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Biomedical subjects

Lutz Dürselen

Publications and source records attributed to Lutz Dürselen.

11 recordsLinked to original sources
PubMed2006

Ligament balancing in TKA: evaluation of a force-sensing device and the influence of patellar eversion and ligament release.

Ligament balancing in total knee arthroplasty may have an important influence on joint stability and prosthesis lifetime. In order to provide quantitative information and assistance during ligament balancing, a device that intraoperatively measures knee joint forces and moments was developed. Its performance and surgical advantages were evaluated on six cadaver specimens mounted on a knee joint loading apparatus allowing unconstrained knee motion as well as compression and varus-valgus loading. Four different experiments were performed on each specimen. (1) Knee joints were axially loaded. Comparison between applied and measured compressive forces demonstrated the accuracy and reliability of in situ measurements (1.8N). (2) Assessment of knee stability based on condyle contact forces or varus-valgus moments were compared to the current surgical method (difference of varus-valgus loads causing condyle lift-off). The force-based approach was equivalent to the surgical method while the moment-based, which is considered optimal, showed a tendency of lateral imbalance. (3) To estimate the importance of keeping the patella in its anatomical position during imbalance assessment, the effect of patellar eversion on the mediolateral distribution of tibiofemoral contact forces was measured. One fourth of the contact force induced by the patellar load was shifted to the lateral compartment. (4) The effect of minor and major medial collateral ligament releases was biomechanically quantified. On average, the medial contact force was reduced by 20% and 46%, respectively. Large variation among specimens reflected the difficulty of ligament release and the need for intraoperative force monitoring. This series of experiments thus demonstrated the device's potential to improve ligament balancing and survivorship of total knee arthroplasty.

Aged↗
PubMed2006

Sagittal curvature of total knee replacements predicts in vivo kinematics.

BACKGROUND: It is known that in vivo kinematics after total knee replacement is influenced by the design of the implant. The goal of this study was to show that the sagittal curvature of two different knee prostheses differing in geometric design predicts their in vivo motion behavior. METHODS: Three-dimensional tibio-femoral displacements of two prosthesis designs (single radius vs. dual radius) were measured during knee extension under weight bearing conditions by in vivo video fluoroscopy. Finite helical axes were computed to represent the tibio-femoral motions. Angular deviation alpha and the spatial localization deviation delta were used to characterize the motions. Angular deviation is the angle between each incremental finite helical axis and the medio-lateral axis of the femoral component of the prosthesis. The spatial localization deviation is the distance between each finite helical axis and the center of the femoral component of the prosthesis. Statistical comparisons were performed using the median and the interquartile range of the angular deviation and the spatial localization deviation. FINDINGS: The single-radius design showed finite helical axes concentrated at a single axis near to the medio-lateral axis of the femoral component. The angular and spatial localization deviation of the dual radius design were larger compared to the single radius design, exhibiting finite helical axes varying between two axes. INTERPRETATION: Video fluoroscopy in combination with finite helical axis analysis proved to be suitable methods to evaluate the in vivo kinematical behavior of total knee arthroplasty, which can be useful for implant designers. Knowledge of in vivo kinematics can also provide surgeons with more background information about the total knee arthroplasty models they implant.

Arthroplasty, Replacement, Knee↗
PubMed2006

Meniscal screw fixation provides sufficient stability to prevent tears from gapping.

BACKGROUND: Many meniscal fixation implants have low pull-out forces. It is still unknown if these forces are higher than the forces the implants must resist in vivo. It was hypothesized that meniscal repair with the meniscal screw as an example for a device of low pull-out force significantly reduces tear gapping. METHODS: Longitudinal tears were set in the posterior horn of the medial menisci of porcine knee joints. To observe the tears a translucent placeholder copying the original articular surface replaced the medial tibial plateau. The knees were moved in a loading and motion simulator under various external moments and axial loads and gapping of the tear was registered. The measurements were repeated after fixation of the tears with three ClearFix Screws, which show a low pull-out force of 20N only. FINDINGS: Maximum gapping (median 1.6mm, min/max 1.1/1.8mm) occurred at 200N axial joint load under the combination of a valgus and external rotation moment. Fixation with the ClearFix Screw significantly reduced tear gapping in all load cases. INTERPRETATION: Moderate joint loads only lead to small gaps of meniscal tears. Meniscal fixation with the ClearFix Screw prevents longitudinal meniscal tears from gapping. This could indicate from a biomechanical point of view that fixation implants of low pull-out strength are not in danger of failure in a normal rehabilitation regimen.

Animals↗
PubMed2006

Evaluation of a 3D object registration method for analysis of humeral kinematics.

