To investigate the effect of instability on the remodelling of a minor articular surface offset, we created a 0.5 mm coronal step-off of the medial femoral condyle in 12 New Zealand white rabbits and transected the anterior cruciate ligament (ACL). A control group of 12 rabbits had only ACL resection and the opposite knee was used as the non-operated control. The osteoarthritic changes at 6, 12 and 24 weeks after surgery were evaluated histologically. In addition, changes in the immunological detection of 3-B-3(-) and 7-D-4 chondroitin-6-sulphate epitopes were determined because of the previous association of such changes with repair of cartilage and early osteoarthritis.

In the instability/step-off group there was rapidly progressing focal degeneration of cartilage on the high side of the defect, not seen in previous step-off studies in stable knees. The rest of the femoral condyles and the tibial plateaux of the instability/step-off group had moderate osteoarthritis similar to that of the instability group. 3-B-3(-) was detectable in the early and the intermediate stages of osteoarthritis but no staining was seen in the severely damaged cartilage zones. Immunoreactivity with 7-D-4 increased as degeneration progressed.

Our findings have shown that even a minor surface offset may induce rapid degeneration of cartilage when the stability of the knee is compromised.

The intermittent administration of parathyroid hormone (PTH) increases the formation of bone by stimulating osteoblastic activity. Our study evaluates the possibility that intermittent treatment with PTH (1-34) may also enhance the implant-bone fixation of stainless-steel screws. Twenty-eight rats received one screw in either one (n = 8) or in both (n = 20) proximal tibiae. We administered either PTH (1-34) in a dosage of 60 μg/kg/day (n = 14) or vehicle (n = 14) over a period of four weeks. At the end of this time, the degree of fixation was assessed by measuring the removal torque on one screw in each rat (n = 28) and the pull-out strength on the contralateral screw (n = 20). PTH increased the mean removal torque from 1.1 to 3.5 Ncm (p = 0.001) and the mean pull-out strength from 66 to 145 N (p = 0.002). No significant differences in body-weight or ash weight of the femora were seen. Histological examination showed that both groups had areas of soft tissue at the implant-bone interface, but these appeared less in the PTH group. These results indicate that intermittent treatment with PTH may enhance the early fixation of orthopaedic implants.

We have studied the beneficial effects of a hydroxyapatite (HA) coating on the prevention of the migration of wear debris along the implant-bone interface. We implanted a loaded HA-coated implant and a non-coated grit-blasted titanium alloy (Ti) implant in each distal femoral condyle of eight Labrador dogs. The test implant was surrounded by a gap communicating with the joint space and allowing access of joint fluid to the implant-bone interface. We injected polyethylene (PE) particles into the right knee three weeks after surgery and repeated this weekly for the following five weeks. The left knee received sham injections. The animals were killed eight weeks after surgery. Specimens from the implant-bone interface were examined under plain and polarised light.

Only a few particles were found around HA-coated implants, but around Ti implants there was a large amount of particles. HA-coated implants had approximately 35% bone ingrowth, whereas Ti implants had virtually no bone ingrowth and were surrounded by a fibrous membrane.

Our findings suggest that HA coating of implants is able to inhibit peri-implant migration of PE particles by creating a seal of tightly-bonded bone on the surface of the implant.

Treatment with corticosteroids is a risk factor for non-traumatic avascular necrosis of the femoral head, but the pathological mechanism is poorly understood. Short-term treatment with high doses of methylprednisolone is used in severe neurotrauma and after kidney and heart transplantation. We investigated the effect of such treatment on the pattern of perfusion of the femoral head and of bone in general in the pig.

We allocated 15 immature pigs to treatment with high-dose methylprednisolone (20 mg/kg per day intramuscularly for three days, followed by 10 mg/kg intramuscularly for a further 11 days) and 15 to a control group. Perfusion of the systematically subdivided femoral head, proximal femur, acetabulum, humerus, and soft tissues was determined by the microsphere technique. Blood flow in bone was severely reduced in the steroid-treated group. The reduction of flow affected all the segments and the entire epiphysis of the femoral head. No changes in flow were found in non-osseous tissue. Short-term treatment with high-dose methylprednisolone causes reduction of osseous blood flow which may be the pathogenetic factor in the early stage of steroid-induced osteonecrosis.

We have investigated whether the particle-stimulated release of inflammatory cytokines from human primary macrophages in vitro was dependent upon the type of bone cement used. Particles of clinically relevant size were produced from Palacos R without radio-opacifier, Palacos R with BaSO₄, Palacos R with ZrO₂ and from CMW3 which contains BaSO₄. All four preparations produced significantly greater release of tumour necrosis factor alpha, interleukin-6 and interleukin-1 beta than a negative control but there were no significant differences between them. The differences in the ability to stimulate bone resorption and in clinical performance between proprietary bone cements previously recorded are not explained by the release of the cytokines most commonly implicated in osteolysis.

Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured.

After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem.

Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain.

We aimed to evaluate the precision and longitudinal sensitivity of measurement of bone mineral density (BMD) in the pelvis and to determine the effect of bone cement on the measurement of BMD in femoral regions of interest (ROI) after total hip arthroplasty (THA).

A series of 29 patients had duplicate dual-energy x-ray absorptiometry (DXA) scans of the hip within 13 months of THA. Pelvic analyses using 3- and 4-ROI models gave a coefficient of variation (CV) of 2.5% to 3.6% and of 2.5% to 4.8%, respectively. Repeat scans in 17 subjects one year later showed a significant change in BMD in three regions using the 4-ROI model, compared with change in only one region with the 3-ROI model (p < 0.05).

