Frank Seehaus

Comparison of the model-based and marker-based roentgen stereophotogrammetry methods in a typical clinical setting.

Roentgen stereophotogrammetric analysis (RSA) is an established method for the precise measurement of implant migration. Model-based RSA (MBRSA) alleviates the need to attach tantalum markers to the prosthesis, which has prevented wider application of RSA. The goal of this study was to investigate the equivalence of both methods for the clinical measurement of implant migration. Tibial component migration was measured in 24 patients using both methods from the same set of radiographs. The maximum agreement interval, mean (+/-2 standard deviations), of the difference between both methods was modest, at 0.002 mm (0.144 mm) and -0.078 degrees (0.782 degrees ). The results suggest that MBRSA can be used interchangeably with the marker-based method and that the advantages of MBRSA do not come at the cost of a loss in accuracy.

Experimental Analysis of Model-Based Roentgen Stereophotogrammetric Analysis (MBRSA) on Four Typical Prosthesis Components

Classical marker-based roentgen stereophotogrammetric analysis (RSA) is an accurate method of measuring in vivo implant migration. A disadvantage of the method is the necessity of placing tantalum markers on the implant, which constitutes additional manufacturing and certification effort. Model-based RSA (MBRSA) is a method by which pose-estimation of geometric surface-models of the implant is used to detect implant migration. The placement of prosthesis markers is thus no longer necessary. The accuracy of the pose-estimation algorithms used depends on the geometry of the prosthesis as well as the accuracy of the surface models used. The goal of this study was thus to evaluate the experimental accuracy and precision of the MBRSA method for four different, but typical prosthesis geometries, that are commonly implanted. Is there a relationship existing between the accuracy of MBRSA and prosthesis geometries? Four different prosthesis geometries were investigated: one femoral and one tibial total knee arthroplasty (TKA) component and two different femoral stem total hip arthroplasty (THA) components. An experimental phantom model was used to simulate two different implant migration protocols, whereby the implant was moved relative to the surrounding bone (relative prosthesis-bone motion (RM)), or, similar to the double-repeated measures performed to assess accuracy clinically, both the prosthesis and the surrounding bone model (zero relative prosthesis-bone motion (ZRM)) were moved. Motions were performed about three translational and three rotational axes, respectively. The maximum 95% confidence interval (CI) for MBRSA of all four prosthesis investigated was better than -0.034 to 0.107 mm for in-plane and -0.217 to 0.069 mm for out-of-plane translation, and from -0.038 deg to 0.162 deg for in-plane and from -1.316 deg to 0.071 deg for out-of-plane rotation, with no clear differences between the ZRM and RM protocols observed. Accuracy in translation was similar between TKA and THA components, whereas rotational accuracy about the long axis of the hip stem THA components was worse than the TKA components. The data suggest that accuracy and precision of MBRSA seem to be equivalent to the classical marker-based RSA method, at least for the nonsymmetric implant geometries investigated in this study. The model-based method thus allows the accurate measurement of implant migration without requiring prosthesis markers, and thus presents new opportunities for measuring implant migration where financial or geometric considerations of marker placement have thus far been prohibitive factors.

Effects of Pedunculopontine Area and Pallidal DBS on Gait Ignition in Parkinson's Disease

BACKGROUND Freezing of gait is a disabling feature of Parkinsons 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 Parkinsons 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 Parkinsons disease.

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.

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.

No effect of conventional vs. minimally invasive surgical approach on clinical outcome and migration of a short stem total hip prosthesis at 2-year follow-up: A randomized controlled study

Background: Short stem hip prostheses have become a viable alternative for the treatment of hip osteoarthritis. In combination with minimally invasive surgery, short stem hip prostheses offer potential advantages of reduced surrounding tissue damage and faster rehabilitation. However, the limited perioperative visibility of these minimally invasive techniques may lead to reduced primary stability compared to conventional techniques. We hypothesized: a) increased migration of the minimally invasive group due to reduced primary stability and b) increased clinical scores of the minimally invasive group. Methods: Sixty total hip arthroplasty patients were randomly assigned to undergo minimally invasive anterolateral modified Watson‐Jones or conventional Hardinge surgery. All patients were treated with a Metha short stem prosthesis. Roentgen stereophotogrammetry and clinical scores were calculated after surgery and at 3, 6, 12, and 24 months postoperatively. Findings: No statistically significant differences in implant migration and clinical scores were observed between the minimally invasive and conventional groups at any follow‐up point. The largest average resultant migrations were 1.22 (SD 1.31) mm (conventional) and 1.18 (SD 1.18) mm (minimally invasive) after 24 months. The mean Harris Hip Score score improved from 54 (SD 10, conventional) and 52 (SD 13, minimally invasive) preoperatively to 97 (SD 5, both groups) after 24 months. Interpretation: Overall, the differences in implant migration and clinical scores between the minimally invasive and conventional surgery groups were marginal and not clinically relevant. The data from this study suggest that good results can be expected from both the investigated approaches. HighlightsImplant migration of the Metha short stem was not influenced by the choice of conventional or minimally invasive surgery.High accuracy migration data of the Metha short hip stem is reported for the first time.Despite higher migration compared to other short stems, the revision rates of the Metha are average for a short stem.

Effects of unstable footwear on joint reactions and muscle forces: an inverse dynamics study

Background Unstable shoe designs should support the muscle activity and promise the treatment of leg, back and foot problems. According to manufacturers, they should activate additional muscles and reduce joint reaction forces. Goal of this study is to investigate the effect of an unstable shoe design to gait patterns of healthy volunteers and by the means of inverse dynamic multi-body simulation.

APPLICABILLITY OF MODEL-BASED RSA FOR AN AXIS SYMMETRIC HIP RESURFACING PROSTHESIS DESIGN

Roentgen Stereophotogrammetric Analysis (RSA) allows the detection of early implant migration, which is of particular clinical relevance because early migration in the first two post-operative years correlates well with a later aseptic loosening [Karrholm, 1994; Ryd, 1995]. Model-based RSA (MBRSA) represents a new approach, which does not require the placement of tantalum markers on the prosthesis [Valstar, 2002; Kaptein, 2003]. The accuracy of MBRSA depends on the geometry of implant design [Hurschler, 2007]. Hip resurfacing arthroplasty (HR), a bone sparing strategy for younger patients, has drawn significant clinical interest, despite some setbacks including revisions due to loosening. The goal of this study, especially in light of the known interaction between geometric design and MBRSA accuracy, was to determine the theoretical accuracy and precision for migration measurements of axis-symmetric implants such as HR. The working hypothesis was that MBRSA provides sufficient accuracy to detect translational migration of total-axis-symmetric implants, despite the fact that the rotation about its symmetry-axis is indeterminate.