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Biomedical subjects

M Müller-Gerbl

Publications and source records attributed to M Müller-Gerbl.

At least 37 records · Page 2Linked to original sources
PubMed1996

[Lesions of the popliteus system and their significance for the stability of the knee joint].

INTRODUCTION: Stäubli postulated a clinical significance of lesions to the popliteus system because of a 95% incidence in acute and 85.7% in chronic ruptures of the cruciate ligaments. The sparse clinical literature on this topic favours conservative or operative treatment as well. OBJECTIVE OF THE STUDY: What is the significance of isolated lesions of the popliteus tendon on translational stability of the knee joint? MATERIAL AND METHODS: The popliteus tendon was severed in six sheep. One year postop. the knee joints were evaluated by means of x-ray, biomechanical testing, computed tomography osteoabsorptiometry (CTOAM) and micromorphology. RESULTS: There were no pathological findings on x-ray. The simulation of the trauma situation ex vivo showed no instability whereas increased translation and progressive loosening of secondary stabilizers was found after one year (posterior and total aptranslation, compliance index p < 0.05). The position of the density maxima of the subchondral mineralization are about the same on the operated and the non-operated knee joint. All tendons healed macroscopically, but micromorphology exhibited a persisting increase of cross-sectional areas, a low differentiated ultrastructure of the tendon and an increased cellularity (p < 0.01). CONCLUSIONS EXPERIMENTAL: 1. intraarticular, extrasynovial tendons heal spontaneously even within the synovial environment; 2. healing is defective even one year postop.; 3. the postulate of the significance of the popliteus system for the stability of the knee is proven. Clinical: 1. (isolated) lesions of the popliteus go undetected with clinical and instrumented examination; 2. conservative treatment eventually results in increased posterior translational instability; 3. this will increase strain and load on the menisci and ACL- reconstructions.

Animals↗
PubMed1995

Morphomechanics of the humero-ulnar joint: II. Concave incongruity determines the distribution of load and subchondral mineralization.

BACKGROUND: A deeper joint socket (concave incongruity) is found at most angles of flexion of the humero-ulnar joint and maintained over a wide range of physiological loading. It is, however, unclear how far this incongruity affects the distribution of load and subchondral mineralization of this joint as compared with a congruous configuration. METHODS: Two nonlinear, axisymmetrical finite element models with two cartilage layers were constructed, one congruous and one incongruous, with a joint space of realistic magnitude. The distribution of subchondral mineralization was determined by computed tomography osteoabsorptiometry in the same six specimens that were investigated in the first part of the study, and compared with the biomechanical data obtained there and the predictions of the models. RESULTS: In the congruous case, the center of the socket is highly loaded, whereas the periphery does not experience mechanical stimulation. A central bone density maximum is predicted. With concave incongruity the position of the contact areas shifts from the joint margin towards the center as the load increases, and the peak stresses are considerably lower. A bicentric ventro-dorsal distribution pattern of subchondral mineralization is predicted, and this is actually found in the six specimens. CONCLUSIONS: Concave incongruity is shown to determine load transmission and subchondral mineralization of the humero-ulnar joint. It is suggested that this shape leads to a more even distribution of stress, provides intermittent stimulation of the cartilaginous tissue, and has beneficial effects on the metabolism, nutrition, and lubrication of the articular cartilage during cyclic loading.

Absorptiometry, Photon↗
PubMed1995

Subchondral bone density in the human elbow assessed by computed tomography osteoabsorptiometry: a reflection of the loading history of the joint surfaces.

The functional adaptation of bone tissue to the mechanical stresses acting on it has been convincingly established. This association should apply as well to the subchondral bone, reflecting the long-term distribution of stress over the joint surfaces. Thirty-six specimens of the human elbow joint were investigated by computed tomography osteoabsorptiometry in order to assess the distribution of the subchondral mineralization. The distal surfaces usually were more highly mineralized than the proximal components of the joint, whereas the humeroulnar and the humeroradial parts exhibited a similar degree of mineralization. The fovea of the radial head always showed a central density maximum, and the trochlear notch usually presented a bicentric distribution pattern, with maxima beneath the ventral and dorsal regions of the articular surface. The different patterns of subchondral mineralization were shown to reflect the loading history of the overlying articular surfaces, which is determined mainly by geometrical factors. The flatter socket of the humeroradial joint leads to central load transmission, but the deeper socket of the humeroulnar joint will, by contrast, give rise to bicentric stress distribution.

Absorptiometry, Photon↗
PubMed1995

[Anatomy and pathology of tendons].

