Introduction: Une procédure fréquente pour la prévention de l’arthrose de la cheville est une ostéotomie corrective du tibia distal (SMOT). Le Distal Tibia Nail (DTN ; Mizuho®), a été développé pour la réduction des fractures du tibia distal. L’objectif de ce projet était d’analyser la faisabilité du DTN pour des procédures SMOT effectuées avec une ouverture médiale (MWO). Méthodes : Au total 16 Sawbones® ont été instrumentés par un DTN ou une plaque (MDTP, Synthes®), suivi par la simulation d’une MWO. Quatre phases d’expérimentation étaient définies : Phase-0, Sawbones sans implant ni MWO ; Phase-1, échantillons avec un implant et MWO. Phase-2, les échantillons de la Phase-1 avec le cortex latéral fracturé ; Phase-3, simulation d’une fracture de type A3. La raideur et le mouvement inter-fragmentaire (IFM) étaient analysés. Des tomographies des échantillons ont été prises à Phases 0 et 1. Résultats : Jusqu’à 80% de différence était présente enter les Sawbones® de Phase-0 ; dans les Phases 1 et 2, des différences importantes se sont montrées entre des implants mais équivalent à <2 mm d’IFM. Le DTN a démontré une résistance très élevée aux charges appliquées en comparaison avec le MDTP pour la fixation des fractures A3. Des facteurs expérimentaux tels que la raideur initiale des Sawbones®, l’axe de chargement, et le positionnement de l’échantillon dans la machine d’essai, peuvent tous avoir une influence importante sur la raideur mesurée. Conclusion : Le DTN peut être considéré comme option pour la fixation des SMOT effectués avec un MWO. Des études futures doivent faire attention aux conditions limites ayant un effet sur des critères d’évaluation et des conclusions tirées / Introduction: Supra-malleolar corrective osteotomies (SMOT) are a common surgical procedure for the prevention of early onset of ankle arthritis. The Distal Tibia Nail (DTN; Mizuho®), was previously developed for the reduction of distal tibia fractures. The aim of this project was to identify error sources in biomechanical testing, and to test the feasibility of the DTN for SMOT performed using the medial wedge opening (MWO) technique. Methods: A total of 16 Sawbones® were each implanted with either a DTN or medial distal tibia plate (MDTP; Synthes®), and a MWO simulated. Four testing phases were defined: Phase-0, testing of Sawbones® without implant/osteotomy; Phase-1, samples with MWO and implant; Phase-2, Phase-1 samples with lateral cortex fractured; Phase-3, samples with an A3 type fracture. Stiffness construct and interfragmentary movement (IFM) were analysed. CT scans were taken of the samples at Phases 0 and 1. Results: Up to 80% difference was noticed between Sawbones® samples in Phase-0; in Phases 1 and 2 significant differences were found between stiffness constructs of the implant groups but this amounted to <2 mm IFM. The DTN was significantly more resistant to compression and torsion when supporting an A3 fractures (Phase-3). Elements such as original Sawbones® stiffness construct, implant position, potting material, loading axis, and sample positioning can have a high influence on measured stiffness and bias the results. Conclusion: The DTN is a viable option for the fixation of SMOT performed with a MWO technique. Future studies should pay careful attention to boundary conditions affecting outcomes measures and drawn conclusions

Background Running is a popular form of exercise that more than 55 million Americans actively participate. Endurance running like marathon and half- marathon is getting increasingly popular among active runners. Although the effect of running is considered beneficial to bone health, the direct relationship between strains and strain gradients occurred during long distance running and bone changes is still not clear. Especially, given a high rate of injury associated with the first-time marathon, understanding the direct effect of strain stimuli on bone health is an important issue. Based on the previous studies, we hypothesized that the higher values of strain will induce bone adaptation more effectively and will lead to higher bone osteogenic changes. Since osteocytes sense shear stress caused by the interstitial fluid flow, which is created by the deformations, and regulate activities of osteoblasts and osteoclast that govern bone adaptation, we also hypothesized that the local strain gradient will create pressure differences within the interstitial fluid network and will increase fluid flow. Furthermore, due to that increased fluid flow, the regions with the higher strain gradient will experience a higher amount of bone adaptation. Thus, in this study, our purpose was to define the effect of the strains and strain gradients on bone changes within distal tibia, which is the most prone anatomical site to low risk stress fracture, during training for first-time marathon. Methods High-resolution and low-resolution computed tomographic (CT) images of the distal tibia were obtained before and after a self-selected training from runners who were actively training to participate in their first-time marathon in the next calendar year. The low resolution scan covered a 69.864 mm length of the distal end of the tibia while the high resolution CT scan covered a 9.02 mm region of the distal tibia. Using low resolution CT image based subject specific finite element (FE) models, the strains and strain gradients of the distal tibia at the instance of the peak ground reaction force (GRF) were calculated. The baseline and follow-up high resolution CT scans were used in high resolution peripheral quantitative CT (HRpQCT) analysis and the estimation of bone changes over the training period. Finally, the effect of strains and strain gradients on the distal tibia bone changes