Patient-specific analyses of deep tissue loads post transtibial amputation in residual limbs of multiple prosthetic users

Active transtibial amputation (TTA) patients are at risk for developing pressure ulcers (PU) and deep tissue injury (DTI) while using their prosthesis. It is therefore important to obtain knowledge of the mechanical state in the internal soft tissues of the residuum, as well as knowledge of the mechanical state upon its surface. Our aim was to apply patient-specific MRI-based non-linear finite element (FE) models to quantify internal strains in TTA prosthetic users (n=5) during load-bearing. By further employing a strain injury threshold for skeletal muscle, we identified patients susceptible to DTI. The geometrical characteristics of the residuum of the TTA participants varied substantially between patients, e.g. the residuum lengths were 7.6, 8.1, 9.2, 11.5 and 13.3 cm. We generally found that internal strains were higher in the bone proximity than in the muscle flap periphery. The highest strains, which in some patients exceeded 50% (engineering strain) for compressive, tensile and shear strains, were found in the shortest residual limbs, i.e. the 7.6 and 8.1 cm-long limbs. Correspondingly, the lowest strains were found in the 13.3 cm-long residuum, which had the bulkiest muscle flap. Yet, even in the case of a long residuum, about a third of the soft tissue volume at the distal tibial proximity area was occupied by large (>5%) internal compressive, tensile and shear strains. For both patients with shorter residual limbs, the internal principal compressive strains above 5% occupied almost the entire distal tibial proximity area. For a patient whose distal tibial end was flat (non-beveled), internal strains were more uniformly distributed, compared to the strain distributions in the other models, where focal elevated strains accumulated in the bone proximity. We found no muscle strains above the immediate injury threshold, indicating that all patients were not at immediate risk for DTI. Two patients whose residuum fat padding was minimal to none, were the only ones identified as theoretically prone to DTI at long (>3 h) continuous weight-bearing periods. We conclude that there is a wide variability in internal mechanical conditions between residual limbs across subjects, which necessitates patient-specific quantitative analyses of internal mechanical states in TTA patients, to assess the mechanical performance of the reconstructed limb and in particular, the individual risk for deep PU or DTI.     

Load transfer mechanics between trans-tibial prosthetic socket and residual limb--dynamic effects

The effects of inertial loads on the interface stresses between trans-tibial residual limb and prosthetic socket were investigated. The motion of the limb and prosthesis was monitored using a Vicon motion analysis system and the ground reaction force was measured by a force platform. Equivalent loads at the knee joint during walking were calculated in two cases with and without consideration of the material inertia. A 3D nonlinear finite element (FE) model based on the actual geometry of residual limb, internal bones and socket liner was developed to study the mechanical interaction between socket and residual limb during walking. To simulate the friction/slip boundary conditions between the skin and liner, automated surface-to-surface contact was used. The prediction results indicated that interface pressure and shear stress had the similar double-peaked waveform shape in stance phase. The average difference in interface stresses between the two cases with and without consideration of inertial forces was 8.4% in stance phase and 20.1% in swing phase. The maximum difference during stance phase is up to 19%. This suggests that it is preferable to consider the material inertia effect in a fully dynamic FE model.     

A finite element model of the lower limb during stance phase of gait cycle including the muscle forces

Background

Results of finite element (FE) analyses can give insight into musculoskeletal diseases if physiological boundary conditions, which include the muscle forces during specific activities of daily life, are considered in the FE modelling. So far, many simplifications of the boundary conditions are currently made. This study presents an approach for FE modelling of the lower limb for which muscle forces were included.

Methods

The stance phase of normal gait was simulated. Muscle forces were calculated using a musculoskeletal rigid body (RB) model of the human body, and were subsequently applied to a FE model of the lower limb. It was shown that the inertial forces are negligible during the stance phase of normal gait. The contact surfaces between the parts within the knee were modelled as bonded. Weak springs were attached to the distal tibia for numerical reasons.

Results

Hip joint reaction forces from the RB model and those from the FE model were similar in magnitude with relative differences less than 16%. The forces of the weak spring were negligible compared to the applied muscle forces. The maximal strain was 0.23% in the proximal region of the femoral diaphysis and 1.7% in the contact zone between the tibia and the fibula.

