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Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear
THEKNE-02392; No of Pages 9 The Knee xxx (2016) xxx–xxx
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The Knee
Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear Helen C. Chong, Liana M. Tennant, David C. Kingston, Stacey M. Acker ⁎ University of Waterloo, 200 University Ave W, Waterloo, ON N2L 3G1, Canada
a r t i c l e
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Article history: Received 21 March 2016 Received in revised form 9 December 2016 Accepted 13 December 2016 Available online xxxx Keywords: Kneeling Kinetics High flexion Kinematics Joint moments
a b s t r a c t 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. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Prolonged or frequent exposure to high knee flexion postures increases the incidence of knee injuries [1], including acute symptomatic pain and chronic pain resulting in lasting trauma to the knee joint [2]. High flexion postures, typically defined as involving knee flexion between 120° and 165° (where full extension is defined as 0°), are required for occupational purposes (e.g. childcare, construction, mining) and hobbies (e.g. gardening) [3,4]. Exposure on the knee joint as a result of high flexion
⁎ Corresponding author at: Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada. E-mail addresses: [email protected] (H.C. Chong), [email protected] (L.M. Tennant), [email protected] (D.C. Kingston), [email protected] (S.M. Acker).
http://dx.doi.org/10.1016/j.knee.2016.12.006 0968-0160/© 2016 Elsevier B.V. All rights reserved.
Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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postures has remained largely unexplored and the information that is available is quite variable and limited. In 2011, Pollard, Porter, and Redfern [5] reported knee angles and net forces and moments during squatting and kneeling postures, but only in the static phases. A study by Nagura et al. (2002) [6] examined double leg descending and ascending as well as a single leg kneel, however, participants did not continue to full flexion (particularly during the single leg kneel), and data was truncated when the knees made contact with the ground, meaning that, after the instant of knee-ground contact, no outcome measures were reported. Additionally, the study was limited in its ability to analyze both legs during the transition, since only one force plate was used resulting in kinetic data being available for a single leg only. A kinematic analysis [7] demonstrated the range of motion (ROM) about the ankle, hip, and knee during various high flexion postures, but neglected to present the kinetics of the tasks. Differences in condition (transitions in comparison to static postures) may account for the wide range of variability that is seen among reported values. These limitations of the current literature highlight the need for study of bilateral kinetics in high flexion. High knee flexion has been correlated with knee osteoarthritis (OA) in occupational settings yet the knee moments required to reach a high knee flexion posture have not been well established [8–10]. Increased external knee adduction moments during gait, as well as increased knee internal rotational moments, have been correlated with knee OA (values during gait are more than double healthy controls within a knee OA population) and this relationship could extend to peak moments during high flexion [8–12]. Knee joint moments are of particular interest because an increased external knee moment can be reflective of increased joint loading [13]. Increased external moments can be the result of increased externally applied loads, or can reflect a change in muscle activation strategies. Peak net flexion moments during high flexion, which occur between 90° and 150° of flexion during a double leg descent, are more than twice as high as those that typically occur in gait [6]. Occupations which require prolonged high flexion kneeling postures are associated with an increased risk of patellofemoral and tibiofemoral knee OA [8,9,14]. Two theories for disease progression are that repeated or prolonged compression of cartilage causes damage [8,15,16], or that kneeling may load areas of cartilage, such as the posterior femoral condyles and the posterior tibial plateau, that are not typically exposed to (and therefore may not be conditioned for) frequent loading [17]. In this theory, “typically” loaded surfaces would be those loaded within the range of 0° to 30° flexion, which is typically the largest range of flexion during the load-bearing phase of level gait. Knee OA is a degenerative disease that cannot be reversed — therefore, prevention is of utmost importance to avoid disease initiation and progression [18]. In this study, knee joint moments were examined as an indicator of knee loading magnitude, and flexion angles corresponding to the peak knee joint moments were examined as an indicator of the cartilage area being loaded since the tibiofemoral contact area changes with flexion angle [19]. Peak moments occurring at flexion angles that are different from the flexion angles that typically correspond to peak moments (for example, during gait) could indicate that poorly conditioned cartilage is experiencing high loads. Although avoiding high flexion in all occupations is unrealistic, recommendations regarding postural techniques that may reduce joint moment, in turn potentially reducing knee OA risk, would be valuable. Although it is understood that high flexion postures are frequently used in specific occupations, and that high flexion postures are associated with an increased risk for knee OA, it is unknown how personal protective equipment required in many of these industries affects OA risk. In particular, these postures are common in many industrial occupations such as flooring or roofing which also have strict requirements for safety equipment (such as requiring approved work boots while on site). A survey of 300 firemen indicated that newly required steel toe boots caused a feeling of restriction during kneeling, crouching, and fast movements [20]. Restrictions may cause altered lower limb mechanics, including joint moments about the knee, during transitions into and out of kneeling, as well as in static kneeling postures. The current study provides an initial investigation into whether or not the use of safety footwear results in knee joint mechanics that could put the worker at a higher risk of knee joint damage compared to the risk already present with kneeling alone. Similar to kneeling, the use of safety footwear cannot (and should not) be avoided in many occupational settings. However, should there be evidence that safety footwear may increase knee OA risk for kneeling workers, that finding could prompt exploration of alternative safety footwear designs with the goal of mitigating this increased risk. The primary purpose of this study is to characterize the knee joint moments and peak knee flexion moment timing during high flexion transitions, with the intent of identifying high-risk postures. The secondary purpose is to determine whether safety footwear (work boots) alters the kinematics and kinetics of transitional and static high flexion postures. It is hypothesized that peak moments will be increased with the addition of safety footwear, indicating increased knee joint loading. This would mean that, in addition to kneeling alone, safety footwear may contribute to loading associated with OA. It is also expected that the sagittal ankle ROM will be decreased when wearing safety footwear; but that the flexion angle of the knee will remain unchanged with the addition of safety footwear. Given that higher muscle activation has been observed in high flexion, compared to midflexion, and that both high flexion activities [8] and increased external adduction moments have been associated with cartilage deterioration in some individuals [11], it is hypothesized that the peak adduction moments observed during transitions between standing and kneeling will be higher than the ranges typically seen during walking and that the peak flexion moments will occur at flexion angles greater than the largest angle exhibited during the load-bearing phase of walking (typically up to 30°). 2. Material and methods 2.1. Participants Fifteen right leg dominant males participated in this study. Participant exclusion criteria included any lower limb injury within the past five years that required medical intervention or time off from work for longer than three days. Trials were excluded as a Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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result of marker drop out, inconsistent movement patterns, or when both feet made contact with the same force plate. For five participants, these trial exclusions resulted in an insufficient number of remaining trials for analysis. Therefore data from ten individuals (age 22.9 S.D. 1.7 years; mass 78.6 S.D. 9.3 kg; height 1.75 S.D. 0.06 m) were included in the analysis. All participants were required to wear the same pair of men's size 10 US safety boots (Operator Steel Toe, Caterpillar Inc., Model: P709254), and so only males with size 10 US feet were recruited. Each participant read and signed an informed consent form approved by the university's research ethics board.
