Alignment of lower-limb prostheses

Alignment of a prosthesis is defined as the position of the socket relative to the other prosthetic components of the limb. During dynamic alignment the prosthetist, using subjective judgment and feedback from the patient, aims to achieve the most suitable limb geometry for best function and comfort. Until recently it was generally believed that a patient could only be satisfied with a unique "optimum alignment." The purpose of this systematic study of lower-limb alignment parameters was to gain an understanding of the factors that make a limb configuration or optimum alignment, acceptable to the patient, and to obtain a measure of the variation of this alignment that would be acceptable to the amputee. In this paper, the acceptable range of alignments for 10 below- and 10 above-knee amputees are established. Three prosthetists were involved in the majority of the 183 below-knee and 100 above-knee fittings, although several other prosthetists were also involved. The effects of each different prosthetist on the established range of alignment for each patient are reported to be significant. It is now established that an amputee can tolerate several alignments ranging in some parameters by as much as 148 mm in shifts and 17 degrees in tilts. This paper describes the method of defining and measuring the alignment of lower-limb prostheses. It presents quantitatively established values for bench alignment position and the range of adjustment required for incorporation into the design of new alignment units.     

A comparative study of conventional and energy-storing prosthetic feet in high-functioning transfemoral amputees

OBJECTIVE: To compare the results of gait analysis, timed walking tests, and socket comfort for transfemoral amputees wearing initially a Multiflex conventional prosthetic foot and then a Vari-Flex energy-storing prosthetic foot. DESIGN: Experimental crossover trial. SETTING: A regional prosthetic and amputee rehabilitation tertiary referral center in a teaching hospital. PARTICIPANTS: Six established unilateral transfemoral prosthetic users. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Gait analysis, a timed walking test, and a Prosthetic Socket Fit Comfort Score for each amputee wearing the Multiflex foot and then repeated wearing the Vari-Flex foot. RESULTS: Wearing the Vari-Flex foot, our subjects walked faster in the gait lab (1.38 +/- 0.13 m/s, P < .001) and took more equal step lengths at fast speed (1.063 +/- 0.05, P < .05). They also had greater peak ankle dorsiflexion at push-off on the prosthetic side (18.3 degrees +/-4.73 degrees, P<.001) and 3 times as much power from the prosthetic ankle at push-off (1.13 +/- 0.22 W/kg, P < .001). There were no significant changes in temporal symmetry or loading of the prosthetic limb, in the timed walking test with each foot, or in the comfort score. CONCLUSIONS: A transfemoral amputee who wears an energy-storing foot can have a more symmetric gait with regard to some measures of spatial symmetry, kinetics, and kinematics than one who wears a conventional foot. However, in this study important aspects such as more symmetric loading and comfort did not differ significantly between the 2 foot types.     

Effects of changes in cadence, prosthetic componentry, and time on interface pressures and shear stresses of three trans-tibial amputees

OBJECTIVE: To evaluate the effects of changes in cadence, prosthetic componentry, and time on interface pressures and resultant shear stresses in trans-tibial amputee case studies. DESIGN: Interface stresses were monitored using custom-designed instrumentation at 13 sites on three subjects with unilateral trans-tibial amputation walking with patellar-tendon-bearing prosthetic limbs. BACKGROUND: Previous studies suggested that week-to-week residual limb changes altered interface stresses more than did alterations in prosthetic alignment. No studies investigating effects of changes in cadence or componentry on interface stress distributions nor comparing their influence with week-to-week changes have been conducted previously. METHODS: Five different prosthetic componentry configurations were tested at each of three cadences in four sessions. Data were analysed for the magnitudes and timings of peak pressures and resultant shear stresses as well as corresponding resultant shear angles. RESULTS: None of the three cadences or five componentry configurations consistently induced significantly (P<0.05) higher or lower interface stress magnitudes for all subjects. However, an Aluminium Pylon/SACH Foot combination compared with an AirStance (pneumatic shank)/Seattle LightFoot unit induced later peak interface stress timings as a percentage of stance phase. Higher and more frequent interface stress changes were seen between the weekly sessions than between different cadences or between different componentry configurations. CONCLUSION: The amputees' capabilities to compensate for week-to-week residual limb changes were less than those for intra-session cadence or componentry alterations. RELEVANCE: Results suggest that effective techniques to accommodate week-to-week residual limb fluctuations could have a greater impact on maintaining consistent interface stress distributions than do adjustments in cadence or componentry.     

