Strain adaptive bone remodelling: influence of the implantation technique.

Total hip arthroplasties (THA) can be performed with cemented and uncemented femoral components. Aseptic loosening of the joint replacement still illustrates a problem for both implantation techniques. This loosening can be caused, among other factors, by resorption of the bone surrounding the implant due to stress shielding. In order to analyse the absolute influence of the implantation technique on the bone degeneration in the periprosthetic femur, the strain adaptive bone remodelling after THA was investigated in a three-dimensional finite element (FE) simulation of a femur provided with a cemented and uncemented BICONTACT (Aesculap, Tuttlingen, Germany) femoral component. For this, a bone density evolution theory was implemented in the FE code MSC.MARC. In these static FE simulations, the muscle and hip resultant forces represent the maximum loading situation in the normal walking cycle. To describe the mechanical properties of the bone, an isotropic material law dependent upon density was used. The situation directly after implantation without any bone ingrowth was simulated. The cemented femoral component was bonded to the bone by a homogenous cement mantle. The numerical results show that proximally, the bone resorption areas surrounding the BICONTACT stem are heavily dependent upon anchoring technique. Furthermore, no significant bone remodelling is calculated in the distal periprosthetic femur in both models.

In vitro investigation of biomechanical changes of the hip after Salter pelvic osteotomy.

BACKGROUND: Salter innominate osteotomy of the pelvis is widely used to improve the coverage of the femoral head in developmental dysplasia of the hip, but the biomechanical and geometric changes after this osteotomy are not well understood. METHODS: A CT dataset of an 8-year-old child with severe dysplasia of both hips was used to create a polyamide model of the left hemipelvis and proximal femur. The hemipelvis was mounted to a holding device and the proximal femur attached to a sensor guided industrial robot. The robot was programmed to apply joint forces and torques based on single-leg stance. Two major muscles were represented by wires connected to hydraulic cylinders; muscle forces were adjusted to balance the joint moments. Resulting joint forces were measured using a pressure measuring sensor before and after Salter osteotomy of the hip. Geometric changes were recorded using a three-dimensional ultrasound measurement system. FINDINGS: The preoperative hip joint resultant force was 583N (270% body weight), while after the operation a mean force of 266N (120% body weight) was measured. Postoperative muscle forces were roughly half the preoperative values. The hip joint was translated medially and caudally. Postoperatively, the length of gluteus medius and maximus muscles increased. INTERPRETATION: The preoperative value of the resultant hip joint force is comparable to values reported in the literature. The results suggest that Salter innominate osteotomy leads to a reduction of hip joint and muscle forces in addition to increasing joint contact area.

Chronic symptomatic proximal tibiofibular instability in a 3-year-old girl.

A 3-year-old girl was presented with recurrent pain at the right knee and a "snapping" when walking. A free range of motion of both knee joints, stable cruciate and collateral ligaments and a ventrally subluxating and snapping fibula when flexing the knee were found. Due to a longer course of recurrent subluxation and pain, an operation was performed and the tibiofibular ligaments and joint capsule were tightened by sutures. Other operative techniques proposed in the literature are discussed; most of them could lead to deformities or growth disturbances. The reports of tibiofibular instability in the literature are presented. The girl is the youngest patient with idiopathic proximal tibiofibular instability reported in the literature at least in the last 75 years.

[Meniscus replacement with quadriceps tendon--a long-term analysis]. / Der Meniskusersatz mit autologer Quadrizepssehne -- eine Langzeitanalyse.

AIM: Early osteoarthritis of the knee is a common consequence ofA'complete meniscectomy. In order to prevent degenerative changes, meniscus replacement by autogenous quadriceps tendon was performed from 1986 until 1999 in 45 patients. In 29 patients, a reconstruction of the anterior cruciate ligament was done simultaneously. This study was intended to detect whether this meniscus replacement led to better subjective, clinical and radiological results in comparison to meniscectomised knees or meniscal allografts reported in the literature. METHODS: A standardised examination of the patients (4-17 years postoperatively, average 9 years) was carried out using the KOOS questionnaire, the IKDC examination form and a weight-bearing radiograph of the knee. RESULTS: 34 patients took part in the study. KOOS subgroups showed fair results for symptoms (25-96 points, average 65), butA'bad results for sports and quality of life (0-100, average 52; QoL 6-94, average 54). Clinical and radiological examination demonstrated on average stable knee joints without effusion (IKDC group A), but X-rays showed in most cases a clear or severe osteoarthritis of the knee (IKDC group C). Clinical and radiological findings demonstrated similar results in comparison with studies investigating results after meniscectomy without meniscus replacement. Concerning subjective results, meniscus replacement with quadriceps tendon was inferior to cryopreserved meniscal allografts. However, patients after meniscal allograft transplantation also show increasing degenerative changes of the respective joint in radiological follow-up studies. CONCLUSION: In the patient group studied here with pre-existing chondromalacia of the respective knee joint compartment and preoperative anterior instability, no advantage of meniscus replacement using quadriceps tendon over the normal course after meniscectomy could be proven. Therefore, this procedure cannot be generally recommended.

Microarray-analysis: a new approach to study the molecular mechanisms of thermo-chemotherapy.

