Fractures in elderly mice demonstrate delayed ossification of the soft callus: a cellular and radiographic study

OBJECTIVES

The aim of this study was to assess the cellular age-related changes in fracture repair and relate these to the observed radiographic assessments at differing time points.

METHODS

Transverse traumatic tibial diaphyseal fractures were created in 12-14 weeks old (young n = 16) and 18 months old (elderly n = 20) in Balb/C wild mice. Fracture calluses were harvested at five time points from 1 to 35 days post fracture for histomorphometry (percent of cartilage and bone), radiographic analysis (total callus volume, callus index, and relative bone mineral content).

RESULTS

The elderly mice produced an equal amount of cartilage when compared to young mice (p > 0.08). However, by day 21 there was a significantly greater percentage of bone at the fracture site in the young group (mean percentage 50% versus 11%, p < 0.001). It was not until day 35 when the elderly group produced a similar amount of bone compared to the young group at 21 days (50% versus 53%, non-significant (ns)). The callus area and callus index on radiographic assessment was not significantly different between young and elderly groups at any time point. Relative bone mineral content was significantly greater in the young group at 14 days (545.7 versus -120.2, p < 0.001) and 21 days (888.7 versus 451.0, p < 0.001) when compared to the elderly group. It was not until day 35 when the elderly group produced a similar relative bone mineral content as the young group at 21 days (888.7 versus 921.8, ns).

CONCLUSIONS

Elderly mice demonstrated a delay in endochondral ossification which was associated with a decreased relative bone mineral content at the fracture site and may help assess these cellular changes in a clinical setting.

The risk of non-union per fracture in children

BACKGROUND

Non-union in children is considered a rare but real complication of fracture management; however there is no information available in the literature regarding its incidence. The aim of this work was to investigate the incidence of fractures and non-union in children for different anatomical regions/age groups, and for the first time to publish data regarding the rate of non-union per fracture in children in a large population.

METHOD

Prospective data for all hospital admissions for paediatric fractures and paediatric fracture non-union in Scotland between 2005 and 2010 was obtained. Regional data for total paediatric fracture numbers was also available enabling total fracture numbers and non-union incidence at a national level to be calculated.

RESULTS

There were 180 non-unions in the 0-14 year olds and 242 non-unions in 15-19 year olds recorded over 5 years in a population of 1.2 million children (0-19 years). The number of fractures during this time period for the same age groups were 92,200 and 68,900 respectively. The risk of fracture increased steadily with age; it was greater in boys than girls and far higher in the upper than lower limb. The overall rate of non-union per fracture was 0.2 % in those 14 years and younger and 0.35 % in the 15-19 year olds. Non-union was highest in the male 15-19 year olds at 0.45 % of all fractures. The risk of non-union was far greater in the lower limb fractures than in the upper limb fractures throughout childhood until the age of 15 where the upper limb NU rate per fracture exceeded that of the lower limb.

CONCLUSIONS

The calculated risk of non-union per fracture is low throughout childhood with a risk of approximately 1 in 500 or less per fracture in boys aged under 14 years and in girls of all ages, however NU increases to approximately 1 in 200 fractures for the older teenage (15-19 years) boys.

Virtual trabecular bone models and their mechanical response

The study of the mechanical behaviour of trabecular bone has extensively employed micro-level finite element (μFE) models generated from images of real bone samples. It is now recognized that the key determinants of the mechanical behaviour of bone are related to its micro-architecture. The key indices of micro-architecture, in turn, depend on factors such as age, anatomical site, sex, and degree of osteoporosis. In practice, it is difficult to acquire sufficient samples that encompass these variations. In this preliminary study, a method of generating virtual finite element (FE) samples of trabecular bone is considered. Virtual samples, calibrated to satisfy some of the key micro-architectural characteristics, are generated computationally. The apparent level elastic and post-elastic mechanical behaviour of the generated samples is examined: the elastic mechanical response of these samples is found to compare well with natural trabecular bone studies conducted by previous investigators; the post-elastic response of virtual samples shows that material non-linearities have a much greater effect in comparison with geometrical non-linearity for the bone densities considered. Similar behaviour has been reported by previous studies conducted on real trabecular bone. It is concluded that virtual modelling presents a potentially valuable tool in the study of the mechanical behaviour of trabecular bone and the role of its micro-architecture.

Elimination of transmissible spongiform encephalopathy infectivity and decontamination of surgical instruments by using radio-frequency gas-plasma treatment

It has now been established that transmissible spongiform encephalopathy (TSE) infectivity, which is highly resistant to conventional methods of deactivation, can be transmitted iatrogenically by contaminated stainless steel. It is important that new methods are evaluated for effective removal of protein residues from surgical instruments. Here, radio-frequency (RF) gas-plasma treatment was investigated as a method of removing both the protein debris and TSE infectivity. Stainless-steel spheres contaminated with the 263K strain of scrapie and a variety of used surgical instruments, which had been cleaned by a hospital sterile-services department, were examined both before and after treatment by RF gas plasma, using scanning electron microscopy and energy-dispersive X-ray spectroscopic analysis. Transmission of scrapie from the contaminated spheres was examined in hamsters by the peripheral route of infection. RF gas-plasma treatment effectively removed residual organic residues on reprocessed surgical instruments and gross contamination both from orthopaedic blades and from the experimentally contaminated spheres. In vivo testing showed that RF gas-plasma treatment of scrapie-infected spheres eliminated transmission of infectivity. The infectivity of the TSE agent adsorbed on metal spheres could be removed effectively by gas-plasma cleaning with argon/oxygen mixtures. This treatment can effectively remove 'stubborn' residual contamination on surgical instruments.

Cutting-edge design to improve cell viability in osteochondral grafts

INTRODUCTION

Autologous osteochondral grafting is in widespread use for focal defects of articular cartilage. There is major concern over the nature of the tissue bridging graft elements and graft/recipient cartilage. Chondrocyte viability is thought to be an important determinant of the quality of repair. The aim of the current study was to compare the zone of death for osteochondral grafts harvested with the commercially available Acufex, and an osteotome with a specially designed cutting-edge.

