The role of obesity, biomechanical constitution of the pelvis and contact joint stress in progression of hip osteoarthritis.

OBJECTIVE: The aim of our study was to explore whether earlier hip arthroplasty for idiopathic osteoarthritis (OA) might be explained by enlarged contact stress in the hip joint, and to what amount can that be attributed to obesity and biomechanical constitution of the pelvis. METHOD: Fifty subjects were selected from a list of consecutive recipients of hip endoprosthesis due to idiopathic OA; standard pelvic radiographs made years prior to surgery were the main selection criteria. For 65 hips resultant hip force and peak contact hip stress normalized to the body weight (R/Wb and p(max)/Wb) were determined from the radiographs with the HIPSTRESS method. Body weight and body mass index (BMI) were obtained with an interview. Regression analysis was used to correlate parameters of obesity (body weight, BMI), biomechanical constitution of the pelvis (R/Wb, p(max)/Wb) and mechanical loading within the hip joint (R, p(max)) with age at hip arthroplasty. RESULTS: Younger age at hip arthroplasty was associated with higher body weight (P=0.009), higher peak contact hip stress normalized to the body weight - p(max)/Wb (P=0.019), higher resultant hip force -R (P=0.027) and larger peak contact hip stress - p(max) (P<0.001), but not with BMI (P=0.121) or R/Wb (P=0.614). CONCLUSION: Our results suggest that enlarged contact stress (p(max)) plays an important role in rapid progression of hip OA with both obesity (increased body weight) and unfavorable biomechanical constitution of the pelvis (greater p(max)/Wb) contributing.

Slotted acetabular augmentation for the treatment of residual hip dysplasia in adults: early results of 12 patients.

INTRODUCTION: Different pelvic osteotomies and various shelf procedures are used for the operative treatment of hip dysplasia. Slotted acetabular augmentation (SAA) is a well-established technique for the treatment of children and adolescents with hip dysplasia. It has not been widely accepted for treating hip dysplasia in adults although good outcomes have been reported with other augmentation techniques in adults. MATERIALS AND METHODS: Since 1997, SAA has been used for the prevention of hip arthrosis in 14 dysplastic hips in 12 female patients. The median age at operation was 38.5 (17-42) years; the median follow-up period was 4 (1-8) years. The patients were evaluated on the basis of radiographic, biomechanical and clinical data prior to surgery and at follow-up. RESULTS: The median centre-edge angle of Wiberg increased from 9 degrees (1-26) before the operation to 43 degrees (31-55) at the latest follow-up (P < 0.001). The median peak stress on the weight-bearing area of the hip, calculated mathematically, was reduced from 14.9 (6.3-28-1) MPa prior to the operation to 4.1 (3-6.1) MPa at the latest follow-up (P < 0.001); the median Harris Hip Score increased from 60 (45-98) points preoperatively to 93 (49-100) points at the follow-up (P < 0.001). There was no difference between the preoperative and follow-up hip joint-space width (P = 0.2). CONCLUSION: There were no postoperative complications. In our series, the procedure has proved reliable and safe. Its advantages include symptomatic pain relief, adequate acetabular roof coverage and reduced peak stress on the weight bearing area of the hip. It can be used to postpone the development of hip arthrosis in adults with acetabular dysplasia.

Permutation entropy improves fetal behavioural state classification based on heart rate analysis from biomagnetic recordings in near term fetuses.

The relevance of the complexity of fetal heart rate fluctuations with regard to the classification of fetal behavioural states has not been satisfyingly clarified so far. Because of the short behavioural states, the permutation entropy provides an advantageous complexity estimation leading to the Kullback-Leibler entropy (KLE). We test the hypothesis that parameters derived from KLE can improve the classification of fetal behaviour states based on classical heart rate fluctuation parameters (SDNN, RMSSD, ln(LF), ln(HF)). From measured heartbeat sequences (35 healthy fetuses at a gestational age between 35 and 40 completed weeks) representative intervals of 256 heartbeats were visually preclassified into fetal behavioural states. Employing discriminant analysis to separate the states 1F, 2F and 4F, the best classification result by classical parameters was 80.0% (SDNN). After additionally considering KLE parameters it was improved significantly (p<0.0005) to 94.3% (ln(LF), KLE_Mean). It could be confirmed that KLE can improve the state classification. This might reflect the consideration of different physiological aspects by classical and complexity measures.

Autonomic Information Flow during awakeness, sleep, and multiple organ dysfunction syndrome assessed by mutual information function of heart rate fluctuations.

The Autonomic Information Flow (AIF) represents the complex communication within the autonomic nervous system (ANS). It can be assessed by the mutual information function (MIF) of heart rate fluctuations (HRF). AIF represented by HRF is based on several interacting physiological mechanisms operating at different time scales. Therefore one prominent time scale for HRF complexity analysis is not given a priori. MIF reflects the information flow at different time scales. This allows a more specific characterization of the complex communication leading to dynamic stability (homeostasis) of the cardiovascular-respiratory system. Three clinically relevant examples of autonomic communication, namely AIF of normals during awake state and deep sleep, and of patients with multiple organ dysfunction syndrome (MODS) were investigated. In these states MIF clearly represents and distinguishes the different communication in dependence on the time scale of information transfer. The results confirm our systems-theoretical concept that AIF, represented by MIF, characterizes the complex communication of the ANS at different time scales.

