How Do Classic (Static) RSA and Patient Motion Artifacts Affect the Assessment of Migration of a TKA Tibial Component? An In Vitro Study.

BACKGROUND: Classic (static) Roentgen stereophotogrammetric analysis (RSA) is the current gold standard to assess, in vivo, the migration of total joint arthroplasty components. To prevent potential patient motion artifacts during the acquisition of paired radiostereometric images, images must be taken by simultaneously firing both X-ray tubes. However, the influence of nonsynchronized RSA paired images or patient motion artifacts on the precision of RSA and the assessment of implant migration is not well understood. QUESTIONS/PURPOSES: We assessed (1) the effect of possible patient motion on the precision of RSA and (2) apparent differences in implant migration among axes (in-plane and out-of-plane translations and in-plane and out-of-plane rotations) of possible motion artifacts. METHODS: Radiographs of two tibial knee arthroplasty components, each fixed in two bone-implant models as a customized phantom, were taken in a uniplanar measurement setup. We evaluated both model-based (implant models from reversed engineering) and marker-based (additional attached implant markers) RSA approaches. Between the simulated reference and follow-up examinations, we used one of the bone-implant models to simulate patient motion and the other to simulate no patient motion in parallel. Two defined protocols were followed for each of the bone-implant models: no-motion and simulated motion protocols. RSA image pairs were analyzed using a model-based RSA software package (MBRSA 4.1, RSA core ). Precision was calculated through repeat examinations, and migration of the two components was assessed for comparison of the components with each other. Measurements were taken along the medial-lateral and posterior-anterior axes for translations and around the cranial-caudal axis for rotations. The maximum total point motion was measured for comparison between the two components. RESULTS: The effect of simulated patient motion was generally small, except in the cranial-caudal axis, but the induced imprecision associated with motion was larger in model-based RSA than it was in marker-based RSA. The mean ± standard deviation values of precision in model-based RSA were 0.035 ± 0.015 mm, 0.045 ± 0.014 mm, and 0.049 ± 0.036 mm greater than those in marker-based RSA, in accordance with the simulated motion protocol in translations along the medial-lateral axis (0.018 ± 0.004 mm; p = 0.01), along the posterior-anterior axis (0.018 ± 0.007 mm; p = 0.003), and rotations around the cranial-caudal axis (0.017 ± 0.006 mm; p = 0.02). Apparent differences in implant migration were the greatest for the maximum total point motion. The maximum total point motion increased from 0.038 ± 0.007 mm for the no-motion protocol to 1.684 ± 0.038 mm (p < 0.001) for the simulated motion protocol in marker-based RSA, and from 0.101 ± 0.027 mm for the no-motion protocol to 1.973 ± 0.442 mm (p < 0.001) for the simulated motion protocol in model-based RSA, and was the worst-case scenario regarding patient motion artifacts. CONCLUSION: Patient motion exceeding 1 mm or 1° on nonsynchronized RSA images affects measurement errors regarding the detection of migration of a tibial component. In clinical RSA studies, the effect of patient motion on the assessment of implant migration should be of particular concern, even if clinical RSA systems have acceptable precision. Specially trained radiographers are crucial for correctly acquiring radiographs, especially when simultaneous radiography exposures are not electronically automated. In general, RSA requires synchronized image acquisition, and this should be the state-of-the-art. CLINICAL RELEVANCE: In clinical RSA studies, precision assessed by repeat examinations may not be reliable using the current standards that are widely used in radiology departments. When assessing implant migration for reliability, comparison of the maximum total point motion between the tested (simulated motion) implant and baseline (no-motion) implant, as in this study, is advocated because of the accurate detection of patient motion artifacts.

Femoral Stem Fracture in Hip Revision Arthroplasty: A Systematic Literature Review of the Real-World Evidence.