Rehabilitation of patients with end-stage renal failure after lower extremity amputation

Four patients with end-stage renal failure on maintenance hemodialysis and one patient with near end-stage renal failure received inpatient rehabilitation following lower extremity amputation. All were prosthetically restored. Three of the patients had bilateral below-knee amputations and were ambulatory at the time of discharge, including the patient with near end-stage renal failure who was on maintenance hemodialysis at follow-up. One unilateral below-knee amputee was also ambulatory at discharge. The other unilateral below-knee amputee had an ulcer on the other foot and used a pylon for transfers only. To assess the prevalence of patients on maintenance hemodialysis with lower extremity amputations, a survey of 310 patients at four dialysis units was performed. Of the 310 patients 2.9 percent had at least one amputated lower extremity and 1.0 percent had bilateral lower extremity amputations. Preliminary data and the potential for functional results following prosthetic restoration suggest the need for further research concerning prosthetic restoration in the lower extremity amputee with end-stage renal failure.     

Biomechanical analysis of the influence of prosthetic feet on below-knee amputee walking

Although energy storing prosthetic feet have achieved widespread clinical acceptance, the effect of these components on the biomechanics of below-knee amputee gait is poorly understood. The purpose of this study was to determine the biomechanical adaptations used by the below-knee amputee while wearing a conventional prosthetic foot and to assess the influence of energy storing prosthetic feet on these adaptations. Mechanical power outputs of the lower extremity in five normal and five below-knee amputee subjects using the SACH, Seattle and Flex feet were studied. Ground reaction forces and kinematic data were collected at a walking speed of 1.5 m/s and were used to determine the muscular power outputs of the lower extremity during stance. Consistent patterns of muscular power output at the hip and knee of the residual limb occur. While wearing the SACH foot, negligible energy generation occurs at the prosthetic foot during pushoff. A decrease in energy absorption at the knee during the first half of stance and an increase in energy generation by the hip extensors were the major adaptations noted in the proximal muscle groups. Compared to the SACH foot, the energy storing feet demonstrated increased energy generation during pushoff. Despite the improvements in the performance of the energy storing prosthetic feet, no significant differences were found in the pattern or magnitude of knee and hip power outputs compared to the SACH foot.     

A comparison of two prosthetic feet on the multi-joint and multi-plane kinetic gait compensations in individuals with a unilateral trans-tibial amputation

OBJECTIVE: To determine the effects of two different prosthetic feet on the three-dimensional kinetic patterns of both the prosthetic and sound limbs during unilateral trans-tibial amputee gait. DESIGN: Eleven individuals with a unilateral trans-tibial amputation participated in two walking sessions: once while using the conventional SAFE foot, the other while using the dynamic Flex foot. BACKGROUND: Despite the wide variation in the design of prosthetic feet, the benefits of these prostheses remain unclear. METHODS: During each test session, peak joint moments and powers in the sagittal, transverse and frontal planes were examined, as subjects walked at a comfortable speed. RESULTS: The majority of the kinetic differences that occurred due to the changing of prosthetic foot type were limited to ankle joint variables in the sagittal plane with greater peak moments and power during propulsion for the Flex foot compared to the SAFE foot. However, effects were also found at joints proximal to the prosthesis (e.g. knee) and differences were also found in the kinetics of the sound limb. CONCLUSION: The dynamic Flex foot allowed subjects to rely more heavily on the prosthetic foot for propulsion and stability during walking with minimal compensations at the remaining joints. RELEVANCE: Determining the biomechanical differences between the conventional and dynamic prosthetic feet may advocate the use of one prosthetic foot type over another. This information, when used in conjunction with subjective preferences, may contribute to higher functioning and greater satisfaction for individuals with a lower limb amputation.     

