Luc Labey

Fixation strength of meniscal repair devices

The aim of this study was to measure and compare the ultimate failure strengths and cyclic fatigue strengths of currently available meniscal suturing devices. No statistically significant difference in failure load was found between a vertical loop suture (mean 46.3 N), a horizontal mattress suture (52.5 N), the T-fix Device (47.5 N), and the 16-mm (39.2 N) and 13-mm (32.8 N) Bionix Arrow. Statistically inferior results were seen with the 10-mm Bionix Arrow (18.8 N), the S.D. Sorb Stapler (4.3 N), and the 12-mm Arthrex Meniscal Dart (10.5 N) (P<0.01). The Mitek Meniscal Repair System (28.1 N) performed intermediate, with significantly better results than the S.D. Sorb Stapler and the 12-mm Arthrex Dart, but significantly worse than the vertical and horizontal sutures, the T-fix and Bionix 16-mm Device (P<0.01). Cyclic fatigue strength was significantly less for the 10-mm Bionix Arrow, the S.D. Sorb Stapler, and the 12-mm Arthrex Meniscal Dart (P<0.01) compared to all other devices. We conclude that the 13- and 16-mm Bionix Arrow and the T-fix Device have comparable ultimate failure strengths and cyclic fatigue strengths to conventional meniscal suturing techniques. The 10-mm Bionix Arrow, S.D. Sorb Stapler, and the 12-mm Arthrex Meniscal Dart, however, have far inferior failure and cyclic fatigue strengths and their clinical application should be questioned.

A new technique for the three-dimensional study of the spine in vitro and in vivo by using a motion-analysis system

We introduce a new method with a motion-analysis system (MAS) to study the vertebral model in vitro. Compared with the currently most accurate technique, roentgen stereophotogrammetric analysis (RSA), the difference between the RSA and the MAS is 0.12 degree +/- 1.64 degrees. An accuracy with an error of 0.08 degree +/- 1.15 degrees is determined by means of an angle gauge. Although a significant difference between the MAS and the goniometer (p = 0.04) is found around the X-axis (theta; transverse plane), it is limited to < 1 degree. The MAS provides an in-depth insight into the mechanism of the three-dimensional rotation at each vertebra in vivo. The backward inclination of the apical vertebra (AV) and forward inclination of the upper-end vertebra (UEV) around the Y-axis (phi) results in a correction of the hypokyphosis shown by the Cobb angle in the sagittal plane. The clockwise rotation of the UEV in the Z-axis (psi) leads to a reduction of the Cobb angle in the frontal plane. Additionally, the MAS as an intraoperative alternative shows different results of the derotation maneuver by the Cotrel-Dubousset instrumentation (CDI) compared with the computed tomography (CT) scan. Our method gives more direct details of the derotation not influenced by patient posture, as observed in the CT scan.

The development of a physiological hip prosthesis: the influence of design and materials

A wooden femur model was used together with matched cementless experimental implants to investigate the influence of some design concepts on the stress distributions within the proximal femur model, with emphasis on the longitudinal stresses on the outer bone surface, because the longitudinal stresses are believed to be the most important stresses in view of the laws of bone remodelling. In addition to the integration of alternative geometrical design concepts in a hip prosthesis design, the effect of using alternative materials upon bone stresses was also investigated. Stress evaluation was made by a combination of two-dimensional finite element analysis and strain-gauge measurements. The results and conclusions drawn from these experiments have led to a prototype of a so-called “physiological” hip prosthesis, in which are integrated a properly oriented collar, a hinge between stem and neck part, and a flexible stem.

Changes in contact area characteristics of the ankle after a cartilage biopsy at the postero-medial rim of the talar dome

OBJECTIVEnStudy the changes in local and generalized biomechanical characteristics of the ankle joint, associated with a well defined cartilage biopsy at the postero-medial rim of the talar dome, to evaluate its safety.nnnMETHODSnTen cadaver ankles were (sub-) physiologically loaded pre- and post-biopsy; in neutral position, 10 degrees of plantar-flexion (PF) and 10 degrees of dorsi-flexion (DF). Fuji film was used as transducer. Qualitatively, the coverage of the biopsy by the tibial plafond, and changes in the shape of the footprint were analyzed. Quantitatively, the pressure profile plot, normalized-tibio-talar contact area and the centroid position of pressure were examined. Results were reported as a mean for all specimens, and as individual values for every single specimen as well.nnnRESULTSnMean results did not show significant changes, but those of some single specimens did. The majority of those changes were in PF. Some occurred in N, and besides two exceptions none occurred in DF. Two specimens did not show any change. One specimen showed an isolated quantitative change. Seven specimens showed both qualitative and quantitative changes. However, all changes were of low-magnitude and contact stresses did not show any rebound effect.nnnCONCLUSIONSnAlthough biopsies at the postero-medial rim of the talar dome did not induce on average significant changes in quantitative contact characteristics, few specimens did show some alterations. Currently, the investigated biopsy site seems safe, but long term follow-up studies in patients are needed for confirmation.