BACKGROUND: Total hip arthroplasty (THA) presents as an excellent treatment for the osteoarthritic hip, demonstrating good survival rates. However, aseptic loosening and infection are the main causes of operative revision. The methods used in revision surgery are non-modular or modular THA implants. In addition to the abovementioned revision reasons for THA, this treatment could be associated with the possibility of femoral stem fracture, especially in the modular system. The topic of material failure has been focused on in the public media. The question arises as to how such media reports correlate with the published literature. The observed mentioned number of cases concerning a femoral stem fracture vary between one single case and up to 18.5% within a clinical study, thus presenting an inhomogeneous data situation with a large span. The specific aim of this systematic review is to establish facts and clarify the number of unforeseen events of a femoral stem fracture based on peer review articles and registry data. This clarification is important to us, as these media reports have led to uncertainty among patients. METHODS: A systematic review was performed in accordance with the PRISMA statement. Peer review articles in English and German, presenting original articles, meta-analyses, or case reports, were searched from the turn of the millennium up to December 2019. Only articles that reported a femoral stem component fracture, with content of clinical data as well as register data, were included. Relevant papers published after the defined research time frame were taken into account within the discussion. RESULTS: In total, 218 fractures of a femoral stem (141 primary and 77 revision THA) component could be identified within the selected literature. Most cases of a femoral stem fracture occurred in the modular THA implants compared to the non-modular stems. Regarding revision THA, in summary, 77 implants, presenting 23 non-modular and 54 modular implants, failed by means of femoral stem fracture. A review of 11 National Joint Registries shows a revision rate between 0.04 and 0.05% in only 2 registers according to the specific subject of a femoral stem fracture. For the remaining 9 registers, however, detailed information is lacking and only nonspecific information such as a generic "implant failure" or "other reason" (which can cover a multitude of causes) is supplied. CONCLUSION: A femoral stem fracture presents a devastating complication for the patient, the surgeon as well as for the manufacturer of the implant. Modular THA implants play an increasingly valuable role concerning restoration of individual anatomy in modern THA revision surgery, especially within complex cases. Regarding revision procedures, data suggests a lower risk of femoral stem fracture for modular implants compared to primary procedures, while the risk of fracture for non-modular implants seems to increase during revision. Ultimately, it cannot be proven whether this is actually applicable, since the absolute number of implanted prosthesis systems is not known. Various implant-, patient-, and surgeon-related factors may lead to these reported femoral stem fractures. However, this systematic review suggests that this is, in general, a rare complication.

Preoperative planning of total knee arthroplasty: reliability of axial alignment using a three-dimensional planning approach.

BACKGROUND: Preoperative templating of total knee arthroplasty (TKA) can nowadays be performed three-dimensionally with software solutions using computed tomography (CT) datasets. Currently there is no consensus concerning the axial orientation of TKA components in three-dimensional (3D) planning. PURPOSE: To assess intra-/inter-observer reliability of detection of different bony landmarks in planning axial component alignment using axial CT images and 3D reconstructions. MATERIAL AND METHODS: Intra- and inter-observer reliability of determination of four predefined axial femoral and tibial axes was calculated using data from CT scans. Axes determination was performed on the axial slices and on the 3D reconstruction using preoperative planning software. In summary, 61 datasets were analyzed by one medical student (intra-observer reliability) and 15 datasets were analyzed by four different observers independently (inter-observer reliability). RESULTS: For the femur, clinical epicondylar axis and posterior condylar axis showed the best reliability with an inter-observer variability of 0.7° and 0.5°, respectively. For the tibia, posterior condylar axis provided best reliability (inter-observer variability: 1.7°). Overall variability was greater for tibial than for femoral axes. Reliability of axis determination was more accurate using axial CT slices rather than 3D reconstructions. CONCLUSION: The femoral clinical epicondylar axis is highly reliable. Landmarks for the tibia are not as easily identifiable as for the femur. The tibial posterior condylar axis presents the axis with highest reliability. Based on these results, clinical epicondylar axis for orientation of the femoral TKA component and posterior condylar axis for the tibial implant, both defined on axial slices can be recommended.

Model-Based Roentgen Stereophotogrammetric Analysis to Monitor the Head-Taper Junction in Total Hip Arthroplasty in Vivo-And They Do Move.