Manual exclusion of cement from femoral ROIs increased the net CV from 1.6% to 3.6% (p = 0.001), and decreased the measured BMD by 20% (t = 12.1, p < 0.001). Studies of two cement phantoms in vitro showed a small downward drift in bone cement BMD giving a measurement error of less than 0.03 g/cm²/year associated with inclusion of cement in femoral ROIs.

Changes in pelvic periprosthetic BMD are best detected using a 4-ROI model. Analysis of femoral ROI is more precise without exclusion of cement although an awareness of its effect on the measurement of the BMD is needed.

In 16 mature New Zealand white rabbits mesenchymal stem cells were aspirated from the bone marrow, cultured in monolayer and implanted on to a full-thickness osteochondral defect artificially made on the patellar groove of the same rabbit. A further 13 rabbits served as a control group. The rabbits were killed after 14 weeks. Healing of the defect was investigated histologically using haematoxylin and eosin and Safranin-O staining and with immunohistochemical staining for type-II collagen. We also used a reverse transcription-polymerase chain reaction (RT-PCR) to detect mRNA of type-I and type-II collagen.

The semiquantitative histological scores were significantly higher in the experimental group than in the control group (p < 0.05). In the experimental group immunohistochemical staining on newly formed cartilage was more intense for type-II collagen in the matrix and RT-PCR from regenerated cartilage detected mRNA for type-II collagen in mature chondrocytes. These findings suggest that repair of cartilage defects can be enhanced by the implantation of cultured mesenchymal stem cells.

Since bone morphogenetic proteins (BMPs) are highly homologous, we investigated the hypothesis that recombinant BMP-4 of the genome of Xenopus laevis (rxBMP-4) may influence the proliferation or differentiation of human primary osteoblast-like cells (HPOC), as occurs with recombinant human BMP (rhBMP-2).

HPOC were incubated in the presence of either rxBMP-4, rhBMP-2 or basic fibroblast growth factor (rh-bFGF). The last two were used as positive controls and are known to induce differentiation or proliferation of HPOC, respectively.

rxBMP-4 (50 ng/ml and 100 ng/ml) induced a differentiation of HPOC to almost the same extent as rhBMP-2, whereas the addition of rh-bFGF, applied in the same concentration, failed to have any influence on cell differentiation. rh-bFGF however, provoked an increase in cell proliferation of up to 150% when compared with non-stimulated HPOC, while rhBMP-2 and rxBMP-4 had no such effect.

Our results indicate an equipotent effect of rhBMP-2 and rxBMP-4 obtained from Xenopus laevis on the differentiation and proliferation of human primary osteoblast-like cells.

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.

We investigated the effect of vitamin D receptor gene (VDRG) polymorphism on the responsiveness to 1,25(OH)₂D₃ in human osteoblast-like cells. The cells were obtained from the femoral heads of 18 women with osteoarthritis of the hip. Three different restriction enzymes, BsmI, ApaI, and TaqI, were used to analyse the polymorphism. The genotypes of the 18 patients were bbAaTT (8), bbaaTT (6), BbAaTt (3), and BbAATt (1).

Our findings showed that there were no differences according to the VDR genotype, but there was a statistically significant difference in the production of osteocalcin between BbAaTt and bbAaTT, and between BbAaTt and bbaaTT. Northern blot analysis of osteocalcin and VDR mRNA showed no significant differences among the three VDR genotypes. These findings suggest that VDR gene polymorphism affects the individual responsiveness of 1,25(OH)₂D₃.

We used laser Doppler flowmetry (LDF) to measure flux in cortical bone fragments as a method of determining their vascular status and viability. In an experimental tibial osteotomy measurements of flux were made from specific cortical sites both before and after osteotomy. Flux levels fell rapidly in non-vascularised fragments and remained significantly reduced throughout the experiment. By contrast, those in vascularised fragments were significantly reduced one and two hours after the osteotomy but then increased. From three hours after the osteotomy there was no significant difference in flux levels between the vascularised fragments and proximal bone stock.

We conclude that measurement of bone flux by LDF may have a role in the objective evaluation of the viability of bone fragments, but that further studies are required to validate the technique before its adoption in the management of the injured patient.

We investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem.

We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified.

There was significantly more ingrowth (p = 0.012) and attachment of bone (p > 0.05) to the porous HA surface (mean bone ingrowth 29.093 ± 2.019%; mean bone attachment 37.287 ± 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 ± 2.068%; mean bone attachment 18.9411 ± 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time.

This study shows that HA coating increases the amount of ingrowth and attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.

Caveolae, specialised regions of the cell membrane which have been detected in a wide range of mammalian cells, have not been described in bone cells. They are plasmalemmal invaginations, 50 to 100 nm in size, characterised by the presence of the structural protein, caveolin, which exists as three subtypes. Caveolin-1 and caveolin-2 are expressed in a wide range of cell types whereas caveolin-3 is thought to be a muscle-specific subtype. There is little information on the precise function of caveolae, but it has been proposed that they play an important role in signal transduction.

As the principal bone-producing cell, the osteoblast has been widely studied in an effort to understand the signalling pathways by which it responds to extracellular stimuli. Our aim in this study was to identify caveolae and their structural protein caveolin in normal human osteoblasts, and to determine which subtypes of caveolin were present. Confocal microscopy showed staining which was associated with the plasma membrane. Transmission electron microscopy revealed the presence of membrane invaginations of 50 to 100 nm, consistent with the appearance of caveolae. Finally, we isolated protein from these osteoblasts, and performed Western blotting using anti-caveolin primary antibodies. This revealed the presence of caveolin-1 and -2, while caveolin-3 was absent.

The identification of these structures and their associated protein may provide a significant contribution to our further understanding of signal transduction pathways in osteoblasts.