was estimated based on the FE model driven strain values and HRpQCT analysis driven bone changes. We used a linear mixed model to define the relationship between strain values and bone changes in the distal tibia. Results The strain values that occurred during marathon training had significant effects on bone changes in the distal tibia. Particularly, the strain gradients showed a higher effect than the strains. In the cortical compartment, the strain gradients, which were calculated as a strain difference of a node from the surrounding nodes (Strain Gradient-1), affected the bone mineral density (BMD) negatively, and per 1000 µε increase resulted in 2.123% decrease in the cortical BMD. The strain gradients, which were calculated as a strain difference of a node from the surrounding nodes normalized to distance to surrounding nodes (Strain Gradient-2), presented a positive effect on the cortical bone volume with a slope of 4.335% / 1000 µε. In the trabecular compartment, the strain gradient-1 showed negative effects on the percent change in BMD and bone mineral density (BMC), whereas the strain gradient-2 showed positive effects on the percent change in BMD and BMC. Conclusion The linear mixed model analysis revealed a statistically significant (p < 0.05) relationship between strain gradients that occurred during running and distal tibia bone changes. The strains, biometrics, and initial parameters of bone did not show any significant effect on the bone changes. The connection between local strain environment and bone changes in the distal tibia investigated in this study is an important step to understand the mechanism of mechanically induced bone adaptation.

Background Running is a popular form of exercise that more than 55 million Americans actively participate. Endurance running like marathon and half- marathon is getting increasingly popular among active runners. Although the effect of running is considered beneficial to bone health, the direct relationship between strains and strain gradients occurred during long distance running and bone changes is still not clear. Especially, given a high rate of injury associated with the first-time marathon, understanding the direct effect of strain stimuli on bone health is an important issue. Based on the previous studies, we hypothesized that the higher values of strain will induce bone adaptation more effectively and will lead to higher bone osteogenic changes. Since osteocytes sense shear stress caused by the interstitial fluid flow, which is created by the deformations, and regulate activities of osteoblasts and osteoclast that govern bone adaptation, we also hypothesized that the local strain gradient will create pressure differences within the interstitial fluid network and will increase fluid flow. Furthermore, due to that increased fluid flow, the regions with the higher strain gradient will experience a higher amount of bone adaptation. Thus, in this study, our purpose was to define the effect of the strains and strain gradients on bone changes within distal tibia, which is the most prone anatomical site to low risk stress fracture, during training for first-time marathon. Methods High-resolution and low-resolution computed tomographic (CT) images of the distal tibia were obtained before and after a self-selected training from runners who were actively training to participate in their first-time marathon in the next calendar year. The low resolution scan covered a 69.864 mm length of the distal end of the tibia while the high resolution CT scan covered a 9.02 mm region of the distal tibia. Using low resolution CT image based subject specific finite element (FE) models, the strains and strain gradients of the distal tibia at the instance of the peak ground reaction force (GRF) were calculated. The baseline and follow-up high resolution CT scans were used in high resolution peripheral quantitative CT (HRpQCT) analysis and the estimation of bone changes over the training period. Finally, the effect of strains and strain gradients on the distal tibia bone changes was estimated based on the FE model driven strain values and HRpQCT analysis driven bone changes. We used a linear mixed model to define the relationship between strain values and bone changes in the distal tibia. Results The strain values that occurred during marathon training had significant effects on bone changes in the distal tibia. Particularly, the strain gradients showed a higher effect than the strains. In the cortical compartment, the strain gradients, which were calculated as a strain difference of a node from the surrounding nodes (Strain Gradient-1), affected the bone mineral density (BMD) negatively, and per 1000 µε increase resulted in 2.123% decrease in the cortical BMD. The strain gradients, which were calculated as a strain difference of a node from the surrounding nodes normalized to distance to surrounding nodes (Strain Gradient-2), presented a positive effect on the cortical bone volume with a slope of 4.335% / 1000 µε. In the trabecular compartment, the strain gradient-1 showed negative effects on the percent change in BMD and bone mineral density (BMC), whereas the strain gradient-2 showed positive effects on the percent change in BMD and BMC. Conclusion The linear mixed model analysis revealed a statistically significant (p < 0.05) relationship between strain gradients that occurred during running and distal tibia bone changes. The strains, biometrics, and initial parameters of bone did not show any significant effect on the bone changes. The connection between local strain environment and bone changes in the distal tibia investigated in this study is an important step to understand the mechanism of mechanically induced bone adaptation.