In 3D image-based studies of joint kinematics, 3D registration methods should be automatic, insensitive to segmentation inconsistencies and use coordinate systems that have clinically relevant orientations and locations because this is important for analyzing rotation angles and translation directions. We developed and evaluated a registration method, which is based on the cylindrical geometry of the humerus shaft and an analysis of the inertia moments of the humerus head, in order to consistently and automatically orient the humerus coordinate system according to its anatomy. Registration techniques must be thoroughly evaluated. In this study we used a well-detectable marker as reference, from which coordinate system determination errors of a 3D object could be measured. This allowed us to quantify by means of unique error analysis the translational and rotational errors in terms of how much and about/along which humeral axis errors occurred. The evaluation experiments were performed using virtual rotations of 3D humeral binary image, a humerus model and a 3D image of a volunteer's shoulder. They indicated that the humeral coordinate system determination errors primarily originated from segmentation inconsistencies, which influenced mostly the humeral transverse axes orientation. The error analysis revealed that the developed registration method reduced the effect of manual segmentation inconsistencies on the orientation of the humeral transverse axes up to 37%, in comparison to the commonly used inertia registration.

Biomechanical Phenomena↗
PubMed2006

Biological response to a new composite polymer augmentation device used for cruciate ligament reconstruction.

A resorbable composite augmentation cord braided of poly(L-lactide) and poly(L-lactide-co-glycolide) fibers was designed for the temporary protection of repaired cruciate ligaments. This study examined the biocompatibility of the new device and the influence of augmentation duration on ligament healing in a sheep model. The anterior cruciate ligament (ACL) was cut close to the femoral insertion and reinserted with sutures. The repaired ACLs were augmented with the slowly degrading new composite cord and alternatively with a faster degrading polydioxanone cord (PDS). A tendon graft group (gold standard) served as control. Histological evaluation and biomechanical testing were performed after 6 months. The composite cord showed no signs of degradation, whereas the PDS was intra-articularly resorbed. Both devices showed only minor foreign body reactions, proving their good biocompatibility. However, 9 of 11 composite cords had ruptured too early because of fatigue at the bone tunnel entrances. All operated knees were less stable than the nonoperated collateral joints. Knees equipped with the composite cord showed the largest anterior instabilities, whereas the PDS-augmented group exhibited in some cases knee instabilities comparable with that of the tendon group. A positive effect of a longer mechanical protection by a slowly degrading augmentation could not yet be shown. The fatigue strength of the device still needs improvement.

Animals↗
PubMed2004

Establishment of a knee-joint coordinate system from helical axes analysis--a kinematic approach without anatomical referencing.

This study establishes a functional knee-joint coordinate system (FCS) derived from active motion. The scale invariant properties of helical axes were used in order to avoid inter-observer errors associated with the traditional anatomical referencing techniques. The algorithm was tested with six cadaveric specimens in a knee-joint motion and loading apparatus. To determine the FCS sensitivity to variable loading, rotational moments were applied to the tibia while extending and flexing the knee. Each derived FCS was compared with the clinically derived anatomical coordinate system (ACS). The FCS was reproducible when the loading condition was the same. Changing the rotational moments from internal to external affected the orientations and the positions of the FCS. The largest displacement of 20.8 mm in average occurred in the medio/lateral direction. The FCS corresponded with the ACS for all specimens and loading conditions. The origin was always located within the femur along the transepicondylar line. The orientations differed less than 16.6 degrees in average, thus allowing the use of clinical terminology. These findings suggest that the FCS might improve the ability to clinically assess kinematic alterations provided that the reference motion is reproducible.

Adult↗
PubMed2003

Control of material stiffness during degradation for constructs made of absorbable polymer fibers.

Augmentation devices for cruciate ligament surgery should provide gradually decreasing mechanical properties with a half-time strength of at least 6 months to temporarily protect healing tendon grafts or sutured ligaments against high tensile loads during the postoperative healing period. The absorbable material of choice that shows such slow degradation kinetics is poly(L-lactide). However, previous studies have shown that poly(L-lactide) fulfills the requirement of a long half-time strength, while the corresponding stiffness decreases at a much slower rate. An augmentation stiffness that does not change much versus time cannot provide a gradual increase in graft load, which is important to stimulate the orientation of the collagenous tissue. Therefore a new augmentation device was designed, which should decrease both in strength and stiffness during degradation. The cord was braided out of two fibers made of poly(L-lactide) and poly(L-lactide-co-glycolide), which degrade at different rates. The cord prototype was degraded in vitro and the rupture force and stiffness was tested at eight different time points up to 60 weeks. The initial rupture force and stiffness was 522.7 +/- 2.8 N and 104.1 +/- 3.8 N/%, respectively. Both strength and stiffness decreased continuously with a half-time strength of 18 weeks and a half-time stiffness of 39 weeks. The gradually decreasing stiffness was achieved by the breakdown of the faster-degrading fiber component made of poly(L-lactide-co-glycolide). Thus the new augmentation device can provide a continuous increase of forces in a tendon graft or in a healing ligament.