2.2. Data collection Synchronous kinematic (Optotrak Motion Capture; Northern Digital, Inc. Waterloo, ON) and kinetic (four embedded OR6-7 force plates; Advanced Mechanical Technology, Inc., Watertown, MA) data were collected bilaterally for each participant. Optotrak hardware (Optotrak data acquisition unit) and software (First Principles) were used to synchronize motion capture and force plate data collection. Rigid bodies were affixed to both feet, shanks, and thighs, and the sacrum. Anatomical landmarks on each segment were digitized with respect to their respective rigid bodies. Data was collected during transitions (descent and ascent) and static kneeling postures while the participant was barefoot and shod in safety footwear. The leg that supported the body during kneeling initiation will be referred to as the ‘lead’ leg (Figure 1; left leg lead) and the opposing leg will be referred to as the ‘trail’ leg (Figure 1; right leg trail). The knee of the trailing leg made contact with the floor first. Participant leg dominance was determined through a series of tests [21]. The order of footwear conditions was randomized before the blocked experimental trials were performed. The movements were demonstrated, and the participant was encouraged to familiarize himself with the task. Participants then complete five blocked sets of three phases: descent, static kneeling, and ascent. The descending and ascending trials were performed by participants at a self-selected speed; participants were required to maintain the static kneeling phase for 10 s. The descent trial began off of the force plates; the participant stepped forward with each foot onto the force plates (generally with their trail leg first), and then kneeled using an asymmetric movement (Figure 1). Some participants took an additional step so that their feet were side-by-side before taking another half-step with the lead leg and kneeling down. Participants were not required to lead with a specific leg; seven participants used the left leg as the lead leg during the descending transition, and eight participants used the left leg as the lead leg during the ascending transition. For static kneeling, the participants were encouraged to achieve heel-gluteal contact when possible. The ascent transition began by raising the knee of the lead leg off the floor, then with their lead foot planted, raising the body and stepping backwards off the force plates. Five trials of each phase were collected, for a total of 15 trials per footwear condition per participant.
Figure 1. Participant performing transitional movement trial while barefoot; lead and trail legs are identified.
Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Table 1 Segment coordinate system definitions for the pelvis, thigh, shank and foot. Pelvis segment coordinate system definitions Origin z-Axis Transverse plane y-Axis x-Axis
Mid-point between the left and right posterior superior iliac spines A vector normal to the transverse plane in the superior direction Formed by the origin and the left and right anterior superior iliac spines Cross product of the z- and x-axes Vector from the origin towards the right posterior superior iliac spine
Thigh segment coordinate system definitions Origin z-Axis Frontal plane y-Axis x-Axis
Hip joint center, estimated based on pelvis ASIS landmarks (Bell et al. (1989, 1990). Vector from the midpoint of the lateral and medial femoral epicondyles to the origin Formed by the z-axis and the transepicondylar line A normal to the frontal plane in the anterior direction Cross product of the y- and z-axes
Shank segment coordinate system definitions Origin z-Axis y-Axis x-Axis
Mid-point between the lateral and medial tibial condyles Vector from the mid-point between the lateral and medial malleoli to the origin Cross product of the z-axis and a line joining the tibial condyles Cross product of the y- and z-axes
Foot segment coordinate system definitionsa Origin z-Axis y-Axis x-Axis
Mid-point between the lateral and medial malleoli Mid-point between the 5th and 1st metatarsal head to the origin Cross product of the z-axis and a line joining the lateral and medial malleoli Cross product of the y-and z-axes
a
The foot segment coordinate system is then rotated to align with the shank segment coordinate system so that a neutral standing posture is 0° ankle flexion.
2.3. Data processing & statistics Kinematic and kinetic data were filtered using a bidirectional low-pass 2nd order Butterworth filter with a 6 Hz cut off. Segmental local coordinate system definitions are shown in Table 1. Peak knee moments in all three tibial coordinate system planes were determined for the transition conditions, together with the flexion angle at the knee when the peak knee flexion moment occurred. The absolute minimum value (peak knee abduction moment) of the frontal tibial coordinate system plane was also determined for the transition conditions since both the peak knee abduction moment and peak knee adduction moment are of interest. Average three-dimensional knee moments, average knee flexion angles, and average ankle flexion angles were calculated for the static postures. Knee moments were resolved into the tibial coordinate system [22]. Statistical analyses (SAS 9.4, Cary, North Carolina, USA) involved two-way repeated measures analyses of variance (RM ANOVA) for two outcomes (angle and moment) and three planes (sagittal, frontal, transverse), containing within subject factors of footwear (shod, barefoot) and leg (lead and trail for the dynamic ascent and descent phases, or right and left for the static phase). Analysis included a total of four ANOVAs per dynamic phase (moments only were analyzed during the dynamic phases in three planes) and a total of twelve ANOVAs during the static phase (average moment and angle in three dimensions for both the knee and ankle joint). For any interactions present, a Tukey post-hoc test was used. The alpha level for these comparisons was preset at 0.05 for both main effects and post-hoc tests. 3. Results Outcome measures with significant interactions and main effects are reported in Table 2. The transitional movement curves for knee and ankle flexion angles are shown in Figure 2. 3.1. Peak external knee moments during transitions An interaction occurred between leg and footwear conditions with respect to the external peak knee adduction moment (p = 0.005) during the descending transition such that the addition of safety footwear compared to the unshod condition caused a significant change in the lead leg peak knee adduction moment only. There was no statistically significant main effect of footwear on the external peak knee adduction moment during transitions. Trail leg external peak knee internal rotational moments were significantly greater than lead leg peak moments in both descent (p = 0.0119) and ascent (p = 0.0129), but were not significantly different between the shod and unshod conditions. 3.2. Mean angles and moments during static kneeling Mean ankle flexion angle during static kneeling was not significantly different between shod (25.1° (13.8°) plantarflexion) and barefoot (16.8° (18.1°) plantarflexion) conditions; however, the nearly 8.3° difference seen may have some biological relevance. Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Table 2 Mean of the peak external moments (normalized to % body weight multiplied by height (BW * Ht) ± standard deviation) for flexion, adduction, abduction, and internal rotational axes for shod and barefoot conditions during the ascent and decent movement phases. Symbols in the leftmost column indicate a main effect or interaction on the variable listed, followed by the corresponding significance (p-value) of that main effect. Lead
Trail
Barefoot Flexion descent Flexion ascent Abduction descent Abduction ascent Adductiona descentb p = 0.005 Adductiona ascent Internal rotation descentc p = 0.0119 Internal rotation ascentc p = 0.0.0129 a b c
−8.37 −6.81 −2.44 −2.63 1.06 0.91 −0.78 −0.73
± ± ± ± ± ± ± ±
Shod 2.14 1.76 1.14 1.28 0.70 0.42 0.24 0.34
−8.81 −7.99 −2.15 −2.64 2.04 1.02 −0.78 −0.88
Barefoot ± ± ± ± ± ± ± ±
1.76 1.81 0.63 1.32 0.66 0.41 0.21 0.38
−8.10 −7.87 −1.93 −2.33 1.01 0.85 −0.88 −0.98
± ± ± ± ± ± ± ±
Shod 1.96 2.43 0.64 0.90 0.31 0.87 0.39 0.23
−9.87 −8.58 −1.97 −2.35 1.13 1.21 −1.18 −1.14
± ± ± ± ± ± ± ±
1.22 1.84 0.95 0.64 0.62 0.59 0.31 0.24
For comparison, peak external adduction moments between two and four percent BW ∗ Ht have been reported for gait. Footwear condition × leg interaction. Main effect of leg.