An in-vitro study of human knee kinematics: natural vs. replaced joint

Cadaver specimens mounted on a knee simulator combined with motion tracking devices have been used for the kinematics study of the human knee. The results of these studies have shown that the classical four bar linkage model of the knee is not adequate. This obviously has repercussions for the design of knee implants. They should at least permit normal kinematic behavior to prevent abnormal loads on the soft tissues and on other joints of the leg. Studies where implant kinematics can be compared to kinematics of the natural knee of the same specimen are very rare, though. In this project, the kinematics of six fresh frozen human cadaver knees in the natural state and after replacement of the knee joint with a bi-cruciate stabilizing implant were evaluated using a knee simulator and stereophotogrammetry. Before testing, frames with reflective markers were fixed to the femur and tibia. Then, a CT scan was made and the images were processed to identify anatomical landmarks and their position with respect to the reflective markers. Thus, an anatomically relevant coordinate system could be defined for each bone. During a squat, the motion of the markers was continuously measured. Several load conditions were considered for each specimen. The data obtained enabled us to calculate the motion of the femur and tibia with respect to each other and present that in clinically relevant terms. After testing, a second CT scan was made to check the position of the implant with respect to the original articular surfaces and also for a control of the position of the marker frames. The results show that kinematics of the natural knee joint are more variable than expected. The knee replacement, on the other hand, produces a consistent kinematics pattern in all the specimens.

The Development of a Physiological Hip Prosthesis: Evaluation of the Strains after Implantation of a Prototype of Hip Implant: Experiment in a Dry Femur

Based upon previous research on the relation between hip prosthesis designs and strain distributions in a proximal femur model, a prototype of a physiological hip prosthesis was designed and manufactured. Strain gauge measurements on a dry femur before and after implantation of this prosthesis were made in different loading conditions simulating one-legged stance with and without torsional loading and two-legged stance. The strains in the outer cortex were within 10% of the physiological values along the whole medial side in all measurement conditions.

Identification of landmarks on lower limb joint from CT images for kinematics studies. A totally semi-automatic procedure

The identification of an accurate, reliable and patient specific coordinate system for a bone is fundamental to analyze the kinematics of a human joint. The accuracy in the localization of anatomical landmarks of joint surfaces is extremely important because even a small variation in their positions could induce a high variation in the definition of anatomical axes and further on the kinematics output. The aim of this study was to develop and validate a semi-automatic, accurate, and reproducible routine able to identify the position of anatomical landmarks on joint surfaces. This routine, starting form a CT of a femoral bone, used as input, is able to identify semi-automatically the femoral head and the medial and lateral distal femoral condyles. Moreover it allows the identification of the following anatomical landmarks: the Femoral Hip Center (FHC), the Femoral Medial Epicondyle (FME) and the Femoral Lateral Epicondyle (FLE). From these points a standard coordinate system of the femur is univocally determined according to previous literature works. Compared to other commercial process, extensive used in this field, one peculiarity of this routine is that it is not necessary to generate the 3D model of the joint in order to define the anatomical landmarks. Usually, to generate a 3D lower limb model, with the commercial process, 4 to 5 hours are needed, with this approach we can significantly reduce this time. To validate the routine we analyze ten different CT of lower limbs. Two different tests were performed. The first test was performed to verify and check the output geometry of the model; the second test was aimed to estimate the repeatability and reproducibility of the procedure. For such task five different operators identified for each model the three anatomical landmarks, three times each. The Intra-Class Correlation coefficient (ICC) values (intra and inter) obtained for the landmarks were always higher than 0.996. Comparing the results obtained with this routine with the results obtained using largely used commercial software we found a significant reduction of the error as regards the evaluation of landmarks in terms of inter and intra-observer variability. For example, in the worst condition, on the identification of the femoral lateral condyle point (FLE), the same operator found an average and maximum distance between the real point and the landmark found of respectively 3.5 and 8.8 mm with the use of the commercial software and of respectively 0.8 and 0.9 mm with the use of our routine

Repeatability and contact stress gradient detection of sealed pressure-sensitive film when used in a physiological joint model

Sealed pressure-sensitive film is frequently used to record contact characteristics in physiological joints. However, the effect on the pressure-recording characteristics of sealing the film when used in these circumstances has never been studied. This study compares the coefficient of variation, the standardized coefficient of variation, the tangent and secant contact stress gradients, and the actual pressures between unsealed and sealed Fuji film, in a simplified physiological joint model with a full-thickness surface defect. Unsealed film and sealed film were loaded through a range of nominal loads and the resulting stains were analysed by use of custom-made macros for the ImageJ image-processing program. The coefficient of variation did not exceed 5.7 per cent (sealed film), and the standardized coefficient of variation did not exceed 1.8 per cent (unsealed and sealed film). Contact stress gradients did not differ significantly. The recorded pressure at the level of surface defects was always about 0.2 MPa higher in the case of sealed film, and therefore predictable. It is concluded that sealing the film will not change the pressure-recording characteristics.

Bone strains and anterior lift-off, measured with three alternative designs of tibial components of TKA.

Total knee replacement is a successful procedure with high clinical success rates. Problems are mostly initiated on the tibial side, and may be due to – amongst others – improper mechanical design of the tibial base plate. In this paper some new design concepts for the tibial component of a total knee prosthesis are presented. They are evaluated experimentally using a model for a proximal tibia, and strain gauge measurements and displacement measurements as experimental techniques. The designs are meant to yield a physiological load sharing between the trabecular and the cortical bone in the proximal tibia, and to minimize anterior lift-off of the tibial base plate. The optimal design required a metal backing of the plastic part and a thin continuous metallic rim in contact with the proximal tibial cortex. An optimal macro-composite structure within the plastic part was obtained by using thin steel wires in the transversal direction, connected to the metallic rim. With this optimal design, it was shown that the force required to close the anterior gap at simulated knee bending was smaller than 250 N, which can easily be applied clinically by an anteriorly placed clamp or bone screw.

Delopment of an experimental set-up for assessment of relative movement of hip prostheses in vitro

Starting from a dear and quantifiable definition of local relative movement between the hip prosthesis and the bone, we developed a method to measure the defined movement and an instrumentation to accomplish the measurements in practice. Measurements were made on a custom-made hip prosthesis.