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Biomedical subjects

J M Kauer

Publications and source records attributed to J M Kauer.

At least 19 recordsLinked to original sources
PubMed2001

Assessment of ulnar variance: a radiological investigation in a Dutch population.

OBJECTIVE: A radiological study was performed to evaluate ulnar variance in 68 Dutch patients using an electronic digitizer compared with Palmer's concentric circle method. Using the digitizer method only, the effect of different wrist positions and grip on ulnar variance was then investigated. Finally the distribution of ulnar variance in the selected patients was investigated also using the digitizer method. DESIGN AND PATIENTS: All radiographs were performed with the wrist in a standard zero-rotation position (posteroanterior) and in supination (anteroposterior). Palmer's concentric circle method and an electronic digitizer connected to a personal computer were used to measure ulnar variance. The digitizer consists of a Plexiglas plate with an electronically activated grid beneath it. A radiograph is placed on the plate and a cursor activates a point on the grid. Three plots are marked on the radius and one plot on the most distal part of the ulnar head. The digitizer then determines the difference between a radius passing through the radius plots and the ulnar plot. RESULTS AND CONCLUSIONS: Using the concentric circle method we found an ulna plus predominance, but an ulna minus predominance when using the digitizer method. Overall the ulnar variance distribution for Palmer's method was 41.9% ulna plus, 25.7% neutral and 32.4% ulna minus variance, and for the digitizer method was 40.4% ulna plus, 1.5% neutral and 58.1% ulna minus. The percentage ulnar variance greater than 1 mm on standard radiographs increased from 23% to 58% using the digitizer, with maximum grip, clearly demonstrating the (dynamic) effect of grip on ulnar variance. This almost threefold increase was found to be a significant difference. Significant differences were found between ulnar variance when different wrist positions were compared.

Adolescent↗
PubMed2001

Ulnar variance and the shape of the lunate bone. A radiological investigation.

The authors designed a study to test the hypothesis that the length of the ulna might affect the shape of the lunate bone because of long-term molding during life. This might then be useful to predict the presence or absence of a dynamic or static ulna plus by the shape of the lunate bone. In a prospective study, posterior-anterior wrist x-rays were taken in a standard fashion in 68 patients with a mean age of 34.5 years. Dominance, grip strength, ulnar variance and the shape of the lunate were recorded. Lunate shape, type 1, which is the least molded, was seen most frequently on both the left and right side and did not correlate with the dominant side. The most molded, type 3, was seen less frequently and almost exclusively on the nondominant side. No correlation was found between dynamic ulna plus and the type 3 lunate. Following statistical analysis, no correlation between ulnar variance and lunate shape was found, indicating that the shape of the lunate bone had no predictive value for predicting the presence or absence of a dynamic ulna plus variance. The hypothesis that the length of the ulna might influence the ultimate shape of the lunate could not be demonstrated.

Adolescent↗
PubMed2000

The long-term effects of force-transmission in an injured wrist, measured with dual-energy X-ray absorphometry: a case report.

PURPOSE: To investigate the feasibility of using a dual-energy X-ray absorphometry (DEXA) scan to predict long-term force-transmission patterns in wrists. MATERIAL AND METHODS: Both wrists of a man with morbid Kienböck stage IIIa disease of his left wrist (avascular necrosis of the lunate) were examined by a DEXA scan to determine the differences in bone density in the distal radius. RESULTS: In the distal radius of the injured wrist, a shift in bone density was seen toward the scaphoid fossa, which resembles the shift in force-transmission pattern described in force-transmission studies of the wrist. CONCLUSIONS: These differences can be interpreted as a result of an altered force-transmission pattern in the injured wrist.

Absorptiometry, Photon↗
PubMed1998

Pelvic osteotomies: anatomic pitfalls at the pubic bone. A cadaver study.