3.3. Occurrence of peak flexion moments during transition Peak flexion moments ranged from 3.33 to 12.6% body weight times height (BW ∗ Ht). The point at which the peak flexion moments occurred varied considerably between participants. The average external flexion moment curves (Figure 3, top row), demonstrate two local minima (flexion is negative) during descent at approximately 40% (generally within 50 ms, just before the trail knee makes contact) and 100% phase (full flexion, at an average of 146.3°). During descent, half of the participants experienced their peak flexion moment in the lead leg around 40% phase, in a deep lunge position (flexion angle between 90 and 125°). The most common point at which the peak flexion moment occurred in the trail leg was during full flexion (100% of the descent phase or 0% of the ascent phase, Figure 3; four of ten participants).
Figure 2. Knee (top row) and ankle (bottom row) flexion angle during ascent and descent while shod and unshod for both the lead and trail legs. The trail leg is represented in blue and a dashed line, while the lead leg is represented in gray and a solid line. Pictorial representations of the descent phase (bottom row, left) and the ascent phase (bottom row, right) are shown to give a visual representation of the postures at a given phase percentage in the top and middle rows. The pelvis is represented as an inverted triangle with the lead leg solid and the trail leg dotted. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
Figure 3. Lead leg knee (solid black line) and trail leg knee (dashed blue line) external moments while wearing safety footwear and while barefoot during downward and upward transitions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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4. Discussion The purpose of this investigation was to assess the kinetic requirements of transitional movements into and out of kneeling, as well as to determine the effect of safety footwear. Mean peak external knee adduction moments during transitions ranged from 1.01 ± 0.31% BW ∗ Ht to 2.04 ± 0.66% BW ∗ Ht (Table 2), whereas peak adduction moments for gait have been reported between two and four percent BW ∗ Ht. Therefore the hypothesis that peak external knee adduction moments during transitions would exceed those exhibited during level walking was rejected, indicating that an increased knee adduction moment magnitude is likely not a main factor in the development of knee OA in occupational kneelers. The hypothesis that peak flexion moments would occur at flexion angles above the maximum flexion angle exhibited during the load-bearing phase of walking (up to approximately 30°) was confirmed, providing support for the theory that the loading of atypical surfaces may play a role in disease development or progression. Our results indicate that occurrences of significant findings tend to be in both the descending and ascending phases, with the exception of the interaction present in the peak knee adduction moment during the descending phase only. Although symmetry of findings with respect to descending or ascending transition may have been expected, previous work has shown that the ascending phase requires a higher level of co-activation than the descending phase, which would tend to decrease the magnitude of net internal moments [23]. With respect to the current study, since the external moments should balance the internal moments, this interpretation would agree with our overall lower magnitude of peak flexion moments during ascent compared descent (Table 2). Peak flexion moments ranged from 3.33 to 12.6% BW ∗ Ht. These values nearly span the range of previously reported values of 6.9–13.5% BW ∗ Ht [5]. Since some participants experienced their peak flexion moments during full flexion, it is necessary to continue data collection until the participant is in a fully flexed, static position. Nagura et al. (2002) [6] studied a single leg descent and ascent, and found that the peak net external moments occurred between 70° and 100° flexion. Similar angles were found in the current study for those participants who reached a peak moment during the transition. However, because that previous study truncated the data at the point of knee contact in the trailing leg, they may have failed to identify the true peak moment for some of their participants. Peak moment timing for four participants was affected by footwear. Safety footwear shifted the time of peak moment from before the trail knee had made contact with the ground to once the participant was in full flexion. It is worth noting that this change in peak moment can occur with a change in footwear so that the effect of footwear can be accounted for in future study protocols. Factors that modulate the effect of footwear for a given individual could be explored in future work. The addition of safety footwear altered the mechanics of static kneeling in participants who reached a greater plantarflexion angle during static kneeling while unshod than the boot allowed for. Four of the participants achieved a much greater plantarflexion angle during unshod kneeling, likely resulting from a difference in technique (these participants used a technique resulting in the dorsal aspect of the foot contacting the ground while unshod). The addition of safety footwear decreased the plantarflexion angle that was achievable by these participants to a greater degree than the remaining six participants who used the same kneeling technique in each condition (the heads of the metatarsals and the plantar forefoot in contact with the ground and the forefoot flexed). Examining the entire study sample, safety footwear resulted in (not statistically significant) decreased ankle plantarflexion angle (by 8.3°, p = 0.48) and increased the internal rotation angle between the shank and foot (by 4.1°, p = 0.51). These kinematic differences at the ankle level did not propagate to the level of the knee in the sample for the current study (10 participants), but decreased knee internal rotation was found in a larger sample size (15 participants) during kneeling as a result of work boot wear [25]. The observed decrease in plantarflexion was expected since the rigid, high cut nature of the boot limits ankle ROM. Increased internal rotation of the knee would have been expected due to the rounded, rigid toe and rigid sole on the boot. We expected that participants would tend to splay the heels apart from one another, increasing knee internal rotation and possibly abduction, however this did not occur. It is possible that the participants used increased muscle activity to maintain a more neutral (less rotated) knee posture compared to the barefoot condition where the flat plantar surface of the forefoot in contact with the ground would help to passively keep the anterior–posterior axes of the feet relatively vertical and