Conclusions

The presented approach based on FE modelling by including muscle forces from inverse dynamic analysis of musculoskeletal RB model can be used to perform analyses of the lower limb with very realistic boundary conditions. In the present form, this model can be used to better understand the loading, stresses and strains of bones in the knee area and hence to analyse osteotomy fixation devices.

     

Residual stress distribution in rabbit limb bones

The presence of the residual stresses in bone tissue has been noted and the authors have reported that there are residual stresses in bone tissue. The aim of our study is to measure the residual stress distribution in the cortical bone of the extremities of vertebrates and to describe the relationships with the osteon population density. The study used the rabbit limb bones (femur, tibia/fibula, humerus, and radius/ulna) and measured the residual stresses in the bone axial direction at anterior and posterior positions on the cortical surface. The osteons at the sections at the measurement positions were observed by microscopy. As a result, the average stresses at the hindlimb bones and the forelimb bones were 210 and 149 MPa, respectively. In the femur, humerus, and radius/ulna, the residual stresses at the anterior position were larger than those at the posterior position, while in the tibia, the stress at the posterior position was larger than that at the anterior position. Further, in the femur and humerus, the osteon population densities in the anterior positions were larger than those in the posterior positions. In the tibia, the osteon population density in the posterior position was larger than that in the anterior position. Therefore, tensile residual stresses were observed at every measurement position in the rabbit limb bones and the value of residual stress correlated with the osteon population density (r=0.55, P<0.01).     

Strains and stresses in sub-dermal tissues of the buttocks are greater in paraplegics than in healthy during sitting

A pressure-related deep tissue injury (DTI) is a severe pressure ulcer, which initiates in muscle tissue overlying a bony prominence (e.g. the ischial tuberosities, IT) and progresses outwards through fat and skin, unnoticed by the paralyzed patient. We recently showed that internal strains and stresses in muscle and fat of individuals at anatomical sites susceptible to DTI can be evaluated by integrating Open-MRI scans with subject-specific finite element (FE) analyzes (Linder-Ganz et al., Journal of Biomechanics, 2007); however, sub-dermal soft tissue strains/stresses from paraplegics are still missing in literature. We hypothesize that the pathoanatomy of the buttocks in paraplegia increases the internal soft tissue loads under the IT, making these patients inherently susceptible to DTI. We hence compared the strain and stress peaks in the gluteus muscle and fat tissues under the IT of six healthy and six paraplegic patients, using the coupled MRI-FE method. Peak principal compression, principal tension, von Mises and shear strains in the gluteus were 1.2-, 3.1-, 1.4- and 1.4-fold higher in paraplegics than in healthy, respectively (p<0.02). Likewise, peak principal compression, principal tension, von Mises and shear stresses in the gluteus were 1.9-, 2.5-, 2.1- and 1.7-fold higher for the paraplegics (p<0.05). Peak gluteal compression and shear stresses decreased by as much as 70% when the paraplegic patients moved from a sitting to a lying posture, indicating on the effectiveness of recommending such patients to lie down after prolonged periods of sitting. This is the first attempt to compare internal soft tissue loads between paraplegic and healthy subjects, using an objective standardized bioengineering method of analysis. The findings support our hypothesis that internal tissue loads are significantly higher in paraplegics, and that postural changes significantly affect these loads. The method of analysis is useful for quantifying the effectiveness of various interventions to alleviate sub-dermal tissue loads at sites susceptible to pressure ulcers and DTI, including cushions, mattresses, recommendations for posture and postural changes, etc.     

Design and analysis of orthogonally compliant features for local contact pressure relief in transtibial prostheses

A very attractive advantage of manufacturing prosthetic sockets using solid freeform fabrication is the freedom to introduce design solutions that would be difficult to implement using traditional manufacturing techniques. Such is the case with compliant features embedded in amputee prosthetic sockets to relieve contact pressure at the residual limb-socket interface. The purpose of this study was to present a framework for designing compliant features to be incorporated into transtibial sockets and manufacturing prototypes using selective laser sintering (SLS) and Duraform material. The design process included identifying optimal compliant features using topology optimization algorithms and integrating these features within the geometry of the socket model. Using this process, a compliant feature consisting of spiral beams and a supporting external structure was identified. To assess its effectiveness in reducing residual limb-socket interface pressure, a case study was conducted using SLS manufactured prototypes to quantify the difference in interface pressure while a patient walked at his self-selected pace with one noncompliant and two different compliant sockets. The pressure measurements were performed using thin pressure transducers located at the distal tibia and fibula head. The measurements revealed that the socket with the greatest compliance reduced the average and peak pressure by 22% and 45% at the anterior side distal tibia, respectively, and 19% and 23% at the lateral side of the fibula head, respectively. These results indicate that the integration of compliant features within the socket structure is an effective way to reduce potentially harmful contact pressure and increase patient comfort.     

