Soft tissue displacement over pelvic anatomical landmarks during 3-D hip movements
Introduction
The movement between markers attached to the skin surface, as used in stereophotogrammetry for the analysis of human motion, and the underlying bone (soft tissue artefact: STA) has been investigated in various body segments and during different motor tasks. This was made possible by simultaneously monitoring the movement of the skin markers and of the underlying bone using methods such as intracortical pins (Andersen et al., 2012; Andriacchi et al., 1998; Benoit et al., 2006; Camomilla et al., 2013; Cappozzo et al., 1996; Cereatti et al., 2009; Dal Maso et al., 2016; Fuller et al., 1997; Lafortune et al., 1992; Ramsey et al., 2003; Reinschmidt et al., 1997; Westblad et al., 2002), percutaneous bone tracking devices (Houck et al., 2004, Holden et al., 1997, Manal et al., 2000), fluoroscopy (Akbarshahi et al., 2010, Charbonnier et al., 2014, Kuo et al., 2011, Sati et al., 1996, Stagni et al., 2005, Tsai et al., 2009, Tsai et al., 2011), or X-rays (Maslen and Ackland, 1994).
Although a reasonable amount of relevant information concerning the lower and upper limb segments is available in the literature (Leardini et al., 2005, Peters et al., 2010), only two studies provided information on the STA that affects the pelvis. One investigation was performed during gait and sit to stand using markers mounted on pins inserted into the sacrum (Rozumalski et al., 2007). This study showed larger STA for the anterior superior than for the posterior iliac spine areas, and in the craniocaudal direction. A non-invasive assessment of pelvic STA was performed relying on the estimate of the pelvic bone-pose provided by a multiple anatomical calibration (Hara et al., 2014). This technique involves static calibrations performed through manual palpation of relevant anatomical landmarks (ALs) and consequent identification of their position using stereophotogrammetry through the range of motion of the joint of interest (Cappello et al., 1997). In this way, the STA issue is bypassed and a reliable pelvis pose can be assessed in each posture of interest. This method, besides not showing the STA components caused by the wobbling of the soft tissues, suffers from unavoidable intra-operator variability in the multiple identification of the ALs. This variability has been found to have a root mean square (rms) value in the range 11–20 mm causing pelvic orientation rms variability between 2 and 4 deg (Della Croce et al., 1999). Moreover, the hip postures investigated in Hara et al. (2014) simulated movements occurring only in the sagittal plane, which is not the case in locomotion and other functional motor tasks. A special case in which the STA affecting the pelvis is generated during a hip 3-D movement, characterised by large flexion-extensions and adduction-abductions excursions (the so-named star-arc movement; Camomilla et al., 2006), is the estimate of the hip joint centre position using a functional approach. The STA affecting this estimate (Kainz et al., 2015) heavily impacts the accuracy of movement analysis (Stagni et al., 2000). This calls for an accurate characterisation of the artefact (Camomilla et al., 2013) as a premise for its compensation (De Rosario et al., 2013, Rouhandeh et al., 2014a). Another limitation of the study of Hara et al. (2014) is that only information relative to normal-weight subjects is provided.
Therefore, the aim of this study was to assess pelvic STA expanding current available knowledge to 3-D hip poses, including those normally occurring during walking and during the above-mentioned star-arc movement, and to volunteers characterised by a wide range of body mass indices (BMIs). An experimental approach similar to that illustrated in Hara et al. (2014) was used, but with an enhanced anatomical calibration technique, named UP–CAST and illustrated in Donati et al., 2007, Donati et al., 2008, which drastically reduces the intra-operator variability of pelvic orientation estimation.
Section snippets
Materials and methods
Five healthy volunteers with body mass index ranging from 22 to 37 (Table 1) participated in the study after signing a written informed consent.
Results
The characteristics of the static positions assumed by the volunteers are reported in Table 2.
For each volunteer and sAL, the STA amplitudes and the STA diameters are reported for the MS and SA postures (Table 3). For the anterior pelvic ALs, the STA amplitudes ranged from 3.1 to 25.4 mm and from 4.6 to 52.1 mm, for normal and overweight volunteers, respectively; for the posterior ALs, from 1.9 to 22.0 mm and from 7.2 to 29.4 mm, for normal and overweight volunteers, respectively. The sRASIS
Discussion
In this study a multiple anatomical calibration based on a non-invasive and highly repeatable approach was performed and pelvic STA was assessed relative to static postures assumed to resemble the mid–stance phase of gait (MS) and the star-arc movement (SA), entailing hip flexion-extension and adduction–abduction ranges of motion larger than during gait. The STA was characterised in terms of amplitude and direction with respect to different ALs, task performed, and subjects’ BMI. Pelvic tilt,
Conflict of interest
The authors do not have any financial or personal relationships with other people or organisations that could inappropriately influence the manuscript.
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