body weight) were predicted at the lower (70-74 degrees) and upper (110 degrees) ranges of initial knee flexion. With combined vastus lateralis and semimembranosus stimulation, the lowest predicted vertical hand-support forces were 2-10% of body weight at initial knee flexion angles between 70-82 degrees. Initial hip flexion angles above 110 degrees were required to prevent walker slipping and tipping in these cases. The development of hip extensor torque with semimembranosus stimulation was critical in reducing the vertical hand-support forces. One implication is that when training with parallel bars for NMES-assisted standing, hand-support forces should be monitored to avoid conditions that would tip a walker. In future models, optimizing the timing sequence for stimulating muscles may produce smoother coordination of joint rotations and further reduce the vertical hand-support forces.