We studied the effect of the surface finish of the stem on the transfer of load in the proximal femur in a sheep model of cemented hip arthroplasty. Strain-gauge analysis and corresponding finite-element (FE) analysis were performed to assess the effect of friction and creep at the cement-stem interface.

No difference was seen between the matt and polished stems. FE analysis showed that the effects of cement creep and friction at the stem-cement interface on femoral strain were small compared with the effect of inserting a cemented stem.

In six unloaded cadaver knees we used MRI to determine the shapes of the articular surfaces and their relative movements. These were confirmed by dissection.

Medially, the femoral condyle in sagittal section is composed of the arcs of two circles and that of the tibia of two angled flats. The anterior facets articulate in extension. At about 20° the femur ‘rocks’ to articulate through the posterior facets. The medial femoral condyle does not move anteroposteriorly with flexion to 110°.

Laterally, the femoral condyle is composed entirely, or almost entirely, of a single circular facet similar in radius and arc to the posterior medial facet. The tibia is roughly flat. The femur tends to roll backwards with flexion.

The combination during flexion of no antero-posterior movement medially (i.e., sliding) and backward rolling (combined with sliding) laterally equates to internal rotation of the tibia around a medial axis with flexion. About 5° of this rotation may be obligatory from 0° to 10° flexion; thereafter little rotation occurs to at least 45°. Total rotation at 110° is about 20°, most if not all of which can be suppressed by applying external rotation to the tibia at 90°.

In 13 unloaded living knees we confirmed the findings previously obtained in the unloaded cadaver knee during flexion and external rotation/internal rotation using MRI. In seven loaded living knees with the subjects squatting, the relative tibiofemoral movements were similar to those in the unloaded knee except that the medial femoral condyle tended to move about 4 mm forwards with flexion. Four of the seven loaded knees were studied during flexion in external and internal rotation. As predicted, flexion (squatting) with the tibia in external rotation suppressed the internal rotation of the tibia which had been observed during unloaded flexion.

We studied active flexion from 90° to 133° and passive flexion to 162° using MRI in 20 unloaded knees in Japanese subjects. Flexion over this arc is accompanied by backward movement of the medial femoral condyle of 4.0 mm and by backward movement laterally of 15 mm, i.e., by internal rotation of the tibia. At 162° the lateral femoral condyle lies posterior to the tibia.

We studied the knees of 11 volunteers using RSA during a step-up exercise requiring extension while weight-bearing from 50° to 0°. The findings on weight-bearing flexion with and without external rotation of the tibia based on MRI were confirmed.

We investigated the effects of low-intensity pulsed ultrasound on distraction osteogenesis in a rabbit model.

Callotasis of the right tibia was performed in 70 male Japanese white rabbits using mini-external fixators. In the first part of the study in 64 animals using normal distraction (waiting period seven days; distraction rate 0.5 mm/12 hours; distraction period ten days), we evaluated the distraction site by radiography, measurement of the bone mineral density (BMD), mechanical testing, and histology. In the second part in six rabbits using fast distraction (waiting period 0 days; distraction rate 1.5 mm/12 hours; distraction period seven days) the site was evaluated radiologically. Half of the animals (35) had received ultrasound to their right leg (30mW/cm²) for 20 minutes daily after ceasing distraction (ultrasound group), while rigid fixation only was maintained in the other half (control group). With normal distraction, the hard callus area, as shown by radiography, the BMD, and the findings on mechanical testing, were significantly greater in those receiving ultrasound than in the control group. Histological analysis showed no tissue damage attributable to exposure to ultrasound. With fast distraction, immature bone regeneration was observed radiologically in the control group, while bone maturation was achieved in the ultrasound group.

We conclude that ultrasound can accelerate bone maturation in distraction osteogenesis in rabbits, even in states of poor callotasis.

The formation of restrictive adhesions around the musculotendinous unit after injury is one of the most vexing processes faced by the surgeon. In flexor tendons it has been shown that the synovial tissue is the source of aggressive fibroblasts which contribute to this process. Using a rabbit model, we have examined the effects of treating the synovial sheath with the antimetabolite 5-fluorouracil (5-FU) for five minutes. Inflammatory, proliferative and molecular markers were compared in the response of the treated and control tendons to injury. Compared with a control group we found that the proliferative and inflammatory responses were significantly reduced (p < 0.001) in the treated tendons. Not only was there a reduction in the cellular and cytokine response, but there also was a significant (p < 0.001) reduction in the level of activity of the known pro-scarring agent, transforming growth factor beta 1 (TGF-β1). These pilot studies indicate that the formation of restrictive adhesions may be modulated using a simple single-touch technique in the hope of producing a better return of function.

In 14 rabbits we determined the origin of the cells effecting healing of the tendon of supraspinatus inserted into a bony trough. After two weeks both the cellularity of the underlying bone and the thickness of the subacromial bursa were significantly increased in the operated compared with the control shoulders. The cellularity of the stump of the tendon, however, was significantly decreased in the operated shoulders. In this model, both the underlying bone and the subacromial bursa but not the stump of the tendon contributed to the process of repair.

We conclude that the medial stump should be debrided judiciously but that cutting back to bleeding tissue is not necessary during repair of the rotator cuff. Moreover, great care should be taken to preserve the subacromial bursa since it seems to play an important role in the healing process.

Our aim was to determine the precision of the measurements of bone mineral density (BMD) by dual-energy x-ray absorptiometry in the proximal femur before and after implantation of an uncemented implant, with particular regard to the significance of retro- and prospective studies.