Rééducation de l’amputé fémoral en fonction du type de genou prothétique

Physiological walking, like the gait of the femoral amputee, must be safe, functional and comfortable. It requires security and stability, efficiency, symmetry of the step, dynamism and mobility. In the transfemoral amputee, prosthetic knees must ensure those objectives of the gait cycle. Four categories of prosthetic knees exist: single axis and lock knee, another one with static control of the stance phase, next one with 5–7 axes and the last one with dynamic control of the stance phase. The choice is based on the activity level of the patient, using on flat ground, slopes and stairways. Knee and foot prosthesis form an inseparable pair during gait. Rehabilitation objectives are improving the balance on the prosthesis to support phase and the correct use of the prosthesis in tilting stage. Principles of rehabilitation vary depending on the type of knee: 1) learn how to use lock-knee should ensure mastery and maximum security; 2) for free knees, common principles of rehabilitation apply to each gait phase - a) during the stance phase, the work of weight bearing is fundamental, completed by the increase of proprioception with the stump-socket couple, the muscle strengthening and rehabilitation of the body’s equilibrium; b) during the swing phase, the regulation of the knee unlock, the control of length of the step and the heel attack moment should be taught. Specific exercises are according to each type of knee prosthesis on flat ground, strong slopes and stairs, incorporating depreciation notions and eccentric or concentric contraction of the gluteus maximus muscle. The global dynamic rehabilitation provides fluidity and optimal speed allowing the patient to gain confidence in prosthesis.     

Custom design in lower limb prosthetics for athletic activity

In summary, the prosthetist is the best source of information with regard to the fast-changing lower extremity prosthetics technology for sports. The needs and desires of the amputee should be outlined and balanced with the cost of the desired components and design. In many cases, one carefully designed prosthesis can serve in dual roles for everyday ambulation and certain athletic activities. In other cases, the amputee is limited severely by a prosthesis that is not designed for a specific activity. Using a prosthesis for activities that it was not designed to accommodate can cause physical injury to the amputee as well as structural failure of the device. A properly designed and fitted prosthesis can open a whole new world of activity to the amputee and helps him or her to reach the desired a vocational goals.     

Sprint kinematics of athletes with lower-limb amputations.

OBJECTIVE: To determine and compare the kinematics of the sound and prosthetic limb in five of the world's best unilateral amputee sprinters. SUBJECTS: Five men, all unilateral lower-limb amputee (one transfemoral, four transtibial) athletes. The individual with transfemoral amputation used a Endolite Hi-activity prosthesis incorporating a CaTech hydraulic swing and stance control unit, a Flex-Foot Modular III, and an ischial containment total contact socket. Those with transtibial amputations used prostheses incorporating a Flex-Foot Modular III and patellar tendon-bearing socket, with silicone sheath liner (Iceross) and lanyard suspension. DESIGN: Case series. Subjects were videotaped sprinting through a performance area. Sagittal plane lower-limb kinematics derived from manual digitization (at 50 Hz) of the video were determined for three sprint trials of the prosthetic and sound limb. Hip, knee, and ankle kinematics of each subject's sound and prosthetic limb were compared to highlight kinematic alterations resulting from the use of individual prostheses. Comparisons were also made with mean data from five able-bodied men who had similar sprinting ability. RESULTS: Sound limb hip and knee kinematics in all subjects with amputation were comparable to those in able-bodied subjects. The prosthetic knee of the transfemoral amputee athlete fully extended early in swing and remained so through stance. In the transtibial amputee athletes, as in able-bodied subjects, a pattern of stance flexion-extension was evident for both limbs. During stance, prosthetic ankle angles of the transtibial amputee subjects were similar to those of the sound side and those of able-bodied subjects. CONCLUSION: Prosthetic limb kinematics in transtibial amputee subjects were similar to those for the sound limb, and individuals achieved an "up-on-the-toes" gait typical of able-bodied sprinting. Kinematics for the prosthetic limb of the transfemoral amputee subject were more typical of those seen for walking. This resulted in a sprinting gait with large kinematic asymmetries between contralateral limbs.     

