Comparison of two methods for reconstruction of the posterior cruciate ligament using a computer based method: quantitative evaluation of laxity, three-dimensional kinematics and ligament deformation measurement in cadaver knees.

The aim of this paper is to present a biomechanical comparison of two different methods for reconstruction of the posterior cruciate ligament in cadaver knees. We used an original computer-based method allowing precise calculation of three-dimensional (3D) knee kinematic parameters as well as the estimation of combined graft deformation (elongation-flexion-torsion). After isolated posterior cruciate ligament (PCL) dissection, double bundle and 'over-the-bottom' methods were performed successively on each knee using synthetic polyester ligaments. The effect of pre-tensioning was tested with the 'over-the-bottom' method. antero-posterior (A-P) and rotational laxity as well as 3D kinematics were recorded and analysed. Our computer based method allowed us to show that both reconstruction methods were equivalent in restoring A-P and rotational laxity as well as kinematic curves. Combined deformation of the prostheses was equivalent for both ligaments.

Computer-based method for the 3-D kinematic analysis of posterior cruciate ligament and postero-lateral corner lesions.

Posterior cruciate ligament (PCL) rupture, whether or not combined with postero-lateral corner (PLC) tears, are more often diagnosed today thanks to improved imaging techniques. However, due to the lack of reliable instrumentation to quantitatively evaluate the knee, much is still unknown about the function of these ligamentous structures. The aim of this paper is to present results on the effect of progressive resection of the PCL and PLC on knee laxity and 3-D knee kinematics. The results show that 3-D movement analysis is important and complements laxity measurements by helping to interpret the complex alteration of knee function.

Computer based method for the three-dimensional kinematic analysis of combined posterior cruciate ligament and postero-lateral complex reconstructions on cadaver knees.

The aim of this study is to evaluate the effect of combined posterior cruciate ligament (PCL) and postero-lateral corner (PLC) reconstruction on laxity and three-dimensional kinematics of cadaver knees. We performed anatomical double bundle PCL reconstruction, and functional one bundle 'over-the-bottom' PCL reconstruction combined with one type of PLC reconstruction, running from the postero-lateral tibia to an isometric point near the lateral epicondyle of the femur. Our results showed that combined reconstruction was necessary to restore rotatory laxity. PLC reconstruction, according to the technique described, invariably created a shift towards internal rotation of the kinematic curves, compared to the intact knee.

[Design, construction and modularity of pressure-fit acetabular cups]. / Form, Konstruktion und Modularität von Pressfit-Hüftpfannen.

To enable a comparison of different pressfit acetabular cups objective criteria are essential. The aim of this study is to describe the design features of this type of cup and to analyse currently available cups. 30 implants were systematically measured and analysed. The mean surface roughness (Ra) was determined and configurations established with the light section technique. For further evaluation the cups were transversely sectioned. The cups are made of pure titanium, titanium alloy or polyethylene coated with titanium. Five implants take the form of monoblocks. The configuration is predominately (n = 25) flattened spherical. The size of eight cups corresponds to the outer diameter, 19 cups have a larger outer diameter (overdimensioning), 3 cups have a smaller outer diameter (underdimensioning). The magnitude of overdimensioning is, on average, 1.9%. 9 cups are provided with plugs, hollow cylinders, fins or rings as outer stabilizers. Surface roughness achieved with corundum blasting is 6.8 microns. Titanium porous-coated implants have a surface roughness of 21-32 microns. 24 cups have polyethylene inserts, most of which are snap-fixed with equatorial lips. For 16 cups, full-ceramic inserts are available. 4 cups have a metal insert. Titanium implants with structured or HAC-coated surfaces have become the accepted standard for cementless acetabular cup implantation. Together with ceramic, metal, or modified polyethylene inserts they meet the requirement for permanent osteo-integrative stability.

[Modification of form, material and modularity of threaded acetabulum cups]. / Modifikationen von Form, Material und Modularität der Schraubpfannen.

