Aims. The aims of this study were to develop an in vivo model of periprosthetic joint infection (PJI) in cemented hip hemiarthroplasty, and to monitor infection and biofilm formation in real-time. Methods. Sprague-Dawley rats underwent cemented hip hemiarthroplasty via the posterior approach with pre- and postoperative gait assessments. Infection with Staphylococcus aureus Xen36 was monitored with in vivo photoluminescent imaging in real-time. Pre- and postoperative gait analyses were performed and compared. Postmortem micro (m) CT was used to assess implant integration; field emission scanning electron microscopy (FE-SEM) was used to assess biofilm formation on prosthetic surfaces. Results. All animals tolerated surgery well, with preservation of gait mechanics and weightbearing in control individuals. Postoperative in vivo imaging demonstrated predictable evolution of infection with logarithmic signal decay coinciding with abscess formation. Postmortem mCT qualitative volumetric analysis showed high contact area and both cement-bone and cement-implant interdigitation. FE-SEM revealed biofilm formation on the prosthetic head. Conclusion. This study demonstrates the utility of a new, high-fidelity model of in vivo PJI using cemented hip hemiarthroplasty in rats. Inoculation with bioluminescent bacteria allows for non-invasive, real-time monitoring of infection. Cite this article: Bone Joint J 2021;103-B(7 Supple B):9–16

We studied the effect of vitamin C on fracture healing in the elderly. A total of 80 elderly Osteogenic Disorder Shionogi rats were divided into four groups with different rates of vitamin C intake. A closed bilateral fracture was made in the middle third of the femur of each rat. Five weeks after fracture the femora were analysed by mechanical and histological testing. The groups with the lower vitamin C intake demonstrated a lower mechanical resistance of the healing callus and a lower histological grade. The vitamin C levels in blood during healing correlated with the torque resistance of the callus formed (r = 0.525). Therefore, the supplementary vitamin C improved the mechanical resistance of the fracture callus in elderly rats. If these results are similar in humans, vitamin C supplementation should be recommended during fracture healing in the elderly

We investigated the effect of progesterone on the nerve during lengthening of the limb in rats. The sciatic nerves of rats were elongated by leg lengthening for ten days at 3 mm per day. On alternate days between the day after the operation and nerve dissection, the progesterone-treated group received subcutaneous injections of 1 mg progesterone in sesame oil and the control group received oil only. On the fifth, tenth and 17th day, the sciatic nerves were excised at the midpoint of the femur and the mRNA expression level of myelin protein P0 was analysed by quantitative real time polymerase chain reaction. On day 52 nodal length was examined by electron microscopy, followed by an examination of the compound muscle action potential (C-MAP) amplitude and the motor conduction velocity (MCV) of the tibial nerve on days 17 and 52. The P0 (a major myelin glycoprotein) mRNA expression level in the progesterone-treated group increased by 46.6% and 38.7% on days five and ten, respectively. On day 52, the nodal length in the progesterone-treated group was smaller than that in the control group, and the MCV of the progesterone-treated group had been restored to normal. Progesterone might accelerate the restoration of demyelination caused by nerve elongation by activating myelin synthesis

Using a rat model the characteristics of the sensory neurones of the dorsal-root ganglia (DRG) innervating the hip were investigated by retrograde neurotransport and immunohistochemistry. Fluoro-Gold solution (FG) was injected into the left hip of ten rats. Seven days later the DRG from both sides between T12 and L6 were harvested. The number of FG-labelled calcitonin gene-related peptide-immunoreactive or isolectin B4-binding neurones were counted. The FG-labelled neurones were distributed throughout the left DRGs between T13 and L5, primarily at L2, L3, and L4. Few FG-labelled isolectin B4-binding neurones were present in the DRGs of either side between T13 and L5, but calcitonin gene-related peptide-immunoreactive neurones made up 30% of all FG-labelled neurones. Our findings may explain the referral of pain from the hip to the thigh or lower leg corresponding to the L2, L3 and L4 levels. Since most neurones are calcitonin gene-related peptide-immunoreactive peptide-containing neurones, they may have a more significant role in the perception of pain in the hip as peptidergic DRG neurones

1. Into osseous defects cut in the pelvis of rats, Kiel bone grafts were implanted after impregnation with the animals' own fresh bone marrow, obtained by femoral puncture. Unimpregnated Kiel bone grafts and Kiel bone grafts impregnated with an antibiotic solution were implanted as controls. 2. Histological examination of the implant area showed that in the marrow-impregnated grafts new bone formation could be observed after twelve days, and that during an observation period of 135 days after implantation bone formation occurred in thirteen out of nineteen rats. In four of these cases a continuous bony bridge developed over the defect. 3. In the unimpregnated grafts no more than a small amount of new bone was seen in only one of seven rats. In the antibiotic-impregnated grafts no bone formation was found in six rats during the same period of observation

Apart from preliminary notices of present work, previous reports of experimental and clinical trials of the effects of a high-peak pulsed electromagnetic field (PEMF) on degeneration and regeneration of peripheral nerves lacked statistical analysis. Therefore, we designed experiments with standardised operative, histological, cytological and morphometric techniques to assess the effect of PEMF on lesions of the common peroneal nerves in paired male rats matched for age, environmental conditions and level and type of lesion. One of two types of lesion was induced in the left common peroneal nerve: in 12 pairs of rats the nerve was crushed just above the knee and in the remaining 12 pairs the nerve was cut and immediately sutured at the same level. The right common peroneal nerve of each rat served as a control. Animals received 15 minutes of PEMF produced by a Diapulse machine or sham treatment daily for periods ranging from three and a half days to eight weeks after injury. Healthy nerves were unaffected, but after damage there were statistically significant differences between PEMF treated and sham treated rats. PEMF accelerated the recovery of injured limbs and the degeneration, regeneration and maturation of myelinated axons; epineural, perineural and intraneural fibrosis was reduced; and the luminal cross-sectional area of intraneural vessels increased after both types of lesion. Findings are discussed and the need for clinical trials is stressed

1. In growing rats oestrogen, cortisone and thyroxine in high doses suppress bone formation, and this effect is probably part of a general suppression of body growth. 2. Growth hormone and thyroxine in small doses stimulate both body growth and bone formation. 3. Testosterone has no effect on bone formation. 4. Oestrogen and cortisone suppress bone resorption. The effect of cortisone may be modified in conditions of calcium depletion. 5. Thyroxine appears on the other hand to increase bone resorption. 6. Testosterone has no effect on bone resorption

1. Experimental arthritis was induced in rats by the intradermal injection of modified Freund's adjuvant. 2. The granulation tissue occurring in and around the joints was examined with the electron microscope. 3. Intracellular collagen was demonstrated in many of the cells. 4. Collagen formation by these cells was studied by autoradiographic techniques using tritiated proline as a label. 5. The proline turnover was rapid, as most of the labelled proline had become extracellular one hour after its injection. 6. It was concluded that the collagen was present within the cells as a result of phagocytosis despite the fact that the cells had the electron microscopic features of fibroblasts

1. The distribution of isotope following a single injection of either Ca. 45. or C. 14. -proline has been studied in young rats in which one tibia had previously been removed, killed and reimplanted. 2. The dead tibia took up about 25 per cent as much Ca. 45. or C. 14. as did the living tibia and the possible processes by which this occurred are discussed. 3. Determination of the "accretion rate " by kinetic analysis of the Ca. 45. data showed that this was much too high unless the physico-chemical process of uptake of isotope by bone was taken into account. 4. Under the conditions of the experiment it was not possible to estimate the rate of bone matrix formation using C. 14. -proline as a tracer

The parameters of cellular proliferation and growth in the growth plates of immature rats were measured after unilateral tibial osteotomy and used to calculate growth rates. Distal osteotomy of one tibia was followed by a bilateral increase in the calculated growth rate of the distal growth plates. However, the ipsilateral distal growth plate grew faster than the contralateral between 12 and 18 days after operation, which appeared to be related to increased cell proliferation and height. Proximal osteotomy led to an increase in growth rates proximally which was more marked on the contralateral side. The lesser response of the ipsilateral growth plate may have been due to local impairment of blood supply, or to greater local release of metabolites after bony damage. Distal tibial osteotomy gave similar results to circumferential release of the distal tibial periosteum. Proximal osteotomy, however, produced a relative impairment of growth on the operated side. This may be of importance in the correction of childhood deformities associated with inequality of leg length

The right sciatic nerve of 50 one-month-old male rats was cut under general anaesthesia. Groups of animals were sacrificed at intervals of up to 12 weeks after operation and the length of the femora, tibiae and first and fifth metatarsals were measured with a caliper accurate to 0.05 mm. From the first week, both metatarsals were between 3% and 5% shorter on the denervated side, but there was no further increase of the discrepancy. The femora were less than 1% longer in the denervated limb at the second and eighth week. No difference was found between the lengths of the tibiae. The various factors which could possibly be responsible for these findings are discussed

1. Dislocation and subluxation of the hip has been produced in young rats by application of splints reaching from the hip to the foot, bringing the hip into extension. 2. Progressive acetabular dysplasia and anatomical abnormalities of the head and neck of the femur occurred. 3. Results of the experiments suggest that post-natal extension of the hip is of importance in the pathogenesis of congenital dislocation of the hip in man

1. A method of constricting sciatic nerves of rats was devised which produced lesions resembling macroscopically and electromyographically those of carpal tunnel and related syndromes. 2. The nerves became swollen and hyperaemic proximal and distal to the constriction. The swellings were largely caused by an accumulation of fluid between the axons, but the axons themselves were also increased in size. 3. This accumulation of fluid was an oedema secondary to a partial obstruction of the vasa nervorum

An orientated substratum has been implicated in the development and regeneration of axons and synapses. We prepared a basement membrane matrix from autogenous striated muscle, used it to repair the sciatic nerve in rats, then investigated the results by histology and electrophysiology. When treated grafts were coaxially aligned with the nerve fascicles functional recovery appeared within 30 days, with good growth of axons into the distal nerve. Grafts with myotubes at right angles to the nerve fascicles supported nerve regeneration but at a slower rate. Grafts of coaxially aligned but untreated muscle allowed axon penetration only through naturally degenerated muscle fibres, with minimal axon penetration of the distal nerve. It is concluded that in the rat a treated graft with correctly orientated empty myotubes can facilitate and guide the regeneration of peripheral nerve after injury and so lead to recolonisation of the distal stump with functional recovery

After the simultaneous administration of radiocalcium and radiophosphorus to young rats the rate of deposition of calcium and of phosphorus in various skeletal parts was computed. Agreement was found between the two sets of data. No difference was thus found in the metabolism of the calcium and of the phosphorus of the bone salt

1. Some physical properties of living and dead bone have been studied in rats; most of these are interrelated and ultimately depend upon the composition of the tissue. 2. Dead bone, remaining within the body, does not take up measurable amounts of mineral from the tissue fluid but retains its original physical properties of radiographic density, specific gravity, strength and composition. 3. The altered radiographic density of avascular bone seen in clinical practice is almost certainly relative unless there has been concomitant appositional new bone formation. 4. Some other explanation must be sought for the finding that dead bone takes up significant amounts of bone-seeking isotopes in radioactive tracer studies