Effects of sitting postures on risks for deep tissue injury in the residuum of a transtibial prosthetic-user: a biomechanical case study

Transtibial amputation prosthetic-users are at risk of developing deep tissue injury (DTI) while donning their prosthesis for prolonged periods; however, no study addresses the mechanical loading of the residuum during sitting with a prosthesis. We combined MRI-based 3D finite element modelling of a residuum with an injury threshold and a muscle damage law to study risks for DTI in one sitting subject in two postures: 30°-knee-flexion vs. 90°-knee-flexion. We recorded skin-socket pressures, used as model boundary conditions. During the 90°-knee-flexion simulations, major internal muscle injuries were predicted (>1000 mm³). In contrast, the 30°-knee-flexion simulations only produced minor injury ( < 14 mm³). Predicted injury rates at 90°-knee-flexion were over one order of magnitude higher than those at 30°-knee-flexion. We concluded that in this particular subject, prolonged 90°-knee-flexion sitting theoretically endangers muscle viability in the residuum. By expanding the studies to large subject groups, this research approach can support development of guidelines for DTI prevention in prosthetic-users.     

Effects of intramuscular fat infiltration, scarring, and spasticity on the risk for sitting-acquired deep tissue injury in spinal cord injury patients

Sitting-acquired deep tissue injury (DTI) is a severe form of pressure ulcer (PU) often affecting patients with spinal cord injury (SCI) who also tend to suffer from intramuscular fat infiltration, soft tissue scarring (due to previous PU), and/or muscle spasticity in their buttocks. We previously used finite element (FE) modeling to evaluate whether abnormal bodyweight is a risk factor for sitting-acquired DTI. Here we hypothesize that fat infiltration, scarring, or spasms increase internal loads in the gluteus muscles in the vicinity of the ischial tuberosities during sitting, which consequently put SCI patients with these conditions at a higher risk for DTI. Our objective was to determine changes in gluteal strains and stresses and tissue volumes exposed to elevated strains/stresses associated with these factors. Thirty-five FE models of coronal slices through the seated buttocks, simulating these conditions at different severities, were developed. We calculated peak strains and stresses in glutei and percentage volumes of muscle tissue exposed to above-critical strains/stresses (compression strain≥50%, compression/von Mises stress≥2?kPa, and strain energy density≥0.5?kPa). Progressive intramuscular fat infiltration increased all the aforementioned outcome measures. Increase in size of scar patterns that were contained in both muscle and fat tissues similarly elevated the outcome measures. Spasms increased muscle stresses and volumetric exposures to stress, but tissue volumes at risk were ～1-2% and increases due to spasticity were slight. We conclude that the above potential risk factors can be listed according to the following order of importance: (i) fat infiltration, (ii) scars contained in both muscle and fat tissues, and (iii) spasms. This information should be considered when prioritizing prevention means and resources for patients with SCI.     

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 during gait in transfemoral and knee-disarticulation prostheses: Case series

The alignment of a lower-limb prosthesis is critical to the successful prosthetic fitting and utilization by the wearer. Loads generated by the socket applied to the residual limb while walking are thought to be different in transfemoral and knee-disarticulation prostheses. The aim of this case series was to compare the socket reaction moments between transfemoral and knee-disarticulation prostheses and to investigate the effect of alignment changes on them. Two amputees, one with a transfemoral prosthesis and another with a knee-disarticulation prosthesis, participated in this study. A Smart Pyramid™ was used to measure socket reaction moments while walking under 9 selected alignment conditions; including nominally aligned, angle malalignments of 6° (flexion, extension, abduction and adduction) and translation malalignments of 15 mm (anterior, posterior, medial and lateral) of the socket relative to the foot. This study found that the pattern of the socket reaction moments was similar between transfemoral and knee-disarticulation prostheses. An extension moment in the sagittal plane and a varus moment in the coronal plane were dominant during stance under the nominally aligned condition. This study also demonstrated that alignment changes might have consistent effects on the socket reaction moments in transfemoral and knee-disarticulation prostheses. Extension and posterior translation of the socket resulted in increases in an extension moment, while abduction and lateral translation of the socket resulted in increases in a varus moment. The socket reaction moments may potentially serve as useful biomechanical parameters to evaluate alignment in transfemoral and knee-disarticulation prostheses.     

