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Prof. Dr. Tim Weber, Dipl.-Ing.(FH)

classical statistical methods
machine learning
SensorLab

Teaching Campus Cham

Professors

Professor

Professor Big Data and Production Management

1.13 (Living Lab / B-Gebäude)

09971/99673-17

Bürozeiten

Wednesday, 10.00 - 11.00

consulting time

Wednesday, 10.00 - 11.00

publications

Sortierung:

NewspaperArticle

P. Olaleru
Tim Weber
Peter Firsching

Reduce Dye-and-Pry Experiments with Simulations.

In: CADFEM Journal vol. 2021

(2021)

Journal article

A. Al-Munajjed
N. Plunkett
J. Gleeson
Tim Weber
C. Jungreuthmayer
T. Levingstone
J. Hammer
F. OBrien

Development of a biomimetic collagen-hydroxyapatite scaffold for bone tissue engineering using a SBF immersion technique.

In: Journal of Biomedical Materials Research Part B: Applied Biomaterials vol. 90B pg. 584‐591

Wiley

(2009)

DOI: 10.1002/jbm.b.31320

show abstract

The objective of this study was to develop a biomimetic, highly porous collagen-hydroxyapatite (HA) composite scaffold for bone tissue engineering (TE), combining the biological performance and the high porosity of a collagen scaffold with the high mechanical stiffness of a HA scaffold. Pure collagen scaffolds were produced using a lyophilization process and immersed in simulated body fluid (SBF) to provide a biomimetic coating. Pure collagen scaffolds served as a control. The mechanical, material, and structural properties of the scaffolds were analyzed and the biological performance of the scaffolds was evaluated by monitoring the cellular metabolic activity and cell number at 1, 2, and 7 days post seeding. The SBF-treated scaffolds exhibited a significantly increased stiffness compared to the pure collagen group (4-fold increase), while a highly interconnected structure (95%) was retained. FTIR indicated that the SBF coating exhibited similar characteristics to pure HA. Micro-CT showed a homogeneous distribution of HA. Scanning electron microscopy also indicated a mineralization of the collagen combined with a precipitation of HA onto the collagen. The excellent biological performance of the collagen scaffolds was maintained in the collagen-HA scaffolds as demonstrated from cellular metabolic activity and total cell number. This investigation has successfully developed a biomimetic collagen-HA composite scaffold. An increase in the mechanical properties combined with an excellent biological performance in vitro was observed, indicating the high potential of the scaffold for bone TE.

Journal article

Tim Weber
S. Dendorfer
S. Dullien
J. Grifka
G. Verkerke
T. Renkawitz

Measuring functional outcome after total hip replacement with subject-specific hip joint loading.

In: Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine vol. 226 pg. 939‐946

SAGE Publications

(2012)

DOI: 10.1177/0954411912447728

show abstract

Total hip replacement is an often-performed orthopedic surgical procedure; the amount of procedures undertaken will increase since our life expectancy is growing. In order to optimize function, hip biomechanics should be restored to as near normal as possible. The goal of this pilot study was to determine whether or not it is feasible to compute the vectorial hip reaction force pathways on the head of the prosthesis and the force angles relative to the cup of the prosthesis that occur during gait in total hip replacement patients, serving as an objective measurement of the functional outcome following hip replacement. A three-dimensional gait analysis, measuring ground reaction forces and kinematics, was performed. The data retrieved from the gait analysis was used as the input for the musculoskeletal model to compute vectorial joint reaction forces for data processing. To evaluate the position and orientation of the joint reaction forces, the force path, as well as the force angles for the operated and non-operated joint, has been calculated during the stance phase of the specific leg. The force path for subject 2 on the non-operated side is only located in the posterior-lateral quarter, as is the force path for subject 1. In contrast to this subject, the force path for subject 2 at the operated hip joint can be found only within the anterior quarter of the head of the implant, where it is nearly equally distributed in the medio-lateral half of the prosthesis head. The force-inclination angles on the cup of subject 1, with respect to the plane of the socket face, indicates that the force vector is mainly positioned in the same quadrant when compared with subject 2 (in a cup-fixed coordinate system). The force-anteversion angle behaves similarly to the force-inclination angle, even when the effects are not as pronounced. The proposed methods in this article are aiming to define two functional outcomes of total hip replacement that are related to wear and rim loading. It is accepted that wear is not only a function of time, but a function of use. Owing to the methods listed in this article, we are able to determine a) the applied force and b) the sliding distance (force pathway) in a subject-specific manner. The computed hip-reaction force angles and the distance to the rim cup are a measurement for cup or rim loading, and occurs in the so-called safe-zones. This method may well give us insight into the biomechanical situation during gait, after receiving total hip replacement, that we need to fully understand the mechanisms acting on a hip joint and to prove a possible increase of functional outcome after receiving total hip replacement.