1. An experimental study of the healing mechanism in circumscribed defects in femora of albino rats of the Wistar strain is described. 2. Only the outer one-fifth of the defect is repaired by subperiosteal bony callus, the rest of the defect being repaired by endosteal callus. 3. Subperiosteal callus does not bridge the defect until endosteal callus is developed fully. 4. As peripheral callus matures the greater part of the endosteal callus is resorbed, with the exception of trabeculae attached to the margin of the defect. 5. The resorbed area in the medullary part of the defect is gradually obliterated by deposition of inner circumferential lamellae. 6. There appear to be differences between the mechanism responsible for repair of fractures of a long bone and that which heals circumscribed bone defects

We examined the cellular responses to various particles injected into the knees and the intramedullary femoral cavities of rats in the presence of polymethyl-methacrylate (PMMA) plugs. The intra-articular particles were mainly ingested by synovial fibroblasts. Increased numbers of macrophages were not detected and there was only a slight increase in synovial thickness. Cellular responses in the intramedullary space were similarly mild and bone resorption around the PMMA plug did not occur. Bone formation was inhibited only by polyethylene particles. In contrast to current views, our study shows that wear particles per se do not initiate bone resorption

Continuous strontium administration first induces typical "rickets" in young rats receiving adequate calcium phosphorus and vitamin D but later the widened cartilage spontaneously calcifies intermittently leaving transverse bands consisting largely of osteoid tissue in the metaphysis; in addition to intermittent calcification bone changes indicate that skeletal growth is not uniformly progressive. Subsequently areas of the epiphysial cartilage fail to calcify and localised defects develop; among these are wedge-shaped metaphysial osteoid tissue masses, "invagination" of the epiphysial plate to form multiple nodules of cartilage with proliferating cells in the middle and hypertrophic ones at the periphery, perforation and fragmentation of the epiphysial plate with formation of large cartilage nodules. Multiple cartilage nodules of different sizes appear in the epiphysis, metaphysis and bone shaft. Most bone margins are lined by osteoid seams which only slowly calcify and concomitantly resorption is decreased so that the rate of remodelling of the skeleton is diminished. This type of process may help to explain the results of treatment of osteoporosis by strontium administration

We have studied the effect of hydroxyapatite (HA) coating in 15 ovariectomised and 15 normal rats which had had a sham procedure. Twenty-four weeks after operation, HA-coated implants were inserted into the intramedullary canal of the right femur and uncoated implants into the left femur. The prostheses were removed four weeks after implantation. Twelve specimens in each group had mechanical push-out tests. Sagittal sections of the other three were evaluated by SEM. The bone mineral density (BMD) of the dissected left tibia was measured by dual-energy x-ray absorptiometry. The difference in BMD between the control and ovariectomised tibiae was 35.01 mg/cm. 2. (95% CI, 26.60 to 43.42). The push-out strength of the HA-coated implants was higher than that of the uncoated implants in both groups (p < 0.0001), but the HA-coated implants of the ovariectomised group had a reduction in push-out strength of 40.3% compared with the control group (p < 0.0001). Our findings suggest that HA-coated implants may improve the fixation of a cementless total hip prosthesis but that the presence of osteoporosis may limit the magnitude of this benefit

The main findings in this experimental work on rats fed on lathyrus odoratus (sweet-pea) meal are as follows:. 1. Growth is retarded. 2. The growth plate is disorganised and normal ossification at the metaphysis is interfered with. 3. The small blood vessels are seriously affected and probably contribute quite largely to the disorganisation and lack of calcification. 4. Alkaline phosphatase activity is increased. 5. Raising of the periosteum and laying down of new bone result in exostoses. The possible underlying etiology and the role of cement substance, endocrine factors and the blood vessels are discussed

It has been shown in experimental animals that the living cells in a bone autograft can make an important contribution to osteogenesis. However, some common clinical techniques, such as the topical use of antibiotic powders on grafts or on the graft bed, are likely to damage or kill the cells. In this experimental study in rats, bone isografts dusted with chloramphenicol or methicillin powder or with Polybactrin spray before subcutaneous implantation produced little or no new bone over a period of two weeks whereas untreated, control grafts showed abundant osteogenesis, as did grafts pretreated with solutions of antibiotics. The effect of short-term storage of the grafts for 3 to 24 hours in air, saline or culture medium before implantation was also examined. Grafts stored in culture medium generally did as well as, or better than, fresh control grafts whereas immersion in saline inhibited osteogenesis. The importance of these results for clinical bone grafting is discussed

Based on a study using a retrograde neurotracer, we have previously found that the dorsal portion of the L5/6 disc in the rat is multisegmentally innervated by dorsal root ganglia (DRG) from the level of T13 to L6, and that sensory nerve fibres from DRG of T13, L1 and L2 pass through the paravertebral sympathetic trunks. In this study in newborn rats, we injected crystals of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylinedocarbocyanine perchlorate (DiI) into the DRG of T13, L1 and L2 and showed DiI-labelled sensory nerve fibres in the dorsal portion of the discs from the level of T13/L1 to L5/6. Our results show that the dorsal portion of the lumbar discs is innervated by the DRG from levels T13 to L2

Revascularisation of syngeneic and allogeneic intramuscular bone grafts have been studied using radioactive microspheres to measure the ingrowth of blood vessels. New bone formation and resorption were measured by 85strontium uptake and by graft weight reduction. Revascularisation, and mineralisation rate were significantly higher in syngeneic grafts than in allogeneic grafts at two, three and six weeks after implantation. The syngeneic grafts lost weight faster indicating that the allogeneic grafts resorbed more slowly. The ingrowth of new vessels is impaired in allogeneic bone, and this probably inhibits the rate of bone formation and resorption of the grafts.

We examined solvent-dried, gamma-irradiated (SD-R) allografts and fresh-frozen (FF) allografts mechanically and morphologically. Before transplantation, FF grafts were more than six times stronger than SD-R grafts. After four weeks, the tensile strength was about the same in both groups. At 24 weeks only collagen fibrils of small diameter were observed in the SD-R grafts while in FF grafts fibrils of small and intermediate diameter were seen. Clinically, we suggest that SD-R grafts could be used as a favourable alternative to FF grafts if care was taken regarding their initial mechanical weakness.

1. The radiographs of paired living and dead rat tibiae, obtained in an experiment previously reported, have been examined by densitometry.

2. The dead bone became progressively less dense than the living bone as the duration of the implantation increased.

3. The change in density was related to the quantity, but not to the quality, of the bone tissue examined.

1. The results of the present investigation indicate that in the foetal rat the juxta-epiphysial vascular bed consists of a dense irregular network of sinusoids in direct contact with the growth cartilage, supplied by end-arteries, and drained by a profusion of metaphysial sinusoids.

2. The circulation is a closed one–that is, the endothelium is unbroken in its continuity and microhaemorrhages do not occur against the cartilage.

3. It is possible that juxta-epiphysial endothelial cells or their derivatives are chondrolytic, and that they participate directly, together with other mesenchymal derivatives, in the removal of cartilage as a preparatory stage in enchondral bone formation.

One of the aims of this work was to find criteria by which the quality of bone as a supporting tissue might be judged. This inevitably involves discussion and, if possible, assessment, of the relative importance of the inorganic and organic material of the bone. It is relatively easy to measure the mineral content, and for that reason it has always received more than its due share of attention.

In the present experiment the composition of the ash of all bones was remarkably constant, with a Ca/P ratio of 2. Furthermore, X-ray crystallography showed that the structure of the inorganic material was the same in all cases. The great difficulty of measuring variations in the quality of the organic material which is, of course, protein in nature makes it impossible to say how much it influences bone strength. Since at least 40 per cent. of the bone is collagen, either a quantitative or a qualitative alteration might alter bone strength. X-ray crystallography revealed no qualitative differences in the collagen material of bones of the three groups; so that for the present it would seem safer to assume that alterations in the physical properties of the bones are due to variations in the relative proportions of organic and inorganic constituents (Dawson 1946, Bell et al. 1947).

These experiments show that the three diets produce highly significant differences in the percentage of ash, in S_B, and in E. It is possible that some variations in the percentage of ash are due to variations in the absolute collagen (weight of collagen in unit volume of bone substance); but the range of variation in the percentage of ash leaves no reasonable doubt that differences in percentage ash between the diet groups are due essentially to differences in absolute ash. Presumably the collagen contributes something to the strength of the bone; but the indications are that it plays a minor part and that the relative weakness and flexibility of rachitic bones is due to decrease in the absolute ash content. Within any one diet group, the relation between percentage ash and the other two variables, S_B and E, is masked by other sources of variation such as those associated with the many measurements involved; and thus the correlation between percentage ash and S_B, and also between percentage ash and E, is not significant.

At first sight, the scatter diagrams (Figs. 5 and 6) appear to indicate a correlation between ash and S_B, and between ash and E. Closer inspection shows, however, that the apparent trend is due largely to differences between the means of the diet groups, and that the points within any one group show no such obvious trend. Figure 7 shows that the position with regard to correlation between S_B and E is very different. Here there is an obvious trend within each diet group; the amount of scatter is very much less. Calculation shows that, even when the differences between the means of diet groups is excluded, there is still a significant correlation between S_B and E. The question of the correlation between the three variables is discussed more fully in the addendum to this paper.

Although the "goodness" of a bone is usually judged by its breaking stress, the experimental findings recorded above suggest that it may be assessed equally well on the basis of elastic properties as shown by Young's modulus. Normal bones, group S in these experiments, were elastic up to 79 per cent. of their breaking stress (Table II): the poorer bones of groups R and N were, however, only a little inferior in this respect. In some cases there was no apparent deviation of the load-deflexion curve from a straight line until the bone was about to break. Such a curve was published in the first paper of this series (Bell, Cuthbertson and Orr 1941), but in the light of further experience this curve is scarcely typical. The terminal falling over of the curve is illustrated in Figure 4 and is much more marked in the bones of group R.

While stress at the upper limit of elasticity varies over a wide range in the three groups (Table II and Fig. 4), the strain at this point is remarkably constant at about 1·5 per cent. This same percentage displacement must occur between the molecules of the bone material at the elastic limit—and it may be that, up to this amount of molecular displacement, the deformation is reversible; but that beyond it, plastic changes occur. We have no evidence as to whether the limiting displacement concerns mineral or protein constituents of the bone, or both.

We have already commented on the remarkable strength of bone material (Bell et al., 1941). The breaking stress of normal rat bone is about the same as that of cast iron, and about half that of mild steel. Young's modulus, however, is only one-tenth that of cast iron and one-twentieth that of steel. Thus bone, despite its lightness (specific gravity about 2·5 as compared with 7·9 for iron), is remarkably strong and at the same time more flexible than might be expected. Presumably the biological advantage is that greater flexibility helps to absorb sudden impacts. It is unusual in metallic substances to find the elastic modulus proportional to the strength; this is more characteristic of materials like concrete and timber. Another remarkable property of bone is that it remains elastic up to three-quarters of the breaking stress. Most metals show considerable ductility before reaching their breaking point.

While Young's modulus is of interest, both on its own account and as an index of the quality of the bone, its close association with breaking stress suggests that it might be used to predict the maximum load which a bone can carry safely. Since E, unlike S_B, can be measured without damage, useful information might be gained by measuring the elasticity of living human bones.