parallel. Muscle activity was not measured in this study. Although safety footwear is an absolute requirement that should not be ignored while working in hazardous areas, future work could examine the possibility of designing footwear with greater plantarflexion range of motion. The exact pathogenesis of knee OA is not fully established. Factors such as increased loading and prolonged exposure in high flexion postures have been implicated, but it is not known whether factors such as increased external knee adduction moments cause disease initiation or are a result of disease progression [8]. During descent, the lead and trail legs experienced significantly different peak knee adduction moments when work boots were worn. The lead leg supports the majority of body weight during descent while the trail leg is lowered (based on this study, 65–85% of the total body weight is typical), which may help explain why the effect of wearing work boots appears to be magnified for the lead leg. Previous work [25] on static kneeling has shown that wearing safety footwear resulted in a shift of the center of pressure under the knee. While the dynamic phases were not reported in that study, those findings may indicate changes in balance or center of mass positioning as a result of safety footwear. These changes may also help explain the interaction for the adduction moment in the current study, where a difference between legs was only significant when footwear was worn. This finding could be important, especially for those with knee pain or knee OA in one knee. If medial loading is of concern, the use of the unaffected knee as the lead leg may reduce aggravation of the existing condition, or reduce pain. In asymptomatic individuals, alternating legs as the lead leg in repetitive transitions would balance the cumulative load between knees. Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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The findings of this study are limited by the following factors. In both previously published work [6] and the current study, the calculation of the flexion moment did not include the effect of thigh-calf contact, which can reduce the flexion moment when the back of the thigh comes into contact with the calf [24]. This limitation would affect the magnitude of the peak flexion moment for those participants whose peak flexion moment occurred at full flexion. As with all studies using skin mounted marker-based motion capture, the tracking of segments was subject to soft tissue artifact. The effect of this artifact is likely more pronounced in the higher flexion range when the thigh and calf come into contact, resulting in more deformation of limbs. This effect would not likely be dependent on footwear condition. Because foot landmarks and the malleoli were used to create the foot coordinate system and foot-mounted markers were used to track the segment, foot and ankle landmarks were digitized twice, once in the barefoot condition and once in the shod condition. Since boot-mounted markers were used to track the foot segment, the accuracy of tracking the foot segment in the shod condition would have been negatively affected by relative motion between the foot and the boot. In the absence of radiographic imaging, there is no way to know exactly how much relative movement occurred between the foot and the boot; however we attempted to minimize this issue by ensuring that the boot was tied tightly to promote a snug fit. The variation in peak external knee joint moments (the standard deviations in Table 2) are in some cases relatively large and may contribute to the finding of few significant differences between the lead and trial legs. However, it should also be noted that the timing of peaks was not a factor in the statistical analysis of the peak moments. The mean moment curves in Figure 3 show that, while the absolute peaks of the curves are similar in many cases, the time point (% Phase) at which the peak moments occurred on average differed between the lead and trial legs. Due to the relatively young, male study cohort, the results of this study should only be generalized to a male population with no knee injuries or pathologies. In summary, this work helps to characterize the moments about the knee during high flexion postures, provides time-series information, and expands the existing knowledge of magnitude and time of occurrence for peak moments during transitions. 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. We have determined that significant differences exist between the lead and trail legs for the transverse plane (internal rotation) moment, and that 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 play a role in disease development or progression. Future work should include more participants to determine why participants are affected differently by safety footwear. Additionally, a more comprehensive examination of different styles of kneeling is required in order to encompass more potential occupational postures. Conflicts of interest None Acknowledgements Funding support was provided by the National Sciences and Engineering Council of Canada (NSERC) Discovery grant #418647 (SA). References [1] Tanaka S, Smith AB, Halperin W, Jensen R. Carpet-layer's knee. N Engl J Med 1982;307(20):1276–7. [2] Thun M, Tanaka S, Smith AB, Halperin WE, Lee ST, Luggen ME, et al. Morbidity from repetitive knee trauma in carpet and floor layers. Br J Ind Med 1987;44: 611–20. [3] Acker SM, Cockburn RA, Krevolin J, Li RM, Tarabichi S, Wyss UP. Knee kinematics of high flexion activities of daily living performed by male Muslims in the Middle East. J Arthroplasty 2011;26(2):319–27. [4] Hefzy MS, Kelly BP, Cooke TDV. Kinematics of the knee joint in deep flexion: a radiographic assessment. Med Eng Phys 1998;20(4):302–7. [5] Pollard JP, Porter WL, Redfern MS. Forces and moments on the knee during kneeling and squatting. J Appl Biomech 2011;27(3):233–41. [6] Nagura T, O'Dyrby C, Alexander EJ, Andriacchi TP. 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Gait and neuromuscular pattern changes are associated with differences in knee osteoarthritis severity levels. J Biomech 2008;41(4):868–76. [13] Shakoor N, Block JA, Shott S, Case JP. Nonrandom evolution of end-stage osteoarthritis of the lower limbs. Arthritis Rheum 2002;46(12):3185–9. [14] Jensen LK, Rytter S, Bonde JP. Exposure assessment of kneeling work activities among floor layers. Appl Ergon 2012;41(2):319–25. [15] Vrezas I, Elsner G, Bolm-Audorf U, Abolmaali N, Seidler A. Case–control study of knee osteoarthritis and lifestyle factors considering their interaction with physical workload. Int Arch Occup Environ Health 2010;83(3):291–300. [16] Metcalfe A, Stewart C, Postans N, Barlow D, Dodds A, Holt C, et al. Abnormal loading of the major joints in knee osteoarthritis and the response to knee replacement. Gait Posture 2013;37(1):32–6.