Lecture

Tim Weber
P. Stezowski
S. Dullien
S. Dendorfer

A biomechanical evaluation of different load scenarios after implantation of a total hip replacement.

In: 89. Jahrestagung der Vereinigung der Bayerischen Chirurgen e.V.

Regensburg

25.-27.07.2012 (2012)

Journal article

Tim Weber
S. Dullien
J. Grifka
T. Renkawitz
S. Dendorfer

Validation of a motion capture laboratory and a new marker placement protocol for clinical applications.

In: Gait & Posture vol. 38 pg. S113‐S114

Elsevier BV

(2013)

DOI: 10.1016/j.gaitpost.2013.07.229

show abstract

Introduction: Clinical gait analysis has been proven to be a valid technique in order to reveal pathologies that concern ones gait. The greatest potential lies in capturing even the smallest abnormalities in ones gait. Body fixed sensors for gait analysis have been introduced several years ago. Following specific marker protocols the (often) motion-capture (MoCap) markers are applied on anatomical (bony) landmarks on the subject's body, which serve to calculate joint kinematics. These results are of course dependent on the examiners themselves and on the used marker placement protocol. This study introduces a method to measure the accuracy and sensitivity of a motion capture gait laboratory, a new marker placement protocol and the examiners conducting the gait analysis in order make evident statements. Patients/materials and methods: This study is divided into three different experiments. First, the gait laboratory itself is compared to a state of art rigid body measuring device without human interaction. Ten markers are placed on a standard cross table in the measuring volume of the gait laboratory. By means of the cross table different spatial positions of the markers are achieved while the measuring devices are capturing the positions simultaneously. The positions are then compared amongst each other. Secondly, the tracking sensitivity of the markers is determined by means of one experiment on a healthy subject. This is being tracked ten times by three different examiners and the positions of the MoCap – markers are compared for every time step, respectively. The third experiment was conducted in order to determine the difference and the significance of applying of the MoCap – markers on the bony landmarks of the subject. The marker protocol was applied ten times on the bony landmarks of the subject by two different examiners in an alternating manner. After each application a gait experiment was conducted, which resulted in comparing marker trajectories and joint kinematics. Results: Differences between rigid body measuring device, the MoCap laboratory and the cross table were not severe enough to limit the gait analysis capabilities of the system. The differences between inexperienced and experienced examiners were present. The application of the marker placement protocol showed differences between the examiners, however once the marker trajectories are translated into joint kinematics the differences were non-significant. Discussion and conclusions: This study introduces a method to measure the accuracy and sensitivity of a fully equipped motion capture gait laboratory, a new marker placement protocol and the examiners conducting the gait analysis. The results indicate differences between examiners. However they mostly disappeared after a learning curve of the persons. Also they had only little influence on the kinematics derived from the marker trajectories. This article analyses a new marker protocol and gait lab set up on several levels and thus validates the accuracy and sensitivity of the system which is crucial in order to be able to make valid statements about gait kinematics.

Journal article

S. Dendorfer
Tim Weber
O. Kennedy

Musculoskeletal Modeling for Hip Replacement Outcome Analyses and Other Applications.