Eyelids and eye socket reconstruction using the expanded forehead flap and scapha composite grafting.

After trauma or excision of malignant tumor, it is difficult to achieve satisfactory results when reconstructing deformed eyelids and the socket for an ocular prosthesis. The authors demonstrate examples of successful reconstruction for a prosthetic eye that provided adequate and aesthetic soft-tissue support achieved by applying a three-step surgical procedure of reconstruction of the eye socket, the eyelids, and the tarsus and eyelid margin. Because it is highly vascularized and its distal end can be divided into two or three portions for easy three-dimensional reconstruction, the expanded forehead flap alone, with a galea flap, or with a free rectus abdominis muscle perforator flap was used. The expanded forehead flap also provides excellent thin upper lid contour and good color-matching with a recipient site. For the eye socket, sufficient volume of tissue was provided from the expanded forehead flap with or without a galea or a free rectus abdominis muscle perforator flap, and a deep and convex fornix was formed. This resulted in a good fit and in stability of the ocular prosthesis. The surface and the inner lining of the eyelids were reconstructed using portions of the expanded forehead flap. For the tarsus and eyelid margin, conventional reconstruction techniques use cartilage of the concha, which has limitations of length and which does not fit the shape of the tarsal margin. The authors used the scapha composite graft, and a natural shape and good elasticity resulted.     

Characterization of in vivo strain in the rat tibia during external application of a four-point bending load.

This paper describes a technique for characterizing strains and stresses induced in vivo in the rat tibia during application of an external four-point bending load. An external load was applied through the muscle and soft tissue with a four-point bending device, to induce strain in a 11 mm section of the right tibiae of ten adult female Sprague-Dawley rats. Induced strains were measured in vivo on the lateral surface of the tibia. Inter-rat difference, leg positioning and strain gage placement were evaluated as sources of variability of applied strains. Beam bending theory was used to predict externally induced in vivo strains. Finite element analysis was used to quantify the magnitude of shear stresses induced by this type of loading. There was a linear relationship between applied load and induced in vivo strains. In vivo strains induced by external loading were linearly correlated (R2 = 0.87) with the strains calculated using beam bending theory. The finite element analysis predicted shear stresses at less than 10% of the longitudinal stresses resulting from four-point bending. Strains predicted along the tibia by finite element analysis and beam bending theory were well-correlated. Inter-rat variability due to tibia size and shape difference was the most important source of variation in induced strain (CV = 21.6%). Leg positioning was less important (CV = 9.5%).     

Variation in fibular robusticity reflects variation in mobility patterns

During hominin plantigrade locomotion, the weight-bearing function of the fibula has been considered negligible. Nevertheless, studies conducted on human samples have demonstrated that, even if less than that of the tibia, the load-bearing function of the fibula still represents a considerable portion of the entire load borne by the leg. The present study assesses whether variation in habitual lower limb loading influences fibular morphology in a predictable manner. To achieve this, both fibular and tibial morphology were compared amongst modern human athletes (field hockey players and cross-country runners) and matched sedentary controls. Peripheral quantitative computed tomography was used to capture two-dimensional, cross-sectional bone images. Geometric properties were measured at the midshaft for each bone. Results show a trend of increased fibular rigidity from control to runners through to field hockey players. Moreover, relative fibular robusticity (fibula/tibia) is significantly greater in hockey players compared with runners. These results are likely the consequence of habitual loading patterns performed by these athletes. Specifically, the repeated directional changes associated with field hockey increase the mediolateral loading on the lower leg in a manner that would not necessarily be expected during cross-country running. The present study validates the use of the fibula in association with the tibia as a mean to provide a more complete picture of leg bone functional adaptations. Therefore, the fibula can be added to the list of bones generally used (tibia and femur) to assess the correspondence between mobility patterns and skeletal morphology for past human populations.     