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[17] Andriacchi TP, Koo S, Scanlan SF. Gait mechanics influences healthy cartilage morphology and knee osteoarthritis. Bone Joint Surg Am 2009;91(Supplement 1): 95–101. [18] Vigorita VJ, Ghelman B, Mintz D. Orthopaedic pathology. 2nd ed. Philadelphia: Lippincott Williams and Wilkins; 2008. [19] Dahlkvist NJ, Mayo P, Seedhom BB. Forces during squatting and rising from a deep squat. Eng Med 1982;11(2):69–76. [20] Marr S. Firefighters safety footwear: an investigation into problems reported by firefighters. J Occup Health Saf 1990;6(4):297–301. [21] Schneiders AG, Sullivan SJ, O'Malley KJ, Clarke SV, Knappstein SA, Taylor LJ. A valid and reliable clinical determination of footedness. PM R 2010;2(9):835–41. [22] Mündermann A, Dyrby CO, Hurwitz DE, Sharma L, Andriacchi TP. Potential strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity: reduced walking speed. Arthritis Rheum 2004;50(4):1172–8. [23] Tennant LM, Maly MR, Callaghan JP, Acker SM. Analysis of muscle activation patterns during transitions into and out of high knee flexion postures. J Electromyogr Kinesiol 2014;24(5):711–7. [24] Zelle J, Barink M, Malefijt MDW, Verdonschot N. Thigh-calf contact: does it affect the loading of the knee in the high-flexion range. J Biomech 2009;42(5):587–93. [25] Tennant LM, Kingston DC, Chong HC, Acker SM. The effect of work boots on knee mechanics and the center of pressure at the knee during static kneeling. J Appl Biomech 2015;31(5):363–9.
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The Knee
Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear Helen C. Chong, Liana M. Tennant, David C. Kingston, Stacey M. Acker ⁎ University of Waterloo, 200 University Ave W, Waterloo, ON N2L 3G1, Canada
a r t i c l e
i n f o
Article history: Received 21 March 2016 Received in revised form 9 December 2016 Accepted 13 December 2016 Available online xxxx Keywords: Kneeling Kinetics High flexion Kinematics Joint moments
a b s t r a c t 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. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Prolonged or frequent exposure to high knee flexion postures increases the incidence of knee injuries [1], including acute symptomatic pain and chronic pain resulting in lasting trauma to the knee joint [2]. High flexion postures, typically defined as involving knee flexion between 120° and 165° (where full extension is defined as 0°), are required for occupational purposes (e.g. childcare, construction, mining) and hobbies (e.g. gardening) [3,4]. Exposure on the knee joint as a result of high flexion
⁎ Corresponding author at: Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada. E-mail addresses: [email protected] (H.C. Chong), [email protected] (L.M. Tennant), [email protected] (D.C. Kingston), [email protected] (S.M. Acker).
http://dx.doi.org/10.1016/j.knee.2016.12.006 0968-0160/© 2016 Elsevier B.V. All rights reserved.
Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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postures has remained largely unexplored and the information that is available is quite variable and limited. In 2011, Pollard, Porter, and Redfern [5] reported knee angles and net forces and moments during squatting and kneeling postures, but only in the static phases. A study by Nagura et al. (2002) [6] examined double leg descending and ascending as well as a single leg kneel, however, participants did not continue to full flexion (particularly during the single leg kneel), and data was truncated when the knees made contact with the ground, meaning that, after the instant of knee-ground contact, no outcome measures were reported. Additionally, the study was limited in its ability to analyze both legs during the transition, since only one force plate was used resulting in kinetic data being available for a single leg only. A kinematic analysis [7] demonstrated the range of motion (ROM) about the ankle, hip, and knee during various high flexion postures, but neglected to present the kinetics of the tasks. Differences in condition (transitions in comparison to static postures) may account for the wide range of variability that is seen among reported values. These limitations of the current literature highlight the need for study of bilateral kinetics in high flexion. High knee flexion has been correlated with knee osteoarthritis (OA) in occupational settings yet the knee moments required to reach a high knee flexion posture have not been well established [8–10]. Increased external knee adduction moments during gait, as well as increased knee internal rotational moments, have been correlated with knee OA (values during gait are more than double healthy controls within a knee OA population) and this relationship could extend to peak moments during high flexion [8–12]. Knee joint moments are of particular interest because an increased external knee moment can be reflective of increased joint loading [13]. Increased external moments can be the result of increased externally applied loads, or can reflect a change in muscle activation strategies. Peak net flexion moments during high flexion, which occur between 90° and 150° of flexion during a double leg descent, are more than twice as high as those that typically occur in gait [6]. Occupations which require prolonged high flexion kneeling postures are associated with an increased risk of patellofemoral and tibiofemoral knee OA [8,9,14]. Two theories for disease progression are that repeated or prolonged compression of cartilage causes damage [8,15,16], or that kneeling may load areas of cartilage, such as the posterior femoral condyles and the posterior tibial plateau, that are not typically exposed to (and therefore may not be conditioned for) frequent loading [17]. In this theory, “typically” loaded surfaces would be those loaded within the range of 0° to 30° flexion, which is typically the largest range of flexion during the load-bearing phase of level gait. Knee OA is a degenerative disease that cannot be reversed — therefore, prevention is of utmost importance to avoid disease initiation and progression [18]. In this study, knee joint moments were examined as an indicator of knee loading magnitude, and flexion angles corresponding to the peak knee joint moments were examined as an indicator of the cartilage area being loaded since the tibiofemoral contact area changes with flexion angle [19]. Peak moments occurring at flexion angles that are different from the flexion angles that typically correspond to peak moments (for example, during gait) could indicate that poorly conditioned cartilage is experiencing high loads. Although avoiding high flexion in all occupations is unrealistic, recommendations regarding postural techniques that may reduce joint moment, in turn potentially reducing knee OA risk, would be valuable. Although it is understood that high flexion postures are frequently used in specific occupations, and that high flexion postures are associated with an increased risk for knee OA, it is unknown how personal protective equipment required in many of these industries affects OA risk. In particular, these postures are common in many industrial occupations such as flooring or roofing which also have strict requirements for safety equipment (such as requiring approved work boots while on site). A survey of 300 firemen indicated that newly required steel toe boots caused a feeling of restriction during kneeling, crouching, and fast movements [20]. Restrictions may cause altered lower limb mechanics, including joint moments about the knee, during transitions into and out of kneeling, as well as in static kneeling postures. The current study provides an initial investigation into whether or not the use of safety footwear results in knee joint mechanics that could put the worker at a higher risk of knee joint damage compared to the risk already present with kneeling alone. Similar to kneeling, the use of safety footwear cannot (and should not) be avoided in many occupational settings. However, should there be evidence that safety footwear may increase knee OA risk for kneeling workers, that finding could prompt exploration of alternative safety footwear designs with the goal of mitigating this increased risk. The primary purpose of this study is to characterize the knee joint moments and peak knee flexion moment timing during high flexion transitions, with the intent of identifying high-risk postures. The secondary purpose is to determine whether safety footwear (work boots) alters the kinematics and kinetics of transitional and static high flexion postures. It is hypothesized that peak moments will be increased with the addition of safety footwear, indicating increased knee joint loading. This would mean that, in addition to kneeling alone, safety footwear may contribute to loading associated with OA. It is also expected that the sagittal ankle ROM will be decreased when wearing safety footwear; but that the flexion angle of the knee will remain unchanged with the addition of safety footwear. Given that higher muscle activation has been observed in high flexion, compared to midflexion, and that both high flexion activities [8] and increased external adduction moments have been associated with cartilage deterioration in some individuals [11], it is hypothesized that the peak adduction moments observed during transitions between standing and kneeling will be higher than the ranges typically seen during walking and that the peak flexion moments will occur at flexion angles greater than the largest angle exhibited during the load-bearing phase of walking (typically up to 30°). 2. Material and methods 2.1. Participants Fifteen right leg dominant males participated in this study. Participant exclusion criteria included any lower limb injury within the past five years that required medical intervention or time off from work for longer than three days. Trials were excluded as a Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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result of marker drop out, inconsistent movement patterns, or when both feet made contact with the same force plate. For five participants, these trial exclusions resulted in an insufficient number of remaining trials for analysis. Therefore data from ten individuals (age 22.9 S.D. 1.7 years; mass 78.6 S.D. 9.3 kg; height 1.75 S.D. 0.06 m) were included in the analysis. All participants were required to wear the same pair of men's size 10 US safety boots (Operator Steel Toe, Caterpillar Inc., Model: P709254), and so only males with size 10 US feet were recruited. Each participant read and signed an informed consent form approved by the university's research ethics board.