MATERIALS/METHODS

The circular osteotomes were the Acufex 4.5mm MP (Smith & Nephew) and the Lissimore, which has a different cutting-tip geometry and sharpness. These implements were used to harvest osteochondral plugs from macroscopically non-degenerate human lateral condyle explants obtained from the anterior femoral cuts of knee replacement surgery. Confocal laser scanning microscopy with vital staining was used to quantify the zone of marginal chondrocyte death for the entire perimeter of the plugs.

RESULTS

The increase in cartilage plug diameter (reference the osteotome minimal internal diameter) was significantly greater for the Acufex (Mann-Whitney; n=5; P=0.0079), with the diameter (mm) increasing by 0.49+/-0.03 (10.9%), compared with 0.16+/-0.02 (3.3%) for the Lissimore. Osteochondral plugs had a significantly (Mann-Whitney; n=5; P=0.0079) lower mean margin of cell death with the Lissimore osteotome (117.8+/-8.97 microm) than the Acufex MP (315.3+/-5.90 microm).

CONCLUSIONS

Cutting-tip profile is an important factor in determining the extent of marginal death in circular osteochondral grafts. We have designed and assessed an alternative cutting-tip, which caused significantly less marginal death than the commercially available Acufex. We conclude that there is scope for improvement of osteochondral harvest techniques.

Use of non-degenerate human osteochondral tissue and confocal laser scanning microscopy for the study of chondrocyte death at cartilage surgery

Although autologous osteochondral grafting has been widely applied in humans, most in vitro work has been on animal models. The aims of this study were to: (i) elaborate a full thickness human femoral condylar model using discard material from knee arthroplasty resections, and (ii) use this model to assess chondrocyte viability in response to surgical trauma. Homogeneous regions of human lateral femoral condyle bone-cartilage were procured from knee arthroplasty resections. These were graded prospectively, firstly by visual inspection, and then by confocal laser scanning microscopy (CLSM). Samples were subjected to tests of tissue hydration, including analysis of water content and swelling after excision from underlying bone. Surgical cuts were made in explants that were macroscopically and microscopically normal (i.e. Grade 0). Associated margins of death were assessed from both transverse and surface perspectives. Thirty-nine samples were obtained from anterior and distal femoral cuts (16 knees from 13 patients) for (1) macroscopic grading, (2) microscopic analysis, (3) analyses of water content as cut and on re-equilibration after excision from bone. Thirteen were Grade 0 on macroscopic viewing--however one showed fibrillation on microscopy and was therefore reassigned Grade 1. Grade 0 tissue had a water content of 73.8+/-0.38%, in agreement with control values from the literature. Tissues of Grades 2 and 3 were significantly (P=0.03, and P=0.004) more hydrated (76.0+/-0.59%, 76.7+/-0.99%) than Grade 0 tissue. Grade 0 tissue from the anterior cut did not swell significantly following excision from subchondral bone. However Grade 0 tissue from the distal cut showed a small but statistically significant (P=0.019) increase in water content (1.68+/-0.39%) following excision. With increasing grade there was increased tendency to swell off the bone (P<0.0001). Transverse imaging showed that the Acufex MP surgical harvester caused a greater margin of cell death (211+/-18.3 microm) in the superficial zone (SZ) than the mid-zone (50.5+/-13.6 microm; P=0.022), or SZ death from a scalpel cut (33.0+/-8.5 microm; P=0.0009). Similarly, in unfixed samples viewed from the surface perspective, the margin of death for the surgical harvester (277+/-7.2 microm) was significantly (P<0.0001) greater than that for the scalpel (38.8+/-7.2 microm). If macroscopically and microscopically non-degenerate, then human lateral femoral condylar cartilage from the anterior cut of knee resections has normal biophysical parameters (water content and lack of swelling on excision). The surgical harvester (Acufex), used in human osteochondral grafting, caused a substantial margin of cell death at the periphery of the graft, and the SZ appeared to be especially vulnerable. This effect may be important in terms of limiting the reparative capacity of the SZ. The harmful effect on viability is likely to impede lateral repair which is fundamental to subsequent structural and functional integrity.

Chondrocyte death associated with human femoral osteochondral harvest as performed for mosaicplasty

BACKGROUND

Autologous osteochondral transfer is an option for the treatment of articular defects. However, there are concerns about graft integration and the nature of the tissue forming the cartilage-cartilage bridge. Chondrocyte viability at graft and recipient edges is thought to be an important determinant of the quality of repair. The purpose of the present study was to evaluate early cell viability at the edges of osteochondral grafts from ex vivo human femoral condyles.

METHODS

Fresh human tissue was obtained from eleven knees at the time of total knee arthroplasty for the treatment of osteoarthritis. Osteochondral cylinders were harvested with use of a 4.5-mm-diameter mosaicplasty osteotome from regions of the anterolateral aspect of the femoral condyle that were macroscopically nondegenerate and histologically nonfibrillated. Plugs were assessed for marginal cell viability by means of confocal laser scanning microscopy.

RESULTS

The diameter of the cartilaginous portion of the osteochondral plugs was a mean (and standard error of the mean) of 4.84 +/- 0.12 mm (as determined on the basis of three plugs). This value was approximately 300 microm greater than the measured internal diameter of the osteotome. There was a substantial margin of superficial zone cell death (mean thickness, 382 +/- 68.2 microm), with >99% cell viability seen more centrally (as determined on the basis of five plugs). Demiplugs were created by splitting the mosaicplasty explants with a fresh number-11 scalpel blade. The margin of superficial zone cell death at the curved edge was significantly greater than that at the site of the scalpel cut (390.3 +/- 18.8 microm compared with 34.8 +/- 3.2 microm; p = 0.0286). Similar findings were observed when the cartilage alone was breached and the bone was left intact, with the margin of superficial zone cell death being significantly greater than that obtained in association with the straight scalpel incision (268 +/- 38.9 microm compared with 41.3 +/- 13.4 microm; p = 0.0286). The margin of superficial zone cell death showed no increase during the time-period between fifteen minutes and two hours after plug harvest. A mathematical approximation of the mosaicplasty region suggested that early cell death of this magnitude affects about one third of the superficial graft area.