Development of an integrated CAD-FEA process for below-knee prosthetic sockets

BACKGROUND: Computer-aided design and manufacturing has been successfully used in prosthetic applications since 1980s. It simplifies the socket rectification process and improves reproducibility but does not introduce any new principle into socket design. Integrating finite element analysis to CAD will provide a more objective assessment of socket fit and improve the chance of a successful first fitting. METHODS: Current study aims to establish a finite element model generation technique directly from geometrical information of commercial prosthetic CAD workstation. A program developed in-house automatically performs meshing of the stump geometry and assigns suitable material properties, load and boundary conditions to the model. The model was validated by comparing predicted pressure with experimentally measured values for one amputee subject. FINDINGS: The predicted pressure distribution has an root-mean-square error of 8.8 kPa compared to experimental values at 10%, 25% and 50% of the gait cycle. INTERPRETATION: Current method was able to develop a finite element model to predict interface pressure reasonably well and can be integrated with prosthetic CAD system to provide quantitative feedback to the prosthetist in an automated process.     

Gait patterns of transtibial amputee patients walking indoors barefoot

OBJECTIVE: To evaluate the gait patterns of lower limb amputee patients walking with and without shoes and to identify differences in barefoot gait patterns when using different prosthetic feet. DESIGN: Optoelectronic three-dimensional motion analysis of gait was performed on six transtibial amputees using a solid ankle cushion heel foot and a single-axis foot, both with and without shoes. RESULTS: Gait abnormalities were observed during barefoot walking when the solid ankle cushion heel foot was used. These included knee joint hyperextension of 9.9 +/- 2.0 degrees and the loss of ankle plantar flexion in the early stance phase. When the single-axis foot was used, knee flexion thrust declined from 9.9 +/- 3.7 degrees to 7.2 +/- 3.8 degrees and ankle plantar flexion decreased from 9.9 +/- 2.8 degrees to 7.0 +/- 2.1 degrees during the early stance phase. CONCLUSIONS: In transtibial amputees, significant gait abnormalities were observed during barefoot walking using the solid ankle cushion heel foot. These gait patterns improved, however, with use of a single-axis prosthetic foot, which permits a further plantar flexion after the initial contact.     

Techniques de rééducation des amputés transfémoraux en utilisant des pieds prothétiques avec restitution d’énergie

This article is intended as a review of the most relevant studies investigating the link between the use of prosthetic components and the rehabilitation approaches required to optimize the functional outcome. It provides an overview of the most important characteristics of prosthetics feet and their influence on the rehabilitation outcome and, in conclusion, it describes how the rehabilitation techniques should be applied to increase the effectiveness of use of the prosthesis. In different studies shock-absorption, flexibility, roll-over characteristics and energy return are proven to be important contributors to the functionality of the prosthetic foot. The techniques described in this article have been used on a large population of transfemoral and transtibial amputees and proven to have a positive influence on gait efficiency, balance and overall functionality. The combination of the techniques applied and the prosthetic components used defines the potential functional outcome of the amputee. It is therefore important to consider the rehabilitation of an amputee as a multidisciplinary task divided between rehabilitation doctors, prosthetists, physical therapists and occupational therapists in some cases.     

Below knee prosthetic socket designs and suspension systems

The prosthetic socket must act as a customized connection between the residual limb's surrounding tissues and the prosthetic components. The socket must be designed to control weight bearing, suspension, and ambulation stability. When making a below-the-knee socket, the prosthetist attempts to maximize loading and minimize displacements, such as vertical, transverse, or rotational. This article discusses the engineering designs or shapes of the two basic forms of below-the-knee prosthetic sockets used today.     