Model-based Roentgen stereophotogrammetric analysis (RSA) using elementary geometrical shape (EGS) models allows migration measurement of implants without the necessity of additional attached implant markers. The aims of this study were: (i) to assess the possibility of measuring potential head-taper movement in THA in vivo using model-based RSA and (ii) to prove the validity of measured head-taper migration data in vitro and in vivo. From a previous RSA study with a 10 years follow-up, retrospectively for n = 45 patients head-taper migration was calculated as the relative migration between femoral ball head and taper of the femoral stem using model-based RSA. A head-taper migration of 0.026 mm/year can be detected with available RSA technology. In vitro validation showed a total migration of 268 ± 11 µm along the taper axis in a similar range to what has been reported using the RSA method. In vivo, a proof for interchangeable applicability of model-based RSA (EGS) and standard marker-based RSA methods was indicated by a significant deviation within the migration result after 12-month follow-up for all translation measurements, which was significantly correlated to the measured head-taper migration (r from 0.40 to 0.67; p < 0.05). The results identified that model-based RSA (EGS) could be used to detect head-taper migration in vivo and the measured movement could be validated in vitro and in vivo as well. Those findings supported the possibility of applying RSA for helping evaluate the head-taper corrosion related failure (trunnionosis).

Effects of Pre- and Post-Exercise Cold-Water Immersion Therapy on Passive Muscle Stiffness.

BACKGROUND: Cold-water immersion (CWI) has become a popular preventive, regenerative and performance-enhancing intervention in various sports. However, its effects on soft tissue, including changes of intramuscular stiffness, are poorly understood. The purpose of this study was to investigate the effect of CWI on muscle stiffness. PATIENTS/MATERIAL AND METHODS: Thirty healthy participants were included and divided into the three following groups (n = 10): 1) post-ESU group: exercise and CWI (post-exercise set-up); 2) control group: exercise without CWI (control condition); 3) pre-ESU group: CWI alone (pre-exercise set-up). Acoustic radiation force impulse (ARFI) elastography was conducted to assess tissue stiffness (shear wave velocity, SWV). Values obtained at resting conditions (baseline, t0) were compared to values post-exercise (t1, for post-ESU group and control group), post-CWI (t2, for post-ESU group and pre-ESU group; rest for control group) and to 60-min follow-up time (t3, for all groups). Data were assessed in superficial and deep muscle tissue (rectus femoris muscle, RF; vastus intermedius muscle, VI). RESULTS: For the post-ESU group (CWI post-exercise), there was no significant difference between the time points of measurements: exercise (t1: RF: 1.63 m/s; VI: 1.54 m/s), CWI (t2: RF: 1.63 m/s; VI: 1.53 m/s) and at 60-min follow-up (t3: RF: 1.72 m/s; VI: 1.61 m/s). In the control group, a significant decrease of SWV was found between baseline conditions at t0 and post-exercise (t1) at VI (VI: 1.37 m/s; p = 0.004; RF: 1.59 m/s; p = 0.084). For t2 and t3, no further significant changes were detected. Regarding the pre-exercise set-up (pre-ESU group), a significant decrease in SWV from baseline to t2 in VI (1.60 m/s to 1.49 m/s; VI: p = 0.027) was found. CONCLUSION: This study shows varying influences of CWI on muscle stiffness. Overall, we did not detect any significant effects of CWI on muscle stiffness post-exercise. Muscle stiffness-related effects of CWI differ in the context of a pre- or post-exercise condition and have to be considered in the implementation of CWI to ensure its potential preventive and regenerative benefits.

The prevalence of osteoarthritis: Higher risk after transfemoral amputation?-A database analysis with 1,569 amputees and matched controls.

BACKGROUND: Several studies have shown that patients with a unilateral amputation have an increased risk of developing osteoarthritis (OA) in the knee of their sound leg. OBJECTIVE: The first objective was to investigate whether amputees are more frequently affected by gon-, cox- or polyarthritis as well as back pain or spinal disorders. We hypothesized that mobile and active transfemoral amputees more often experience OA and spinal disorders than non-amputees. The second objective was to compare the mean age of the patients with OA. PATIENTS: Patients with a unilateral transfemoral amputation (n = 1,569) and five abled-body control groups (each n = 1,569) matched in terms of age and gender resulting in total of 9,414 participants. METHODS: Groups were analyzed regarding the prevalence of six selected diagnoses regarding musculoskeletal disorders. RESULTS: A significantly decreased prevalence of OA and specific disorders of the spine in transfemoral amputees compared to a control group was found. The amputees with OA are significantly younger than patients with OA in the control group. CONCLUSION: The results from the presented study contradict previously published literature. Apparently circumstances of life play an important role, like physical work and strenuous activities which are likely to be underrepresented in the amputee group. The results of the study need to be used cautiously due to the major limitation of the study which is the lack of detail in individual patients caused by the methodology.