CONCLUSIONS

The results of the present study suggest that mosaicplasty, while capable of transposing viable hyaline cartilage, is associated with an extensive margin of cell death that is likely to compromise lateral integration and articular reconstruction.

Osteoprogenitor cells of mature human skeletal muscle tissue: an in vitro study

The presence of osteogenic progenitors in human skeletal muscle is suggested by the formation of ectopic bone in clinical and experimental conditions, but their direct identification has not yet been demonstrated. The aims of this study were to identify osteogenic progenitor cells in human skeletal muscle tissue and to expand and characterize them in culture. Specimens of gracilis and semitendinosus muscle were obtained from young adults and digested to separate the connective tissue and satellite cell fractions. The cells were cultured and characterized morphologically and immunohistochemically using antibodies known to be reactive with primitive osteoprogenitor cells, pericytes, intermediate filaments, and endothelial cells. Alkaline phosphatase activity and osteocalcin gene expression were also determined. In the early stages of culture, the connective tissue cells obtained were highly positive for primitive osteoprogenitor cell and for pericyte markers. Alkaline phosphatase activity was detectable at early stages of culture and rose as a function of time, whereas primitive osteoprogenitor cell markers declined and osteocalcin mRNA expression became detectable by reverse transcriptase-polymerase chain reaction (RT-PCR). It is shown that human skeletal muscle connective tissue contains osteogenic progenitor cells. Their identification as pericytes, perivascular cells with established osteogenic potential, suggests a cellular link between angiogenesis and bone formation in muscle tissue. These cells are easily cultured and expanded in vitro by standard techniques, providing an alternative source of osteogenic progenitor cells for possible cell-based therapeutic use in certain conditions.

Growth factor expression during the development of atrophic non-union

The aim of the study was to determine, for the first time, the distribution of expression of several important growth factors during the development of atrophic non-unions using an animal model. The sites of expression of TGFbeta, PDGF, FGFb, and BMP 2/4 were determined at the osteotomy sites of both normally healing bones and within atrophic non-unions at 1 and 8 weeks after operation using immunolocalization techniques. At 1 week after operation, the osteotomy gaps of the control group contained fracture haematoma and surrounding granulation tissue, whereas the osteotomy gaps of the non-union group contained only haematoma. The tissues of both the non-union and control groups demonstrated the same presence and distribution of growth factors. By 8 weeks after the operation, the control group osteotomy gaps were filled with bone within which the active osteoblasts stained positively for each of the growth factors. At 8 weeks, the osteotomy gaps of the non-union group contained only fibrous tissue, which failed to stain positively for any of the factors. These findings suggest that the development of atrophic non-union is not directly due to a lack of these four growth factors.

Toxic effect of rifampicin on human osteoblast-like cells

We examined the effects of rifampicin on osteoblast-like cells derived from adult human bone in vitro. Cancellous bone was collected from five different individuals during elective orthopaedic operations and cultured in antibiotic-free media. Total DNA, 3H-thymidine incorporation and alkaline phosphatase (ALP) activity were measured after the cells were cultured for 4 days in media containing concentrations of rifampicin ranging from 0 to 1000 microg/ml. Mean total DNA was decreased at concentrations of 10 microg/ml and above in the cultures obtained from four out of five individuals but these decreases were significant in the cultures from only two individuals. 3H-thymidine incorporation, a more sensitive indicator of change in cell proliferation, and ALP activity were significantly decreased (P < 0.05) in all of the cultures containing 3 and 7 microg/ml, respectively. In the clinical setting, serum concentrations of rifampicin often exceed 10 microg/ml after systemic administration. The present study has shown that rifampicin, at these concentrations, can inhibit the proliferation of osteoblast-like cells in vitro. Further studies should be carried out to assess whether rifampicin is detrimental to the bone repair process in vivo.

Skin closure after acute shortening

Z-plasty is used to lengthen scars and wounds. We describe the use of a modified technique to shorten wounds in ten consecutive patients undergoing acute shortening of a limb as part of an Ilizarov procedure. The modified technique gave good exposure, easy closure of the wound and fewer problems with healing than standard incisions.

Loss of knee range of motion in leg lengthening

STUDY DESIGN

Prospective longitudinal study.

OBJECTIVE

To determine factors predictive of loss of movement in a cohort of patients undergoing femoral lengthening.

BACKGROUND

Loss of joint movement due to poor adaptation of the muscle is a major problem during limb lengthening but remains poorly documented in the literature.

METHODS AND MATERIALS

A validated technique using a modified goniometer was used to measure knee motion. Measurements were taken before surgery, prelengthening, during lengthening, and at 6 and 12 months post frame removal. The subjects were 35 patients with a mean age of 22 years (+/-12.8 years), 23 men and 12 women, undergoing femoral lengthening by the Ilizarov method.

RESULTS

The pattern of recovery of knee range of movement that was observed showed that 88% of knee flexion was regained by 6 months, 92% of patients regained their knee flexion by 12 months, and 97% by 18 months. Significant loss of knee flexion occurred in the latent period prior to lengthening, mean loss 79 degrees (+/-22.8 degrees). All patients regained full knee extension by the end of lengthening, but 2 patients who had fixed flexion deformities of > 40 degrees developed posterior subluxation of the knee.

CONCLUSIONS

The unexpected loss of movement observed in the prelengthening period indicates that physical therapy efforts must be directed to this phase in order to accelerate the recovery of joint range and reduce the muscle-related complications that can occur during limb lengthening.

Chronic osteomyelitis. The effect of the extent of surgical resection on infection-free survival

We studied prospectively a consecutive series of 50 patients with chronic osteomyelitis. Patients were allocated to the following treatment groups: 1) wide resection, with a clearance margin of 5 mm or more; 2) marginal resection, with a clearance margin of less than 5 mm; and 3) intralesional biopsy, with debulking of the infected area. All patients had a course of antibiotics, intravenously for six weeks followed by orally for a further six weeks. No patients in group 1 had recurrence. In patients treated by marginal resection (group 2), 8 of 29 (28%) had recurrence. All patients who had debulking had a recurrence within one year of surgery. We performed a survival analysis to determine the time of the recurrence of infection. In group 2 there was a higher rate of recurrence in type-B hosts (p < 0.05); no type-A hosts had recurrence. This information is of use in planning surgery for chronic osteomyelitis.