Experimentally produced fractures in long bones studied by light and electron microscopic histochemistry were found to heal by a process of enchondral calcification. There was intense proliferation in the cells of the cambium layer of the periosteum, with differentiation to chondroblasts and osteoblasts, suggesting that this layer was the primary tissue responsible for development of the callus. Cytoplasmic processes of the hypertrophic chondrocytes appeared to bud and produce matrix vesicles. Alkaline phosphatase activity was detected along the plasma membrane of the hypertrophic chondrocytes and around the matrix vesicles, before any signs of mineral deposition. Calcification took place by deposition of hydroxyapatite crystals in and around these matrix vesicles which frequently showed alkaline phosphatase activity. It is suggested that there is a close functional association between alkaline phosphatase activity and calcification in the process of fracture healing, which is another type of enchondral calcification mediated by matrix vesicles.

1. The process of repair after fracture of the humerus of the growing rat has been studied by histological, histochemical and biochemical methods.

2. Both periosteal and surrounding mesenchymal cells take part in the process of repair.

3. The primary framework of collagen bridging the gap is mainly formed by the mesenchymal cells, while calcification and ossification of the framework is largely a function of the periosteum.

4. The mucopolysaccharide content rises rapidly in the first week after injury, and is followed by a rise in the collagen content during the second week. The deposition of calcium phosphate during the third and fourth weeks causes an apparent fall in the collagen content during that period. The collagen content tends to return to normal during the phase of remodelling in the fifth and sixth weeks.

5. The tensile strength of the healing bone bears a close relation to its collagen content.

Cartilage formation was provoked in the skull vault of the young rat by making multiple incisions, and scraping the periosteum to reduce the blood supply to the injured area. The hypothesis that ischaemia induces osteogenic cells to produce cartilage in the course of fracture repair thus receives experimental support.

1. It has been shown that in experimental rickets the well known changes in the epiphysial cartilage which so seriously affect growth are accompanied by severe interference with the progress of the metaphysial vessels into the growth cartilage.

2. Further evidence has been found that, by the repeated increase in their number, the cartilage cells occupying the more distal part of the proliferative segment become more and more affected by their remoteness from the epiphysial vessels, which supply the transudates to these cells. At a given distance these cells are affected and change, becoming hypertrophic, with increasingly large vacuolae, and are rich in glycogen and alkaline phosphatase.

3. The hypertrophic cells alter the nature of the intercellular substance they deposit and this becomes calcifiable. Provided that the metaphysial vessels are situated at an appropriate distance–about three cell capsules away–and that the blood has its necessary components, calcification occurs.

4. Calcification produces the advancing, rigid multitubular structure within which the progressing metaphysial vessels are protected.

5. The interruption of calcification by the withdrawal of fat-soluble vitamins breaks down the whole mechanism of growth and stops the vessels growing into their proper position. The administration of the required vitamins re-establishes the normal sequence of events and allows the vessels to play their decisive role in osteogenesis.

6. Any mechanism which causes the interruption of the vascular progression, whether from metaphysial ischaemia (Trueta and Amato 1960), from severe pressure (Trueta and Trias 1961) or from lack of calcification by withdrawing the fat-soluble vitamins, equally interrupts growth.

The reduced stability of hydroxyapatite (HA)-coated implants in osteopenic conditions is considered to be a major problem. We therefore developed a model of a boosted cementless implantation in osteopenic rats. Twelve-week-old rats were either ovariectomised (OVX) or sham-operated (SO), and after 24 weeks plain or HA-coated implants were inserted. They were treated with either a prostaglandin EP4 receptor agonist (ONO-4819) or saline for one month. The EP4 agonist considerably improved the osteoporosis in the OVX group. Ultrastructural analysis and mechanical testing showed an improvement in the implant-bone attachment in the HA-coated implants, which was further enhanced by the EP4 agonist. Although the stability of the HA-coated implants in the saline-treated OVX rats was less than in the SO normal rats, the administration of the EP4 agonist significantly compensated for this shortage. Our results showed that the osteogenic effect of the EP4 agonist augmented the osteoconductivity of HA and significantly improved the stability of the implant-bone attachment in the osteoporotic rat model

Conventional non-steroidal anti-inflammatory drugs (NSAIDs) and newer specific cyclo-oxygenase-2 (cox-2) inhibitors are commonly used in musculoskeletal trauma and orthopaedic surgery to reduce the inflammatory response and pain. These drugs have been reported to impair bone metabolism. In reconstruction of the anterior cruciate ligament the hamstring tendons are mainly used as the graft of choice, and a prerequisite for good results is healing of the tendons in the bone tunnel. Many of these patients are routinely given NSAIDs or cox-2 inhibitors, although no studies have elucidated the effects of these drugs on tendon healing in the bone tunnel. In our study 60 female Wistar rats were randomly allocated into three groups of 20. One received parecoxib, one indometacin and one acted as a control. In all the rats the tendo-Achillis was released proximally from the calf muscles. It was then pulled through a drill hole in the distal tibia and sutured anteriorly. The rats were given parecoxib, indometacin or saline intraperitoneally twice daily for seven days. After 14 days the tendon/bone-tunnel interface was subjected to mechanical testing. Significantly lower maximum pull-out strength (p < 0.001), energy absorption (p < 0.001) and stiffness (p = 0.035) were found in rats given parecoxib and indometacin compared with the control group, most pronounced with parecoxib

This study was designed to test the hypothesis that the sensory innervation of bone might play an important role in sensing and responding to low-intensity pulsed ultrasound and explain its effect in promoting fracture healing. In 112 rats a standardised mid-shaft tibial fracture was created, supported with an intramedullary needle and divided into four groups of 28. These either had a sciatic neurectomy or a patellar tendon resection as control, and received the ultrasound or not as a sham treatment. Fracture union, callus mineralisation and remodelling were assessed using plain radiography, peripheral quantitative computed tomography and histomorphology. Daily ultrasound treatment significantly increased the rate of union and the volumetric bone mineral density in the fracture callus in the neurally intact rats (p = 0.025), but this stimulating effect was absent in the rats with sciatic neurectomy. Histomorphology demonstrated faster maturation of the callus in the group treated with ultrasound when compared with the control group. The results supported the hypothesis that intact innervation plays an important role in allowing low-intensity pulsed ultrasound to promote fracture healing

Bone marrow mesenchymal stromal cells were aspirated from immature male green fluorescent protein transgenic rats and cultured in a monolayer. Four weeks after the creation of the osteochondral defect, the rats were divided into three groups of 18: the control group, treated with an intra-articular injection of phosphate-buffered saline only; the drilling group, treated with an intra-articular injection of phosphate-buffered saline with a bone marrow-stimulating procedure; and the bone marrow mesenchymal stromal cells group, treated with an intra-articular injection of bone marrow mesenchymal stromal cells plus a bone marrow-stimulating procedure. The rats were then killed at 4, 8 and 12 weeks after treatment and examined. The histological scores were significantly better in the bone marrow mesenchymal stromal cells group than in the control and drilling groups at all time points (p < 0.05). The fluorescence of the green fluorescent protein-positive cells could be observed in specimens four weeks after treatment

This in vivo controlled laboratory study was performed to evaluate various intra-articular clinical injection regimes that might be less toxic than some in vitro studies suggest. We hypothesised that low-concentration, preservative-free, pH-balanced agents would be less toxic than high-concentration non-pH-balanced agents with preservatives, and that injections of individual agents are less toxic than combined injections. The left knees of 12- to 13-week-old Sprague–Dawley rats were injected once with eight different single agents, including low and high concentrations of ropivacaine and triamcinolone, alone and in combination, as well as negative and positive controls. The rats were killed at one week or five months, and live–dead staining was performed to quantify the death of chondrocytes. All injections except pH-balanced 0.2% ropivacaine combined with preservative-free 1 mg/ml triamcinolone acetonide resulted in statistically significant decreases in chondrocyte viability, compared with control knees, after one week and five months (p < 0.001). After one week there was no significant difference in viability between 0.2% and 0.5% ropivacaine; however, 4 mg/ml triamcinolone resulted in a lower viability than 1 mg/ml triamcinolone. Although many agents commonly injected into joints are chondrotoxic, in this in vivo study diluting preservative-free 10 mg/ml triamcinolone 1:9 in 0.2% pH-balanced ropivacaine resulted in low toxicity. Cite this article: Bone Joint J 2015; 97-B:933–8

We investigated the effect of mitomycin-C on the reduction of the formation of peritendinous fibrous adhesions after tendon repair. In 20 Wistar albino rats the tendo Achillis was cut and repaired using a modified Kessler technique. The rats were divided into two equal groups. In group 1, an injection of mitomycin-C was placed between the tendon and skin of the right leg. In group 2, an identical volume of sterile normal saline was injected on the left side in a similar fashion. All the rats received mitomycin-C or saline for four weeks starting from the day of operation. The animals were killed after 30 days. The formation of peritendinous fibrous tissue, the inflammatory reaction and tendon healing were evaluated. The tensile strength of the repaired tendons was measured biomechanically. Microscopic evidence of the formation of adhesions and inflammation was less in group 1. There was no significant difference in the tensile load required to rupture the repaired tendons in the two groups. Mitomycin-C may therefore provide a simple and inexpensive means of preventing of post-operative adhesions

Soaking bone grafts in a bisphosphonate solution before implantation can prevent their resorption and increase the local bone density in rats and humans. However, recent studies suggest that pre-treatment of allografts with bisphosphonate can prevent bone ingrowth into impaction grafts. We tested the hypothesis that excessive amounts of bisphosphonate would also cause a negative response in less dense grafts. We used a model where non-impacted metaphyseal bone grafts were randomised into three groups with either no bisphosphonate, alendronate followed by rinsing, and alendronate without subsequent rinsing, and inserted into bone chambers in rats. The specimens were evaluated histologically at one week, and by histomorphometry and radiology at four weeks. At four weeks, both bisphosphonate groups showed an increase in the total bone content, increased newly formed bone, and higher radiodensity than the controls. In spite of being implanted in a chamber with a limited opportunity to diffuse, even an excessive amount of bisphosphonate improved the outcome. We suggest that the negative results seen by others could be due to the combination of densely compacted bone and a bisphosphonate. We suggest that bisphosphonates are likely to have a negative influence where resorption is a prerequisite to create space for new bone ingrowth

Rotator cuff tears are common in middle-aged and elderly patients. Despite advances in the surgical repair of rotator cuff tears, the rates of recurrent tear remain high. This may be due to the complexity of the tendons of the rotator cuff, which contributes to an inherently hostile healing environment. During the past 20 years, there has been an increased interest in the use of biologics to complement the healing environment in the shoulder, in order to improve rotator cuff healing and reduce the rate of recurrent tears. The aim of this review is to provide a summary of the current evidence for the use of forms of biological augmentation when repairing rotator cuff tears.

Cite this article: Bone Joint J 2024;106-B(9):978–985.