We examined 60 patients to determine the difference in preoperative BMD between osteoarthritic and healthy hips. The results showed a preoperative BMD of the affected hip which was lower by a mean of 4% and by a maximum of 9% compared with the opposite side. In addition, measurements were made in the operated hip before and at ten days after operation to determine the effect of the implantation of an uncemented custom-made femoral stem. The mean increase in the BMD was 8% and the maximum was 24%. Previous retrospective studies have reported a marked loss of BMD on the operated side.

The precision of double measurements using a special foot jig showed a modified coefficient of variation of 0.6% for the non-operated side in 15 patients and of 0.6% for the operated femur in 20 patients.

The effect of rotation on the precision of the measurements after implantation of an uncemented femoral stem was determined in ten explanted femora and for the operated side in ten patients at 10° rotation and in 20 patients at 30° rotation. Rotation within 30° influenced the precision in studies in vivo and in vitro by a mean of 3% and in single cases in up to 60%.

Precise prediction of the degree of loss of BMD is thus only possible in prospective cross-sectional measurements, since the effect of the difference in preoperative BMD, as well as the apparent increase in BMD after implantation of an uncemented stem, is not known from retrospective studies. The DEXA method is a reliable procedure for determining periprosthetic BMD when positioning and rotation are strictly controlled.

Our aim was to analyse the effect of avascularity on the morphology and mechanical properties (tensile strength, viscoelasticity) of human bone-patellar-tendon-bone (BPTB) grafts in vitro. These were harvested at postmortem and stored submerged in denaturated human plasma at a constant pH, pO₂, pCO₂, temperature and humidity under sterile conditions. Mechanical testing was performed two and four weeks after removal of the graft. The mean ultimate strength was 1085.7 ± 255.8 N (control), 1009.0 ± 314.9 N (two weeks cultured) and 1076.8 ± 414.8 N (four weeks cultured). There was no significant difference in linear stiffness or deformation to failure between the groups. There was a difference in viscoelasticity between the control group and the avascular grafts and the latter had significant lower peak load-to-load ratios after 15 minutes compared with the control group. After two and four weeks the graft contained viable fibroblasts. There was regular cellularity in the superficial layers and decreased cellularity in the midportion. The structure of the collagen including the crimp pattern appeared to be normal in polarised light.

We conclude that avascularity does not significantly affect ultimate failure loads or stiffness of BPTB grafts. Slight changes in viscoelasticity were induced, but the significance of the increased stress relaxation is not fully understood.

We aimed to highlight the relationship between age and the architectural properties of trabecular bone, to outline the patterns in which the variations in these properties take place, and to investigate the influence of the architecture on the mechanical properties of trabecular bone in growing animals. We studied 30 lambs in three age groups and 20 sheep in two age groups. Cubes of subchondral bone were cut from the proximal tibia according to a standardised protocol. They were serially sectioned and their architectural properties were determined. Similar cubes were obtained from the identical anatomical position of the contralateral tibia and their compressive mechanical properties measured. The values obtained from the skeletally immature and mature individuals were compared. Multiple regression analyses were performed between the architectural and the mechanical properties.

The bone volume fraction, the mean trabecular volume, the architectural and the mechanical anisotropy, the elastic modulus, the bone strength, the energy absorption to failure, and the elastic energy correlated positively with increasing age whereas the connectivity density, the bone surface density, the ultimate strain, the absorption of viscoelastic energy and the relative loss of energy correlated inversely. The values of all variables were significantly different in the skeletally mature and immature groups. We determined the patterns in which the variations took place. The bone volume fraction of the trabecular bone tissue was found to be the major predictor of its compressive mechanical properties. Together with the mean trabecular volume and the bone surface density, it explained 81% of the variations in the compressive elastic modulus of specimens obtained from the contralateral tibiae.

We compared wear particles from two different designs of total hip arthroplasty with polycrystalline alumina-ceramic bearings of different production periods (group 1, before ISO 6474: group 2, according to ISO 6474). The neocapsules and interfacial connective tissue membranes were retrieved after mean implantation times of 131 months and 38 months, respectively. Specimen blocks were freed from embedding media, either methylmethacrylate or paraffin and digested in concentrated nitric acid. Particles were then counted and their sizes and composition determined by SEM and energy-dispersive x-ray analysis (EDXA).

The mean numbers and sizes of most alumina wear particles did not differ for both production periods, but the larger sizes of particle in group 1 point to more severe surface destruction. The increased metal wear in group 2 was apparently due to alumina-induced abrasion of the stems. In this study the concentrations of particles in the periprosthetic tissues were 2 to 22 times lower than those observed previously with polyethylene and alumina/polyethylene wear couples.

Mononuclear osteoclast precursors are present in the wear-particle-associated macrophage infiltrate found in the membrane surrounding loose implants. These cells are capable of differentiating into osteoclastic bone-resorbing cells when co-cultured with the rat osteoblast-like cell line, UMR 106, in the presence of 1,25(OH)₂ vitamin D₃. In order to develop an in vitro model of osteoclast differentiation which more closely parallels the cellular microenvironment at the bone-implant interface in situ, we determined whether osteoblast-like human bone-derived cells were capable of supporting the differentiation of osteoclasts from arthroplasty-derived cells and analysed the humoral conditions required for this to occur.

Long-term co-culture of arthroplasty-derived cells and human trabecular-bone-derived cells (HBDCs) resulted in the formation of numerous tartrate-resistant-acid-phosphatase (TRAP) and vitronectin-receptor (VNR)-positive multinucleated cells capable of extensive resorption of lacunar bone. The addition of 1,25(OH)₂ vitamin D₃ was not required for the formation of osteoclasts and bone resorption. During the formation there was release of substantial levels of M-CSF and PGE₂. Exogenous PGE₂ (10⁻⁸ to 10⁻⁶M) was found to stimulate strongly the resorption of osteoclastic bone. Our study has shown that HBDCs are capable of supporting the formation of osteoclasts from mononuclear phagocyte precursors present in the periprosthetic tissues surrounding a loose implant. The release of M-CSF and PGE₂ by activated cells at the bone-implant interface may be important for the formation of osteoclasts at sites of pathological bone resorption associated with aseptic loosening.