Introduction: Below knee amputation is the safest treatment for aggressive benign and malignant bone tumours of the distal tibia yielding good oncological and functional results. However, in selected patients where limb salvage is feasible and amputation unacceptable to the patient, limb salvage using a distal tibial replacement (DTR) can be considered. This study aims to present the oncological and functional results of the use of this treatment method in our unit. Patients &amp; Methods: A retrospective folder review was performed for all 10 patients who received a modular distal tibial replacement between 01/01/2005 and 31/01/2019 for a primary bone tumour either benign aggressive or malignant. Six were female and the mean age was 31 (1275) years. There were five patients with giant cell tumour of bone, four with osteosarcoma and one with a low-grade chondrosarcoma. The patients with osteosarcoma had neo-adjuvant chemotherapy before surgery. Function was assessed by the Musculoskeletal Tumor Society (MSTS) score. Results: There were six females and four males, with a mean age of 31 (12-75) years. Two patients had local recurrence treated with a BKA and one other patient died of metastases three years postoperatively. At a mean follow-up of three years, the remaining eight patients had a mean MSTS score of 83% (67–93%). There were no radiological signs of loosening, and no revision surgeries. Conclusion: Endoprosthetic replacement of the distal tibia for primary bone tumours can be a safe treatment option in very selected cases.

Dual energy X-ray absorptiometry (DXA) has been well established in both clinical and research settings for measurement of bone mineral density (BMD), and is becoming more widely utilized for assessment of body composition. Reliability and validity are essential factors in both applications of this technique; however, neither have been confirmed for the QDR-4500A DXA at Virginia Tech. Therefore, measurements of the whole body (WB), lumbar spine (LS), total proximal femur (TPF) and total forearm (TF) were made in a group of young-adult males and females at two time-points, 5-7 days apart. Significant differences were not found in BMD (g/cm2) at these body sites with repeated measurements by DXA. Furthermore, measures of percent body fat (%BF), lean body mass (LBM), and fat mass (FM) by DXA were reliable. Validity of %BF by DXA was assessed from comparison to single-frequency bioelectrical impedance analysis (BIA). Significant differences were not found in measures of %BF by DXA and BIA. A second study investigated the reliability and validity of the QDR-4500A DXA in measurements of distal tibia (DT) BMD. Significant differences were not found between repeated measurements. Validity was established by a significant correlation between WB BMD and DT BMD. A third study examined the influence of navel jewelry on the accuracy of LS DXA measurements. Repeated measurements with a spine phantom revealed that both a navel ring and a barbell produced significantly greater measures of LS BMD compared to the spine phantom alone. Manual correction of navel jewelry did not eliminate BMD inaccuracies. Data from these studies confirmed that the QDR-4500A DXA at Virginia Tech was a reliable and valid device in measurement of WB, LS, TPF, TF and DT BMD, as well as %BF, LBM, and FM. In addition, effects of navel jewelry on LS BMD have been recognized. Further studies investigating the reliability and validity of DT BMD measures as well as effects of different types, gauges, and shapes of body jewelry on BMD measures in human subjects are warranted. / Master of Science