Effect of prosthetic alignment changes on socket reaction moment impulse during walking in transtibial amputees.

The alignment of a lower limb prosthesis affects the way load is transferred to the residual limb through the socket, and this load is critically important for the comfort and function of the prosthesis. Both magnitude and duration of the moment are important factors that may affect the residual limb health. Moment impulse is a well-accepted measurement that incorporates both factors via moment-time integrals. The aim of this study was to investigate the effect of alignment changes on the socket reaction moment impulse in transtibial prostheses. Ten amputees with transtibial prostheses participated in this study. The socket reaction moment impulse was measured at a self-selected walking speed using a Smart Pyramid in 25 alignment conditions, including a nominal alignment (clinically aligned by a prosthetist), as well as angle malalignments of 2°, 4° and 6° (abduction, adduction, extension and flexion) and translation malalignments of 5 mm, 10 mm and 15 mm (lateral, medial, anterior and posterior). The socket reaction moment impulse of the nominal alignment was compared for each condition. The relationship between the alignment and the socket reaction moment impulse was clearly observed in the coronal angle, coronal translation and sagittal translation alignment changes. However, this relationship was not evident in the sagittal angle alignment changes. The results of this study suggested that the socket reaction moment impulse could potentially serve as a valuable parameter to assist the alignment tuning process for transtibial prostheses. Further study is needed to investigate the influence of the socket reaction moment impulse on the residual limb health.

Effect of alignment changes on socket reaction moments while walking in transtibial prostheses with energy storage and return feet.

BACKGROUND: Energy storage and return feet are designed for active amputees. However, little is known about the socket reaction moments in transtibial prostheses with energy storage and return feet. The aim of this study was to investigate the effect of alignment changes on the socket reaction moments during gait while using the energy storage and return feet. METHODS: A Smart Pyramid™ was used to measure the socket reaction moments in 10 subjects with transtibial prostheses while walking under 25 alignment conditions, including a nominal alignment (as defined by conventional clinical methods), as well as angle malalignments of 2°, 4° and 6° (flexion, extension, abduction, and adduction) and translation malalignments of 5mm, 10mm and 15mm (anterior, posterior, lateral, and medial) referenced from the nominal alignment. The socket reaction moments of the nominal alignment were compared with each malalignment. FINDINGS: Both coronal and sagittal alignment changes demonstrated systematic effects on the socket reaction moments. In the sagittal plane, angle and translation alignment changes demonstrated significant differences (P<0.05) in the minimum moment, the moment at 45% of stance and the maximum moment for some comparisons. In the coronal plane, angle and translation alignment changes demonstrated significant differences (P<0.05) in the moment at 30% and 75% of stance for all comparisons. INTERPRETATION: The alignment may have systematic effects on the socket reaction moments in transtibial prostheses with energy storage and return feet. The socket reaction moments could potentially be a useful biomechanical parameter to evaluate the alignment of the transtibial prostheses.

Influence of malalignment on socket reaction moments during gait in amputees with transtibial prostheses.

Alignment - the process and measured orientation of the prosthetic socket relative to the foot - is important for proper function of a transtibial prosthesis. Prosthetic alignment is performed by prosthetists using visual gait observation and amputees' feedback. The aim of this study was to investigate the effect of transtibial prosthesis malalignment on the moments measured at the base of the socket: the socket reaction moments. Eleven subjects with transtibial amputation were recruited from the community. An instrumented prosthesis alignment component was used to measure socket reaction moments during ambulation under 17 alignment conditions, including nominally aligned using conventional clinical methods, and angle perturbations of 3° and 6° (flexion, extension, abduction, and adduction) and translation perturbations of 5mm and 10mm (anterior, posterior, lateral, and medial) referenced from the nominal alignment. Coronal alignment perturbations caused systematic changes in the coronal socket reaction moments. All angle and translation perturbations revealed statistically significant differences on coronal socket reaction moments compared to the nominal alignment at 30% and 75% of stance phase (P<0.05). The effect of sagittal alignment perturbations on sagittal socket reaction moments was not as responsive as that of the coronal perturbations. The sagittal angle and translation perturbations of the socket led to statistically significant changes in minimum moment, maximum moment, and moments at 45% of stance phase in the sagittal plane. Therefore, malalignment affected the socket reaction moments in amputees with transtibial prostheses.

Perception of socket alignment perturbations in amputees with transtibial prostheses.