New perspectives on nursing lower limb amputees

New perspectives on nursing lower limb amputees arise from the author's researches into amputee rehabilitation and a summary of other recent research findings. These are dealt with in the context of basic amputee treatment and the nursing process. There is new material on the psychological and neurological sequelae of amputation, the practical problems of loss of a limb and the prosthetic dimension of treatment. The patients' reactions to lower limb amputation were found to vary from intense grief to intense relief, many noting it to be of minor or moderate consequence. The model of sudden and shocking loss is largely incorrect. Attention is drawn to an unrecognized ordinariness which should become part of amputee nursing. Patients have many practical problems. These are social and economic, personal and domestic. The ward environment is unsuited to these needs but, working closely with therapists, nurses can do much to facilitate amputee rehabilitation. The modern purpose of amputation surgery is prosthetic replacement. Nurses should be working with some urgency towards uniting patient and prosthesis. Pain and discomfort are underestimated and research shows them to be a major characteristic of amputation continually and for many years after surgery. A variety of pain syndromes are involved.     

Suction socket suspension for below-knee amputees

In this study the current use of suction suspension for below-knee prostheses is examined by means of two questionnaire surveys. The experience of 56 below-knee (B-K) amputees wearing suction socket prostheses is evaluated comparing suction prostheses with previously worn limbs. A high degree of satisfaction was found, with amputees on the whole reporting improved skin condition, diminished pain, and increased activity levels compared to previous prosthetic history. The experience and opinions of 466 certified prosthetist members of the American Orthotist Prosthetist Association are examined in the second survey, including degree of contact, success, and evaluation of problems in using suction suspension for the B-K amputee. This survey indicated limited contact and familiarity with B-K suction suspension, with only 22% stating they had made this type of prosthesis. Prosthetists cited characteristics of the B-K residual limb as the chief deterrent to a successful fitting.     

Biomechanical adaptations of transtibial amputee sprinting in athletes using dedicated prostheses

OBJECTIVE: To determine the biomechanical adaptations of the prosthetic and sound limbs in two of the world's best transtibial amputee athletes whilst sprinting. DESIGN: Case study design, repeated measures. BACKGROUND: Using dedicated sprint prostheses transtibial amputees have run the 100 m in a little over 11 s. Lower-limb biomechanics when using such prostheses have not previously been investigated. METHODS: Moments, muscle powers and the mechanical work done at the joints of the prosthetic and sound limbs were calculated as subjects performed repeated maximal sprint trials using a Sprint Flex or Cheetah prosthesis. RESULTS: An increased hip extension moment on the prosthetic limb, with an accompanying increase in the amount of concentric work done, was the most notable adaptation in Subject 1 using either prosthesis. In Subject 2, an increased extension moment at the residual knee, and an accompanying increase in the amount of total work done, was the most notable adaptation using either prosthesis. This later adaptation was also evident in Subject 1 when using his Sprint Flex prosthesis. CONCLUSIONS: Increased hip work on the prosthetic limb has previously been shown to be the major compensatory mechanism that allow transtibial amputees to run. The increased work found at the residual knee, suggests that the two amputee sprinters used an additional compensatory mechanism. RELEVANCE: These findings provide an insight into the biomechanical adaptations that allow a transtibial amputee to attain the speeds achieved when sprinting.     

Causes and correction of abnormal gait patterns due to prosthesis in above-knee amputees

Abnormal gait patterns cause an increase in the energy cost of walking in above-knee amputees. Disturbances of the walking pattern are often caused both by the amputated patient himself and by incorrect prosthetic fitting. The early detection and correction of causative factors is of great importance for successful rehabilitation of these amputees. During the follow-up examinations the prosthesis must be inspected for a correct fitting and individually appropriate knee stabilizing components. Prior to any corrective measures it must be excluded that the artificial limb has been put on incorrectly by the amputee himself.     

Prosthetics, orthotics, and assistive devices. 3. Prosthetics

This self-directed learning module highlights new advances in prosthetics. It is part of the chapter on prosthetics, orthotics, and assistive devices for the Self-Directed Medical Knowledge Program Study Guide for practitioners and trainees in physical medicine and rehabilitation. This section contains information regarding conventional and myoelectric upper limb prosthetics, above-knee (AK) socket designs and materials, and foot and ankle systems. New advances that are covered in this section include the narrow medial-lateral AK socket, the flexible AK socket, and new prosthetic foot and ankle systems. Proper understanding and clinical application of this technology is essential for the optimal prosthetic rehabilitation of the amputee.