2.2. Data collection Synchronous kinematic (Optotrak Motion Capture; Northern Digital, Inc. Waterloo, ON) and kinetic (four embedded OR6-7 force plates; Advanced Mechanical Technology, Inc., Watertown, MA) data were collected bilaterally for each participant. Optotrak hardware (Optotrak data acquisition unit) and software (First Principles) were used to synchronize motion capture and force plate data collection. Rigid bodies were affixed to both feet, shanks, and thighs, and the sacrum. Anatomical landmarks on each segment were digitized with respect to their respective rigid bodies. Data was collected during transitions (descent and ascent) and static kneeling postures while the participant was barefoot and shod in safety footwear. The leg that supported the body during kneeling initiation will be referred to as the ‘lead’ leg (Figure 1; left leg lead) and the opposing leg will be referred to as the ‘trail’ leg (Figure 1; right leg trail). The knee of the trailing leg made contact with the floor first. Participant leg dominance was determined through a series of tests [21]. The order of footwear conditions was randomized before the blocked experimental trials were performed. The movements were demonstrated, and the participant was encouraged to familiarize himself with the task. Participants then complete five blocked sets of three phases: descent, static kneeling, and ascent. The descending and ascending trials were performed by participants at a self-selected speed; participants were required to maintain the static kneeling phase for 10 s. The descent trial began off of the force plates; the participant stepped forward with each foot onto the force plates (generally with their trail leg first), and then kneeled using an asymmetric movement (Figure 1). Some participants took an additional step so that their feet were side-by-side before taking another half-step with the lead leg and kneeling down. Participants were not required to lead with a specific leg; seven participants used the left leg as the lead leg during the descending transition, and eight participants used the left leg as the lead leg during the ascending transition. For static kneeling, the participants were encouraged to achieve heel-gluteal contact when possible. The ascent transition began by raising the knee of the lead leg off the floor, then with their lead foot planted, raising the body and stepping backwards off the force plates. Five trials of each phase were collected, for a total of 15 trials per footwear condition per participant.
Figure 1. Participant performing transitional movement trial while barefoot; lead and trail legs are identified.
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Table 1 Segment coordinate system definitions for the pelvis, thigh, shank and foot. Pelvis segment coordinate system definitions Origin z-Axis Transverse plane y-Axis x-Axis
Mid-point between the left and right posterior superior iliac spines A vector normal to the transverse plane in the superior direction Formed by the origin and the left and right anterior superior iliac spines Cross product of the z- and x-axes Vector from the origin towards the right posterior superior iliac spine
Thigh segment coordinate system definitions Origin z-Axis Frontal plane y-Axis x-Axis
Hip joint center, estimated based on pelvis ASIS landmarks (Bell et al. (1989, 1990). Vector from the midpoint of the lateral and medial femoral epicondyles to the origin Formed by the z-axis and the transepicondylar line A normal to the frontal plane in the anterior direction Cross product of the y- and z-axes
Shank segment coordinate system definitions Origin z-Axis y-Axis x-Axis
Mid-point between the lateral and medial tibial condyles Vector from the mid-point between the lateral and medial malleoli to the origin Cross product of the z-axis and a line joining the tibial condyles Cross product of the y- and z-axes
Foot segment coordinate system definitionsa Origin z-Axis y-Axis x-Axis
Mid-point between the lateral and medial malleoli Mid-point between the 5th and 1st metatarsal head to the origin Cross product of the z-axis and a line joining the lateral and medial malleoli Cross product of the y-and z-axes
a
The foot segment coordinate system is then rotated to align with the shank segment coordinate system so that a neutral standing posture is 0° ankle flexion.
