Stacey M. Acker

Knee adduction moment relates to medial femoral and tibial cartilage morphology in clinical knee osteoarthritis

The objective was to determine the extent to which the external peak knee adduction moment (KAM) and cumulative knee adductor load explained variation in medial cartilage morphology of the tibia and femur in knee osteoarthritis (OA). Sixty-two adults with clinical knee OA participated (61.5 ± 6.2 years). To determine KAM, inverse dynamics was applied to motion and force data of walking. Cumulative knee adductor load reflected KAM impulse and loading frequency. Loading frequency was captured from an accelerometer. Magnetic resonance imaging scans were acquired with a coronal fat-saturated sequence using a 1.0 T peripheral scanner. Scans were segmented for medial cartilage volume, surface area of the bone-cartilage interface, and thickness. Forward linear regressions assessed the relationship of loading variables with cartilage morphology unadjusted, then adjusted for covariates. In the medial tibia, age and peak KAM explained 20.5% of variance in mean cartilage thickness (p<0.001). Peak KAM alone explained 12.3% of the 5th percentile of medial tibial cartilage thickness (i.e., thinnest cartilage region) (p=0.003). In the medial femur, sex, BMI, age, and peak KAM explained 44% of variance in mean cartilage thickness, with peak KAM contributing 7.9% (p<0.001). 20.7% of variance in the 5th percentile of medial femoral cartilage thickness was explained by BMI and peak KAM (p=0.001). In these models, older age, female sex, greater BMI, and greater peak KAM related with thinner cartilage. Models of KAM impulse produced similar results. In knee OA, KAM peak and impulse, but not loading frequency, were associated with cartilage thickness of the medial tibia and femur.

Knee power is an important parameter in understanding medial knee joint load in knee osteoarthritis.

To determine the extent to which knee extensor strength and power explain variance in knee adduction moment (KAM) peak and impulse in clinical knee osteoarthritis (OA).

Muscle activation and knee biomechanics during squatting and lunging after lower extremity fatigue in healthy young women

Muscle activations and knee joint loads were compared during squatting and lunging before and after lower extremity neuromuscular fatigue. Electromyographic activations of the rectus femoris, vastus lateralis and biceps femoris, and the external knee adduction and flexion moments were collected on 25 healthy women (mean age 23.5 years, BMI of 23.7 kg/m(2)) during squatting and lunging. Participants were fatigued through sets of 50 isotonic knee extensions and flexions, with resistance set at 50% of the peak torque achieved during a maximum voluntary isometric contraction. Fatigue was defined as a decrease in peak isometric knee extension or flexion torque ≥25% from baseline. Co-activation indices were calculated between rectus femoris and biceps femoris; and between vastus lateralis and biceps femoris. Fatigue decreased peak isometric extension and flexion torques (p<0.05), mean vastus lateralis activation during squatting and lunging (p<0.05), and knee adduction and flexion moments during lunging (p<0.05). Quadriceps activations were greater during lunging than squatting (p<0.05). Thus, fatigue altered the recruitment strategy of the quadriceps during squatting and lunging. Lunging challenges quadriceps activation more than squatting in healthy, young women.

Analysis of muscle activation patterns during transitions into and out of high knee flexion postures

Increased risk of medial tibiofemoral osteoarthritis (OA) is linked to occupations that require frequent transitions into and out of postures which require high knee flexion (>90°). Muscle forces are major contributors to joint loading, and an association between compressive forces due to muscle activations and the degeneration of joint cartilage has been suggested. The purpose of this study was to evaluate muscle activation patterns of muscles crossing the knee during transitions into and out of full-flexion kneeling and squatting, sitting in a low chair, and gait. Both net and co-activation were greater when transitioning out of high flexion postures, with maximum activation occurring at knee angles greater than 100°. Compared to gait, co-activation levels during high flexion transitions were up to approximately 3 times greater. Co-activation was significantly greater in the lateral muscle group compared to the medial group during transitions into and out of high flexion postures. These results suggest that compression due to activation of the medial musculature of the knee may not be the link between high knee flexion postures and increased medial knee OA observed in occupational settings. Further research on a larger subject group and workers with varying degrees of knee OA is necessary.

Peak activation of lower limb musculature during high flexion kneeling and transitional movements.

Abstract Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions. Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.

The Effect of Work Boots on Knee Mechanics and the Center of Pressure at the Knee During Static Kneeling

Occupational kneeling is associated with an increased risk for the development of knee osteoarthritis. Previous work studying occupational kneeling has neglected to account for the fact that in many industrial settings, workers are required to wear steel-toe work boots. Thus, the purpose of this study was to evaluate the effect of work boot wear on the center of pressure location of the ground reaction force, knee joint angle, and magnitude of the ground reaction force in a kneeling posture. Fifteen healthy males were fit with 3D motion capture markers and knelt statically over a force plate embedded in the floor. Using the tibial tuberosity as the point of reference, the center of pressure in shod condition was shifted significantly medially (on average 0.009 m [P = .005]) compared with the barefoot condition. The knee was significantly less internally rotated (shod: -12.5° vs. barefoot: -17.4° [P = .009]) and the anterior/posterior shear force was significantly greater in the shod condition (shod: 6.0% body weight vs. barefoot: 1.5% body weight [P = .002]). Therefore, wearing work boots alters the kneeling posture compared with barefoot kneeling, potentially loading different surfaces of the knee, as well as altering knee joint moments.

Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear

AIM (1) Characterize knee joint moments and peak knee flexion moment timing during kneeling transitions, with the intent of identifying high-risk postures. (2) Determine whether safety footwear worn by kneeling workers (construction workers, tile setters, masons, roofers) alters high flexion kneeling mechanics. METHODS Fifteen males performed high flexion kneeling transitions. Kinetics and kinematics were analyzed for differences in ascent and descent in the lead and trail legs. RESULTS Mean±standard deviation peak external knee adduction and flexion moments during transitions ranged from 1.01±0.31 to 2.04±0.66% body weight times height (BW∗Ht) and from 3.33 to 12.6% BW∗Ht respectively. The lead leg experienced significantly higher adduction moments compared to the trail leg during descent, when work boots were worn (interaction, p=0.005). There was a main effect of leg (higher lead vs. trail) on the internal rotation moment in both descent (p=0.0119) and ascent (p=0.0129) phases. CONCLUSION Peak external knee adduction moments during transitions did not exceed those exhibited during level walking, thus increased knee adduction moment magnitude is likely not a main factor in the development of knee OA in occupational kneelers. Additionally, work boots only significantly increased the adduction moment in the lead leg during descent. In cases where one knee is painful, diseased, or injured, the unaffected knee should be used as the lead leg during asymmetric bilateral kneeling. Peak flexion moments occurred at flexion angles above the maximum flexion angle exhibited during walking (approximately 60°), supporting the theory that the loading of atypical surfaces may aid disease development or progression.

Thigh-calf contact parameters for six high knee flexion postures: Onset, maximum angle, total force, contact area, and center of force.

In high knee flexion, contact between the posterior thigh and calf is expected to decrease forces on tibiofemoral contact surfaces, therefore, thigh-calf contact needs to be thoroughly characterized to model its effect. This study measured knee angles and intersegmental contact parameters in fifty-eight young healthy participants for six common high flexion postures using motion tracking and a pressure sensor attached to the right thigh. Additionally, we introduced and assessed the reliability of a method for reducing noise in pressure sensor output. Five repetitions of two squatting, two kneeling, and two unilateral kneeling movements were completed. Interactions of posture by sex occurred for thigh-calf and heel-gluteal center of force, and thigh-calf contact area. Center of force in thigh-calf regions was farther from the knee joint center in females, compared to males, during unilateral kneeling (82 and 67 mm respectively) with an inverted relationship in the heel-gluteal region (331 and 345 mm respectively), although caution is advised when generalizing these findings from a young, relatively fit sample to a population level. Contact area was larger in females when compared to males (mean of 155.61 and 137.33 cm2 across postures). A posture main effect was observed in contact force and sex main effects were present in onset and max angle. Males had earlier onset (121.0°) and lower max angle (147.4°) with onset and max angles having a range between movements of 8° and 3° respectively. There was a substantial total force difference of 139 N between the largest and smallest activity means. Force parameters measured in this study suggest that knee joint contact models need to incorporate activity-specific parameters when estimating loading.

Representing fine-wire EMG with surface EMG in three thigh muscles during high knee flexion movements

Activation waveforms of vastus intermedius, adductor magnus, and semimembranosus have not been reported for high knee flexion activities such as kneeling or squatting, likely due to the invasive procedures required for their measurement. Their relatively large physiological cross sectional areas would suggest their contributions to knee joint loading could be considerable. Therefore, the purpose of this study was to quantify the activities of these muscles using fine-wire EMG and to assess easy to measure surface sites (vastus lateralis, rectus femoris, vastus medialis, semitendinosus, and biceps femoris) for their potential as proxy measures using <10 %MVC RMS and >0.85 R2 as criteria for successful representation of deep muscle activity by that measured at a surface site. Overall, no surface and fine-wire site pair met both criteria for these movements. When fine-wire measurement of muscle activity is infeasible or impractical, the waveforms presented in supplementary material could be used as a guide for the activity of these deep muscles. Although select muscles for some participants satisfied our criteria, inter-participant variability was considerable. Therefore, future muscle models may benefit from fine-wire measurement of these muscles, but researchers should be cautious of electrode site specificity.

The effects of a simulated occupational kneeling exposure on squat mechanics and knee joint load during gait

Abstract Occupational kneeling is associated with an increased risk for tibiofemoral knee osteoarthritis. Forces on the knee in the kneeling posture, as well as the greater incidence of meniscus tears among workers, likely contribute to the increased risk. We hypothesise that an additional mechanism may contribute – altered neuromuscular control due to prolonged high knee flexion. Forty participants (20 male, 20 female) completed an evaluation of gait and squatting before, immediately following, and 30 min following a 30 min simulated occupational kneeling exposure. An increase in the peak external knee adduction moment and a delay in vastus medialis activation onset during walking were observed post-kneeling, as well as increased frontal plane knee motion during squatting. This was the first investigation to find changes in high flexion transitions as a result of kneeling. Greater frontal plane knee motion may increase the risk for meniscal tears, and subsequently, knee osteoarthritis. Practitioner Summary: A 30 min simulated occupational kneeling exposure resulted in small but significant gait changes. The greatest effect was on frontal plane knee movement during squatting, which is especially relevant to occupations requiring frequent kneeling/squatting. This increased motion may indicate an increased risk of injury, which supports a link to knee osteoarthritis.