Model-based roentgen stereophotogrammetric analysis using elementary geometrical shape models: 10 years results of an uncemented acetabular cup component.

BACKGROUND: Non-cemented acetabular cup components demonstrated different clinical performance depending on their surface texture or bearing couple. However, clinical osseointegration needs to be proved for each total joint arthroplasty (TJA) design. Aim of this study was to detect the in vivo migration pattern of a non-cemented cup design, using model-based roentgen stereophotogrammetric analysis with elementary geometrical shape models (EGS-RSA) to calculate early cup migration. METHODS: Interchangeable applicability of the model-based EGS-RSA method next to gold standard marker-based RSA method was assessed by clinical radiographs. Afterwards, in vivo acetabular cup migration for 39 patients in a maximum follow up of 120 months (10 years) was calculated using model-based EGS-RSA. RESULTS: For the axes with the best predictive capability for acetabular cup loosening, mean (±SD) values were calculated for migration and rotation of the cup. The cup migrated 0.16 (±0.22) mm along the cranio-caudal axis after 24 months and 0.36 (±0.72) mm after 120 months, respectively. It rotated - 0.61 (±0.57) deg. about the medio-lateral axis after 24 months and - 0.53 (±0.67) deg. after 120 months, respectively. CONCLUSIONS: Interchangeable applicability of model-based EGS-RSA next to gold standard marker-based RSA method could be shown. Model-based EGS-RSA enables an in vivo migration measurement without the necessity of TJA specific surface models. Migration of the investigated acetabular cup component indicates significant migration values along all the three axes. However, migration values after the second postoperative year were within the thresholds reported in literature, indicating no risk for later aseptic component loosening of this TJA design.

Osteoarthritis in a symptomatic coracoclavicular joint.

Coracoclavicular joint (CCJ) is a rare cause of shoulder pain. CCJ is not described in most orthopaedic textbooks, leading to lack of awareness in the general orthopaedic community. In that way the incidence of symptomatic cases is underestimated. We present the case of a symptomatic osteoarthtritic CCJ in a 46-year-old male patient with nearly complete relief of pain after therapeutic injection of the CCJ. The radiological signs of CCJ are briefly discussed to increase awareness of this very rare entity.

Dynamic Time Warping compared to established methods for validation of musculoskeletal models.

By means of Multi-Body musculoskeletal simulation, important variables such as internal joint forces and moments can be estimated which cannot be measured directly. Validation can ensued by qualitative or by quantitative methods. Especially when comparing time-dependent signals, many methods do not perform well and validation is often limited to qualitative approaches. The aim of the present study was to investigate the capabilities of the Dynamic Time Warping (DTW) algorithm for comparing time series, which can quantify phase as well as amplitude errors. We contrast the sensitivity of DTW with other established metrics: the Pearson correlation coefficient, cross-correlation, the metric according to Geers, RMSE and normalized RMSE. This study is based on two data sets, where one data set represents direct validation and the other represents indirect validation. Direct validation was performed in the context of clinical gait-analysis on trans-femoral amputees fitted with a 6 component force-moment sensor. Measured forces and moments from amputees' socket-prosthesis are compared to simulated forces and moments. Indirect validation was performed in the context of surface EMG measurements on a cohort of healthy subjects with measurements taken of seven muscles of the leg, which were compared to simulated muscle activations. Regarding direct validation, a positive linear relation between results of RMSE and nRMSE to DTW can be seen. For indirect validation, a negative linear relation exists between Pearson correlation and cross-correlation. We propose the DTW algorithm for use in both direct and indirect quantitative validation as it correlates well with methods that are most suitable for one of the tasks. However, in DV it should be used together with methods resulting in a dimensional error value, in order to be able to interpret results more comprehensible.