A person with amputation's subjective perception is the only tool available to describe fit and comfort to a prosthetist. However, few studies have investigated the effect of alignment on this perception. The aim of this article is to determine whether people with amputation could perceive the alignment perturbations of their prostheses and effectively communicate them. A randomized controlled perturbation of angular (3 and 6 degrees) and translational (5 and 10 mm) alignments in the sagittal (flexion, extension, and anterior and posterior translations) and coronal (abduction, adduction, and medial and lateral translations) planes were induced from an aligned condition in 11 subjects with transtibial prostheses. The perception was evaluated when standing (static) and immediately after walking (dynamic) using software that used a visual analog scale under each alignment condition. In the coronal plane, Friedman test demonstrated general statistical differences in static (p < 0.001) and dynamic (p < 0.001) measures of perceptions with angular perturbations. In the sagittal plane, it also demonstrated general statistical differences in late-stance dynamic measures of perceptions (p < 0.001) with angular perturbations, as well as in early-stance dynamic measures of perceptions (p < 0.05) with translational perturbations. Fisher exact test suggested that people with amputation's perceptions were good indicators for coronal angle malalignments but less reliable when defining other alignment conditions.

Evaluating antimicrobials and implant materials for infection prevention around transcutaneous osseointegrated implants in a rabbit model.

Transcutaneous osseointegrated implants can improve function for select amputee patients, but infection serves as a significant limitation of implantable transcutaneous devices. This study examined the efficacy of an antimicrobial, pexiganan acetate (SUPONEX), and a porous tantalum implant material (Trabecular Metal) in preventing pin tract infection of osseointegrated implants in a rabbit model. Thirty-seven rabbits were randomized to three groups: Ti-control group (n = 11) with titanium alloy implant and no antimicrobial, Ti-Pexiganan group (n = 8) with titanium alloy implant and topical pexiganan acetate 1% applied daily at the skin/implant interface, and Ta-control group (n = 18) with porous tantalum implant and no antimicrobial. All implants were placed transcutaneously through skin, muscle, and bone. Rabbits were monitored for infection for 24 weeks. We observed a 75% reduction in rates of pin tract infection in the Ti-Pexiganan group compared to that observed in the Ti-control group (p = 0.019). No difference in rates of infection was observed between the Ta-control group and the Ti-control group (p = 0.230). In conclusion, pexiganan acetate may be an important antimicrobial for transcutaneous osseointegrated implants. Porous tantalum will not likely prevent pin tract infection without additional methods of soft tissue immobilization around the implant site.

Effectiveness of resonance frequency in predicting orthopedic implant strength and stability in an in vitro osseointegration model.

Developing noninvasive tools that determine implant attachment strength to bone and monitor implant stability over time will be important to optimize rehabilitation protocols following insertion of osseointegrated implants in patients with limb loss. While resonance frequency has been previously shown to correlate with implant stability in dental implants placed in the mandible and maxilla, this tool has not been evaluated with implants placed in the medullary canal of long bones. In an in vitro model used to simulate irregular medullary canal implant contact and osseointegration, a strong positive correlation was determined between resonance frequency implant stability quotient values and the force required for implant pushout. The force required for implant displacement also correlated to the distance from the point of fixation to the transducer at the proximal end of the implant (point of resonance frequency monitoring).

The relationship between femoral periprosthetic cortical bone geometry and porosity after total hip arthroplasty.

Stress shielding from the presence of a femoral component can cause adverse changes to cortical bone geometry and porosity leading to increased fracture risk in the periprosthetic cortical bone. The objectives of this study were to determine if porosity increased after total hip arthroplasty along the principal axes, and to determine if a relationship existed between cortical bone porosity and geometry. Ten postmortem donors allowed comparisons of implanted femurs to the contralateral nonimplanted femurs. Transverse cross-sections of the femur were taken at 25, 45, 65, and 85% along the length of the femoral component. The cortical bone principal axes' location (degrees) and rigidity values (mm(4)) were based on cortical bone geometry by using digitized images of the cortical bone cross-sections. Percent porosity was measured along the principal axes using backscatter electron imaging. Cortical bone porosity increased in the more distal sections of the implanted femurs by approximately 3%, but did not preferentially increase along a particular principal axis. No correlation was found between changes in porosity and rigidity values. In conclusion, the porosity increases in the implanted femurs may have regionally reduced cortical bone strength. The locations of higher porosity did not appear related to the cortical bone geometry.