Taking into account its detailed morphology, an attempt has been made to explain a tendon's ability to transmit force between its muscular origin and skeletal insertion. This ability depends upon the aggregation and binding capacity of the molecular elements of type I collagen and is known to decrease with advancing age. The internal structure of a tendon is modified both at the muscle-tendon junction and near its attachment to bone. The very low elasticity of tendinous tissue (about 3% to 8%) is due partly to the texture (pseudo-elasticity) and partly to the molecular composition. The so-called degenerative changes in a tendon begin with deterioration of the internal vascular network and are obviously--so far as its failing capacity is concerned--both initiated and accelerated by the degree of over-loading.

Aging↗
PubMed1994

[Change in subchondral mineralization after reconstruction of the anterior cruciate ligament of the sheep].

The cruciate ligaments are generally regarded as regulators of the joint kinematics, but also increasingly as a "Sensory organ" regulating the periarticular musculature, which influences the position of the contact surfaces and the direction and magnitude of the resultant forces. Indirectly, therefore, they influence the long-term stress distribution, which is itself reflected in the distribution of the subchondral mineralisation. An experimental investigation was therefore undertaken to see whether, in terms of this distribution, the distribution of the stress alters postoperatively, since this could be regarded as an early cause of degenerative change. We examined the distribution of the subchondral mineralisation of six tibiae from six adult Merino sheep 1 year after anterior cruciate ligament reconstruction with patellar tendon. The contralateral tibia we used as controls. Maximum subchondral mineralisation of both the medial and the lateral joint surfaces in all the control joints was found to be central. In the treated knees, however, the medial joint surface maxima were found to have been displaced towards the dorsomedial edge of the surface in every case. If the density pattern on the control side is accepted as the expression of a normal stress distribution, the distribution patterns on the treated side must indicate a pathologic distribution of stress. Reconstruction of the anterior cruciate ligament is therefore--at least in the animal model--not able to prevent the development of a pathologic stress distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Stress distribution in the trochlear notch. A model of bicentric load transmission through joints.

In 16 cadaver humeroulnar joints, the distribution of subchondral mineralisation was assessed by CT osteoabsorptiometry and the position and size of the contact areas by polyether casting under loads of 10 N to 1280 N. Ulnas with separate olecranon and coronoid cartilaginous surfaces showed matching bicentric patterns of mineralisation. Under small loads there were separate contact areas on the olecranon and coronoid surfaces; these areas merged centrally as the load increased. They occupied as little as 9% of the total articular surface at 10 N and up to 73% at 1280 N. Ulnas with continuous cartilaginous surfaces also had density patterns with two maxima but those were less prominent, and in these specimens the separate contact areas merged at lower loads. The findings indicate a physiological incongruity of the articular surfaces which may serve to optimise the distribution of stress.

Aged↗
PubMed1993

Physiological incongruity of the humero-ulnar joint: a functional principle of optimized stress distribution acting upon articulating surfaces?

Investigations into the distribution of subchondral bone density in the human elbow have suggested that the geometry of the trochlear notch deviates from a perfect fit with the trochlea, and that the load is transmitted ventrally and dorsally rather than through the centre of the humero-ulnar joint. We therefore decided to make a quantitative assessment of the degree of incongruity between the two components in 15 human specimens (age distribution 60 to 93 years) with different types of joint surface. Polyether casts of the joint cavity were prepared under loads of 10, 40, 160 and 640 N. The thickness of the casts was then measured at 50 predetermined points, and an area distribution of the width of the joint space represented in a two-dimensional template of the trochlear notch. The reproducibility of this procedure was tested by image analysis. At a load of 10 N, only a narrow space was present ventrally and dorsally in the joint, but in the depths of the trochlear notch a width of 0.5 to 1 mm was recorded in the centre, and up to 3 mm as its medial and lateral edges. Specimens with continuous articular cartilage showed a lower degree of incongruity than those with a divided articular surface. As the load was increased to 640 N, however, the original incongruity between the articular surfaces disappeared almost completely.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Cartilage degeneration in the human patellae and its relationship to the mineralisation of the underlying bone: a key to the understanding of chondromalacia patellae and femoropatellar arthrosis?