Our aim was to determine the relationship between age and the mechanical and physical properties of trabecular bone, to describe the patterns in which the variations in these properties take place, and to investigate the influence of the physical properties on the mechanical characteristics of trabecular bone during growth. We used 30 lambs in three age groups and 20 sheep in two age groups. Cubes of subchondral bone were cut from the proximal tibia according to a standardised protocol. We performed non-destructive compression tests of the specimens in three orthogonal directions and compression tests to failure in the axial direction. The physical properties of the specimens were also determined. The data were correlated with age and compared in skeletally immature and mature animals. Multiple regression analyses were performed between the mechanical and the physical properties.

Age correlated positively with elastic modulus, bone strength, energy absorption to failure, elastic energy, mechanical anisotropy ratio, tissue density, apparent density, apparent ash density, and bone mineral content, and inversely with ultimate strain, viscoelastic energy absorption, relative energy loss, the collagen content of bone and the percentage porosity. The values of all variables were significantly different in the skeletally mature and immature groups. The apparent density of trabecular bone tissue was found to be the major predictor of its compressive mechanical properties. Together with the content of bone muscle and bone collagen, the apparent density could explain 84% of the variation in the elastic modulus, whereas only a small portion of the variation in ultimate strain could be explained by the variation in apparent density.

We performed positron emission tomography (PET) with ¹⁸fluorine-fluoro-2-deoxy-D-glucose (FDG) on 55 patients with tumours involving the musculoskeletal system in order to evaluate its role in operative planning. The standardised uptake value (SUV) of FDG was calculated and, to distinguish malignancies from benign lesions, the cases were divided into high (≥ 1.9) and low (< 1.9) SUV groups.

The sensitivity of PET for correctly diagnosing malignancy was 100% with a specificity of 76.9% and an overall accuracy of 83.0%. The mean SUV for metastatic lesions was twice that for primary sarcomas (p < 0.0015).

Our results suggest that the SUV may be useful in differentiating malignant tumours from benign lesions. However, some of the latter, such as schwannomas, had high SUVs so that biopsy or wide resection was selected as the first operation. Thus, some other quantitative analysis may be required for preoperative planning in cases of high-SUV neurogenic benign tumours. The reverse transcription-polymerase chain reaction revealed that the RNA message of a key enzyme in glucose metabolism, phosphohexose isomerase (PHI)/autocrine motility factor, was augmented in only high FDG-uptake lesions, suggesting that a high expression of the PHI message may be associated with accumulation of FDG in musculoskeletal tumours.

We compared the peripheral blood and periprosthetic tissues of 53 patients at revision arthroplasty with those of 30 patients at primary arthroplasty to determine whether there is a systemic difference in lymphocytes in patients with worn hip implants. The absolute number and relative proportion of lymphocytes bearing CD2, CD3, CD4, CD8, CD16, CD19, HLA-DR, kappa and lambda antigens were compared with the levels of IL-1β, IL-6 and PGE₂ in the pseudosynovial membrane as well as with a semiquantitative estimate of metal and polyethylene particles, necrosis and chronic inflammation and the total concentration of metals within the periprosthetic tissues.

There was a significant increase in the relative proportion of CD2-positive T-cells and CD16-positive natural killer cells in the peripheral blood at revision arthroplasty compared with primary arthroplasty and an increased proportion of CD8-positive T-cells and a decreased ratio of CD4 to CD8 (helper inducer/suppressor cytotoxic cells). Three control patients, who went on to have revision surgery, had values at primary arthroplasty which were similar to those of patients at the time of revision surgery. These differences did not correlate with the local concentration of metal, plastic or cement or inflammatory response or the type of prosthesis. An inverse correlation was noted between the necrosis in the periprosthetic tissue and both the local production of IL-6 and the absolute numbers of T-cells in peripheral blood.

We conclude that there may be several cell-mediated systemic immune responses to aseptic loosening, at least one of which may be directly related to events in the periprosthetic tissues. We cannot exclude the possibility that the changes in the proportion of CD8-positive cells reflected a predisposition, rather than a reaction, to loosening of the implant.

Frozen shoulder is a chronic fibrosing condition of the capsule of the joint. The predominant cells involved are fibroblasts and myofibroblasts which lay down a dense matrix of type-I and type-III collagen within the capsule. This subsequently contracts leading to the typical features of pain and stiffness. Cytokines and growth factors regulate the growth and function of the fibroblasts of connective tissue and remodelling of the matrix is controlled by the matrix metalloproteinases (MMPs) and their inhibitors.

Our aim was to determine whether there was an abnormal expression or secretion of cytokines, growth factors and MMPs in tissue samples from 14 patients with frozen shoulder using the reverse transcription/polymerase chain reaction (RT/PCR) technique and to compare the findings with those in tissue from four normal control shoulders and from five patients with Dupuytren’s contracture.

Tissue from frozen shoulders demonstrated the presence of mRNA for a large number of cytokines and growth factors although the frequency was only slightly higher than in the control tissue. The frequency for a positive signal for the proinflammatory cytokines Il-1β and TNF-α and TNF-β, was not as great as in the Dupuytren’s tissue. The presence of mRNA for fibrogenic growth factors was, however, more similar to that obtained in the control and Dupuytren’s tissue. This correlated with the histological findings which in most specimens showed a dense fibrous tissue response with few cells other than mature fibroblasts and with very little evidence of any active inflammatory cell process. Positive expressions of the mRNA for the MMPs were also increased, together with their natural inhibitor TIMP. The notable exception compared with control and Dupuytren’s tissue was the absence of MMP-14, which is known to be a membrane-type MMP required for the activation of MMP-2 (gelatinase A).

