Effects of alignment on the roll-over shapes of prosthetic feet

Recent work suggests that a prosthetic ankle-foot component's roll-over shape - the effective rocker it conforms to between initial contact and opposite initial contact (the 'roll-over' interval of walking) - is closely linked to its final alignment in the prosthesis (as determined by a skilled prosthetist using heuristic techniques). If true, this information may help to determine the appropriate alignment for a lower limb prosthesis before it is built, or a priori. Knowledge is needed for future models that will incorporate the roll-over shape including the relative effect of alignment on the roll-over shape's radius of curvature and arc length. The purpose of this study was to evaluate the hypotheses that: (i) Changes in prosthesis alignment alter the position and orientation of a foot's roll-over shape in prosthesis-based coordinates, and (ii) these changes occur without changing the radius of curvature or arc length of the roll-over shape. To examine the hypotheses, this study examined the effects of nine alignment settings on the roll-over shapes of two prosthetic feet. The idea that alignment changes move and rotate roll-over shapes of prosthetic feet in prosthesis coordinates is supported by this work, but the hypothesis that the radius of curvature and arc length do not change for different alignments is not strongly supported by the data. A revised approach is presented that explains some of the changes to the roll-over shape parameters due to changes in rotational alignment.     

Characterisation of prosthetic feet used in low-income countries

Eleven kinds of prosthetic feet that were designed for use in low-income countries were mechanically characterised in this study. Masses of the different kinds of prosthetic feet varied substantially. Dynamic properties, including damping ratios and resonant frequencies, were obtained from step unloading tests of the feet while interacting with masses comparable to the human body. Data showed that for walking, the feet can be appropriately modeled using their quasistatic properties since natural frequencies were high compared to walking frequencies and since damping ratios were small. Roll-over shapes, the effective rocker (cam) geometries that the feet deform to under walking loads, were determined using a quasistatic loading technique and a spatial transformation of the ground reaction force's centre of pressure. The roll-over shapes for most of the prosthetic feet studied were similar to the roll-over shape of the SACH (solid-ankle cushioned heel) prosthetic foot. All roll-over shapes showed a lack of forefoot support, which may cause a "drop-off" experience at the end of single limb stance and shorter step lengths of the contralateral limb. The roll-over shapes of prosthetic feet appear useful in characterization of foot function.     

Prosthetic foot roll-over shapes with implications for alignment of trans-tibial prostheses

Roll-over shape is introduced as a significant characteristic of prosthetic feet. The roll-over shapes of the Flexwalk, Quantum, SACH, and SAFE prosthetic feet were determined using three methods; two involving quasi-static loading and one dynamic loading. The results show that foot roll-over shape properties obtained by quasi-static and by dynamic methods are similar. Relationships between foot roll-over shape and the alignment of trans-tibial prostheses are introduced that suggest ways to align trans-tibial prostheses without walking trials and iterations. The relationships may explain what prosthetists attempt to accomplish when they dynamically align a trans-tibial limb. They also explain why prosthetic feet with different mechanical properties usually necessitate different alignments, and may explain why a number of gait studies of trans-tibial amputees do not show major gait differences when walking is executed on various kinds of prosthetic feet.     

Effect of prosthetic ankle units on the gait of persons with bilateral trans-femoral amputations