Stiffness, strength and healing assessment in different bone fractures--a simple mathematical model

External fixators can only be removed safely when fractures have healed sufficiently to restore mechanical integrity to the bone. A bending stiffness of 15 N m/ degrees has been suggested as a means of estimating mechanical integrity. To examine whether this end point stiffness value can be applied to all fractures, the present study examined the degree of variability in predicted stiffness and strength that arises from variations in bone dimensions. Results imply that there is no common value for the end-point of bending stiffness in different bones. At an end point value of 15 N m/degrees, the maturity of the fracture repair tissue (represented by its elastic modulus) can vary 500-fold between an adult femur with a 0.5-mm gap to a child's mid diaphyseal tibia with a 1.0-mm gap. Fortunately, the strength does not vary by as large an extent as the modulus. However, even though two fractures each have reached a stiffness of 15 N m/degrees, a fracture in a bone of 50 mm diameter may exhibit only 60% of the strength of repair in a bone of 30 mm diameter. Therefore, caution should be exercised when using the bending stiffness as an end point indicator for different bones.

Advantages and disadvantages of pinless external fixation

The AO pinless external fixator (PEF) uses trocar tipped clamps to grip the outer tibial cortex rather than pins to transfix it. Its main advantage is to avoid further contamination of the medullary canal in open tibial fractures where a nail may subsequently be used. We tested the anatomical safety of this device and its effect on plastic surgical procedures compared with a standard unilateral external fixator (UEF).The PEF and UEF were placed on two amputated limbs which were then dissected. Structures at risk were traced on ten cadaver limbs. We found that important anatomical structures were endangered by the PEF and that safe zones could not always be defined. The UEF avoided these structures. Plastic surgical approaches were made more difficult by the PEF which imposed limitations on local flap design and endangered the arterial perforators which supply them. We conclude that safety is compromised by the PEF because margins for error are small. It poses additional problems in soft tissue reconstruction and highlights the need for co-operation between plastic surgical and orthopaedic teams in choice of fixation device.

A murine model of distraction osteogenesis

Distraction osteogenesis is both a valuable clinical technique and a useful tool for investigating the basic mechanisms involved in bone tissue regeneration. Here we describe the development of a murine model of this procedure that can be used in transgenic animals to investigate the role of specific genes in tissue regeneration. Ring fixators were applied to the lower leg of 12 normal adult male mice. An osteotomy was made in the diaphysis of the tibia, and 7 days after the operation the bone fragments were distracted by 0.25 mm twice a day for 10 days. Specimens were examined immediately at the end of distraction and after 14-70 days of consolidation. At the end of distraction, the distraction gap was filled with fibroblast-like cells arranged longitudinally. After 14 days of consolidation, there was radiographical evidence of bone formation in the distraction gap and, after 28 days of consolidation, the bone fragments were fused with regenerated bone. By 70 days of consolidation, the regenerated bone had been almost completely remodeled and the intramedullary canal reestablished. This study is the first to report consolidation of the distraction gap with regenerated bone in a murine model of distraction.

Tissues formed during distraction osteogenesis in the rabbit are determined by the distraction rate: localization of the cells that express the mRNAs and the distribution of types I and II collagens

An experimental model of leg lengthening was used to study the morphology of, the collagenous proteins present, and the collagen genes expressed in the regenerating tissue following 20% lengthening at four different distraction rates. At a distraction rate of 0.3 mm/day (8 weeks distraction), the regenerate consists of intramembranous bone and localized areas of fibrocartilage. At rates of 0.7 (4 weeks) and 1.3 mm/day (2 weeks), the bone that grows from the cut ends of the cortical bone is separated by fibrous tissue and cartilage is present. At 2.7 mm/day (1 week), only fibrous tissue and sparse bone are present. Type I collagen is present in the matrices around the cells expressing its mRNA and similarly, type II collagen is located around the chondrocytes. Type I collagen mRNA is expressed predominantly by the fibroblasts in the fibrous tissue, the bone surface cells and to a reduced extent by the osteocytes. Type II collagen mRNA is expressed by chondrocytes. The results suggest that osteoblasts and chondrocytes within the regenerate originate from the same pool of progenitor cells, and the differentiation of these cells and the expression of types I and II collagen genes are altered by different rates of distraction. These observations suggest that the optimal rate of distraction in the model is 0.7 mm/day.

Fracture after distraction osteogenesis

We reviewed 173 patients undergoing distraction osteogenesis to determine the incidence, location and timing of fractures occurring as a complication of the procedure. There were 17 fractures in 180 lengthened segments giving an overall rate of fracture of 9.4%. Unexpectedly, the pattern and location of the fractures were very variable; six were within the regenerate itself, six at the junction between the regenerate and the original bone and five at distant sites in the limb. Of those occurring in the regenerate, five were noted to be associated with compression and partial collapse of the regenerate. In three patients collapse and deformity developed gradually in the distracted segment over the six months after removal of the frame. The method of treatment of these fractures should be chosen to take into account multiple factors, which are additional and often different from those to be considered during management of acute traumatic injuries. Internal fixation appears to be most appropriate for displaced fractures, although in small children, or in those in whom there has been, or is, infection of the screw tracks, a new period of treatment using external fixation may be needed. Fixation by intramedullary nailing was associated with a risk of infection, even if screw tracks were assessed as healthy at the time of insertion of the nail. Internal fixation with the use of plates is safe for displaced, unstable fractures in children.

Anatomical effects of periosteal elevation

Research that involves harvesting the periosteum is common. The exact technique of harvesting is rarely described; however, it may be of vital importance because techniques may vary in their ability to raise the osteogenic cambial layer, which is reported to be tightly adherent to the underlying cortex. This study was performed to define how the cambial and fibrous layers of the periosteum are affected by different techniques of stripping. The periosteum was raised from the tibia and the humerus of adult rabbits with four stripping techniques. The stripped bone surface was examined histologically and with a scanning electron microscope to determine whether the fibrous and cambial layers of the periosteum had been removed and whether there had been damage to the underlying cortex. The results from the two anatomical sites were the same. Raising the periosteum with cortical bone chips (shingling) or with a periosteal elevator removed both layers of the periosteum and caused considerable damage to the surface of the cortex. Raising the periosteum with a sharp scalpel or by simply pulling it off removed the fibrous layer but left the osteogenic layer intact adherent to the cortex. We conclude that some techniques of periosteal elevation fail to harvest the osteogenic layer and therefore may lead to unexpected experimental results. We suggest that authors describe the exact technique of periosteal stripping that was employed.