Understanding the control mechanisms which play a part in the pathogenesis of frozen shoulder may lead to the development of new regimes of treatment for this common, protracted and painful chronic fibrosing condition.

Aseptic loosening and osteolysis around prosthetic joints are the principal causes of failure and consequent revision. During this process activated macrophages produce cytokines which are thought to promote osteolysis by osteoclasts. Changes in pressure within the space around implants have been proposed as a cause of loosening and osteolysis. We therefore studied the effect of two different regimes of cyclic pressure on the production of interleukin-1β (IL-1β), IL-6 and tumour necrosis factor-α (TNF-α) by cultured human monocyte-derived (M-D) macrophages. There was a wide variation in the expression of cytokines in non-stimulated M-D macrophages from different donors and therefore cells from the same donor were compared under control and pressurised conditions.

Both regimes of cyclic pressure were found to increase expression of IL-6 and TNF-α. Expression of IL-1β was increased by a higher-frequency regime only. Our findings suggest that M-D macrophages are activated by cyclic pressure. Further work will be required to understand the relative roles of frequency, amplitude and duration of applied pressure in the cellular effects of cyclic pressure in this system.

Immobilisation causes denervation-like changes in the motor endplates, decreases the content of IGF-I, and increases the number of IGF-I receptors in the spinal cord. In the rat we investigated whether similar changes occur after a fracture of the midshaft of the femur which had been treated by intramedullary fixation with adequate or undersized pins.

A more pronounced reduction in muscle wet weight was seen after fixation by undersized pins as well as decreased ash density of the ipsilateral tibia which did not completely return to normal within the 12-week experimental period. The nicotinic cholinergic receptors in the motor endplates of tibialis anterior were increased (p < 0.01) and there was a significant increase (p < 0.02) in IGF-I receptors in the lumbar spinal cord ipsilateral to the fracture after treatment by undersized nails. These changes may be associated with the impaired proprioception, co-ordination and motor activity which are sometimes seen after fractures.

We used a rat model in vivo to study the effects of the concentration of polyethylene particles on the bone-implant interface around stable implants in the proximal tibia. Intra-articular injections of 10⁴, 10⁶ or 10⁸ high-density polyethylene (HDPE) particles per joint were given 8, 10 and 12 weeks after surgery. The animals were killed after 14 and 26 weeks and the response at the interface determined.

Fibrous tissue was seen at the bone-implant interface when the head of the implant was flush with the top of the tibia but not when it was sunk below the tibial plateau. In the latter case the implant was completely surrounded by a shell of bone. The area of fibrous tissue and that of the gap between the implant and bone was related to the concentration of particles in the 14-week group (p < 0.05).

Foreign-body granulomas containing HDPE particles were seen at the bone-implant interface in animals given 10⁸ particles. The pathology resembles that seen around prostheses with aseptic loosening and we suggest that this is a useful model by which to study this process.

Mechanical loading during physical activity produces strains within bones. It is thought that these forces provide the stimulus for the adaptation of bone. Tibial strains and rates of strain were measured in vivo in six subjects during running, stationary bicycling, leg presses and stepping and were compared with those of walking, an activity which has been found to have only a minimal effect on bone mass.

Running had a statistically significant higher principal tension, compression and shear strain and strain rates than walking. Stationary bicycling had significantly lower tension and shear strains than walking. If bone strains and/or strain rates higher than walking are needed for tibial bone strengthening, then running is an effective strengthening exercise for tibial bone.

Chondrocytes at the lower zone of the growth plate must be eliminated to facilitate longitudinal growth; this is generally assumed to involve apoptosis. We attempted to provide definitive electron-microscopic evidence of apoptosis in chondrocytes of physes and chondroepiphyses in the rabbit. We were, however, unable to find a single chondrocyte with the ultrastructure of ‘classical’ apoptosis in vivo, although such a cell was found in vitro. Instead, condensed chondrocytes had a convoluted nucleus with patchy chromatin condensations while the cytoplasm was dark with excessive amounts of endoplasmic reticulum. These cells were termed ‘dark chondrocytes’. A detailed study of their ultrastructure combined with localisation methods in situ suggested a different mechanism of programmed cell death. In addition, another type of death was identified among the immature chondrocytes of the chondroepiphysis. These cells had the same nucleus as dark chondrocytes, but the lumen of the endoplasmic reticulum had expanded to fill the entire non-nuclear space, and all cytoplasm and organelles had been reduced to dark, worm-like inclusions. Since these cells appeared to be ‘in limbo’, they were termed ‘paralysed’ cells. It is proposed that ‘dark chondrocytes’ and ‘paralysed cells’ are examples of physiological cell death which does not involve apoptosis. It is possible that the confinement of chondrocytes within their lacunae, which would prevent phagocytosis of apoptotic bodies, necessitates different mechanisms of elimination.

We evaluated the efficacy and biocompatibility of porous apatite-wollastonite glass ceramic (AW-GC) as an intramedullary plug in total hip replacement (THR) for up to two years in 22 adult beagle dogs. Cylindrical porous AW-GC rods (70% porosity, mean pore size 200 3m) were prepared. Four dogs were killed at 1, 3, 6 and 12 months each and six at 24 months after implantation.

Radiological evaluation confirmed the efficacy of porous AW-CG as an intramedullary plug. Histological evaluation showed osteoconduction at one month and resorption of the porous AW-GC, which was replaced by newly-formed bone, at 24 months. Our findings indicate that porous AW-GC can be used clinically as an intramedullary plug in THR.

