The function of the human foot is described dichotomously as a compliant structure during mid-stance and a stiff lever during push-off. The arch-spring and the windlass mechanisms, respectively, describe each of these behaviours; however, their interaction has not been quantified to date. We hypothesized that by engaging the windlass mechanism with metatarsophalangeal joint (MTPJ) dorsiflexion, we would observe stiffening of the arch and reduced energy absorption and dissipation during dynamic compressions of the foot. Using a custom apparatus, the MTPJ angle was fixed at 30 degrees of plantarflexion, neutral or 30 degrees of dorsiflexion for nine participants, with the shank positioned similarly to the end of mid-stance. The arch was compressed at two speeds, with the faster speed comparable to walking around 1.5 m s Six cameras captured the compression and elongation of the arch, along with other kinematic variables, synchronously with the ground reaction force. Combining these measures, we computed the energy absorbed, returned and dissipated in the arch. Contrary to our hypothesis, when the windlass mechanism was engaged, the arch elongated more, and absorbed and dissipated more energy than when it was not engaged. This engagement of the windlass altered the rotational axis of the mid-foot, which probably oriented the arch-spanning structures closer to their resting length, increasing their compliance. This study provides novel evidence for an interplay between the windlass and arch-spring mechanisms that aids in regulation of energy storage within the foot.

The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia's shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off.

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A statistical shape model of the tibia-fibula complex: sexual dimorphism and effects of age on reconstruction accuracy from anatomical landmarks A statistical shape model was created for a young adult population and used to predict tibia and fibula geometries from bony landmarks. Reconstruction errors with respect to CT data were quantified and compared to isometric scaling. Shape differences existed between sexes. The statistical shape model estimated tibiafibula geometries from landmarks with high accuracy (RMSE = 1.51-1.62 mm), improving upon isometric scaling (RMSE = 1.78 mm). Reconstruction errors increased when the model was applied to older adults (RMSE = 2.11-2.17 mm).Improvements in geometric accuracy with shape model reconstruction changed hamstring moment arms 25-35% (1.0-1.3 mm) in young adults.

BACKGROUND Surgical training requires high‐fidelity models to in vivo. Embalmed cadaveric material has long been used as the standard. However, conventional formalin embalming is known to affect the quality of the tissue, compromising the tissue quality for optimal realistic surgical training. The aim of our study was to qualitatively compare Thiel and phenol‐based soft‐embalming techniques in a surgical training setup and to quantitatively compare the mechanical properties of embalmed skin to fresh tissue state. METHODS Twenty‐eight participants (4 experienced ENT and 6 residents; 8 Orthopaedic residents; 4 experienced OTL; 5 experienced Trauma and 1 resident) were involved in surgical workshops comparing Thiel and phenol‐based embalmed bodies. Participants were asked to evaluate pre‐defined aspects pertaining to their appreciation of the skin quality as the usability for skin dissection and suturing. In parallel, mechanical testing of skin flaps was conducted. Skin flaps were harvested from 6 fresh‐frozen thawed cadaveric upper limbs. Skin flaps from each specimen were divided in 3 equal in size sections; one subsection was refrozen, one was Thiel embalmed and the other one was phenol‐based embalmed. The three tissue states were compared together for each specimen, one month of embalming (n=3) or one year after embalming (n=3). Specimens were preloaded and pre‐conditioned before displacement‐controlled cycles were applied using an axial tensile testing machine (MTS, Eden Prairie, MN, USA). The tensile elasticity (Young's modulus) was calculated between loading and unloading state. Statistical analysis was performed using a two‐ way mixed ANOVA with a Holm‐Sidak correction for multiple comparisons. RESULTS Qualitatively, 18% of participants rated Thiel as more realistic and preferred this model for skin dissection and suturing; 64% preferred Phenol‐based soft‐embalmed; and 18% rated that both embalming states were comparable. Quantitatively, there were significant differences between the embalming techniques (p < 0.05), but no significant difference were made between embalming time (p = 0.47). Thiel embalmed skin had a significantly lower Young's modulus values compared to fresh state (p < 0.0001). There were no significant differences between phenol‐based embalmed skin and fresh state (p = 0.30). CONCLUSION Although there was variability in the relationship between tissue states, fresh and phenol‐based embalmed state were not consistently stiffer than the other, but both were stiffer than the Thiel embalmed samples; Thiel solution caused the samples to be less stiff than the fresh state. Based on our results, phenol‐based soft‐ embalming preserves the integrity of the skin tensile elasticity better, which could explain the better rating of this embalming technique for the practice of surgical exposures, simulated reconstructions and wound closure. Moreover, phenol‐based embalmed specimens can be prepared for a third of the cost and with none of the elaborate setup required for Thiel embalming. This abstract is ...