Metabolic activity of a new atrophic nonunion model in rabbits

The aetiology of atrophic nonunions is not well understood: they are often thought to be nonreactive and metabolically inactive. Investigation of their biological processes is hampered by the lack of a useful animal model. Current models involve either wide segmental excision of the diaphysis or interposition of Silastic to impede the normal healing processes. neither of which resembles the clinical situation. We therefore aimed to establish a model of atrophic nonunion that more closely resembles the clinical situation and to use this model to evaluate the metabolic activity of the gap tissue of the nonunion. A simple and reliable model of atrophic nonunion has been developed in rabbits. It more closely represents the clinical situation by avoiding large segmental excisions and the interposition of foreign materials. Clinical, radiological, and histological data support the diagnosis of atrophic nonunion in the model. The concentration of adenosine triphosphate in the gap tissue of the nonunion served as a marker of metabolic activity. The gap tissue of established atrophic nonunions had a significantly higher concentration of adenosine triphosphate than did the control specimens. In this model, the gap tissue is metabolically active; therefore, under certain conditions, it may be possible to induce union if the correct stimulus is provided.

Clinical and radiographic analysis of osteochondromas and growth disturbance in hereditary multiple exostoses

Hereditary multiple exostoses (HME) is traditionally described as a skeletal dysplasia. However, the discovery that the EXT family of tumour suppressor genes are responsible for HME suggests that it is more appropriate to classify HME as a familial neoplastic trait. In a clinical and radiographic analysis of paired bone length and exostoses number and dimensions in a HME cohort, the local presence of osteochondromas was consistently associated with growth disturbance. In particular, an inverse correlation between osteochondroma size and relative bone length (p<0.01) was found. These data suggest that the growth retardation in HME may result from the local effects of enlarging osteochondromas rather than a skeletal dysplasia effect. This study provides the first clinical rationale for ablation of rapidly enlarging exostoses to reduce growth disturbance.

Comparison of fluorescent single-strand conformation polymorphism analysis and denaturing high-performance liquid chromatography for detection of EXT1 and EXT2 mutations in hereditary multiple exostoses

EXT1 and EXT2 are two genes responsible for the majority of cases of hereditary multiple exostoses (HME), a dominantly inherited bone disorder. In order to develop an efficient screening strategy for mutations in these genes, we performed two independent blind screens of EXT1 and EXT2 in 34 unrelated patients with HME, using denaturing high-performance liquid chromatography (DHPLC) and fluorescent single-strand conformation polymorphism analysis (F-SSCP). The mutation likely to cause HME was found in 29 (85%) of the 34 probands: in 22 of these (76%), the mutation was in EXT1; seven patients (24%) had EXT2 mutations. Nineteen of these disease mutations have not been previously reported. Of the 42 different amplicon variants identified in total in the cohort, 40 were detected by DHPLC and 39 by F-SSCP. This corresponds to mutation detection efficiencies of 95% and 93% respectively. We have also found that we can confidently distinguish between different sequence variants in the same fragment using F-SSCP but not DHPLC. In light of this, and the similarly high sensitivities of the two techniques, we propose to continue screening with F-SSCP.

Leg lengthening over an intramedullary nail

Distraction osteogenesis is widely used for leg lengthening, but often requires a long period of external fixation which carries risks of pin-track sepsis, malalignment, stiffness of the joint and late fracture of the regenerate. We present the results of 20 cases in which, in an attempt to reduce the rate of complications, a combination of external fixation and intramedullary nailing was used. The mean gain in length was 4.7 cm (2 to 8.6). The mean time of external fixation was 20 days per centimetre gain in length. All distracted segments healed spontaneously without refracture or malalignment. There were three cases of deep infection, two of which occurred in patients who had had previous open fractures of the bone which was being lengthened. All resolved with appropriate treatment. This method allows early rehabilitation, with a rapid return of knee movement. There is a lower rate of complications than occurs when external fixation is used on its own. The time of external fixation is shorter than in other methods of leg lengthening. The high risk of infection calls for caution.

Contamination of the medullary canal following pin-tract infection

We developed an ovine model of an external-fixator pin-tract infection. With use of a novel method of tissue sampling, infection of the medullary canal was confirmed in all (10 of 10) external-fixator pins that were contaminated with Staphylococcus aureus after they were inserted. In addition, all (five of five) adjacent, uncontaminated pins became infected. We demonstrated that pin-tract infection can be difficult to diagnose clinically, despite gross infection of the tract, and that bacteria can spread within the medulla. Three of the infected pins (20%) did not appear clinically infected, were not loose, and were normal on radiographs after 1 week. Staphylococcus aureus was isolated from the medulla around all 15 pin tracts, and nine other organisms were isolated from the tracts. Despite the presence of infection, the majority of the pins remained well fixed in the bone after 2 weeks.

Pyoderma gangrenosum. A diagnosis not to be missed

We describe a case of pyoderma gangrenosum which presented with severe wound breakdown after elective hip replacement. The patient was treated successfully with minimal wound debridement and steroids. This diagnosis should always be considered when confronted with an enlarging painful skin lesion which does not grow organisms when cultured and fails to respond to antibiotic therapy, especially if there are similar lesions in other sites. In patients who have a past history of pyoderma gangrenosum, prophylactic steroids may be indicated at the time of surgery or may be required early in the postoperative period.