In able-bodied individuals, the ankle joint functions to provide shock absorption, aid in foot clearance during the swing phase, and provides a rocker mechanism during stance phase to facilitate forward progression of the body. Prosthetic ankles currently used by persons with lower limb amputations provide considerably less function than their anatomical counterparts. However, increased ankle motion in the sagittal plane may improve the gait of persons with lower limb amputations while providing a more versatile prosthesis. The primary aim of this study was to examine and quantify temporal-spatial, kinematic, and kinetic changes in the gait of four male subjects with bilateral trans-femoral amputations who walked with and without prosthetic ankle units. Two prosthesis configurations were examined: (i) Baseline with only two Seattle LightFoot2 prosthetic feet, and (ii) with the addition of Endolite Multiflex Ankle units. Data from the gait analyses were compared between prosthetic configurations and with a control group of able-bodied subjects. The amputee subjects' freely-selected walking speeds, 0.74 +/- 0.19 m/s for the Baseline condition and 0.81 +/- 0.15 m/s with the ankle units, were much less than that of the control subjects (1.35 +/- 0.10 m/s). The amputee subjects demonstrated no difference in walking speed, step length, cadence, or ankle, knee, and hip joint moments and powers between the two prosthesis configurations. Sagittal plane ankle range of motion, however, increased by 3-8 degrees with the addition of the prosthetic ankle units. Compared to the control group, following initial contact the amputee subjects passively increased the rate of energy storage or dissipation at the prosthetic ankle joint, actively increased the power generation at the hip, and increased the extension moment at the hip while wearing the prosthetic ankle configuration. The amputee subjects increased the power generation at their hips, possibly as compensation for the reduced rate of energy return at their prosthetic ankles. Results from subject questionnaires administered following the gait analyses revealed that the prosthetic ankle units provided more comfort during gait and did not increase the perceived effort to walk. The subjects also indicated that they preferred walking with the prosthetic ankle units compared to the Baseline configuration. The results of the study showed that the prosthetic ankle units improved sagittal plane ankle range of motion and increased the comfort and functionality of the amputee subjects' prostheses by restoring a significant portion of the ankle rocker mechanism during stance phase. Therefore, prosthetic ankle mechanisms should be considered a worthwhile option when prostheses are prescribed for persons with trans-femoral amputations.     

Weight distribution of below-knee amputee and able-bodied children during standing.

The purpose of this investigation was to compare weight distributions of a relatively large number of below-knee (BK) amputee and able-bodied children during two different standing positions. Twenty-one BK amputees and 200 able-bodied children volunteered as subjects for this investigation. Each child stood on a pressure plate and three sets of trial data were collected. One set of trial data was collected with both feet together on the pressure plate and two were collected with feet placed 20cm apart. The total force applied by each foot to the pressure plate was normalised by dividing by subject weight to yield foot force to body weight ratios. Data were separated into forefoot and rearfoot areas, force for the forefoot area was then calculated and normalised by dividing by total foot force to yield forefoot to whole-foot force ratios. Ratios for the two foot placement conditions and for non-prosthetic, prosthetic, dominant, and non-dominant feet were compared using paired t-tests (p < 0.05). Results indicated that: 1) BK amputee children placed more weight on their non-prosthetic limb than their prosthetic limb, yet this was not different from able-bodied children in respect of weight distribution between dominant and non-dominant limbs; 2) approximately 90% of the load on the prosthetic foot was placed on the forefoot; and 3) the load on the non-prosthetic foot was evenly distributed between the forefoot and rearfoot like that of able-bodied children. It was concluded that except for substantially more weight on the forefoot of the prosthetic leg BK amputee children stood in the same way as able-bodied children.     

Alignment of trans-tibial prostheses based on roll-over shape principles

The authors examined the roll-over shape alignment hypothesis, which states that prosthetic feet are aligned by matching their roll-over shapes with an "ideal" shape. The "ideal" shape was considered to be the roll-over shape of the able-bodied foot-ankle system. An alignment algorithm and computational alignment system were developed to set trans-tibial alignments based on this hypothesis. Three prosthetic feet with considerably different roll-over shapes were either aligned using the alignment system or not aligned (i.e. used previous foot's alignment), and then were aligned by a team of prosthetists. No significant differences were found between roll-over shapes aligned by the computational alignment system and those based on standard clinical techniques (p = 0.944). Significant differences were found between the "no alignment" shapes and the prosthetist alignment shapes (p = 0.006), and between the "no alignment" shapes and the computational alignment system shapes (p = 0.024). The results of the experiment support the hypothesis that the goal of alignment is to match the prosthetic foot's roll-over shape, as closely as possible, with an "ideal" shape. The hypothesis is also supported by its ability to explain the results of previous studies. Using an "ideal" roll-over shape or surface as a goal for prosthetic alignment could lead to a priori alignment, eliminating the need for alignment hardware in some cases. Being able to build the alignment into a prosthesis without special hardware could be beneficial in low-income countries and in the fabrication of lightweight prostheses for the elderly.     

