An experimental in vivo study was performed to test if the effect of Pulsed Electromagnetic Fields (PEMFs) on chondrocyte metabolism and adenosine A2a agonist activity could have a chondroprotective effect on the knee of Dunkin Hartley guinea-pigs of 12 months with spontaneously developed osteoarthritis (OA). After a pilot study, 10 animals were randomly divided into two groups: PEMF-treated group (6 hlday for 3 months) and Sham-treated group. Microradiography and histomorphometry were performed on the entire articular surface of knee joints used in evaluating chondropathy severity, cartilage thickness (CT), cartilage surface Fibrillation Index (FI), subchondral bone plate thickness (SBT) and histomorphometric characteristics of trabecular epiphyseal bone. The PEMF-treated animals showed a significant reduction of chondropathy progression in all knee examined areas (p < 0.05). CT was significantly higher (p < 0.001) in the medial tibia plateaus of the PEMF-treated group when compared to the Sham-treated group. The highest value of FI was observed in the medial tibia plateau of the Sham-treated group (p < 0.05). Significant lower values were observed in SBT of PEMF-treated group in comparison to Sham-treated group in all knee examined areas (p < 0.05). The present study results show that PEMFs preserve the morphology of articular cartilage and slower the progression of OA lesions in the knee of aged osteoarthritic guinea pigs. The chondroprotective effect of PEMFs was demonstrated not only in the medial tibia1 plateau but also on the entire articular surface of the knee.

Ultrasound (US) has been studied by several researchers to assess its possible use in screening for osteoporosis; among other sites the phalanxes have been proposed as a possible site for investigation with US. In the present experimental work we studied the morphostructural characteristics of the second phalanx of the pig; then, in vitro, we investigated the behaviour of an ultrasound signal at 1.25 MHz crossing the distal metaphysis of the second phalanx. In particular, we studied the effects of milling or drilling on US velocity, and on the energy and shape of the signal generated by the US at the receiving probe. We demonstrated that the US velocity decreases by an average of 496 m/s (-21%) when axial perforations are made in the central marrow. A decrease is also noted in the number of peaks, and the normalized energy of the US signal received falls on average by 11.3 mV microseconds (-84%). The characteristics of the signal at the receiving probe can be broadly reconstituted if, after extensive drilling, the bone cavity is filled with polymerized styrene resin. In contrast, if phalanx milling is performed to remove the outermost bone tissue, the normalized energy increases by 15.5 mV microseconds (+84%) and the velocity of US increases by 163 m/s (+7%). It was also noted that the complexity of the signal received (i.e. number of peaks) and the signal normalized energy depend on the integrity of the bone structures traversed. The results reported here provide useful indications for interpreting the findings of clinical investigations with US, most specifically those performed on the phalanx of the hand.

Effects of pulsed electromagnetic fields (PEMFs, 75 Hz, 1.6 mT) were investigated in 12 rabbits after placing hydroxyapatite (HA) implants in their femoral condyles. Six animals were stimulated with PEMFs for three consecutive weeks, 6 h/day, while the remaining animals were sham-treated (Control Group). Rabbits were sacrificed at 3 and 6 weeks (after a 3-week non-stimulation period) for histomorphometric analysis and microhardness testing (at 200, 500, 1000, 2000 pm from the implant) around the implants. Histomorphometric analysis did not highlight any significant changes. On the contrary, there were statistically significant differences between the effects produced by PEMFs and Control Groups ( F = 149.70, p < 0.0005) on the Affinity Index results, as well as by the experimental time of 6 and 3 weeks ( F = 17.12, p = 0.001) on the same results. In PEMF-stimulated animals the microhardness (HV) values measured in trabecular bone at a distance of 200 and 500 pm from the implants, were significaiitly higher with respect to controls. At 6 weeks, HV values at the bone-implant interface in PEMF-stimulated animals were not significantly different with respect to normal bone, while they remained significantly lower in control animals. Both morphological and structural results demonstrated a positive therapeutic effect of PEMFs in accelerating HA osteointegration in trabecular bone.