Mathematical estimation of stress distribution in normal and dysplastic human hips.

By using a mathematical model of the adult human hip in the static one-legged stance position of the body, the forces acting on the hip, peak stress in the hip joint and other relevant radiographic and biomechanical parameters were assessed. The aims were to examine if the peak stress in dysplastic hips is higher than in normal hips and to find out which biomechanical parameters contribute significantly to higher peak stress. The average normalized peak stress in dysplastic hips (7.1 kPa/N) was markedly higher (to approximately 100%) than the average normalized peak stress in normal hips (3.5 kPa/N). The characteristic parameters that contributed to higher peak stress in dysplastic hips included the smaller lateral coverage of the femoral head, the larger interhip distance, the wider pelvis, and the medial position of the greater trochanter. These results are consistent with the hypothesis that stress distribution over weight-bearing surface of the hip joint is the relevant parameter for assessment of the risk for developing coxarthrosis.

Evaluation of biomechanical status of dysplastic human hips.

The evaluation of the biomechanical status of human hip joint was performed. Required parameters were assessed from standard antero-posterior rentgenographs and the value of contact stress on the weight bearing area is calculated. We analysed 45 dysplastic human hips and compared measured values to 81 healthy hips. The peak contact stress on the weight bearing area is considerably and statistically significantly higher in dysplastic hips compared to healthy hips. The Wiberg centre-edge angle is statistically significantly smaller in group of dysplastic hips compared to healthy hips.

Increased muscle stiffness after anterior cruciate ligament reconstruction--memory on injury?

Residual impairment of knee function was tested in 25 patients 6 to 12 months after successful unilateral reconstruction of the anterior cruciate ligament. The control group comprised 25 healthy individuals. Jumping onto one foot from a height of 20 cm was taken as a prototype of similar everyday activities. We measured maximum flexion of the knee during the landing phase of the jump, and the degree of knee flexion at the time of maximum deceleration of the knee against gravity during jumping using the three-dimensional optical motion analysis system-ELITE. In the group of patients, measured parametres were significantly smaller on the operated side than on the unaffected side. These two measured values were significantly smaller on both legs in group of patients as compared to the values in the control group. The results of our study indicate that functional disturbance persisted for 6 to 12 months after anterior cruciate reconstruction. This may be due to the changed muscle activation pattern of the knee causing increased stiffness of knee muscles. It seems that re-programming of the central nervous system occurred in order to protect the injured lower extremities from another injury.

[Rational preparation of thin bone sections by mechanical grinding. I. Method]. / Rationelle Herstellung von Knochendünnschliffen durch maschinelles Schleifen. I. Mitteilung: Methode.

A grinding machine for preparing thin nondecalcified bone sections after methacrylate embedding is described. A second micrometer screw with diamond is mounted in a specimen holder to adjust exactly the final thickness of the sections. The bone specimens are ground by a turnably mounted rough glass plate. The desired thickness of the sections is reached as soon as the diamond tip of the micrometer screw touches the glass surface. The sections can are used for microradiography, fluorescence microscopy, and histochemical investigations.

[Rational simplified plastic embedding with polymethacrylate for non-decalcified bone sections]. / Rationelle und vereinfachte Kunststoffeinbettung mit Polymethakrylat für unentkalkte Knochenschnitte.

A exact judgment of bone and bone marrow tissue is based on an undecalcified treatment technique by means of plastics embedding and hard section microtomy. All hitherto existing routine techniques of plastics embedding of bone tissue used monomeres of methakrylate with addition of so-called emollient substances for polymerisation. Disadvantages of a stronger shrinking of the polymerisation product and uncontrolled, not always avoidable accelerations of the polymerisation process which have an essentially negative influence on the histological results should thus be avoided. A very exact observance of the treatment steps is here necessary. In the further development of our embedding method we turned to the polymethacrylates. The polymerisation adhesive Kalloplast R used in industry proved as the most suitable initial substance for the new method. The yielded results lie in a considerable shortening and further simplification of the embedding technique. The results are always well reproducible. Undesirable shrinking or polymerisation artefacts with impairment of the histological results do no more appear.

[Simplified method of methacrylate embedding for undecalcified bone sections (author's transl)]. / Vereinfachte Methacrylateinbettung für unentkalkte Knochenschnitte.

A simplified technique of methacrylate embedded bone biopsies for the diagnosis of bone and haemoblastic disorders is described. Hard tissues are fixated for routine purposes in the Schaffner mixture. Fixations are carried out for fluorescent marked bone using Carnoy mixture and for histochemical methods using 4% purified formaldehyde buffered in 0.1 M solidum cacodylate at pH 7.2. Then, the bone cylinders are dehydrated, defetted and stored at 4 degrees C in methacrylate solution (1 vol. of methyl-methacrylate, 3 vol. of butylmethacrylate, 2.5% benzodylderoxide for 24 hours in vacuum). After the immersion the bones are transferred to plastic capsules filled with the methacrylate mixture described above. The polymerisation takes place in a water bath at 25--26 degrees C. Sections of 4--6 micron thickness can be cut on a special microtome, and after removal of the plastic material by means of toluene they are stained. Results of the method are demonstrated by micrographs.