Pelvic osteotomies for acetabular dysplasia include an osteotomy of the pubic bone. The anatomical consequences of two different approaches to the pubic bone were assessed by performing a triple osteotomy on a series of 12 fresh cadaver hemipelvises. The medial approach through a separate incision over the pubic symphysis was compared with the lateral approach through the incision used for the innominate osteotomy. Although the medial approach appears technically easy, there are several anatomical structures at risk, such as the femoral vein and the corona mortis. The lateral approach is safer, and it is easier to make the osteotomy close to the hip joint. The closer the osteotomy is to the hip joint, the smaller the chance of developing a non-union.

Acetabulum↗
PubMed1998

Pelvic osteotomies: anatomic pitfalls at the ischium. A cadaver study.

Pelvic osteotomies for acetabular dysplasia include an osteotomy of the ischium. The potential anatomical hazards of three different osteotomies of the ischium were assessed by performing a triple osteotomy in a series of 8 fresh cadaver pelvises. An oblique osteotomy above the sacrospinous ligament using a posterior approach requires that the inferior gluteal and pudendal neurovascular bundles be mobilised and retracted. A transverse osteotomy below the sacrospinous ligament using a posterior approach can be performed in a relatively safe area between the pudendal and sciatic nerves. A transverse osteotomy from anterior can be performed through a modified Smith Peterson approach. The pudendal nerve medially, the sciatic nerve laterally and the medial circumflex artery distally are not visualised and are prone to damage.

Cadaver↗
PubMed1998

Three-dimensional displacement of the hip joint after triple pelvic osteotomy. A postmortem radiostereometric study.

Triple pelvic osteotomy reorients the acetabulum relative to the pelvis in order to improve acetabular coverage of the femoral head in cases of acetabular dysplasia. We undertook a radiostereometric analysis (RSA) on 6 osteotomized cadaver hips to determine the actual three-dimensional reorientation obtained. The centers of the femoral head were all translated posteriorly between 11 and 41 mm, and distally up to 13 mm. 4 were lateralized up to 8 mm, and 2 were medialized up to 5 mm. All acetabuli rotated anteriorly about the lateral to medial axis (X-axis), and 4 rotated outwards around the distal to proximal axis (Y-axis). The correlations between measurements performed on conventional anteroposterior radiographs and the RSA measurements were poor: variations in the lateral-medial direction ranged from -16 to +6 mm, and in the distal-proximal direction between -10 and +12 mm. The changes in orientations measured will significantly affect the load across the hip joint, since the dimensions of the pelvis change and the moment arms of the muscles, their lengths and lines of action are changed as well. We conclude that, with the procedures presently performed, the loads across the hip joint are bound to change, and that the reorientation can hardly be checked with conventional radiographs.

Acetabulum↗
PubMed1998

Anatomic basis of Tönnis' triple pelvic osteotomy for acetabular dysplasia.

Dysplasia of the hip in adults can be treated by a pelvic osteotomy. In order to assess pelvic anatomy in relation to surgical approach and osteotomy sites, 12 cadaver hips were studied. A triple pelvic osteotomy as described by Tönnis [6] through ilium, pubis and ischium was performed, followed by an intrapelvic and anterior and posterior dissection of the hip. At the ischium, the pudendal and inferior gluteal neurovascular bundles are most at risk medially and proximally respectively. Much less in danger is the sciatic n. as it runs 1 to 3 cm lateral to the osteotomy site. At the pubis osteotomy the femoral v. lies close on the bone and is prone to damage. The artery lies further off the bone. The ilium osteotomy starts just proximal to the anterior inferior iliac spine and exits posteriorly at the sciatic notch. Here the sciatic n. and the superior gluteal neurovascular bundle may be damaged. The practical surgical implications of these three osteotomies are discussed, especially with respect to the requirement of meticulous subperiostal dissection and accurate placement of retractors.

Acetabulum↗
PubMed1997

An inverse dynamics modeling approach to determine the restraining function of human knee ligament bundles.