Prosthetic limb use in Australia 1981-1985 under the Free Limb Scheme

A study has been made of data on 19,421 prosthetic limbs prescribed for 12,143 Australians under the Free Limb Scheme in the years 1981-1985. These prostheses consisted of 18,119 legs and 1,302 arms. The mean age of the lower limb prosthesis user was 52.8 and the upper limb prosthesis user 31.3 years. Males outnumbered females by 3 to 1 in the upper limb prosthesis users, and 2.8 to 1 with lower limb prosthesis users. Below-knee prostheses, patellar-tendon-bearing and thigh-lacing prostheses, made up 58.7% of all prostheses prescribed in the time span. Below-elbow prostheses were the commonest upper limb prostheses with children being the most frequent users. Comparisons with other studies of large number of prosthesis users show an older mean age in Australia and more below-knee prosthesis users than in American studies.     

Shoe adaptation after amputation of the II - V phalangeal bones of the foot

In The Netherlands, about 50% of all amputations of the lower limb are toes and forefoot amputations. Traumata of toes and mid-foot are rare. Preservation of the foot is the primary goal for treatment. Crush injuries of the foot may be associated with prolonged morbidity. This case study presents an insole solution for the solitary first phalangeal bone after amputation of the phalangeal bones II - V. The normal adaptation for forefoot amputations is stiffening of the sole of the shoe and a rocker bar to improve the toe off phase with load reduction of the forefoot. Because the patient had to do excessive stair climbing during work another solution was chosen. As a foot orthosis, a metal soleplate was made in order to have free movement during loading and toe-off during walking. The soleplate gives safety and provides self-adjusting properties after toe off. This enables the shoe technician to make a shoe without a rocker bar or an extra stiff insole. The 0.5 mm custom-made spring-steel plate is also used as a protective in industrial safety shoes. To improve shoe adaptation more research and case reports have to be published in order to inform doctors and shoe technicians about everyday solutions to partial foot amputations.     

Running gait impulse asymmetries in below-knee amputees.

In running, large gait asymmetry is expected due to the inability of the foot prosthesis to comply with the kinematic demands and produce a powerful plantarflexion moment. In this work, interlimb asymmetry in below-knee (BK) amputee running gait was assessed for one rigid and three flexible keel prostheses, using vertical and anteroposterior ground reaction forces and respective impulses. Nine BK amputees and 6 controls participated in this study. The running speed was monitored by two light sensitive detectors while the ground reaction forces were measured with a Kistler force plate. Between the prosthetic side and the sound limb the impulse indicator showed greater asymmetry than the force. Interlimb asymmetry was very much present in all types of prosthesis tested but is less pronounced in the flexible keel prostheses. In the latter, the asymmetry may be associated with the force-time history modulation rather than its magnitude alone. Generally, the impulses better describe interlimb asymmetry and the forces allow a greater discrimination between prosthetic foot types.     

Graphic analysis of forces acting upon a simplified model of the foot

Application of a graphical technique to analyse internal forces on a simplified model of the foot in various external loading patterns. The method is applied when the external load is acting purely upon the forefoot, the hindfoot and on both locations. The pes planus situation and the effect of the "rocker" and inlay sole are studied.     