The influence of pulsed low-frequency electromagnetic fields (PEMFs) on bone formation was investigated in studies of the healing process of transcortical holes, bored at the diaphyseal region of metacarpal bones of six adult horses, exposed for 30 days to PEMFs (28 G peak amplitude, 1.3 ms rise time, and 75 Hz repetition rate). A pair of Helmholtz coils, continuously powered by a pulse generator, was applied for 30 days to the left metacarpal bone, through which two holes, of equal diameter and depth, had been bored at the diaphyseal region. Two equal holes, bored at the same level in the right metacarpal and surrounded by an inactive pair of Helmholtz coils, were used as controls. All horses were given an intravenous injection of 25-30 mg/kg of tetracycline chloride on the 15th and again on the 25th day after the operation and were killed 5 days later. The histomorphometric analysis indicated that both the amount of bone formed during 30 days and the mineral apposition rate during 10 days (deduced from the interval between the two tetracycline labels) were significantly greater (p < 0.01 and p < 0.0001, respectively) in the PEMF-treated holes than in the controls. As did a previous investigation, these preliminary findings indicate that PEMFs at low frequency not only stimulate bone repair but also seem to improve the osteogenic phase of the healing process, at least in our experimental conditions.

Summary. Size and density of osteocyte lacunae were evaluated at different levels of long bones to investigate whether or not the proportion of bone tissue occupied by osteocytes changes in skeletal regions, characterized by clear-cut differences in bone turnover rates. Statistical analysis of the results shows that the mean cross-sectional area of osteocyte lacunae (C) is lowest in compact bone of diaphysis and metaphysis, highest in spongy bone of metaphysis and epiphysis. On the contrary, the mean surface of bone tissue surrounding each osteocyte (T = bidimensional osteocyte territory, indirectly calculated from the number of lacunae/mm ~ of bone) is largest in compact bone of diaphysis, smallest in metaphyseal spongiosa, and shows intermediate values in the cortex of metaphysis and in epiphyseal spongiosa. The proportion of bone tissue occupied by osteocyte lacunae (% C/T) appears to follow at different levels of long bones, the same pattern recorded for the data of bone turnover rate, by the tetracycline labeling technique: it is lowest in mid-diaphyses, highest in metaphyses, and intermediate in epiphyses. On the basis of these findings, it is suggested that the action exerted by osteocytes on the surrounding calcified matrix, whatever the function of these cells, is not uniform throughout the skeleton and is to some extent correlated with the activity of the other bone cells--osteoblasts and osteoclasts.The significance of some of the data reported is also discussed in relation to investigations of periosteocytic lacunar morphometry.Key words: Osteocyte lacuna--Osteocyte bidimensional territory --Osteolysis metabolically active cells. Their precise function, however, still remains somewhat obscure. It has long been maintained that osteocytes are capable of reabsorbing and laying down layers of calcified matrix which surround both their cell body and cytoplasmic processes; these are termed their osteolytic and osteoplastic activity, respectively [1-4]. While there is no doubt that osteocytes have osteogenetic properties, at least during their maturation from osteoblasts, the concept of periosteocytic osteolysis has been seriously questioned in recent years [5][6][7][8][9]. Another hypothesis on the function of osteocytes assigns to these cells the task of transporting ions and organic substances from the fluid compartment of bone to blood [10,11].Whatever their function may be, if the osteocytes intervene in regulating local skeletal metabolism and/or mineral homeostasis, as has been suggested, the degree of their action on the surrounding calcified matrix should change in each skeletal region in relation to the metabolism of that region. For instance, it should differ between compact and spongy bone, as has been shown for the activity of osteoclasts and osteoblasts. Starting out from this working hypothesis and assuming that the intensity with which osteocytes act on calcified matrix depends on the proportion of bone tissue occupied by their protoplasm, we undertook a series of investigations on the dimens...