During knee motion, the fiber bundles of ligaments are nonuniformly loaded in a recruitment pattern which is different for successive knee-joint positions. As a result, the restraining functions of these ligaments are variable. To analyze the relative restraint contributions of the fiber bundles in different knee-joint positions, a new method was developed. Its application was illustrated for the cruciate ligaments of one knee-joint specimen. The methods developed to estimate bundle forces comprise five steps. First, the three-dimensional motions of a knee specimen are measured for anterior-posterior forces, using Röntgen Stereophotogrammetric Analysis. Second, bone-ligament-bone tensile tests are performed to evaluate the mechanical properties of these structures in several relative orientations of the bones. Third, multiple fiber bundles are identified in each ligament, based on the main fiber orientations. Fourth, the nonlinear force-length relationship of each functional bundle, as defined by a stiffness and a recruitment parameter, is determined by combining the multidirectional tensile tests with a multiline-element ligament model. Finally, the information obtained is combined in a whole-joint computer model of the knee, to determine the internal forces in the initial kinematic experiment, using an inverse dynamics approach. The technique appeared to be extremely time consuming and technologically involved. However, it was demonstrated to be useful and effective. The preliminary results reveal that the fiber bundle restraints are extremely sensitive to the knee flexion angle and the restraining forces are highly variable within the ligaments. For both cruciate ligaments, a gradual transition was demonstrated in load transfer from the posterior bundles to the more anteriorly positioned ones during knee flexion. Furthermore, it appeared that relatively high forces were carried by only a few fiber bundles at each flexion angle. Based on these preliminary results, it is concluded that the determination of forces in multiple ligament bundles is important for the understanding of failure mechanisms of ligaments. In particular, alternate loading of different fiber bundles suggests that successful operative reconstruction of the cruciate ligaments may not be achieved simply by a one-bundle preparation.

Algorithms↗
PubMed1997

Connections between the tendons of the musculus flexor digitorum profundus involving the synovial sheaths in the carpal tunnel.

In the carpal tunnel anatomical interconnections between the tendons of the musculus flexor digitorum profundus are systematically present. These interconnections limit the mutual tendon displacements, which decreases finger independence and may be problematic in a musician's hand. The present study investigates a possible role of the synovial sheaths in the formation of these intertendinous connections in the carpal tunnel. To this end a morphological model is provided which correlates the often distinctly fibrous structure of the deep flexor tendons in the carpal tunnel and the frequent exchange of tendon fibres between the tendons to the different fingers, with the tendency of the synovial membranes to strongly adhere to the tendons. This model is validated by gross dissection results, and by cross sections of the flexor tendons in the carpal tunnel. In agreement with the model, the anatomic data show that the synovial membranes tend to invade and become trapped in tendons made up from individualised tendon strands, and also strongly adhere to the substantial amounts of tendon fibres which may be exchanged between the flexor tendons proximal to the lumbrical origins. These fibres and the synovial membranes may form a strong fabric able to withstand substantial stretching forces of interconnected oppositely pulled flexor tendons.

Adult↗
PubMed1996

Characterization of the mechanical behavior of human knee ligaments: a numerical-experimental approach.

During knee-joint motions, the fiber bundles of the knee ligaments are nonuniformly loaded in a recruitment pattern, which depends on successive relative orientations of the insertion sites. These fiber bundles vary with respect to length, orientation and mechanical properties. As a result, the stiffness characteristics of the ligaments as a whole are variable during knee-joint motion. The purpose of the present study is to characterize this variable mechanical behavior. It is hypothesized that for this purpose it is essential to consider the ligaments mechanically as multi-bundle structures in which the variability in fiber bundle characteristics is accounted for, rather than as one-dimensional structures. To verify this hypothesis, bone-ligament-bone preparations of the ligaments were subjected to series of unidirectional subfailure tensile tests in which the relative insertion orientations were varied. For each individual test specimen, this series of tensile tests was simulated with a mathematical ligament model. Geometrically, this model consists of multiple line elements, of which the insertions and orientations are anatomically based. In a mathematical optimization process, the unknown stiffness and recruitment parameters of the line elements are identified by fitting the variable stiffness characteristics of the model to those of the test series. Thus, lumped parameters are obtained which describe the mechanical behavior of the ligament as a function of the relative insertion orientation. This method of identification was applied to all four knee ligaments. In all cases, a satisfactory fit between experimental results and computer simulation was obtained, although the residual errors were lower for the cruciate ligaments (1.0-2.4%) than for the collateral ligaments (3.7-8.1%). It was found that models with three or less line elements were very sensitive to geometrical parameters, whereas models with more than 7 line elements suffered from mathematical redundancy. Between 4 and 7 line elements little difference was found. It is concluded that the present ligament models can realistically simulate the variable tensile behavior of human knee ligaments. Hereby the hypothesis is verified that it is essential to consider the ligaments of the knee as multi-bundle structures in order to characterize fully their mechanical behavior.