Currently, there is no animal model in which to evaluate the underlying physiological processes leading to the heterotopic ossification (HO) which forms in most combat-related and blast wounds. We sought to reproduce the ossification that forms under these circumstances in a rat by emulating patterns of injury seen in patients with severe injuries resulting from blasts. We investigated whether exposure to blast overpressure increased the prevalence of HO after transfemoral amputation performed within the zone of injury. We exposed rats to a blast overpressure alone (BOP-CTL), crush injury and femoral fracture followed by amputation through the zone of injury (AMP-CTL) or a combination of these (BOP-AMP). The presence of HO was evaluated using radiographs, micro-CT and histology. HO developed in none of nine BOP-CTL, six of nine AMP-CTL, and in all 20 BOP-AMP rats. Exposure to blast overpressure increased the prevalence of HO. This model may thus be used to elucidate cellular and molecular pathways of HO, the effect of varying intensities of blast overpressure, and to evaluate new means of prophylaxis and treatment of heterotopic ossification. Cite this article: Bone Joint J 2015;97-B:572–6

Aims

A local injection may be used as an early option in the treatment of Morton’s neuroma, and can be performed using various medications. The aim of this study was to compare the effects of injections of hyaluronic acid compared with corticosteroid in the treatment of this condition.

Aims

Gram-negative periprosthetic joint infection (PJI) has been poorly studied despite its rapidly increasing incidence. Treatment with one-stage revision using intra-articular (IA) infusion of antibiotics may offer a reasonable alternative with a distinct advantage of providing a means of delivering the drug in high concentrations. Carbapenems are regarded as the last line of defense against severe Gram-negative or polymicrobial infection. This study presents the results of one-stage revision using intra-articular carbapenem infusion for treating Gram-negative PJI, and analyzes the characteristics of bacteria distribution and drug sensitivity.

MicroRNAs (miRNAs ) are small non-coding RNAs that regulate gene expression. We hypothesised that the functions of certain miRNAs and changes to their patterns of expression may be crucial in the pathogenesis of nonunion. Healing fractures and atrophic nonunions produced by periosteal cauterisation were created in the femora of 94 rats, with 1:1 group allocation. At post-fracture days three, seven, ten, 14, 21 and 28, miRNAs were extracted from the newly generated tissue at the fracture site. Microarray and real-time polymerase chain reaction (PCR) analyses of day 14 samples revealed that five miRNAs, miR-31a-3p, miR-31a-5p, miR-146a-5p, miR-146b-5p and miR-223-3p, were highly upregulated in nonunion. Real-time PCR analysis further revealed that, in nonunion, the expression levels of all five of these miRNAs peaked on day 14 and declined thereafter. . Our results suggest that miR-31a-3p, miR-31a-5p, miR-146a-5p, miR-146b-5p and miR-223-3p may play an important role in the development of nonunion. These findings add to the understanding of the molecular mechanism for nonunion formation and may lead to the development of novel therapeutic strategies for its treatment. Cite this article: Bone Joint J 2015; 97-B:1144–51

Systemic antibiotics reduce infection in open fractures. Local delivery of antibiotics can provide higher doses to wounds without toxic systemic effects. This study investigated the effect on infection of combining systemic with local antibiotics via polymethylmethacrylate (PMMA) beads or gel delivery. An established Staphylococcus aureus contaminated fracture model in rats was used. Wounds were debrided and irrigated six hours after contamination and animals assigned to one of three groups, all of which received systemic antibiotics. One group had local delivery via antibiotic gel, another PMMA beads and the control group received no local antibiotics. After two weeks, bacterial levels were quantified. . Combined local and systemic antibiotics were superior to systemic antibiotics alone at reducing the quantity of bacteria recoverable from each group (p = 0.002 for gel; p = 0.032 for beads). There was no difference in the bacterial counts between bead and gel delivery (p = 0.62). . These results suggest that local antibiotics augment the antimicrobial effect of systemic antibiotics. Although no significant difference was found between vehicles, gel delivery offers technical advantages with its biodegradable nature, ability to conform to wound shape and to deliver increased doses. Further study is required to see if the gel delivery system has a clinical role. Cite this article: Bone Joint J 2015;97-B:1423–7

We have examined the deterioration of implant fixation after withdrawal of parathyroid hormone (PTH) in rats. First, the pull-out force for stainless-steel screws in the proximal tibia was measured at different times after withdrawal. The stimulatory effect of PTH on fixation was lost after 16 days. We then studied whether bisphosphonates could block this withdrawal effect. Mechanical and histomorphometric measurements were conducted for five weeks after implantation. Subcutaneous injections were given daily. Specimens treated with either PTH or saline during the first two weeks showed no difference in the mechanical or histological results (pull-out force 76 N vs 81 N; bone volume density 19% vs 20%). Treatment with PTH for two weeks followed by pamidronate almost doubled the pull-out force (152 N; p < 0.001) and the bone volume density (37%; ANOVA, p < 0.001). Pamidronate alone did not have this effect (89 N and 25%, respectively). Thus, the deterioration can be blocked by bisphosphonates. The clinical implications are discussed

Platelet-derived growth factor (PDGF) is known to stimulate osteoblast or osteoprogenitor cell activity. We investigated the effect of locally applied PDGF from poly-. d. ,l-lactide (PDLLA)-coated implants on fracture healing in a rat model. A closed fracture of the right tibia of four-month-old Sprague-Dawley rats (n = 40) was stabilised with implants coated with a biodegradable PDLLA versus implants coated with PDLLA and PDGF. Radiographs were taken throughout the study, and a marker of DNA activity, bromodeoxyuridine (BrdU), was injected before the rats were killed at three, seven and ten days. The radiographs showed consolidation of the callus in the PDGF-treated group compared with the control group at all three time points. In the PDGF-treated group, immunohistochemical staining of BrdU showed that the distribution of proliferating cells in all cellular events was higher after ten days compared with that at three and seven days. These results indicate that local application of PDGF from biodegradable PDLLA-coated implants significantly accelerates fracture healing in experimental animals. Further development may help fracture healing in the clinical situation.

The nervous system is known to be involved in inflammation and repair. We aimed to determine the effect of physical activity on the healing of a muscle injury and to examine the pattern of innervation. Using a drop-ball technique, a contusion was produced in the gastrocnemius in 20 rats. In ten the limb was immobilised in a plaster cast and the remaining ten had mobilisation on a running wheel. The muscle and the corresponding dorsal-root ganglia were studied by histological and immunohistochemical methods. In the mobilisation group, there was a significant reduction in lymphocytes (p = 0.016), macrophages (p = 0.008) and myotubules (p = 0.008) between three and 21 days. The formation of myotubules and the density of nerve fibres was significantly higher (both p = 0.016) compared with those in the immobilisation group at three days, while the density of CGRP-positive fibres was significantly lower (p = 0.016) after 21 days. Mobilisation after contusional injury to the muscle resulted in early and increased formation of myotubules, early nerve regeneration and progressive reduction in inflammation, suggesting that it promoted a better healing response

Several experimental models have been used to produce intravascular fat embolism. We have developed a simple technique to induce fat embolism using corn oil emulsified with distilled water to form fatty micelles. Fat embolism was produced by intravenous administration of these fatty micelles in anaesthetised rats, causing alveolar oedema, haemorrhage and increased lung weight. Histopathological examination revealed fatty droplets and fibrin thrombi in the lung, kidney and brain. The arteriolar lumen was filled with fatty deposits. Following fat embolism, hypoxia and hypercapnia occurred. The plasma phospholipase A. 2. , nitrate/nitrite, methylguidanidine and proinflammatory cytokines were significantly increased. Mass spectrometry showed that the main ingredient of corn oil was oleic acid. This simple technique may be applied as a new animal model for the investigation of the mechanisms involved in the fat embolism syndrome

We have used an experimental model employing the bent tail of rats to investigate the effects of mechanical forces on bones and joints. Mechanical strain could be applied to the bones and joints of the tail without direct surgical exposure or the application of pins and wires. The intervertebral disc showed stretched annular lamellae on the convex side, while the annulus fibrosus on the concave side was pinched between the inner corners of the vertebral epiphysis. In young rats with an active growth plate, a transverse fissure appeared at the level of the hypertrophic cell layer or the primary metaphyseal trabecular zone. Metaphyseal and epiphyseal trabeculae on the compressed side were thicker and more dense than those of the distracted part of the vertebra. In growing animals, morphometric analysis of hemiepiphyseal and hemimetaphyseal areas, and the corresponding trabecular bone density, showed significant differences between the compressed and distracted sides. No differences were observed in adult rats. We found no significant differences in osteoclast number between compressed and distracted sides in either age group. Our results provide quantitative evidence of the working of ‘Wolff’s law’. The differences in trabecular density are examples of remodelling by osteoclasts and osteoblasts; our finding of no significant difference in osteoclast numbers between the hemiepiphyses in the experimental and control groups suggests that the response of living bone to altered strain is mediated by osteoblasts

In order to clarify the role of cytokines in the remodelling of the grafted tendon for ligament reconstruction we compared the responses to interleukin (IL)-1β, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-β1 of extrinsic fibroblasts infiltrating the frozen-thawed patellar tendon in rats with that of the normal tendon fibroblasts, in regard to the gene expression of matrix metalloproteinase (MMP)-13, using Northern blot analysis. We also examined, immunohistologically, the local expression of IL-1β, PDGF-BB, and TGF-β1 in fibroblasts infiltrating the frozen-thawed patellar tendon. Northern blot analysis showed that fibroblasts derived from the patellar tendon six weeks after the freeze-thaw procedure in situ showed less response to IL-1β than normal tendon fibroblasts with respect to MMP-13 mRNA gene expression. The immunohistological findings revealed that IL-1β was over-expressed in extrinsic fibroblasts which infiltrated the patellar tendon two and six weeks after the freeze-thaw procedure in situ, but neither PDGF-BB nor TGF-β1 was over-expressed in these extrinsic fibroblasts. Our findings indicated that IL-1β had a close relationship to matrix remodelling of the grafted tendon for ligament reconstruction, in addition to the commencement of inflammation during the tissue-healing process

Thrombin has many biological properties similar to those of growth factors. In a previous study, we showed that thrombin improves healing of the rat tendo Achillis. Low molecular weight heparin (LMWH) inhibits the activity and the generation of thrombin. We therefore considered that LMWH at a thromboprophylactic dose might inhibit tendon repair. Transection of the tendo Achillis was carried out in 86 rats and the healing tested mechanically. Low molecular weight heparin (dalateparin) was either injected a few minutes before the operation and then given continuously with an osmotic mini pump for seven days, or given as one injection before the operation. In another experiment ,we gave LMWH or a placebo by injection twice daily. The anti-factor Xa activity was analysed. Continuous treatment with LMWH impaired tendon healing. After seven days, this treatment caused a 33% reduction in force at failure, a 20% reduction in stiffness and a 67% reduction in energy uptake. However, if injected twice daily, LMWH had no effect on tendon healing. Anti-factor Xa activity was increased by LMWH treatment, but was normal between intermittent injections. Low molecular weight heparin delays tendon repair if given continuously, but not if injected intermittently, probably because the anti-factor Xa activity between injections returns to normal, allowing sufficient thrombin stimulation for repair. These findings indicate the need for caution in the assessment of long-acting thrombin and factor Xa inhibitors