The fixation principle of threaded cups ensures high primary stability. Inadequate results with first-generation threaded cups led to modifications of surface machining. 10 threaded cups of the first generation, and 27 of the second and third generations were systematically analysed and their shapes measured using a no-touch light section technique. In addition, measurements of surface roughness were performed. Implants of the first generation made of polyethylene, ceramic or cobalt-chrome have an average surface roughness (Ra) of 1.5 microns. Approximately one-half of these implants have a conical shape, and one-third a height that is greater than the radius. Threaded cups of the second generation are made either of CP-titanium or titanium alloy. The average corundum-blasted surface roughness is 4.5 microns. Hydroxyapatite-coated (HA) implants have a surface roughness of 5.0 microns. Approximately 45% of the implants have a conical, biconical or flattened-conical shape, while one-third are of hemispherical shape. Approximately 90% of the cups have a height that is up to 23% smaller than the radius. A few cups have a height that approximates the radius. Implants of the third generation with identical surface structure can be supplied with crosslinked-polyethylene inlays or, optionally, with metal/metal or ceramic/ceramic contact surfaces. Primary stability, biocompatible materials and a structured surface are essential for ensuring osseointegration over the long-term. Corundum-blasted pure titanium or titanium alloys with corundum-blasted or HA-coated implants can be considered standard for these cups.

Criteria for success with threaded cups (design, material and modularity).

PURPOSE OF THE STUDY: Over a period of three generations, threaded cups were developed and have become viable contemporary cementless hip implants. A few implants already have a high success rate over the mid and long term. Aim of this study was to evaluate contemporary threaded cups. MATERIAL AND METHODS: 30 of the second and third generation cups were systematically analyzed and measured using by a no-touch light section technique. Construction of inner form was determined with half sections. RESULTS: Approximately 50% have a conical shape, although there is a trend towards a more anatomical shape. 83% of the cups have a height up to 23% smaller than the radius. Only conical threaded cups have a relatively thin and constant wall thickness (1 mm-1.8 mm). Corundum blasted pure titanium, titanium alloys or HA coated implants are considered the standard materials. The insert is pre-assembled in two implants, otherwise the cups have modular inserts. Total ceramic inserts are found in four cups. Ceramic inserts with a sandwich construction are found in six cups. One cup has a full-metal insert. All other cups with metal-metal inserts have a sandwich construction. DISCUSSION: The studies by Kody (6) and our own studies (10) show that the V-cut threads have high values for turning moment and tilting stability. CONCLUSION: The screw-in behavior of threaded cups is largely determined by the design of the threads. Material and surface of threaded cups influence osseointegration and therefore long-term results. Contemporary threaded cups have a narrow V-cut and saw threads or flat threads with depths up to 3 mm, on average 4 turns, and pith values of approximately 4.5 mm. Three generations of threaded cups development were necessary to procure the current form with highly satisfactory mid- and long-term results.

[Biomechanics of the knee joint]. / Biomechanik des Kniegelenks.

The capsular and ligamentous structures as control system of a healthy knee-joint supported by the muscular system are responsible for the rolling and gliding motion of the femoral condyles on the tibial plateau. Both the condyles and the tibial plateau have individually developed but to each other adjusted shapes and fine structures thereby. These structures consist of hyaline cartilage at their three-dimensional surfaces and of closely packed fibrils (lamina splendens) as the final gliding zone for tensile load. The orientation of the collagenous fibres can be made visible by split lines. The chondral surfaces are indirectly in contact to each other and orthogonally stressed at the particular point of contact. The indirect contact of the cartilaginous surfaces happens under interposition of the menisci. The meniscus serves to reduce and equalize the surface pressure by its own projected surface on the one hand and by maintaining of a hydraulic pressure of the synovial fluid on the other hand. Deviations of the condylar position as a result on ligamentous instabilities or ruptures with a following occurring loss of congruence, meniscal lesions or traumatic ruptures lead to a rapid discharge of the synovial fluid under load. The result is a hydraulic head loss with direct contact of the chondral surfaces under stress leading to arthrotic deformations. Severe arthrotic deformations or very much every meniscectomy produce intraarticular lumped loads resulting in a hyper-physiologic chondral pressure and malnutrition thereby. Further on there develop subchondral stress concentrations (caused by the lumped loads) leading to osseous damages, too. MR-pictures can make visible these damages. Chondromalacia, fissure or even chondrolysis are arthroscopically detectable sometimes. As after-effects of deficient knee ligaments occur pathological deviations of the femoral condyles and resulting destructions of the articular surfaces under stress enormously intensified by strongly dynamic stress after ruptures of the cruciate ligaments with a too late muscular compensation. The reconstruction of cruciate ligaments is consequently required from biomechanical view to preserve the physiological position of the articular surfaces.(ABSTRACT TRUNCATED AT 400 WORDS)