The neoplastic pathogenesis of solitary and multiple osteochondromas

Many theories of osteochondroma pathogenesis have been advanced. Genetic research into the inherited multiple form, hereditary multiple exostoses, has revealed a new family of tumour suppressor genes denoted EXT. Patterns of EXT gene mutation in hereditary multiple exostoses, in solitary and multiple osteochondromas, and in chondrosarcoma are analogous to those found in other tumour suppressor genes responsible for family cancer traits and associated malignancies. With one exception, most features of osteochondroma behaviour are comparable to those of benign neoplasms. The neoplastic pathogenesis of osteochondromas provides an alternative to the traditional 'skeletal dysplasia' theory to explain the growth disturbance associated with hereditary multiple exostoses. Recent studies on the physiological function of EXT genes are reviewed and implications for osteochondroma 'cell-of-origin' theories are discussed.

Effect of lengthening rate on angiogenesis during distraction osteogenesis

This study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg-lengthening. Immunostaining was performed with use of specific antibodies to type-IV collagen and endothelial cell antigen to examine semiquantitatively the presence of blood vessels in the developing tissues. With use of the Chalkley counting method, the greatest number of positive-staining blood vessel cells was found in the central fibrous zone of the groups that underwent lengthening at 0.7 and 1.3 mm/day compared with any other zone in any group (p < 0.05, t test). There were no statistical differences in the positive labeling indices in the mineralization front and the new bone zone adjacent to the mineralization front in any of the groups. However, the decrease in the number of positive-staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction osteogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary network at the junction of the mineralization front and the fibrous zone. The angiogenic response was weaker in the more mature regions within the new bone zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vascularization process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3 mm/day.

Repeatability of goniometer measurements of the knee in patients wearing an Ilizarov external fixator: a clinic-based study

OBJECTIVE

To examine the intra-tester and inter-tester reliability of three different methods of measurement of knee range of motion in patients undergoing limb reconstruction with the Ilizarov external fixator.

DESIGN

Twenty-five patients had the passive range of motion of their knee measured by 13 physiotherapists who were experienced in the use of goniometry. The testers were assigned into random pairs, each tester measured three or four patients who were allocated to them using the three different methods. These were: (1) a universal goniometer aligned against anatomical landmarks, (2) a universal goniometer aligned against the Ilizarov frame and (3) a modified universal goniometer.

SETTING

Orthopaedic limb reconstruction outpatient clinics.

SUBJECTS

Twenty-five patients undergoing limb reconstruction using an Ilizarov external fixator on both the femur and tibia.

RESULTS

Comparison of the three different goniometry methods showed that using a modified goniometer there was enhanced reliability compared with other methods. This method demonstrated good repeatability for both intra-tester and inter-tester measurements.

CONCLUSIONS

When serial measurements of knee range of motion are taken in patients wearing an Ilizarov external fixator the modified model of goniometer should be used.

The role of chondrocytes in intramembranous and endochondral ossification during distraction osteogenesis in the rabbit

We have used a rabbit leg-lengthening model for detailed studies of the histology of distraction osteogenesis. Some unusual features of the endochondral ossification that occurs during the rapid transition of cartilage to bone in the regenerate were observed. Histological staining techniques together with immunohistochemistry and nonradioactive in situ mRNA hybridization for cartilage and bone-related molecules have been used to document the presence of an overlapping cartilage-bone phenotype in cells of the cartilage-bone transitional region. In those particular areas, some chondrocytes appeared to be directly transformed into newly formed bone trabeculae which are surrounded by bone matrix. Acid phosphatases were found within the cartilage matrix in some of the cartilage/bone transitional regions and type I collagen mRNA and type II collagen protein were found together in some of the marginal hypertrophic chondrocytes. This study indicates an unusual role of chondrocytes in the process of ossification at a distraction rate of 1.3 mm/day in the rabbit. Further direct evidence is required to prove the hypothesis that the hypertrophic chondrocytes may transdifferentiate into bone cells in this model.

Biologic model of bone transport distraction osteogenesis and vascular response

We developed an experimental model in the rabbit of distraction osteogenesis through bone transport that closely corresponds to the clinical use of bone transport in humans. We also applied injection angiography to study the arterial response of a limb undergoing bone transport. This model includes a proximal osteotomy and bone transport to fill in a segmental tibial diaphyseal defect. Regenerate bone formed well in the gap that was created that trailed the transport segment, and slow healing at the docking site was observed, as seen in humans. The angiographic techniques clearly revealed, by radiography and anatomic dissection, the arterial response to bone transport. The results showed that the transport segment had an arterial supply after osteotomy and after transport. They also demonstrated an extensive increase in vessels in limbs that had undergone distraction osteogenesis, an observation made clinically in humans but not well demonstrated experimentally. Furthermore, angiography showed proximal stretching and distal kinking of the major artery of the leg. This model closely resembles distraction osteogenesis through bone transport in humans and definitively demonstrates that the transport segment can maintain blood supply and remain viable during the transport process. The results of this study provide a basis for further work on factors that enhance and interfere with successful bone transport in humans.

Measurement of impact force, simulation of fall and hip fracture

It has been shown that the incidence of hip fracture in the elderly may be influenced by the type of floor covering commonly used in homes for the elderly. This study describes the development of a method for modelling a fall during a hip fracture event, to examine the influence of different floors on impact force. An impact transducer is dropped in free fall through a smooth plastic tube. The impactor nose of the transducer models the curvature of the greater trochanter, and a steel spring is used to simulate the compliance of the skeletal structure. A weight, which corresponds to one-sixteenth of average body mass, compresses the spring and applies force to the impactor nose on striking the floor. The temporal variation in the force of impact with the floor is measured by the transducer to within 0.41 percent (SD = 0.63%, n = 10). Five common floor coverings were tested over a concrete floor slab (vinyl, loop carpet and pile carpet--both with and without underpad). ANOVA analysis showed that the differences between mean forces for each floor covering were highly significant (p > 0.001), with the thicker coverings producing 7 percent lower forces. The transducer may be used to examine the correlation between impact force and fracture incidence for a variety of different floors in homes for the elderly.