Posterior dynamic stabilization in the lumbar spine - 24 months results of a prospective clinical and radiological study with an interspinous distraction device.

BACKGROUND: Interspinous distraction devices (IDD) are due to maintain or restore intersegmental range of motion (iROM) in a controlled fashion with the aim of stabilization the affected level dynamically. The following study is the first to present clinical and radiological data with the Wallis® spacer during a follow-up of 24 months. METHODS: Ten patients underwent posterior dynamic stabilization (PDS) of the lumbar spine with an IDD (Wallis® spacer) and were controlled clinically and radiologically after 3, 6, 12, and 24 months in a prospective study design. Pain intensity, functional disability and life quality were assessed by use of subjective scores. Motion analyses were performed with the help of lateral functional x-rays to determine the iROM of the operated segments and total ROM (tROM) of the lumbar spine. In addition, roentgen stereophotogrammetric analysis (RSA) was used to measure the iROM of the treated levels. RESULTS: During the postoperative course pain and disability most clinical scores were significantly improved. After 24 months we observed statistically significant reduction in back pain intensity with a mean value of 6.0 on visual analog scale (VAS) before surgery and of 2.7 at the latest evaluation. The leg pain was also decreased without statistical significance from 4.7 preoperatively to 2.1 at final follow-up. The functional disability according to Oswestry Disability Index (ODI) and Roland-Morris Disability Questionnaire (RM) was decreased both with statistical significance at all examination dates with a mean value in ODI of 40.0 % before operation and of 17.3 % after 2 years and an initial mean value in RM of 55.2 and of 23.5 % after latest follow-up. After 24 months, the results of the health related quality of life score also showed much better values with only two exceptions. The iROM of the treated levels was reduced during each follow-up examination with preserved residual mobility. Directly postoperatively and after 3 and 12 months intersegmental mobility was statistically significantly decreased with an average iROM of 6.62° before operation and of 2.69° few days after surgery, of 3.79° and 3.16° 3 and 12 months later. At 6 (4.37°) and 24 (4.01°) months follow-up iROM was also but not statistically significantly reduced. The mean tROM did not change significantly during all postoperative controls. CONCLUSIONS: The radiological findings support the thesis of posterior dynamic stabilization by the used implant. The positive clinical findings should be interpreted with caution because of the limited number of patients and the missing control group.

Analysis of migration of the Nanos® short-stem hip implant within two years after surgery.

PURPOSE: Short-stem implants provide a bone-preserving alternative in total hip arthroplasty. However, some evidence exists that the smaller implant-bone contact surface may compromise primary stability and impair osseo-integration. The purpose of this study was to analyse the migration characteristics of the Nanos® short stem over two years by means of model-based roentgen stereophotogrammetric analysis (MBRSA). METHODS: Eighteen patients aged 53.6 ± 7.2 years were included. After being treated with a Nanos implant, 14 patients were followed-up radiologically at three, six, 12 and 24 months by means of MBRSA. Early implant migration was calculated. Clinical data have been assessed in addition. RESULTS: Highest translational migration was observed with a mean value of -0.22 ± 0.39 mm along the proximo-distal axis after three months and highest rotational migration with 0.8 ± 3.2° also around the y-axis after two years. The resulting total migration was 0.46 ± 0.31 mm, with the largest proportion occurring within three months after surgery (0.40 ± 0.34 mm). CONCLUSION: The Nanos short-stem hip implant shows only a slight initial migration within three months after implantation, followed by secondary stabilisation. These results suggest both good primary stability and osseo-integration, suggesting a low risk of aseptic loosening.

Use of single-representative reverse-engineered surface-models for RSA does not affect measurement accuracy and precision.