[Considerations in differential therapy of insufficiency of the anterior cruciate ligament. Principles and clinical consequences]. / Uberlegungen zur differenzierten Therapie bei Insuffizienz des vorderen Kreuzbandes. Grundlagen und klinische Konsequenzen.

Ruptures of the anterior cruciate ligament are among the most frequent injuries of the joints. There is no longer any doubt regarding the necessity for surgical intervention. Several clinical and experimental studies suggest that the instability of the knee joint results in an accelerated degeneration of the menisci and cartilage. There are differences of opinion regarding the type of surgical procedures to stabilize the knee-joint. Although there are many different surgical procedures described in various publications, only one technique emerges as the preferred one. This paper will demonstrate different therapeutic concepts, based on the biomechanical background for the treatment of the anterior knee instability. It will consider the morphology of injuries, the demands of the patient and the full range of rehabilitative possibilities. Described herein are the indications and techniques of augmentation, protection and prosthetic replacement.

[Alloplastic replacement of the anterior cruciate ligament. Material technical and biomechanical principles, surgical technique]. / Alloplastischer Ersatz des vorderen Kreuzbandes. Materialtechnische und biomechanische Grundlagen, Operationstechnik.

The Trevira-ligament of Polyaethylenter-ephthalat (= Trevira-hochfest 730) seems to be the best qualified replacement of the anterior cruciate ligament at the present. It meets all material and technical requirements and makes allowances for all biomechanical knowledges. The modified over-the-top-technique by arthroscopy or mini-arthrotomy (minimal operative trauma) makes it possible to conserve still existing ligamentous and soft tissue and guarantees the post-operative immediate functional therapy. A potential reinstability--independent of each cause--doesn't imply worse starting conditions and enables corrections including the substitute of a ruptured synthetic ligament.

Computational fluid dynamics model of avian tracheal temperature control as a model for extant and extinct animals.

Respiratory evaporative cooling is an important mechanism of temperature control in bird. A computational simulation of the breathing cycle, heat and water loss in anatomical avian trachea/air sac model has not previously been conducted. We report a first attempt to simulate a breathing cycle in a three-dimensional model of avian trachea and air sacs (domestic fowl) using transient computational fluid dynamics. The airflow in the trachea of the model is evoked by changing the volume of the air sacs based on the measured tidal volume and inspiratory/expiratory times for the domestic fowl. We compare flow parameters and heat transfer results with in vivo data and with our previously reported results for a two-dimensional model. The total respiratory heat loss corresponds to about 13-19% of the starvation metabolic rate of domestic fowl. The present study can lend insight into a possible thermoregulatory function in species with long necks and/or a very long trachea, as found in swans and birds of paradise. Assuming the structure of the sauropod dinosaur respiratory system was close to avian, the simulation of the respiratory temperature control (using convective and evaporative cooling) in the extensively experimentally studied domestic fowl may also help in making simulations of respiratory heat control in these extinct animals.

Microstructural mechanical study of a transverse osteon under compressive loading: The role of fiber reinforcement and explanation of some geometrical and mechanical microscopic properties.

This Finite Element study aims at understanding the transverse osteon as a composite microstructure, and at differentiating the actions of each of its main components and their interactions. Three components of the osteon have been distinguished: the lamellae mineral-collagen matrix, the lamellae mineral-collagen reinforcement fibers and the Haversian canal content made of intracortical fluid and soft tissues. Numerical compression experiments have been performed, varying the microstructure properties. Our results show that fiber reinforcement of transverse osteons is only efficient at resisting dynamic compressive loadings, but that the improvement of the static compressive properties is very poor. Furthermore, the modeled stress distribution within the matrix and reinforcement fibers may explain why transverse osteons are often limited to a small number of lamellae (<8) and why internal lamellae could be stiffer than external ones.