急诊绿色通道对胫腓骨开放骨折治疗效果的分析

目的:比较开通急诊绿色通道与同期常规急诊处置治疗胫腓骨开放骨折的效果,探讨急诊绿色通道对开放骨折合理处置的意义。方法:对2016年1月至2017年12月通过绿色通道处置的35例胫腓骨开放骨折患者的治疗效果进行总结分析,并选取同期按照常规急诊诊疗流程进行处置的52例胫腓骨开放骨折患者作为对照。比较和分析两组患者的接诊至手术时间、死亡率、保肢率、骨折愈合率、并发症发生率和下肢功能评分的差异。结果:87例患者中,62例获得6-24个月(平均12.6个月)的完整随访,其中绿色通道组33例,对照组29例。绿色通道组接诊至手术平均时间5.2±1.8 h,显著短于对照组的49.6±15.4 h(P0.05)。两组各有1例患者死亡,死亡率无显著差异(P0.05)。绿色通道组的保肢率(100%)和骨折愈合率(90.9%)显著高于对照组(79.3%和6.90%)(P0.05)。对照组血栓形成、伤口感染、骨不连、关节功能障碍等并发症的发生率为51.7%显著高于绿色通道组18.2%(P0.05)。参照下肢Johner-wruhs疗效评定标准,绿色通道组优良率为81.2%,显著高于对照组48.3%(P0.05)。结论:胫腓骨开放骨折常伴随神经、血管以及皮肤软组织等复合损伤,通过开通急诊绿色通道能够显著提高治疗成功率,降低肢体伤残,有效节约治疗时间。     

Method for the design and analysis of a non-linear anisotropic lower limb prosthetic socket

A simplified computer-based structural analysis procedure has been developed for evaluating the stresses in a lower limb prosthetic socket when subjected to external loads. This technique has been tested by studying a simple linear axisymmetric shell subjected to uniform loads. It was found that the stress and strain distributions obtained are close to those determined by a finite element technique. The method that has been proposed involves an incremental procedure, which can be used to analyse the behaviour of a prosthetic socket of irregular shape made from non-linear anisotropic materials. By employing the proposed procedure to study an example, in which a simplified lower limb prosthetic socket is subject to internal pressure and frictional forces, the effects of the material non-linearity have been found to be significant.     

A general model for estimating lower extremity inertial properties of individuals with transtibial amputation

Lower extremity joint moment magnitudes during swing are dependent on the inertial properties of the prosthesis and residual limb of individuals with transtibial amputation (TTA). Often, intact limb inertial properties (INTACT) are used for prosthetic limb values in an inverse dynamics model even though these values overestimate the amputated limb’s inertial properties. The purpose of this study was to use subject-specific (SPECIFIC) measures of prosthesis inertial properties to generate a general model (GENERAL) for estimating TTA prosthesis inertial properties. Subject-specific mass, center of mass, and moment of inertia were determined for the shank and foot segments of the prosthesis (n = 11) using an oscillation technique and reaction board. The GENERAL model was derived from the means of the SPECIFIC model. Mass and segment lengths are required GENERAL model inputs. Comparisons of segment inertial properties and joint moments during walking were made using three inertial models (unique sample; n = 9): (1) SPECIFIC, (2) GENERAL, and (3) INTACT. Prosthetic shank inertial properties were significantly smaller with the SPECIFIC and GENERAL model than the INTACT model, but the SPECIFIC and GENERAL model did not statistically differ. Peak knee and hip joint moments during swing were significantly smaller for the SPECIFIC and GENERAL model compared with the INTACT model and were not significantly different between SPECIFIC and GENERAL models. When subject-specific measures are unavailable, using the GENERAL model produces a better estimate of prosthetic side inertial properties resulting in more accurate joint moment measurements for individuals with TTA than the INTACT model.     

A theoretical model to study the effects of cellular stiffening on the damage evolution in deep tissue injury

Pressure induced deep tissue injury (DTI) is a severe form of pressure ulcers that is hard to detect in early stages and difficult to prevent and treat. High prevalence figures are partly due to a lack of understanding of pathological pathways involved in DTI. The aim of this study was to investigate, whether changes in material properties of damaged tissue can play a role in DTI aetiology. A numerical model was developed based on muscle microstructure and tissue engineering experiments. A time dependent damage law was proposed and stiffening of dead cells incorporated. The results obtained in the microstructural investigations were used to include the stiffening information in a pre-existing macroscopic model based on animal experiments, which correlated strains to tissue damage measured in the tibialis anterior muscle in rat limbs. With the modelling approach employed in this paper, the damaged area in the rat limb models increased up to 1.65-fold and the rate of damage progression was up to 2.1 times higher in microstructural simulations when stiffening was included.     

