Thigh-calf contact parameters for six high knee flexion postures: Onset, maximum angle, total force, contact area, and center of force
Introduction
The magnitude and location of contact forces between thigh-calf and heel-gluteal structures during high knee flexion postures are critical parameters for understanding knee joint loading. In this study, high knee flexion postures are defined as exceeding 120° flexion (Kingston et al., 2016, Zelle et al., 2009). Given the increased incidence of degenerative knee diseases in populations that regularly assume high knee flexion postures (Baker et al., 2003, Bombardier et al., 2011, Kirkeshov Jensen, 2008), further study to refine potential initiating mechanisms is warranted. A leading theoretical injury mechanism for high knee flexion postures—the exposure of under-conditioned tissues to high joint contact forces (Andriacchi et al., 2004, Andriacchi and Favre, 2014)—does not consider the unloading effect of thigh-calf or heel-gluteal contact on the joint. Therefore, the limited in vitro data available from testing knee joint compressive forces, up to 135° of flexion, are likely over-estimates (Hofer et al., 2012, Victor et al., 2009). This potential for over-estimation was first supported by Zelle et al. (2009), who used a finite element model of the knee with external thigh-calf contact forces (taken from Zelle et al. (2007) in vivo data). Decreases from 4.37 to 3.07 times body weight (BW) in knee joint compression and 1.31 to 0.72 times BW in shear during a flatfoot squat movement were estimated (Zelle et al., 2009). However, accurate magnitude and location data from a variety of high flexion movements are critical to improve estimates of joint contact forces in future computational models and in vitro evaluations of high knee flexion postures (Thompson et al., 2015).
A variety of high knee flexion postures exist in activities of daily living where intersegmental contact data could be used to improve estimates of mechanical loading exposure. Islamic religious practices and traditional East Asian cultural customs involve symmetric high flexion kneeling with the feet in dorsiflexion or plantarflexion (Hefzy et al., 1998, Hemmerich et al., 2006). High knee flexion squatting is also common during childcare, sport, and toileting in many cultures (Hemmerich et al., 2006, Kurosaka et al., 2002). Finally, single-leg (unilateral) kneeling is used during many occupational tasks (Gallagher et al., 2011, Pollard et al., 2011) and is a primary shooting position used in military theater (Army, 2010). During symmetric kneeling, thigh-calf contact force has been reported at up to 34% BW (Zelle et al., 2007) with a separate study reporting heel-gluteal contact forces of approximately 11% BW (Pollard et al., 2011). However, only a dorsiflexed foot position was tested during kneeling, and there is no known thigh-calf or heel-gluteal contact data for unilateral kneeling positions. Further investigation of heel-gluteal contact is needed as the large moment arm has resulted in similar knee extension moments to thigh-calf contact with considerably smaller forces (Pollard et al., 2011). Therefore, also including heel-gluteal contact forces in future modelling efforts is needed to improve the biofidelity of tibial compressive loads.
Prior work on thigh-calf contact involved assessment only in the sagittal plane and pressure sensors were not attached to segments. Small sample sizes (10 participants) prevented the investigation of sex differences in prior work (Pollard et al., 2011, Zelle et al., 2007). Given anthropometric (Power and Schulkin, 2008) and flexibility differences between sexes (Krivickas and Feinberg, 1996), females may be disproportionally exposed to lower joint compressive loads as a result of increased thigh-calf and heel-gluteal contact in high flexion postures. In addition, females generally have a higher distribution of body-fat in the pelvic and thigh region (Cnop et al., 2003, Nielsen et al., 2004) which may also result in different intersegmental loading when compared to males. Past studies have relied on manually positioning, or having participants hold, pressure sensors in place while performing movement trials (Pollard et al., 2011, Zelle et al., 2007). This reduced repeatability between trials, and did not allow for unilateral postures as larger pressure sensors designed for seating applications (Conformat model #5330, Tekscan, South Boston, MA, USA) were used. Finally, prior studies used sensors with a spatial resolution of 0.5 sensels per cm2, and were collected at a maximum of 8 Hz (Pollard et al., 2011, Zelle et al., 2007).
Therefore, the purpose of this study was to define the following parameters for thigh-calf and heel-gluteal contact from six high knee flexion postures: (1) knee flexion angle at which thigh-calf contact begins (‘onset’), (2) maximum knee flexion range (‘max angle’), (3) contact force magnitude (‘force’), (4) contact force area (‘area’), and (5) longitudinal center of force (‘CoF’) location. All reported outcomes occurred simultaneously, with the exception of onset. A secondary objective of this study was to investigate sex differences in these outcome parameters.
Section snippets
Participants
Twenty-eight male and thirty female participants (Table 1) were recruited from a sample of convenience in the university’s student body. Exclusion criteria consisted of any low back, or lower limb injury within the past year that required medical intervention or time off from work for longer than three days, and any history of surgical interventions to the back or lower limb. Only one participant was not right leg dominant. Each participant read and signed an informed consent form approved by
Results
ICC(2,1) estimates were excellent (lowest value 0.932) between masking attempts at different kPa display levels (Cicchetti, 1994). Likewise, ICC(2,3) values were excellent between raters (lowest single and mean values 0.873 and 0.954 respectively). A complete set of mean values and standard deviations for dependent variables is in Table 2. Notable differences are reported below.
Discussion
The purpose of this investigation was to define thigh-calf and heel-gluteal contact parameters for six high knee flexion movements and to investigate potential sex differences. Results indicate that unilateral kneeling movements have the highest thigh-calf contact forces occurring at CoF locations farthest from the knee joint center. These activities would therefore theoretically result in the greatest reduction of knee joint flexion moments for the right knee, although not necessarily the
Conclusion
Our results suggest that thigh-calf and heel-gluteal contact can result in considerable force transfer between the thigh and shank segments during high knee flexion movements. While previous work has quantified these effects at the joint loading level (Pollard et al., 2011, Zelle et al., 2009) future work is required to incorporate thigh-calf contact parameters into a 3D musculoskeletal model (Thompson et al., 2015). It is noteworthy that the population used in this study—consisting of young,
Acknowledgements
We would like to acknowledge that SM Acker is funded through an NSERC Discovery Grant #418647. This funding source was not involved with study implementation or submission.
Conflict of interest
The authors have no financial and personal relationships with other people or organizations that could inappropriately influence their work.
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