Fracture repair occurs by two broad mechanisms: direct healing, and indirect healing with callus formation. The effects of bisphosphonates on fracture repair have been assessed only in models of indirect fracture healing. A rodent model of rigid compression plate fixation of a standardised tibial osteotomy was used. Ten skeletally mature Sprague–Dawley rats received daily subcutaneous injections of 1 µg/kg ibandronate (IBAN) and ten control rats received saline (control). Three weeks later a tibial osteotomy was rigidly fixed with compression plating. Six weeks later the animals were killed. Fracture repair was assessed with mechanical testing, radiographs and histology. The mean stress at failure in a four-point bending test was significantly lower in the IBAN group compared with controls (8.69 Nmm. -2. (. sd. 7.63) vs 24.65 Nmm. -2. (. sd. 6.15); p = 0.017). On contact radiographs of the extricated tibiae the mean bone density assessment at the osteotomy site was lower in the IBAN group than in controls (3.7 mmAl (. sd. 0.75) vs 4.6 mmAl (. sd. 0.57); p = 0.01). In addition, histological analysis revealed progression to fracture union in the controls but impaired fracture healing in the IBAN group, with predominantly cartilage-like and undifferentiated mesenchymal tissue (p = 0.007). . Bisphosphonate treatment in a therapeutic dose, as used for risk reduction in fragility fractures, had an inhibitory effect on direct fracture healing. We propose that bisphosphonate therapy not be commenced until after the fracture has united if the fracture has been rigidly fixed and is undergoing direct osteonal healing. Cite this article: Bone Joint J 2013;95-B:1263–8

We have developed an animal model to examine the formation of heterotopic ossification using standardised muscular damage and implantation of a beta-tricalcium phosphate block into a hip capsulotomy wound in Wistar rats. The aim was to investigate how cells originating from drilled femoral canals and damaged muscles influence the formation of heterotopic bone. The femoral canal was either drilled or left untouched and a tricalcium phosphate block, immersed either in saline or a rhBMP-2 solution, was implanted. These implants were removed at three and 21 days after the operation and examined histologically, histomorphometrically and immunohistochemically. Bone formation was seen in all implants in rhBMP-2-immersed, whereas in those immersed in saline the process was minimal, irrespective of drilling of the femoral canals. Bone mineralisation was somewhat greater in the absence of drilling with a mean mineralised volume to mean total volume of 18.2% (. sd. 4.5) versus 12.7% (. sd. 2.9, p < 0.019), respectively. Our findings suggest that osteoinductive signalling is an early event in the formation of ectopic bone. If applicable to man the results indicate that careful tissue handling is more important than the prevention of the dissemination of bone cells in order to avoid heterotopic ossification

To clarify the pathomechanisms of discogenic low back pain, the sympathetic afferent discharge originating from the L5-L6 disc via the L2 root were investigated neurophysiologically in 31 Lewis rats. Sympathetic afferent units were recorded from the L2 root connected to the lumbar sympathetic trunk by rami communicantes. The L5-L6 discs were mechanically probed, stimulated electrically to evoke action potentials and, finally, treated with chemicals to produce an inflammatory reaction. We could not obtain a response from any units in the L5-L6 discs using mechanical stimulation, but with electrical stimulation we identified 42 units consisting mostly of A-delta fibres. In some experiments a response to mechanical probing of the L5-L6 disc was recognised after producing an inflammatory reaction. This study suggests that mechanical stimulation of the lumbar discs may not always produce pain, whereas inflammatory changes may cause the disc to become sensitive to mechanical stimuli, resulting in nociceptive information being transmitted as discogenic low back pain to the spinal cord through the lumbar sympathetic trunk. This may partly explain the variation in human symptoms of degenerate discs

1. Autografts, isografts and homografts of fibrocartilaginous callus were observed in the anterior chamber of the eye in rats. Proliferation of cartilage ceased, endochondral ossification followed, and the end-product was a new and complete ossicle with a cortex and a marrow cavity. The size and shape of the ossicle was determined by the size and shape of the sample of callus. Thus the callus in the eye performed the function of a cartilage model like that of the developing epiphysis or a healing fracture of a long bone. 2. Fibrocartilaginous callus, heavily labelled with . 3. H-thymidine, was transplanted to the eye twenty-four hours after the last injection, when there was little if any radioactive thymidine circulating in the blood. A few small chondrocytes with labelled nuclei persisted in the cores of new bone trabeculae, but the largest part of the labelled callus was resorbed and replaced by unlabelled new bone. 3. Homografts of labelled callus produced the same results as autografts at twenty-five days, but between twenty-five and forty-five days the donor cells were destroyed by the immune response of the host. 4. Isogenous transplants in host rats treated with . 3. H-thymidine between nine and thirteen days, when the callus was invaded by new blood vessels, produced many osteogenetic cells with labelled nuclei and made it possible to trace the origin of the new bone. The label appeared in the progenitor cells within twenty-four hours. While remaining thereafter in progenitor cells, it appeared also in osteoclasts (or chondroclasts) and osteoblasts in forty-eight to seventy-two hours, and in osteocytes in ninety-six to 120 hours. Chondrocytes did not proliferate and were not labelled in the eye. 5. Homogenous transplants in host rats treated with . 3. H-thymidine between five and one days before the operation also produced new bone, but contained no labelled osteoprogenitor or bone cells after twenty-five days in the eye. At forty-five days the donor tissue had been destroyed by the immune response of the host. 6. Devitalised callus was encapsulated in inflammatory connective tissue and scar. When the dead callus was absorbed by the capillaries of the host new bone formation by induction produced a scanty deposit as a delayed event in a few instances. 7. Irrespective of whether it originated in the donor or the host, a connective-tissue cell type that proliferated rapidly and became labelled with . 3. H-thymidine was identified as a progenitor cell. Differentiation and specialisation as osteoprogenitor cells occurred after the growth of blood vessels into the interior of the callus, and developed inside of excavation chambers in cartilage. Except that the interaction of the donor tissue and host cells leading to new bone formation by induction takes place in the interior of the excavation chamber, the biophysico-chemical mechanism is unknown

We examined whether enamel matrix derivative (EMD) could improve healing of the tendon–bone interface following reconstruction of the anterior cruciate ligament (ACL) using a hamstring tendon in a rat model. ACL reconstruction was performed in both knees of 30 Sprague-Dawley rats using the flexor digitorum tendon. The effect of commercially available EMD (EMDOGAIN), a preparation of matrix proteins from developing porcine teeth, was evaluated. In the left knee joint the space around the tendon–bone interface was filled with 40 µl of EMD mixed with propylene glycol alginate (PGA). In the right knee joint PGA alone was used. The ligament reconstructions were evaluated histologically and biomechanically at four, eight and 12 weeks (n = 5 at each time point). At eight weeks, EMD had induced a significant increase in collagen fibres connecting to bone at the tendon–bone interface (p = 0.047), whereas the control group had few fibres and the tendon–bone interface was composed of cellular and vascular fibrous tissues. At both eight and 12 weeks, the mean load to failure in the treated specimens was higher than in the controls (p = 0.009). EMD improved histological tendon–bone healing at eight weeks and biomechanical healing at both eight and 12 weeks. EMD might therefore have a human application to enhance tendon–bone repair in ACL reconstruction

This study was undertaken to elucidate the mechanism of biological repair at the tendon-bone junction in a rat model. The stump of the toe flexor tendon was sutured to a drilled hole in the tibia (tendon suture group, n = 23) to investigate healing of the tendon-bone junction both radiologically and histologically. Radiological and histological findings were compared with those observed in a sham control group where the bone alone was drilled (n = 19). The biomechanical strength of the repaired junction was confirmed by pull-out testing six weeks after surgery in four rats in the tendon suture group. Callus formation was observed at the site of repair in the tendon suture group, whereas in the sham group callus formation was minimal. During the pull-out test, the repaired tendon-bone junction did not fail because the musculotendinous junction always disrupted first. In order to understand the factors that influenced callus formation at the site of repair, four further groups were evaluated. The nature of the sutured tendon itself was investigated by analysing healing of a tendon stump after necrosis had been induced with liquid nitrogen in 16 cases. A proximal suture group (n = 16) and a partial tenotomy group (n = 16) were prepared to investigate the effects of biomechanical loading on the site of repair. Finally, a group where the periosteum had been excised at the site of repair (n = 16) was examined to study the role of the periosteum. These four groups showed less callus formation radiologically and histologically than did the tendon suture group. In conclusion, the sutured tendon-bone junction healed and achieved mechanical strength at six weeks after suturing, showing good local callus formation. The viability of the tendon stump, mechanical loading and intact periosteum were all found to be important factors for better callus formation at a repaired tendon-bone junction

The effects of extracorporeal shock waves (ESWT) on tendon healing were assessed by observing histological and biomechanical parameters in a rat model of injury to the tendo Achillis. The injury was created by inserting an 18-G needle through tendo Achillis in 48 adult Wistar albino rats. The animals were divided into three groups. The first group received radiation only after the operation. The second received no shock waves and the third had 500 15 KV shocks on the second post-operative day. All the rats were killed on the 21st day after surgery. Histopathological analysis showed an increase in the number of capillaries and less formation of adhesions in the study group compared with the control group (p = 0.03). A significantly greater force was required to rupture the tendon in the study group (p = 0.028). Our findings suggest a basis for clinical trials using ESWT

A computerised image analyser has been used experimentally to determine its possible usefulness in quantifying bone density. Rats were prepared for this purpose and ash weight/volume readings were obtained on femora which had been radiographed and studied to estimate radiographic density by means of the image analyser. The findings indicated that rats can be prepared by administering oestradiol or by allowing an additional week's growth, both of which give a statistically significant increase of bone density. The computerised image analyser was able to detect these differences but the correlations, although real and linear, between ash weight/volume and radiographic density were not large. Further refinements in techniques will be needed before the system is applied clinically

Cancer-induced bone diseases are often associated with increased bone resorption and pathological fractures. In recent years, osteoprotective agents such as bisphosphonates have been studied extensively and have been shown to inhibit cancer-related bone resorption in experimental and clinical studies. The third-generation bisphosphonate, ibandronate (BM 21.0955), is a potent compound for controlling tumour osteolysis and hypercalcaemia in rats bearing Walker 256 carcinosarcoma. We have studied the effect of ibandronate given as an interventional treatment on bone strength and bone loss after the onset of tumour growth in bone. Our results suggest that it is capable of preserving bone quality in rats bearing Walker 256 carcinosarcoma cells. Since other bisphosphonates have produced comparable results in man after their success in the Walker 256 animal models our findings suggest that ibandronate may be a powerful treatment for maintaining skeletal integrity in patients with metastatic bone disease

We immobilised the right hindlimbs of six-month-old female Wistar rats for four weeks using a biplanar external fixation bridging the knee. The untreated left limbs served as a control group. An additional group of rats was allowed to recover for four weeks after removal of the frame. Immobilisation caused reduction in the wet weights of approximately 50% in the gastrocnemius, quadriceps, soleus and plantaris muscles; this was not restored completely after remobilisation. There was an increase in the activity of acid phosphatase of approximately 85% in the gastrocnemius and quadriceps muscles whereas that of creatine phosphokinase was reduced by about 40%. These values returned to nearly normal after remobilisation. Histological and ultrastructural examination showed a marked myopathy of the gastrocnemius muscle after immobilisation although the morphology was largely restored after remobilisation. We conclude that after four weeks of remobilisation, hind-limb muscles do not return to preimmobilisation weights, although biochemical activities and ultrastructural appearance are largely restored