Aged↗
PubMed1996

The gross and histologic anatomy of the ligaments of the capitohamate joint.

The capitohamate (CH) joint was studied with the use of 11 dissected adult cadaver wrists, 3 serially sectioned adult cadaver wrists, and 3 serially sectioned fetal wrists. Three CH interosseous ligaments were clearly identified: the dorsal, deep, and palmar interosseous ligaments. In addition, the unique longitudinal interosseous ligament is described in detail. Previously not described are the anterior interconnecting bands, which originate from the palmar interosseous ligament and have their insertion at the interosseous recess between capitate and hamate. Morphologic data of the most important osseous and ligamentous structures is provided.

Aged↗
PubMed1996

A global verification study of a quasi-static knee model with multi-bundle ligaments.

The ligaments of the knee consist of fiber bundles with variable orientations, lengths and mechanical properties. In concept, however, these structures were too often seen as homogeneous structures, which are either stretched or slack during knee motions. In previous studies, we proposed a new structural concept of the ligaments of the knee. In this concept, the ligaments were considered as multi-bundle structures, with nonuniform mechanical properties and zero force lengths. The purpose of the present study was to verify this new concept. For this purpose, laxity characteristics of a human knee joint were compared as measured in an experiment and predicted in a model simulation study. In the experiment, the varus-valgus and anterior-posterior laxities of a knee-joint specimen containing the ligaments and the articular surfaces only, were determined. From this knee-joint, geometric and mechanical parameters were derived to supply the parameters for a three-dimensional quasi-static knee-joint model. These parameters included (i) the three-dimensional insertion points of bundles, defined in the four major knee ligaments, (ii) the mechanical properties of these ligament, as functions of their relative insertion orientations and (iii) three-dimensional representations of the articular surfaces. With this model the experiments were simulated. If knee-model predictions and experimental results agree, then the multi-bundle ligament models are validated, at least with respect to their functional role in anterior-posterior and varus-valgus loading of the joint. The model described the laxity characteristics in AP-translation and VV-rotation of the cadaveric knee-joint specimen reasonably well. Both display the same patterns of laxity changes during knee flexion. Only if a varus moment of 8 N m was applied and if the tibia was posteriorly loaded, did the model predict a slightly higher laxity than that measured experimentally. From the model-experiment comparisons it was concluded that the proposed structural representations of the ligaments and their mechanical property distributions seem to be valid for studying the anterior-posterior and varus-valgus laxity characteristics of the human knee-joint.

Biomechanical Phenomena↗
PubMed1995

The effect of variable relative insertion orientation of human knee bone-ligament-bone complexes on the tensile stiffness.

In order to evaluate the contribution of the knee ligaments to restrain joint motions, knowledge about their structural properties is required. Due to the variable relative insertion orientation of the ligaments during knee motion, however, different fiber bundles are recruited, each with their specific mechanical properties. Hence, the structural properties vary as a function of knee motion. For this reason, a relationship between the structural tensile properties and the relative insertion orientation is required in order to define the role of the ligaments in knee mechanics. In the present study, this relationship is determined by performing a series of tensile tests in which the relative orientations of the insertion sites of human knee bone-ligament-bone preparations were varied systematically. The experimentally obtained stiffness was significantly affected by the relative orientation of the insertion sites, but more profoundly for the anterior and posterior cruciate ligaments (ACL and PCL) as compared to the medial and lateral collateral ligaments (MCL and LCL). The average decreases in stiffness per 5 degrees tilt of the insertion sites were estimated at -11.6 +/- 3.5 N mm-1 (ACL), -20.9 +/- 2.7 N mm-1 (PCL), -2.6 +/- 0.9 N mm-1 (MCL) and -3.7 +/- 0.3 N mm-1 (LCL). For the PCL and the MCL these changes in stiffness with tilt were rather insensitive to the side of the femoral insertion site which was lifted. The ACL and the LCL, conversely, displayed significant differences in stiffness changes between the different tilt directions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

The fibre bundle anatomy of human cruciate ligaments.

