Biomechanics Research Laboratory

Ann Arbor, MI, United States

Biomechanics Research Laboratory

Ann Arbor, MI, United States

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Chen L.,University of Michigan | Chen L.,Biomechanics Research Laboratory | Ramanah R.,University of Franche Comte | Hsu Y.,University of Utah | And 2 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2013

Introduction and hypothesis: The cardinal ligament (CL) and deep uterosacral ligament (US) play a critical role in utero-vaginal support. This study aims to quantify their geometrical relationships in living women using a MRI-based 3D technique. Methods: The angles between ligaments, the ligaments length and curvature were assessed on 3D models constructed from twenty MRIs of volunteers with normal support. How angle variation theoretically affects ligament tension was investigated using a simplified biomechanical model. Results: The CLs are 18.1 °± 6.8 (SD) from the cephalic-caudal body axis, and the USs are dorsally directed and 92.5° ± 13.5 from the body axis. The CLs are longer and more curved than US. The theoretical calculated tension on CL is 52 % larger than that on US. Conclusions: The CL is relatively parallel to the body axis while the US is dorsally directed. The tensions on these ligaments are affected by their orientations. © 2012 The International Urogynecological Association.


Hernandez M.E.,Biomechanics Research Laboratory | Hernandez M.E.,USA Mobility | Ashton-Miller J.A.,Biomechanics Research Laboratory | Ashton-Miller J.A.,USA Mobility | And 4 more authors.
Human Movement Science | Year: 2012

Rapid center of pressure (COP) movements are often required to avoid falls. Little is known about the effect of age on rapid and accurate volitional COP movements. We hypothesized that COP movements to a target would be slower and exhibit more submovements in older versus younger adults, particularly in posterior versus anterior movements. Healthy older (N= 12, mean age = 76. years) and young women (N= 13, mean age = 23. years) performed anterior and posterior lean movements while standing on a force plate, and were instructed to move their COP 'as fast and as accurately as possible' using visual feedback. The results showed that rapid posterior COP movements were slower and had an increased number of submovements and ratio of peak-to-average velocity, in comparison to anterior movements (p< .005). Moreover, older compared to younger adults were 27% slower and utilized nearly twice as many compensatory submovements (p< .005), particularly when moving posteriorly (p< .05). Older women also had higher ratios of peak-to-average COP velocity than young (p< .05). Thus, despite moving more slowly, older women needed to take more frequent submovements to maintain COP accuracy, particularly posteriorly, thereby providing evidence of a compensatory strategy that may be used for preventing backward falls. © 2011 Elsevier B.V.


Yousuf A.,University of Michigan | Chen L.,University of Michigan | Chen L.,Biomechanics Research Laboratory | Larson K.,University of Michigan | And 2 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2014

Introduction and hypothesis: In cystoceles, the distal anterior vaginal wall (AVW) bulges out through the introitus and is no longer in contact with the posterior vaginal wall or perineal body, exposing the pressure differential between intra-abdominal pressure and atmospheric pressure. The goal of this study is to quantify the length of the exposed vaginal wall length and to investigate its relationship with other factors associated with the AVW support, such as most dependent bladder location, apical location, and hiatus diameter, demonstrating its key role in cystocele formation.Methods: Fifty women were selected to represent a full spectrum of AVW support. Each underwent supine, dynamic MR imaging. Most dependent bladder location and apical location were measured relative to the average normal position on the mid-sagittal plane using the Pelvic Inclination Correction System. The length of the exposed AVW and the hiatus diameter were measured as well. The relationship between exposed AVW and most dependent bladder location, apical location, and hiatus diameter were examined.Results: A bilinear relationship has been observed between exposed vaginal wall length and most dependent bladder location (R2 = 0.91, P < 0.001). When the bladder descents up to the inflection point (about 4.4 cm away from its normal position), there is little change in the exposed AVW length. With further descent, the exposed vaginal wall length increases significantly, with a 2 cm increase in exposed AVW length for every additional 1 cm of drop bladder location. A similar but weaker bilinear relationship exists between exposed AVW and apical location. Exposed vaginal wall length is also highly correlated with hiatus diameter (R2 = 0.85, P < 0.001).Conclusion: A bilinear relationship exists between exposed vaginal wall length and most dependent bladder location and apical location. It is when the bladder descent is beyond the inflection point that exposed vaginal wall length increases significantly. © 2014, The International Urogynecological Association.