BACKGROUND: Experimental studies for the treatment of relapsed neuroblastoma include the use of hyperthermia in combination with chemotherapeutic drugs. Cytotoxic effects of alkylants and platinum compounds on tumor cells can be enhanced by hyperthermia in various in vitro models. However, the underlying molecular mechanisms are still largely unknown. METHOD: In this study, we used microarray-analysis as a new biological approach to gain insight into the pharmacogenomics and possible target genes of thermochemotherapy. As a model, LAN 1 neuroblastoma cells were treated for 1 h with low doses of cisplatin alone, with simultaneous heating to 42 degrees C or with hyperthermia alone. Gene expression was analyzed at five time points 0 to 24 h after treatment using U95Av2 oligonucleotide arrays (Affymetrix Inc). Significant changes of gene expression levels were calculated by similarity metrices and Pearson correlation. RESULTS: Only a few genes (n = 23) demonstrated altered expression following treatment of LAN 1 cells with cisplatin alone. Hyperthermia alone resulted in significant expression changes of 136 genes in comparison to untreated control cells. Combination therapy of cisplatin and hyperthermia resulted in expression changes of 251 genes, interestingly including 131 genes with unchanged expression under treatment with either cisplatin or hyperthermia alone. Significant changes of expression levels could be annotated to genes involved in heat shock response, protein degradation and apoptosis. These results are now being validated on mRNA- and protein levels by RT-PCR and Western Blot analysis. CONCLUSION: Microarray-Analysis is a suitable new approach for the identification of target genes, which might play an important role for the synergistic effect of hyperthermia and chemotherapy in tumor cells.

[Bone adaptation changes mechanical stress in the femur--a prospective two years follow up after Hüft-TEP implantation]. / Knöcherne Anpassung ändert mechanische Beanspruchung des Femurs--eine zweijährige prospektive Studie nach Hüft-TEP Implantation.

AIM: Periprosthetic adaptive bone remodeling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodeling theory with finite element analysis. Unfortunately, there is still a lack of clinical validation data. The collection of prospective volumetric bone density data with a clinical computerized tomography study after THA was previously conducted. The objective of the study presented here is an additional evaluation of femoral strain. METHOD: In a prospective clinical trial with 7 female patients after THA computerized tomography (CT) and finite element (FE) modeling was patient specifically combined immediately after surgery, as well as at three and 24 months postoperatively. Mechanical strain was expressed by strain energy density. RESULTS: Corresponding to a bone density decrease, a decrease of the femoral strain energy density was observed during the two year follow-up after surgery (approximately 20 %). The predominant change occurred within the first three months and was found to be distally stronger than proximally. CONCLUSION: As far as we are aware, this is the first combination of fully prospective 3D CT density data in vivo with patient-specific finite element modeling. The assessment of mechanical strain data during a follow-up trial should be a new approach for analyzing hip stems in clinical biomechanics. A future confirmative study based on a statistical case number calculation would increase the evidence of the results presented here.

Bone remodelling in humeral arthroplasty: follow-up using CT imaging and finite element modeling--an in vivo case study.

Little material is available in the literature about remodelling of the human humerus after implantation of a shoulder hemiarthroplasty. A 73-year-old patient was examined by CT 4 years after implantation of a right shoulder hemiarthroplasty, and the bone density as represented by Hounsfield values was compared with the contralateral side. Additionally, a three-dimensional finite-element model was generated from the image data and analysed. Bone density was reduced around the prosthesis when compared with the contralateral side. The stresses were transmitted through the prosthesis, while low bone stresses were found surrounding the prosthesis. Distally from the prosthesis, high stresses were found. On the control side, a more homogeneous stress distribution was noted. The results could be explained by bone resorption around the prosthesis caused by stress shielding; this hypothesis has to be confirmed by future studies.

Size and direction of hip joint forces associated with various positions of the acetabulum.

When total hip replacement is performed, the position of the acetabular component may affect wear and component survival time. We considered the questions: In what way does displacement of the hip joint center alter (1) the magnitude and (2) the direction of the resultant force? Biomechanical tests were carried out on a human multibody model. After displacement of the hip joint center, the resultant forces were calculated for the single leg stance. With the flexed single leg stance, maximum hip joint forces were observed with lateral, cranial, posterior displacement. The peak forces were affected by the modeling of a gluteus maximus wrapping point at the ischial tuberosity and were overestimated when this was removed. With the straight single leg stance, posterior displacement decreases the total load on the hip joint because of the increased leverage of the rectus femoris. With regard to the direction of the resultant force, medial displacement increases the angles in both planes, cranial displacement increases it in the sagittal plane (cranial, posterior-caudal, anterior), and anterior displacement decreases the angle in the sagittal plane and increases it in the frontal plane (medial, cranial-lateral, caudal). The direction of the force is relatively insensitive to displacement of the hip joint center. The results presented here indicate a marked increase in the force after lateral, cranial, posterior displacement of the center in the flexed single leg stance. To avoid extreme joint loading and to reduce the wear after total hip arthroplasty, the cranial and posterior regions of the acetabulum should be fully reconstructed. A high hip joint center has an adverse effect on the magnitude of the force, although the directions are hardly affected by it.

Functions of hip joint muscles.

The relative torque components (percentages of total hip torque) of 26 hip muscles about three joint axes were calculated using a human multibody model to determine muscle actions as a function of hip joint angle. It was demonstrated that the muscle actions obtained from this straight line model of hip musculature were in good agreement with published functions; the data on muscle function changes during hip joint motions exceed the data available in the literature and could extend the anatomical knowledge which is available today.