Wear particles commonly used for experiments may carry adherent endotoxin on their surfaces, which may be responsible for the observed effects. In this study, we attached titanium plates to the tibiae of 20 rats. After osseointegration, endotoxin-contaminated or uncontaminated high-density-polyethylene (HDPE) particles were applied. Contaminated specimens showed a dramatic resorption of bone after seven days but new bone filled the site again at 21 days. Uncontaminated specimens showed no resorption. In 18 rats we implanted intramuscularly discs of ultra-high-molecular-weight polyethylene (UHMWPE) with baseline or excess contamination of endotoxin. Excess endotoxin disappeared within 24 hours and the amount of endotoxin remained at baseline level (contamination from production). Uncontaminated titanium discs did not adsorb endotoxin in vivo. The endotoxin was measured by analytical chemistry. Locally-applied endotoxin stimulated bone resorption similarly to that in experiments with wear particles. Endotoxin on the surface of implants and particles appeared to be inactivated in situ. A clean implant surface did not adsorb endotoxin. Our results suggest that endotoxin adhering to orthopaedic implants is not a major cause for concern

Extraskeletal bone formation can be induced in rodents by implantation of demineralised bone matrix and such implantation has been used to treat bone defects in man, but it is uncertain if induction or merely conduction occurs. We studied bone induction in primates by excising segments of the fibulae of adult squirrel monkeys, defatting and demineralising them before reimplanting them into the quadriceps of the same animal. As a control experiment, rat matrix was prepared in exactly the same way and implanted in rats. After six weeks the implants were harvested and either ashed and analysed for calcium content or prepared for histology. In the rats, the calcium content indicated that about 20% of the original matrix had been replaced by new bone. In the monkeys the calcium content was about the same as that in normal body fluid and no bone was seen in histological sections. This result casts doubt on the use of demineralised human bone matrix as a bone inductor, although it may function by other mechanisms

We have compared the density of nerve fibres in the synovium in club foot with that of specimens obtained from the synovium of the hip at operations for developmental dysplasia. The study focused on the sensory neuropeptides substance P; calcitonin gene-related peptide; protein gene product 9.5, a general marker for mature peripheral nerve fibres; and growth associated protein 43, a neuronal marker for new or regenerating nerve fibres. In order to establish whether there might be any inherent difference we analysed the density of calcitonin gene-related peptide-positive nerve fibres in the hip and ankle joints in young rats. Semi-quantitative analysis showed a significant reduction in the number of sensory and mature nerve fibres in the synovium in club foot compared with the control hips. Calcitonin gene-related peptide (CGRP) positive fibres were reduced by 28%, substance P-positive fibres by 36% and protein gene product 9.5-positive fibres by 52% in club foot. The growth associated protein 43-positive fibres also seemed to be less in six samples of club foot. No difference in the density of CGRP-positive nerve fibres was observed in the synovium between ankle and hip joints in rats. The lack of sensory input may be responsible for the fibrosis and soft-tissue contractures associated with idiopathic club foot

We used a rat model in vivo to study the effects of particulate bone cements at the bone-implant interface. A ceramic pin was implanted into the tibiae of 48 rats. Three types of particle of clinically relevant size were produced from one bone-cement base without radio-opacifier, with zirconium dioxide (ZrO. 2. ) and with barium sulphate (BaSO. 4. ). The rats were randomly assigned to four groups to receive one of the three bone cements or normal saline with 2% v/v Sprague-Dawley serum as the control. A total of 10. 9. particles was injected into the knee at 8, 10 and 12 weeks after the original surgery. The animals were killed at 14 weeks and the tibiae processed for histomorphometry. The area of fibrous tissue and the gap between the implant and bone were measured using image analysis. All three types of particle were associated with a larger area of bone resorption than the control. Only in the case of the BaSO. 4. -containing cement did this reach statistical significance (p = 0.01). Particles of bone cement appear to promote osteolysis at the bone-implant interface and this effect is most marked when BaSO. 4. is used as the radiopaque agent

Porous blocks of calcium hydroxyapatite ceramic were evaluated as delivery systems for the sustained release of antibiotics. We tested gentamicin sulphate, cefoperazone sodium, and flomoxef sodium in powder form placed in a cylindrical cavity in calcium hydroxyapatite blocks, using in vitro studies of elution and in vivo studies in rats. Gentamicin sulphate gave a maximum concentration within the first week, which gradually decreased but was still effective at 12 weeks, when 70% of the antibiotic had been released. Even at this stage the antibiotic concentration from a 75 mg dose was five times the minimum inhibitory concentration for staphylococci. In the in vivo studies the release of gentamicin sulphate into the normal bone of rats was at similar rates and levels. The bacteriocidal activity of the drugs was not affected by packing into calcium hydroxyapatite ceramic and the blocks were completely biocompatible on histology. This new system overcomes the disadvantages of other drug delivery systems, avoiding thermal damage to the antibiotics and a second operation for the removal of the carrier. Some mechanical strength is provided by the ceramic and healing may be accelerated by bone ingrowth into its micropores

Ceramics have many properties which might make them suitable alternatives to bone grafts. This present study was done to find a suitable biodegradable porous ceramic for human bone replacement. Three different porous ceramics (calcium aluminate, calcium hydroxyapatite and tricalcium phosphate), with interlinked pores of two size ranges (150 to 210 micron), were implanted into the skulls of rats and rabbits for up to six months; the interaction with surrounding bone, which is virtually devoid of bone marrow, was then assessed. The ceramics caused no adverse biological response. Tissue ingrowth into pores throughout the implant was seen in all three types and in both pore sizes of ceramic, but the density of the penetrating tissue was far less for calcium aluminate than for calcium hydroxyapatite or tricalcium phosphate. For each type of ceramic, the soft-tissue ingrowth was more dense with the larger pore size, and with a longer period of implantation. Bone ingrowth was not usually seen within the pores of any ceramic. There were no differences in the histological findings between the rats and the rabbits. The results demonstrate that it is possible to produce ceramic materials with a porous structure which allows ingrowth of tissue and biological fluids

1. Isografts of articular cartilage of young rats, with mucoproteins labelled with . 35. S, extracellular fibrous proteins labelled with . 3. H-glycine, and nuclei labelled with . 3. H-thymidine, were transplanted into the anterior chamber of the eye. 2. Thin split-thickness transplants of the cells of the gliding surface of immature articular cartilage induced the formation of fibrous tissue. 3. Thick transplants and subsurface slices of immature articular cartilage, containing germinal cells of the epiphysial cartilage, induced the formation of new bone consistently within 4 weeks. 4. Full-thickness transplants in articular cartilage from senile rats induced only the formation of fibrous tissue. 5. Slices of growing cartilage, devitalised by cryolysis, or extraction of acid-soluble proteins, produced scanty deposits of bone or cartilage, or both, but only infrequently and generally after a lag phase extending from six to twelve weeks. 6. Reduction in the amount of mucoprotein in the cartilage matrix by papain, and suppression of the resynthesis of tissue proteins by cortisone, retarded but did not prevent bone induction. 7. Bone induction is the product of a series of interactions between inducing cells and responding cells by intracellular and intercellular reactions too complex to characterise in physico-chemical terms at this time

Our aim was to investigate whether nitric oxide synthase (NOS) isoforms, responsible for the generation of NO, are expressed during the healing of fractures. To localise the sites of expression compared with those in normal bone we made standardised, stabilised, unilateral tibial fractures in male Wistar rats. Immunostaining was used to determine the precise tissue localisation of the different NOS isoforms. Western blotting was used to assess expression of NOS isoform protein and L-citrulline assays for studies on NOS activity. Control tissue was obtained from both the contralateral uninjured limb and limbs of normal rats. Immunohistochemistry showed increased expression of endothelial NOS (eNOS) to be strongest in the cortical blood vessels and in osteocytes in the early phase of fracture repair. Western blot and image analysis confirmed this initial increase. Significantly elevated calcium-dependent NOS activity was observed at day 1 after fracture. Inducible NOS (iNOS) was localised principally in endosteal osteoblasts and was also seen in chondroblasts especially in the second week of fracture healing. Western blotting showed a reduction in iNOS during the early healing period. Significantly reduced calcium-independent NOS activity was also seen. No neuronal NOS was seen in either fracture or normal tissue. Increased eNOS in bone blood vessels is likely to mediate the increased blood flow recognised during fracture healing. eNOS expression in osteocytes may occur in response to changes in either mechanical or local fluid shear stress. The finding that eNOS is increased and iNOS reduced in early healing of fractures may be important in their successful repair

Extracorporeal shock-wave (ESW) treatment hasbeen shown to be effective in promoting the healing of fractures. We aimed to determine whether ESW could enhance the growth of bone-marrow osteoprogenitor cells. We applied ESW to the left femur of rats 10 mm above the knee at 0.16 mJ/mm. 2. in a range of between 250 and 2000 impulses. Bone-marrow cells were harvested after ESW for one day and subjected to assessment of colony-forming unit (CFU) granulocytes, monocytes, erythocytes, megakaryocytes (CFU-Mix), CFU-stromal cells (CFU-S) and CFU-osteoprogenitors (CFU-O). We found that the mean value for the CFU-O colonies after treatment with 500 impulses of ESW was 168.2 CFU-O/well (. sem. 11.3) compared with 88.2 CFU-O/well (. sem. 7.2) in the control group. By contrast, ESW treatment did not affect haematopoiesis as shown by the CFU-Mix (p = 0.557). Treatment with 250 and 500 impulses promoted CFU-O, but not CFU-Mix formations whereas treatment with more than 750 impulses had an inhibiting effect. Treatment with 500 impulses also enhanced the activity of bone alkaline phosphatase in the subculture of CFU-O (p< 0.01), indicating a selective promotion of growth of osteoprogenitor cells. Similarly, formation of bone nodules in the long-term culture of bone-marrow osteoprogenitor cells was also significantly enhanced by ESW treatment with 500 impulses. The mean production of TGF-β1 was 610 pg/ml (. sem. 84.6) in culture supernatants from ESW-treated rats compared with 283 pg/ml (. sem. 36.8) in the control group. Our findings suggest that optimal treatment with ESW could enhance rat bone-marrow stromal growth and differentiation towards osteoprogenitors presumably by induction of TGF-β1

In a rabbit model we investigated the efficacy of a silk fibroin/hydroxyapatite (SF/HA) composite on the repair of a segmental bone defect. Four types of porous SF/HA composites (SF/HA-1, SF/HA-2, SF/HA-3, SF/HA-4) with different material ratios, pore sizes, porosity and additives were implanted subcutaneously into Sprague-Dawley rats to observe biodegradation. SF/HA-3, which had characteristics more suitable for a bone substitite based on strength and resorption was selected as a scaffold and co-cultured with rabbit bone-marrow stromal cells (BMSCs). A segmental bone defect was created in the rabbit radius. The animals were randomised into group 1 (SF/HA-3 combined with BMSCs implanted into the bone defect), group 2 (SF/HA implanted alone) and group 3 (nothing implanted). They were killed at four, eight and 12 weeks for visual, radiological and histological study. The bone defects had complete union for group 1 and partial union in group 2, 12 weeks after operation. There was no formation of new bone in group 3. We conclude that SF/HA-3 combined with BMSCs supports bone healing and offers potential as a bone-graft substitute