The properties of impacted morsellised bone graft (MBG) in revision total knee arthroplasty (TKA) were studied in 12 horses. The left hind metatarsophalangeal joint was replaced by a human TKA. The horses were then randomly divided into graft and control groups. In the graft group, a unicondylar, lateral uncontained defect was created in the third metatarsal bone and reconstructed using autologous MBG before cementing the TKA. In the control group, a cemented TKA was implanted without the bone resection and grafting procedure. After four to eight months, the animals were killed and a biomechanical loading test was performed with a cyclic load equivalent to the horse’s body-weight to study mechanical stability. After removal of the prosthesis, the distal third metatarsal bone was studied radiologically, histologically and by quantitative and micro CT.

Biomechanical testing showed that the differences in deformation between the graft and the control condyles were not significant for either elastic or time-dependent deformations. The differences in bone mineral density (BMD) between the graft and the control condyles were not significant. The BMD of the MBG was significantly lower than that in the other regions in the same limb. Micro CT showed a significant difference in the degree of anisotropy between the graft and host bone, even although the structure of the area of the MBG had trabecular orientation in the direction of the axial load. Histological analysis revealed that all the grafts were revascularised and completely incorporated into a new trabecular structure with few or no remnants of graft. Our study provides a basis for the clinical application of this technique with MBG in revision TKA.

We have studied in vitro the effect of a hydroxyapatite (HA) tricalcium phosphate material coated with hepatocyte growth factor (HA-HGF) on cell growth, collagen synthesis and secretion of metalloproteinases (MMPs) by human osteoblasts.

Cell proliferation was stimulated when osteoblasts were incubated with untreated HA and was further increased after exposure to HA-HGF. The uptake of [³H]-proline was increased after treatment with HA. When osteoblasts were exposed to HA-HGF, collagen synthesis was increased with respect to HA. The secretion of MMPs in control cells was undetectable, but in HA and HA-HGF cells MMP 2 and MMP 9 were clearly synthesised.

Our results suggest that HA can promote osteoblast activity and that HGF can further increase its bioactivity.

Spines are often stabilised posteriorly by internal fixation and anteriorly by a bone graft. The effect of an autologous bone graft from the iliac crest on implant loads is unknown. We used an internal spinal fixation device with telemetry to measure implant loads for several body positions and activities in nine patients before and after anterior interbody fusion. With the body upright, implant loads were often higher after than before fusion using a bone graft. Distraction of the bridged region led to high implant loads in patients with a fractured vertebra and to marked changes in load in those with degenerative instability. Leaving the lower of the bridged intervertebral discs intact led to only small changes in fixator load after anterior interbody fusion. A bone graft alone does not guarantee a reduction of implant loads.

In a study combining tissue mechanics and fracture morphology for the first time, we examined the ruptured surfaces of anterior cruciate ligaments of rabbits and related their appearance to the initial loading conditions. Sixteen specimens were stretched to failure at rates of displacement of 10 and 500 mm/min. We used video images to study the changes which occurred during the fracture process and SEM to examine the appearance of the ruptured surfaces.

The surfaces of ligaments tested at 10 mm/min had more pulled-out collagen fibres and the fibres had more pronounced waviness compared with those tested at 500 mm/min. We have shown that the macroscopic appearance of ruptured ligaments can be related to their microscopic appearance and that it is possible to deduce whether failure was by gradual tearing of the fibres or catastrophic failure.

Periprosthetic osteolysis is a major cause of aseptic loosening in artificial joint replacement. It is assumed to occur in conjunction with the activation of macrophages. We have shown in vitro that human osteoblast-like cells, isolated from bone specimens obtained from patients undergoing hip replacement, phagocytose fine particles of titanium alloy (TiAlV).

The human osteoblast-like cells were identified immunocytochemically by the presence of bone-specific alkaline phosphatase (BAP). With increasing duration of culture, a variable number of the osteoblastic cells became positive for the macrophage marker CD68, independent of the phagocytosis of particles, with a fine granular cytoplasmic staining which was coexpressed with BAP as revealed by immunodoublestaining. The metal particles were not toxic to the osteoblastic cells since even in culture for up to four weeks massively laden cells were vital and had a characteristic morphology. Cells of the human osteosarcoma cell line (HOS 58) were also able to phagocytose metal particles but had only a low expression of the CD68 antigen. Fluorescence-activated cell scanning confirmed our immunocytochemical results. Additionally, the cells were found to be negative for the major histocompatibility complex-II (MHC-II) which is a marker for macrophages and other antigen-presenting cells. Negative results of histochemical tests for tartrate-resistant acid phosphatase excluded the contamination by osteoclasts or macrophages in culture.

Our observations suggest that the osteoblast can either change to a phagocytosing cell or that the phagocytosis is an underestimated property of the osteoblast. The detection of the CD68 antigen is insufficient to prove the monocytic lineage. In order to discriminate between macrophages and osteoblasts additional markers should be used. To our knowledge, this is the first demonstration of cells of an osteoblastic origin which have acquired a mixed phenotype of both osteoblasts and macrophages.

We studied the effects of irradiation on the reintegration of autologous osteoarticular grafts over a period of 24 weeks in a canine model. In 16 foxhounds the medial femoral condyle was resected, irradiated and immediately replanted. In the control group resection and replantation were performed without irradiation. Reintegration was assessed by macroscopic analysis, histology, radiography and gait analysis.

Reintegration was equal at 12 weeks, but significantly inferior in the irradiated group after 24 weeks with delayed bone remodelling. The articular cartilage showed modest degeneration. Conventional radiography and histology showed corresponding changes. Limb function was adequate but the gait was inferior in the treated group.