In: Journal of the American Academy of Orthopaedic Surgeons vol. 22 pg. 268‐269

Ovid Technologies (Wolters Kluwer Health)

(2014)

DOI: 10.5435/JAAOS-22-04-268

show abstract

The ability to quantify internal stress distributions within the musculoskeletal system is of particular importance for joint arthroplasty in orthopaedics and subsequent outcome analyses. Musculoskeletal analysis and modeling (MM), which traditionally used rather theoretic algorithms and applications, has now developed to the point that numerically stable and anatomically correct simulations are possible. Importantly, these analyses can now be performed on a patient-specific level. Patient-specific MM considers individualized anatomic features and can incorporate specific movement patterns derived from activities of daily living through motion capture. Whole-joint models consisting of bone, muscle, and joint definitions allow for analysis of joint reaction forces and muscle activation patterns. By taking advantage of increased computational power and more sophisticated modeling techniques, important fundamental and clinical research questions can be addressed. Recently, MM techniques have been successful in the evaluation of biomechanical outcomes for total hip replacement and resurfacing procedures by several research groups. Focus areas include joint impingement and wear rates, both of which are related to rim (or edge) loading of the acetabular cup. Obviously, implant positioning has a major influence on these parameters. However, patient-specific motion patterns may also have a considerable influence on, for example, wear parameters.1 To study these effects, a combined workflow of experimental and numeric methods is typically used. Gait analysis (three-dimensional) and ground reaction forces are used as kinematic and kinetic input parameters to MM. Then generic musculoskeletal models are scaled and adjusted to the patient’s anatomy using anthropometric and medical image data. The accuracy of these subject-specific simulations has already surpassed levels that were previously possible. Despite these advancements, MM models, as with all computational simulations, are still subject to sensitivity checks to ensure that accuracy is maintained. Thus, with knowledge of implant position via postoperative scans or intraoperative navigation, hip reaction forces and relative orientations with respect to the acetabular cup can be computed. Then detailed biomechanical analyses of the postoperative loading conditions can be performed—for example, the differences between operated and nonoperated joints can be quantified.2 Furthermore, this approach can then be combined with simulation at the tissue level through, for example, finite element analysis, to tease out the mechanobiologic effects of surgical intervention.3 In addition to becoming a standard analysis tool for surgery and postoperative analyses, MM is also set to have an impact on longer-term follow-up issues such as rehabilitation programs, further improving patient care.4 During hospital stay or in-house rehabilitation programs, patient-specific MM may also be used to draw attention to potentially deleterious aspects of activities of daily living.5 There are other fields of orthopaedics in which similar musculoskeletal modeling techniques could be applied. For example, the biomechanical basis for trauma and subsequent tissue degeneration, which is seen in knee joint injury and subsequent posttraumatic osteoarthritis, is an excellent candidate for this approach. In the case of anterior cruciate ligament rupture, whole joint modeling, incorporating bone, muscle, and other joint tissues, would allow for analysis of joint reaction forces at the time of injury, as well as the new equilibrium state following loss of ligamentous restraint. Then, combining these data with finite element analysis could provide insights into the tissue-level changes that occur both within the joint and, particularly, in the adjacent tissues of the subchondral compartment. As is the case with all computational simulations, experimental validation of these models will be an important consideration. Therefore, procedures and strategies have been developed to validate various elements of musculoskeletal analysis.6 For example, electromyography is used to compare computed and in vivo muscle activity.7 However, it still remains a challenge to validate the simulated data against in vivo force data; the use of animal models may prove to be useful in this regard. Musculoskeletal models may also come to play a role in the prevention of long-term degenerative diseases. With the recent advances in motion-sensing devices, such as those used in the interactive entertainment industry, usually based on accelerometer and optical sensor technology, completely novel methods of disease detection and diagnosis may be possible. If these motion-sensing input devices can be used to generate accurate patient-specific kinematic data, then computational procedures such as those discussed above could be applied to detect early stages of joint degeneration to define optimal medical or surgical management and to optimize postoperative rehabilitation strategies. MM has now evolved to the point at which accurate patient-specific applications are a realistic option. This approach offers the ability to generate individualized patient-specific models that can quantify changes in joints and tissues following surgery or as a result of injury or disease.

Journal article

Tim Weber
A. Al-Munajjed
G. Verkerke
S. Dendorfer
T. Renkawitz

Influence of minimally invasive total hip replacement on hip reaction forces and their orientations.