Luo J.,University of Michigan | Luo J.,Biomechanics Research Laboratory | Larson K.A.,University of Michigan | Larson K.A.,Eastern Virginia Medical School | And 3 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2012

Introduction and hypothesis: Two-dimensional magnetic resonance imaging (MRI) of posterior vaginal prolapse has been studied. However, the three-dimensional (3-D) mechanisms causing such prolapse remain poorly understood. This discovery project was undertaken to identify the different 3-D characteristics of models of rectocele-type posterior vaginal prolapse (PVP R) in women. Methods: Ten women with (cases) and ten without (controls) PVPR were selected from an ongoing case-control study. Supine, multiplanar MR imaging was performed at rest and maximal Valsalva. Three-dimensional reconstructions of the posterior vaginal wall and pelvic bones were created using 3D Slicer v. 3.4.1. In each slice the posterior vaginal wall and perineal skin were outlined to the anterior margin of the external anal sphincter to include the area of the perineal body. Women with predominant enteroceles or anterior vaginal prolapse were excluded. Results: The case and control groups had similar demographics. In women with PVPR two characteristics were consistently visible (10/10): (1) the posterior vaginal wall displayed a folding phenomenon similar to a person beginning to kneel ("kneeling" shape) and (2) a downward displacement in the upper two thirds of the vagina.Also seen in some, but not all of the scans were: (3) forward protrusion of the distal vagina (6/10), (4) perineal descent (5/10), and (5) distal widening in the lower third of the vagina (3/10). Conclusions: Increased folding (kneeling) of the vagina and an overall downward displacement are consistently present in rectocele. Forward protrusion, perineal descent, and distal widening are sometimes seen as well. © The International Urogynecological Association 2012.


Luo J.,University of Michigan | Luo J.,Biomechanics Research Laboratory | Betschart C.,University of Michigan | Betschart C.,University of Zürich | And 2 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2016

Introduction and hypothesis: We present a technique for quantifying inter-individual variability in normal vaginal shape, axis, and dimension, and report findings in healthy women. Methods: Eighty women (age: 28∼70 years) with normal pelvic organ support underwent supine, multi-planar proton-density MRI. Vaginal width was assessed at five evenly-spaced locations, and vaginal axis, length, and surface area were quantified via ImageJ and MATLAB. Results: The mid-sagittal plane angles, relative to the horizontal, of three vaginal axes were 90 ± 11, 72 ± 21, and 41 ± 22° (caudal to cranial, p < 0.001). The mean (± SD) vaginal widths were 17 ± 5, 24 ± 4, 30 ± 7, 41 ± 9, and 45 ± 12 mm at the five locations (caudal to cranial, p < 0.001). Mid-sagittal lengths for anterior and posterior vaginal walls were 63 ± 9 and 98 ± 18 mm respectively. The vaginal surface area was 72 ± 21 cm2 (range: 34 ∼ 164 cm2). The coefficient of determination between any demographic variable and any vaginal dimension did not exceed 0.16. Conclusions: Large variations in normal vaginal shape, axis, and dimensions were not explained by body size or other demographic variables. This variation has implications for reconstructive surgery, intravaginal and surgical product design, and vaginal drug delivery. © 2016, The International Urogynecological Association.


Spahlinger D.M.,University of Michigan | Spahlinger D.M.,Duke University | Newcomb L.,University of Michigan | Ashton-Miller J.A.,University of Michigan | And 3 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2014

Objectives: To develop and test a method for measuring the relationship between the rise in intra-abdominal pressure and sagittal plane movements of the anterior and posterior vaginal walls during Valsalva in a pilot sample of women with and without prolapse. Methods: Mid-sagittal MRI images were obtained during Valsalva while changes in intra-abdominal pressure were measured via a bladder catheter in 5 women with cystocele, 5 women with rectocele, and 5 controls. The regional compliance of the anterior and posterior vagina wall support systems were estimated from the ratio of displacement (mm) of equidistant points along the anterior and posterior vaginal walls to intra-abdominal pressure rise (mmHg). Results: The compliance of both anterior and posterior vaginal wall support systems varied along different regions of vaginal wall for all three groups, with the highest compliance found near the vaginal apex and the lowest near the introitus. Women with cystocele had more compliant anterior and posterior vaginal wall support systems than women with rectocele. The movement direction differs between cystocele and rectocele. In cystocele, the anterior vaginal wall moves mostly toward the vaginal orifice in the upper vagina, but in a ventral direction in the lower vagina. In rectocele, the direction of the posterior vaginal wall movement is generally toward the vaginal orifice. Conclusions: Movement of the vaginal wall and compliance of its support is quantifiable and was found to vary along the length of the vagina. Compliance was greatest in the upper vagina of all groups. Women with cystocele demonstrated the most compliant vaginal wall support. © 2014 The International Urogynecological Association.