1. Experiments to examine the antigenicity of homologous bone tissues in rats are reported. The tissues studied included fresh marrow-free cortical bone blocks and chips, fresh, boiled, frozen and freeze-dried marrow-containing iliac bone, fresh iliac bone devoid of marrow, and fresh red marrow. 2. The various tissues were transplanted from hooded to Wistar rats. Three weeks later a skin graft from each donor was transplanted to its respective host to detect the presence of transplantation immunity, which was indicated by the early rejection of the skin graft. 3. Homografts of fresh cortical bone evoked transplantation immunity indicating that it contained transplantation antigens which were also in the skin. 4. Homografts of fresh marrow-containing iliac bone also evoked transplantation immunity, which was shown to be caused by the red marrow. 5. Fresh iliac homografts devoid of marrow did not elicit transplantation immunity. This suggests that iliac bone tissue may not contain transplantation antigens or that the small amount of iliac bone inserted was insufficient. 6. Microscopy of the grafts, removed after three weeks, showed that the inflammatory infiltrations around the bone homografts and autografts were not very different, but that the amount of new bone formed was different. The autografts produced a lot of new bone, the homografts only a little. 7. It is suggested that the immune response evoked in the host by the foreign graft impairs the formation of new bone by fresh homografts of cortical blocks, cortical chips and marrow-containing iliac bone. 8. The impairment of new bone formation by homografts of marrow-free iliac bone is discussed. Such bone grafts fail to evoke detectable transplantation immunity. Why these grafts do not form more new homologous bone than the other homografts studied, is not clear. 9. Homografts of boiled and frozen iliac bone do not evoke any detectable change in the sensitivity of the host to donor tissue. 10. Homografts of freeze-dried marrow-containing iliac bone elicit a slight but significant prolongation of the survival of skin homografts. The implication, in terms of modern immunological theory, is that in such grafts certain tissue antigens still persist

When large daily doses of vitamin D were administered to rats endochondral growth was inhibited and bone resorption occurred; later in the process uncalcified matrix (osteoid) like that seen in rickets formed on trabecular margins. When vitamin D was given only for a short period and then discontinued, little resorption of bone was seen during the withdrawal period and wide seams of osteoid material appeared which eventually calcified in an irregular manner. When normal endochondral growth was resumed a wide transverse band of dense bone with enclosed cartilaginous cores was left in the marrow cavity. If, after a few days, a second large dose of the vitamin was given resorption again occurred and calcification of osteoid material was accelerated, the first microscopic sign being a dense, wide, granular, deeply staining line at the junction of the bone and new osteoid. After a second withdrawal period a second layer of osteoid formed; eventually another transverse band appeared in the metaphysis. If this hypervitaminosis D cycle (+4 -12) was continued rats continued to form new bone with relatively little remodelling, so that after three such cycles bones became dense and hard. Histological study showed that little marrow cavity remained in either skull, vertebrae or epiphyses and a dense mass of bone enclosing cartilage cores filled the metaphysial part of the long bones. In addition, ankylosis ofteeth, calcification of spinal ligaments and widespread metastatic calcification were present. When hypervitaminosis D cycles (+1 -12, +1 -21) were adjusted to produce minimal resorptive changes a wide range of bone change was observed. This varied from uniform dense metaphysial bone containing abnormal cartilage matrix arranged in longitudinal striations, dense transverse bands parallel to the epiphysial cartilage, to remnants of dense trabeculae extending into the marrow cavity. Bone changes in osteopetrosis structurally closely resembled the induced bone changes in the rat. It is concluded that an important mechanism in the production of osteopetrosis is an accentuated rhythm of bone change like that shown experimentally to be produced in these animals. It is emphasised that these changes are but part of a range of bone disorders associated with abnormalities of cycles of resorption and deposition of bone, the type of change differing with the nature of the cycles

Antibiotic resistance represents a threat to human health. It has been suggested that by 2050, antibiotic-resistant infections could cause ten million deaths each year. In orthopaedics, many patients undergoing surgery suffer from complications resulting from implant-associated infection. In these circumstances secondary surgery is usually required and chronic and/or relapsing disease may ensue. The development of effective treatments for antibiotic-resistant infections is needed. Recent evidence shows that bacteriophage (phages; viruses that infect bacteria) therapy may represent a viable and successful solution. In this review, a brief description of bone and joint infection and the nature of bacteriophages is presented, as well as a summary of our current knowledge on the use of bacteriophages in the treatment of bacterial infections. We present contemporary published in vitro and in vivo data as well as data from clinical trials, as they relate to bone and joint infections. We discuss the potential use of bacteriophage therapy in orthopaedic infections. This area of research is beginning to reveal successful results, but mostly in nonorthopaedic fields. We believe that bacteriophage therapy has potential therapeutic value for implant-associated infections in orthopaedics.

Cite this article: Bone Joint J 2021;103-B(2):234–244.

The efficacy of locally implanted antibiotic-calcium hydroxyapatite ceramic composites was investigated for the treatment of experimentally produced, implant-related osteomyelitis in rats. High concentrations of antibiotics were detected at the site of infection and bacteria were eradicated without removal of the metal implants. Parenteral antibiotics and surgical debridement, alone or in combination with antibiotic-impregnated acrylic bone cement, all failed to eradicate the infections

1. Reports of the lipaemia-clearing effect of heparin suggested that this drug might be of therapeutic value in fat embolism. 2. In an experimental trial with rats, heparin was found both to accelerate death and to increase the number of deaths after fat embolism. 3. It is accordingly concluded that a clinical trial of heparin in human fat embolism would not be warranted

1. The effects of frozen irradiated homogenous bone grafts on the healing of circumscribed defects in the mandibles and femora of forty albino rats have been studied. 2. The grafts were well tolerated by the host animals and did not appear in any way either to stimulate or to inhibit osteogenesis. The rate of healing of the defects containing the homografts compared favourably with that of the control defects

This paper describes a procedure of activating osteogenesis by the use of the "petal" technique. The osteogenetic effect of these "petals" has been established in experimentally produced fractures and pseudarthroses in rats by radiographical, biomechanical, mechanical and histological examinations. The conventional concept of the osteogenetic activity of bone transplants is discussed. The authors feel that this method will find its clinical application in the operative treatment of pseudarthroses and, in selected cases, of fractures that are known for their tendency to unite slowly

1 . The repair of a simple crush injury was studied in rats, in both normally innervated and completely denervated muscle. In each case the histological findings at periods from two hours to thirty-two weeks are described. 2. The denervated muscle showed active and effective repair. 3. A comparison with the findings in normally innervated muscle establishes that the cellular processes of repair do not depend on connections with the central nervous system

1. Experimental fracture callus in rats contains mast cells as a normal morphological element. 2. The mast cell count undergoes peculiar variations in the normal course of events in experimentally delayed or accelerated bone repair. 3. A hypothesis is presented in which the tissue mast cell granules are regarded as calcium transporters in the mineral phase of callus formation, a process probably corresponding to Selye's concept of "mastocalciphylaxis" and "mastocalcergy."

The tissue surrounding carbon fibre reinforced epoxy resin plates applied to forearm and tibial fractures was biopsied in 32 patients at the time the plates were removed. The reaction was minimal and was compared with that in a control group of 16 similar patients in whom stainless steel plates were used. No significant histological differences were found. A series of experiments on rats, in which the histology was studied from 2 to 78 weeks, also showed that there was very little reaction to carbon fibre reinforced plastic

We studied the calcium content and mechanical strength of cortical bone from rats and dogs after different periods of demineralisation, showing that the rate of demineralisation differed considerably between the species. Specimens from the rat were further treated by chemical extraction and autolysis and tested for osteoinductive properties. We showed that partially demineralised cortical bone retained adequate mechanical strength, while retaining the biological effects of completely demineralised bone. This shows that it is possible to prepare allografts which have adequate mechanical strength and still retain osteo-inductive properties

We have compared the rates of infection and resistance in an animal model of an orthopaedic procedure which was contaminated with a low-dose inoculum of Staphylococcus epidermidis. We randomised 44 Sprague-Dawley rats to have bone cement implanted subcutaneously containing either gentamicin or saline (control). The wound was inoculated with a dilute solution of gentamicin-sensitive Staphylococcus epidermidis. At two weeks the cement was retrieved and microbiologically tested. A lower overall rate of infection was seen in the gentamicin-loaded cement group, but there was a significantly higher rate of gentamicin-resistant infection in this group (Fisher’s exact test, p < 0.01). Antibiotic-impregnated cement has an optimum surface for colonisation and prolonged exposure to antibiotic allows mutational resistance to occur. Gentamicin-loaded cement may not be appropriate for revision surgery if it has been used already in previous surgery

Synthetic bone substitutes provide an alternative to autograft but do not give equivalent clinical results. Their performance may be enhanced by adding osteogenic growth factors. In this study, TGFβ1 was absorbed on to a carrier of β tricalcium phosphate and Gelfoam® and used to fill a defect around a tibial implant in a rat model of revision arthoplasty. We added 0.0, 0.02 μg, 0.1 μg or 1.0 μg of TGFβ1 to the carrier and then implanted it around an hydroxyapatite-coated stainless-steel pin in the proximal tibia of rats. The tibiae were harvested at three, six or 26 weeks and the amount of bone formation and ceramic resorption were assessed. TGFβ1 had no effect on the amount of bone in the defect, the amount of fluorescent label incorporated or the rate of mineral apposition. The growth factor did not significantly affect the amount of β TCP remaining in the tissue at any of the time points

Dorsal root ganglion neurones with dichotomising axons are present in several species and are considered to play a role in referred pain. Clinically, patients with lesions in the lower lumbar discs occasionally complain of pain in the groin. We investigated the existence of dichotomising afferent neurones projecting axons both to the lumbar disc and to the groin skin, using the double fluorescent-labelling technique in rats. We observed neurones labelled with a tracer applied at the ventral portion of the L5-L6 disc and another tracer placed on the groin skin in L1 and L2 dorsal root ganglia. Our results showed that the double-labelled neurones had peripheral axons which dichotomised into both the L5-L6 disc and the groin skin, indicating the convergence of afferent sensory information from the disc and groin skin. Our findings provide a possible neuroanatomical mechanism for referred groin pain in patients with disc lesions

1. The influence of various methods of preserving bone on the calcifying mechanism of the tibial epiphysial cartilage of rachitic rats was studied. An in vitro calcification technique was employed. 2. Preservation by deep freezing, aqueous merthiolate, boiling, or acetone inactivated the calcifying mechanism. 3. The inactivation was reversed with calcium ions, most readily in the deep-frozen bones, less readily in the merthiolate treated bones, still less readily in the acetone stored bones, and least in boiled bones. 4. Exposure to calcium ions before preservation in the deep-freeze chest prevented inactivation. 5. The inactivation, reactivation and survival of the calcifying mechanism were confirmed by metachromasia studies. 6. The theory of the mode of action of calcium chloride on reactivation and survival of the calcifying mechanism is presented