Three-dimensional stress analysis of threaded cups - a finite element analysis.

A three-dimensional model of the left acetabulum with inserted threaded cup has been generated, based on the finite element method, to calculate stress patterns in the standing phase during walking. In this study, a hemispherical cup with sharp threads, a parabolic cup with flat threads and a conical cup with sharp threads were analysed and compared. Stress patterns in both implant components and adjacent bony structures were calculated in a directly postoperative situation. The different cups were found to induce different stress patterns, deformations and shifting tendencies. The inlays deform notably and show characteristic rotational movement patterns together with the shell. The inclination angle increases in the hemispherical cup and decreases in the parabolic cup. The conical cup levers outward almost parallel to the bone stock by approximately 0.05 mm. The pole surfaces of the various cups - especially the very convex area next to the threads - induce increased compressive stress in the superior section of the acetabular base. This is increased by a factor of three in the conical cup in comparison to the hemispherical cup and less so in comparison to the parabolic cup. This study illustrates that three-dimensional stress calculations are suitable for procuring additional biomechanical information to augment clinical studies, for evaluating implants and for establishing stability prognoses, especially for newly developed prototypes.

[Screw-in performance of threaded cups]. / Eindrehverhalten von Schraubpfannen.

INTRODUCTION: For threaded cups, cup diameter, the shape of the threads and the shape of the cup have a major influence on the screw-in performance. The designs of standard implants vary greatly, making it difficult to carry out comparative studies to provide clear-cut results on the effect of individual parameters on the insertion process. MATERIAL AND METHODS: 15 different prototype cups were manufactured for this study. Three sizes, three shapes and five thread designs were tested using artificial bone. Screw-in performance was measured with the slope of insertion torque before and after reaching the seating point, the torque at the seating point, the insertion angle and the change of slopes at the seating point. RESULTS: Modified trapezoid threads have the lowest insertion resistance and the clearest seating point as well as the most distinct change of slope at the seating point. Flat threads show lower insertion resistance and more increased slopes at the seating point than sharp threads. The slope of insertion torque before and at the seating point is higher for sharp threads in comparison to the other threads, the change of slop is however low. Larger cups show a higher insertion resistance. CONCLUSION: Screw-in performance is decisively influenced by the design of the threads. Modified trapezoid threads are the easiest to insert with excellent manual control, thus reducing the risk of intra-operative overturning. Flat threads also have a low screw-in resistance. Sharp threads have an unsatisfactory screw-in performance because the seating point cannot be "felt".

[Cementless stems of the hip. Current status]. / Zementfreie Hüftschäfte. Aktueller Stand.

Optimal fixation of cementless stems is a precondition for long-lasting stability. Thus, anchorage, stabilizers, material and surface are of essential importance. To achieve primary stability, good rotational, tilting and axial stability is necessary. Stabilizers such as fins and ribs optimize stability. The CCD-angle and length of neck-axis determine the offset (laterality), leg-length and center of rotation. The stem, is responsible for the fixation of the prosthesis and for transmitting forces to the bone. The types of fixation are epiphyseal (the femoral head is covered by a cup prosthesis), metaphyseal and meta-diaphyseal (with straight or anatomically shaped monoblock-prostheses of different lengths, modular and custom-made prostheses) and diaphyseal (using predominantly modular systems). Titanium alloys are the predominate material for cementless stems. The surfaces are generally corundum-blasted or plasma sprayed. For metaphyseal and meta-diaphyseal stems, survival rates from 95 to 98% have been reached after 15 years. Diaphyseal-fixed stems have mid-term survival-rates of 92-99%.

Function-dependent shape characteristics of the human skull.