Biomaterial particle phagocytosis by bone-resorbing osteoclasts

Abundant implant-derived biomaterial wear particles are generated in aseptic loosening and are deposited in periprosthetic tissues in which they are phagocytosed by mononuclear and multinucleated macrophage-like cells. It has been stated that the multinucleated cells which contain wear particles are not bone-resorbing osteoclasts. To investigate the validity of this claim we isolated human osteoclasts from giant-cell tumours of bone and rat osteoclasts from long bones. These were cultured on glass coverslips and on cortical bone slices in the presence of particles of latex, PMMA and titanium. Osteoclast phagocytosis of these particle types was shown by light microscopy, energy-dispersive X-ray analysis and SEM. Giant cells containing phagocytosed particles were seen to be associated with the formation of resorption lacunae. Osteoclasts containing particles were also calcitonin-receptor-positive and showed an inhibitory response to calcitonin. Our findings demonstrate that osteoclasts are capable of phagocytosing particles of a wide range of size, including particles of polymeric and metallic biomaterials found in periprosthetic tissues, and that after particle phagocytosis, they remain fully functional, hormone-responsive, bone-resorbing cells.

Mutation screening of the EXT1 and EXT2 genes in patients with hereditary multiple exostoses

Hereditary multiple exostoses (HME), the most frequent of all skeletal dysplasias, is an autosomal dominant disorder characterized by the presence of multiple exostoses localized mainly at the end of long bones. HME is genetically heterogeneous, with at least three loci, on 8q24.1 (EXT1), 11p11-p13 (EXT2), and 19p (EXT3). Both the EXT1 and EXT2 genes have been cloned recently and define a new family of potential tumor suppressor genes. This is the first study in which mutation screening has been performed for both the EXT1 and EXT2 genes prior to any linkage analysis. We have screened 17 probands with the HME phenotype, for alterations in all translated exons and flanking intronic sequences, in the EXT1 and EXT2 genes, by conformation-sensitive gel electrophoresis. We found the disease-causing mutation in 12 families (70%), 7 (41%) of which have EXT1 mutations and 5 (29%) EXT2 mutations. Together with the previously described 1-bp deletion in exon 6, which is present in 2 of our families, we report five new mutations in EXT1. Two are missense mutations in exon 2 (G339D and R340C), and the other three alterations (a nonsense mutation, a frameshift, and a splicing mutation) are likely to result in truncated nonfunctional proteins. Four new mutations are described in EXT2. A missense mutation (D227N) was found in 2 different families; the other three alterations (two nonsense mutations and one frameshift mutation) lead directly or indirectly to premature stop codons. The missense mutations in EXT1 and EXT2 may pinpoint crucial domains in both proteins and therefore give clues for the understanding of the pathophysiology of this skeletal disorder.

Assessment of cell proliferation in regenerating bone during distraction osteogenesis at different distraction rates

An experimental model of lengthening of the lower limb was used to study the morphology and cellular proliferation of regenerating bone tissue after 20% lengthening at four rates of distraction. Groups of rabbits were killed at different times 1-8 weeks after surgery. The regenerated area was divided into three zones: fibrous, primary mineralization front, and new bone. As the rate of distraction increased, the size of the fibrous zone increased and that of the new bone zone decreased. Necrosis, formation of cysts, and cartilage were found in the regenerated area at the higher distraction rates. Cell proliferation was assessed by in vivo labelling with bromodeoxyuridine, and the positive staining index for anti-bromodeoxyuridine antibody was calculated in the zones of the regenerated tissue. The index values for the fibrous zones and the new bone zones did not differ significantly in any of the groups. The value increased significantly (p < 0.05) in the primary mineralization front as the rate of distraction increased from 0.3 to 0.7 mm/day, but there was no further significant increase at higher distraction rates. In conclusion, cell proliferation was increased at all of the higher rates (more than 0.3 mm/day) of distraction studied. Higher rates of distraction caused tissue damage. A distraction rate of 0.7 mm/day appeared optimal for cell proliferation and histological characteristics.

Prevention of deformity during limb lengthening

Deformity occurs frequently at the site of distraction during leg lengthening and can add to disability. The elastic and nonelastic displacements have been measured in a model that simulates leg lengthening in the laboratory. Measurements have been made for different fixator systems. The angulation in the vertical plane that occurs during leg lengthening is minimized if the distance between the bone and the fixator bar is kept as small as possible, if three screws are inserted in the proximal and distal bone fragments, and if the peak loads on the fixator are reduced by adjusting the rhythm of distraction. However, even if these precautions are taken, the results show that some fixators designed for leg lengthening will fail and lead to deformity at the osteotomy site. This may occur under the repeated cycles of high loads associated with the rises in soft tissue tension that are known to occur in certain groups of patients. This study suggests that deformity can be prevented by the proper selection of a suitable frame and the adjustment of its configuration to meet the loading requirements.

A method of examining the magnitude and origin of "soft" and "hard" tissue forces resisting limb lengthening

Complications arising from limb-lengthening procedures such as muscle contracture, axial malalignment of the bone and traction injuries to the nerves and vessels, are often severe. Often complications arise from the build-up of forces in the biological tissues which are resisting lengthening. Little is known about the origin and magnitude of these forces, although three studies have identified the regenerate (new bone tissue) as the dominant resisting tissue. This study describes the development of a method to examine these forces. It employs load measurement devices in the structural columns of Ilizarov fixators which measure the compressive load on the frame exerted by the biological tissues. The distribution of this load between the columns of the frame, in conjunction with a transverse radiograph of the limb at the regenerate site, is used to examine the origin of the resisting force. Accuracy was determined by a laboratory simulation which found the predicted position of the force to be within 5 mm of the actual position in all four cases tested. Mean error in the total measured force was 2 N (SD, 1 N). A pilot study on a patient undergoing a 60 mm femoral lengthening revealed a peak force of 717 N originating in the Vastus Lateralis or the illiotibial tract. Negligible contribution to resistance was provided by the regenerate, contrary to that found with other studies.

