Effects of fluid-induced shear on articular chondrocyte morphology and metabolism in vitro

This study tested the effects of fluid-induced shear on high density monolayer cultures of adult articular chondrocytes. Fluid-induced shear (1.6 Pa) was applied by cone viscometer to normal human and bovine articular chondrocytes for periods of 24, 48, and 72 hours. At 48 and 72 hours, fluid-induced shear caused individual chondrocytes to elongate and align tangential to the direction of cone rotation. Fluid-induced shear stimulated glycosaminoglycan synthesis by 2-fold (p < 0.05) and increased the length of newly synthesized chains in human and bovine chondrocytes. In human chondrocytes, the hydrodynamic size of newly synthesized proteoglycans also was increased. After 48 hours of fluid-induced shear, the release of prostaglandin E₂ from the chondrocytes was increased 10 to 20-fold. In human chondrocytes, mRNA signal levels for tissue inhibitor of metalloproteinase increased 9-fold in response to shear compared with the controls. In contrast, mRNA signal levels for the neutral metalloproteinases, collagenase, stromelysin, and 72 kD gelatinase, did not show such major changes. This study demonstrated that articular chondrocyte metabolism responds directly to physical stimulation in vitro and suggests that mechanical loading may directly influence cartilage homeostasis in vivo.     

Effects of ingrowth, geometry, and material on stress transfer under porous-coated hip surface replacements

Three different interface geometries for porous ingrowth surface replacements of the hip were examined using two-dimensional linear and nonlinear contact finite element analyses. The results indicate that incorporation of a nearly flat prosthesis interface between the surface replacement and the underlying cancellous bone may reduce stress shielding and improve stress transfer from the component. For all designs analyzed, the bone stress shielding was insensitive to component material stiffness when the elastic modulus was greater than 30 MPa. The use of titanium instead of cobalt-chrome (Co--Cr) as the prosthesis material therefore had a negligible effect on stress shielding.     

Bone density studies: current technology.

Osteoporosis is a serious public health problem that causes at least 1.3 million fractures and costs more than $6 billion annually. Bone densitometry studies provide clinicians with a way to detect this silent disease in the early stages, before skeletal fragility has occurred. This article describes the three major techniques of bone densitometry and provides guidelines for screening individuals at risk and for understanding the results in clinical practice. Controversies over techniques and management issues are also discussed.     

Neuroblastoma metastatic to the liver in infants

Four infants are described who presented with rapid enlargement of the liver. This was found to be due to neuroblastoma which had metastasized to the liver; the condition was associated with high levels of urinary vanillylmandelic acid (VMA). In 3 infants the primary tumour was in the adrenal gland and in one it was not identified. One infant died after laparotomy and 2 infants survive disease free with normal VMA levels, one after adrenalectomy and hepatic irradiation and one after a short course of chemotherapy. The fourth patient responded initially to hepatic irradiation and chemotherapy, but relapsed 2 years later with recurrent disease; at the same time the VMA level which had been normal, again rose. The importance of screening for an abnormal VMA level in any infant with a rapidly enlarging liver in order to obtain an early diagnosis is stressed. Careful follow-up, with serial VMA estimations, is essential to detect recurrent disease. The prognosis for some infants with this distribution of neuroblastoma which has metastasized to the liver, but not to the bones or oribt, is good.     

Contact finite element stress analysis of the hip joint

Two-dimensional finite element analyses were conducted of the normal hip using contact elements at the joint surface. The models studied were constructed for a slice through the pubis, acetabulum, and ilium. In the analyses the proximal femur was pressed into the acetabulum and intraarticular pressures and principal stresses in the joint region were determined for different load magnitudes and directions and various boundary conditions. Three sets of boundary conditions were examined: (a) deformable pubic symphysis, (b) rigid pubic symphysis, and (c) simulations of experimental studies. In the deformable model the pubic symphysis was free to displace in the sagittal plane and rotate. In the rigid model the pubic symphysis was rigidly fixed. Superoposterior loading resulted in high-contact pressures at the acetabular dome for all sets of boundary conditions. For the deformable model subject to a more medially directed load the acetabulum closed in such a manner as to squeeze the head of the femur creating high-contact pressures superiorly and inferiorly. This resulted in significant compressive stresses in the superior dome cancellous bone and inferior cancellous bone. The cumulative effect of this squeezing action with normal biological remodeling may cause elongation of the femoral head resulting in asphericity and incongruity of the unloaded hip joint articular surfaces. Rigidly fixing the pubic symphysis stiffened the model and resulted in principal stress patterns that did not reflect trabecular density or orientations as well as those of the deformable pubic symphysis model. Finite element simulations of previous experimental studies modeled the close proximity of the fixation to the excised acetabulum. These boundary conditions prevented the squeezing caused by pelvis deformations. The resulting contact areas, pressure distributions, and bone stresses were very different from those of the more anatomic, deformable pubic symphysis model. These findings demonstrate the sensitivity of hip contact pressures and stresses to imposed boundary conditions and indicate that care should be taken to simulate anatomic conditions in experimental and theoretical studies.     

Total condylar knee replacement. A study of factors influencing range of motion as late as two years after arthroplasty

The factors influencing the range of motion of the knee after total condylar knee replacement were analyzed in fifty-five consecutive patients who had seventy-one replacements and a minimum follow-up of two years. Statistically significant improvement in flexion occurred between the first postoperative evaluation in the hospital, the evaluation at discharge, and the evaluations at three months and one year after replacement. Postoperative range of motion was not influenced by the patient's gender, by the extent of the disease (monoarticular in comparison with polyarticular), or by treatment with a unilateral or bilateral procedure. The knees of patients with rheumatoid arthritis gained extension at the expense of flexion. The average flexion arcs of the knees with rheumatoid arthritis and of those with osteoarthritis were the same two years after operation as they had been preoperatively. Knees with preoperative flexion of more than 100 degrees had lost flexion at follow-up, whereas those with preoperative flexion of less than 100 degrees had gained flexion. Significant improvement in extension occurred only before discharge. For the patients whose preoperative flexion contracture was 10 degrees or more, virtually all improvement in the contracture occurred at the time of surgery. Patients who had a simultaneous bilateral total knee replacement did as well as those with a single knee replacement.(ABSTRACT TRUNCATED AT 250 WORDS)