Implant migration can be accurately quantified by model-based Roentgen stereophotogrammetric analysis (RSA), using an implant surface model to locate the implant relative to the bone. In a clinical situation, a single reverse engineering (RE) model for each implant type and size is used. It is unclear to what extent the accuracy and precision of migration measurement is affected by implant manufacturing variability unaccounted for by a single representative model. Individual RE models were generated for five short-stem hip implants of the same type and size. Two phantom analyses and one clinical analysis were performed: "Accuracy-matched models": one stem was assessed, and the results from the original RE model were compared with randomly selected models. "Accuracy-random model": each of the five stems was assessed and analyzed using one randomly selected RE model. "Precision-clinical setting": implant migration was calculated for eight patients, and all five available RE models were applied to each case. For the two phantom experiments, the 95%CI of the bias ranged from -0.28 mm to 0.30 mm for translation and -2.3° to 2.5° for rotation. In the clinical setting, precision is less than 0.5 mm and 1.2° for translation and rotation, respectively, except for rotations about the proximodistal axis (<4.1°). High accuracy and precision of model-based RSA can be achieved and are not biased by using a single representative RE model. At least for implants similar in shape to the investigated short-stem, individual models are not necessary. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:903-910, 2016.

Influence of transfemoral amputation length on resulting loads at the osseointegrated prosthesis fixation during walking and falling.

BACKGROUND: Transfemoral amputation is a surgical measure in which the surgeon typically conserves as much tissue and bone as possible. Osseointegrated fixation of prostheses is a promising alternative to conventional socket-based fixation. However, osseointegrated prostheses pose some risk of possible bone fracture under unexpected high-impact loading scenarios, such as a fall, and this should be protected against by a safety element. The aim of the present study was to determine the effect of amputation height on the forces and moments at the bone-prosthesis interface during normal gait and three falling scenarios. METHODS: Forces and moments at four amputation heights were determined from a multi-body simulation driven by data captured from an able-bodied participant. FINDINGS: In all three falling scenarios, forces were relatively independent of amputation height, while moments generally displayed considerable increases with shorter residual limb length. Peak moments ranged from 105Nm (SD 75) (most distal amputation height) to 229Nm (SD 99) (most proximal amputation height) for a "falling during gait" scenario. INTERPRETATION: Our findings reveal the dependence of interface loads on amputation height in normal gait and falling. This information may lead to improved prosthesis safety elements against bending moments.

Effects of pedunculopontine area and pallidal DBS on gait ignition in Parkinson's disease.

BACKGROUND: Freezing of gait is a disabling feature of Parkinson's disease, and so far no established treatment exists. Deep brain stimulation of the pedunculopontine area has been proposed to treat refractory gait disorders, yet data on measurable effects, especially in combination with stimulation of other targets, are scarce. METHODS: Acute effects of either low frequency pedunculopontine stimulation or high frequency stimulation of the posteroventral lateral globus pallidus internus and a combination of both in a 66-year-old man with advanced Parkinson's disease were assessed. Four weeks after the intervention, the gait was examined with patient blinded in each condition using computerized gait analysis. RESULTS: Isolated pedunculopontine or pallidal stimulation had a mild impact on gait ignition and freezing of gait, but combined stimulation had a marked effect. CONCLUSIONS: Combined multifocal stimulation may be a promising option for gait ignition and freezing of gait in advanced Parkinson's disease.

Dependence of model-based RSA accuracy on higher and lower implant surface model quality.

BACKGROUND: Model-based Roentgen Stereophotogrammetric Analysis (MBRSA) allows the accurate in vivo measurement of the relative motion between an implant and the surrounding bone (migration), using pose-estimation algorithms and three dimensional geometric surface models of the implant. The goal of this study was thus to investigate the effect of surface model resolution on the accuracy of the MBRSA method. METHODS: Four different implant geometries (knee femoral and tibial components, and two different hip stems) were investigated, for each of which two reversed engineering (RE) models of differing spatial digitizing resolution were generated. Accuracy of implant migration measurement using MBRSA was assessed in dependence on surface model resolution using an experimental phantom-model set up. RESULTS: When using the lower quality RE models, the worst bias observed ranged from -0.048 to 0.037 mm, and -0.057 to 0.078 deg for translation and rotation respectively. For higher quality reverse engineering models, bias ranged from -0.042 to 0.048 mm, and -0.449 to 0.029 deg. The pair-wise comparisons of digitizing resolution (higher vs. lower quality) within the different implant type revealed significant differences only for the hip stems (p < 0.001). CONCLUSION: The data suggest that the application of lower resolution RE models for MBRSA is a viable alternative method for the in vivo measurement of implant migration, in particular for implants with non symmetrical geometries (total knee arthroplasty). Implants with larger length to width aspect ratio (total hip arthroplasty) may require high resolution RE models in order to achieve acceptable accuracy. Conversely, for some axis the bias for translation are clearly worse for translation, and are marginally better for rotations using the lower resolution RE models instead of the higher ones. However, performed box plots ranges were well within what has been reported in the literature. The observed lower accuracy and precision of the measurements for hip stem components for rotations about the superior-inferior direction is presumably the result of the nature of the MBRSA method. This well known effect within MBRSA for rotations about the axis of symmetry of axially-symmetric objects do not change the contour of the projected image to as large a degree as motion about a non-symmetric axes. It is not possible to detected this small motion as accurately using pose-estimation methods. This may affect the "higher" accuracy for the applied lower resolution RE models.