Osteoclasts are capable of particle phagocytosis and bone resorption

Osteoclasts are multinucleated cells specialized for the function of lacunar bone resorption. Although they are known to be capable of phagocytosis of inert particles, it is not known whether this abolishes their ability to respond to hormones or to form resorption lacunae. Human and rat osteoclasts were isolated from giant cell tumours of bone and rat long bones, respectively, and cultured on coverslips and cortical bone slices, both in the presence and in the absence of particles of latex (1 micron diameter) and polymethylmethacrylate (PMMA) (< 50 microns). By light microscopy, it was evident that osteoclasts which had phagocytosed both latex and PMMA particles remained responsive to calcitonin. Osteoclast phagocytosis of particles was also evident on scanning electron microscopy, where it could also be seen that these cells were associated with the formation of resorption lacunae. These findings underline the fact that the osteoclast is a true member of the mononuclear phagocyte system and that phagocytosis does not abrogate either its hormonal response to calcitonin or its highly specialized function of bone resorption. That osteoclasts which have phagocytosed biomaterial particles such as PMMA are still able to carry out lacunar bone resorption is of interest in clinical conditions such as aseptic loosening, where a heavy foreign body particle load is often associated with extensive bone resorption.

The forces which develop in the tissues during leg lengthening. A clinical study

Axial forces were measured during limb lengthening in a series of ten patients with varying pathologies in order to assess the mechanical characteristics of the distracted tissues and the levels of axial force to which soft tissues are subjected during leg lengthening. The pattern of force was found to vary according to the underlying pathology. For post-traumatic shortening in adults both the peak and the resting forces rose steadily during lengthening reaching maximum forces of the order of 300 N. Patients with congenitally short limbs developed very high peak forces (in some cases over 1000 N) and also showed large amounts of force relaxation (typically 400 to 500 N). When very high levels of force were recorded, there was a higher complication rate. In particular, there was a high instance of angular deformity. This occurred because the loads encountered resulted in failure of some of the external fixation frames.

Manual assessment of fracture stiffness

A fracture stiffness of 15 Nm/degree measured biomechanically has been proposed as a reliable indicator of early fracture union. This study used a fracture model to examine the ability of orthopaedic surgeons to assess the stiffness of a fracture manually. Twenty orthopaedic surgeons were tested along with 20 controls. They each estimated the stiffness of seven rods representing mid-shaft diaphyseal fractures at different stages of healing, and were asked whether the stiffness suggested that union had progressed to the stage where the stabilizing device could be removed. Surgeons were unable to estimate the fracture stiffness accurately, and greatly overestimated rod stiffness particularly for the lower values. This meant that on 83 per cent of occasions when the stiffness was less than 15 Nm/degree, the surgeons considered the fracture models united to a sufficient degree to prescribe removal of the fixator. The results suggest that clinical assessment of fracture stiffness alone may put 83 per cent of patients at risk of refracture or malunion. Manual testing of the mechanical stability of a fracture appears not to be reliable.

Accidents with horses: what has changed in 20 years?

Horse riding is a dangerous pastime with more accidents occurring per hour than during motor-cycling. Since a prospective survey of horse-related injuries conducted at a major centre in 1971-1972, equestrian groups and the medical profession have encouraged improvements in training and protective riding wear. By conducting a similar study at the same centre 20 years later we hoped to assess the effects of these measures on the pattern of injuries resulting from contact with horses. Patient and injury details were recorded prospectively for all those presenting to the Accident Service at Oxford during the whole of 1991. Total admissions fell by 46 per cent on average. Most of the decrease was due to a near fivefold fall in those admitted with head injuries (P < 0.001). A reduction in the severity of such injuries was associated with an increased use of riding helmets. However, the most commonly injured group remained amateur young female riders suggesting the need for increasing awareness and training of this group. In seven cases, severe digital injuries were caused by the habit of entwining reins around the fingers. This practice should be discouraged. Up to 12 per cent of all injuries might have been prevented if adequate footwear had been worn.

How to minimize failures of fixation of unstable intertrochanteric fractures

Sliding hip screws have improved the treatment of unstable intertrochanteric hip fractures and their success, compared with fixed devices, is in large part due to the sharing of load between the implant and the fracture fragments. In a prospective study of 100 patients with such fractures, five factors concerned with the fracture and its fixation were studied and odds ratios calculated of their relative importance in prediction of failure. The most important factor affecting the load borne by the fracture fragments was the amount of slide available within the device, and that affecting the load carried by the device was the position of the screw in the femoral head. For fractures fixed with a device allowing less than 10 mm of slide, and those with superior screw position, the risk of failure was increased by factors of 3.2 and 5.9, respectively. Anatomical reduction alone, rather than osteotomy, together with sliding hip screw fixation, has been recommended for these fractures in three prospective randomized trials. It is calculated here that to allow sufficient slide when employing this technique, it is essential to use a short barrel device when using dynamic screws of 85 mm or less. This has not been demonstrated before.

Use of the Russell-Taylor reconstruction nail in femoral shaft fractures

Of 242 patients with injuries treated by locked intramedullary nailing of the femur, 52 (22 percent) were considered suitable for insertion of the reconstruction nail. The Russell-Taylor reconstruction nail was found to be useful in a greater variety of fractures than those for which it was originally designed. In addition to ipsilateral neck and shaft fractures, the Russell-Taylor reconstruction nail proved successful in high-energy comminuted subtrochanteric fractures, elderly subtrochanteric fractures and pathological lesions. In two cases, problems were encountered due to the relative straightness of the nail, but in the remaining patients there were no technical problems. In the 43 elderly patients and those with pathological lesions, seven complications occurred: a number which compares favourably with published reports for extramedullary devices. There were no cases of implant failure and in all patients the device supported the fracture to union or death.

The response of muscle to leg lengthening

We used an experimental rabbit model of leg lengthening to study the morphology and function of muscle after different distraction rates. Lengthening was in twice-daily increments from 0.4 to 4 mm per day. New contractile tissue formed during lengthening, but some damage to the muscle fibres was seen even at rates of less than 1 mm per day; abnormalities increased with larger rates of lengthening. There was proliferation of fibrous tissue between the muscle fibres at distraction rates of over 1 mm per day. Active muscle function showed adaptation when the rate was 1.0 mm per day or less, but muscle compliance was normal only after rates of 0.4 mm per day. Muscle responded more favourably at rates of distraction slower than those shown to lead to the most prolific bone formation. At present the rate of distraction in clinical practice is determined mainly by factors which enhance osteogenesis. Our study suggests that it may be advisable to use a slower rate of elongation in patients with poor muscle compliance associated with the underlying pathology; this will allow better accommodation by the contractile and connective tissues of the muscles.