Unlike most other tumours, myeloma causes bone destruction without an osteoblastic reaction; we tried to assess whether myeloma secretes a humoral factor that inhibits osteoblasts. Human bone-derived cells were either co-cultured with myeloma cells, or cultured in medium conditioned by myeloma cells. Bone-derived cell growth was measured by cell counts and by uptake of tritiated thymidine (3H-Tdr); growth was inhibited when cultured in medium conditioned by myeloma cells and some inhibition was seen when the bone-derived cells were co-cultured with myeloma cells. The inhibiting effect was dose-dependent and also dependent upon the density of the myeloma cells conditioning the medium. The results of our study suggest that myeloma secretes an osteoblast inhibiting factor of less than 50,000 Dalton molecular weight.

Ferrography is a technique for analysing wear by means of the magnetic separation of wear particles. To evaluate its application in human joints, the results of the ferrographic analysis of saline washings of symptomatic human knees were compared with the results of the arthroscopic examination of the same knees. Ferrography was found to be an extremely sensitive monitor of articular erosion, with a resolution far greater than that of arthroscopy. This was particularly apparent with knees suffering from a torn anterior cruciate ligament: arthroscopy detected no damage to the cartilaginous surfaces whereas ferrography detected a substantial level of "microdamage". The spectrum of wear particles showed qualitative and quantitative alterations depending upon the condition of the knee. Ferrography thus holds much promise as a potential differential diagnostic technique of great sensitivity, with particular relevance to the very early changes which precede clinical symptoms. Study of wear particles is also justified by evidence indicating an active role in the pathophysiological progression of arthritis.