A Comparison of the In Vivo Contact Pressure at the Tibiotalar Joint During Walking and Running

Category: Ankle Introduction/Purpose: Knowledge of cartilage pressure distribution in healthy ankle joints during gait is important for understanding the loading environment of articular cartilage and for providing a basis for comparison to evaluate how ankle pathology and surgical procedures affect cartilage loading. Finite element models of the ankle have been developed to examine in vitro loads at the tibiotalar joint during simulated standing in healthy and injured ankle joints [1, 2]. However, there are currently no in vivo studies of tibiotalar cartilage pressure during dynamic loading activities. The goal of this study was to develop a subject-specific finite element model of the tibiotalar joint to estimate contact pressure during walking and running. Methods: Informed consent was obtained from one healthy male, age 23 yrs., BMI 27 kg/m2). Synchronized biplane radiographs of the ankle were acquired at 100 and 150 frames per second during the support phase of overground walking and running, respectively, at a self-selected pace (1.5 m/s and 3.0 m/s, respectively). CT-based bone models of the tibia and talus were matched to the stereoradiographic images to precisely track the three-dimensional bone movement [3]. Six degrees-of-freedom joint kinematics were calculated for each bone model, and used to position bone models in the finite element analysis. Cartilage volumes for the distal tibia and proximal talus were created in Geomagic software by extruding the articulating bone surface. Bones were modeled as rigid bodies and cartilage was modeled as deformable bodies with uniform thickness of 1.3 mm [4-7]. Simulations were performed using FEBio software. The primary outcome parameter was peak cartilage pressure in the tibiotalar joint. Results: On average, peak tibiotalar cartilage pressure was approximately 25% greater during the midstance phase of running in comparison to walking (Figure 1). During walking, peak contact pressure occurred on the lateral-central region of the tibiotalar cartilage throughout the entire stance phase. During the early support phase of running, the location of peak contact pressure was also on the lateral-central region of the tibiotalar cartilage. During running push-off, pressure increased in the medial-central cartilage region and the overall peak cartilage pressure increased. Conclusion: A novel finding of this study is that the peak pressure in tibiotalar cartilage moves from the lateral to medial side of the joint during running, but remains on the lateral side throughout the support phase of walking. This suggests that the location and magnitude of the loads seen by tibiotalar joint cartilage are activity dependent, even in the healthy ankle joint. Future work will investigate cartilage loading in pathologic ankles before and after surgical intervention, as well as during other common athletic activities

Characterizing the Maternal Adaptations of Pregnancy and Recovery Following Vaginal Delivery in the Rodent Model

ABSTRACT Pelvic organ prolapse and urinary incontinence are common conditions in women that significantly diminish quality of life. Vaginal delivery and maternal birth injury are the number one risk factors for the development of pelvic floor disorders. The goal of this study was to characterize maternal adaptations throughout pregnancy and recovery after vaginal delivery in terms of the passive quasi-static mechanical properties of the vagina using a rodent model. Virgin (n=8), mid-pregnant (n=7, day 15-16), late-pregnant (n=7, day 20-21), immediate postpartum (n=8, <2 hours post delivery), and 4 week postpartum (n=6) Long-Evans female rats were utilized in this study. The mechanical properties (tangent modulus, tensile strength, ultimate strain, and strain energy density) were quantified by testing longitudinal sections of vaginal tissue to failure. The tangent modulus of virgin animals (25.1±5.1 MPa) was significantly higher compared to mid-pregnant (11.7±7.7 MPa, p=0.003), late-pregnant (7.9±4.0 MPa, p<0.001), and immediate postpartum (8.5±4.7 MPa, p=0.001) animals. A similar trend was also observed in the tensile strength, whereas the ultimate strain increased throughout pregnancy until the time of vaginal delivery. Recovery was observed four weeks postpartum as no significant difference was found from virgin animals for any of the parameters. This study has shown a significant decrease in the tangent modulus and tensile strength along with an increase in the ultimate strain of longitudinal sections of vaginal tissue throughout pregnancy. These maternal adaptations are likely to increase the overall distensibility of the vagina and allow for vagina delivery with minimal injury. This process appears to be effective in the rodent model as the properties recovered to virgin levels by 4 weeks. In the future, we hope to alter these adaptations or exceed them in order to study the risk and impact of birth injury in this model