|Quantitative analysis of hemodynamic state and muscle atrophy of residual limb after trans-femoral amputation
|Wong, M. S. (BME)
Zhang, Ming (BME)
Leung, K. L. Aaron (BME)
|Hong Kong Polytechnic University -- Dissertations
Leg -- Amputation
Leg -- Blood-vessels
|Department of Biomedical Engineering
|xi, 250 pages : color illustrations
|Amputation is defined as a destructive surgical procedure that removes the limbs which have lost the physiological function and activity or have endangered the life safety. After the lower limb amputation, no matter what the reason and the level, amputees would face many complex postoperative problems and various potential complications, such as edema, blisters, ulcers and other skin problems, deep tissue injury, muscle atrophy, etc. Among these problems, the most prevalent clinical issue is residual limb (RL) muscle atrophy. Continuous changes of the RL shape and volume caused by muscle atrophy would lead to many negative consequences, especially in patients' rehabilitation, and also greatly increase the expense and time cost for fitting prosthesis. To carry out systematic and thorough investigation on muscle atrophy and other RL problems, the lower limb blood circulation system is a crucial factor from the physiological and biomechanical point of view. It nourishes the entire lower extremity musculoskeletal system while it could be a major cause of amputation. In addition, the emergence of those RL issues usually involves blood circulation disorders, vascular lesions and other angioneurotic issues. In fact, the spatial structure of RL arterial tree has undergone tremendous changes after amputation, and that would inevitably cause the changes of endovascular hemodynamic parameters and lead to high possibility that the blood flow within RL is different from sound limb (SL). Therefore, this thesis launched a comprehensive study focusing on the muscle atrophy and arterial hemodynamic state of thigh RL (trans-femoral level), including the analysis of the correlation between their morphological changes, the flow field comparison and discussion of each main artery based on three kinds of numerical model and calculation method. Through the case study of 8 unilateral trans-femoral amputees, the morphological indices analysis of muscle atrophy, artery narrowness, and their relationship was carried out. The collected data showed that after trans-femoral amputation, the degree of atrophy of each RL muscle was different: the quadriceps were larger and the hamstrings were smaller. The change of each main artery of RL was also different: the superficial femoral artery was the largest while the deep femoral artery or medial femoral circumflex artery was the smallest. Meanwhile, the case difference in both muscles and arteries mainly depended on the use of prosthesis. Those subjects not using prostheses showed greater atrophy degree gaps between muscles but smaller stenosis degree gaps between arteries. Based on the blood nourishing relationship, the subjects using prostheses exhibited positive correlation between muscle atrophy and the narrowness of its main blood-supply artery. However, this kind of correlation was not clear in the subjects who did not use prostheses. Thereafter, the Hausdorff distance was applied to quantify the spatial difference of arterial tree in comparing the vessel deformation between two follow-up subjects, and between their SLs and RLs. The results demonstrated that the subject wearing prosthesis presented greater arterial tree deformation in the RL than in the SL, and the bilateral deformation degree gap decrease over time while the subject not using prosthesis showed an opposite result. These phenomena implied that the key impact factor on bilateral arterial tree deformation could be the mobility pattern of the amputee --- prostheses usage. Through these two sections of morphological investigation, the findings suggested that using prostheses not only achieve the functional compensation for RL effectively, but also promote the physiological adjustment of the muscles and arteries in both lower limbs in order to accommodate a new gait and body balance, and facilitate the original bipedal locomotion.
In the hemodynamic study section, this research performed three kinds of numerical simulation method on the bilateral thigh main arteries of Case-1 and Case-2: the steady flow calculation of 3D models, the unsteady flow calculation of 3D-constant resistance (3D-CR) coupling models and 3D- three-element Windkessel (3D-WK) coupling models. The results of the 3D models showed that, under steady flow conditions, there are significant differences in the numerical results and phenomena between the two cases, especially in the value ranges of wall pressure (WP) and wall shear stress (WSS). However, their common findings were that, the arterial tree bifurcation site and the upper half of the deep femoral artery of RL displayed high WP, low WSS and disordered velocity fields that could induce high risk for arterial diseases. By comparing the results of unsteady flow of the 3D-CR models and 3D-WK models with the measured ultrasonic data of Case-1 in a cardiac cycle, it illustrated that the 3D-CR models could achieve a qualitative description of pulse wave propagation, but the 3D-WK models had obvious advantage in the accuracy of numerical results. Therefore, the following summaries were drawn from the 3D-WK models coupling calculation results of Case-1 and Case-2: the WP of bilateral arterial trees were at the highest level during the rapid ejection period; from slow ejection period, larger low shear stress areas (LSSAs) appeared in RL with lower WSS value compared with SL; the velocity field disturbance in the bifurcation segment of RL was more severe than that of SL, and RL displayed more disordered secondary flow directions at the cross sections near the bifurcation site. These results demonstrated that the occurrence of atherosclerosis and other vascular lesions could be greater in RL than in SL, especially in the high-risk zones with LSSAs which located at the arterial tree bifurcation site and the upper half of deep femoral artery. The differences of the two cases were summarized as: Case-1's WSS state in SL was better than that in RL, while Case-2 had similar bilateral WSS situations; Case-2 exhibited larger bilateral LSSAs with lower WSS values than in Case-1. In addition to the same high-risk sites with Case-1, the upper half of lateral femoral circumflex artery in Case-2's both limbs was also susceptible to vascular diseases. From the above findings, amputees without using prosthesis might have greater chance of arterial lesions and larger bilateral high-risk areas than prosthesis users. The conclusion and main contribution of this thesis are summarized as follows: (1) after trans-femoral amputation, patients using prosthesis showed a positive correlation between RL muscle atrophy and blood-supply artery narrowness, and exhibited a joint adjustment of the spatial structures of bilateral arterial trees during the follow-up period that showed prosthesis usage being a key factor affecting the states of RL muscles and arteries. Thus, it is necessary to consider vascular system and blood flow in the studies focusing on lower RL especially related to prosthesis design; (2) the chance of various arterial lesions was found greater in RL than that in SL, especially in the high WP, low WSS, disordered velocity field zones which located at the arterial tree bifurcation site and the upper half of deep femoral artery but how to reduce the risk of vascular diseases in RL needed further researches; (3) since the range, the distribution and the changes of various hemodynamic parameters in a cardiac cycle were found different between RL and SL, the hemodynamic state of RL deserved more in-depth and meticulous targeted research; (4) compared with prostheses users, amputees without using prosthesis could have greater chance of arterial lesions in both SL and RL; (5) in each phase of a cardiac cycle, the values and distributions of WP, WSS and blood flow velocity were different, thus the qualitative analysis for above single parameter could employ the characteristic velocity in different phases to perform relatively simple steady flow calculation on the 3D model; (6) as for multi-scale coupling calculation, the 3D-CR model should have the function to describe the pulse wave propagation, and the availability to illustrate the qualitative hemodynamic states in a cardiac cycle, but the 3D-WK model could provide obvious advantage in numerical precision, especially in RL. Therefore, according to specific research objectives, the 3D-CR model or 3D-WK model could be selected by considering the measured data, calculation scale and time consuming, etc. The findings of this thesis, including the descriptions of RL muscle atrophy, artery narrowness and potential vascular lesion areas, together with full discussion on the hemodynamic state of bilateral main arteries and suggestions for the numerical study methodology of lower limb arteries, would provide useful reference data and theoretical support for lower limb amputation researches involving muscle and blood flow situations, and could give some inspirations for various clinical and biomedical studies to eventually promote the comprehensive rehabilitation.
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