CONSERVATION OF HERITAGE MASONRY IN CANADA: A CURRENT PERSPECTIVE

Canada is a young country with respect to its built heritage. The need to conserve examples of its structures as a record of the history of settlement and growth has been recognized for some time by the somewhat small conservation community. The heritage conservation sector is growing compared to new construction. Unfortunately, there is a distinct lack of professional expertise (architects and engineers) familiar with the older traditional construction materials and methods, leading to some recommendations with respect to heritage structures being inconsistent with conservation principles. There is even less knowledge with respect to understanding how modern interventions will affect the construction supposedly being conserved. There is therefore a need for education in conservation principles and methodology. Two new programs are described, one at the undergraduate level at Carleton University, and the other at the graduate level at the University of Calgary. Both of these programs are being developed with advice from the Heritage Conservation Directorate of Public Works and Government Services Canada. The potentially negative consequences of the current lack of expertise for heritage structures are compounded by the current system for deciding whether or not a structure has heritage value. The system is inconsistent across the country, depending on how the guidelines interpreted and enforced. The federal and provincial and some municipal governments have collaborated in establishing guidelines for their areas of responsibility, but there is no overarching regulation for the protection of heritage across the country

DOES IN VIVO LIGAMENT FORCE PASS THROUGH LIGAMENT INSERTIONS?: A ROBOTIC STUDY

INTRODUCTION Post traumatic osteoarthritis (PTOA) is a subset of osteoarthritis that arises after traumatic joint injury. Approximately half of patients suffering from anterior cruciate ligament (ACL) injuries have been shown to progress towards PTOA within fifteen years[1]. One of the areas of research for PTOA is examining the biomechanical changes following an ACL injury. A recent study[2] examined the effects of ACL transection (ACLx) in an ovine model. In vivo stifle joint motions were recorded, and recreated in vitro using a novel robotic testing platform. Joint and tissue loads were simultaneously recorded during reproduction of in vivo joint motion[2]. This novel approach was shown to be able to reproduce in vivo motions within less than 0.1° and 0.1mm[2].   The main objective of the present study was to determine if in vivo ligament forces, obtained using the principle of superposition, pass through respective ligament insertional footprints. This study evaluated the accuracy of the measured ligament forces, as they should pass through their bony insertions. This accuracy was examined for medial and lateral collateral ligaments (MCL and LCL), and posterior cruciate ligament (PCL) in ACLx sheep.   METHODS Stifle joints from N=4 sheep that had been previously examined in ACLx kinematics studies were digitized using a coordinate measuring machine. The ligament insertional areas were thoroughly recreated in 3D space, along with the spatial position of the kinematic measurement device. Anatomic coordinate systems were defined on the femur and the tibia. These data were then exported to MATLAB scripts for further analysis. The ligament insertional areas were approximated as planes using least squares regression technique. The intersection of the ligament force vectors with the plane approximations were then calculated. The direction of a ligament force was deemed accurate if the distance between the calculated intersection and footprint centroid was within a determined threshold. A preliminary threshold was calculated as the maximum distance between the centroid and measured points of the footprint. RESULTS Analysis of the data indicated that the technique increases in accuracy for high ligament loads (Figure 1). That is to say as the ligament loads increase, the intersection-centroid distance is reduced. For lower ligament loads (mainly within the “toe” region of the ligament force-displacement behavior), however, the method requires further refinement. DISCUSSION AND CONCLUSIONS This study indicated that the method requires further refinement based on the limitations induced currently. Preliminary data shows that accuracy increases as ligament load magnitudes increase as well. Finding the intersections on plane approximations of the insertional footprints can lead to very large error when the planes approach a parallel state. In these states, a small angular change in force direction can cause a very large change in intersection-centroid distance. Each ligament and its insertions have different functions and geometries, and as such require separate limitations. Future studies would require modifications to the analysis method to account for the limitations involved with the current method

