Biomechanical comparison of methods used to treat Kienböck's disease.

The surgical approach to Kienböck's disease is largely dependent on the stage of the disease and the ulnar variance pattern. Many of the surgical treatments are designed to unload the lunate, halt disease progression, and allow for possible revascularization. This article reviews a collection of studies investigating the biomechanical effects of load-altering procedures. Knowledge of the biomechanical impact of the various operative interventions is clinically useful in creating a treatment algorithm.

Two cell lines from bone marrow that differ in terms of collagen synthesis, osteogenic characteristics, and matrix mineralization.

Two cloned cell lines were isolated from cultures of mouse bone-marrow cells. One of the lines, D1, exhibited osteogenic properties and synthesized type-I collagen (alpha 1)2 alpha 2. The second cell line, D2, was not osteogenic and produced a collagen homotrimer (alpha 1)3. Whereas the extracellular matrix of the D1 cell cultures contained striated collagen fibrils, presumably composed of type-I collagen, the homotrimer-producing D2 cells did not demonstrate striated collagen fibrils. Instead, they had thin filaments without detectable striations. Sodium ascorbate stimulated collagen synthesis at the transcriptional level in both the D1 and the D2 cells. The bone-producing characteristics of D1 in vitro included high levels of alkaline phosphatase, increased cyclic adenosine monophosphate on treatment with parathyroid hormone, and expression of osteocalcin mRNA. The D1 cells, unlike the D2 cells, produced a mineralized matrix in vitro. Mineralization in the cultures of the D1 cells occurred in nodules of increased cell density, which also contained the cells with the highest concentrations of collagen mRNA, as shown by in situ hybridization. When the D1 cells were implanted in a diffusion chamber in vivo, a mixture of both osteogenic and adipogenic tissues was formed. This indicates that the D1 cell line is derived from an early marrow stromal precursor that is multipotential.

Matrix mineralization in hypertrophic chondrocyte cultures. Beta glycerophosphate increases type X collagen messenger RNA and the specific activity of pp60c-src kinase.

The phenomenon of chondrocyte hypertrophy is accompanied by the expression of type X collagen and the appearance of matrix mineralization. These events are also associated with changes in the phosphorylation of intracellular proteins. In this study the addition of 10 mM beta-glycerophosphate to hypertrophic chondrocytes resulted in stimulation of type X collagen synthesis up to 10 days in culture and an increase in the expression of type X collagen mRNA. This was followed by the onset of mineralization and the appearance of calcium hydroxyapatite. In contrast, the addition of beta-glycerophosphate to non-hypertrophic chondrocytes failed to induce expression of type X collagen or to produce changes in calcium and phosphate. The increased formation of type X collagen and of mineral in hypertrophic chondrocytes was accompanied by changes in the tyrosine kinase pp60c-src. While the level of c-src protein decreased approximately 2.5-fold in hypertrophic chondrocytes after 17 days of beta-glycerophosphate treatment, the specific activity of pp60c-src kinase increased approximately 3-fold in the cells that could be induced to mineralize but remained unchanged in cells that did not exhibit this property. Regulation of kinase activity may be an important event in endochondral ossification.

Characterization of tissue from the bone-polymethylmethacrylate interface in a rat experimental model. Demonstration of collagen-degrading activity and bone-resorbing potential.

In previous studies, we described a layer of tissue that formed around methylmethacrylate cement that had been implanted into the posterior cervical spine of dogs. We are now reporting on a rat model in which we induced, in the interface between the bone of the posterior elements of the dorsal spine and methylmethacrylate, the formation of a layer of tissue that was morphologically similar to the tissue that had been produced in the dogs. As in the dogs, we noted macrophages and giant cells and we demonstrated that the interface tissue synthesized several basement-membrane components (type-IV collagen, laminin, and fibronectin). In addition, we demonstrated the synthesis of an additional extracellular-matrix protein--type-VI collagen. We also showed that extracts of organ cultures of tissue from the rat model degraded type-I collagen into three-quarter and one-quarter-length fragments. Such enzymatic activity is characterized of mammalian collagenase, an enzyme that is known to play a critical role in the resorption of bone.