Modelling the effect of repositioning on the evolution of skeletal muscle damage in deep tissue injury

Deep tissue injury (DTI) is a localized area of tissue necrosis that originates in the subcutaneous layers under an intact skin and tends to develop when soft tissue is compressed for a prolonged period of time. In clinical practice, DTI is particularly common in bedridden patients and remains a serious issue in todays health care. Repositioning is generally considered to be an effective preventive measure of pressure ulcers. However, limited experimental research and no computational studies have been undertaken on this method. In this study, a methodology was developed to evaluate the influence of different repositioning intervals on the location, size and severity of DTI in bedridden patients. The spatiotemporal evolution of compressive stresses and skeletal muscle viability during the first 48 h of DTI onset was simulated for repositioning schemes in which a patient is turned every 2, 3, 4 or 6 h. The model was able to reproduce important experimental findings, including the morphology and location of DTI in human patients as well as the discrepancy between the internal tissue loads and the contact pressure at the interface with the environment. In addition, the model indicated that the severity and size of DTI were reduced by shortening the repositioning intervals. In conclusion, the computational framework presented in this study provides a promising modelling approach that can help to objectively select the appropriate repositioning scheme that is effective and efficient in the prevention of DTI.     

Estimation of accuracy of patient-specific musculoskeletal modelling: case study on a post polio residual paralysis subject

For patients with patterns ranging out of anthropometric standard values, patient-specific musculoskeletal modelling becomes crucial for clinical diagnosis and follow-up. However, patient-specific modelling using imaging techniques and motion capture systems is mainly subject to experimental errors. The aim of this study was to quantify these experimental errors when performing a patient-specific musculoskeletal model. CT scan data were used to personalise the geometrical model and its inertial properties for a post polio residual paralysis subject. After having performed a gait-based experimental protocol, kinematics data were measured using a VICON motion capture system with six infrared cameras. The musculoskeletal model was computed using a direct/inverse algorithm (LifeMod software). A first source of errors was identified in the segmentation procedure in relation to the calculation of personalised inertial parameters. The second source of errors was subject related, as it depended on the reproducibility of performing the same type of gait. The impact of kinematics, kinetics and muscle forces resulting from the musculoskeletal modelling was quantified using relative errors and the absolute root mean square error. Concerning the segmentation procedure, we found that the kinematics results were not sensitive to the errors (relative error < 1%). However, a strong influence was noted on the kinetics results (deviation up to 71%). Furthermore, the reproducibility error showed a significant influence (relative mean error varying from 5 to 30%). The present paper demonstrates that in patient-specific musculoskeletal modelling variations due to experimental errors derived from imaging techniques and motion capture need to be both identified and quantified. Therefore, the paper can be used as a guideline.     

Estimation of accuracy of patient-specific musculoskeletal modelling: case study on a post polio residual paralysis subject

For patients with patterns ranging out of anthropometric standard values, patient-specific musculoskeletal modelling becomes crucial for clinical diagnosis and follow-up. However, patient-specific modelling using imaging techniques and motion capture systems is mainly subject to experimental errors. The aim of this study was to quantify these experimental errors when performing a patient-specific musculoskeletal model. CT scan data were used to personalise the geometrical model and its inertial properties for a post polio residual paralysis subject. After having performed a gait-based experimental protocol, kinematics data were measured using a VICON motion capture system with six infrared cameras. The musculoskeletal model was computed using a direct/inverse algorithm (LifeMod software). A first source of errors was identified in the segmentation procedure in relation to the calculation of personalised inertial parameters. The second source of errors was subject related, as it depended on the reproducibility of performing the same type of gait. The impact of kinematics, kinetics and muscle forces resulting from the musculoskeletal modelling was quantified using relative errors and the absolute root mean square error. Concerning the segmentation procedure, we found that the kinematics results were not sensitive to the errors (relative error<1%). However, a strong influence was noted on the kinetics results (deviation up to 71%). Furthermore, the reproducibility error showed a significant influence (relative mean error varying from 5 to 30%). The present paper demonstrates that in patient-specific musculoskeletal modelling variations due to experimental errors derived from imaging techniques and motion capture need to be both identified and quantified. Therefore, the paper can be used as a guideline.