In: Journal of Orthopaedic Research vol. 32 pg. 1680‐1687

Wiley

(2014)

DOI: 10.1002/jor.22710

show abstract

Minimally invasive surgery (MIS) is becoming increasingly popular. Supporters claim that the main advantages of MIS total hip replacement (THR) are less pain and a faster rehabilitation and recovery. Critics claim that safety and efficacy of MIS are yet to be determined. We focused on a biomechanical comparison between surgical standard and MIS approaches for THR during the early recovery of patients. A validated, parameterized musculoskeletal model was set to perform a squat of a 50th percentile healthy European male. A bilateral motion was chosen to investigate effects on the contralateral side. Surgical approaches were simulated by excluding the incised muscles from the computations. Resulting hip reaction forces and their symmetry and orientation were analyzed. MIS THR seemed less influential on the symmetry index of hip reaction forces between the operated and nonoperated leg when compared to the standard lateral approach. Hip reaction forces at peak loads of the standard transgluteal approach were 24% higher on the contralateral side when compared to MIS approaches. Our results suggest that MIS THR contributes to a greater symmetry of hip reaction forces in absolute value as well as force-orientation following THR.

Journal article

Tim Weber
S. Dendorfer
J. Grifka
G. Verkerke
T. Renkawitz

Does Computer-Assisted Femur First THR Improve Musculoskeletal Loading Conditions?.

In: BioMed Research International vol. 2015 pg. 1‐16

Hindawi Limited

(2015)

DOI: 10.1155/2015/625317

show abstract

We have developed a novel, computer-assisted operation method for minimal-invasive total hip replacement (THR) following the concept of “femur first/combined anteversion,” which incorporates various aspects of performing a functional optimization of the prosthetic stem and cup position (CAS FF). The purpose of this study is to assess whether the hip joint reaction forces and patient’s gait parameters are being improved by CAS FF in relation to conventional THR (CON). We enrolled 60 patients (28 CAS FF/32 CON) and invited them for gait analysis at three time points (preoperatively, postop six months, and postop 12 months). Data retrieved from gait analysis was processed using patient-specific musculoskeletal models. The target parameters were hip reaction force magnitude (hrf), symmetries, and orientation with respect to the cup. Hrf in the CAS FF group were closer to a young healthy normal. Phase-shift symmetry showed an increase in the CAS FF group. Hrf orientation in the CAS FF group was closer to optimum, though no edge or rim-loading occurred in the CON group as well. The CAS FF group showed an improved hrf orientation in an early stage and a trend to an improved long-term outcome.

Journal article

T. Renkawitz
M. Weber
H.-R. Springorum
E. Sendtner
M. Woerner
K. Ulm
Tim Weber
J. Grifka

Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty.

In: The Bone & Joint Journal vol. 97-B pg. 890‐898

British Editorial Society of Bone & Joint Surgery

(2015)

DOI: 10.1302/0301-620X.97B7.34729

show abstract

We report the kinematic and early clinical results of a patient- and observer-blinded randomised controlled trial in which CT scans were used to compare potential impingement-free range of movement (ROM) and acetabular component cover between patients treated with either the navigated ‘femur-first’ total hip arthroplasty (THA) method (n = 66; male/female 29/37, mean age 62.5 years; 50 to 74) or conventional THA (n = 69; male/female 35/34, mean age 62.9 years; 50 to 75). The Hip Osteoarthritis Outcome Score, the Harris hip score, the Euro-Qol-5D and the Mancuso THA patient expectations score were assessed at six weeks, six months and one year after surgery. A total of 48 of the patients (84%) in the navigated ‘femur-first’ group and 43 (65%) in the conventional group reached all the desirable potential ROM boundaries without prosthetic impingement for activities of daily living (ADL) in flexion, extension, abduction, adduction and rotation (p = 0.016). Acetabular component cover and surface contact with the host bone were > 87% in both groups. There was a significant difference between the navigated and the conventional groups’ Harris hip scores six weeks after surgery (p = 0.010). There were no significant differences with respect to any clinical outcome at six months and one year of follow-up. The navigated ‘femur-first’ technique improves the potential ROM for ADL without prosthetic impingement, although there was no observed clinical difference between the two treatment groups.