The functional demands on the intact limb during walking for active trans-femoral and trans-tibial amputees

The aim of this study was to investigate the loading demands placed on the intact limb in terms of joint moments and power for active trans-femoral and trans-tibial amputees in comparison to a group of able-bodied subjects. Four (4) trans-tibial, 4 trans-femoral amputees and 10 able-bodied subjects walked at 1.2m.s(-1) along a walkway whilst kinematic data from both the intact and prosthetic limbs, and kinetic data from the intact limb only were collected. A Panasonic VHS video camera was used to film subjects walking in the sagittal plane with simultaneous force data collected from a Kistler force platform. The amputees were found to compensate for the functional loss of one or more joints by increasing net joint moments and power output on their intact limb compared to able-bodied subjects. At the intact limb ankle, the range of motion, peak dorsiflexor moment and power generation at toe-off increased. At the intact limb knee, power generation during stance and extensor moments and power absorption at toe-off increased. At the intact limb hip, extensor moment and power absorption during stance, and hip flexor moment and power generation at toe-off increased. These findings were partly attributed to the prostheses used but mainly to adaptation mechanisms displayed by trans-femoral and trans-tibial amputees. They have implications for the mobility of amputees and the long term health of their joints. It was recommended that prosthesis design, prosthesis fitting and training in the use of the prosthesis were all factors which could be investigated with a view to minimising intact limb loading.     

Alterations in plantar pressure with different walking boot designs

BACKGROUND: Specialized walking devices, such as total contact casts and removable walking boots, have been shown to be effective noninvasive treatment options for plantar ulcers. Attempts at improving patient compliance frequently lead to new boot designs; however, the effect of the design modifications on plantar pressures or on the contralateral limb often is unknown. The purpose of this study was to determine the effect of different walking-boot calf heights and rocker sole designs on regional plantar pressures, as well as, on contralateral limb loading during walking. METHODS: Twenty-six subjects, 20 to 54 years of age, without foot pathology were tested using four different configurations: high calf, rocker sole (HCR); low calf, rocker sole (LCR); low calf, modified rocker sole (LCMR), and shoe. Peak pressures, pressure-time integrals, and contact areas were measured using the Novel Pedar-X insole pressure measurement system. Average peak force was calculated for the contralateral limb. RESULTS: Greatest forefoot peak pressure reduction was found in the HCR group (37.3% reduction compared to shoe condition), followed by 31.6% and 19.8% in the LCR and LCMR groups, respectively (p<0.0001). Forefoot pressure-time integrals were reduced for HCR and LCR (22.1% and 21.5%, respectively) compared to the LCMR (13.0%) (p<0.0001). CONCLUSIONS: Isolated modifications in walking boot designs resulted in plantar pressure modifications. LCR and LCMR designs favorably altered plantar pressures, but of a lesser magnitude than the HCR design. If lower calf, lower sole walking boot designs are recommended because of anticipated improvement in patient compliance, healing times may be prolonged.     

Radiographic Assessment of Aseptic Loosening of Tumor‐Type Knee Prosthesis in Distal Femur

ObjectiveTo measure the full‐length anteroposterior and lateral radiographs of lower limbs after the resection of a tumor in the distal femur and tumor‐type knee prosthesis replacement and to analyze the factors leading to aseptic loosening of the prosthesis.MethodsA total of 26 cases of tumor‐type knee prosthesis replacement or revision due to the distal femoral tumor at our hospital from January 2007 to December 2019 were retrospectively analyzed. The patients were divided into the loosening and unloosening groups depending on whether aseptic loosening occurred after surgery. Full‐length anteroposterior and lateral radiographs of lower limbs were used to measure bone resection length, length of prosthesis, distance of proximal apex of the medullary stem of the femoral prosthesis from the maximum arc of the anterior femoral arch, diameter of the medullary stem, etc. Data were analyzed, and the risk factors for aseptic loosening of the prosthesis were explored.ResultsThe ratio of the prosthetic length to the femoral length (63.72 ± 5.21) and the ratio of the femoral medullary stem diameter to the femoral diameter (26.03 ± 8.45) were smaller in the loosening group than in the unloosening group. The difference was statistically significant (p < 0.05). The distance between the apex of the medullary stem and the maximum arc of the anterior femoral arch was significantly shorter in the loosening group (3.47 ± 2.96) than in the unloosening group, and the difference was statistically significant (p < 0.05). The measurement of the lower limb alignment showed significant differences between the loosening and unloosening groups in terms of HKAA, mLDFA, and distance between the lower limb alignment and the center of the knee joint (p < 0.05). The logistic regression analysis showed that less than 30% ratio between the medullary stem diameter and the femoral diameter, less than 3 cm distance between the apex of the medullary stem and the maximum curvature of the anterior arch of the femur, distance between the lower limb alignment and the center of the knee joint, and presence of varus knee and valgus knee after the surgery were the risk factors for aseptic loosening of the prosthesis.ConclusionsThe diameter of the femoral medullary stem of the prosthesis, the apex position of the prosthetic stem, and the lower limb alignment are the risk factors for aseptic loosening of the prosthesis.     