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.

After cemented total hip arthroplasty (THA) there may be failure at either the cement-stem or the cement-bone interface. This results from the occurrence of abnormally high shear and compressive stresses within the cement and excessive relative micromovement.

We therefore evaluated micromovement and stress at the cement-bone and cement-stem interfaces for a titanium and a chromium-cobalt stem. The behaviour of both implants was similar and no substantial differences were found in the size and distribution of micromovement on either interface with respect to the stiffness of the stem.

Micromovement was minimal with a cement mantle 3 to 4 mm thick but then increased with greater thickness of the cement. Abnormally high micromovement occurred when the cement was thinner than 2 mm and the stem was made of titanium.

The relative decrease in surface roughness augmented slipping but decreased debonding at the cement-bone interface. Shear stress at this site did not vary significantly for the different coefficients of cement-bone friction while compressive and hoop stresses within the cement increased slightly.

We used dual-energy x-ray absorptiometry (DEXA) to evaluate the extent of periprosthetic bone remodelling around a prosthesis for distal femoral reconstruction, the Kotz modular femoral tibial replacement (KMFTR; Howmedica, Rutherford, New Jersey). A total of 23 patients was entered into the study which had four parts: 1) 17 patients were scanned three times on both the implant and contralateral legs to determine whether the precision of DEXA measurements was adequate to estimate bone loss surrounding the anchorage piece of the KMFTR; 2) in 23 patients the bone mineral density (BMD) in different regions of interest surrounding the diaphyseal anchorage was compared with that of the contralateral femur at the same location to test whether there was consistent evidence of loss of BMD adjacent to the prosthetic stem; 3) in 12 patients sequential studies were performed about one year apart to compare bone loss; and 4) bone loss was compared in ten patients with implants fixed by three screws and in 13 without screws.

The mean coefficients of variation (SD/mean) for the 17 sets of repeated scans ranged from 2.9% to 7.8% at different regions of interest in the KMFTR leg and from 1.4% to 2.5% in the contralateral leg. BMD was decreased in the KMFTR leg relative to the contralateral limb and the percentage of BMD loss in general increased as the region of interest moved distally in the femur. Studies done after one year showed no consistent pattern of progressive bone loss between the two measurements. The ten patients with implants fixed by screws were found to have a mean loss of BMD of 42% in the most distal part of the femur, while the 13 without screw fixation had a mean loss of 11%.

DEXA was shown to have adequate precision to evaluate loss of BMD around the KMFTR. This was evident relative to the contralateral leg in all patients and generally increased in the most distal part of the femur. In general, it stabilised between two measurements taken one year apart and was greater surrounding implants fixed by cross-locking screws.

Intermittent treatment with parathyroid hormone (PTH) has an anabolic effect on both intact cancellous and cortical bone. Very little is known about the effect of the administration of PTH on the healing of fractures or the incorporation of orthopaedic implants. We have investigated the spontaneous ingrowth of callus and the formation of bone in a titanium chamber implanted at the medioproximal aspect of the tibial metaphysis of the rat. Four groups of ten male rats weighing approximately 350 g were injected with human PTH (1-34) in a dosage of 0, 15, 60 or 240 μg/kg/day, respectively, for 42 days from the day of implantation of the chamber.

During the observation period the chamber became only partly filled with callus and bone and no difference in ingrowth distance into the chamber was found between the groups. The cancellous density was increased by 90%, 132% and 173% in the groups given PTH in a dosage of 15, 60 or 240 μg/kg/day, respectively. There was a linear correlation between bone density and the log PTH doses (r²= 0.6).

Our findings suggest that treatment with PTH may have a potential for enhancement of the incorporation of orthopaedic implants as well as a beneficial effect on the healing of fractures when it is given in low dosages.

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.

The treatment of large bony defects by callus distraction is well accepted, but the duration of treatment is long and the rate of complications increases accordingly. We have examined the effect of the stiffness of the axial fixator on reducing the time for maturation of callus.

We created a mid-diaphyseal defect of 15 mm in the metatarsal bone in sheep and stabilised it with a ring fixator. After four days a bony segment was transported for 16 days at 1 mm per day. After 64 days the animals were divided into four groups, three with axial interfragmentary movement (IFM) of 0.5, 1.2 and 3.0 mm, respectively, and a control group.

The 3.0 mm IFM group had the smallest bone density (p = 0.001) and area of callus and the largest IFM after 12 weeks; it also had typical clinical signs of hypertrophic nonunion. The most rapid stiffening of the callus was in the 0.5 mm group which had the smallest IFM (p = 0.04) after 12 weeks and radiological signs of bridging of the defect. These results indicate that suitable dynamic axial stimulation can enhance maturation of distraction callus when the initial amplitude is small, but that a large IFM can lead to delayed union.

Injury to muscles is very common. We have previously observed that basic fibroblast growth factor (b-FGF), insulin growth factor type 1 (IGF-1) and nerve growth factor (NGF) are potent stimulators of the proliferation and fusion of myoblasts in vitro. We therefore injected these growth factors into mice with lacerations of the gastrocnemius muscle. The muscle regeneration was evaluated at one week by histological staining and quantitative histology. Muscle healing was assessed histologically and the contractile properties were measured one month after injury.

Our findings showed that b-FGF, IGF and to a less extent NGF enhanced muscle regeneration in vivo compared with control muscle. At one month, muscles treated with IGF-1 and b-FGF showed improved healing and significantly increased fast-twitch and tetanus strengths. Our results suggest that b-FGF and IGF-1 stimulated muscle healing and may have a considerable effect on the treatment of muscle injuries.