DEVELOPMENT OF A LOADING DEVICE FOR IMAGING RABBIT MCL ENTHESES WITH SECOND HARMONIC GENERATION MICROSCOPY

INTRODUCTION Entheses are transitional structures in the body between a flexible material and a much stiffer material: ligament and bone, respectively. A gradual transition of mineral content and collagen fibre organization enables the enthesis to dissipate stress concentrations and transfer load between the adjoining elements, contributing to normal joint function [1]. Damage to this small region is associated with conditions like tennis elbow and jumper’s knee. Enthesis tears do not repair well, causing long term weakness. To date, the challenge of observing entheses under applied load has inhibited understanding of their mechanical behaviour. Second Harmonic Generation (SHG) microscopy is a technology that can be used to image highly polarizable proteins like collagen without the need for section fixation or molecular excitation [2]. Given that collagen fibre structure affects load transfer at entheses, SHG microscopy is an ideal tool to elucidate the fibre structure at MCL entheses. The purpose of the project described was to develop a custom device to allow observation of the collagen fibre network of the rabbit medial collateral ligament (MCL) enthesis in the SHG microscope as tensile load is applied. METHODS After generating a morphological chart of alternative solutions, the optimal option was chosen based on project requirements. The design was created with CAD software (SolidWorks 2015) and where possible, the proposed design was modified to optimize objectives— minimizing cost and maximizing movement accuracy. With CAD, it is easy to modify components of a model while assessing its impact on the model as a whole. RESULTS In the final design, the rabbit bones can be secured to bone pots at a physiological angle of 70°, with the MCL in the line of action of the applied force. One bone pot remains stationary as the other, sliding on rail guides which constrain pot movement, is pulled by a linear actuator. A custom load cell will collect force data as the load is applied. For its light-weight property and potential to be scanned using MRI, Perspex is the material of choice for the device. The completed design, shown in Figure 1, satisfies all the requirements previously established and requires only one hand for operation. This model allows for a testing procedure simulating physiological conditions while maximizing accuracy of the recorded data through incorporating rail guides and making use of a linear actuator. DISCUSSION AND CONCLUSIONS With some minor modifications to the bone pots, this device can be used as a reference product for the study of other tissues under load. However, it would be worthwhile to consider interchanging the bone pots between uses since the bone cement is difficult to remove. The small size of entheses has stymied researchers’ efforts to characterize their inhomogeneous material behavior. However, this device will enable the observation of collagen fibre behaviour under load, which will provide insight into mechanisms of load transfer in the enthesis and in time, contribute to improved surgical attachment procedures

CONTROLLING INFLAMMATION WITH DEXAMETHASONE AFTER ANTERIOR CRUCIATE LIGAMENT INJURY

INTRODUCTION Anterior Cruciate Ligament (ACL) injuries are increasingly common, with about 250 000 ACL ruptures occurring per year in the US [1]. The current treatment for ACL rupture is ACL reconstructive surgery (ACL-R), which aims to successfully restore the biomechanical function of the knee. However, individuals who suffer from ACL injuries, including those who undergo ACL reconstruction, have a 50% chance of developing osteoarthritis (OA) within 10-20 years [2]. Inflammation of the knee joint has been hypothesized to be a factor [3]. Dexamethasone (DEX) is a type of corticosteroid used to control inflammation [4]. The purpose of this study was to determine if DEX treatment following anterior cruciate ligament reconstruction was an effective mechanism of long-term joint protection against the progression of osteoarthritis. METHODS Six female Suffolk cross sheep were allocated into one of three groups: sham surgery, idealized ACL-R surgery, and control. Surgeries were previously accomplished by arthrotomy to the right stifle joint. Animals that underwent idealized ACL reconstructive surgery received a single injection of DEX at the time of the surgery. At 2 weeks post surgery animals were sacrificed and cartilage samples were harvested from both standard as well as visibly damaged locations on the patella (PAT), femoral groove (FG), lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibial condyle (LTC), and medial tibial condyle (MTC). These samples were then blinded and graded by three experienced observers on the modified Mankin scale. This scale gives a grade out of 24 based on four categories: safranin-O staining, structure, cell density, and cluster formation. ANOVA with Bonferroni post-hoc analysis was used to determine differences in histological scores between groups, using SPSS 19.0.   RESULTS The average histological grades (and standard deviations) for the PAT, FG, LTP, MTP, LFC, and MFC are displayed in Figure 1. No significant differences were observed between the sham (n=2), ACL-R + DEX (n=2), and control groups in all locations. DISCUSSION AND CONCLUSIONS The similarity between the ACL-R+DEX and control groups indicates that DEX treatment has the potential to have a protective effect against the progression of OA, however further studies must be conducted to ensure long-term efficacy. Increasing the sample size as well as looking at longer time points is recommended to better understand the effect of dexamethasone on the progression of osteoarthriti

USING THE RESERVOIR WAVE APPROACH TO STUDY THE HORIZON EFFECT

INTRODUCTION Differing theories and models have been explored in the field of arterial hemodynamics in an effort to better understand how the blood flows in the body. The existence of discrete reflection sites remains a source of disagreement. As a wave proceeds along an artery, any local change in impedance will result in partial reflection. Thus, because of the great complexity of the arterial system, it has been suggested that no distinct reflector sites should exist. On the other hand, there is recent experimental evidence using the reservoir-wave approach (RWA) that implies discrete positive and negative reflection sites. The pattern of wave propagation and reflection is plausible, as are the modifications produced by pharmacologic interventions [1]. The classical, frequency-domain, “impedance analysis” approach uses Fourier analysis to break down pressure and flow waveforms into summations of sinusoids, resulting in an impedance spectrum [2]. The RWA is a novel alternative, positing that measured pressures and flows are the instantaneous sums of “excess” (wave-related) and reservoir (volume-related) components [2]. The “Horizon Effect” (HE) [3] implies that a reflector site can never be reached no matter how far into the periphery one measures (Figure 1). As such, it supports the idea that there are no distinct reflector sites. Measuring peripheral pressure and flow and using the RWA, the purpose of this study was to evaluate the HE and the question of fixed reflector sites. METHODS Eight anesthetized pigs were catheterized and pressure and flow were measured simultaneously at 4 locations: the aortic root and the brachial, carotid and renal arteries. Pharmacologic interventions were used to manipulate propagation and reflection patterns. MatLab (The MathWorks Inc., Natick, MA) was used to calculate the reservoir pressure, the local wave speed and to carry out wave intensity analysis (WIA) to obtain the forwards and backwards components of pressure. RESULTS Analysis has been completed on 4 of the 8 animals studied. Each showed minimal backward wave activity at the aortic root and in the carotid artery. However, in the brachial and renal arteries, no backward waves could be detected. DISCUSSION AND CONCLUSIONS Backward waves were scarcely detected in the periphery using either the RWA or classical analysis. This may suggest that the pig model was inappropriate to study the HE. Porcine anatomy does not allow measurement at remote peripheral sites and reflection sites cannot be studied if no reflections are to be found. Further analysis of the data is needed before more definitive conclusions can be made