Thesis

Tim Weber
G. Verkerke

The biomechanical outcome after total hip replacement: Quantitative biomechanical evalulation of computer-assisted femur first THR.

Rijksuniversiteit Groningen University of Groningen Groningen, The Netherlands Faculty of Medical Sciences

2015 (2015)

show abstract

Sub-optimal implant positioning is one of the leading causes for implant failure in Total Hip Replacement (THR). Computer-assisted surgery in combination with ‘femur first’ (CAS FF) is believed to improve implant positioning and post-operative hip biomechanics. Combining patient-specific anatomy with patient-specific motion allows the computation of patient-specific biomechanics by means of musculoskeletal models (MM). This work applies MM to investigate operation-dependent differences between conventional THR and CAS FF in terms of biomechanics also focusing on MIS-approaches. A computational study showed that MIS approaches are superior to conventional approaches in terms of biomechanics. A prospective randomized controlled trial showed that CAS FF leads to a significantly improved hip reaction force (hrf) orientation compared to conventional THR. A trend for improved gait post-operatively for the CAS FF group did not reach statistical significance. The Improved hrf symmetry of the CAS FF group indicates a possible long-term benefit. Biomechanical load-cases as quantified by MM are an integral measure of patient-specific motion and anatomy and therefore able to provide a more complete picture of patients or populations in terms of biomechanics. The improved hrf orientation shows that the concept of combined anteversion leads to a favorable load-case scenario at an early stage.

Journal article

M. Weber
Tim Weber
M. Woerner
B. Craiovan
M. Worlicek
S. Winkler
J. Grifka
T. Renkawitz

The impact of standard combined anteversion definitions on gait and clinical outcome within one year after total hip arthroplasty.

In: International Orthopaedics vol. 39 pg. 2323‐2333

Springer Science and Business Media LLC

(2015)

DOI: 10.1007/s00264-015-2777-8

show abstract

Purpose Different target areas within the concept of combined cup and stem anteversion have been published for total hip arthroplasty (THA). We asked whether component positioning according to eight standard combined anteversion rules is associated with (1) more physiological gait patterns, (2) higher improvement of gait variables and (3) better clinical outcome after THA. Methods In a prospective clinical study, 60 patients received cementless THA through an anterolateral MIS approach in a lateral decubitus position. Six weeks postoperatively, implant position was analysed using 3D-CT by an independent external institute. Preoperatively, six and 12 months postoperatively range of motion, normalized walking speed and hip flexion symmetry index were measured using 3D motion-capture gait analysis. Patient-related outcome measures (HHS, HOOS, EQ-5D) were obtained by an observer blinded to 3D-CT results. Eight combined anteversion definitions and Lewinnek’s “safe zone” were evaluated regarding their impact on gait patterns and clinical outcome. Results Combined cup and stem anteversion according to standard combined anteversion definitions as well as cup placement within Lewinnek’s “safe zone” did not influence range of motion, normalized walking speed and/or hip flexion symmetry index six and 12 months after THA. Similarly, increase of gait parameters within the first year after THA was comparable between all eight combined anteversion rules. Clinical outcome measures like HHS, HOOS and EQ-5D did not show any benefit for either of the combined anteversion definitions. Conclusions Standard combined cup and stem anteversion rules do not improve postoperative outcome as measured by gait analysis and clinical scores within one year after THA.

Lecture

Tim Weber
S. Dendorfer
S. Bulstra
J. Grifka
G. Verkerke
T. Renkawitz

Navigated Femur First Total Hip Arthroplasty leads to improved Biomechanical Outcome after surgery.

In: Orthopaedic Research Society (ORS) 2015 Annual Meeting

Las Vegas, NV, USA

28.-31.03.2015 (2015)

Lecture

A. Billing
J. Götz
Tim Weber
S. Dendorfer

Positionsanalyse von winkelstabilen Plattenosteosynthesesystemen zur Versorgung von Metatarsalfrakturen mit Hilfe von patienten- spezifischen biomechanischen Modellen [Position Analysis of an angle-stable osteosynthesis plating system for treatment of metatarsal fractures using patient-specific biomechanical models].