Using the FEM-program ANSYS 5.4, we have shaped a model of the human skull in which the flow of forces and the relative location and magnitudes of stresses are investigated. Forces are applied from below through the tooth row of the upper jaw. An ample volume is provided for the transmission of these bite forces upward to the roof of the braincase, where bearings counteract the forces from below. Within this volume, no other morphological features are considered than two cone-shaped orbits and a nasal channel which has a rounded, triangular cross section, extending upward between the orbits. Under loads (= bite forces) acting simultaneously in the directions and relative sizes of realistic bite- and chewing forces, there occurred stress concentrations inside the model which resemble closely the morphological characteristics of the human skull. The most remarkable pathways of stresses correspond to Toldt's and Benninghoff's nasal, zygomatic and pterygoid pillars. Aside from these stress concentrations, stress-free regions become visible at places, where the skull shows excavations: the vaulted palate with canalis incisivus, the canine fossa, superior and inferior orbital fissure, or cavities like the maxillary sinuses and cavum cranii. Behind the posterior molars and the pterygoid, the stresses disappear abruptly, and in the side wall of the nasal cavity a maxillary hiatus remains without stresses. A flow of forces comparable to, but not at the exact position of the zygomatic arch extends from the highly stressed zygomatic bone rearward and upward. In a later step of simulation, somewhat deeper, at the place of the really existing zygomatic arch, a series of small forces was applied, which correspond to the resultant force that is created by the redirection of the pull of the m. masseter into the temporal fascia. This--biologically reasonable--manipulation of the model leads to a reduction of the forces in the zygomatic bone, and to a downward shift of the zygomatic arch and its isolation from the skull's side wall by a deep, stress-free temporal fossa. The similarity between the stress flow in the model and the shape of the skull seems to indicate that the skull, like the bones of the postcranial skeleton, develops its shape in dependence from the mechanic stressing through the process of causal histogenesis. In view of experimental results, the possibility cannot be ruled out, that the safety factors in the skull deviate from those in the postcranial skeleton.

Functional structure of the skull in hominoidea.

Finite elements stress analysis (FESA) was used to investigate the flow of compressive forces which occur if a homogenous, three-dimensional body representing the skull is loaded by simulated bite forces against the tooth row. Model 1 represents the snout alone. Bite forces are applied simultaneously, but increase rearward. Stresses in the model concentrate along the anterior contour and the lower surface of the model, leaving unstressed a nasal opening and a wide naso-oral connection. Model 2 represents the facial region, as far as the temporomandibular joint. The orbits and the nasal cavity are assumed to be present a priori. Model 3 applies reactions to the bite forces in the temporal fossa, corresponding to the origins of the masticatory muscles. Regions of the model under compressive stress correspond closely to the arrangement of bony material in a hominoid skull. If only the stress-bearing finite elements on each section are combined, and the stress-free parts neglected, the resulting three-dimensional shape is surprisingly similar to a hominoid skull. If bite forces are applied to parts of the tooth row only, the stress patterns are lower, asymmetrical and do not spread into all regions that are stress-bearing in simultaneous biting on all teeth. In model 2, the highest stresses occur at the tooth roots and along the forehead on top of the nasal roof. There are no marked stress concentrations on top of the orbits. The resulting shape resembles that of an orang-utan. In model 3, the highest stresses also occur at the tooth roots, but the circles of force mostly close below the brain case, so that the stress concentration in the forehead region remains much less marked. In this model, however, the stress concentrations are very similar to hollow brow ridges. The entire resulting shape resembles that of gorilla or chimpanzee skulls. A typical gracile australopithecine skull (STS-5) also shows clear similarities to the patterns of stress flow in our models. Compared to our earlier study of the modern human skull, differences relate to: the relative length and width of the dental arcade, the relative size of the brain case and the position of the arcade relative to the brain case. It seems that these traits are the points of attack of selective pressures, while all other morphological details are simply consequences of stress flow.

[Thread design of screw-in acetabulum prostheses]. / Gewindedesign von Schraubpfannen.