According to the literature subchondral bone plays a significant role in the transmission of load through joints and in the pathogenesis of osteoarthrosis. Therefore the degeneration of the articular cartilage was investigated in the patellae from 30 dissecting-room specimens and of 20 patients, previously submitted to arthroscopy, and subchondral mineralisation of their underlying bone was at the same time assessed by means of CT osteoabsorptiometry. Lateral cartilage lesions were localised over highly mineralised subchondral bone; these appear to be due to long-term stress. They were mainly found in the older specimens and showed a high rate of progression with increasing age. Medially localised cartilage lesions, on the other hand, were situated in a transitional region between moderate and slight subchondral mineralisation; they may be caused by infrequent stress peaks and by shear stress in the articular cartilage, the very medial part of the joint being deprived of mechanical stimulation for much of the time. These lesions were to be found predominantly in the younger specimens and showed little progress with advancing age. Patients with lateral cartilage degeneration exhibited higher, patients with medial chondromalacia patellae lower mineralisation than normals. Their density patterns therefore indicate a different mechanical pathogenesis of the cartilage lesions in the lateral and medial facet. It could be shown that CT osteoabsorptiometry allows an assessment of the mechanical situation, present in individual femoro-patellar joints, and that this situation is highly relevant for the pathogenesis of patellar cartilage degeneration.

Absorptiometry, Photon↗
PubMed1993

[Areas of contact in human humero-ulnar joints as a function of pressure, their connection through subchondral mineralization and joint surface morphology of the incisura trochlearis].

Evaluation of the stress distribution in joints can be obtained directly from contact areas and pressure forces, and also indirectly from the functional adaptation of the connective tissues. Therefore 8 human humero-ulnar joints, fixed in formalin, were examined for size and position of contact areas (polyether casting/Vidas image analyser) and their dependence upon the joint forces (Zwick material testing machine). The distribution of subchondral mineralisation was assessed, using CT osteoabsorptiometry. Depending on the joint force, the contact areas increase from about 10% of the total surface (20 N) to approximately 60% (1280 N). With weak forces they are localised ventrally and dorsally in the joint, with more powerful forces they run together centrally. With a divided articular surface they join at about 160-640 N, with a continuous surface, at about 40-80 N. Divided joint surfaces show a bicentric mineralisation pattern of the subchondral bone with ventral and dorsal maxima. Continuous surfaces, on the other hand, usually show central maxima. Both the mineralisation pattern and the position of the contact areas suggest a physiological incongruity of the humero-ulnar joint surfaces, which vanishes with increasing pressure due to viscoelastic deformation of articular cartilage and subchondral bone. More marked incongruity is postulated for the divided surfaces than for the others. The consequent peripheral transmission of pressure seems to involve a functional principle, which, present in several human joints, leads to both optimal distribution of the stress and better nutrition of the articular cartilage.

Aged↗
PubMed1993

[Mechanical stress and subchondral mineralization of the human elbow joint. A CT-osteoabsorptiometric study].

We examined 21 elbow joints (age 60-97 years; mean 79 years) that had been fixed in 3.7% formalin. The articular surface of the trochlear notch was completely divided in 10 cases, undivided in 5, and only partially divided in the medial aspect of the joint surface in 6. Subchondral mineralisation was investigated by means of CT osteoabsorptiometry (Müller-Gerbl et al. 1989) on sections 2 mm apart with a Siemens Somatom SF CT scanner. Two-dimensional reconstruction of the surface distribution was achieved by dividing it into 8 Hounsfield ranges (< 300 HU > 900 HU) and using a joint template. Higher values for the subchondral mineralisation are usually found in the distal and medial parts of the joint, indicating greater stress there. Whereas the radial head and the capitulum show a distribution pattern with mineralisation falling off more or less concentrically from the centre outwards, the trochlea and trochlear notch are often poorly mineralised in the centre. There is one maximum on the proximal and one on the distal aspect of the joint surface. Such "two-peak" distribution patterns are more often found when there is complete central division of the articular cartilage of the trochlear notch than when it is continuous. In the latter case, a more central localisation of higher subchondral density is common. In the humero-radial part of the joint, the mineralisation pattern suggests central pressure transmission, probably a result of the fovea capitis radii being slightly less curved than the opposing capitulum.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1992

Demonstration of subchondral bone density patterns by three-dimensional CT osteoabsorptiometry as a noninvasive method for in vivo assessment of individual long-term stresses in joints.

Since the work of Pauwels and his successors, it has been possible to use the distribution of subchondral bone density within a joint surface as a metric parameter that can reflect the principal long-term stress acting upon a joint. However, the x-ray densitometry method he employed cannot be applied to living people. A procedure was therefore developed whereby CT osteoabsorptiometry (CT OAM), based on the use of computed tomography, allows the distribution pattern of the density to be demonstrated in living subjects. This method has now been further developed, so that the form of the individual joint surfaces can be included by means of a three-dimensional reconstruction program. This method is presented here. In addition, selected representative examples of various joints from normal people, athletes, and patients are used to demonstrate the use of CT OAM. In these examples from living subjects, regularly occurring, reproducible distribution patterns of subchondral bone density can be recorded, reflecting changes in mechanical stresses on a joint (increased stress, reduced stress, and disorders of joint mechanics). CT osteoabsorptiometry is demonstrated as a suitable noninvasive technique for investigating the individual long-term stresses (loading history) acting on a living joint.