Loads on the prosthesis-socket interface of above-knee amputees during normal gait: validation of a multi-body simulation.

The treatment of above-knee amputees with a prosthesis based on a socket is currently considered the standard clinical treatment. Nevertheless there are few investigations on mechanical loading conditions on these devices under realistic circumstances. Further insight in this matter might improve the design of sockets for everyday application. The presented study investigates the loads acting on the socket-interface with a multi-body simulation (MBS). Aim of this study is to validate the quality of the applied MBS next to a direct measurement device. Therefore a custom strain gauge based force-moment sensor is integrated into the conventional socket-based prosthesis of six above-knee amputees. Each subject performs level-walking with kinematic and kinetic data being recorded in a gait laboratory. The data of the marker trajectories is processed in an inverse dynamics MBS where loads at the location of the sensor are determined. The comparison of both methods shows a good agreement of forces and moments and the simulation can be considered fully validated. RMSD is 4.7%BW for the forces and 27.0%BWM for the moments. The model will be used in further research to determine loads on the socket-prosthesis interface of above-knee amputees especially in high risk situations such as falling scenarios, where direct measurement with amputees is not possible for ethical reasons.

Multi-body simulation of various falling scenarios for determining resulting loads at the prosthesis interface of transfemoral amputees with osseointegrated fixation.

Conventionally, transfemoral amputees are treated with a shaft prosthesis fitted over the residual limb. To improve the quality of life of such patients, in particular those with complications relating to conventional attachment (e.g., skin irritation, stump ulcers, and poor motor-control with short stumps), osseointegrated prosthesis fixation implants have been developed and implanted in a limited population of patients. To assess possible damage to the implant/prosthesis during falling scenarios, the loads in high-risk situations were estimated using a multi-body simulation of motion. Five falling scenarios were identified and performed by healthy volunteer wearing safety equipment. Kinematic data and ground reaction forces were captured as input for the inverse-dynamics-based simulations, from which the forces and moments at a typical implant-prosthesis interface location were computed. The estimated peak loads in all five scenarios were of a magnitude that could lead to bone fracture. The largest peak force observed was 3274 ± 519 N, with an associated resultant moment of 176 ± 55 Nm on the prosthesis-implant interface. A typical femur is prone to fracture under this load, thus illustrating the need for a safety-release element in osseointegrated prosthesis fixation.

Biomechanical in vitro - stability testing on human specimens of a locking plate system against conventional screw fixation of a proximal first metatarsal lateral displacement osteotomy.

INTRODUCTION: The aim of this study was to examine resistance to angulation and displacement of the internal fixation of a proximal first metatarsal lateral displacement osteotomy, using a locking plate system compared with a conventional crossed screw fixation. MATERIALS AND METHODOLOGY: Seven anatomical human specimens were tested. Each specimen was tested with a locking screw plate as well as a crossed cancellous srew fixation. The statistical analysis was performed by the Friedman test. The level of significance was p = 0.05. RESULTS: We found larger stability about all three axes of movement analyzed for the PLATE than the crossed screws osteosynthesis (CSO). The Friedman test showed statistical significance at a level of p = 0.05 for all groups and both translational and rotational movements. CONCLUSION: The results of our study confirm that the fixation of the lateral proximal first metatarsal displacement osteotomy with a locking plate fixation is a technically simple procedure of superior stability.