2.3. Data processing & statistics Kinematic and kinetic data were filtered using a bidirectional low-pass 2nd order Butterworth filter with a 6 Hz cut off. Segmental local coordinate system definitions are shown in Table 1. Peak knee moments in all three tibial coordinate system planes were determined for the transition conditions, together with the flexion angle at the knee when the peak knee flexion moment occurred. The absolute minimum value (peak knee abduction moment) of the frontal tibial coordinate system plane was also determined for the transition conditions since both the peak knee abduction moment and peak knee adduction moment are of interest. Average three-dimensional knee moments, average knee flexion angles, and average ankle flexion angles were calculated for the static postures. Knee moments were resolved into the tibial coordinate system [22]. Statistical analyses (SAS 9.4, Cary, North Carolina, USA) involved two-way repeated measures analyses of variance (RM ANOVA) for two outcomes (angle and moment) and three planes (sagittal, frontal, transverse), containing within subject factors of footwear (shod, barefoot) and leg (lead and trail for the dynamic ascent and descent phases, or right and left for the static phase). Analysis included a total of four ANOVAs per dynamic phase (moments only were analyzed during the dynamic phases in three planes) and a total of twelve ANOVAs during the static phase (average moment and angle in three dimensions for both the knee and ankle joint). For any interactions present, a Tukey post-hoc test was used. The alpha level for these comparisons was preset at 0.05 for both main effects and post-hoc tests. 3. Results Outcome measures with significant interactions and main effects are reported in Table 2. The transitional movement curves for knee and ankle flexion angles are shown in Figure 2. 3.1. Peak external knee moments during transitions An interaction occurred between leg and footwear conditions with respect to the external peak knee adduction moment (p = 0.005) during the descending transition such that the addition of safety footwear compared to the unshod condition caused a significant change in the lead leg peak knee adduction moment only. There was no statistically significant main effect of footwear on the external peak knee adduction moment during transitions. Trail leg external peak knee internal rotational moments were significantly greater than lead leg peak moments in both descent (p = 0.0119) and ascent (p = 0.0129), but were not significantly different between the shod and unshod conditions. 3.2. Mean angles and moments during static kneeling Mean ankle flexion angle during static kneeling was not significantly different between shod (25.1° (13.8°) plantarflexion) and barefoot (16.8° (18.1°) plantarflexion) conditions; however, the nearly 8.3° difference seen may have some biological relevance. Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Table 2 Mean of the peak external moments (normalized to % body weight multiplied by height (BW * Ht) ± standard deviation) for flexion, adduction, abduction, and internal rotational axes for shod and barefoot conditions during the ascent and decent movement phases. Symbols in the leftmost column indicate a main effect or interaction on the variable listed, followed by the corresponding significance (p-value) of that main effect. Lead
Trail
Barefoot Flexion descent Flexion ascent Abduction descent Abduction ascent Adductiona descentb p = 0.005 Adductiona ascent Internal rotation descentc p = 0.0119 Internal rotation ascentc p = 0.0.0129 a b c
−8.37 −6.81 −2.44 −2.63 1.06 0.91 −0.78 −0.73
± ± ± ± ± ± ± ±
Shod 2.14 1.76 1.14 1.28 0.70 0.42 0.24 0.34
−8.81 −7.99 −2.15 −2.64 2.04 1.02 −0.78 −0.88
Barefoot ± ± ± ± ± ± ± ±
1.76 1.81 0.63 1.32 0.66 0.41 0.21 0.38
−8.10 −7.87 −1.93 −2.33 1.01 0.85 −0.88 −0.98
± ± ± ± ± ± ± ±
Shod 1.96 2.43 0.64 0.90 0.31 0.87 0.39 0.23
−9.87 −8.58 −1.97 −2.35 1.13 1.21 −1.18 −1.14
± ± ± ± ± ± ± ±
1.22 1.84 0.95 0.64 0.62 0.59 0.31 0.24
For comparison, peak external adduction moments between two and four percent BW ∗ Ht have been reported for gait. Footwear condition × leg interaction. Main effect of leg.
3.3. Occurrence of peak flexion moments during transition Peak flexion moments ranged from 3.33 to 12.6% body weight times height (BW ∗ Ht). The point at which the peak flexion moments occurred varied considerably between participants. The average external flexion moment curves (Figure 3, top row), demonstrate two local minima (flexion is negative) during descent at approximately 40% (generally within 50 ms, just before the trail knee makes contact) and 100% phase (full flexion, at an average of 146.3°). During descent, half of the participants experienced their peak flexion moment in the lead leg around 40% phase, in a deep lunge position (flexion angle between 90 and 125°). The most common point at which the peak flexion moment occurred in the trail leg was during full flexion (100% of the descent phase or 0% of the ascent phase, Figure 3; four of ten participants).
Figure 2. Knee (top row) and ankle (bottom row) flexion angle during ascent and descent while shod and unshod for both the lead and trail legs. The trail leg is represented in blue and a dashed line, while the lead leg is represented in gray and a solid line. Pictorial representations of the descent phase (bottom row, left) and the ascent phase (bottom row, right) are shown to give a visual representation of the postures at a given phase percentage in the top and middle rows. The pelvis is represented as an inverted triangle with the lead leg solid and the trail leg dotted. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
Figure 3. Lead leg knee (solid black line) and trail leg knee (dashed blue line) external moments while wearing safety footwear and while barefoot during downward and upward transitions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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4. Discussion The purpose of this investigation was to assess the kinetic requirements of transitional movements into and out of kneeling, as well as to determine the effect of safety footwear. Mean peak external knee adduction moments during transitions ranged from 1.01 ± 0.31% BW ∗ Ht to 2.04 ± 0.66% BW ∗ Ht (Table 2), whereas peak adduction moments for gait have been reported between two and four percent BW ∗ Ht. Therefore the hypothesis that peak external knee adduction moments during transitions would exceed those exhibited during level walking was rejected, indicating that an increased knee adduction moment magnitude is likely not a main factor in the development of knee OA in occupational kneelers. The hypothesis that peak flexion moments would occur at flexion angles above the maximum flexion angle exhibited during the load-bearing phase of walking (up to approximately 30°) was confirmed, providing support for the theory that the loading of atypical surfaces may play a role in disease development or progression. Our results indicate that occurrences of significant findings tend to be in both the descending and ascending phases, with the exception of the interaction present in the peak knee adduction moment during the descending phase only. Although symmetry of findings with respect to descending or ascending transition may have been expected, previous work has shown that the ascending phase requires a higher level of co-activation than the descending phase, which would tend to decrease the magnitude of net internal moments [23]. With respect to the current study, since the external moments should balance the internal moments, this interpretation would agree with our overall lower magnitude of peak flexion moments during ascent compared descent (Table 2). Peak flexion moments ranged from 3.33 to 12.6% BW ∗ Ht. These values nearly span the range of previously reported values of 6.9–13.5% BW ∗ Ht [5]. Since some participants experienced their peak flexion moments during full flexion, it is necessary to continue data collection until the participant is in a fully flexed, static position. Nagura et al. (2002) [6] studied a single leg descent and ascent, and found that the peak net external moments occurred between 70° and 100° flexion. Similar angles were found in the current study for those participants who reached a peak moment during the transition. However, because that previous study truncated the data at the point of knee contact in the trailing leg, they may have failed to identify the true peak moment for some of their participants. Peak moment timing for four participants was affected by footwear. Safety footwear shifted the time of peak moment from before the trail