Absorptiometry, Photon↗
PubMed1992

Distribution of subchondral bone density and cartilage thickness in the human patella.

Subchondral bone density (by means of CT osteoabsorptiometry), and cartilage thickness (directly measured on photocopies of frozen sections), were examined in 30 human patellae, with an age range from 47 to 90 y. A surface demonstration of the distribution was prepared, and representative pictures produced by summation with a computer. Subchondral bone-density maxima were found in the proximal part of the lateral facet, and the density pattern interpreted as the expression of the long-term distribution of stress in the joint. It is reasonable to assume that cartilage thickness, of which two-thirds of the maximum values occupy a lateral position, is also dependent on the local stress. The 2 distributions show correlation coefficients > 0.5 in approximately a third of the cases we examined. Displacement of the higher values of cartilage thickness relative to the subchondral density maxima is attributed to incongruence in the medial part of the joint.

Aged↗
PubMed1992

[Anatomic characteristics of the pelvic girdle].

The most recent methods of investigation (CT osteoabsorptiometry) were applied in an attempt to reconstruct from their morphological structure the way in which connections between the bones of the pelvic girdle undergo stress. Thus, both sacroiliac articulation and symphysis pubis show characteristic distribution of the subchondral bone density and layout of the tensile collagen fibrous material as expression of a strongly varying qualitative pattern of stress during walking. In the region of sacroiliac articulation are the highest subchondral densities, both at the cranial and caudal edges, whereas the central part of the two auricular surfaces is less heavily mineralized. This distribution matches the thickness of the hyaline cartilage of the joint. There are striking sexual differences in the distribution of the subchondral bone density at the bordering surfaces of the symphysis pubis. During walking, all components of sacroiliac articulation and the symphysis pubis are apparently subjected to sudden changes in stress. Independent of this, the os sacrum is constantly exposed to torque on account of the weight of the upper body, and this is balanced out by the sacrospinal and sacrotuberal ligaments.

Bone Density↗
PubMed1991

[Functional anatomy of the foot].

The foot is presented in all its complexity as an entity that is the result of evolution as a morphological compromise between the static and dynamic demands made upon it. The subchondral mineralization of the ankle joints and the morphology of the ligaments is described in detail. A point of particular interest is the plantar aponeurosis and the septa plantaria. Additionally, the kinematic and dynamic aspects are discussed with respect to their relationship to the whole foot. Finally, an overview of the most important vessels and topographical regions is given.

Ankle Joint↗
PubMed1990

[Pelvic abnormalities affecting the statics of the vertebral column].

Of all the bony anomalies of the pelvis, unilateral developmental disturbances of the body of the iliac bone and the lateral parts of the os sacrum mainly affect the statics of the vertebral column. After a short description of the normal development of the os coxae and os sacrum, an attempt is made to systematize these anomalies and explain them from a developmental point of view. This is achieved by studying anatomical specimens and clinical cases. Primary disturbances concerning the growing of the cartilaginous epiphysis itself or secondary disturbances, which result from unilateral muscular palsy, can be responsible for retarded development of the body of the iliac bone. Unilateral dysplasia of the lateral part of the os sacrum could be based on disturbances of the precartilage. This is also thought to be the reason for asymmetrical formations of so-called transitional vertebrae.

Adolescent↗
PubMed1989

Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints.

To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject.

Absorptiometry, Photon↗
PubMed1988

[Functional anatomy of the elbow joint].

An attempt has been made to describe the combined action of the bony elements of the elbow joint, together with the capsular ligaments, as a single unit. Particular emphasis is laid upon the mechanisms that prevent abrupt limitation of movement. The account of the periarticular structures, including the adjacent muscles, is followed by a discussion of the various possible surgical approaches to the joint. Finally, a general survey is given of the kinematics and kinetics of the elbow joint. It is suggested that the distribution of the hyaline articular cartilage and the density of the underlying bone are morphological reflections of the stresses acting upon the joint. It follows that the axial pressure acts upon both the ulnar and the radial components of the elbow; therefore, if the joint is to remain stable, at least one of its distal bony elements must be functionally effective.

Biomechanical Phenomena↗