Biocompatible Materials↗
PubMed2003

Cyclic joint loading can affect the initial stability of meniscal fixation implants.

OBJECTIVE: To identify the effect of cyclic joint loads on the initial fixation strength of different meniscal repair techniques. DESIGN: Three different meniscal refixation implants and one suturing technique were tested for initial stability in porcine knee joints after cyclic joint loading. BACKGROUND: Existing studies tested the initial pull out strength of meniscal fixation implants. It remains unknown how such implants perform under cyclic joint loading. METHODS: The Meniscal Fastener, the Meniscal Arrow, the ClearFix Screw, and a horizontal suture (PDS 1) were implanted in 64 porcine knee joints after setting a tear in the posterior horn of the medial meniscus. In one group of each device the menisci were excised directly after implantation and subsequently subjected to a pull out test. The knee joints of the other groups were exposed to 5000 axial load cycles between 10 and 200 N prior to the pull out test. RESULTS: The horizontal suture showed the highest pull out force (103 N, SD 19 N). Arrow (52 N, SD 18 N), Meniscal Fastener (29 N, SD 3 N), and Meniscal Screw (22 N, SD 8 N) failed at significantly lower loads. Cyclic loading led to a decreased initial pull out force only for the horizontal suture (82 N, SD 26 N) and the Meniscal Fastener (23 N, SD 5N). CONCLUSIONS: Cyclic joint loading can lead to reduced fixation strength especially of meniscal refixation implants and sutures with relatively low stiffness. However, it remains unclear which fixation strength is necessary to provide conditions for meniscal healing. RELEVANCE: The current study adds information to the understanding of how meniscal fixation systems perform mechanically especially after cyclic joint loads.

Absorbable Implants↗
PubMed2003

Gapping phenomenon of longitudinal meniscal tears.

OBJECTIVE: To investigate the gapping behaviour of longitudinal meniscal tears. DESIGN: The gap size of longitudinal meniscal tears was measured in porcine knee joints under various joint loading conditions. BACKGROUND: Many meniscal fixation implants have low pull out forces. However, it is unknown if these forces are less than the forces the implants must resist in vivo. It is also unknown if gapping occurs in longitudinally torn menisci and what joint loads induce gapping. METHODS: Longitudinal tears were set in the medial menisci of eight porcine knee joints. To observe the tears an opaque placeholder of the same shape as the original articular surface replaced the medial tibial plateau. The knees were exposed to flexion-extension cycles in a loading and motion simulator under 30 and 200 N axial joint load without external moments, under tibial rotation moments, varus or valgus moments, and combined moments. For each load condition the maximum gap of the tear was registered. RESULTS: Maximum gapping (1.59 mm, SD 0.47) occurred in the 3 cm tear at 200 N axial joint load under the combination of a valgus and external rotation moment. An internal tibial rotation moment produced the smallest gaps in tears of any length and at any axial joint load. CONCLUSIONS: The maximum gap size found in this study and the previously published pull out stiffnesses of meniscal fixation implants reveal maximum forces on the implant in vivo of only 8.4 N. This explains why meniscal tears fixed with implants of low pull out strength can heal. RELEVANCE: The current study shows that moderate joint loads only lead to small gaps of meniscal tears. Clinically, this means that fixation implants of low pull out strength are not in danger of failure in a normal rehabilitation regimen.

Animals↗
PubMed2003

Accurate determination of a joint rotation center based on the minimal amplitude point method.

In many computer-assisted surgery procedures in the field of joint replacement a joint rotation center must be located. To this end, joints such as the hip or the shoulder are approximated as spherical joints, and the most commonly used numerical method is the sphere-fitting algorithm. However, this method has a numerical instability where there is a limited range of motion caused by, for example, joint impingement. The aim of the present study was to develop an alternative kinematic method called the minimal amplitude point method. This method estimates the localization of the rotation center and can easily be integrated into program codes of computer-assisted surgery modules. It mainly consists of identifying the point of a mobile segment that moves least in the reference coordinate system of an immobile segment using an optimization procedure (genetic algorithm). The point determined can then be assumed to be the rotation center of the joint. To compare results of the two methods, an experimental set-up of two rigid solids linked by a spherical joint with known geometry was used to compute the rotation center. In contrast to the sphere-fitting method, the minimal amplitude point method permits the evaluation of the rotation center with an error of less than 4.1 mm, having a range of motion (ROM) of 5 degrees. An equivalent accuracy for the sphere-fitting method requires an ROM of 45 degrees.

Algorithms↗