The influence of prosthetic foot alignment on trans-tibial amputee gait

An optimally aligned prosthesis, as accomplished by the subjective judgment of the prosthetist, guarantees the best quality of gait. Yet, amputees can adapt to a large variety of geometrical configurations of the prosthetic components. Different external rotation angles of the foot in trans-tibial (TT) prostheses were investigated. The study tried to identify (a) the relationship between foot angle and other gait parameters and (b) the compensating pattern of the amputees to excessive external rotation of the foot. Eight (8) TT amputees, fitted with an identical type of prosthesis, were investigated during ambulation. The prosthetic foot was externally rotated as follows: optimal angle (10.94 x degrees +/- 5.21 degrees), optimal angle plus another 18 degrees, and optimal angle plus another 36 degrees. Analysis of gait was performed with the aid of an electronic walkway. Speed of gait, stance and swing time, and foot angle were monitored in 4 runs for each of the three foot angles. Speed of gait remained almost constant in the three tests. Stance and swing time, as well as step length, significantly changed when 36 degrees were added to the optimal foot angle. This foot position significantly influenced inter-legs time difference and symmetry between the legs. During ambulation, prosthetic foot external rotation was decreased by internal rotation of the limb at the hip joint level. It is concluded that TT amputees can maintain an efficient speed of gait even when the prosthetic foot is malpositioned in excessive external rotation. Although such a malalignment significantly influences other gait parameters during walking, amputees are able to adapt themselves by internal rotation of the hip joint in the amputated leg.     

全髋关节置换术均衡双下肢长度的探讨

目的探讨全髋关节置换术均衡双下肢长度的临床意义和手术设计. 方法回顾性分析2000年3月～2004年10月行单侧全髋关节置换手术患者48例,男26例,女22例,年龄44～82岁,平均64.3岁.股骨头缺血性坏死12例,退变性骨关节炎8例,先天性髋关节发育不良6例,股骨颈头下型骨折20例,其他2例.其中采用骨水泥型假体12例,混合型假体36例.术前双下肢等长30例,患肢短缩1.0～2.0 cm 10例,短缩2.0～4.0 cm 6例,短缩4.0～6.0 cm 2例.通过术前肢体长度测量及X线片测量制定手术方案,选择假体,预估股骨颈长和截骨平面;术中磨削髋臼,寻找最佳旋转中心,结合透视及特殊试验修正截骨平面,调节假体颈长,以均衡双下肢长度. 结果术后获随访3～42个月.采用Harris评分,优30例,良12例,中4例,差2例.术前双下肢等长的30例患者,术后5例患侧延长1.0～2.0 cm,1例延长2.5 cm;术前不等长的18例患者,术后恢复等长10例,患侧延长1.0～2.0 cm 6例,其中2例先天性髋关节发育不良患者术前短缩4.0～6.0 cm,术后仍然短缩2.0～3.0 cm.Harris评分：术后肢体等长的34例患者平均92.3分,术后肢体不等长的14例患者平均88.6分. 结论全髋关节置换术的手术设计、手术技巧及假体设计等诸多因素影响下肢长度,术后肢体不等长降低了患者的满意度.术前测量及术中应用综合评价方法,重视软组织平衡技术和下肢长度调节方法,掌握全髋关节置换术中均衡下肢长度的手术技巧,是进一步提高手术效果的关键.     