The cruciate ligaments of the knee consist of numerous fascicles, groups of which comprise fibre bundles. The stabilising function of these ligaments is established by changes in the lengths and orientations of the fascicles. Understanding the function of knee ligaments thus requires an understanding of their 3-dimensional fascicle architecture. Hitherto, the cruciate ligaments have been considered functionally as single-dimensional 'ropes' or, at the most, as consisting of anterior and posterior parts. It is evident from the appearance of these ligamentous structures, however, that fascicles in more than 2 directions are present. This study investigated how many and which fibre bundles are minimally needed to preserve the main fascicle directions in the ligaments. An anatomical analysis of the cruciate ligaments was performed using a 3-dimensional measuring device. Three anterior and 3 posterior cruciate ligaments were isolated and their fascicles measures. Based on the courses of the fascicles, fibre bundles were defined, dissected bluntly, and their corresponding insertion sites measured. Finally, the insertion sites of the bundles were connected into straight-line representations by a computer and transformed to the anatomical position of the knee, so as to be useful for functional analyses of the ligaments. It was found that 6-10 bundles are sufficient to represent the main fascicle directions of the ligaments. Although the number of fibre bundles is not identical for all ligaments, the femur and the tibia are connected in a consistent way by these bundles. Even the ways in which the fibre bundles change their interrelationship from the femoral to the tibial insertion sites are comparable. The results serve as a detailed anatomical basis for functional analyses of the cruciate ligaments.

Anterior Cruciate Ligament↗
PubMed1994

Nonuniform distribution of collagen density in human knee ligaments.

It is generally recognized that the mechanical properties of soft connective tissues are affected by their structural components. We documented collagen density distributions in human knee ligaments to quantify differences in density within and between these ligaments. In order to explain the variations in mechanical properties within and between different knee ligaments as described in the literature, the distributions of collagen density were correlated with these biomechanical findings. Human knee ligaments were shown to be nonhomogeneous structures with regard to collagen density. The anterior bundles of all ligaments contained significantly more collagen mass per unit of volume than the posterior bundles did. The percentage differences between the anterior and posterior bundles, in relation to the posterior bundles, were about 25% for the anterior cruciate ligament (ACL) and the collateral ligaments and about 10% for the posterior cruciate ligament (PCL). Along the cruciate ligaments, the central segments had higher collagen densities than did segments adjacent to the ligament insertions (ACL 9%, PCL 24%). The collagen density in the ACL was significantly lower than that in the other ligaments. These variations within and between the ligaments correlate well with the variations in mechanical properties described in the literature; however, other structural differences have to be taken into account to fully explain the variations in mechanical properties from the structural components.

Aged↗
PubMed1993

Method to determine collagen density distributions in fibrous tissues.

We present a method for the measurement of hydroxyproline density distributions, as an estimate for collagen density distributions, in fibrous tissues such as ligaments and tendons. To evaluate this method, a single flexor tendon of a human hand was divided into seven tissue locations. Triplicate determinations of the dry weight tissue mass, volume, and hydroxyproline mass were made at each location: two samples were analyzed at the same time (a and b) and one was analyzed later (c). The intralocation variation is an estimate for the measurement error variance, which indicates both the precision (a compared with b) and the repeatability (b compared with c) of the technique for determination of volume, dry weight tissue mass, hydroxyproline concentration, and hydroxyproline density. The precision was about 5% for all variables, and the repeatability ranged from 1.5-4.3%. In comparison with the interlocation variations, the error variances were small, except for collagen concentration. This indicates that despite the measurement errors, differences in hydroxyproline density can be detected within fibrous tissues with the proposed method. The use of only a single tendon is adequate to evaluate the measurement error of the method, but more tendons should be measured to generalize the absolute values of the variables.

Aged↗