INTRODUCTION AND AIM OF STUDY: The screw-in behaviour and correct positioning of threaded cups is largely determined by the design of the thread. Up to now the various thread designs have not been systematically classified. METHODS: The thread designs of 10 first generation and 27 second generation threaded cups were analyzed using a tool setter and a no-touch light section technique. The following parameters were evaluated: thread shape, pitch, number of turns, rows of teeth, tooth length and shape. RESULTS: Threads of the first generation were V-cut or saw shaped. Thread depth was 3.1 mm on average; the mean width was 0.9-3 mm. Single-thread patterns predominated. The number of turns ranged from 1-7; the pitch was from 2.5-5 mm (single thread), or up to 20 mm (triple and quadruple threads). Cups had 3-16 rows of teeth. Threads of the second generation are V-cut, saw or flat shaped. Thread depth is 3 mm on average; mean width ranges from 0.3-2.2 mm. 72% of the threads have single-thread patterns. The number of turns ranges from 2-5; the pitch is from 2.5-6.2 mm (single thread). Cups have 4-24 rows of teeth. CONCLUSIONS: There are many different thread patterns with widely varying parameters. Contemporary threaded cups have a narrow V-cut and saw shaped threads or flat thread with depths up to 3 mm, no more than 5 turns, and pitch values of approx. 4.5 mm.

Pneumatized spaces, sinuses and spongy bones in the skulls of primates.

The earliest attempts to understand the "pneumatized spaces" in the skulls of primates in general were focussed on the hollow spaces and the epithelium which covers their surfaces. More recent approaches consider the sinuses as a means to optimise skull architecture. Still, many attempts to get hold of the meaning of the intriguing pneumatized spaces circle around the air filled volumes they enclose. Here, we would like to reverse the approach and focus our biomechanic interpretation on the walls surrounding the big, empty, or at least not mechanically resistant spaces, and their mechanical properties. As a working hypothesis, we consider not only the walls of the more or less closed cavities, or sinuses, but also the braincase, the orbits, and the nasal channel as thin-walled shells of which we know that they can carry surprisingly large loads with a minimum of material. Details of the wall's profiles fit with this approach. From the same viewpoint, the bubble-like, air-filled cavernous systems in the ethmoid or temporal bones, and the marrow-filled spongy substance in the upper jaw are looked at as honeycomb-structures, which provide mechanical properties that are biologically advantageous and allow the saving of weight.

The role of the zygomatic arch in the statics of the skull and its adaptive shape.

The zygomatic arch of mammals is usually considered a phylogenetic relic of the fenestrations of the skull roof which may be observed in morphological sequences of primitive vertebrate skulls. If this concept is correct, the element is comparable (though not homologous) to the jugal arches of diapsid reptiles. Two major questions then remain unanswered: why different elements are maintained in reptiles and mammals during evolution, and why the arches are maintained as relics of ancestral forms. It is tempting to respond to the latter question with a very simple answer, namely that the elements function in order to sustain mechanical stresses. In this paper, we raise the questions which quality of stresses occurs in a primate skull within the zygomatic arches and what relationship these stresses hold to the morphology of these bony elements. An answer has been sought by means of finite element stress analysis. We found that the zygomatic arch in primate skulls represents a structure which carries, under all biologically relevant conditions, either compressive or tensile stresses. In a very simple model of the human skull under bite forces, a strip of stresses occurs lateral to the orbits, which seems roughly comparable to the zygomatic arch. Once such a structure exists and is used as an insertion of adductor muscles, it will be exposed to bending stress in side view and in frontal view. Morphological details of the zygomatic arch (curvature, profile, suture) are well suited to sustain the evoked stresses by a minimum of material.

[Baker's cyst--a pre-arthrotic factor?]. / Die Baker-Zyste--ein präarthrotischer Faktor?

Between July 1989 and 1994 127 Baker-cysts have been operated and histologically examined with synovial biopsies out of the same knee. All Baker-cysts and synovial biopsies - including out of synovial membranes without macroscopically pathological findings and without other pathological intraarticular causal lesions - revealed a chronic synovitis. The Baker-cyst has to be regarded as a primary or secondary causative factor of chronic effusions and involves the development of a chronic synovitis by the disorder of the synovial and hydraulic system of the knee-joint. The exstirpation of the Baker-cyst as a prearthrotic factor is advised therefore.