C. J. Joyner

Stromal colonies with fibroblastic morphology grown from rabbit marrow cells in culture supplemented with foetal calf serum. In this study the same marrow cells cultured with autologous rabbit plasma and hydrocortisone form colonies of a single lineage that express the adipocytic phenotype. A comparison of the potential for differentiation of cloned cell populations grown from fibroblastic and adipocytic colonies has been made using an in vivo diffusion chamber assay. The adipocytic colonies differentiated and grew to a limited size in medium with rabbit plasma and hydrocortisone, but attempts to isolate them and expand them in this medium failed. When the serum supplement was changed to foetal calf serum at day 10 the cells in the adipocytic colonies acquired a less differentiated morphology, there was a large increase in colony growth and cells were produced in sufficient numbers for the diffusion chamber assay. Thirty one fibroblastic colonies and twenty one adipocytic colonies were isolated either by limiting dilution or ring cloning and then expanded. Of these, eleven fibroblastic and eight adipocytic colonies provided enough cells (2 x 10(5) to 2 x 10(6] for implantation and culture in the chambers. Four of the eleven fibroblastic and three of the eight adipocytic colonies formed an osteogenic tissue in the chambers. It was concluded that cells that have differentiated in an adipocytic direction are able to revert to a more proliferative stage and subsequently to differentiate along the osteogenic pathway. Adipocytic and fibroblastic cells cultured in vitro from marrow have, with osteogenic cells, a common precursor in adult marrow.

Fibroblastic colonies, each of which is derived from a single precursor cell (CFU-F), are formed when suspensions of marrow cells are cultured in vitro. The ability of marrow CFU-F to differentiate in vitro was investigated using the expression of alkaline phosphatase activity as a marker for osteogenic differentiation. In cultures of rabbit marrow cells the colonies formed varied in size, morphology and expression of enzyme activity, indicating that marrow stromal CFU-F are a heterogeneous population. Growth and differentiation of marrow CFU-F can be modified in vitro. Epidermal growth factor increased average colony size and reduced clonal expression of alkaline phosphatase activity to very low levels. Hydrocortisone activated the osteogenic differentiation programme within the cellular progeny of a wide spectrum of CFU-F. The results support the possible development of in vitro clonal methods for the study of differentiation and regulation of the osteogenic and other fibroblastic cell lines of the marrow stromal system.

Abstract A small proportion of fractures progress to non‐union. Non‐unions are routinely classified into two groups either hypertrophic or atrophic according to their radiological appearance. It is a common preconception that non‐unions with a hypertrophic appearance on X‐ray are biologically active and vascular with potential to heal given the correct stable environment. Atrophic non‐unions are considered to be avascular and inert and will not heal even under the correct stable environment. Non‐unions are either infected or aseptic. In the present study, we tested the hypothesis that aseptic atrophic non‐unions are less vascular than aseptic hypertrophic non‐unions and healing fractures. Biopsies were taken from the fracture gap of patients with healing fractures, hypertrophic non‐unions and atrophic non‐unions. A dual labelling technique was used with antibodies against CD31 (JC70) and Collagen IV. Blood vessels were quantified using a Chalkley point eyepiece graticule. There was no statistically significant difference in the median vessel count between the three fracture groups. These findings do not support the hypothesis that established atrophic fracture non‐union are less vascular than hypertrophic non‐unions or healing fractures. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.