In: 63. Jahrestagung der Vereinigung Süddeutscher Orthopäden und Unfallchirurgen e.V. 2015

Baden-Baden

30.04.-02.05.2015 (2015)

Lecture

Tim Weber
T. Renkawitz
J. Grifka
S. Bulstra
B. Verkerke
S. Dendorfer

Biomechanics of Computer-Assisted vs. Conventional THR after One Year Follow Up.

In: XXV Congress of the International Society of Biomechanics (ISB) 2015

Glasgow, Scotland

12.-16.07.2015 (2015)

Lecture

Tim Weber
S. Dendorfer
J. Grifka
M. Weber
M. Wörner
S. Dullien
B. Verkerke
T. Renkawitz

Verbessert die computerassistierte Femur-First-Operationstechnik für die Hüftendoprothetik den muskuloskelettalen Lastfall auf das Hüftgelenk?.

In: Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU) 2015

Berlin

20.-23.10.2015 (2015)

Journal article

Tim Weber
S. Dendorfer
S. Bulstra
J. Grifka
G. Verkerke
T. Renkawitz

Gait six month and one-year after computer assisted Femur First THR vs. conventional THR. Results of a patient- and observer- blinded randomized controlled trial.

In: Gait & Posture vol. 49 pg. 418‐425

Elsevier BV

(2016)

DOI: 10.1016/j.gaitpost.2016.06.035

show abstract

A prospective randomized controlled trial is presented that is used to compare gait performance between the computer assisted Femur First (CAS FF) operation method and conventional THR (CON). 60 patients underwent a 3D gait analysis of the lower extremity at pre-operative, 6 months post-operative and twelve months post-operative. Detailed verification experiments were facilitated to ensure the quality of data as well as to avoid over-interpreting of the data. The results confirm a similar data-quality as reported in the literature. Walking speed, range of motion and symmetry thereof improved over the follow-up period, without significant differences between the groups. While all parameters do significantly increase over the follow-up period for both groups, there were no significant differences between them at any given time-point. Patients undergoing CAS FF showed a trend to improved hip flexion angle indicating a possible long-term benefit.

Journal article

T. Renkawitz
Tim Weber
S. Dullien
M. Woerner
S. Dendorfer
J. Grifka
M. Weber

Leg length and offset differences above 5 mm after total hip arthroplasty are associated with altered gait kinematics.

In: Gait & Posture vol. 49 pg. 196‐201

Elsevier BV

(2016)

DOI: 10.1016/j.gaitpost.2016.07.011

show abstract

We aimed to investigate the relationship between postoperative leg length/offset (LL/OS) reconstruction and gait performance after total hip arthroplasty (THA). In the course of a prospective randomized controlled trial, 60 patients with unilateral hip arthrosis received cementless THA through a minimally-invasive anterolateral surgical approach. One year post-operatively, LL and global OS restoration were analyzed and compared to the contralateral hip on AP pelvic radiographs. The combined postoperative limb length/OS reconstruction of the operated hip was categorized as restored (within 5 mm) or non-restored (more than 5 mm reduction or more than 5 mm increment). The acetabular component inclination, anteversion and femoral component anteversion were evaluated using CT scans of the pelvis and the femur. 3D gait analysis of the lower extremity and patient related outcome measures (HHS, HOOS, EQ-5D) were obtained pre-operatively, six months and twelve months post-operatively by an observer blinded to radiographic results. Component position of cup and stem was comparable between the restored and non-restored group. Combined LL and OS restoration within 5 mm resulted in higher Froude number (p < 0.001), normalized walking speed (p < 0.001) and hip range-of-motion (ROM) (p = 0.004) during gait twelve months postoperatively, whereas gait symmetry was comparable regardless of LL and OS reconstruction at both examinations. Clinical scores did not show any relevant association between the accuracy of LL or OS reconstruction and gait six/twelve months after THA. In summary, postoperative LL/OS discrepancies larger than 5 mm relate to unphysiological gait kinematics within the first year after THA.