Luo J.,University of Michigan | Luo J.,Biomechanics Research Laboratory | Betschart C.,University of Michigan | Betschart C.,University of Zürich | And 3 more authors.
International Urogynecology Journal and Pelvic Floor Dysfunction | Year: 2014

Introduction and hypothesis: A method was developed using 3D stress magnetic resonance imaging (MRI) and was piloted to test hypotheses concerning changes in apical ligament lengths and lines of action from rest to maximal Valsalva. Methods: Ten women with (cases) and ten without (controls) pelvic organ prolapse (POP) were selected from an ongoing case - control study. Supine, multiplanar stress MRI was performed at rest and at maximal Valsalva and was imported into 3D Slicer v. 3.4.1 and aligned. The 3D reconstructions of the uterus and vagina, cardinal ligament (CL), deep uterosacral ligament (USL d), and pelvic bones were created. Ligament length and orientation were then measured. Results: Adequate ligament representations were possible in all 20 study participants.When cases were compared with controls, the curve length of the CL at rest was 71 ±16 mm vs. 59±9 mm (p =0.051), and the USLd was 38±16 mm vs. 36±11 mm (p =0.797). Similarly, the increase in CL length from rest to strain was 30±16 mm vs. 15±9 mm (p =0.033), and USLdwas 15±12 mm vs. 7±4 mm (p =0.094). Likewise, the change in USLd angle was significantly different from CL (p <0.001). Conclusions: This technique allows quantification of 3D geometry at rest and at strain. In our pilot sample, at maximal Valsalva, CL elongation was greater in cases than controls, whereas USLd was not; CL also exhibited greater changes in ligament length, and USLd exhibited greater changes in ligament inclination angle. © The International Urogynecological Association 2013.


Hernandez M.E.,Biomechanics Research Laboratory | Hernandez M.E.,USA Mobility | Ashton-Miller J.A.,Biomechanics Research Laboratory | Ashton-Miller J.A.,University of Michigan | And 3 more authors.
Journals of Gerontology - Series A Biological Sciences and Medical Sciences | Year: 2013

Background.Downward reaching may lead to falls in older adults, but the underlying mechanisms are poorly understood. This study assessed differences between younger and older adults in postural control and losses of balance when performing a forward reach to the floor in 2 possible real-world situations, with and without full foot contact with the floor.Methods.Healthy younger (n = 13) and older (n = 12) women reached as fast as possible to a target placed at their maximal forward reaching distance on floor, either standing on their whole foot or on the shortest base of support (BOS) that they were willing to perform a toe touch with.Results.Compared with younger women, older women used a 50% larger BOS when stooping down to touch their toes and had 22% less maximal forward reaching distance on the floor. Older women were twice as likely to lose their balance as younger women while performing a rapid forward floor reach (χ2(2) = 3.9; p <. 05; relative risk = 1.91; 95% CI = 0.99-3.72). Postural sway, measured as center of pressure excursions and center of pressure root mean square error, did not differ between younger and older women anteriorly, but posteriorly, older women decreased their sway in full foot BOS and increased their sway in forefoot BOS (Age × BOS, p <. 05). Leg strength was reduced in older versus younger women and was correlated with maximal reach distance (r =. 65-.71).Conclusions.Healthy older women performing a rapid maximum forward reach on the floor, particularly when using their forefoot for support, are at an increased risk for losing their balance. © The Author 2013.


PubMed | Biomechanics Research Laboratory
Type: Journal Article | Journal: Human movement science | Year: 2012

Rapid center of pressure (COP) movements are often required to avoid falls. Little is known about the effect of age on rapid and accurate volitional COP movements. We hypothesized that COP movements to a target would be slower and exhibit more submovements in older versus younger adults, particularly in posterior versus anterior movements. Healthy older (N=12, mean age=76 years) and young women (N=13, mean age=23 years) performed anterior and posterior lean movements while standing on a force plate, and were instructed to move their COP as fast and as accurately as possible using visual feedback. The results showed that rapid posterior COP movements were slower and had an increased number of submovements and ratio of peak-to-average velocity, in comparison to anterior movements (p<.005). Moreover, older compared to younger adults were 27% slower and utilized nearly twice as many compensatory submovements (p<.005), particularly when moving posteriorly (p<.05). Older women also had higher ratios of peak-to-average COP velocity than young (p<.05). Thus, despite moving more slowly, older women needed to take more frequent submovements to maintain COP accuracy, particularly posteriorly, thereby providing evidence of a compensatory strategy that may be used for preventing backward falls.

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