LONG TERM IN VIVO KINEMATICS OF THE OVINE STIFLE JOINT FOLLOWING ANTERIOR CRUCIATE LIGAMENT TRANSECTION

INTRODUCTION Osteoarthritis (OA) is a degenerative joint disease involving the breakdown of articular cartilage, which is common after injury or with aging1. Following knee injury, sheep develop OA at a slightly accelerated rate compared to humans but with some similar patterns2. In an ovine knee injury model3,4, altered gait mechanics and degradation of the cartilage has been observed 20 weeks post anterior cruciate ligament (ACL) transection (Tx) surgery; however, potential alterations in gait at 40 weeks post ACL Tx surgery remain to be determined. Therefore, the objective of this study was to investigate the in vivo kinematics of the ovine stifle joint over time (20 weeks and 40 weeks) following ACL Tx. METHODS Force Plate Testing. Three skeletally mature 3 to 4-year-old female Suffolk-cross sheep (average weight 77.1kg) were led across an embedded force platform (Kistler Instrumente, Winterthur, Switzerland) until 20 hind limb hoof strikes were recorded at 1200 Hz. Peak hind limb vertical ground reaction force was determined prior to surgical plate implantation, and then serially prior to each kinematic data collection. Surgical Procedure. All sheep had a bone plate implanted onto each of the proximomedial aspect of the tibia and the distolateral aspect of the femur of their right hind limb, four weeks prior to kinematic testing. Kinematic Collection and Bone Digitization. On the day of kinematic testing, a stainless steel post was attached to each plate and an instrumented spatial linkage (ISL) mounted between them. The ISL consisted of six rotational encoders providing a measurement of position and orientation in six degrees of freedom (6-DOF) to its motion throughout gait. The in vivo kinematics of the stifle joint were measured while the sheep walked on a treadmill at 2 mph (0.89 m/s). Each sheep then underwent arthroscopic ACL Tx surgery on their right hind limb. The in vivo gait kinematics were measured again over time at 20 and 40 weeks post ACL Tx. Following kinematic testing at 40 weeks, the animals were euthanized. A coordinate measuring machine was used to measure anatomic landmarks on the bone with respect to the ISL in order to create an anatomically relevant coordinate system. Analysis. Data are presented as mean ± SD. RESULTS Figure 1: The 6-DOF in vivo gait kinematics of the ovine stifle joint, intact (black), 22 weeks post ACL Tx (red), and 40 weeks post ACL Tx (blue). DISCUSSION AND CONCLUSIONS These data indicate that the in vivo kinematics of the ovine stifle joint do change over time following ACL Tx. The kinematic changes appear to be more drastic after 22 weeks, and do not entirely return back to pre-injury mechanics in all rotations and translations after 40 weeks. As shown in Figure 1, the medial-lateral as well as posterior-anterior translation of the joint is progressively altered post ACL Tx over time. Rotationally, the internal-external kinematic curve at 22 weeks is dissimilar to the intact motion, however by 40 weeks a recovery towards the intact measurement is seen as the animal compensates for the injury. In the future, principal component analysis will be utilized to compare these gait changes. In conclusion, the transection of the ACL causes long-term changes in the in vivo kinematics of the joint. Alterations of the kinematics may result in degradation of cartilage due to abnormal loading of the joint and overall damage in the joint due to compensation of the instability post ACL Tx, which is a painful and destructive condition

Failure of the cores of partially reinforced masonry under lateral cyclic loading

Partially reinforced masonry (PRM), consists of grout filled reinforced cores, bond and lintel beams, and unreinforced masonry panels. Even though the reinforced cores are designed to carry out-of-plane flexure caused by the horizontal loads, the behaviour of PRM to loading is neither well defined nor well understood, particularly the response of the lightly reinforced cores. Therefore the response of the reinforced cores of PRM to constant axial and cyclic lateral loading was studied. The mode of failure, the hysteretic moment-curvature curves and the bond characteristics of the reinforcing bars are presented in this paper