A biomechanical study of two postoperative prostheses for transtibial amputees: a custom-molded and a prefabricated adjustable pneumatic prosthesis

We evaluated an adjustable pneumatic prefabricated prosthesis and a rigid custom-molded prosthesis for immediate postoperative use. Twelve transtibial amputations were performed on cadaver limbs. Differential variable reluctance transducers were placed subcutaneously across the wound edge medially and laterally. The limbs were then placed in either the pneumatic prosthesis (five limbs) or the rigid prosthesis (seven limbs). The specimens underwent static and cyclic loading to simulate weight bearing. The strain readings for static and cyclic loading were greater in the rigid prosthetic group. Only the mean medial strain measurement after cyclic loading was statistically significant. The results demonstrate that the pneumatic prosthesis places less strain across the wound than a rigid prosthesis.     

Trans-femoral amputee gait: socket-pelvis constraints and compensation strategies

The paper deals with the identification of motor strategies adopted by trans-femoral amputees to compensate for the constraints of hip motion induced by the interference of the socket with the pelvis and, particularly, with the ischial tuberosity. A group of 11 subjects with trans-femoral amputation, three of whom wore two different prostheses, giving a sample size of 14 cases, were studied by gait-analysis protocols: the present paper focuses on the pelvis-thigh kinematics at foot strike. The results showed that, at the prosthetic side, the hip is significantly less flexed and less extended, respectively, at the ipsilateral and contralateral foot strike. Moreover, the pelvis is significantly more anterior tilted at sound foot strike. The anterior step length showed a decreased sound limb anterior step in 12 out of 14 cases. The authors interpret these results as a combination of mechanical constraints and compensatory actions: the reduced prosthetic hip extension is determined by the mechanical constraint involved in the pelvis-socket interference; and the increased pelvis tilt and sound hip flexion occurring at the same time are compensating strategies, adopted by the amputees, in order to obtain a functional step length and symmetrical thigh inclinations. Those factors determine a gait pattern which is functional, only slightly slower than normal gait, and without any perceivable alterations. On the other hand, the authors show that the increased pelvis tilting necessarily overloads the lumbar tract of the spine and may be related to the frequent occurrence of low-back pain in amputee subjects, despite the positive functional gait recovery.     

Foot skin blood flow following infrainguinal revascularization for critical lower limb ischemia.

INTRODUCTION: The aim of this study was to assess the blood flow in the feet before and after lower limb revascularization using laser Doppler imaging (LDI). METHODS: Ten patients with critical lower limb ischemia were prospectively enrolled from June to October 2004. All patients underwent successful unilateral surgical interventions including above-knee bypass, distal bypass and endarterectomy. Skin blood flow (SBF) over the plantar surface of both forefeet and heels was measured by LDI 24h before and 10 days after revascularization, expressed in perfusion units (PU), and reported as mean+/-SD. RESULTS: Measurements in the forefoot and heel were similar. Before revascularization mean SBF was significantly lower in the ischemic foot (130+/-71 PU) compared to the contralateral foot (212+/-68 PU), p<0.05. After revascularization a significant increase of the SBF in the forefoot (from 135+/-67 to 202+/-86 PU, p=0.001) and hindfoot (from 148+/-58 to 203+/-83, p=0.001) was observed on the treatment side. However, a large decrease of the SBF was seen in forefoot and hindfoot on the untreated side (from 250+/-123 PU to 176+/-83 and from 208+/-116 to 133+/-40, p=0.001, respectively). CONCLUSION: This study confirms the benefits of revascularization in patients with nonhealing foot lesions due to critical limb ischemia. A significant increase of the SBF was observed on the treatment side. However, an unexpected decrease was observed on the untreated side.