knee had made contact with the ground to once the participant was in full flexion. It is worth noting that this change in peak moment can occur with a change in footwear so that the effect of footwear can be accounted for in future study protocols. Factors that modulate the effect of footwear for a given individual could be explored in future work. The addition of safety footwear altered the mechanics of static kneeling in participants who reached a greater plantarflexion angle during static kneeling while unshod than the boot allowed for. Four of the participants achieved a much greater plantarflexion angle during unshod kneeling, likely resulting from a difference in technique (these participants used a technique resulting in the dorsal aspect of the foot contacting the ground while unshod). The addition of safety footwear decreased the plantarflexion angle that was achievable by these participants to a greater degree than the remaining six participants who used the same kneeling technique in each condition (the heads of the metatarsals and the plantar forefoot in contact with the ground and the forefoot flexed). Examining the entire study sample, safety footwear resulted in (not statistically significant) decreased ankle plantarflexion angle (by 8.3°, p = 0.48) and increased the internal rotation angle between the shank and foot (by 4.1°, p = 0.51). These kinematic differences at the ankle level did not propagate to the level of the knee in the sample for the current study (10 participants), but decreased knee internal rotation was found in a larger sample size (15 participants) during kneeling as a result of work boot wear [25]. The observed decrease in plantarflexion was expected since the rigid, high cut nature of the boot limits ankle ROM. Increased internal rotation of the knee would have been expected due to the rounded, rigid toe and rigid sole on the boot. We expected that participants would tend to splay the heels apart from one another, increasing knee internal rotation and possibly abduction, however this did not occur. It is possible that the participants used increased muscle activity to maintain a more neutral (less rotated) knee posture compared to the barefoot condition where the flat plantar surface of the forefoot in contact with the ground would help to passively keep the anterior–posterior axes of the feet relatively vertical and parallel. Muscle activity was not measured in this study. Although safety footwear is an absolute requirement that should not be ignored while working in hazardous areas, future work could examine the possibility of designing footwear with greater plantarflexion range of motion. The exact pathogenesis of knee OA is not fully established. Factors such as increased loading and prolonged exposure in high flexion postures have been implicated, but it is not known whether factors such as increased external knee adduction moments cause disease initiation or are a result of disease progression [8]. During descent, the lead and trail legs experienced significantly different peak knee adduction moments when work boots were worn. The lead leg supports the majority of body weight during descent while the trail leg is lowered (based on this study, 65–85% of the total body weight is typical), which may help explain why the effect of wearing work boots appears to be magnified for the lead leg. Previous work [25] on static kneeling has shown that wearing safety footwear resulted in a shift of the center of pressure under the knee. While the dynamic phases were not reported in that study, those findings may indicate changes in balance or center of mass positioning as a result of safety footwear. These changes may also help explain the interaction for the adduction moment in the current study, where a difference between legs was only significant when footwear was worn. This finding could be important, especially for those with knee pain or knee OA in one knee. If medial loading is of concern, the use of the unaffected knee as the lead leg may reduce aggravation of the existing condition, or reduce pain. In asymptomatic individuals, alternating legs as the lead leg in repetitive transitions would balance the cumulative load between knees. Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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The findings of this study are limited by the following factors. In both previously published work [6] and the current study, the calculation of the flexion moment did not include the effect of thigh-calf contact, which can reduce the flexion moment when the back of the thigh comes into contact with the calf [24]. This limitation would affect the magnitude of the peak flexion moment for those participants whose peak flexion moment occurred at full flexion. As with all studies using skin mounted marker-based motion capture, the tracking of segments was subject to soft tissue artifact. The effect of this artifact is likely more pronounced in the higher flexion range when the thigh and calf come into contact, resulting in more deformation of limbs. This effect would not likely be dependent on footwear condition. Because foot landmarks and the malleoli were used to create the foot coordinate system and foot-mounted markers were used to track the segment, foot and ankle landmarks were digitized twice, once in the barefoot condition and once in the shod condition. Since boot-mounted markers were used to track the foot segment, the accuracy of tracking the foot segment in the shod condition would have been negatively affected by relative motion between the foot and the boot. In the absence of radiographic imaging, there is no way to know exactly how much relative movement occurred between the foot and the boot; however we attempted to minimize this issue by ensuring that the boot was tied tightly to promote a snug fit. The variation in peak external knee joint moments (the standard deviations in Table 2) are in some cases relatively large and may contribute to the finding of few significant differences between the lead and trial legs. However, it should also be noted that the timing of peaks was not a factor in the statistical analysis of the peak moments. The mean moment curves in Figure 3 show that, while the absolute peaks of the curves are similar in many cases, the time point (% Phase) at which the peak moments occurred on average differed between the lead and trial legs. Due to the relatively young, male study cohort, the results of this study should only be generalized to a male population with no knee injuries or pathologies. In summary, this work helps to characterize the moments about the knee during high flexion postures, provides time-series information, and expands the existing knowledge of magnitude and time of occurrence for peak moments during transitions. 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. We have determined that significant differences exist between the lead and trail legs for the transverse plane (internal rotation) moment, and that 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 play a role in disease development or progression. Future work should include more participants to determine why participants are affected differently by safety footwear. Additionally, a more comprehensive examination of different styles of kneeling is required in order to encompass more potential occupational postures. Conflicts of interest None Acknowledgements Funding support was provided by the National Sciences and Engineering Council of Canada (NSERC) Discovery grant #418647 (SA). References [1] Tanaka S, Smith AB, Halperin W, Jensen R. Carpet-layer's knee. N Engl J Med 1982;307(20):1276–7. [2] Thun M, Tanaka S, Smith AB, Halperin WE, Lee ST, Luggen ME, et al. Morbidity from repetitive knee trauma in carpet and floor layers. Br J Ind Med 1987;44: 611–20. [3] Acker SM, Cockburn RA, Krevolin J, Li RM, Tarabichi S, Wyss UP. Knee kinematics of high flexion activities of daily living performed by male Muslims in the Middle East. J Arthroplasty 2011;26(2):319–27. [4] Hefzy MS, Kelly BP, Cooke TDV. Kinematics of the knee joint in deep flexion: a radiographic assessment. Med Eng Phys 1998;20(4):302–7. [5] Pollard JP, Porter WL, Redfern MS. Forces and moments on the knee during kneeling and squatting. J Appl Biomech 2011;27(3):233–41. [6] Nagura T, O'Dyrby C, Alexander EJ, Andriacchi TP. 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Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006
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Please cite this article as: Chong HC, et al, Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear, Knee (2016), http://dx.doi.org/10.1016/j.knee.2016.12.006