1. A study has been made of the repair of bony defects in the calvaria of albino rats. 2. An accelerated rate of bone repair was observed in experimental defects into which chondroitin sulphate-treated demineralised bone was implanted. 3. Acid-soluble collagen reconstituted with chondroitin sulphate was also more effective as an implant than was acid-soluble collagen reconstituted with sodium chloride. 4. It is concluded from these studies that chondroitin sulphate treatment accelerated the rate of new bone formation induced by demineralised bone, by reconstituted acid-soluble collagen, and to a lesser extent by Gelfoam. It was also found that demineralised bone and fresh homogenous bone promoted bone repair, but that chondroitin sulphate-treated demineralised bone promoted the most rapid rate of bone repair among the substances tested. 5. The possible role of chondroitin sulphate in bone formation is discussed

Using in situ hybridisation and the terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end-labelling (TUNEL) reaction in rats with osteonecrosis of the femoral head we have studied the effect of ischaemia on the gene expression of the stress proteins oxygen-regulated protein 150 (ORP150) and haemoxygenase 1 (HO1) and the death mechanism of the cells involved in osteonecrosis. Both ORP150 and HO1 have been reported to have important roles in the successful adaptation to oxygen deprivation. ORP150 and HO1 mRNA expression was induced by ischaemia in osteoblasts and osteocytes. In proliferative chondrocytes, these signals were detected constitutively. During the development of ischaemic osteonecrosis, the mechanism of cell death was apoptosis as indicated by DNA fragmentation and the presence of apoptotic bodies in osteocytes, chondrocytes and bone-marrow cells. After the initial ischaemic event, expression of ORP150 and HO1 mRNA, the TUNEL-positive reaction and empty lacunae were found sequentially. These findings were exclusive and may be considered to be markers for each stage in the development of osteonecrosis

In ten male rats we inserted ceramic ‘drawing-pin’ implants in weight-bearing positions within the right proximal tibia. Two animals were killed 6 weeks after surgery and two more 14 weeks after surgery. The remaining six received intra-articular injections of either high-density polyethylene (4 rats) or saline (2 rats) at 8, 10 and 12 weeks after surgery. These animals were killed two weeks after the last injection. Histological examination of the bone-implant interface in the control animals showed appositional bone growth around the implant at both 6 and 14 weeks. Polyethylene, but not saline, caused a chronic inflammatory response with numerous foreign-body giant cells in periprosthetic tissues. Our model of a stable, weight-bearing bone-implant interface provides a simple and reliable system in which to study in vivo the effects of particulate materials used in orthopaedic surgery

We implanted nails made of titanium (Ti6Al4V) and of two types of glass ceramic material (RKKP and AP40) into healthy and osteopenic rats. After two months, a histomorphometric analysis was performed and the affinity index calculated. In addition, osteoblasts from normal and osteopenic bone were cultured and the biomaterials were evaluated in vitro. In normal bone the rate of osseointegration was similar for all materials tested (p > 0.5) while in osteopenic bone AP40 did not osseointegrate (p > 0.0005). In vitro, no differences were observed for all biomaterials when cultured in normal bone-derived cells whereas in osteopenic-bone-derived cells there was a significant difference in some of the tested parameters when using AP40. Our findings suggest that osteopenic models may be used in vivo in the preclinical evaluation of orthopaedic biomaterials. We suggest that primary cell cultures from pathological models could be used as an experimental model in vitro

In 65 mature Wistar rats a Kirschner wire was introduced into the medullary cavity of each femur. A closed transverse mid-shaft fracture of one femur was produced by a three-point bending technique. Subsequently the mechanical characteristics of the healing fracture, including the torque and angle of twist required to take the callus to its yield point and to ultimate failure, were compared with those for the opposite femur of each rat. Controls were killed in groups at two, three, four, five and seven weeks. Test animals were given bovine growth hormone in a daily dose of five milligrams before being killed in groups at two, three and four weeks. A significant increase in torque index was found in the two-week group of test animals but not in subsequent groups. No evidence was found that growth hormone given alone could produce an overall shortening of the healing time in fresh fractures

1. The humoral immune response of rats against sheep iliac bone grafts has been examined. 2. Fresh, marrow-containing grafts elicited a brisk and sustained antibody response. Attempts to wash out the marrow were not uniformly successful in removing cellular antigens from the grafts. 3. Decalcifying and freezing bone grafts at —20 degrees Celsius do not impair immunogenicity to any significant extent. Immunogenicity was found to be reduced in grafts subjected to freeze-drying. 4. Deproteinised Oswestry bone grafts and Kiel grafts gave rise to antibody production in a few recipients, and in the case of the former this response did not occur until after six or seven weeks from grafting. 5. The highest degree of osteogenesis in composite bone xenograft-autografts was found by Salama and colleagues (1973) to occur in Oswestry bone grafts. It is suggested that osteogenesis in xenografts may be impaired by an immune response

It has been thought that lumbar intervertebral discs were innervated segmentally. We have previously shown that the L5-L6 intervertebral disc in the rat is innervated bilaterally from the L1 and L2 dorsal root ganglia through the paravertebral sympathetic trunks, but the pathways between the disc and the paravertebral sympathetic trunks were unknown. We have now studied the spines of 17 rats to elucidate the exact pathways. We examined serial sections of the lumbar spine using immunohistochemistry for calcitonin gene-related peptide, a sensory nerve marker. We showed that these nerve fibres from the intervertebral disc ran through the sinuvertebral nerve into the rami communicantes, not into the corresponding segmental spinal nerve. In the rat, sensory information from the lumbar intervertebral discs is conducted through rami communicantes. If this innervation pattern applies to man, simple decompression of the corresponding nerve root will not relieve discogenic pain. Anterior interbody fusion, with the denervation of rami communicantes, may be effective for such low back pain

We investigated the possible use of acrylic cement containing chemotherapeutic drugs in the treatment of malignant lesions in bone. The diffusion of methotrexate (MTX) from methylpolymethacrylate implants was studied in vitro: polymerisation of the cement did not destroy the drug; liberation began immediately and about 10% was released by 18 hours. Some release continued for as long as six months. In vivo experiments on rats with induced osteosarcoma showed that MTX in cement had both local and general effects which were dependent on the dosage. A series of 17 large dogs with spontaneous osteosarcoma were then treated by local resection and cement containing MTX. General chemotherapeutic effects were detectable from 2 hours to 5 days, survival was increased and local recurrence was reduced, but there were four cases of delayed wound healing. Preliminary studies in human patients confirm the possibility that this method of local chemotherapy could be a useful addition to the treatment of malignant tumours of bone

The release of various penicillins and other antibiotics from two brands of polymerised bone cement has been studied in vitro and in vivo in mice. Bone cement plugs containing antibiotics demonstrated antibacterial activity as a result of diffusion of antibiotic from the plugs into the surrounding medium. With all antibiotics tested, from 2-5 to 10 per cent of the antibiotic in the cement was released in vitro in active form within twenty-four hours. Most of the activity appeared within three hours of the start of the test, but in some cases low levels of activity were detected after four days. Antibiotic cement plugs implanted in mice and rats produced low concentrations of antibiotic in the blood up to two hours after implantation, but activity was seldom detected subsequently. In general, penicillins and non-penicillin antibiotics showed similar diffusion characteristics, and the pattern of release in vitro and in vivo was consistent with the leaching of antibiotic from, or near, the surface of the bone cement

1. Experimental defects in the cranial vaults of young adult rabbits were implanted with decalcified, deproteinised and deep frozen homogenous whole bone. The experiments were similar to those of Ray and Holloway (1957) except that these workers used rats as the experimental animals. In addition, six control defects were made and not implanted. 2. All animals were killed six weeks after operation and thirty-four defects were studied by radiology and by histology. 3. All implants became surrounded by connective tissue and in all cases some new bone formed in apposition to implanted fragments. The degree of incorporation of the implants in new bone varied widely, not only between the three implanted groups, but also within each group. In general, new bone formation was greatest in defects implanted with deproteinised and whole bone, least in defects implanted with decalcified bone. 4. The fate of bone implants and the extent to which they can be said to induce osteogenesis are discussed

Ischaemia-reperfusion injury (IRI) is caused by endothelial and subendothelial damage by neutrophil-derived oxidants. Vitamin C is an antioxidant which attenuates endothelial injury after IRI. Our aim was to evaluate the effect of oral vitamin C in the prevention of IRI in skeletal muscle. We used a model of cross-clamping (3 hours) and reperfusion (1 hour) of the cremaster muscle in rats. Muscle function was assessed electrophysiologically by electrical field stimulation. Infiltration by neutrophils was determined by the activity of tissue myeloperoxidase (MPO) and tissue oedema by the wet-to-dry ratio. Neutrophil respiratory burst activity was measured in control animals and groups pretreated with vitamin C. IRI significantly decreased muscle function and increased muscle neutrophil MPO activity and muscle oedema. Pretreatment with vitamin C preserved muscle function and reduced tissue oedema and neutrophil infiltration. Neutrophil respiratory burst activity was reduced in the group treated with vitamin C compared with the control group. We conclude that pretreatment with oral vitamin C protects against acute muscle IRI, possibly by attenuating neutrophil respiratory burst activity

Coating titanium alloy implants with titanium nitride (TiN) by the method of Powder Immersion Reaction Assisted Coating (PIRAC) produces a stable layer on their surface. We have examined the ability of the new TiN coating to undergo osseointegration. We implanted TiN-coated and uncoated Ti6Al4V alloy pins into the femora of six-month-old female Wistar rats. SEM after two months showed a bone collar around both TiN-coated and uncoated implants. Morphometrical analysis revealed no significant differences between the percentage of the implant-bone contact and the area and volume of the bone around TiN-coated compared with uncoated implants. Electron-probe microanalysis indicated the presence of calcium and phosphorus at the implant-bone interface. Mineralisation around the implants was also confirmed by labelling with oxytetracycline. Strong activity of alkaline phosphatase and weak activity of tartrate-resistant acid phosphatase were shown histochemically. Very few macrophages were detected by the non-specific esterase reaction at the site of implantation. Our findings indicate good biocompatibility and bone-bonding properties of the new PIRAC TiN coatings which are comparable to those of uncoated Ti6Al4V alloy implants

The present investigation has shown that crude papain can be used to produce rapid changes in the epiphysial cartilage of various young laboratory animals (rabbits, mice, rats, guinea pigs and cats). 1. Single injections of crude papain produce profound changes in the epiphysial cartilage. These changes disappear within a few days. They are radiographically visible as a narrowing of the epiphysial plates. Histologically, the formation of bony trabeculae in the primary spongiosa is found to be arrested. 2. Repeated injections of crude papain cause permanent damage to the epiphysial cartilage, often with bony closure. Consequently, the longitudinal growth of the injected animals, when compared to the controls, is found to be retarded or permanently arrested, and there may be severe bony deformity. 3. Using inactivated crystalline papain, we have been able to produce changes in the epiphysial cartilage identical with those caused by the injection of crude papain. 4. The injection of crude papain is dispelled by the addition of cysteine, but retains its full strength if hydrogen peroxide is added