Journal article

T. Hölscher
Tim Weber
I. Lazarev
C. Englert
S. Dendorfer

Influence of rotator cuff tears on glenohumeral stability during abduction tasks.

In: Journal of Orthopaedic Research vol. 34 pg. 1628‐1635

Wiley

(2016)

DOI: 10.1002/jor.23161

show abstract

One of the main goals in reconstructing rotator cuff tears is the restoration of glenohumeral joint stability, which is subsequently of utmost importance in order to prevent degenerative damage such as superior labral anterior posterior (SLAP) lesion, arthrosis, and malfunction. The goal of the current study was to facilitate musculoskeletal models in order to estimate glenohumeral instability introduced by muscle weakness due to cuff lesions. Inverse dynamics simulations were used to compute joint reaction forces for several static abduction tasks with different muscle weakness. Results were compared with the existing literature in order to ensure the model validity. Further arm positions taken from activities of daily living, requiring the rotator cuff muscles were modeled and their contribution to joint kinetics computed. Weakness of the superior rotator cuff muscles (supraspinatus; infraspinatus) leads to a deviation of the joint reaction force to the cranial dorsal rim of the glenoid. Massive rotator cuff defects showed higher potential for glenohumeral instability in contrast to single muscle ruptures. The teres minor muscle seems to substitute lost joint torque during several simulated muscle tears to maintain joint stability. Joint instability increases with cuff tear size. Weakness of the upper part of the rotator cuff leads to a joint reaction force closer to the upper glenoid rim. This indicates the comorbidity of cuff tears with SLAP lesions. The teres minor is crucial for maintaining joint stability in case of massive cuff defects and should be uprated in clinical decision-making.

Journal article

F. Völlner
Tim Weber
M. Weber
T. Renkawitz
S. Dendorfer
J. Grifka
B. Craiovan

A simple method for determining ligament stiffness during total knee arthroplasty in vivo.

In: Scientific Reports vol. 9

Springer Science and Business Media LLC

(2019)

DOI: 10.1038/s41598-019-41732-x

show abstract

A key requirement in both native knee joints and total knee arthroplasty is a stable capsular ligament complex. However, knee stability is highly individual and ranges from clinically loose to tight. So far, hardly any in vivo data on the intrinsic mechanical of the knee are available. This study investigated if stiffness of the native ligament complex may be determined in vivo using a standard knee balancer. Measurements were obtained with a commercially available knee balancer, which was initially calibrated in vitro. 5 patients underwent reconstruction of the force-displacement curves of the ligament complex. Stiffness of the medial and lateral compartments were calculated to measure the stability of the capsular ligament complex. All force-displacement curves consisted of a non-linear section at the beginning and of a linear section from about 80 N onwards. The medial compartment showed values of 28.4 ± 1.2 N/mm for minimum stiffness and of 39.9 ± 1.1 N/mm for maximum stiffness; the respective values for the lateral compartment were 19.9 ± 0.9 N/mm and 46.6 ± 0.8 N/mm. A commercially available knee balancer may be calibrated for measuring stiffness of knee ligament complex in vivo, which may contribute to a better understanding of the intrinsic mechanical behaviour of knee joints.

Lecture

Tim Weber

Klimawandel in der Elektronik.

Haus der Technik Regensburg

2021 (2021)

labs

SensorLab

Forschungs- und Lehrgebiete

Big Data and Production Managment
Design of Experiment
Production Statistics
Machine Learning in production
SixSigma
failed part analysis of mechanical and electronical components and -assemblies

Vita

professorship

Big Data and Production Management (2024 - )

professional experience

Leiter Werkstofftechnik, Analyse- und Werkstofftechnik (RD), Zollner Elektronik AG
Postdoctoral Research Fellow, OTH Regensburg

doctorate

cooperative doctorate:

University of Groningen
Laboratory for Biomechanics, OTH Regensburg
Chair of Orthopedics and Trauma Surgery, UKR Regensburg

academic studies

Mechanical Engineering (Researach and Development), OTH Regensburg